COMMISSION K: Electromagnetics in Biology
and Medicine (November
2004 – October 2007)
Edited by Tsukasa Shigemitsu
Introduction
K1
Biological Effects of Electromagnetic Fields
K1.1 DC and
ELF Electric Fields
K1.2 Magnetic
Orientation-microorganisms and Agarose
K1.3 DC and
ELF Magnetic Fields
K1.3.1 In Vivo Studies
K1.3.2 In Vitro Studies
K1.3.3 Other
Studies
K1.4 IF
Magnetic Field
K1.5 RF
Electromagnetic Field and Microwaves
K1.5.1 In Vivo Studies
K1.5.2 In Vitro Studies
K1.5.3 Other
Studies
K2
Field measurement, Dosimetry and Exposure Asessment
K2.1 DC and
ELF Fields
K2.2 IF
Magnetic Field
K2.3 RF
Electromagnetic Field and Microwaves
K3
Tissue Properties, Materials, and Phantoms
K3.1 Design
Methods of the Electromagnetic Environment
K3.2 Phantoms
and Tissue Properties-Bioelectromagnetics Parameters
K4
Biomedical Applications
K4.1 Magnetic Stimulation
K4.2 Thermal
Therapy
K4.3 Thermal
Therapy-Soft Heating and Inductive Heating
K4.4 MRI and
Current Distribution MRI
K4.5 Contactless Power Transmission
System
K4.6 Electromagnetic Intereference
Acknowledgements
References
Introduction
The
research activities on the biological effects of electromagnetic fields in
This report
does not describe every paper of the member of Japanese Commission K that has
been carried out during 2005-2007. It begins with a chapter describing the
recent published papers of the biological effects of electromagnetic fields.
Next chapter reviews the results of electromagnetic field measurement,
dosimetry and exposure assessment. Third and forth chapters provide a
state-of-the-art review of biomedical applications using thermal therapy,
hyperthermia with soft-and inductive-heating, MRI, and current distribution
MRI, and further discuss some of the EMI issue on implantable medical devices.
K1 Biological Effects of
Electromagnetic Fields
K1.1 DC and ELF Electric
Fields
To elucidate
the mechanism of field perception, Shimizu et
al. conducted a fundamental study on the movement of body hair in field
exposure [
Kagawa
et al.
have pursued the possibility to control immune functions by ELF
electro-stimulation [Kagawa, 2006]. The effect of ELF electro-stimulation on
the nitiric oxide (NO) producing ability of macrophages was examined. The
decrease of NO production due to the electro-stimulation was observed with
statistical significance. The measurement showed the decrease of the NO
synthesizing enzyme with statistical significance, as well. These facts
suggested that the ELF electro-stimulation suppressed the emergence of the NO
synthesizing enzyme and that the amount of NO production was consequently
decreased by the electro-stimulation. This suggested the feasibility to control
the immune function by applying ELF electro-stimulation from outside the body.
Hirata et al. investigated the effect of low-frequency (ELF) electric
stimulation to muscle oxygenation level by NIRS (near infrared spectroscopy) from
comparing with V-Ex (voluntary exercise) [Hirata, 2006]. ELF electric
stimulaiton voltage was started at 20 V (20 Hz, pulse duration: 200 μs, duty-cycle: 1s-1s), and then was
increased at a rate of 3 V/30 s until maximal tolerance level. In ELF electric
stimulation and V-Ex, tissue oxygenation index was decreased with decrease in O2Hb
(oxy-hemoglobin) and increase in HHb (deoxyhemoglobin), and muscle oxygenation
levels at the end of test were very alike. Oxygen consumption, heart rate,
systolic and diastolic blood pressure in ELF electric stimulation and V-Ex
increased significantly, however, the degree of change in ELF electric
stimulation was significantly lower than V-Ex. Blood lactate was significantly
increased in both tests. Adrenaline and noradrenaline were significantly
increased in V-Ex, even though they showed no change in ELF electric
stimulation. These results suggest that ELF electric stimulation is an
effective technique activated muscle hypoxia and glycolytic pathway metabolism
with low stress on respiratory, circulatory and sympathetic nervous systems.
Muraki et al. investigated cardiorespiratory responses and muscle
oxygenation during prolonged electrical stimulation (ES)-evoked leg cycling in
individuals with paraplegia (
Miyazaki et al. measured somatosensory evoked fields (SEFs) by electric
stimulus to the right finger using a 39-channel SQUID system [
Oinuma et al. studied the influence of high-frequency monopolar
stimulation (HFMS) on the rat cerebral cortex [Oinuma, 2007]. Direct
stimulation of the brain with 500 Hz HFMS is one of the most common methods to
produce motor evoked potentials (MEP). HFMS of 1.5-50 mA were applied to the
rat sensorimotor cortex. There was no change in the parameters of MEP in any of
the rats exposed to HFMS. Histologically, there was significant swelling of the
dendrites in rats immediately after exposure to 40 and 50 mA. The 50 mA
stimulation group also exhibited slight swelling of the mitochondria. These
findings were not obtained in any of the rats 30 days after stimulation. In
rats exposed to 30 mA or less, no morphological or electrophysiological changes
were observed.
Nishiyama et al. investigated the effects of electrostatic fields on
the storage of red blood cell concentrates [Nishiyama, 2007]. The Na+ concentration decreased with time but was
significantly lower in the 0 V than in the 500, 1500, and 3000 V groups. K+
and free hemoglobin concentrations increased with time, with significantly
higher values in the 0 V than in the 500, 1500, and 3000 V groups. The pH
decreased in the 500, 1500, and 3000 V groups, while it did not change in the 0
V group. The pH decrease was smaller in the 500 V than in the 1500 and 3000 V
groups. Electrostatic fields of 500-3000 V could decrease hemolysis in the preparation. Considering the lower
pH decrease, it is suggested that 500 V might be the field of choice.
Harakawa et al. examined the effects of exposure to
extremely low frequency (ELF) electric fields on plasma lipid peroxide levels
and antioxidant activity (AOA) in Sprague-Dawley rats [Harakawa, 2005]. The
test was based on comparisons among rats treated with a combination of the
oxidizing agent, 2,2-azobis(2-aminopropane) dihydrochloride (AAPH) and 50 Hz
electric field of 17.5 kV/m for 15 min per day for 7 days, AAPH alone, ELF
electric field alone or no treatment. The ELF electric field significantly
decreased the plasma peroxide level in rats treated with AAPH, similar to
treatment by ascorbic acid or the superoxide dismutase. Ascorbic acid increased
AOA; however, ELF electric field and superoxide dismutase did not change AOA
compared with sham exposure in stressed rats. No influence on the lipid
peroxide level and AOA in unstressed rats was observed with ELF electric field
exposure alone. Although the administration of AAPH decreased AOA, this
decrease did not change when electric field was added. These data indicate that
the ELF electric field influenced the lipid peroxide level in an oxidatively
stressed rat.
K1.2 Magnetic
Orientation-microorganisms and Agarose
The past
studies showed that the collagen fibers and adherent cells can be effectively
oriented under the exposure to strong magnetic field. These challenges can lead
to the development of bone tissue engineering. In order to achieve more clearly
this phenomena, Saito et al.
investigated the relationship between collagen orientation and magnetic field
intensity [Saito, 2006]. The osteoblast cells were prepared and mixed with
collagen solution. These mixed solutions were exposed to magnetic field with
2.5, 3 and 8 T. Five days later, the configulation of the osteoblasts was
observed under microscope. These results showed the magnetic field intensity
over 3 T is necessary to effectively control collagen orientation.
Several studies were carried out on the control of cellular
orientation and morphology by applying strong static magnetic fields. Iwasaka et
al. found that the motion of
adherent cells (MC3T3-E1) was influenced by a static magnetic field of 8 T and
was parallel to the static magnetic field [Iwasaka, 2005]. During the exposure, most cells showed a
back-and-forth motion along the direction of the static magnetic field.
Specifically, the direction of cell extension immediately after cell division was
parallel to the static magnetic field. Cytoskeletons inside the cells were
oriented in parallel with the static magnetic field, and introduced a cell
motion parallel with the static magnetic field. The experiments showed that
living cells consisting of diamagnetic materials had their motion restricted by
the direction of the applied static magnetic field.
Diamagnetic anisotropy in cellular components provided a
change in the fluidity of membrane assembly which was detected by fluorescent
measurements in-situ under magnetic
field exposures [Iwasaka, 2006c]. A novel phenomenon was discovered on the
structures of giant vesicles which were formed under 8 T magnetic fields, and
the contributions of both diamagnetic anisotropies of collagen molecules and
lipid molecules were explained on a mathematical model [Suzuki, 2007a].
Effects of static
magnetic fields on the optical property of cytochrome oxidase, which is
involved in an enzymatic system of mitochondria, were investigated by utilizing
purified enzymes and rabbit with a non-invasive oxygen monitor, and the results
indicated a slight increment in oxidation of cytochrome oxidase by 14 T
magnetic fields [Iwasaka, 2006a]. Iwasaka et al. reported the effects of
intense static magnetic field (up to 14 T) on the near-infrared (NIR) optical
properties of cytochrome oxidase in rabbits. The static magnetic field changed
the oxidation of cytochrome oxidase (aa3) periodically depending on the
magnetic flux density. Measurements with a cooled CCD system revealed that the
absorbance at 830 nm was slightly increased by a static magnetic field of 8 T.
A static magnetic field of 14 T was applied to the head of the rabbit, and the
results showed the enhanced oxidation of cytochrome oxidase in the mitochondria
of cells under the static magnetic field. The effects of the static magnetic
field on the paramagnetic behavior of oxygen, electron transfer in cytochromes,
and cell membrane conformation in mitochondria may play a role in increasing
the sensitivity to NIR light for detecting cytochrome oxidase oxidation, which
is one of the primary indicators of cellular activity.
Iwasaka et
al. further reported a method of controlling the magnetic orientation of osteoblasts
by utilizing a ferromagnetic particle chain and a diamagnetic collagen [Iwasaka, 2006b]. A cell culture
medium with cells and magnetic particles (MP) was mixed with a collagen
solution and incubated for 24 h. During the first 3 h of incubation, the medium
in the cell culture dish was exposed to static magnetic field of up to 8 T. The exposure caused the aggregation of MP, which formed
chains in parallel with the static magnetic field and at the same time oriented
the polymerized collagen fibers perpendicular to the static magnetic fields. A
lattice pattern of MP chains and collagen fibers was observed on the bottom of
the culture flask. After 24 h of incubation, the spindle like cells had become
oriented in parallel with the MP chains or the collagen fibers. The results
indicate the possibility of a technique of cellular manipulation with
MP-collagen hybrid that could be used to control cellular orientation.
An
experiment to clarify the effects of the static magnetic field of up to 8 T on cell
membrane fluidity by using red blood cell ghosts and a fluorescence dye,
1-aminonaphthalene-8-sulfonic acid (ANS) was performed [Iwasaka, 2006c]. The emission
intensity at 480 nm increased when the temperature of the cell holder was
increased from 20 to 38-46°C for 15 min. A change in temperature exhibited an
increase in the fluidity of the lipid molecules in the hydrophobic cell
membrane and increased the population of ANS molecules emitting light at 480 nm
in the cell membrane. A discontinuous change in fluorescence at 38-40°C was
exhibited under exposure to a 5 T static magnetic field,
while the temperature dependency was continuous without exposure. In addition,
under exposure to the static magnetic field, the fluorescence during a decrease
in temperature from 38 to 20°C remained at a level close to the fluorescence
during an increase in temperature. The results indicated that the fluidity of
the molecules in the cell membrane was decelerated by 5 T static
magnetic field. They speculated that the magnetic orientation in a part
of the lipid membrane disturbed the release of ANS molecules from a hydrophobic
region of the membrane.
According to
applications of magnetic forces, which are of a spatial gradient of magnetic
flux density, for a biological process, Moses’ effect was applied to the
patterning of adhered cells by using a field modulator under 1 T [Kimura,
2005]. Also, two kinds of new
approaches in magnetic separation techniques for biological materials were
reported, one of which was called “magnetic liquid chromatography” [Iwasaka,
2007], and the other was an application of the Magneto-Archimedes separation
[Yokoyama, 2007].
Kimura et
al. presented a new technique of cell micropatterning using a
magnetic field [Kimura, 2005]. Mouse
osteoblast cells (MC3T3-E1) were seeded on a substrate whose surface was
exposed to a periodically modulated magnetic field (a line pattern with a 200-
or 600-μm pitch) produced by a field modulator inserted into a homogeneous
static magnetic field of 1 T. The cells were trapped consistent with the line
profile of the modulated magnetic field. The trapping efficiency was enhanced
by adding Mn (II) EDTA (paramagnetic) to the cultivation medium. The cells were
subsequently incubated in the magnetic field. The same technique was applied to
whole blood to pattern red blood cells.
Eguchi et
al. examined the role of cytoskeletons, such as stress fibers, on magnetic
orientation of Schwann cells after the static magnetic field exposure (8 T in
maximum) [Eguchi, 2005]. Schwann cells were cultured from dissected sciatic
nerves of neonatal rats. Schwann cells oriented parallel to the static magnetic
field after 60 h of more than 4 T. Actin fibers oriented in the direction of
the static magnetic field after 60 h of 8 T static magnetic field exposure but
randomly oriented without static magnetic field. Orientation of Schwann cells
was not observed by inhibiting stress fiber formation using Y-27632, an
inhibitor of small guanosine triphosphatases (GTPase) Rho-associated kinase.
These results indicate that the static magnetic field elicits reorientation of
actin fibers through
Eguchi et al.
further
examined cleavage and survival of fertilized Xenopus embryos exposed to 8 T static magnetic field [Eguchi, 2006]. Fertilized
Xenopus embryos exposed to static magnetic field either in a static chamber or
in a rotating culture system. The results showed that the static magnetic field
exposure changed the third cleavage furrow from the usual horizontal one to a
perpendicular one; however, when the direction of gravity was randomized by
exposing embryos to the static magnetic field in a rotating culture system, the
third cleavage furrow were formed horizontally. These findings suggest that the
observed distortion of the third cleavage furrow in static magnetic field
exposed embryos was accomplished by altering gravity effects which were
elicited by diamagnetic force due to high gradient magnetic field. These
results also showed that the exposure to the static magnetic field did not
damage survival. These results demonstrate that static magnetic field and
altering gravity cause distortion of the third cleavage furrow and show that
effects of exposing cleavage embryos to static magnetic field were transient
and did not affect the post-cleavage development. They also showed that static
magnetic field is not hazardous to the cleavage and blastula-gastrula
transition of developing embryonic cells.
Shinohara et
al. reported highly oriented collagen structures were successfully
synthesized using a conventional superconducting magnet with static magnetic
field of 2.5 to 8 T [Shinohara, 2006]. The relationship between the orientation
order parameters f2D of
osteoblastic cells (the orientation of collagens) and the magnetic field
intensity was mainly investigated. As a result, it was clarified that collagens
highly oriented perpendicular to the c direction were obtained by exposure to a
static magnetic field of 3 T.
After the
short-time exposure of pregnant mice (60 min on 1 day from 7.5 to 14.5 days of
pregnancy) to a strong magnetic field of 400 mT (exposure direction was in a
dorso-ventral direction), Saito et al.
evaluated the teratologic effects of developing fetuses [Saito, 2006]. 160 animals
were used in the exposure experiment; exposed and control groups consisted of
10 pregnant mice each. Teratological evaluation was performed on day 18.5. The
number of live and dead fetuses and fetal resorption sites were counted. All
fetuses were examined from gross malformation and gender. They observed various
malformations and the type of malformations were polydactylism, abdominal
fissure, fused rib, vestigial 13th rib, lumber rib, brain hernia and
curled tail. In control groups only a low incidence (up to 2.8 %) of curled
tail was observed. The mentioned these deforations apparently caused by static
magnetic field.
A National
Project Group for research on strong static magnetic field effects on
physico-chemical processes partially including biological matters collected
results of recent topics [Yamaguchi and Tanimoto, 2006].
K1.3 DC and ELF Magnetic
Fields
During past three years, three comprehensive review papers have been
appeared [Kato, 2006; Miyakoshi, 2005a; Ueno, 2007b]. Kato edited the book
entitled “Electromagnetics in Biology”. This comprehensive book covered the
fundamental concept of biological issue in electromagnetics and the topical
reviews of the published literature. Miyakoshi reviewed the effects of static
magnetic feld at cellular level. As a result through reviewing many past
published studies, he mentioned that static magnetic field alone does not have
a lethal effect on basic propertes of cell growth and survival under normal
culture condition regardless of the magnetic density. Most studies have also
suggested that a static magnetic field has no effect on changes in cell growth
rate. Most interest area is whether static magnetic fields cause DNA damage.
Ueno and Shigemitsu reviewed some of the more recent information on biological
effects and medical applications of static magnetic fields. In their review,
with exposure to about 1 T and above, there are no adverse effects on
reproduction and development, genotoxicity, and molecular and cellular systems,
and no consistent evidence on behavioral effects. Most important point they
mentioned was that the International Agency for Research on cancer (IARC) has
stated the static magnetic field are not
classifiable as to their carcinogenicity to humans by inconclusive carcinogenic
evidence.
K1.3.1 In Vivo Studies
Okano et al. reported that the
homeostatic effect of the static magnetic field might influence nitric oxide
(NO) pathways [Okano, 2005a]. When the genetically hypertensive rats were
exposed to a gradient static magnetic field of 5 mT for up to 12 weeks, blood
pressure (BP) and/or plasma concentration of NO metabolites (NOx),
angiotensin II and/or aldosterone were reduced. Specifically, 5 mT exposures
reduced mean BP during 3-6 weeks. Young spontaneously hypertensive rats (SHR)
are known to have increased levels of NOx, likely due to the
upregulation of nitric oxide
synthase (NOS). Exposure to a 5 mT static magnetic field for 6 weeks
significantly reduced the concentration of NOx. A 1 mT static
magnetic field did not have an effect on the NOx. A 5 mT static
magnetic field reduced angiotensin II and aldosterone during 3-6 weeks. Similar
significant reductions in angiotensin II and aldosterone were seen with the 1
mT static magnetic field. However, until the 9th week of exposure, irrespective
of the longer duration of exposure, all significant antihypertensive effects of
static magnetic field disappeared, due to the development of hypertension in
young SHR.
The
above findings were partially elucidated when SHR were exposed to a 180 mT
static magnetic field (a magnet was implanted in the neck) for up to 14 weeks
[Okano, 2005d, 2006a]. The static magnetic field enhanced the hypotensive
effect of nicardipine and caused a further increase in NOx during
the 6th week of exposure compared with rats that also received nicardipine but
were exposed to a sham field (control). Thus, the synergistic effect of the
static magnetic field appeared to be related to NO. The static magnetic field
alone (without nicardipine), however, did not induce any change in NOx
concentration. It is speculated that NO increase by static magnetic field, in
part, might be due to the upregulation of inducible NOS rather than neuronal
NOS or endothelial NOS [Okano, 2006a].
The
homeostatic effects of a static magnetic field were again reinforced when
reserpine, an indole alkaloid, was used to induce hypotension and deplete
catecholamine reserves in conscious rats [Okano, 2005b]. The static magnetic
field exposure (25 mT for 12 weeks) significantly reduced the effect of the
reserpine, reducing the hypotension caused by the drug. A 10mT static magnetic
field did not have any effect. It is concluded that a 25 mT static magnetic
field could potentially reduce hypotension
in vivo.
The combined effects of a static magnetic
field (12 mT for 10 weeks) and two different sympathetic agonists were
investigated in conscious rats [Okano, 2007a]. The two different sympathetic
agonists, a α1-adrenoceptor agonist, phenylephrine and a β1-adrenoceptor
agonist, dobutamine, induced hypertension and different hemo- dynamics:
phenylephrine increased BP and decreased heart rate, skin blood flow, skin
blood velocity, and the number of rearing responses; dobutamine increased BP
and heart rate, increased skin blood flow and velocity, and the number of
rearing responses. Continuous neck exposure to the static magnetic field alone
for up to 10 weeks induced no significant changes in any of the measured
cardiovascular and behavioral parameters. The static magnetic field exposure
for at least 2 weeks (1) significantly depressed phenylephrine effects on BP,
skin blood flow and velocity, and rearing activity, and (2) significantly
depressed dobutamine effects on BP, skin blood flow and velocity, and
suppressed dobutamine-induced increase in the rearing activity. These results
suggest that continuous neck exposure to a 12 mT static magnetic field for at
least 2 weeks may depress or suppress sympathetic agonists-induced
hypertension, hemodynamics, and behavioral changes by modulating sympathetic
nerve activity.
In the case of neck application of the
static magnetic field, Okano et al. found that the exposure to 5.5 mT for 30 min induced significant
increases in baroreflex
sensitivity (BRS) values during the post-exposure period of 40-60 min in norepinephrine-elevated BP compared
with sham exposure in conscious rabbits [Okano, 2005c]. Moreover, the exposure to the static magnetic field for 5-8
weeks significantly suppressed or delayed the development of hypertension
together with increased BRS in SHR [Okano, 2005d]. Furthermore,
it is postulated through theoretical calculations that the applied static
magnetic field can be converted into a changing magnetic field in the
baroreceptor region by means of the carotid artery pulsation [Okano, 2005d].
Therefore, it is speculated that the changing magnetic field and the magnetic
field modulated by the pulse rate, may influence the activity of baroreceptor
and baroreflex function.
Xu
et al. investigated the effects of
the static magnetic field (180 mT for 3 weeks) on the vascularization in bone
using an ischemic bone model, where rat femoral artery was ligated [Xu, 2007].
Magnetized and unmagnetized samarium-cobalt rods were implanted transcortically
into the middle diaphysis of the ischemic femurs. Collateral circulation was
evaluated by injection of microspheres into the abdominal aorta at the third
week after ligation. It was found that the bone implanted with a magnetized rod
showed a larger amount of trapped microspheres than that with an unmagnetized rod
at the proximal and the distal region. There were no significant differences at
the middle and the distal region. This tendency was similar to that of the bone
mineral density (BMD) in the static magnetic field exposed ischemic bone.
Taniguchi
et al. examined the effects of the
static magnetic field (30 mT for 12 weeks) on osteopenia in an ovariectomized
(OVX) rat model [Taniguchi, 2007]. The bone mineral densigty (BMD) was assessed
mainly using dual-energy X-ray absorptiometry (DEXA).
Thirty-six female Wistar rats were divided into three
groups. The rats in the OVX-M group were exposed to the static
magnetic field for 12 weeks after ovariectomy. The ovariectomized rats in
the OVX-D group were not exposed to the static magnetic field as a control. The
rats in the normal group received neither ovariectomy nor exposure to
the static magnetic field. Twelve-week exposure to the static magnetic field in
the OVX-M group inhibited the reduction in BMD that was observed in
the OVX-D group. Moreover, in the OVX rats, before exposure to the
static magnetic field, there was no clear difference in the level of
locomotor activity between the active and resting phases, and the
pattern of locomotor activity was irregular. After exposure of OVX
rats to the static magnetic field, the pattern of locomotor activity
became diphasic with clear active and resting phases, as observed in
the normal group. In the OVX-M group, the continuity of the
trabecular bone was maintained more favorably and bone mass was
higher than the respective parameters in the OVX-D group. These
results demonstrate that exposure to the static magnetic field increased
the level of locomotor activity in OVX rats, thereby increasing BMD.
Goto et al. examined the
effects of the static magnetic field (100 mT for 2 h, four times per day for 7
days) affects higher order neural functions in vivo [Goto, 2006]. When
embryonic 12-day-old or newborn mice were successively exposed to the static
magnetic field at 100 mT for 2 h, four times per day until the postnatal seventh
day, Ntan1 mRNA was significantly increased about 1.5-2-fold in the hippocampus
in vivo. The mice exposed to the static magnetic field under the same condition
showed significantly decreased locomotor activity. These results suggest that
the static magnetic field affects higher order neural functions through
modulation of genes expression.
Toyomaki et al. investigated the static magnetic
field (1.5 T) affects brain activity such as arousal level [Toyomaki, 2007].
They compared the electroencephalography (EEG) inside an MRI scanner in the
presence/absence of the static magnetic field in two different arousal levels
of task and rest conditions in humans. Cardiac-related pulsations of head and
blood flow induce an electric voltage at each EEG electrode in a static
magnetic field. This induced voltage overlaps with the intrinsic EEG signal and
becomes a large confounding factor. No significant difference was observed in
the intrinsic EEG in the absence of a magnetic field, whereas in the presence
of the static magnetic field, the theta frequency band of the intrinsic EEG
increased, especially during the task condition, but other frequency bands did
not change. These results demonstrate that a static magnetic field affects
brain activity.
Sekino
et al. investigate the effects of
strong static magnetic field (up to 8 T) on the action potentials of the rat
sciatic nerve [Sekino, 2006c]. A pair of needle electrodes was inserted beneath
the skin of the heel for applying electrical stimulations. Compound action potentials
of the left sciatic nerve were measured from a pair of electrodes attached to
the nerve bundle under the static magnetic field. We identified the action
potentials originating from the A and C fibers. The exposure to static magnetic
field did not affect the amplitude of the A fiber’s action potentials. An
increase in the static magnetic field increases the amplitudes of the peaks of
the C fiber. These results indicated that exposure to strong static magnetic
field enhances the excitation of nerve fibers, and this effect depends on the
type of fibers involved. These result implies that exposure to a strong static
magnetic field enhances pain perception because the C fiber is responsible for
pain transmission.
Komazaki et
al. examined the influence
of an extremely low frequency (ELF) magnetic field (50 Hz, 5-30 mT) on early
development of amphibian embryos [Komazaki, 2007]. When the embryos developed
under the influence of an ELF magnetic field, the rate of early development was
accelerated. The effect of ELF magnetic field was exerted preferentially at the
gastrula stage, and the period of gastrulation was shortened. Histological
observations showed that ELF magnetic field promoted morphogenetic cell
movements during the gastrulation. ELF magnetic field increased intracellular
Ca2+ ([Ca2+]i) particularly in the cells
isolated from gastrula. These results suggest that ELF magnetic field
specifically increased the [Ca2+]i of gastrula cells,
thereby accelerating the rate of morphogenetic cell movements during
gastrulation.
In order to
study the infleunce of magnetic field (60 Hz, 0.5 T, one hour exposure) on the
nervous system of nematode C.elegans,
Maeda et al. observed the behavior of
the worm in response to certain chemicals (DA and CuSO4) both during
the exposure and after exposure to magnetic field [Maeda, 2006]. They suggested
that the parts of the worm’s nervous system are influenced by magnetic fields
and there are more effects on the nervous system during than after exposure to
magnetic fields.
Suzuki et al. investigated the effect of static
magnetic field of 4.7 T on the induction of micronuclei induced by some
mutagens in order to confirm the co-mutagenic effect [Suzuki, 2006].
Seven-week-old BALB/c male mice with body weights between 22-27 g were exposed
to 4.7 T magnetic fields just after the injenction of carboquone (0.5, 1.0 and
2.0 mg/kg), colemid (1.25, 2.5, 5.0 and 7.5 mg/kg), mitomycin C (0.3, 0.5 and
0.7 mg/kg), vincristine (0.02, 0.03 and 0.04 mg/kg), sodium fluoride (10. 20
and 30 mg/kg) or ENU (9. 18 and 36 mg/kg). After exposure to magnetic field,
the mice were sacrified by cervical dislocation. Bone marrow smears were
prepared. The number of micronucleated polychromatic erythrocytes in 1000
polychromatic erythrocytes per animal was counted under a light microscope. The
frequency of micronuclei induced by above six mutagens increased after
co-exposure to magnetic field. The authors concluded that an
additive/synergistic effect of magnetic field was observed from the results of
increased frequency of micronuclei by mutagens in mouse bone marrow
erythrocytes.
Ogiue-Ikeda et al. investigated the acquisition of ischemic
tolerance in the rat hippocampus using repetitive transcranial magnetic
stimulation (rTMS) which is a type of ELF-pulsed magnetic fields
(ELF-PEMF) [Ogiue-Ikeda, 2005]. Rats
received ELF-PEMF (0.75 T, 1000 pulses/day) for 7 days, and the field
excitatory postsynaptic potentials were measured in the hippocampal CA1. After slices
were exposed to ischemic conditions, long-term potentiation (LTP) was induced.
The LTP of the stimulated group was enhanced compared with the LTP of the sham
control group in each ischemic condition, suggesting that ELF-PEMF has the potential to protect hippocampal
function from ischemia.
Funamizu et al. examined
the effects of an ELF-PEMF on
neurological and psychiatric disorders [Funamizu, 2005] As an animal model, the
lesioned rats were made by administering the neurotoxin MPTP
(l-methyl-4-phenyl-l, 2, 3, 6-tetrahydropyridine). Forty-eight hours after MPTP injection,
the rats received ELF-PEMF (1.25 T,
2000 pulses/day) for 1 day, and tyrosine hydroxylase (TH) and NeuN expressions were investigated in
the substantia nigra. The functional observational battery-hunched posture
score for the MPTP-ELF-PEMF group was
significantly lower and the number of rearing events was higher compared with
the MPTP-sham group, these behavioral parameters reverted to control levels.
These results suggest that ELF-PEMF treatment could reactivate the dopaminergic system in lesion rats.
Yamaguchi et al. investigated the effects of an
ELF-PEMF on tumor development processes and immune functions in vivo [Yamaguchi, 2005ab, 2006a].
ELF-PEMF were applied at
pulse width = 238 μs, peak magnetic field = 0.25 T, frequency = 25 pulses/s,
1,000 pulses/sample/day and magnetically induced eddy currents = 0.79-1.54 A/m2.
B16-BL6 melanoma model mice were exposed to the ELF-PEMF for 16 days from the
day of injection of cancer cells. A tumor growth study revealed a significant
tumor weight decrease in the ELF-PEMF group. These results showed the
anti-tumor effect and immunomodulatory effects of ELF-PEMF.
Yamaguchi et al. further examined the combination
effect of an ELF-PEMF and an anticancer agent on human chronic myelogenous
leukemia-derived cell line TCC-S using molecular target drug (selective
tyrosine kinase inhibitor) imatinib mesylate (imatinib) [Yamaguchi, 2006b]. The
stimulus conditions were determined as follows: 0.1, 0.25, and 0.5 T,
25pulses/s, 1000, 3000, and 6000 pulses/day. TCC-S cells were cultured with
imatinib (100 nM) and exposed to ELF-PEMF for up to 56 h after drug treatment.
The significant combination effects of ELF-PEMF and imatinib occurred by the
stimulus intensity and pulse dose depended manner. To clarify the effects of
ELF-PEMF on human normal lymphocytes, PBMCs were also exposed to ELF-PEMF with
or without imatinib. ELF-PEMF had no effect on the viability of PBMCs. These
results indicate that ELF-PEMF possibly improve the effectiveness of anticancer
agents.
Mano et al. investigated the effect of ELF
magnetic field (60 Hz, 5 mT) on the germination of seeds [Mano, 2006]. The
germination of seeds of Arabidopsis
thaliana, Lactuca sativa and Zinnia
elegans were decreased by 8-21 day-incubation in 90 % relative humidity at
37 ℃. ELF magnetic field applied to seeds
during the incubation suppressed these decreases in the germination. The ELF
magnetic field suppressed irreversible deterioration of the seeds, rather than
dormancy, probably preventing water absorption. ELF magnetic field can be
helpful for the storage of humidity-vulnerable seeds.
K1.3.2 In Vitro Studies
Hirai et al. reported
repetitive daily exposure to a static magnetic field (100 mT for 15 min per day
for 8 days) led to a decrease in the expression of microtubule-associated
protein-2 (MAP-2), without significantly affecting cell viability or the
expression of neuronal nuclei (NeuN) and growth-associated protein-43 (GAP-43)
[Hirai, 2005a]. However, the repetitive static magnetic field exposure
prevented decreases in both brain-derived neurotrophic factor (BDNF) mRNA and
MAP-2 and additionally increased the expression of NR2A subunit, without
altering NR1 expression in neurons cultured in the presence of the antagonist
for N-methyl-D-aspartate (NMDA) receptors dizocilpine (MK-801). Repetitive
static magnetic field exposure was also effective in preventing the decrease by
MK-801 in the ability of NMDA to increase intracellular free Ca2+
ions, without affecting the decrease in the maximal response. These results
suggest that repetitive static magnetic field exposure may at least in part
counteract the neurotoxicity of MK-801 through modulation of the expression of
particular NMDA receptor subunits in cultured rat hippocampal neurons.
Hirai et al. examined the
effects of a static magnetic field (100 mT for 15 min) on cultured rat
hippocampal neurons using polymerase chain reaction [Hirai, 2005b]. The results
suggest that the static magnetic field may modulate cellular integrity and
functionality through expression of a variety of responsive genes required for
gene transcription and translation, proliferation, differentiation, maturation,
survival, and so on. in cultured rat hippocampal neurons. Hirai et al. screened genes responsive to a
brief static magnetic field （100 mT for 15 min) in
cultured rat hippocampal neurons using differential display analysis [Hirai,
2006]. These results suggest that a brief static magnetic field leads to the induction
of amidohydrolase for N-terminal asparagines (Ntan1) responsible for MAP2
protein degradation through ubiquitin-proteasome pathway in rat hippocampal
neurons.
Okano et al. reported the effects of the
static magnetic field (120 mT for 10 days) on increased endothelial tubular
formation mostly in the absolute field gradient range of more than 28 mT/mm (28
T/m) in the target cells [Okano 2006b, 2007b, 2007c]. These studies
investigated the spatial magnetic gradient effects of static magnetic field on
endothelial tubular formation. The effects of gradient static magnetic field on
tubular formation were compared with those of uniform static magnetic field
that has no spatial gradients on the entire bottom area of culture wells [Okano
2007c]. Five experimental groups of 25 samples each were examined: (1) sham
exposure (control); (2) peak gradient exposure in the peripheral part; (3) peak
gradient exposure in the central part; (4) uniform exposure to 20 mT; (5)
uniform exposure to 120 mT. The static magnetic field or sham exposure was
carried out for 10 days. Photomicrographs of tubular cells, immunostained with
an anti-platelet-endothelial cell adhesion molecule-1 (PECAM-1 [CD31]) antibody
as a pan-endothelial marker, were analyzed after the 10-day culture. Gradient
static magnetic field in the peripheral or central part was found to
significantly promote tubular formation in terms of the area density and length
of tubules in each peak gradient/force part of the wells, compared with the
sham exposure. In contrast, uniform static magnetic field did not induce any
significant change in the tubular formation. These findings suggest that tubule
formation can be promoted by applying the peak gradient/force to a target site
of culture wells.
Haneda et al. examined the effects of the
static magnetic field (300 mT for several hours) on single suspension-cultured
plant cells (Catharanthus roseus)
[Haneda, 2006]. Exposure of intact cells to the static magnetic field did not
result in any changes within experimental error, while exposure of regenerating
protoplasts significantly increased the measured forces and stiffened
regenerating protoplasts. The diameters of intact cells or regenerating
protoplasts were not changed after exposure. Measured forces for regenerating protoplasts
with and without exposure increased linearly with incubation time, with these
forces being divided into components based on the elasticity of synthesized
cell walls and cytoplasm. No changes in cell wall synthesis were noted after
exposure. Analysis suggested that the static magnetic field roughly tripled the
Young's modulus of the newly synthesized cell wall without any lag.
Sakurai et al. reported that exposure to the
static magnetic field of up to 10 T promoted osteoblast differentiation in vitro
[Sakurai, 2007a]. Prostaglandins respond early to exogenous mechanical loading,
and play an important role in bone formation. The magnetic field gradient was
highest (41.7 T/m) at 6 T. Prostaglandin E2 (PGE2)
secretion was not affected at 10 T compared with sham exposure, but was
enhanced at 6 T. Similarly, PGE2-synthesizing enzyme, cyclooxygenase
2 (Cox-2) expression and the transcription factor nuclear factor κB (NF-κB)
translocation were not enhanced at 10 T, but increased at 6 T. These findings
suggested that exposure to a high magnetic field gradient induced secretion of
PGE2 and expression of the Cox-2 protein via increased translocation
of NF-κB.
Sakurai et al. evaluated the effects of an
extremely low frequency (ELF) magnetic field on glucose-stimulated insulin
secretion from HIT-T15 cells and investigated the mechanisms of these effects
[Sakurai, 2005b]. They demonstrated that ELF magnetic field at 5 mT and 60 Hz
decreased glucose-stimulated insulin secretion by preventing the increases in
cellular adenosine 5'-triphosphate/adenosine 5'-diphosphate, membrane
depolarization, and cytosolic free Ca2+ concentration. The
glucose-induced upregulation of insulin mRNA expression was also attenuated by
exposure to ELF magnetic field, although cell viability was not affected. These
findings demonstrate the potential of exposure to ELF magnetic field for
clinical use as a novel inhibitory method of insulin secretion.
Because there
are few studies about the effects of an ELF magnetic field on β-cell survival and
function, Sakurai et al. investigated
the effects of 5 mT of 60 Hz magnetic fields on cell survival and function
[Sakurai, 2005a]. The used cultured cell was a hamster-derived
insulin-secreting cell line (HIT-T15). They cultured HIT-T15 cells under the exposure
to sham and ELF magnetic field conditions. It was found that exposure to ELF
magnetic field for 5 days in the absence of glucose increased cell number,
exposure for 2 days without glucose aand for 5 days with 100 mg/dl glucose
increased the insulin secretion, and exposure for 2 and 5 days with 40 and 100
mg/dl glucose increased intracellular insulin concentration in HIT-T15 cells.
The increase in cell number under apoptotic culture condition by exposure to
ELF magnetic field can lead to new therapeutic applications in the treatment of
diabetes.
Koyama et al. investigated the effects of an
ELF magnetic field (5 mT and 60 Hz) on the number of apurinic/apyrimidinic (AP)
sites in human glioma A172 cells [Koyama, 2007a]. There was no difference in
the number of AP sites between cells exposed to ELF magnetic field and sham
controls. With methyl methane sulfonate (MMS) or H2O2
alone, the number of AP sites increased with longer treatment times. ELF
magnetic field in combination with the genotoxic agents increased AP-site
levels compared with the genotoxic agents alone. The results suggest that the
number of AP sites induced by the genotoxic agents is enhanced by ELF magnetic
field, presumably thereby lengthening
the lifetime of radical pairs.
Fukushima et al. examined the effects of an ELF
magnetic field applied phosphate buffered saline solution (PBS) or water on ATP
activity [
Ono et al. evaluated the effect of 44 mT
static magnetic field on glucose uptake as the energy source of the metabolic
change, and on gene expression of glucose transporters (GLUT1 and GLUT3) [Ono,
2006]. The static magnetic field was applied to the cultured cells (30 x 104
cells/mL) for 8 or 24 h. The target cell was neuroblastoma NG108-15.
Glucose uptake of the cells and mRNA expression was measured by the
phenol-sulfuric acid method and RT-PCR technique, respectively. The results
showed that the glucose uptake of the cells was enhaced in 8 h exposure, while
the GLUT1 and GLUT3 mRNA expression shows no change. In contrast, in 24 h
exposure to static magnetic field, the glucose uptake and GLUT1 and GLUT3 mRNA
expression were suppressed. The authors suggested tha the metabolic activity
change observed during the 24 h exposure may attribute to the change in glucose
uptake and modification of GLUT1 and GLUT3 gene expression.
K1.3.3 Other Studies
Koyama et al. examined the effects of an ELF magnetic field (5 mT and 60 Hz) and/or
X-rays on mutations in the supF gene carried by pTN89 plasmids in Escherichia coli (E. coli) [Koyama, 2005]. The plasmids were subjected to sham exposure or exposed to ELF
magnetic field, with or without X-ray irradiation (10 Gy). Increased mutant
fraction was not detected following exposure to ELF magnetic field alone, or
after sham exposure. The mutant fraction for X-rays followed by an ELF magnetic
field was significantly higher than those of other treatments. Sequence
analysis of the supF mutant plasmids revealed that base substitutions were
dominant on exposure to X-rays alone and X-rays plus an ELF magnetic field.
Several types of deletions were detected in only the combined treatments, but
not with X-rays alone. There were no mutant colonies in sham irradiated and an
ELF magnetic field alone treatment, but exposure to ELF magnetic field
immediately before or after X-ray irradiation may enhance the mutations. These
results indicate that an ELF magnetic field increases mutation and alters the
spectrum of mutations.
Ohkubo et al. reviewed the effects of static
magnetic field of 0.3-180 mT, ELF magnetic field of 0.1-30 mT and microwave,
1.5 GHz with SAR of 0.08-8 W/kg on microcirculary system in different tissues
in experimental animals of rat, rabbit, house and human [Ohkubo, 2007]. He
emphasized that there is an importance of understanding the effects of magnetic
fields on microcirculatory system. It may have direct and indirect role in
interaction of magnetic fields with different tissues. The results obtained from
ELF and RF electromagnetic field failed to show any changes in microcirculatory
system except for leukocyte and endotherlial cell interaction. The animal study
can contribute to evaluate possible health risks of electromagnetic field.
K.1.4 IF Magnetic Field
Chuman et al. first, investigated the effect
of 20 kHz intermediate frequency (IF) magnetic field on Xenopus laevis [Chuman,
2007]. They compared the tail-length of frogs between exposed and control
groups after exposure to IF magnetic field. The parameters were the exposure
time and strength of magnetic field intensity. They used two exposure
equipments, the commercial available induction heater (IH) cooker and Merritt
coil type exposure facility. The results showed that the exposure may spped up
metamorphosis of frog.
Tachi et al. investigated whether 20 kHz magnetic field of 0.5 mT and 1
mT induce DNA damage or physiologically abnormality in bacterial cells
containing bacteriophage λ [Tachi, 2005]. Their results showed that after
exposure to magnetic field for about 4 and 8 hours, the prophages shifted to
lytic growth more often than control group. The results were compared to the
result of 60 Hz, 45 mT magnetic field exposure experiments. The comparison gave
the both IF and ELF magnetic fields induce physiological damage in bacterial
cells.
Morimoto et al. examined the effects of an
intermediate frequency (IF) electromagnetic field (10 MHz for 24 h) on
production of endothelin-1 (ET-1) in cultured endothelial cells [Morimoto, 2005].
IF electromagnetic field reduced ET-1 basal levels in human umbilical vein and
microvascular endothelial cells, but failed to reduce ET-1 basal levels in
bovine and human aortic endothelial cells. IF electromagnetic field
significantly inhibited thrombin-stimulated ET-1 production in all four
endothelial cell types in a dose-dependent manner. IF electromagnetic field
significantly inhibited thrombin-induced endothelin-1 mRNA expression in all
four cell types. The inhibitory effect of IF electromagnetic field on ET-1
production was abolished by the NOS inhibitor, NG-monomethyl-L-arginine (10-3
M). These results demonstrate that IF electromagnetic field modulates ET-1
production in cultured vascular endothelial cells and the inhibitory effect of
IF electromagnetic field is, at least partly, mediated through a NO-related
pathway.
Miyakoshi et
al. examined the cellular genotoxicity of an IF magnetic field (532±20 μT
at 23 kHz) in cultured cells [Miyakoshi, 2007]. Exposure to IF magnetic field
for 2 h did not affect the growth of Chinese hamster ovary (CHO)-K1 cells and
caused no mutagenic effects in bacterial mutation assays. Exposure to the IF
magnetic field for 2 h induced neither single nor double DNA strand breaks in
comet assays, and caused no significant change in the mutation frequency at the
hypoxanthine-guanine phosphoribosyl
transferase (HPRT) locus
compared to sham exposure. The results suggest that exposure to an IF magnetic
field for 2 h does not cause cellular genotoxicity in bacteria and in CHO
cells.
Haga
et al. investigated the effects of IF magnetic fields with 20 kHz, 600μT on
living biological cells using a highly sensitive mutagenesis assay method
[Haga, 2005]. A bacterial gene expression system for mutation repair (umu
system) was used for the sensitive evaluation of damage in DNA molecules. Salmonella typhimurium TA 1535 (pSK
1002) was used in this study. No effect from exposure to 20 kHz, 600 μT
magnetic field in terms of damage in DNA molecules were observed.
Shigemitsu et al. reviewed the biological effects
of IF electromagnetic fields with around 20 kHz from in vivo and in vitro
studies [Shigemitsu, 2007]. After the short review based on published papers,
they concluded that the available research data is inadequate for health risk
assessment of IF electromagnetic fields. They also recommended that the study
and exposure experiment of the biological and health effect of IF
electromagnetic fields are very important.
K1.5 RF and Microwaves
K1.5.1 In Vivo Studies
Hata et al. studied the effects on melatonin synthesis in rats after
short term exposure to a 1439 MHz time division multiple access (TDMA)
electromagnetic field [Hata, 2005]. The average specific absorption ratio (SAR)
of the brain was 7.5 W/kg, and the average SAR of the whole body were 1.9 and
2.0 W/kg for male and female rats, respectively. No significant differences in
melatonin and serotonin levels were observed between the exposure, sham, and
cage control groups. These results suggest that short term exposure to a 1439
MHz TDMA electromagnetic field (about four times stronger than that emitted by
mobile phones) did not alter melatonin and serotonin synthesis in rats.
Kuribayashi et
al.
investigated the effects of
1439 MHz electromagnetic field exposure on the blood-brain barrier (BBB) were
using immature (4 weeks old) and young (10 weeks old) rats [Kuribayashi, 2005].
Alteration of BBB related genes, such as those encoding p-glycoprotein,
aquaporin-4, and claudin-5, was assessed at the protein and mRNA levels in the
brain after local exposure of the head to electromagnetic field at 0, 2, and 6
W/kg SAR for 90 min/day for 1 or 2 weeks. Although expression of the 3 genes
was clearly decreased after administration of 1, 3-dinitrobenzene (DNB) as a
positive control, when compared with the control values, there were no
pathologically relevant differences with the electromagnetic field at any
exposure levels at either age. Vascular permeability was not affected by
electromagnetic field exposure. Thus, these findings suggest that local
exposure of the head to 1439 MHz electromagnetic field exerts no adverse
effects on the BBB in immature and young rats.
Yuasa et al.
investigated whether the radiofrequency electromagnetic fields (RF-EMF) emitted
by a mobile phone for 30 min has short-term effects on human somatosensory
evoked potentials (SEP) [Yuasa,
2006].
Neither SEP nor their recovery function was affected by exposure to RF
electromagnetic field or sham phone use. The results suggest that 30 min mobile
phone use has no short-term effects on the human sensory cortex.
Inomata-Terada et
al. investigated whether RF electromagnetic
fields emitted by a mobile phone has
short-term effects on the human motor cortex [Inomata-Terada, 2007]. They
measured motor evoked potentials (MEP) elicited by single pulse transcranial
magnetic stimulation (TMS), before and after mobile phone exposure (active and
sham) in 10 normal volunteers. Three sites were stimulated (motor cortex (CTX),
brainstem (BST) and spinal nerve (Sp)). The short interval intracortical
inhibition (SICI) of the motor cortex reflecting GABAergic interneuronal
function was also studied by paired pulse TMS method. MEP to single pulse TMS
was also recorded in two patients with multiple sclerosis (MS) showing
temperature dependent neurological symptoms (hot bath effect). Neither MEP to
single pulse TMS nor the SICI was affected by 30 min of RF electromagnetic
field exposure from mobile phones or
sham exposure. In two MS patients, mobile phone exposure had no effect on any
parameters of MEP even though conduction block occurred at the corticospinal
tracts after taking a bath.
Terao et al.
investigated whether exposure to pulsed high-frequency electromagnetic field
(pulsed EMF) emitted by a mobile phone has short-term, 30 min, effects on
saccard performances [Terao, 2007]. Using 10 normal subjects (4 male, 6 female,
with 33.1±8.6 years (23-52 years), they studied the performance of visulally
guided saccarde (VGS), gap saccade (GAP), and memory guided saccade (MGS) tasks
before and after exposure to 800 MHz EMF with 0.054±0.02 W/kg of 10 g. They
also implemented a hand reaction time (RT) task in response to a visual signal.
In conclusion, Thiry minutes of moble phone exposure has no significant
short-term effect on the performance of various saccade tasks, which suggests
that the cortical processing for saccades and attention is not affected.
Shirai et al. evaluated the
effects of a 2-year exposure to a RF electromagnetic equivalent
to that generated by cellular phones on tumor development in the central
nervous system (CNS) of rats [Shirai, 2005, 2007]. Pregnant F344 rats were given a single administration
of N-ethylnitrosourea (ENU) on gestational day 18. A 1.439 GHz time division multiple access (TDMA)
signal for the Personal Digital Cellular (PDC), Japanese standard cellular
system was used for the exposure of the rat head starting from 5 weeks of age,
90 min a day, 5 days a week, for 104 weeks [Shirai, 2005]. A 1.95 GHz
wide-band code division multiple access (W-CDMA) signal for the International
Mobile Telecommunication 2000 (IMT-2000) cellular system was also employed [Shirai, 2007]. Under the present
experimental conditions, exposure of heads of rats to both RF electromagnetic
field signals for a 2-year period was not demonstrated to accelerate or
otherwise affect ENU-initiated brain tumorigenesis.
Jia et al. monitored local temperature changes in rabbit pinnae, which were evoked by RF electromagnetic field for 20 min at local SAR levels of 0 (sham exposure), 2.3, 10.0, and 34.3 W/kg over 1.0 g rabbit ear tissue [Jia, 2007]. The effects of exposure RF electromagnetic field on skin temperature were measured under normal blood flow and without blood flow in the ear. The results showed: (1) blood flow clearly modified the RF electromagnetic field-induced thermal elevation in the pinna as blood flow significantly suppressed temperature increases even at 34.3 W/kg; (2) under normal blood flow conditions, exposures at 2.3 and 10.0 W/kg, approximating existing safety limits for the general public (2 W/kg) and occupational exposure (10 W/kg), did not induce significant temperature rises in the rabbit ear. However, 2.3 W/kg induced local skin temperature elevation under no blood flow conditions. These results demonstrate that the effects of blood flow should be considered when extrapolating modeling data to living animals, and particular caution is needed when interpreting the results of modeling studies that do not include blood flow.
Masuda
et al. examined the influence of RF
electromagnetic field on rat skin using Global System for Mobile Communication
(GSM)-900 or -1800 Radio Frequency Radiation (RFR) [Masuda, 2007a]. Hairless female rats were exposed or sham-exposed
for 2 h to GSM-900 or -1800 signals, using a loop-antenna located on the right
part of the rats' back. The local SAR at skin level was 5 W/kg. A skin biopsy
was done at the end of the experiment not only at the location of exposure, but
also on the symmetrical part of the back. Analysis of skin sections using
hematoxylin eosin saffron (HES) coloration showed no difference in skin
thickness or apparent cell toxicity among the animal groups. Histological
analysis of the epidermis showed that the ratio between cells expressing the
antigen Ki-67 (cellular proliferation marker) and the total number of cells
remained within the range of normal proliferation ratio for the exposed side of
the animal. No Ki-67 labelling was observed at the dermis level. Results on
filaggrin, collagen and elastin levels also showed an insignificant influence
of RFR. These results do not demonstrate any major physical and histological
variations at skin level induced by RFR used in mobile telephony.
Masuda
et al. further investigated the
effects of RF electromagnetic field on cerebral microcirculation in rat brain [Masuda, 2007bc]. The head of the rat
was exposed for 10 min to 1439 MHz RF electromagnetic field at 0.6, 2.4 and 4.8
W/kg of brain averaged SAR [Masuda,
2007b], and for 4 weeks (60 min/day, 5 days/week) to RF electromagnetic
field at 2.4 W/kg of brain averaged SAR [Masuda, 2007c]. Four microcirculatory parameters (BBB
permeability, leukocyte behavior, plasma velocity, and vessel diameter) were
measured before and after RF electromagnetic field exposure using a closed
cranial window method. No extravasation of intravenously injected dyes from
pial venules was found at any SAR level. No significant changes in the number
of endothelial-adhering leukocytes after exposure were found. The hemodynamics
indicated that the plasma velocities and vessel diameters remained constant
within the physiological range throughout each exposure. These findings suggest
that there were no effects on the cerebral microcirculation under the given RF
electromagnetic field exposure conditions.
Ushiyama
et al. investigated the effect on
Blood Cerebrospinal fluid Barrier (BCB) function of rat by RF electromagnetic
fields exposure [Ushiyama, 2007]. They set up a real-time measuring system for
BCB function using a micro-perfusion method. After the short time exposure (30
min), 1.5 GHz RF electromagnetic field at the brain average SARs of 9.5 W/kg
for adult and 10.4 W/kg for juvenile did not affedct BCB function in rats.
The
uncertainty of a large-scale long-term in
vivo study on brain tumor has been evaluated by Wang et al. and Wake et al.
[Wang 2006d 2006e: Wake, 2007a]. They found that the uncertainty of brain SAR
in the rats in the exposure setup is higher for male rats than for female rats.
Wake et al. developed an exposure
setup for local exposure of a rabbit eye in order to evaluate the threshold of
ocular effects such as cataract at 2.45 GHz [Wake, 2007b].
K1.5.2 In Vitro Studies
Wang et al. examined the effects of 2450 MHz
RF electromagnetic field on malignant changes in mouse C3H10T1/2 cells [Wang,
2005a]. The cells were exposed to the RF electromagnetic field alone in SAR
from 5 to 200 W/kg for 2 h and/or were treated with a known initiating
chemical, methylcholanthrene (MC) (2.5 μg/ml). No significant differences were
observed in the malignant transformation frequency between the controls and RF
electromagnetic field with or without 12-O- tetra decanoylphorbol-13-acetate
(TPA) (0.5 ng/ml), a tumor promoter that could enhance transformation frequency
initiated by MC in multistage carcinogenesis. However, the transformation
frequency for RF electromagnetic field in SAR of more than 100 W/kg with MC or
MC plus TPA was increased compared with MC alone or MC plus TPA. In contrast,
the corresponding heat groups (heat alone, heat + MC, and heat + MC + TPA) did
not increase transformation compared with each control level. The results
suggest that 2450 MHz RF electromagnetic field could not contribute to the
initiation stage of tumor formation, but it may contribute to the promotion
stage in very high SAR (>100 W/kg).
Wang et al. further investigated the effects
of 2450 MHz RF electromagnetic field on a stress response in A172 cells, using
heat shock proteins (HSP)70 and HSP27 as stress markers [Wang, 2006b]. The
cells were exposed to the RF electromagnetic field with a wide range of SAR
(5-200 W/kg) or sham conditions. Since the RF electromagnetic field in 50-200
W/kg SAR causes temperature increases in culture medium, appropriate heat
control groups (38-44 °C) were also included. The results showed that the
expression of HSP70 increased in a time and dose-dependent manner in >50
W/kg SAR for 1-3 h. A similar effect was also observed in corresponding heat
controls. There was no significant change in HSP27 expression caused by RF
electromagnetic field at 5-200 W/kg or by comparable heating for 1-3 h.
However, HSP27 phosphorylation increased transiently at 100 and 200 W/kg to a greater
extent than at 40-44°C. Phosphorylation of HSP27 reached a maximum after 1 h
exposure at 100 W/kg RF electromagnetic field. The results suggest that
exposure to a RF electromagnetic field has little or no apparent effect on
HSP70 and HSP27 expression, but it may induce a transient increase in HSP27
phosphorylation in A172 cells in very high SAR (>100 W/kg).
Komatsubara et al. investigated
the effects of RF electromagnetic field on chromosomal aberrations in mouse m5S
cells [Komatsubara 2005a]. The RF
electromagnetic field exposure was performed at 2.45 GHz for 2 h at average SAR
of 5-100 W/kg with continuous wave-form (CW), or at a mean SAR of 100 W/kg
(with a maximum of 900 W/kg) with pulse wave-form (PW). The effects of RF
electromagnetic field exposure were compared with those in sham-exposed
controls and with mitomycin C (MMC) or X-ray treatment as positive controls. No
significant differences were observed following exposure to RF electromagnetic
field in SAR from 5 to 100 W/kg CW and at a mean SAR of 100 W/kg PW compared
with sham-exposed controls, whereas treatments with MMC and X-rays increased
the frequency of chromatid-type and chromosome-type aberrations. RF
electromagnetic field exposures at 2.45 GHz for 2 h with up to 100 W/kg SAR CW
and an average 100 W/kg PW do not induce chromosomal aberrations in m5S cells.
Furthermore, there was no difference between exposures to CW and PW RF
electromagnetic field.
Takashima et
al. examined the effects of 2.45 GHz RF electromagnetic field with SAR from
0.05 to 1500 W/kg in vitro [Takashima, 2006]. When cells (CHO-K1 and MO54)
were exposed to a continuous RF electromagnetic field in SAR from 0.05 to 100
W/kg for 2 h, cellular growth rate, survival, and cell cycle distribution were
not affected. At 200 W/kg, the cell growth rate was suppressed and cell
survival decreased. When the cells were exposed to an intermittent RF
electromagnetic field at 300 W/kg (pk), 900 W/kg (pk) and 1500 W/kg (pk) (100
W/kg [mean]), no significant differences were observed between these conditions
and intermittent wave exposure at 100 W/kg. When cells were exposed to a SAR of
50 W/kg for 2 h, the temperature of the medium around cells rose to 39.1°C, 100
W/kg exposure increased the temperature to 41.0°C, and 200 W/kg exposure
increased the temperature to 44.1°C. Exposure to RF electromagnetic field
results in heating of the medium, and the thermal effect depends on the mean
SAR. Hence, these results suggest that the proliferation disorder is caused by
the thermal effect.
Koyama et al. investigated the effects of 2.45
GHz RF electromagnetic field on bacterial mutations and the HPRT gene mutations
[Koyama, 2007b]. Bacteria were exposed to RF electromagnetic field for 30 min
in SAR from 5 to 200 W/kg. In all strains, there was no significant difference
in the frequency of revertant colonies between sham exposure and RF
electromagnetic field-exposed groups. In examination of mutations of the HPRT
gene, CHO-K1 cells were exposed to RF electromagnetic field for 2 h in SAR from
5 to 200 W/kg. A combination effect of simultaneous exposure to RF
electromagnetic field and bleomycin was detected at the respective SAR. A
statistically significant difference was observed between the cells exposed to
RF electromagnetic field at the SAR of 200 W/kg. Cells treated with the
combination of RF electromagnetic field in SAR from 50 to 200 W/kg and
bleomycin exhibited increased HPRT mutations. As the exposure to RF
electromagnetic field induced an increase in temperature, these increases of
mutation frequency may be a result of activation of bleomycin by a thermal
effect.
Sakuma et
al.
conducted a large-scale in vitro study focused on the effects of
RF
electromagnetic field
from mobile radio base stations employing the IMT-2000 cellular system [Sakuma,
2006]. First, they evaluated the responses of human cells to microwave exposure
at a SAR of 80 mW/kg, which corresponds to the limit of the average whole body
SAR for general public exposure defined as a basic restriction in the ICNIRP
guidelines. Second, they investigated whether continuous wave (CW) and Wideband
Code Division Multiple Access (W-CDMA) modulated signal RF electromagnetic
field at 2.1425 GHz induced different levels of DNA damage. Human glioblastoma
A172 cells and normal human IMR-90 fibroblasts were exposed to RF
electromagnetic field.
A172 cells were exposed to W-CDMA radiation at SARs of 80, 250, and 800 mW/kg
and CW radiation at 80 mW/kg for 2 and 24 h, while IMR-90 cells were exposed to
both W-CDMA and CW radiations at a SAR of 80 mW/kg for the same time periods.
Under the same RF electromagnetic field exposure conditions, no significant
differences in the DNA strand breaks were observed between the test groups and
the sham-exposed control groups. These results confirm that low level exposures
do not act as a genotoxicant up to a SAR of 800 mW/kg.
Hirose et
al.
investigated the effects of RF
electromagnetic field
on apoptosis or other cellular stress response through p53 activation or the
p53-signaling pathway [Hirose, 2006]. Under the RF electromagnetic field conditions described above (IMT-2000), no
significant differences in the percentage of apoptotic cells were observed
between the test groups and the sham-exposed control groups. No significant
differences in expression levels of phosphorylated p53 at serine 15 or total
p53 were observed between the test groups and the sham-exposed control groups.
Moreover, there were no noticeable differences in gene expression of the
subsequent downstream targets of p53 signaling involved in apoptosis between
the test groups and the sham-exposed control groups. These results confirm that
RF
electromagnetic field
up to 800 mW/kg does not induce p53-dependent apoptosis, DNA damage, or other
stress response in human cells.
Hirose et
al.
further examined the effects
of RF
electromagnetic field on phosphorylation and overexpression of a heat shock protein HSP27
[Hirose, 2007]. Under the RF field exposure conditions described above
(IMT-2000), no significant differences in the expression levels of
phosphorylated HSP27 at serine 82 (HSP27 [pS82]) were observed between the test
groups and the sham-exposed control groups. Moreover, no noticeable differences
in the gene expression of hsps were observed between the test groups and the
sham-exposed control groups. These results confirm that e RF
electromagnetic field
up to 800 mW/kg does not induce phosphorylation of HSP27 or expression of hsp
gene family.
Using of
human glioma MO54 cells, Miyakoshi et al. investigated whether radio frequency
field exposure (1950 MHz with SAR of 1, 2 and 10 W/kg) could activate stress
response genes [Moyakoshi, 2005b]. After the exposure up to 2 h, cell growth
and cell number were counted at 0-4 days after exposure. Expression of HSP27,
HSP70 and the level of phoshorylated HSP27 (78Ser) protein were determined. The
results suggested that although exposure to a 1950 MHz RF electromagnetic field
has no effect on cell proliferation and expression of HSP27 and HSP70, it may
inhibit the phosphorylation of HSP27 at Serine 78 in MO54 cells.
Hikage et al. performed in vitro experiments on
free radical production due to 900 MHz and 2.45 GHz mobile radio wave exposure
[Hikage, 2006, 2007b]. Using of human white blood cell exposed to 900 MHz RF
electromagnetic field, they investigated the estimation of hydroxyl free
radical production due to non-thermal effects. Including 900MHz wave, the six
different sets of exposure conditions were used: 1) continouse wave, 2) pulse
modulation, 3) GSM (Global System for Mobile Communication) basic signal
modulation, 4) PDC (Personal Digital Cellular) signal modulation and 5) CDMA
(Code Divison Multiple Access) 2000 signal modulation. The exposure level can
be changed from cellular level to high SAR level (up to 150 W/kg). The cell’s
temperatures were kept below 39 ℃. The experimental data
confirms that there is no statistically significant influence of 900 MHz RF
electromagnetic field exposure on human white blood cells and that there is a
correlation between radical production and cell temperature. In addition,
Hikage et al. tried to confirm the
effects of 900 MHz and 2.45 GHz RF electromagnetic field exposures on the
production of free radical in human fibroblasts cells.
K1.5.3 Other Studies
There have
been increased in the number of cellular phone users. With increasing there
have been many reports of health disorders related to RF electromagnetic
fields. Kawasaki et al. considered
and confirmed the dependency of students (Thai university and high school) on
cellular phones and compared the results with the dependency of Japanese
students (University and high school) [Kawasaki, 2006]. A survey form (cellular
phone dependence questionnaire; CPDQ) was distributed to 181 female and 177
male Thai university students and to 240 female and 140 male Thai high school
students. Aftere factor analysis, the total scores for the Thai university was
higher than the scores for the Thai high school students. The total socre of
the questionnaire was high, indicating a strong tendency toward cellular phone
dependence.
Due to the
rapid increase of cellular phone use in
K2 Field measurement,
Dosimetry and Exposure Asessment
K2.1 DC and ELF Fields
Moriyama et al. assessed ELF magnetic field
originating from equipment used for assisted reproduction, umbilical cord-blood
and peripheral-blood stem cell transplantation, transfusion, and hemodialysis
[Moriyama, 2005a]. The ELF magnetic field values were 0.1-1.2 μT on clean
benches, <0.1-8.0 μT on inverted microscopes, <0.1-13.6 μT in CO2
incubators, 4.3-11.5 μT in centrifuges, 0.4-18.8 μT in programmed freezers,
<0.1-0.3 μT in deep freezers, 0.3-3.1 μT on cell separators, and 0.2-0.9 μT
in hemodialysers. Frequencies of ELF magnetic field were nominally 60 Hz, but
some devices showed non-sinusoidal 120 Hz. Such ELF magnetic field can be
reduced by shielding the sources or altering the protocols employed.
Moriyama et al. measured ELF magnetic field at
696 points in a room of a typical Japanese apartment building [Moriyama,
2005b]. ELF magnetic field exceeded 0.4 μT in 24 % of the living space, and the
maximum value, 1.8 μT, was detected at floor level. Analysis of the ELF
magnetic field distribution revealed that 60 Hz 100 V electrical wiring for
room lights within the floor and ceiling had been laid out in large rectangles,
equivalent to 1 turn coils. Further plotting of the vertical components every
0.01 m on the floor indicated that the depth of the cable was 0.23 m. Further
studies should be conducted in order to confirm that the building investigated
in this pilot study is typical of Japanese apartment buildings in terms of ELF
magnetic field.
Kabuto et al. evaluated the effects of
residential power-frequency ELF magnetic field as a possible human carcinogen
by the International Agency for Research on Cancer (IARC) [Kabuto, 2006]. In
response to great public concern, the World Health Organization (WHO) urged
that further epidemiologic studies should be conducted in high-exposure areas
such as
Yamazaki et al. examined the association between
residential proximity to 60 Hz high voltage (22-500 kV) overhead transmission
lines (HVOTL) and mental health [Yamazaki, 2006]. The prevalence of poor mental
health was 15 %. Among the 223 subjects, 10 lived within 100 m of a HVOTL. The
adjusted odds ratios (OR) for poor mental health among those who lived 101-300
m or within 100 m from HVOTL were 1.29 (95 % confidence interval (CI):
0.35-10.13) and 1.87 (95 % CI: 0.35-10.13), respectively, against the reference
category (>300 m). Mental health status was not significantly associated
with the distance between the subject's residence and the closest HVOTL.
Hamada presented
a fast-multpile surface-charge-simulation method for calculating
three-dimentional Laplacian fields in voxel models. This method treats a
surface of a voxel that has different inside and outside conductivities as a
surface element of the indirect boundary element method [Hamada, 2006]. This
method was successfully applied to calculate the electric field induced by an
applied homogeneous EMF magnetic field in a human head model that has 1 m x 1 m
x 1 m voxel size.
In
Kitano et al. formulated mathematically the
induced electric field in a spherical conductor exposed to arbital EMF dople
magnetic field source [Kitano, 2006]. They confirmed its validity by comparing
the analytical solution with numerical solution by the equivalent multiple
moment method.
Kobayashi et al. carried out the rejection of
magnetic noise from the wire in magnetocardiogram (MCG) measurement [Kobayashi,
2005]. MCG were measured from two subjects with and without attachment of the
wire. In order to reduce the effects of magnetic noise from the wire, signal
orocessing by independent component analysis, digital-high-pass filter, and singer
value decomposition was carried out. Due to the reduction of the magnetic noise
from the wire by independent component analysis, independent component analysis
is the effective technique.
Miyata et al. proposed the free scanning method for the magnetic field
distribution measurements by recording the position of the moved sensor
automatically [Miyata, 2007]. The magnetic field sensor has two kinds of range
of the measurement frequency, low frequency (30 Hz to 1 kHz) and high frequency
(1 kHz to 100 kHz). In their study, they tried to measure two dimensional
magnetic flux density distributions in the vicinity of the induction heating
(IH) cooker.
Oikawa et al. measured the environmental
magnetic field of 50 Hz and 60 Hz in the room very close to power-receiving and
transformer rooms in two buildings [Oikawa, 2006].
In highly
non-uniform ELF magnetic field, the compliance test in accordance with
guidelines has been a crtical issue. When the measured maximum magnetic fields
on the surface of the human body exceed the reference level, the basic
restriction should be investigated in a different way. Yamazaki et al. proposed a new simplified method
for the estimation of the maximum induced current from magnetic field
measurements in practical complex [Yamazaki, 2005, 2007]. The method is based
on the reduction rate of the magnetic field within a spherical model.The
relationship between the reduction rate of magnetic field and the rate of
maximum induced current to that of uniform field exposure was approximated
using a simple regression curve. The results have practical values for
assessing compliance with guidelines.
Nishizawa et al. investigated the magnetic field
properties and dosimetry at 50 Hz, ELF with the coil model [Nishizawa, 2007].
This coil model is prescribed as substitute source model fro real household
appliances in European standard EN50366 (CENELEC). The accuracy of the magnetic
field vectors and the values of the induced current density were compared with
the results of two test appliances (a drill machine and a hand mixer) obtained
from the equivalent source model. The magnetic fields obtained using the coil
model and real appliance show an agreement with each other with a maximum
difference of 5 dB. The calculated induced current densities in the numerical
human body models (homogeneous and anatomical body models) and the real
appliances also show a good agreement with each other with a maximum difference
by a factor of 1.6. Based on the totally obtained results in this study, the
applicability of the coil model prescribed in EN50366 confirms that of the two
applied test appliances.
Takuma et al. reviewed and summarized the
recent developed topics related the basic formulas for field calculation,
effects of electromagnetic fields, calculation methods, activity of
Investigation Committte in the IEEJ, and future research subjects [Takuma,
2006].
K2.2 IF Magnetic Field
Yamazaki et al. developed IF magnetic field
exposure facility for in vivo exposure
experiment with small animal [Yamazaki, 2006a, 2006b]. Before constructing
facility, they first, investigated the effect of architectural structure on the
uniform magnetic field generated from their proposed coils by the 3D magnetic
field analysis. It is shown that the distance between coil and architectural
structure in the direction of magnetic field should be determined taking into
account the frequency. Also, the architectural structure has shielding effect.
IF magnetic field generates the eddy current inside the reinforcing steel bar,
so, the magnetic field disturbance is substantially greater in reinforced
concrete building. After these preliminary considerations, Shigemitsu et al. have developed a 20 kHz (IF)
magnetic field exposure system for in
vivo studies [Shigemitsu, 2007]. The dimensions of the exposure system are
1.6 m x 1.6 m x 1.616 m high located in the specific pathogen free (SPF)
exposure room. The system is designed to provide magnetic fields with
vertically polarized sinusoidal 20 kHz wave form up to 200 μT with the
uniformity within ±5 % over the space occupied by an animals.
Fujita et al. have developed an IF magnetic
field exposure system in vitro [Fujita,
2007]. This system mainly consists of an IF magnetic field generating coil
housed inside an incubator, inside which cultured cells can be exposed to IF
magnetic field. Two systems were prepared to allow the experiment to be
conducted in a double-blind manner. The level of the generated IF magnetic
field was set to 532 μT rms in the exposure space, 23 kHz, 80 times the value
in the International Commission on Non-ionizing Radiation Protection (ICNIRP)
guidelines, with spatial field uniformity better than 3.8 %. The waveforms were
nearly sinusoidal. The parasitic electric field was 157 V/m rms and the induced
electric field was 1.9 V/m rms. The temperature was maintained at 36.5 ± 0.5 °C
for 2 h. The leaked magnetic flux density was 0.7 mT rms or lower in the
stopped system when the other system was being operated, and the environmental
magnetic flux density was 0.1 mT rms or lower. This system could be
successfully used to evaluate the biological effects of exposure to IF magnetic
field.
Kamimura et al. evaluated the magnetic field
exposure of human body near an induction heating (IH) cooker with 20 kHz by
using of SPFD method [Kamimura, 2006]. They calculated the maximum induced
current density among thee kinds of human body models (Japanese adult
male/female and American adult male) and compared the calculated current
density with the guideline of ICNIRP. They showed that the maximum induced
current densities are different among three models. They also showed that the
induced current exceeding the guideline of ICNIRP may not flow inside human
body in the case with a portable type IH cooker and a pan designed for the IH
cooker.
Nishizawa et al. investigated the magnetic field properties and dosimetry at
21 kHz, intermediate frequency for an induction heater (IH) with the coil model
[Nishizawa, 2006]. This coil model is prescribed as substitute source model in
European standard EN50366 (CENELEC). The accuracy of the magnetic field vectors
and the values of the induced current density were compared with the results of
realistic model for IH obtained from the equivalent source model. The coil
model coincided well for the magnitude of the magnetic field strength around
the IH. On the other hand, the dominant field vector of the coil model differs
significantly from the real IH, which leads to induced current densities in the
body model, three times larger. These results showed that the application of
the coil model prescribed in the EN50366 is confirmed for the IH.
Suzuki and
Taki measured the magnetic field around induction heating hobs operated at 20
kHz and evaluated the compliance with ICNIRP guideline [Suzuki, 2005]. At the
very proximity to the device, the distribution of the magnetic flux density was
highly inhomogeneous and the maximum flux density can exceed the reference
levels of the guideline. Using of anatomical human model, the induced current
densities exposed to magnetic field were calculated numerically by impedance
method. The induced current densities were sufficiently lower than the basic
restriction of INCIRP guideline.
Tarao et al. calculated the induced current
in an anatomiccaly high-resolution human model exposed to 20.9 kHz operated
house-hold (IH) induction cooker [Tarao, 2006ab]. In case of the adult human
model exposed to highly inhomogeneous 20.9 kHz magnetic field, they calculated
that the induced current ranging from 5 to 19 mA/m2 is obtained for
between the shoulder and lower abdomen. However, for child model, it can be
obtained that the currents between 5 and 21 mA/m2 are induced for
between the head and abdomen. They also obtained the result that the induced
current in the child model are 2.1 to 6.9 times larger compared of the adult
model under the exposure condition. They further studied the induced current in
an anatomically human model of 2.5 x 2.5 x 2 mm voxel size exposed to 20.9 kHz
magnetic fields generated from IH cooker by impedande method. In calculation,
the maximum about 2 μT magnetic field near the lower abdomen of the body was
assumed. ICNIRP guideline gives that the basic restriction is expressed in term
of a current densities averaged over a cross-section of 1 cm2 perpendicular
to the direction of the current. Tarao et
al. proposed the conversion of computed results to corresponding current
densities by averaging the current over the cross section of any 1 cm2
of the model. The calculation results showed that the maximum averaged current
densities, 5.31 mA/m2 appears at the muscle of the abdomen, close to
the magnetic sources. This value is 1/8 of the ICNIRP basic restriction level
for the public exposure. In calculation at certain voxel, the averaging is key
procedure. For example, the maximum value with the averaging decreased by 60 %
from 13.2 mA/m2 without the averaging to 4.31 mA/m2.
Induction heating (IH) cooker is
recently very popular in
K2.3 Radio frequency
electromagnetic fields and Microwaves
Wang et al. reported some detailed dosimetry results
for the Salford-used transverse electromagnetic (TEM) cell in rats [Wang,
2006a]. The whole-body average SAR and the brain-average SAR varied up to 1.5
times and 2.7 times, respectively. For an input of 1 W to the TEM cell, the
whole-body average SAR was 1.1 W/kg, while the brain-average SAR was 1.0 W/kg.
This means that the TEM cell structure obviously produces not a local but a
whole body exposure.
Wang et al. evaluated RF electromagnetic field
in experimental fusion facilities for safety guidelines to ensure workers’
safety [Wang, 2005b]. Since the leaked RF electromagnetic field has
time-varying characteristics whose amplitudes vary according to a stochastic
process, a measurement of the amplitude probability distribution (APD) was
conducted. An approach was then presented to derive from the measured APD and
SAR in an exposed human body. The statistically-averaged whole-body-averaged
SAR showed that the leaked field intensities were low enough to not cause any
thermal hazards for the workers in the specific RF electromagnetic field
environment. The statistically averaged SAR also showed fair agreement with the
SAR derived from the time average over 6 min as specified in the safety guidelines.
This finding suggests the usefulness of the APD measurement in lieu of a field
measurement over a 6-min period because the APD can be obtained in a time
period much less than 6 min.
Wang et al. made a detailed error analysis in
the whole-body average SAR calculation for the finite-difference time-domain
(FDTD) method in conjunction with the perfectly matched layer (PML) absorbing
boundaries [Wang, 2006b]. They derived a basic rule for the PML employment
based on a dielectric sphere and the Mie theory solution. They then attempted
to clarify to what extent the whole-body average SAR may reach using an
anatomically based Japanese adult model and a scaled child model. The results
showed that the whole-body average SAR under the ICNIRP reference level exceeds
the basic safety limit nearly 30 % for the child model both in the resonance
frequency and 2 GHz band [Wang, 2006c].
Hirata
investigated the effect of frequency, polarization, and angle of incidence of
an ELF electromagnetic field on the SAR and maximum temperature increase in the
human eye at 900 MHz, 1.5 GHz, and 1.9 GHz [Hirata, 2005a]. The SAR and
temperature increased in the eye, largely dependent on the separation between
the eye and a source, and the frequency, polarization, and angle of incidence of
the ELF electromagnetic fields wave. The maximum temperature increased
(0.303-0.349 °C) in the lens of the adult for the SAR value of 2.0 W/kg for the
eye tissue (about 10 g) was marginally affected by the above-mentioned factors.
No clear difference of a maximum temperature increase in the lens at the SAR
limit was observed between the adult and children models.
Hirata et al. investigated statistically the
maximum temperature increases in the head and brain for the SAR averaging
schemes prescribed in the ICNIRP and IEEE guidelihnes [Hirata, 2005b]. They
paid much attention to the correlation between peak SARs and maximum
temperatures. They found that maximum temperature increases iin the head are
well correlated with peak spatial average SARs calculated with different
schemes. Maximum temperature increases in the head for peak SAR values are
largely dependent in the averaging scheme.
Hikage et al. estimated the electromagnetic
field exciation by cellular radios in actual train carriages [Hikage, 2005b]. They
mentioned; with regard to the electromagnetic compatibility (EMC) of the
portable radio terminals such as cellular phones and data communication
transceivers, the important issue is to prevent the occurrence of unwanted
effects on the human health due to the RF exposure. As example, they conducted
the precise computer numerical stimulating, FDTD method, using 800 MHz and 2
GHz transmitter in an actual train carriage and estimated the electromagnetic
field distribution excited inside train carriage. The parallel FDTD computer
simulation could be considered to be effective for estimating the complicated
electromagnetic field excitation problems precisely.
Hikage et al. developed a 900 MHz
ridged-waveguide microwave exposure equipment to achieve high power density
irradiation for in vitro experiments
[Hikage, 2007d]. This exposure system consists of a vector signal generator,
100 watts transistor amplifer, stub tuner, the ridged waveguide and terminator.
Ishikawa and
Tanimura visualized the magnetic leakage flux from cellular phone [Ishikawa,
2006]. As a result of the visualization, the magnetic leakage flux from some
parts of cellular phones can be clearly observed even when the cellular phone
is turned off. The magnetic leakage flux can be estimated roughly to be about
0.01 mT. They emphasized this visualizing technique is usefull for the research
areas of human health, environmental medicine, scientific education and
engineering.
Although there are several papers on the
evaluation of electromagnetic wave exposure in the fetues, the abdomen model,
of pregnant women, the structure inside the models is not representive of
actual situation due to the organ and tissue complexity of the mother and
fetus. So, Kawai et al. presented a
simple abdomen modcel of pregnant women and evaluated the SAR inside the
proposed model close to normal mode helical antennas (NHAs) [Kawai, 2006]. The
SAR was calculated using FDTD method. They confirmed that the 10-g average SAR
in the fetus is sufficiently less than 2 W/kg, when the output power of NHAs is
5 W which is the maximum power of portable radio terminals in
Nagaoka et al. developed an anatomicazlly
realistic whole-body pregnant-woman model for electromagnetic dosimetry
[Nagaoka, 2007]. The numerical dosimetry of pregnant women is an important
issue in electromagnetic field safety. They constructed a new fetus model
including inherent tissues of pregnant women based on abdominal magnetic
resonance imaging data of a 26-week-pregnant woman. The whole-body pregnant woman
model was developed by combining the fetus model and a nonpregnant-woman model.
The modle consists of about 7 million cubical voxels of 2mm size and is
segmented into 56 tissues and organs.First, this pregnant-woman model is
completely anatomically realistic voxel model that includes a realistic fetus
model and enables a numerical simulation of electromagnetic dosimetry up to the
gigahertz band. In this paper, the basic specific absorption rate
characteristics of the pregnant-woman model exposed to vertically and
horizontally polarized electromagnetic waves from 10 MHz to 2 GHz.
With rapid
increase in the use of the mobile phones in enclosed environments such as
trains and elevators, public concern regarding the possibility of the RF
exposure in such areas exceeding the basic restriction of the ICNIRP exposure
guideline has been growing. Using of FDTD calculation method, Simba et al. carried out to determine whether
the exposure in the elevator can exceed the basic restriction, 0.08 W/kg,
whole-body average SAR [Simba, 2007a, 2007b]. They performed the FDTD
calculation of the 10 g average SAR as a function of the human body position
inside an elevator at 900, 1500 and 2000 MHz. The SAR results are below the
ICNIRP exposure guideline.
Wang et al have developed a formulation to
approximate complex permittivities of biological tissues and organs as function
of age [2006e]. The model is based on the dependence on water-content ratio
which is dominant to determine the complex permittivitis in GHz band.
A novel technique
to evaluate SAR experimentally has been developed by Suzuki et al. [Suzuki, 2006]. Using liquid crystal sensitive to
temperature, they measured temperature elevation due to microwave exposure.
Standardization
of procedures for compliance tests of wireless terminals is also one of
important topics. Mochizuki et al.
clarified the effects of the size and shape of head phantoms on SAR
distributions during exposure to near-field from a cellular phones [Mochizuki,
2007]. Ishii et al. investigated on
applicability of a small antenna in phantom liquid for calibration of SAR
probes [Ishii, 2007].
K3 Tissue Properties,
Materials, and Phantoms
K3.1 Design Methods of
the Electromagnetic Environment
Tosaka et al. developed a measuring system
using a tri-axial search coil in order to measure the magnetic field noise
around electric devices [Tosaka, 2005]. They chose the measuring frequency is
less than 100 kHz and the sensitivity is of the order of pico Tesla. In
conclusion, the crosstalk of the orthogonal search coil is less than -40dB
between the tri-axial search coil sensors. The sensitivity of the search coil
is 10 pT/√Hz at 1 kHz.
K3.2 Phantoms andTissue
Properties-Bioelectromagnetics Parameters
Hirata et al.
quantified induced current in anatomically based Japanese male and female
models for exposure to low-frequency electric fields [Hirata, 2007b]. A quasi-static FDTD method was applied to analyze this problem. For the
computational results, the difference of the induced current density averaged
over an area of 1 cm2 between Japanese male and female models was
less than 30 % for each nerve tissue. The difference of induced current density
between the present study and earlier works was less than 50 % for the same
conductivities, despite the different morphology. Particularly, maximum current
density in central nerve tissues appeared in the retina of Japanese models, the
same as in the earlier works.
Hirata et al. computationally verified the effect
of anesthesia on temperature variations in the rabbit eye due to microwave
energy [Hirata, 2006a]. The FDTD method was used for calculating the SAR and
temperature variation in rabbits. They used a computational rabbit phantom,
which is comprised of 12 tissues (including 6 eye tissues) with a resolution of
1 mm. Thermal constants of the rabbit were derived by comparing measured and
calculated temperatures. For intense microwave exposure to the rabbit eye, time
courses of calculated and measured temperatures were in good agreement for
cases both with and without the administration of anesthesia. The point to be
stressed is that under anesthesia the thermoregulatory response was
inactivated, and blood flow and basal metabolism was reduced.
The correlation
between the peak spatial-average SAR and maximum temperature increase for
antennas attached to the human trunk was reported [Hirata, 2006b]. Frequency
bands considered are 150, 400, and 900 MHz, which are assigned for occupational
communications. The effect of variation of thermal constants on the temperature
increase is revealed by using one-dimensional model. Computational results
suggests that one of the most dominant factors which affect the correlation
between peak SAR and maximum temperature increase is blood flow in tissues.
Hirata
proposed an improved heat transfer model of the eye for exposure to RF
electromagnetic field. Particular attention was paid to the difference from the
simplified heat transfer model commonly used in this field [Hirata, 2007a].
From the computational results, the temperature elevation in the eye calculated
with the simplified heat transfer model was largely influenced by the RF
electromagnetic field-induced SAR outside the eyeball, but not when using their
improved model.
Hirata et al. reported that a RF
electromagnetic field-induced SAR of the human body for far-field exposure at the International
Commission on the ICNIRP reference level has two peaks in the resonance
frequency and GHz regions [Hirata, 2007d]. Dominant factors influencing whole-body
average SAR in these two frequency regions have not yet been revealed
sufficiently. The main purpose of this study is to clarify the dominant factors
influencing the SAR in terms of whole-body average SAR in an anatomically based
model compared with those in a homogeneous anthropomorphic model and
corresponding cuboid models. Computational results show that the SAR peak in
the resonance frequency region greatly depends on the electric properties of
tissue, while the peak in the GHz region is affected mainly by the surface area
of the model.
Hirata et al. investigated the effect of blood temperature
variation modeling on body-core temperature [Hirata, 2007c]. The computational results show that the
modeling of blood temperature variation was the dominant factor influencing the
body-core temperature. This is because the temperature in the inner tissues is
elevated via the circulation of blood whose temperature was elevated due to the
RF electromagnetic field-induced SAR. Even at different frequencies, the
body-core temperature elevation at an identical whole-body average SAR was
almost the same, suggesting the effectiveness of the whole-body average SAR as
a measure in the ICNIRP guidelines. Next, they discussed the effect of sweating
on the temperature elevation and thermal time constant of blood. The
variability of temperature elevation caused by the sweating rate was found to
be 30%. The blood temperature elevation at the basic restriction in the ICNIRP
guidelines of 0.4 W/kg is 0.25°C even for a low sweating rate. The thermal time constant of blood
temperature elevation was 23 min and 52 min for a man with a lower and a higher
sweating rate, respectively, which is longer than the average time of the SAR
in the ICNIRP guidelines. Thus, the whole-body average SAR required for blood
temperature elevation of 1 °C was 4.5 W/kg in the model of a human with the lower sweating
coefficients for 60 min exposure. From a comparison of this value with the
basic restriction in the ICNIRP guidelines of 0.4 W/kg, the safety factor was
11.
Hirata et al. investigated the temperature elevation in the
eye of anatomically based human head models for plane-wave exposures [Hirata,
2007e]. The
finite-difference time-domain method is used for analyzing the RF
electromagnetic field-induced SAR and temperature elevation. The eyes in the anatomic models
have average dimensions and weight. Computational results show that the ratio
of maximum temperature in the lens to the eye-average SAR is almost uniform
(0.112-0.147°C W/kg) in the frequency region below 3 GHz.
Above 3 GHz, this ratio increases gradually with an increase of frequency,
which is attributed to the penetration depth of RF electromagnetic field. Particular attention is paid to the
difference in the heating factor for the lens between this study and earlier
works. Considering causes clarified in this study, compensated heating factors
in all these studies are found to be in good agreement.
Hirata et al. investigated the SAR and
temperature elevation in an anatomically-based human model for RF
electromagnetic field exposure [Hirata, 2007f]. First, they investigated the
effect of blood temperature variation and thermoregulation modeling on
body-core temperature. The modeling of blood temperature variation was found to
be the dominant factor influencing the body core temperature. This is because
the temperature in the inner tissues is elevated via the circulation of blood
warmed due to the RF electromagnetic field-induced SAR. For the same whole-body
average SAR at different frequencies, the body-core temperature elevation was
almost same, suggesting the effectiveness of the measure used in the ICNIRP
guidelines. Then, they discussed the effect of sweating rate on the temperature
elevation and thermal time constant of blood temperature. The uncertainty of
temperature elevation due to the sweating rate was 30% or so.
Saito and Ito
have been studying various coaxial-slot antennas for microwave hyperthermia.
Saito et al. presented the effectiveness
of the coaxial-slot antenna and the array applicators composed of two or four
coaxial-slot antenna through clinical trials [Saito, 2005]. Then, as an
example, they have developed a coaxial-slot antennas aiming at intracavitary
heating for bile duct carcdinoma [Saito, 2006; Hiroe, 2006]. They estimated the
heating performance of such antenna for the actual treatments and confirmed the
possibility of this treatment by use of the proposed coaxial-slot antenna.
Phantoms are
used to evaluate amounts of absorbed electromagnetic energy. Ito and his
research groups developed phantoms for use in the frequency range from 3 to 10
GHz. Takimoto et al. evaluated the
effectiveness of the biological tissue-equivalent solid phantom for Ultra
WideBand (UWB) communications [Takimoto, 2006]. Solid phantom can be obtained
manufactually the arbitrary shapes. Such solid phantom have neen developed and
used for the frequency bands between 3-10 GHz It was shown that it is possible
to investigate antenna characteristics using this developed phantom in wide
frequency ranges in mobile terminal. Ito
et al. reviewed the development of solid biological tissue-equivalent
phantoms for UWB communications band and evaluated the interaction between
human bodies (called biological tissue-equivalent phantom) and radio terminals
[Ito, 2007b].
Hiroe et al. developed the phantom for
measurement of temperature rises inside biological tissue by electromagnetic
wave exposure [Hiroe, 2007]. Iwai et al.
also developed a realistic human phantom in a PDA (Personal Digital Assistance)
position for electromagnetic wave evaluation of handset antennas [Iwai, 2006].
There are few
data of electrical properties of biological tissues and organs in
millimeter-wave (MMW) while new wireless technology will be operated in the
frequency regions. Wakatsuchi et al.
recently tried to measure complex permittivities of whole-blood sample upto 50
GHz [Wakatsuchi, 2007].
K4 Biomedical
Applications
K4.1 Magnetic
stimulation
Hirayama et al. examined the effects of rTMS on pain in patients with intractable
deafferentation pain [Hirayama, 2006]. Twenty patients received ten trains of
rTMS (5 Hz for 10 seconds at 50 second interval) of the primary motor cortex
(M1), the postcentral gyrus (S1), premotor area (preM), and supplementary motor
area (SMA). Results indicated a statistically significant effect lasting for 3
hours after the stimulation of M1. Stimulation of other targets was not
effective. The M1 was the sole target for treating intractable pain with rTMS,
in spite of the fact that M1, S1, preM, and SMA are located adjacently.
Saitoh et al. also investigated the effects of rTMS on pain in patients
with intractable deafferentation pain [Saitoh, 2006, 2007a]. Ten trains of rTMS
(5Hz for 10 seconds at 50 second interval) were applied to the M1, S1, preM and
SMA. Only M1 stimulation was effective for pain reduction (50%). Motor cortex
stimulation (MCS) procedures were performed. The success rate of MCS was around
63%, and seemed to be higher in cases of pain with spinal cord and peripheral
origins, while it was lower in cases of post-stroke pain.
Saitoh et al. further evaluated the effects of rTMS on pain
in patients with a cerebral lesion or with a noncerebral lesion [Saitoh,
2007b]. Ten trains of rTMS (5Hz for 10 seconds at 50 second interval) were
applied to the M1, S1, pre-. The rTMS was applied to all the patients at frequencies of 1, 5, and 10
Hz and as a sham procedure in random order. High-frequency (5 or 10 Hz) rTMS of
the precentral gyrus can reduce intractable deafferentation pain, but
low-frequency stimulation (at 1 Hz) cannot. Patients with a noncerebral lesion
are more suitable candidates for high-frequency rTMS of the precentral gyrus.
Sakihara et al. investigated whether the
vestibulospinal tract mediates late electromyographic response with a latency
of 100ms evoked bilaterally in soleus muscles following rTMS (1.4 T ELF-PEMF)
over the left cerebellum [Sakihara, 2007]. The vestibulospinal tract was
activated by optokinetic stimulation. The results show that the latency of the
soleus electromyographic response is shortenedby optokinetic stimulation, but
the latency of the motor response evoked by the corticospinal tract is
unchanged. These findings support our hypothesis that vestibulospinal tracts
mediate late electromyographic responses, and allow the development of
techniques to assess the human vestibulospinal system function.
Ueno and
Sekino reviewed medical applications of the recently developed techniques in
biomagnetics and bioimaging such as transcranial magnetic stimulation,
magnetoencephalography, magnetic resonance imaging, cancer thrapy based on
magnetic stimulation, and magnetic control of cell orientation and cell growth.
They emphasized that these techniques are leading medicine and biology into a
new horizon through the novel application of magnetism [Ueno, 2006].
First, Sekino et al. calculated eddy current
distributions in transcranial magnetic stimulation (TMS) under various
conditons and compared ther calculated results with the current distribution in
electroconvulsive therapy (ECT) in order to find an optimum conditions of TMS
as an alternative to ECT [Sekino, 2005d]. Then, they performed numerical
simulation of the eddy current induced by transcranial magnetic stimulation
(TMS) to the cerebellum [Sekino, 2006a]. Solutions were obtained on a
three-dimensional human head model with inhomogeneous conductivity. The maximum
current density in the cerebellum was 2.9A/m2 in a magnetic field intensity of
0.56 T. Distribution of the eddy current in the cerebellum was limited to
approximately 1 cm beneath the surface of the cerebellum.
Maeda et al. designed and developed the
magnetic separator for biomaterials labeled by magnetic beads [Maeda, 2007].
Magnetic separation is an important method for purifying of cells or NDA. Their
developed magnetic separator consisted of three rectangular coils, two circular
coils, and a separation chamber. A separation rate over 90 % was obtained with
this sytem in a separation test using magnetic beads.
K4.2 Thermal Therapy
Tanaka et
al. investigated the therapeutic effects of dendritic cell (DC) therapy
combined with magnetite cationic liposomes (MCL)-induced hyperthermia on mouse
melanoma [Tanaka, 2005]. In an in vitro
study, when immature DC was pulsed with mouse B16 melanoma cells heated at 43°C, major histocompatibility complex (MHC) class
I/II, costimulatory molecules CD80/CD86 and CCR7 in the DC were upregulated,
thus resulting in DC maturation. C57BL/6 mice bearing a melanoma nodule were
subjected to combination therapy using hyperthermia and DC immunotherapy in vivo by means of tumor-specific
hyperthermia using MCL and directly injected immature DC. Mice were divided
into 4 groups: group I (control), group II (hyperthermia), group III (DC
therapy) and group IV (hyperthermia + DC therapy). Complete regression of
tumors was observed in 60% of mice in group IV, while no tumor regression was
seen among mice in the other groups. Increased cytotoxic T lymphocyte and
natural killer activity was observed on
in vitro cytotoxicity assay using splenocytes in the cured mice treated
with combination therapy, and the cured mice rejected a second challenge of B16
melanoma cells. This study has important implications for the application of
MCL-induced hyperthermia plus DC therapy in patients with advanced malignancies
as a novel cancer therapy.
Mochiki et
al.
applied a new treatment
modality using a combination of gastrectomy with postoperative intraperitoneal
hyperthermo-chemotherapy (PIHC) using a heating device Thermotron RF-8 (8 MHz
EMF) [Mochiki, 2007]. They evaluated the feasibility of PIHC in advanced
gastric carcinoma patients with peritoneal seeding. The PIHC group received a
60-min PIHC with a cisplatin (80 mg/m2) two weeks after surgery, and
the control group received surgery alone. The PIHC group had a significantly
higher survival rate and better prognosis compared with the control group.
Ito and Saito
described two types of heating schemes which can be used with microwave enery, and
provided brief explanations of the basic engineering involved [Ito, 2007a]. In
addition, they pointed out the evaluation method of antenna performance. Ito
reviewed the antenna technology to medicine [Ito, 2006]. His review included
the diagnosis, hyperthermia, MRI, computed tomography and telemetering system.
K4.3 Thermal
Therapy-Soft heating and Inductive Heating
In
hyperthermia, high frequency electromagnetic fields are used to heat the cancer
cells. These electromagnetic fields fall into two frequency ranges and produced
some side effects such as the heating of healthy cells or the impact on the
body of invasive surgery required to exposed deep-lying cells. To reduce these
side effects, Matsumoto et al.
proposed the use of lower microwave frequencies with phase control [Matsumoto,
2007]. They confirmed that the phase control technique for long-wavelength, 430
MHz, microwaves was effective in producing localized heating. In order to use
the brain tumor, Kikuchi et al.
estimated the heating pattern for interstitial microwave hyperthermia by a
coaxial-dipole antenna [Kikuchi, 2006]
Saito and Ito
described the fundamental characteristics of microwave inside the biological
tissue and two types of heating schemes for the hyperthermic treatments [Saito,
2007]. In Addition, they introduced the actual treatment of newly developed
microwave antenna. Microwave energy is one of the heating sources used for
thermal therapy of cancer.
Stents are one method of treatment for stenosis of lumens
organ from various causes. The cylindrical metallic stents are composed of
alloy wire. After stents are implanted, however, the stenosis may recur due to
a tumor or abscess again. It is particularly difficult to remove tumors or
abscesses of the bile duct by surgical repair, because the duct is in a deep
portion of the abdomen. Oya et al. proposed
a noninvasive remedying method for tumors and abscesses by using thermotherapy
with magnetically excited metallic stents [Oya, 2006; 2007]. Currently,
clinical stents are not manufactured to allow for heating. We made experimental
stents by magnetic shunt steel to heat the stents and control the heat of
stents by external magnetic excitation for thermo-therapeutic applications
[Hodaka, 2005].
A series of research papers about the soft-heating from
Takura et al. created a complex heater composed
of thermosensitive ferrite wound on a metallic ring which produces a greater
amount of heat due to losses through hysteresis and inductive current than
thermosensitive ferrite alone [Takura, 2007a]. The temperature of the heater
was controlled by using the Curie-point. They comment that it is necessary to
miniaturize the element and achieve optimal performance if their technique is
used. They also developed the miniaturization of micro implantable devices with
thermosensitive ferrite for soft-heating hyperthermia [Takura, 2007b].
K4.4 MRI and Current
Distribution MRI
Two
strategies-motor and visual- are considered to be used for performing mental
rotation. The former involves the function of the motor-related areas of the
brain, whereas the latter does not. Subject’s experience influence strategy
selection during the mental rotation of three-dimensional (3D) shapes. However,
it remains questionable as to whether the attributes of 3D objects enhace the
motor-related activities. Kawamichi et
al. compared the brain activities during two types of mental
rotations-two-dimensional (2D) and 3D rotation using functional magnetic
resonance imaging (fMRI) [Kawamichi, 2007a]. Then, they measured
spatio-temporal brain activities during two types (two dimensional (2D) and 3D
rotation tasks) of mental rotation of 3D objects using magnetoencephalography
(MEG), task difficulty enhanced by rotation dimensionality is a major factor
related to the selection of motor strategy [Kawamichi, 2007b].
Sekino et al. performed numerical simulations
of the eddy current induced by TMS/ELF-PEMF to the cerebellum [Sekino, 2006a].
Solutions were obtained on a three-dimensional human head model with
inhomogeneous conductivity. The stimulating coil consisted of a pair of
circular coil elements with a diameter of 110 mm. The electric current applied
to the coil had an intensity of 44.2 kA Turn, which resulted in a magnetic
field intensity of 0.56 T at the center of a coil element. The maximum current
density in the cerebellum was 2.9 A/m2. Distribution of the eddy
current in the cerebellum was limited to approximately 1 cm beneath the surface
of the cerebellum. The eddy current had a localized distribution in the
cerebellum, while the magnetic field had a broad distribution.
Detection of
weak magnetic fields induced by electrical currents using MRI is necessary for
mapping neuronal activities in the brain. Such detection is dependent on the
signal-to noise ratio and sensivitiy of MRI. Hatada et al. computed the brain eddy current distributions induced by RF
magnetic field from a birdcage coil in MRI by simulations based on the finite
element method (FEM) and calculated Johnson noise from the head [Hatada, 2005a,
2005b].
Imae et al. obtained the minimization of
discrete errors in diffusion simulation of nuclear magnetization [Imae, 2007].
Simulations of finite-difference diffusion are used for solving the diffusion
equation of nuclear magnetization in discrete space and time. They evaluated
the difference between a discrete solution and an exact solution that had been
derived from the manetization diffusion equation..
Tanaka et al. proposed a method of estimating mechanical strain in
biological tissue using diffusion MRI [Tanaka, 2007]. Mechanical strain in
biological tissues causes a change in the diffusion properties of water
molecules. Measurements were carried out on uncompressed and compressed chicken
skeletal muscles. A theoretical model of the diffusion of water molecules in
muscle fibers was derived based on Tanner’s equation. The intracedllualr
duffusion coefficient was changed by mechanical strain.
Kodama and
Takeuchi assessed relationships between six texture features and changes in
atrophy of the cerebral parenchyma, the hippocampus, and the parahippocampal
gyrus in the Alzheimer-type dementia (ATD) brain to determine whether or not
the features reflect cerebral atrophy in ATD patients [Kodama, 2005]. The
subjects were 10 ATD patients consisted of three men and seven women (the mean
age of 71.4±6.7 years) underwent an MRI test of the head annually for at least
3 consecutive years. These results indicate that the six texture features were
shown to reflect gray matter atrophy associated with ATD and to change with the
progress of the disease. The texture features should be a more effective
instrument for identifying the progress of ATD.
Kumagai et al. prepared PEG-coated beta-FeOOH
nanoparticles through electrostatic complex formation of iron oxide
nanoparticles with poly (ethylene glycol0-poly (aspartic acid) block copolymer
[PEG-P (Asp)] in distilled water [Kumagai, 2007]. The nanoparticle size was
determined to be 70 nm with narrow distribution. The PEG-coated nanoparticles
revealed excellent solubility and stability in aqueous solution as well as in
physiological solution. The experiments on tumor-bearing mice demonstrated that
this nanoparticle achieved an appreciable accumulation into solid tumor.
Using of
Wistar rats at nine weeks olds, Saotome et
al. obtained 1H magnetic resonance spectra of skeletal muscles,
with and without atrophy and evaluated the content of creatine in the muscles
[Saotome, 2005]. Tissues have diffusional anisotropy. Their diffusion
properties are denoted by a tensor. Saotome
et al. evaluated the diffusional anisotropy and microscopic structure in
atrophied skeletal muscles using the pulsed-gradient spin-echo (PGSE) nuclear
magnetic resonance (NMR) method [Saotome, 2006]. In this study, the left
sciatic nerve was severed in twelve 9-week-old rats. The proposed method is
effective for evaluating changes in the microscopic structure of skeletal
muscles.
Sekino et al. obtained the spatial distribution
of anisotropic conductivity of the human brain using MRI [Sekino, 2005a].
Estimaiton of conductivity is based on the proportionality between the
conductivity and the diffusion coefficient of water. The gray matter did not
have a clear dependence of conductivity on direction. In some rejoin in the
white matter, conductivity exhibited high anisotropy. This method has potential
applications in current source estimations of EEG and MEG. Then, Sekino et al. investigated the effect of
strain on diffusion tensor MRIs of muscles using numerical simulations and
animal experiments [Sekino, 2005b]. A compression of a tissue caused a decrease
in the effective coefficient in the direction of compression and an increase in
the fractional anisoptropy of diffusion.
Generally,
non-invasive imaging techniques is usefull for analysis of electromagnetic
fields, current distributions in electric stimulation and magnetic stimulation,
the calculation of the absorption of electromagnetic waves from mobile phones,
current source estimation in EEG andc MEG. Sekino and Ueno reviewed the new
methods for MRI of electric properties in living bodies [Sekino, 2007]. They
recommend that new methods have potential applications in biomedical
engineering involving electromagnetic field analysis and new diagnostic imaging
techniques.
K4.5
Contactless power transmission system
Matsuki and Sato explain the fundamental operation of
circuit, and outlines trends in circuits for various contactless power supply
application including home electrical appliances and electric automobiles
[Matsuki, 2007].
Contactless power supply systems transit electric power by
electromagnetic induction with a pair of coils. The efficiency and the output
voltage depend on parameters of coils. The suitable parameter values that
realize stable high efficiency contactless power supply have been obtained. In
the application with low output voltage, the voltage drop of he diodes becomes
dominant power loss. A synchronous rectification was proposed as a solution of
this problem. The contactless power supply system for an artificial heart
operates at 190 kHz. The planar coils with Mn-Zn ferrite course were applied.
Highly stable output voltage and 93.4% of maximal efficiency (dc-dc) were
realized.
The devices were designed in view
of the biomedical compatibility, gradually sloped coils and the flexibility of
the primary coil prevent pressure necroses of the skin. The rectifier circuit
board was placed in the internal space of the ferrite core to reduce the number
of the implanted devices.
Implant medical devices are physically isolated from power
sources required to supply driving energy to them. A well-known contactless power
transmission technology is the transcutaneous energy transmission system
(TETS), which applies electromagnetic induction between two disk-like spiral
coils (a primary coil outside the body, and a secondary coil inside the body).
Implant devices that require a temperature rise for their actuation must be
prevented from overheating, and transcutaneous control and monitoring of the
devices7 temperature is necessary. A small inductor with a thermosensitive
ferrite core was developed as a thermo-sensing device. This inductor controls
the temperature automatically inside the body in combination with TETS. A
coupling factor change between the two coils of a TETS transformer also affects
the stability of power transmission characteristics. A suitable excitation
frequency was designed to ensure stable driving. The control system referred to
above has been applied in an artificial anal sphincter system that is now being
developed, and appropriate driving has been observed [Arai, 2005; Kakubari,
2006a, 2006b; Matsuki, 2007; Miura, 2005a, 2005b, 2006].
K4.6 Electromagnetic interference
The use of implantable
cardiac pacemakers has become more widespread in the world. In
Hanada
proposed that most problems with the electromagnetic environment of medical
institutions have been related to radiated electromagnetic field and have been
constructed from reports about electromagnetic interference (EMI) with
electronic medical equipment by the radio waves emitted from mobile telephone
handsets [Hanada, 2007]. Examples of measurements and measuring methods were
shown for radiated electromagnetic field, the static magnetic field,
power-source noise, and common components of the medical electromagnetic
environment.
Tarusawa et al.
clarified the impact of electromagnetic interference (EMI) from cellular base
station (BS) antennas on implantable cardiac pacemaker [Tarusawa, 2005b]. The
estimation of the impact is based on in
vitro experiments conducted using simulated multicarrier and multicode
signals. These signals are transmitted from actual BS antennas and dipole
antennas as the radiation source of the BS antenna. The results showed that
pacemaker EMI depends on the average power of the transmission signal and does
not depend on the peak-to-average power ratios of the transmission signals. No
pacemaker EMI is detected in the immediate vicinity under the BS antenna at an
input power level for typical operation. It is clear that the pacemaker EMI
should not pose a concern in residential environments.
Futatsumori et
al. investigated the the EMI effect of RFID reader/writer on pacemakers and
ICDs using newly constructed in vitro experimental
system based on an Irnich’s flat torso phantom [Futatsumori, 2006abcd]. The in vitro EMI test, experiments on 10
types of RFID reader/writer and 13 types of implantable pacemakers and
defibrillators were conducted. The frequency bands were 125 kHz, HF (13.56
MHz), UHF (950 MHz) and 2.45 GHz. Futatsumori et al. have been carried out the detailed in-vitro experiments to assess the EMI due to RFID reader/writers
for implantable medical devices (RFID/IMD-EMI). They proposed a novel
RFID/IMD-EMI assessment methodology based on the total magnetic flux integrated
across the pacemaker and the lead cross-section [Futatsumori, 2007ab]. Taguchi et al. developed three-dimensional
automatic mearuement system for the assessment methodology of implantable
medical devices EMI due to RFID reader/writers [Taguchi, 2007].
Hikage et al. estimated the EMI risk to
pacemakers by cellular radio transmission considering of the effect of
electromagnetic field absorption and shielding due to a human’s body inside the
elevator [Hikage, 2007a]. Large
scale FDTD analysis for implantable cardiac pacemakers EMI due to mobile radios
in train carriage of complicate situation were carried out by Higaki et al
[Hikage, 2007c].
Hirose et al.
invetigated quantitatively the EMI caused by an induction oven in implantable
unipolar cardiac pacemakers and measured the distribution profile of the
magnetic field strength both with and without a pan on the induction oven
[Hirose, 2005]. Then, they performed the inhibition test and asynchrorous test
using four kinds of pacemakers housed in the standardized Irnich human body
model and the maximum distance from the induction oven up to which the EMI occurred.
The maximum EMI distance from the oven was 34 cm for one of the pacemakers. The
safe distance from an induction oven of a patient with an implanted cardiac
pacemaker is considered to be 50 cm or more.
Although the Computed Tomography (CT) is widely used
in clinical practice, there has not been a detailed report of its effect on the
function of pacemakers. Yamaji et al.
investigated the effect of CT on a pacemaker in a human body mode with and
without shielding by rubber or lead and measured ECGs in 11 patients with
pacemakers and electromagnetic field in the CT room during CT scanning [Yamaji,
2006]. Transient malfunctions of pacemakers during CT occurred in 6 of 11
patients. The malfunction was prevented by lead but not by rubber. The
alternating electric field was 150 V/m and the alternating magnetic field was
15μT on the CT scanning line. These field strengths were lower than the level
of influencing pacemaker functions.
Acknowledgements
I
would like to thank Dr Okano and the members of Commission K Japan for their
tremendous efforts.
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