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Chapter Twelve - Magnetic
Fields
Biological Effects to Strong Magnetic Fields
Do static fields effect cardiac pacemakers?
Effects on cardiac pacemakers have been reported
for fields as low as 1.7 mT. The most common effect was
triggering of the asynchronous mode; the effect is very model and
orientation dependent, and in the models tested normal operation
resumed when the pacemaker was removed from the field. Some
pacemakers also exhibited significant torque when exposed. For
this reason current static field guidelines restrict exposures for
wearers of cardiac pacemakers to 0.5 mT. It would be prudent
to apply this restriction to other implanted electronic devices, and
to prosthetic devices as well, although not all standards are
explicit on this point.
In contrast to the above, a 2000 study found that
MR imaging could be safely performed at 500 milliT in patients with
cardiac pacemakers.
Do static fields decrease fertility, cause
birth defects or increase miscarriage rates?
There is no consistent evidence for such effects.
Fertility: Mur et al, found
no significant effects on the fertility of men exposed to 4-30 mT
static fields in the aluminum industry; and Evans et al, found no
effect of fertility in female MRI operators. One animal study
reported evidence for decreased male fertility at 1500 mT, but two
other studies at 500-700 mT found no such effect. A fourth
animal study reported decreased female fertility at 80 mT, but not
at 30 mT.
Miscarriages: Baker et al,
found that MRIs done at 1500 mT in the second and third trimester
did not increase the miscarriage rate; and Evens et al, found no
significant effect on miscarriage rates in female MRI operators.
Two animal studies reported decreased fetal viability at 30 mT and
80 mT, but other studies at 500-1000 mT and 6300 mT found no such
effect.
Birth defects: Baker et al,
found that MRIs done at 1500 mT in the second and third trimester
did not produce birth defects; and Evans et al, found no increase in
birth defects in children of female MRI operators. One animal
study reported adverse effects on development at 1500 mT; but other
studies found no increase in birth defects at 30 mT, 500-1000 mT or
6300 mT. Two animal MRI studies done at 1500 mT reported
increases in birth defects, but heating due to the radiofrequency (RF)
radiation used in MRI cannot be ruled out as a factor. A third
MRI study at 1500 mT found no such effect.
References:
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Medical College of Wisconsin - General Clinical Research Center
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J.E. Moulder and K.R. Foster, "Biological
Effects of Power-frequency Fields as They Relate to Carcinogenesis";
Proc Soc Exp Med Biol, 209:309-324 (1995).
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J.E. Moulder, "Biological Studies of
Power-frequency Fields and Carcinogenesis"; IEEE Eng Med Biol,
15:31-49 (July/Aug 1996).
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K.R. Foster, L.S. Erdreich, J.E. Moulder,
"Weak Electromagnetic Fields and Cancer in the Context of Risk
Assessment"; Proc IEEE, 85:733-746 (1997).
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J.E. Moulder, "Power-frequency Fields and
Cancer"; Crit Rev Biomed Engineering", 26:1-116 (1998).
Last Update:
2006-09-21
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