Article: PDF OnlyNuclear Magnetic Resonance (NMR) In Vivo Studies Known Thresholds for Health EffectsBudinger, Thomas F.Author Information Donner Laboratory and Lawrence Berkeley Laboratory, University of California, Berkeley, California. Journal of Computer Assisted Tomography: December 1981 - Volume 5 - Issue 6 - p 800-811 Buy Abstract Three sources of harmful health effects from nuclear magnetic resonance (NMR) in vivo techniques have been examined with the following conclusions: (a) Static magnetic fields. Harmful effects on humans and reproducible cellular, biochemical, or genetic effects have not yet been observed at fields less than 2 Tesla (20,000 gauss), (b) Changing magnetic fields. The threshold for effects of induced currents is above that produced from < 1 to 100 Hz sinusoidal field changes with a maximum field of 5 mT (50 gauss). Waveform, repetition rate, maximum B field, and duration of exposure are parameters requiring further study, (c) Radiofrequency (RF) heating. A practical upper level for absorbed power is 4 W/kg in medically important studies of short duration (less than 10 min). For long-term studies, 1.5 W/kg is a reasonable level in low humidity environments. The power absorbed by the subject can be estimated by measuring the RF coil Q before and after the subject is placed in the NMR instrument. Large metal objects will absorb power in proportion to the conductivity of the device or prosthesis. © Lippincott-Raven Publishers.