ID Number		1054
Study Type		Human / Provocation
Model		2.4 to 170 MHz RF exposure from MRI to human volunteers and analysis of microwave hearing
Details		Human volunteers (n=6) were exposed to RF from head coils used in magnetic resonance imaging (MRI) at 3 kW peak power with normal masking acoustic noise from the MRI device turned off and foam earmuffs worn to attenuate any additional background noise. RF pulses were heard as distinct clicks with pulse widths less than 50 us. At longer pulse widths, creaky or gnashing clacks of lower pitch were heard. A threshold of 16 +/- 4 mJ pulse energy was found in the 2.4 - 170 MHz range with pulse widths of 3-100 us. The RF pulse threshold changed at the transition range of 30 - 300 us from constant pulse energy threshold to constant peak power threshold as a function of pulse width (as predicted by theory). The results from the study confirm theoretical predictions from the thermoelastic expansion model and compare well with reported thresholds from other studies at 425 - 3000 MHz. MRI systems operating at 15 kW (5X higher than used in this study) are not uncommon and, at this power level, the perceived RF-evoked sound was calculated to be about 40 dB (100X) above the pressure level at the RF hearing threshold. The author stated that there was no evidence known for detrimental health effects arising from the RF auditory response associated with use of clinical MRI systems.
Findings		Not Applicable to Bioeffects
Status		Completed With Publication
Principal Investigator		Philips GmbH Forschungslaboratorium Hamburg, FRG
Funding Agency		Private/Instit.
Country		GERMANY
References		Roschmann, P Magn Reson Med, (1991) 21:197-215
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