Thermal thresholds for teratogenicity, reproduction, and development

Figures & data

Table I.  Common sources of RF radiation and potential for significant heating of foetus.

RF source	Frequency	Penetration (cm)	Significant heating of foetus
AM radio	0.6 MHz	>100	No
Short wave diathermy	27.2 MHz	14.3	Yes
TV	100.0 MHz	6.7	No
Analogue cell phone	900.0 MHz	3.1	No
Radar	1.0 GHz	2.5	No
Digital cell phone	2.0 GHz	2.0	No
Microwave oven	2.45 GHz	1.7	No
Microwave diathermy	2.45 GHz	1.7	Yes
Airport scanners	40.0 GHz	0.06	No

Note: Frequencies are typical values for each source. Penetration is the distance travelled into the skin for the RF amplitude to decrease to 36.8% of its initial value. Significant heating of foetus refers to whether or not the source has sufficient energy or penetration to cause a 1°C temperature elevation.

Table II.  Maximum temperature elevations from MRI examinations.

MRI scanning level	Max SAR	Max temperature rise
For whole body scans
Normal level	2 W/kg	0.5°C
First level	4 W/kg	1.0°C
Second level	>4 W/kg	>1.0°C
For partial body scans (<25% of body)
Normal levelNormal level	8 W/kg	1.1°C

Table III.  Maximum allowed intensities for ultrasound applications.

Application	Max intensity (mw/cm^2)*
Foetal and general imaging	720
Cardiac	720
Peripheral vascular	720
Ophthalmologic	50

*Spatial-peak, temporal-average intensity measured in water and derated by 0.3 dB cm^-1MHz^-1.

Table IV.  Diagnostic ultrasound instruments.

Ultrasound sources	Acoustic output mW/cm^2	Temperature elevation
Doppler foetal heart monitor	20	<1°C
B-scanner	35	1°C
Colour flow Doppler	450	3°C
Duplex Doppler	400	2°C
Ophthalmic scanner	40	<1°C

Note: Acoustic outputs are typical values of derated spatial-peak temporal-average intensity values. Also provided are possible temperature elevations in the foetus.