An investigation into the effect of pulsed ultrasound on the brain

The effect of pulsed ultrasound on the human brain, for longer times than that administered in diagnostic work, in five adult patients and one child was studied by clinical evaluation, electro-encephalography, biochemical and histopathological studies.

Exposure for one hour to pulsed ultrasound, through scalp and bone, with a 2MHz frequency crystal, emitting 430 pulses/sec, with each pulse lasting for 1 μs, was found harmless. The pulse strength of the apparatus used in one microsecond is about 10 watts, resulting in a mean strength of about 5 milliwatts and an ultrasonic dose of 1 milliwatt per centimetre square.