Auditory phenomena during transcranial Doppler insonation of the basilar artery.

During transcranial Doppler insonation of the basilar artery, 15 normal subjects heard high-frequency tones similar to tinnitus. The pitch of the tones equated with the PRF, and intensity equated with loudness. Alteration of pulse length did not change the tones heard, and the effect was highly dependent on probe position and direction. This is an example of ultrasonography acting as a sensory stimulus. The exact mechanism and implications of this effect will need to be clarified by further investigation. Although this phenomenon is not proved to be harmful, it would seem prudent to use the minimum transmitted power necessary to obtain a satisfactory signal from the basilar artery.