Design considerations for a transcranial Doppler coupled to a stereotacticposition arm

We present the localization error analysis for a stereotactic positioning a rm, transcranial Doppler (TCD) system. Localization displacement errors wer e determined with a custom phantom head. A bubble apparatus was built to me asure sample volume (SV), From interface plane relationships, biological ma terial properties, and human computerized tomography (CT) scan data, an alg orithm for computing the actual TCD signal path was developed, Localization resolution was diminished by constraints intrinsic to the TCD instrument ( +/- 1 mm) and the positioning arm (1.9 +/- 0.9 mm), The overall SV localiza tion error ranged from 3.3 mm from the target, to complete signal loss at a critical cumulative angle of 31 degrees, one third of which may be reached at the TCD probe/skin interface, Any stereotactic ultrasound system must I nclude correction for the beam path, The "failed ultrasound window," may be predicted by signal loss based on refraction alone, The use of stereotacti c TCD may enhance the clinical applications of TCD, (C) 1998 World Federati on for Ultrasound in Medicine & Biology.