✓ Vessel identification during a transcranial Doppler (TCD) ultrasound examination is usually based on well-established inferential criteria without confirmation by imaging. Part of a routine study involves taking measurements from the M1 segment of the middle cerebral artery (MCA) and the A1 segment of the anterior cerebral artery (ACA) at the points of maximum mean linear blood flow velocity (LBFV). The authors tested the hypothesis that insonation is from the midpoints of the M1 and A1 segments during clinical TCD examinations.
Conventional hand-held TCD examinations were performed on five volunteers. The points of maximum mean LBFV of the M1 and A1 segments of the MCA and ACA were located. Measurements were also taken from the midpoints of the M1 and A1 segments using a magnetic resonance (MR) imaging-guided stereotactic TCD technique. Values for depths of insonation and maximum mean LBFV obtained with the two techniques were compared. There was no significant difference between the two techniques for the measured values of depth of insonation of either the individual vessels (p > 0.11) or the aggregate (p = 0.46). There was a significant difference between the aggregate maximum mean LBFV measurements (p = 0.0022). The hand-held technique systematically produced higher maximum mean LBFV than the MR-guided stereotactic technique. The authors conclude that when using traditional criteria for TCD examination of the ACA and MCA, the points of insonation approximate the middle of the A1 and M1 segments.