Figure 38-22 A, Normal transcranial Doppler (TCD) tracing from the middle cerebral artery at a depth of 55 mm. B, TCD tracing from a patient with cerebral vasospasm. Notice the very high flow velocities beyond the ability of the machine to quantify. C, TCD pattern from the middle cerebral artery in a case of brain death. Notice the brief systolic inflow of blood followed by flow reversal in diastole.