The significance of Doppler signals detected by TCD in the diagnosis of embolism in neurosurgery and cerebral angiography

Abstract

Recently, several authors have reported the character of embolic signals in TCD (transcranial Doppler sonography) as follows: (1) high intensity signals (3-60 dB) greater than the background Doppler spectrum;(2) random occurrence within the cardiac cycle; (3) transient appearance and short duration; (4) bell-shaped signals focused on a small band of frequencies within the Doppler spectrum; (5) harmonic sound quality; (6) monitoring time of over 30 minutes; required and (7) signals must be differentiated from artifacts. We studiedthe detectability of embolic signals using a Doppler recording system. Embolic signals of the middle cerebralartery were monitored by TCD using an experimental animal model and 3 patients with epilepsy or brain tumor who underwent cerebral angiography by the Seldinger method. In the animal model, artificial air emboli were easily detected as short-term and hyper-intense ultrasonic signals, while thrombotic emboli were not identified definitely. Furthermore, our clinical cases suggested that microscopic air emboli at the site of injection of the contrast medium may be prevented by slow washout with saline. We propose new criteria for embolic signals.