Doppler Ultrasound

• High-resolution ultrasound combined with colour-coded Doppler flow analysis (Duplex sonography) has become a clinical tool of great value permitting bedside noninvasive diagnosis of the extracranial and intracranial vessel pathology.

The accuracy of the description of the degree of carotid stenosis has been demonstrated in several studies. Each neurosonology laboratory uses several standardized criteria which are refined according to the technical advances in Doppler ultrasound techniques combined with regular auto-evaluation. Velocity criteria [2], pre- and post-stenotic Doppler spectrum and collateral flow allow the best evaluation of the degree of stenosis.

The detection of a floating thrombus and some characterization of the atheromatous plaque consistency is also used in evaluating the degree of instability of the arterial lesion.

Microembolic signals (HITS) in the post-stenotic flow also permit the prediction of stroke risk in high-grade stenosis.

Recently, echocontrast agents have been shown to improve Doppler ultrasound image quality, permitting a better diagnosis of pseudo-occlusions and intracranial vessel disease [8].

Doppler ultrasound techniques have the advantage that they can be repeated easily and even allow continuous monitoring of the acute stroke patient [7]. Transcranial Doppler can also be applied during carotid surgery to help decide whether a shunt should be placed and verify its patency.

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