NEW DEVELOPMENTS IN CEREBROVASCULAR ULTRA SOUND IMAGING

Noninvasive Doppler and B-mode sonography of the extra- and intracrani al arteries are highly sensitive and specific. They provide important diagnostic information and are routinely used in a wide spectrum of di sorders including stenosis due to arteriosclerosis, vascular malformat ions and subarachnoid haemorrhage. New developments include extracrani al colour-coded Duplex sonography that improves the evaluation of athe rosclerotic plaques and the differentiation of high grade stenosis fro m complete occlusion. Colour-coded transcranial Duplex sonography is c urrently evaluated and shows promising preliminary results. Indirect f low parameters can be used to assess increased intracranial pressure o r complete circulatory arrest as in suspected brain death. Such parame ters have also been used successfully in subcortical arteriosclerotic microangiopathy and vasculitis. Functional Doppler tests have been dev eloped to estimate the cerebrovascular reserve capacity as in high gra de carotid stenosis when cerebral perfusion may be critically low. Ear ly results using Doppler to detect increased cerebral blood flow after cognitive or mental stimuli are currently evaluated. Transcranial Dop pler monitoring during cardio- and cerebrovascular surgery and interve ntional neuroradiological procedures provide important information on cerebral haemodynamics. Embolic material originating from various sour ces can be detected using transcranial Doppler monitoring. The introdu ction of echo enhancing contrast agents that are stable during heart-l ung passage will improve the accuracy of ultrasound imaging even in th ick skulls. Other new developments concentrate on high resolution intr avascular Doppler measurements to reconstruct vascular structures or t he real-time assessment of the dynamics of arteriosclerotic lesions.