Ultrasound Perfusion Imaging of Cerebrovascular Disease

Ultrasound perfusion imaging of the cerebral microcirculation is a new semi-invasive bedside technique to evaluate human brain perfusion. Several approaches have been evaluated for the qualitative assessment of brain perfusion in healthy subjects and in patients suffering from acute ischemic stroke. The analysis of ultrasound contrast agent bolus kinetics yields various time-intensity curve parameters that qualitatively describe regional brain perfusion. In healthy subjects, there is a close correlation between the time to peak intensity measurements as performed by perfusion ultrasound and perfusion-weighted MRI. In the acute phase of ischemic stroke, the peak signal increase is the most useful curve parameter to predict the area of definite infarction. Ultrasound perfusion imaging performed in the early phase can predict the outcome of the individual stroke patient. Diminution and Replenishment kinetics are new modalities for the visualization of brain perfusion, the latter being more promising because of the fast imaging time resulting in a lower vulnerability to movement artifacts. The different approaches will have to be compared regarding their ability to provide valid thresholds for differentiation between normal and abnormal perfusion in the acute stroke situation. At present, the foremost limitations of transcranial ultrasound perfusion imaging are attenuation phenomena, caused by the temporal bone, which might be overcome by new imaging systems that are currently under development.