An overview of transcranial ultrasound

Transcranial Doppler ultrasound, a noninvasive tool for exploring the hemodynamics of intracranial vessels, has evolved significantly over the past decade. Blind vessel integration has been replaced by color Doppler sonography combined with B-mode ultrasound and pulse-wave Doppler. These modalities allow rapid, reproducible, and accurate vessel identification, thus enhancing the detection and diagnosis of intracranial pathologies. Power Doppler is more sensitive than color Doppler in detecting low-velocity flow and flow in small vessels, making it extremely useful for evaluating intracranial blood flow. Intravenous transpulmonary ultrasound contrast media increase the signal/noise ratio of blood flow and make vessels easier to identify. Power Doppler associated with ultrasound contrast improves the quality of transcranial Doppler imaging, allowing magnetic resonance angiography-quality images to be obtained at the patient's bedside. The techniques and clinical uses of transcranial Doppler are discussed, with emphasis on normal hemodynamic data values.