The American College of Radiology (ACR) lists indications for TCD in its "ACR Practice Guideline for the Performance of Transcranial Doppler Ultrasound for Adults and Children" (www.acr.org/SecondaryMainMenuCategories/quality_safety/guidelines/us/us_transcranial_doppler.aspx). For example, indications for TCD in adults include "detection of stenosis or occlusion in a major intracranial artery in the circle of Willis and vertebrobasilar system, including monitoring thrombolytic therapy for acute stroke patients" and "follow-up of patients with known stenosis or occlusion of a major intracranial artery in the circle of Willis and vertebrobasilar system." In children, indications include "evaluation of stenosis or occlusion in the circle of Willis and vertebrobasilar system in patients with sickle cell anemia to determine the need for and continuation of blood transfusions" and "detection of vasculopathy, such as moyamoya."