Problem: Transcranial Doppler in a 4-year-old boy who has sickle cell anemia reveals elevated velocities of greater than 200 cm/sec in several intracranial arteries. Results of a repeat study 5 weeks later are unchanged. The most appropriate next step in management is to: A. Obtain cerebral angiography. B. Obtain computed tomography of the brain. C. Start a chronic transfusion program. D. Start hydroxyurea therapy. E. Repeat the transcranial Doppler in another 3 months