Publisher Summary Observation of the cerebral blood flow profile following intravenous injection of a gamma-emitting isotope is a safe, atraumatic, and almost indefinitely repeatable method of obtaining clinically useful information about the cerebral circulation that is immediately available and readily interpreted by the responsible physician. The RCG in patients with A-V malformation is diagnostic, and can only be partly simulated by severe thyrotoxicosis. The state of spasm of the intracerebral vessels can be followed after subarachnoid hemorrhage without recourse to further angiography. This helps the surgeon to choose the optimum time for operative intervention. The management of intracranial hypertension is facilitated by knowledge of the behavior of the cerebral circulation in response to treatment by operation, intravenous hypertonic solutions and steroids. In the acute head injury maintenance or loss of autoregulation in response to changing blood pressure or arterial P, is an important guide to the use of positive pressure ventilation in the treatment of hypoxia. This function can be serially investigated by RCG. Cerebral vascular disorders can be investigated in both the acute and chronic stages of cerebral deprivation, and the RCG profile, basic and in response to treatment, is a valuable guide to both immediate therapy and prognosis. During radiological contrast studies, RCG can assist the radiologist in timing the X-ray exposures following injection and can inform him whether injection has temporarily increased or decreased blood flow.