Purpose or Case Report: Chronic cerebrovascular disease is common in pediatric sickle cell patients, and these children often require serial imaging to assess cerebral blood flow perfusion. ASL MRI has been shown to be an effective technique to assess cerebral blood flow, but the evaluation of perfusion reserve is also of value to ordering clinicians. This educational exhibit describes the use of the vasodilator acetazolamide to gauge potential changes in perfusion as determined by ASL MRI. The biochemical basis for cerebrovascular autoregulation and mechanism of acetazolamide are discussed.
Methods & Materials: Conventional MRI and Time-Of-Flight MRA is performed, and baseline cerebral blood flow perfusion is evaluated using dynamic pseudo-continuous Arterial Spin Labeling (pCASL). Acetazolamide (15 mg/kg) is given intravenously over a 3-5 minute period, and additional pCASL images are acquired 10-15 minutes after injection. Intravenous contrast is not given. Perfusion maps are calculated and compared. Cerebrovascular reserve is defined as the change in perfusion divided by the baseline perfusion.
Results: Perfusion changes in response to acetazolamide occur in three patterns. In the first, there is normal blood flow at baseline with acetazolamide-induced increased perfusion. Patients with the second pattern have a decreased baseline perfusion, but the vasodilator improves flow. In the third pattern, there is also a decreased baseline perfusion, but acetazolamide exacerbates the relative regional blood flow deficit. In the third pattern, the chronically ischemic territory is felt to be perfused by vessels that are already maximally dilated, and the apparent paradoxical response to the vasodilator is due to a steel phenomenon.
Conclusions: Acetazolamide challenge is a useful technique in the diagnostic evaluation of pediatric sickle cell patients with chronic cerebrovascular disease. Arterial-spin labeling obviates the need for intravenous contrast which is an important factor in the sickle cell population due to the inherent renal vulnerability of these patients.