Time course of vascular reactivity using repeated phase-contrast MR angiography in patients with carotid artery stenosis.

BACKGROUND AND PURPOSE Cerebral vascular reactivity assessment is typically performed with 2 perfusion measurements before and after a vasodilatory challenge. The aim of this study was to assess the time course of the vasodilatory effect in the brain-feeding arteries after a challenge with acetazolamide in patients with a stenosis of the internal carotid artery (ICA). METHODS Twenty-one patients with a symptomatic ICA stenosis and 18 healthy control subjects underwent 2-dimensional phase-contrast MR angiography to repeatedly measure the blood flow (mL/min) in both ICAs at baseline and in 5-minute intervals for 30 minutes after intravenous administration of acetazolamide. RESULTS At baseline, the blood flow was significantly lower in the stenosed ICAs of patients (155 ± 17 mL/min) than in the contralateral ICAs (237 ± 21 mL/min, P<0.05) and the ICAs of healthy control subjects (249 ± 15 mL/min, P<0.05) and remained lower throughout the time course. The maximum vasodilatory effect in the stenosed ICAs was observed after 15.3 ± 0.9 minutes, which was significantly later than in the contralateral ICAs (within 12.9 ± 0.7 minutes, P<0.05) and healthy ICAs (within 12.8 ± 0.8 minutes, P<0.05). CONCLUSIONS The onset of the maximum vasodilatory effect after administration of acetazolamide is delayed in patients with a symptomatic ICA stenosis.