Background and Purpose-Vasomotor reactivity (VMR) testing can identify patients with hemodynamically critical cerebrovascular disease. The use of VMR has been limited by the invasiveness of most of the available methods and of acetazolamide as VMR stimulus. In the present study, we evaluated a completely noninvasive VMR approach by combining quantitative phase-contrast magnetic resonance imaging (MRI) with a breath-hold challenge. Methods-Volume flow rates in the right and left internal carotid artery (ICA), basilar artery (BA), superior sagittal sinus, and sinus rectus were measured on 2-dimensional phase-contrast MR angiograms (MRAs) with a temporal resolution of 4.3 seconds. In 20 healthy control subjects, the VMR was assessed during 2 consecutive 30-second periods of breath-holding. Results-A flow increase on breath-holding of 66% was found for the left ICA (240Ϯ54 mL/min to 398Ϯ120 mL/min; PϽ0.01), 59% for the right ICA (253Ϯ98 mL/min to 402Ϯ159 mL/min; PϽ0.01), 71% for the BA (107Ϯ48 mL/min to 184Ϯ79 mL/min; PϽ0.01), 62% for the superior sagittal sinus (232Ϯ75 mL/min to 375Ϯ130 mL/min; PϽ0.01), and 65% for the sinus rectus (77Ϯ30 mL/min to 127Ϯ38 mL/min; PϽ0.01). The coefficient of variation for the total volume flow increase in the brain feeding arteries (ICAs and BA) between the first and the second breath-holds was 18%. Conclusion-The combination of MRA phase-contrast volume flow measurements and a breath-holding challenge allows for a fast, completely noninvasive, and reproducible assessment of VMR.

Regional assessment of cerebral perfusion and VMR with SPECT demonstrated the heterogeneity of cerebral hemodynamics and the importance of collateral flow via the anterior circle of Willis.