Comparison of Blood Oxygenation Level–Dependent fMRI and Provocative DSC Perfusion MR Imaging for Monitoring Cerebrovascular Reserve in Intracranial Chronic Cerebrovascular Disease

Left: Contrast agent concentration–time curves (blue curves) for 3 vascular territories (upper, middle, lower) are similar for normal vessels. No pressure differential exists between vascular territories to open potential leptomeningeal collateral vessels (dotted red line). Right: Stenosis (S) of the middle territory causes distal dilation, producing a pressure differential that opens leptomeningeal collateral vessels (C) from neighboring vascular territories (upper, lower). The contrast agent concentration–time curve of the compromised territory (middle blue curve) becomes the sum of 3 unresolved inputs (red, yellow, and green curves) temporally displaced due to the increased vascular path lengths from the other territories. MTT lengthens in the compromised territory (temporally displaced middle blue curve compared with the upper and lower blue curves). Pharmacologic vasodilation dilates all capillary beds, thereby decreasing the pressure difference between normal and compromised territories to further delay collateral leptomeningeal flow and increase the temporal separations of the multiple AIFs to lengthen MTT but not necessarily reflecting inadequate flow.

A, Normal sensorimotor activation pattern for BOLD fMRI with the HR assessment paradigm. Areas of activation are the following: 1) right primary sensorimotor cortex (right sMCA), 2) left primary sensorimotor cortex (left sMCA), and 3) left and right supplementary motor area (left and right ACA, respectively). The color scale reflects the continuous t value (threshold t = 3 red, t > 3 yellow) of the activation-detection statistics. B, Normal quantitative perfusion map of MTT at the same level as A remains symmetric before and after vasodilation. The color scale is in seconds.

Representative patient with MMD showing concordance. A, BOLD fMRI shows activation in the right (1) but not the left primary sensorimotor area or supplementary motor areas bilaterally. The task was performed correctly because bilateral cerebellar motor and visual activations were present (not shown). B, Quantitative MTT maps through the same level as in A before (left) and after (right) vasodilation. The lengthening of the MTT values after vasodilation would normally be interpreted as loss of HR. The color scale is same as in Fig 3.