Quantitative measurement of cerebrovascular reactivity by blood oxygen level-dependent MR imaging in patients with intracranial stenosis: preoperative cerebrovascular reactivity predicts the effect of extracranial-intracranial bypass surgery

Abstract

Background and purpose: CVR is a measure of cerebral hemodynamic impairment. A recently validated technique quantifies CVR by using a precise CO(2) vasodilatory stimulus and BOLD MR imaging. Our aim was to determine whether preoperative CO(2) BOLD CVR predicts the hemodynamic effect of ECIC bypass surgery in patients with intracranial steno-occlusive disease.

Materials and methods: Twenty-five patients undergoing ECIC bypass surgery for treatment of intracranial stenosis or occlusion were recruited. CVR was measured preoperatively and postoperatively and expressed as %ΔBOLD MR signal intensity per mm Hg ΔPetCO(2). Using normative data from healthy subjects, we stratified patients on the basis of preoperative CVR into 3 groups: normal CVR, reduced CVR, and negative (paradoxical) CVR. Wilcoxon 2-sample tests (2-sided, α = 0.05) were used to determine whether the 3 groups differed with respect to change in CVR following bypass surgery.

Results: The group with normal preoperative CVR demonstrated no significant change in CVR following bypass surgery (mean, 0.22% ± 0.05% to 0.22% ± 0.01%; P = .881). The group with reduced preoperative CVR demonstrated a significant improvement following bypass surgery (mean, 0.08% ± 0.05% to 0.21 ± 0.08%; P < .001), and the group with paradoxical preoperative CVR demonstrated the greatest improvement (mean change, -0.04% ± 0.03% to 0.27% ± 0.03%; P = .028).

Conclusions: Preoperative measurement of CVR by using CO(2) BOLD MR imaging predicts the hemodynamic effect of ECIC bypass in patients with intracranial steno-occlusive disease. The technique is potentially useful for selecting patients for surgical revascularization.

Fig 1.

Graph shows the effect of ECIC bypass on CO₂ BOLD CVR in gray matter vascular territories ipsilateral and contralateral to the bypass. Whiskers mark the 10th and 90th percentiles, and boxes are bounded by the 25th and 75th percentiles.

Fig 2.

Gray matter CVR map overlaid on anatomic T1-weighted images for a representative patient (patient 24). Top row is before bypass, and bottom row is after bypass surgery. CVR units are %ΔBOLD MR signal intensity per mm Hg ΔPetCO₂. Images demonstrate decreased, and in fact paradoxical (negative), CVR in the left MCA territory cortex and deep gray matter before bypass and marked improvement postbypass surgery.

Fig 3.

Boxplots show the change in ipsilateral MCA territory CVR following ECIC bypass surgery for 3 groups: normal preoperative CVR, reduced preoperative CVR, and paradoxical preoperative CVR. Units of CVR are %ΔBOLD MR signal intensity per mm Hg ΔPetCO₂.