Cerebrovascular reactivity measurement in cerebral small vessel disease: Rationale and reproducibility of a protocol for MRI acquisition and image processing

Background: Impaired autoregulation may contribute to the pathogenesis of cerebral small vessel disease. Reliable protocols for measuring microvascular reactivity are required to test this hypothesis and for providing secondary endpoints in clinical trials. Aims: To develop and assess a protocol for acquisition and processing of cerebrovascular reactivity by MRI, in subcortical tissue of patients with small vessel disease and minor stroke. Methods: We recruited 15 healthy volunteers, testing paradigms using 1- and 3-min 6% CO₂ challenges with repeat scanning, and 15 patients with history of minor stroke. We developed a protocol to measure cerebrovascular reactivity and delay times, assessing tolerability and reproducibility in grey and white matter areas. Results: The 3-min paradigm yielded more reproducible data than the 1-min paradigm (CV respectively: 7.9–15.4% and 11.7–70.2% for cerebrovascular reactivity in grey matter), and was less reproducible in white matter (16.1–24.4% and 27.5–141.0%). Tolerability was similar for the two paradigms, but mean cerebrovascular reactivity and cerebrovascular reactivity delay were significantly higher for the 3-min paradigm in most regions. Patient tolerability was high with no evidence of greater failure rate (1/15 patients vs. 2/15 volunteers withdrew at the first visit). Grey matter cerebrovascular reactivity was lower in patients than in volunteers (0.110–0.234 vs. 0.172–0.313%/mmHg; p < 0.05 in 6/8 regions), as was the white matter cerebrovascular reactivity delay (16.2–43.9 vs. 31.1–47.9 s; p < 0.05 in 4/8 regions). Conclusions: An effective and well-tolerated protocol for measurement of cerebrovascular reactivity was developed for use in ongoing and future trials to investigate small vessel disease pathophysiology and to measure treatment effects.