Mapping hypercapnia-induced cerebrovascular reactivity using BOLD MRI

Severe carotid artery stenosis or occlusion may put patients at risk for ischaemic stroke. Reduced cerebrovascular reserve capacity is a possible indicator of an imminent ischaemic event and can be determined by assessment of cerebrovascular reactivity to a vasodilative stimulus. However, little is known about the distribution of cerebrovascular reactivity in healthy individuals. In 13 healthy volunteers, dynamic T₂* MR images, acquired at alternating inspiratory pCO₂ levels, showed a high percentage of signal change in grey matter, with a strong linear correlation with end-tidal pCO₂. The mean percentages of signal change for grey and white matter were 5.9±1.2% and 1.9±0.5%, respectively. The mean time lag between CO₂ stimulus and haemodynamic response was 15±4 s for grey matter and 180±12 s for white matter. Parameter mapping revealed a hemispherically symmetrical and homogeneous distribution of cerebrovascular reactivity over the entire grey matter. These findings indicate that it may be feasible to detect exhausted cerebrovascular autoregulation in patients with a compromised cerebral vasculature.