MRI mapping of cerebrovascular reactivity using square wave changes in end-tidal PCO2

Cerebrovascular reactivity can be quantified by correlating blood oxygen le vel dependent (BOLD) signal intensity with changes in end-tidal partial pre ssure of carbon dioxide (PCO2). Four 3-min cycles of high and low PCO2 were induced in three subjects, each cycle containing a steady PCO, level lasti ng at least 60 sec. The BOLD signal closely followed the end-tidal PCO2, Th e mean MRI signal intensity difference between high and low PCO2 (i,e,, cer ebrovascular reactivity) was 4.0 +/- 3.4% for gray matter and 0.0 +/- 2.0% for white matter. This is the first demonstration of the application of a c ontrolled reproducible physiologic stimulus, i,e,, alternating steady state levels of PCO2, to the quantification of cerebrovascular reactivity, (C) 2 001 Wiley-Liss, Inc.