MRI mapping of cerebrovascular reactivity using square wave changes in end‐tidal PCO 2

Cerebrovascular reactivity can be quantified by correlating blood oxygen level dependent (BOLD) signal intensity with changes in end‐tidal partial pressure of carbon dioxide (PCO 2 ). Four 3‐min cycles of high and low PCO 2 were induced in three subjects, each cycle containing a steady PCO 2 level lasting at least 60 sec. The BOLD signal closely followed the end‐tidal PCO 2 . The mean MRI signal intensity difference between high and low PCO 2 (i.e., cerebrovascular 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 controlled reproducible physiologic stimulus, i.e., alternating steady state levels of PCO 2 , to the quantification of cerebrovascular reactivity. Magn Reson Med 45:1011–1013, 2001. © 2001 Wiley‐Liss, Inc.