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

Cerebrovascular reactivity can be quantified by correlating blood oxygen level dependent (BOLD) signal intensity with changes in end‐tidal partial pressure of carbon dioxide (PCO2). Four 3‐min cycles of high and low PCO2 were induced in three subjects, each cycle containing a steady PCO2 level lasting at least 60 sec. The BOLD signal closely followed the end‐tidal PCO2. The mean MRI signal intensity difference between high and low PCO2 (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 PCO2, to the quantification of cerebrovascular reactivity. Magn Reson Med 45:1011–1013, 2001. © 2001 Wiley‐Liss, Inc.