Assessment of cerebrovascular reactivity with functional magnetic resonance imaging: comparison of CO2 and breath holding

Cerebral blood flow (CBF) and oxygenation changes following both a simple breath holding test (BHT) and a CO2 challenge can be detected with functional magnetic resonance imaging techniques. The BHT has the advantage of not requiring a source of CO2 and acetazolamide and therefore it can easily be performed during a routine MR examination. In this study we compared global hemodynamic changes induced by breath holding and CO2 inhalation with blood oxygenation level dependent (BOLD) and CBF sensitized fMRI techniques. During each vascular challenge BOLD and CBF signals were determined simultaneously with a combined BOLD and flow-sensitive alternating inversion recovery (FAIR) pulse sequence. There was a good correlation between the global BOLD signal intensity changes during breath holding and CO2 inhalation supporting the notion that the BHT is equivalent to CO2 inhalation in evaluating the hemodynamic reserve capacity with BOLD fMRI. In contrast, there was no correlation between relative CBF changes during both vascular challenges, which was probably due to the reduced temporal resolution of the combined BOLD and FAIR pulse sequence.