Quantitative Combined ASL/BOLD Imaging: Implications for the Interpretation of the BOLD Post-Stimulus Undershoot

Valerie Griffeth¹, Aaron Simon¹, Joanna Perthen¹, Richard Buxton²

Two theories for the mechanism of the BOLD post-stimulus undershoot seen with brain activation are a slow recovery of CBV or a slow recovery of CMRO2. Dual-echo spiral ASL measurements of responses to a visual stimulus were analyzed to determine apparent M0 and R2* values for both the total signal and the tagged component delivered by arterial flow. In addition to CBF and BOLD responses, that allowed calculation of CMRO2 with a calibrated BOLD approach, a CBV-effect (similar to VASO) was also isolated. In this study the BOLD post-stimulus undershoot was not associated with a slow recovery of CBV nor with a slow recovery of CMRO2. Instead, it was consistent with a vascular origin due to a slight undershoot of CBF.