Iterative analysis of cerebrovascular reactivity dynamic response by temporal decomposition.

Objective: To improve quantitative cerebrovascular reactivity (CVR) measurements and CO arrival times, we present an iterative analysis capable of decomposing different temporal components of the dynamic carbon dioxide- Blood Oxygen-Level Dependent (CO -BOLD) relationship.

Experimental Design: Decomposition of the dynamic parameters included a redefinition of the voxel-wise CO arrival time, and a separation from the vascular response to a stepwise increase in CO (Delay to signal Plateau - DTP) and a decrease in CO (Delay to signal Baseline -DTB). Twenty-five (normal) datasets, obtained from BOLD MRI combined with a standardized pseudo-square wave CO change, were co-registered to generate reference atlases for the aforementioned dynamic processes to score the voxel-by-voxel deviation probability from normal range. This analysis is further illustrated in two subjects with unilateral carotid artery occlusion using these reference atlases.

Principal Observations: We have found that our redefined CO arrival time resulted in the best data fit. Additionally, excluding both dynamic BOLD phases (DTP and DTB) resulted in a static CVR, that is maximal response, defined as CVR calculated only over a normocapnic and hypercapnic calibrated plateau.

Conclusion: Decomposition and novel iterative modeling of different temporal components of the dynamic CO -BOLD relationship improves quantitative CVR measurements.