Cerebral perfusion metrics calculated directly, model-free, from a hypoxia-induced step change in deoxyhemoglobin

Dynamic susceptibility contrast (DSC) perfusion MRI measures blood flow metrics via application of a BOLD pulse sequence during transit of a gadolinium-based contrast agent (GBCA), We have previously shown that can also be performed using endogenous deoxyhemoglobin (dOHb) as a replacement for GBCA since dOHb also has the necessary paramagnetic properties similar to GBCA 1. Conventional analysis with these contrast agents includes deconvolution of an arterial input function (AIF) assuming a kinetic model. However, the immediate decrease in dOHb that occurs during reoxygenation from a transient hypoxia constitutes a step reduction in susceptibility that permits direct, model-free, calculation of relative resting perfusion metrics. The metrics from this step analysis for seven healthy volunteers were compared to those from a conventional analysis of GBCA and dOHb. Voxel-wise maps of mean transit time, and relative cerebral blood flow and cerebral blood volume, had a high spatial congruence for all three analyses and were similar in appearance to published maps. The time course of the T2*-weighted signal step response identifies both the arrival time, the distribution of the step increase in arterial oxygen saturation, SaO2, and the voxel filling phase. The analysis of a step change in dOHb during rapid reoxygenation is an alternative way of calculating perfusion metrics directly from measurements of the resulting T2*-weighted signal, avoiding the potential errors from the use of a kinetic model and requirement for selection of an AIF. ### Competing Interest Statement JAF and DJM contributed to the development of the automated end-tidal targeting device, RespirAct (Thornhill Research Inc., TRI) used in this study and have equity in the company. OS and JD receive salary support from TRI. TRI provided no other support for the study. All other authors have no disclosures to report.