Feasibility of QUantitative Imaging of eXtraction of Oxygen and TIssue Consumption (QUIXOTIC) to assess functional changes in venous oxygen saturation during visual stimulus

Introduction: Functional MRI has been extensively used to indirectly measure changes in neuronal activation via the BOLD (blood oxygenation level dependent) effect. While BOLD fMRI provides a relative signal that fluctuates based on changes in venous oxygenation, the absolute value of venous oxygen saturation at baseline and during activation is unknown. Additionally, the BOLD response is highly variable, resulting in large intersubject differences in response size, leading to decreased statistical power in group comparisons [1]. Recently, Lu and colleagues [2] have shown that baseline venous blood oxygen saturation modulates the BOLD response amplitude in a predictable way, thus providing a physiologic explanation for the variability. These observations suggest that an fMRI technique able to directly evaluate functional changes in absolute venous oxygen saturation may be a more repeatable and physiologically relevant way to assess neuronal activation. A newly developed fMRI technique called QUantitative Imaging of eXtraction of Oxygen and TIssue Consumption (QUIXOTIC) MRI allows direct measurement of venous oxygen saturation (Yv) [3]. QUIXOTIC MRI involves exclusively imaging blood spins flowing above a cutoff velocity (VC) on the venous side of circulation. In this study, we assess the feasibility of using QUIXOTIC to quantitatively measure functional changes in local venous oxygen saturation, in response to a visual stimulus.