Assessment of the Linearity of the R2* Dependence on Blood Oxygenation and Measurement of Venous CBV Using Hyperoxia at 7T

Paula L. Croal¹, Ian D. Driver¹, Emma L. Hall¹, Susan T. Francis¹, Penny A. Gowland¹

The linearity of R2* with blood oxygenation is a critical assumption in most models of the BOLD signal, and in the measurement of venous cerebral blood volume (vCBV) using hyperoxia. We used isocapnic hyperoxic to test the linearity of R2* in grey matter across a dynamic range of precisely targeted PETO2 levels. A strong linear relationship was found between oxygenation and R2*, allowing calculation of GM vCBV (1.97%). The advantage of this method over previous methods of measuring vCBV using hyperoxia is that it does not assume that the relaxivity of the oxygen is the same in the vein and tissue.