A reference-based PET/MRI method for quantifying activation-induced changes in cerebral oxygen metabolism

Hybrid PET/MRI can overcome the complexity of PET imaging of the cerebral metabolic rate of oxygen (CMRO2), while retaining the ability to directly measure oxygen uptake in the brain. One technique, PMROx, incorporates complementary MRI methods acquired simultaneously with 15OO2-PET. Specifically, the MRI-based method arterial spin labelling (ASL) to image cerebral blood flow (CBF) and MR-susceptometry to measure whole-brain CMRO2. PMROx is non-invasive with imaging times around 5 min, making it feasible to image CMRO2 under different conditions in one session. This study presents the first application of PMROx to humans with the aims of evaluating its reliability and sensitivity to increased CMRO2 during functional activation (right-handed sequential finger tapping). In addition, blood-oxygen level dependent (BOLD) images were acquired to compare BOLD contrast to underlying changes in CBF and CMRO2. Across 14 participants, mean CMRO2 was 3.2 ± 0.5 mLO2/100 g/min with excellent within-session repeatability. Significant increases in CBF, CMRO2 and BOLD contrast were detected in the primary sensorimotor cortex, supplementary motor area and secondary somatosensory cortex. This study demonstrated the ability of PMROx to image CMRO2 non-invasively, its sensitivity to increased regional CMRO2 and how PET/MRI provides the opportunity to compare BOLD contrast to underlying changes in perfusion and oxygen metabolism.