Abstract
Hybrid PET/MRI can overcome the complexity of PET imaging of the cerebral metabolic rate of oxygen (CMRO(2)), while retaining the ability to directly measure oxygen uptake in the brain. One technique, PMROx, incorporates complementary MRI methods acquired simultaneously with [(15)O]O(2)-PET. Specifically, the MRI-based method arterial spin labelling (ASL) to image cerebral blood flow (CBF) and MR-susceptometry to measure whole-brain CMRO(2). PMROx is non-invasive with imaging times around 5 min, making it feasible to image CMRO(2) 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 CMRO(2) 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 CMRO(2). Across 14 participants, mean CMRO(2) was 3.2 ± 0.5 mLO(2)/100 g/min with excellent within-session repeatability. Significant increases in CBF, CMRO(2) 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 CMRO(2) non-invasively, its sensitivity to increased regional CMRO(2) and how PET/MRI provides the opportunity to compare BOLD contrast to underlying changes in perfusion and oxygen metabolism.