Simultaneous quantitative assessment of cerebral physiology using respiratory-calibrated MRI and near-infrared spectroscopy in healthy adults

- A setup to simultaneously quantify oxygen saturation with MRI and NIRS is presented.
- Healthy adults were subjected to two episodes of hypercapnia breathing.
- NIRS oxygen saturation had a good correlation with fMRI/BOLD oxygen saturation.
- NIRS oxygen saturation had the best correlation with the fMRI BOLD signal.
- Deoxygenated haemoglobin had the second best correlation with the fMRI BOLD signal.

BackgroundFunctional near-infrared spectroscopy (fNIRS) and functional MRI (fMRI) are non-invasive techniques used to relate activity in different brain regions to certain tasks. Respiratory calibration of the blood oxygen level dependent (BOLD) signal, and combined fNIRS-fMRI approaches have been used to quantify physiological subcomponents giving rise to the BOLD signal. A comparison of absolute oxygen metabolism parameters between MRI and NIRS, using spatially resolved (SRS) NIRS and respiratory calibrated MRI, could yield additional insight in the physiology underlying activation.Materials and methodsChanges in the BOLD signal, cerebral blood flow (CBF), and oxygen saturation (SO2) were derived from a single MRI sequence during a respiratory challenge in healthy volunteers. These changes were compared to SO2 obtained by a single probe SRS NIRS setup. In addition, concentration changes in oxygenated (O2Hb), deoxygenated (HHb), and total haemoglobin (tHb), obtained by NIRS, were compared to the parameters obtained by MRI.ResultsNIRS SO2 correlated with end-tidal CO2 (0.83, p < 0.0001), the BOLD signal (0.82, p < 0.0001), CBF (0.85, p < 0.0001), and also MRI SO2 (0.82, p < 0.0001). The BOLD signal correlated with NIRS HHb (− 0.76, p < 0.0001), O2Hb (0.41, p = 0.001), and tHb (r = 0.32, p = 0.01).ConclusionsGood correlations show that changes in cerebral physiology, following a respiratory challenge, go hand in hand with changes in the BOLD signal, CBF, O2Hb, HHb, NIRS SO2, and MRI SO2. Out of all NIRS derived parameters, the SO2 showed the best correlation with the BOLD signal.