Non-invasively studying whole brain activity is the advantage of MRI technique. We try to utilize this advanced technique to investigate brain tissue and vascular physiology under inspired air modulation. For instance, 5% CO2 and 21% O2 – which is noted as hypercapnia – notably increases blood flow.
Whether the brain activity depends on CO2 level is a more interesting topic in clinic application. Blood oxygen level dependent (BOLD) MRI, the conventional technique for brain fMRI, is not optimal for hypercapnia studies because BOLD contrast comes from neuro-vascular coupling mechanism, which is disturbed by CO2 inhalation. We developed a technique (TRUST MRI combined with Phase Contrast MRI) to estimate absolute global cerebral metabolic rate of oxygen (CMRO2), a measure closely related to neural activity but insolated from the vascular effect’s contamination.