Zero Echo Time ¹⁷O-MRI Reveals Decreased Cerebral Metabolic Rate of Oxygen Consumption in a Murine Model of Amyloidosis

The cerebral metabolic rate of oxygen consumption (CMRO2) is a key metric to investigate the mechanisms involved in neurodegeneration in animal models and evaluate potential new therapies. CMRO2 can be measured by direct O-17 magnetic resonance imaging (O-17-MRI) of (H2O)-O-17 signal changes during inhalation of O-17-labeled oxygen gas. In this study, we built a simple gas distribution system and used 3D zero echo time (ZTE-)MRI at 11.7 T to measure CMRO2 in the APP(swe)/PS1(dE9) mouse model of amyloidosis. We found that CMRO2 was significantly lower in the APP(swe)/PS1(dE9) brain than in wild-type at 12-14 months. We also estimated cerebral blood flow (CBF) from the post-inhalation washout curve and found no difference between groups. These results suggest that the lower CMRO2 observed in APP(swe)/PS1(dE9) is likely due to metabolism impairment rather than to reduced blood flow. Analysis of the O-17-MRI data using different quantification models (linear and 3-phase model) showed that the choice of the model does not affect group comparison results. However, the simplified linear model significantly underestimated the absolute CMRO2 values compared to a 3-phase model. This may become of importance when combining several metabolic fluxes measurements to study neuro-metabolic coupling.