Modeling oxygen effects in tissue-preparation neuronal-current MRI

Tissue-preparation neuronal-current MRI (ncMRI) was recently developed to directly detect neuronal activity without hemodynamic contamination. However, as a paramagnetic substance, the oxygen molecules present in the tissue may also alter the ncMRI signal through relaxivity and susceptibility effects. To study the effects of oxygen on the ncMRI signal and estimate their impact on tissue-preparation experiments, oxygen-induced MRI signal changes were formulated as a function of oxygen concentration (OC) of gas, oxygen consumption rate, and imaging parameters. Under favorable conditions of these parameters, the maximum oxygen-induced signal magnitude and phase change were estimated to be 0.32% and 3.85°, respectively. Considering that the ncMRI signal changes obtained in previous tissue-preparation experiments (3-5% in magnitude, 0.8-1.7° in phase) were tens or hundreds of times larger than the corresponding oxygen-induced signal changes (0.03% in magnitude, 0.03-0.07° in phase), it is concluded that the oxygen had negligible effects in the previous experiments.