Quantification of Oxygenation and Oxygen Consumption Rates in the Mouse Brain Based on Tissue Oxygen Level-Dependent (TOLD) MRI.

A noninvasive method to estimate oxygenation and oxygen (O) consumption rates in mouse brain tissue based on T-weighted tissue oxygen level-dependent (TOLD) MRI was developed. The aim of the present study was to estimate the kinetics of O in tissue in order to facilitate the planning of radiation therapy. The relationship between the proton T relaxation rate and O concentrations was examined in water and corn oil samples, which are models of the aqueous and lipidic phases of cell components. T maps of the mouse brain were obtained under breathing high oxygen concentration gas, carbogen (95% O + 5% CO), or 100% O, and shifts in the concentration of O from the physiological state in the brain were then estimated. Pseudo-TOLD signals in blood samples, hemoglobin, and myoglobin aqueous solutions under oxygenation were measured to examine the effects of heme iron on T. O metabolism in mouse brains was evaluated by the enhancement/diminishment rates of the TOLD signal when the breathing gas was switched from air to carbogen or 100% O and when it was switched back to air. Carbogen or 100% O inhalation increased cortical O levels by 0.28 or 0.26 mmol/L, respectively. By analyzing the time course profile of the TOLD signal, the oxygenation rate, oxygenation level, and O consumption rate were successfully estimated. TOLD MRI has potential as a useful tool to estimate the quantitative indices of oxygenation and O consumption rates in brain tissue.