Simplified methods for calculating cerebral metabolic rate of oxygen based on ¹⁷O magnetic resonance spectroscopic imaging measurement during a short ¹⁷O₂ inhalation

It has recently been shown that ¹⁷O magnetic resonance (MR) spectroscopic imaging at ultrahigh fields provides a reliable method for measuring CMRO₂ during a short period of ¹⁷O₂ gas inhalation. The mathematical (or complete) model used in the ¹⁷O MR method for calculating CMRO₂ requires simultaneous measurements of multiple parameters including the concentration of H₂¹⁷O produced in the brain tissue from inhaled ¹⁷O₂ gas (C _b), CBF, and the input function for the H₂¹⁷O concentration in the feeding artery (C_a). Both invasive and noninvasive measurements are involved in determining all of these parameters. In this article, two simplified methods are proposed and validated for calculating CMRO₂ based on ¹⁷O MR measurement(s): the first method requires the measurements of C_b and CBF, but not C_a, and the second method only requires a single noninvasive measurement of C _b. The simplified methods were used to calculate CMRO₂ in anesthetized rat brain, and the results were compared with those obtained using the complete model. The results from this work show (1) the validity of the simplified methods for quantifying CMRO₂, and (2) the feasibility for establishing a completely noninvasive ¹⁷O MR approach for imaging CMRO₂ in vivo.