Validation of T<sub>2</sub>‐based oxygen extraction fraction measurement with <sup>15</sup>O positron emission tomography
Dengrong Jiang, Shengwen Deng, Crystal Franklin, Michael W. O’Boyle, Wei Zhang, Betty L. Heyl, Pan Li, Paul Jerabek, Peter T. Fox, Hanzhang Lu
Abstract
Purpose To evaluate the accuracy of T 2 ‐based whole‐brain oxygen extraction fraction (OEF) estimation by comparing it with gold standard 15 O‐PET measurements. Methods Sixteen healthy adult subjects underwent MRI and 15 O‐PET OEF measurements on the same day. On MRI, whole‐brain OEF was quantified by T 2 ‐relaxation‐under‐spin‐tagging (TRUST) MRI, based on subject‐specific hematocrit. The TRUST OEF was compared to the whole‐brain averaged OEF produced by 15 O‐PET. Agreement between TRUST and 15 O‐PET whole‐brain OEF measurements was examined in terms of intraclass correlation coefficient (ICC) and in absolute OEF values. In a subset of 10 subjects, test‐retest reproducibility of whole‐brain OEF was also evaluated and compared between the two modalities. Results Across the 16 subjects, the mean whole‐brain OEF of TRUST and 15 O‐PET were 36.44 ± 4.07% and 36.45 ± 3.65%, respectively, showing no difference between the two modalities ( P = .99). TRUST whole‐brain OEF strongly correlated with that of 15 O‐PET (N = 16, ICC = 0.90, P = 4 × 10 −7 ). The coefficient‐of‐variation of TRUST and 15 O‐PET whole‐brain OEF measurements were 1.79 ± 0.67% and 2.06 ± 1.55%, respectively, showing no difference between the two modalities (N = 10, P = .64). Further analyses on the effect of hematocrit revealed that correlation between PET OEF and TRUST OEF with assumed hematocrit remained significant (ICC = 0.8, P < 2 × 10 −5 ). Conclusion Whole‐brain OEF measured by TRUST was in excellent agreement with gold standard 15 O‐PET, with highly comparable accuracy and reproducibility. These findings suggest that TRUST MRI can provide accurate quantification of whole‐brain OEF noninvasively.