Validation Of T-2-Based Oxygen Extraction Fraction Measurement With(15)O Positron Emission Tomography

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 x 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 x 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.