Dependence of Blood T2 on Oxygenation at 7 T: In Vitro Calibration and In Vivo Application

PurposeThe calibratable relationship between blood oxygenation (Y) and T-2 allows quantification of cerebral venous oxygenation. We aim to establish a calibration plot between blood T-2, Y, and hematocrit at 7 T, and using T-2-relaxation-under-spin-tagging MRI, determine human venous blood oxygenation in vivo. MethodsIn vitro experiments were performed at 7 T on bovine blood samples using a Carr-Purcell-Meiboom-Gill-T-2 sequence, from which we characterized the relationship among T-2, Y, and hematocrit. T-2-relaxation-under-spin-tagging MRI was implemented at 7 T to measure venous blood T-2 in vivo, from which oxygenation was estimated using the in vitro calibration plot. Hyperoxia was performed to test the sensitivity of the method to oxygenation changes, and the 7 T results were compared with those at 3 T. ResultsIn vitro data showed that arterial and venous T-2 at 7 T are 68 and 20 ms, respectively, at a typical hematocrit of 0.42. In vivo measurement showed a cerebral venous oxygenation of 64.7 5.0% and a test-retest coefficient-of-variation of 3.6 +/- 2.4%. Hyperoxia increased Y-v by 9.0 +/- 1.4% (P = 0.001) and the 3 and 7 T results showed a strong correlation (R = 0.95) across individuals. ConclusionWe provided an in vitro calibration plot for conversion of blood T-2 to oxygenation at 7 T and demonstrated its utility in vivo. Magn Reson Med 71:2035-2042, 2014. (c) 2013 Wiley Periodicals, Inc.