Dependence of blood T 2 on oxygenation at 7 T: In vitro calibration and in vivo application

Purpose The 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. Methods In 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. Results In 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. Conclusion We 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. © 2013 Wiley Periodicals, Inc.