T2-prepared balanced steady-state free precession (bSSFP) for quantifying whole-blood oxygen saturation at 1.5T

PurposeTo establish a calibration equation to convert human blood T-2 to the full range of oxygen saturation levels (HbO(2)) and physiologic hematocrit (Hct) values using a T-2-prepared balanced steady-state free precession sequence (T-2-SSFP) at 1.5T. MethodsBlood drawn from 10 healthy donors (29.13.9 years old) was prepared into samples of varying HbO(2) and Hct (n=79), and imaged using T-2-SSFP sequence at 37 degrees C and interrefocusing interval (180)=12 ms. The relationship between blood T-2, HbO(2), and Hct was established based on the model R2=R2,plasma+Hct(R2,RBC-R2,plasma)+k<bold>Hct</bold>(1-Hct)<bold></bold>(1-HbO2)2. Measured R-2 and HbO(2) levels were fit by the model yielding values of R2,plasma, R2,RBC, and k. T-2-SSFP and the established calibration equation were applied to extract HbO(2) at the superior sagittal sinus (SSS) in vivo and were compared with susceptometry-based oximetry. ResultsConstants derived from the fit were: k=74.2 [s(-1)], R2,plasma =1.5 [s(-1)], R2,RBC =11.6 [s(-1)], the R-2 of the fit was 0.95. Average HbO(2) at the SSS in seven healthy volunteers was 65%+/- 7% and 66%+/- 7% via T-2- and susceptometry-based oximetry, respectively. Bland-Altman analysis indicated agreement between the two oximetric methods with no significant bias. ConclusionThe calibration constants presented here should ensure improved accuracy for whole-blood oximetry based on T-2-SSFP at 1.5T. Magn Reson Med 79:1893-1900, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.