In vivo venous blood T1 measurement using inversion recovery true-FISP in children and adults.

A time-efficient method is described for in vivo venous blood T(1) measurement using multiphase inversion-recovery-prepared balanced steady-state free precession imaging. Computer simulations and validation experiments using a flow phantom were carried out to demonstrate the accuracy of the proposed method for measuring blood T(1) by taking advantage of the continuous inflow of fresh blood with longitudinal magnetization undisturbed by previous radiofrequency pulses. In vivo measurement of venous blood T(1) in the sagittal sinus was carried out in 26 healthy children and adults aged 7-39 years. The measured venous blood T(1) values decreased with age as a whole (P = 0.006) and were higher in females than males (P = 0.013), matching the expected developmental changes and gender differences in human hematocrit level. The estimated mean blood T(1) values were highly correlated with normal hematocrit levels across age and gender groups (Spearman's r = 0.93, P = 0.008). The longitudinal repeatability of this technique was 4.0% as measured by the within-subject coefficient of variation. The proposed multiphase inversion recovery-prepared balanced steady-state free precession imaging method is a feasible technique for fast (< 1 min) and reliable in vivo venous blood T(1) measurement and may serve as an index of hematocrit level in individual subjects.