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

Abstract

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.

Figure 1

The sequence diagram of the multi-phase IR-TrueFISP used in this study.

Figure 2

Simulated signal-time curves for multi-phase IR-TrueFISP imaging.

Figure 3

IR-trueFISP images (a) and time courses (b) from a representative subject. In (a), the numbers below images are the corresponding inversion times (TI’s) in the unit of ms. In (b), time courses are plotted for the regions-of-interest at sagittal sinus and gray matter respectively, and for different flip angles (α = 10°, 30°, and 50°).

Figure 4

Comparison of the T₁ measurements with different flip angles.

Figure 5

Measured blood T₁ as a function of age and gender with fitted lines for each gender in 18 children aged 7–17 (a), in 8 adults aged 19–39 (b), and in 26 children and adults aged 7 to 39 (c) (Red diamond and line = female; Black square and line = male; gender=0 for female and 1 for male).

Figure 6

Scatter plot of mean venous blood R1 values and mean normal Hct values based on literature across 3 age groups and 2 genders. Error bars indicate SD.