The measurement of myocardial T1 relaxation times in humans with inversion recovery EPI

Changes in myocardial longitudinal relaxation time (T1) are important for evaluating myocardial blood flow with first-pass contrast-enhanced MRI. Relaxation dynamics for inversion recovery echo planar imaging (I-EPI) are less complex than partial flip angle, field echo techniques. The goal of this project is to develop and evaluate a robust method for measuring T1 in intact, beating human hearts. I-EPI was performed on eight asymptomatic volunteers using a 1.5 Tesla MRI system. Imaging parameters were: FOV=42.5 cm, phase sampling ratio = 0.609-0.781, 64×112 matrix, TE_eff =47.8 ms., at least six inversion times, TI, ranging from 72 to 1400 ms, one shot. Four short axis slices were obtained for each TI. Signal intensities were measured for four ROI myocardial segments in each slice and plotted versus TI. T1 measurements were validated using a phantom containing gadolinium contrast at various dilutions. Linear interpolation was used following logarithmic transformation to calculate myocardial T1 based on the determination of the null point. The mean global myocardial T1 value was 811 ms+/- 49.8 ms (mean +/- SD). We conclude that myocardial T1 measurements, specific to each patient, can be measured with good accuracy and reproducibility using IR-EPI.