Measurement of T1 relaxation times of cardiac phosphate metabolites using BIR‐4 adiabatic RF pulses and a variable nutation method

T1 relaxation times of PCr and beta-ATP in human cardiac and skeletal muscle were evaluated using a variable nutation method. This allows T1 measurements with a constant TR and a significant reduction in acquisition time compared with the partial saturation method. Four 1D CSI datasets were obtained using 30 degrees, 45 degrees, 60 degrees, and 90 degrees BIR-4 adiabatic RF pulses within 40 min. The T1 of the phosphate phantom obtained with this method agreed with values obtained with the partial saturation method. The T1s of PCr and beta-ATP in heart are 3.98 +/- 0.18 s and 1.86 +/- 0.16 s (mean +/- SE). Our results demonstrated that T1 values in heart and skeletal muscle are not significantly different.