Triple repetition time saturation transfer (TRiST) 31 P spectroscopy for measuring human creatine kinase reaction kinetics

Human cardiac phosphorus MR saturation transfer experiments to quantify creatine kinase forward rate constants ( k f ) have previously been performed at 1.5 T. Such experiments could benefit from increased signal‐to‐noise ratio (SNR) and spectral resolution at 3 T. At 1.5 T, the four‐angle saturation transfer method was applied with low‐angle adiabatic pulses and surface coils. However, low‐angle adiabatic pulses are potentially problematic above 1.5 T due to bandwidth limitations, power requirements, power deposition, and intrapulse spin‐spin relaxation. For localized metabolite spin‐lattice relaxation time ( T 1 ) measurements, a dual repetition time approach with adiabatic half‐passage pulses was recently introduced to solve these problems at 3 T. Because the saturation transfer experiment requires a T 1 measurement performed while one reacting moiety is saturated, we adapt the dual repetition time approach to measure k f using a triple repetition time saturation transfer (TRiST) method. A new pulsed saturation scheme with reduced sensitivity to static magnetic field inhomogeneity and compatibility with cardiac triggering is also presented. TRiST measurements of k f are validated in human calf muscle against conventional saturation transfer and found to agree within 3%. The first 3‐T TRiST measurements of creatine kinase k f in the human calf ( n = 6), chest muscle, and heart ( n = 8) are 0.26 ± 0.04 s −1 , 0.23 ± 0.03 s −1 , and 0.32 ± 0.07 s −1 , respectively, consistent with prior 1.5 T values. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.