Echo time optimization for J-difference editing of glutathione at 3T

Purpose: To investigate the echo time (TE) dependence of J-difference editing of glutathione and to determine the optimal TE for in vivo measurements at 3T. Methods: Spatially resolved density-matrix simulations and phantom experiments were performed at a range of TEs to establish the spatial and TE modulation of glutathione signals in editing-on, editing-off, and difference spectra at 3T. In vivo data were acquired in five healthy subjects to compare a TE of 68 ms and a TE of 120 ms. At the longer TE, high-bandwidth, frequency-modulated, slice-selective refocusing pulses were also compared with conventional amplitude-modulated pulses. Results: Simulations and relaxation-corrected phantom experiments suggest that the maximum edited signal occurs at TE 160 ms, ignoring transverse relaxation. Considering in vivo T₂ relaxation times of 67–89 ms, the optimal in vivo TE is estimated to be 120 ms. In vivo measurements showed that this TE yielded 15% more signal than TE 68 ms. A further gain of 57% resulted from using improved slice-selective refocusing pulses. Conclusion: J-difference editing of glutathione using TE 120 ms delivers increased signal due to improved editing efficiency that more than offsets T₂ losses. The additional TE also allows for use of improved slice-selective refocusing pulses, which results in additional signal gains. Magn Reson Med 77:498–504, 2017.