Calibration of the 1H decoupling field strength and experimental evaluation of the specific RF absorption rate in 1H-decoupled human 13C-MRS.

For patient safety in human 1H decoupled 13C-MRS, it is absolutely necessary to evaluate the specific RF absorption rate (SAR) of the tissue exposed to 1H frequency irradiation. With the use of surface coils, the local SAR at the body surface is of most concern due to the inherent RF field inhomogeneity. An empirical procedure to spatially calibrate the decoupler power level and to evaluate the local SAR at the body surface is described. For head, liver, muscle gastrocnemius, and muscle vastus lateralis, the SAR at the body surface was estimated for an 1H/13C double surface coil setup. Optimized duty cycle values obtained with this procedure show that broad-band 1H-decoupled 13C-MR spectroscopy is clinically feasible at 1.5 T for such a coil configuration within safety guidelines.