SAR and tissue heating with a clinical P-31 MRS protocol using surface coils, adiabatic pulses, and proton-decoupling

In MRS studies using surface transmit coils, accurate assessment of local S AR and RF heating represents a difficult problem involving the coil geometr y and electromagnetic and geometric tissue properties. Methodologies to det ermine the optimum operating parameters for dual-resonant surface coil meas urements are presented, based on a standardized coil and protocol used in a multicenter P-31 NIRS clinical trial, using adiabatic pulses and bilevel p roton decoupling. Spatial distributions of absorbed radiation in human calf and in a tissue-equivalent gel phantom were modeled using finite-element s imulations and realistic conductivity and permittivity values. Local SAR in worst-case 1 cm(3) volumes of interest (VOIs) in calf is predicted to be b elow international guidelines, and the temperature at the skin surface was found to increase due to the RF by less than 2 degreesC and remain below 37 degreesC, The heating rate and maximum temperature in the gel, at position s guided by the simulations, were within guideline values for both extremit ies and trunk and in reasonable agreement with that predicted. (C) 2000 Wil ey-Liss, Inc.