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

A. Schwarz, M. Rijpkema, D. Collins, G. Payne, T. Prock, A. Woodward, A. Heerschap and M. Leach

CRC Clinical Magnetic Resonance Research Group, Institute of Cancer Research and Royal Marsden Hospital, Sutton, Surrey, UK.
Nov, 2000



In MRS studies using surface transmit coils, accurate assessment of local SAR and RF heating represents a difficult problem involving the coil geometry and electromagnetic and geometric tissue properties. Methodologies to determine the optimum operating parameters for dual-resonant surface coil measurements are presented, based on a standardized coil and protocol used in a multicenter (31)P MRS clinical trial, using adiabatic pulses and bilevel proton decoupling. Spatial distributions of absorbed radiation in human calf and in a tissue-equivalent gel phantom were modeled using finite-element simulations and realistic conductivity and permittivity values. Local SAR in worst-case 1 cm(3) volumes of interest (VOIs) in calf is predicted to be below international guidelines, and the temperature at the skin surface was found to increase due to the RF by less than 2 degrees C and remain below 37 degrees C. The heating rate and maximum temperature in the gel, at positions guided by the simulations, were within guideline values for both extremities and trunk and in reasonable agreement with that predicted.

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