B(1) field homogeneity and specific absorption rate in ultra-high field magnetic resonance imaging for guiding high-intensity focused ultrasound / 南方医科大学学报

ABSTRACT

<p><b>OBJECTIVE</b>To study the efficacy of B1 field shimming technique and evaluate the specific absorption rate (SAR) in ultra-high field magnetic resonance imaging (MRI) for MRI-guided high-intensity focused ultrasound (HIFU).</p><p><b>METHODS</b>An electromagnetic model of the female pelvis with a temperature gradient was established. B1 field homogeneity and local SAR were simulated and calculated using regular and optimized B1 shimming coefficients.</p><p><b>RESULTS</b>The maximum local SAR reached 10.24 W/kg, which exceeded the safe threshold of 10 W/kg, as calculated using regular B1 shimming coefficients in the normal model. Using the optimized B1 shimming coefficients, the maximum local SAR of the tissue was 9.65 W/kg, which was below the safe threshold.</p><p><b>CONCLUSION</b>The temperature distributions in the body generated by ultrasound energy need to be considered in ultra-high field MRI-guided HIFU surgery. The proposed optimized B1 shimming strategy based on the temperature gradient can be used to control the local SAR levels.</p>