title: [B(1) field homogeneity and specific absorption rate in ultra-high field magnetic resonance imaging for guiding high-intensity focused ultrasound].
abstract: OBJECTIVE
  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).
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China.E-mail: gsy_17@126.com.
authors.forename: Shiyong
authors.initials: S
authors.lastname: Gu
authors.forename: Xuegang
authors.initials: X
authors.lastname: Xin
mesh_terms: D005260:Female; D057086:High-Intensity Focused Ultrasound Ablation; D006801:Humans; D008279:Magnetic Resonance Imaging; D010388:Pelvis; D014464:Ultrasonic Therapy