title: Effect of Sonication Duration and Power on Ablation Depth During MR-Guided Focused Ultrasound of Bone.
abstract: To evaluate the effect of differences in sonication duration and power on the size of postcontrast ablation zone following magnetic resonance-guided focused ultrasound (MRgFUS) of bone in a swine femoral bone model.
  
  
  
  Experimental procedures received approval from the Institutional Committee on Animal Research. MRgFUS was used to create two thermal lesions in the left femur of six pigs. Each target was subjected to six sonications. 400J of energy was used for each sonication. However, the distal target received the standard sonication duration of 20 seconds (20W), while the proximal target received a longer sonication duration of 40 seconds (10W). MRgFUS lesions were imaged with fat-saturated spoiled gradient echo sequence at 3.0T MRI 10 minutes following the administration of contrast. Maximum three-plane dimensions of the hypoenhanced ablation area were measured.
  
  
  
  Postcontrast MR images demonstrated ovoid regions of hypoenhancement at each target. The average depth of ablation was significantly greater for the shorter high-power sonications (7.3 mm), compared to the longer lower-power sonications (4.5 mm), P = 0.026. The craniocaudal dimension was also greater for the shorter ablations 26.7 mm compared to the longer sonications 21.0 mm, P = 0.006.
  
  
  
  Contrary to anecdotal clinical experience, this preclinical model suggests that during MRgFUS of bone, standard duration, higher-power sonications resulted in deeper ablation volumes compared to long duration, lower-power sonications. These results suggest that to achieve deeper ablations, if longer sonications are used, then the power should be relatively maintained, for a net energy increase.
  
  
  
  1 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:1418-1422.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Bucknor
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Eugene
authors.initials: E
authors.lastname: Ozhinsky
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Rutwik
authors.initials: R
authors.lastname: Shah
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Roland
authors.initials: R
authors.lastname: Krug
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Viola
authors.initials: V
authors.lastname: Rieke
mesh_terms: D000162:Acoustics; D000818:Animals; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D057086:High-Intensity Focused Ultrasound Ablation; D008279:Magnetic Resonance Imaging; D013010:Sonication; D025321:Surgery, Computer-Assisted; D013552:Swine; D013696:Temperature; D014463:Ultrasonography
chemical_list: D003287:Contrast Media
keywords: MR-guided focused ultrasound; MRI; bone ablation; high intensity focused ultrasound