title: Bone remodeling after MR imaging-guided high-intensity focused ultrasound ablation: evaluation with MR imaging, CT, Na(18)F-PET, and histopathologic examination in a swine model.
abstract: OBJECTIVE
  To serially monitor bone remodeling in the swine femur after magnetic resonance (MR) imaging-guided high-intensity focused ultrasound (HIFU) ablation with MR imaging, computed tomography (CT), sodium fluorine 18 (Na(18)F)-positron emission tomography (PET), and histopathologic examination, as a function of sonication energy.
  
  
  METHODS
  Experimental procedures received approval from the local institutional animal care and use committee. MR imaging-guided HIFU was used to create distal and proximal ablations in the right femurs of eight pigs. The energy used at the distal target was higher (mean, 419 J; range, 390-440 J) than that used at the proximal target (mean, 324 J; range, 300-360 J). Imaging was performed before and after ablation with 3.0-T MR imaging and 64-section CT. Animals were reevaluated at 3 and 6 weeks with MR imaging (n = 8), CT (n = 8), Na(18)F-PET (n = 4), and histopathologic examination (n = 4). Three-dimensional ablation lengths were measured on contrast material-enhanced MR images, and bone remodeling in the cortex was measured on CT images.
  
  
  RESULTS
  Ablation sizes at MR imaging 3 and 6 weeks after MR imaging-guided HIFU ablation were similar between proximal (low-energy) and distal (high-energy) lesions (average, 8.7 × 21.9 × 16.4 mm). However, distal ablation lesions (n = 8) demonstrated evidence of subperiosteal new bone formation at CT, with a subtle focus of new ossification at 3 weeks and a larger focus of ossification at 6 weeks. New bone formation was associated with increased uptake at Na(18)F-PET in three of four animals; this was confirmed at histopathologic examination in four of four animals.
  
  
  CONCLUSIONS
  MR imaging-guided HIFU ablation of bone may result in progressive remodeling, with both subcortical necrosis and subperiosteal new bone formation. This may be related to the use of high energies. MR imaging, CT, and PET are suitable noninvasive techniques to monitor bone remodeling after MR imaging-guided HIFU ablation.
authors.affiliation: From the Department of Radiology and Biomedical Imaging, University of California-San Francisco, 185 Berry St, Suite 350, San Francisco, CA 94107-5705.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Bucknor
authors.forename: Viola
authors.initials: V
authors.lastname: Rieke
authors.forename: Youngho
authors.initials: Y
authors.lastname: Seo
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Horvai
authors.forename: Randall A
authors.initials: RA
authors.lastname: Hawkins
authors.forename: Sharmila
authors.initials: S
authors.lastname: Majumdar
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Link
authors.forename: Maythem
authors.initials: M
authors.lastname: Saeed
mesh_terms: D000818:Animals; D016723:Bone Remodeling; D001842:Bone and Bones / Q000473:pathology* / Q000601:surgery*; D005260:Female; D005462:Fluorine Radioisotopes; D057086:High-Intensity Focused Ultrasound Ablation; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D049268:Positron-Emission Tomography; D012964:Sodium; D013552:Swine; D014057:Tomography, X-Ray Computed
chemical_list: D005462:Fluorine Radioisotopes; D012964:Sodium