title: Spatio-temporal quantitative thermography of pre-focal interactions between high intensity focused ultrasound and the rib cage.
abstract: OBJECTIVE
  The aim of this paper is to quantitatively investigate the thermal effects generated by the pre-focal interactions of a HIFU beam with a rib cage, in the context of minimally invasive transcostal therapy of liver malignancies.
  
  
  METHODS
  HIFU sonications were produced by a phased-array MR-compatible transducer on Turkey muscle placed on a sheep thoracic cage specimen. The thoracic wall was positioned in the pre-focal zone 3.5 to 6.5 cm below the focus. Thermal monitoring was simultaneously performed using fluoroptic sensors inserted into the medullar cavity of the ribs and high resolution MR-thermometry (voxel: 1 × 1 × 5 mm3, four multi-planar slices).
  
  
  RESULTS
  MR-thermometry data indicated nearly isotropic distribution of the thermal energy at the ribs' surface. The temperature elevation at the focus was comparable with the pericostal temperature elevation around unprotected ribs, while being systematically inferior, by more than a factor of four on average, to the intra-medullar values. The spatial profiles of the pericostal and intra-medullar thermal build-up measurements could be smoothly connected using a Gaussian function. The dynamics of the post-sonication thermal relaxation as determined by fluoroptic measurements was demonstrated to be theoretically coherent with the experimental observations.
  
  
  CONCLUSIONS
  The experimental findings motivate further efforts for the transfer towards clinical routine of effective rib-sparing strategies for hepatic HIFU.
authors.affiliation: Hepatobiliary Interventional Radiology, Faculty of Medicine, University of Geneva , Geneva, Switzerland .
authors.forename: Lorena
authors.initials: L
authors.lastname: Petrusca
authors.forename: Rares
authors.initials: R
authors.lastname: Salomir
authors.forename: Gibran
authors.initials: G
authors.lastname: Manasseh
authors.forename: Christoph D
authors.initials: CD
authors.lastname: Becker
authors.forename: Sylvain
authors.initials: S
authors.lastname: Terraz
mesh_terms: D000818:Animals; D057086:High-Intensity Focused Ultrasound Ablation / Q000009:adverse effects* / Q000379:methods; D006358:Hot Temperature; D008113:Liver Neoplasms / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000009:adverse effects / Q000379:methods*; D012272:Ribs / Q000528:radiation effects*; D012756:Sheep; D013817:Thermography / Q000379:methods*; D062125:Thermometry; D014159:Transducers; D014422:Turkeys
keywords: MRgHIFU; pre-focal interactions; rib cage; thermal effects