title: In vivo optimisation study for multi-baseline MR-based thermometry in the context of hyperthermia using MR-guided high intensity focused ultrasound for head and neck applications.
abstract: OBJECTIVE
  In this in vivo study, the feasibility to perform hyperthermia treatments in the head and neck using magnetic resonance image-guided high intensity focused ultrasound (MRgHIFU) was established using a porcine acute model.
  
  
  METHODS
  Porcine specimens with a weight between 17 and 18 kg were treated in the omohyoid muscle in the neck. Hyperthermia was applied with a target temperature of 41 °C for 30 min using a Sonalleve MRgHIFU system. MR-based thermometry was calculated using water-proton resonance frequency shift and multi-baseline look-up tables indexed by peak-to-peak displacement (Dpp) measurements using a pencil-beam navigator. Three hyperthermia experiments were conducted at different Dpp values of 0.2, 1.0 and 3.0 mm. An optimisation study was carried out to establish the optimal parameters controlling the multi-baseline method that ensured a minimisation of spatial-average peak-to-peak temperature (TSA-pp) and temperature direct current bias (TSA-DC).
  
  
  RESULTS
  The multi-baseline technique reduced considerably the noise on both TSA-pp and TSA-DC. The reduction of noise was more important when Dpp was higher. For Dpp = 3 mm the average (±standard deviation (SD)) of TSA-pp and TSA-DC was reduced from 4.5 (± 2.5) and 2.5 (±0.6) °C, respectively, to 0.8 (± 0.7) and 0.09 (± 0.2) °C.
  
  
  CONCLUSIONS
  This in vivo study showed the level of noise in PRFS-based thermometry introduced by respiratory motion in the context of MRgHIFU hyperthermia treatment for head and neck and the feasibility of reducing this noise using a multi-baseline technique.
authors.affiliation: Sunnybrook Health Sciences Centre , Toronto , Ontario, Canada .
authors.forename: Samuel
authors.initials: S
authors.lastname: Pichardo
authors.forename: Max
authors.initials: M
authors.lastname: Köhler
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
authors.forename: Kullervo
authors.initials: K
authors.lastname: Hynnyen
mesh_terms: D000818:Animals; D006258:Head and Neck Neoplasms / Q000628:therapy*; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D006979:Hyperthermia, Induced; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012119:Respiration; D013552:Swine; D062125:Thermometry / Q000379:methods*
keywords: Cancer; HIFU; MRI; head and neck; pre-clinical