title: Head phantoms for transcranial focused ultrasound.
abstract: OBJECTIVE
  In the ongoing endeavor of fine-tuning, the clinical application of transcranial MR-guided focused ultrasound (tcMRgFUS), ex-vivo studies wlkiith whole human skulls are of great use in improving the underlying technology guiding the accurate and precise thermal ablation of clinically relevant targets in the human skull. Described here are the designs, methods for fabrication, and notes on utility of three different ultrasound phantoms to be used for brain focused ultrasound research.
  
  
  METHODS
  Three different models of phantoms are developed and tested to be accurate, repeatable experimental options to provide means to further this research. The three models are a cadaver, a gel-filled skull, and a head mold containing a skull and filled with gel that mimics the brain and the skin. Each was positioned in a clinical tcMRgFUS system and sonicated at 1100 W (acoustic) for 12 s at different locations. Maximum temperature rise as measured by MR thermometry was recorded and compared against clinical data for a similar neurosurgical target. Results are presented as heating efficiency in units (°C/kW/s) for direct comparison to available clinical data. The procedure for casting thermal phantom material is presented. The utility of each phantom model is discussed in the context of various tcMRgFUS research areas.
  
  
  RESULTS
  The cadaveric phantom model, gel-filled skull model, and full head phantom model had heating efficiencies of 5.3, 4.0, and 3.9 °C/(kW/s), respectively, compared to a sample clinical heating efficiency of 2.6 °C/(kW/s). In the seven research categories considered, the cadaveric phantom model was the most versatile, though less practical compared to the ex-vivo skull-based phantoms.
  
  
  CONCLUSIONS
  Casting thermal phantom material was shown to be an effective way to prepare tissue-mimicking material for the phantoms presented. The phantom models presented are all useful in tcMRgFUS research, though some are better suited to a limited subset of applications depending on the researchers needs.
authors.affiliation: Focused Ultrasound Foundation, Charlottesville, Virginia 22903.
authors.forename: Matthew D C
authors.initials: MD
authors.lastname: Eames
authors.affiliation: Focused Ultrasound Foundation, Charlottesville, Virginia 22903.
authors.forename: Mercy
authors.initials: M
authors.lastname: Farnum
authors.affiliation: Department of Neurosurgery, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Khaled
authors.affiliation: Department of Neurosurgery, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: W Jeff
authors.initials: WJ
authors.lastname: Elias
authors.affiliation: Focused Ultrasound Foundation, Charlottesville, Virginia 22903 and Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: Arik
authors.initials: A
authors.lastname: Hananel
authors.affiliation: Focused Ultrasound Foundation, Charlottesville, Virginia 22903 and Department of Neurosurgery, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: John W
authors.initials: JW
authors.lastname: Snell
authors.affiliation: Focused Ultrasound Foundation, Charlottesville, Virginia 22903 and Department of Neurosurgery, University of Virginia, Charlottesville, Virginia 22908.
authors.forename: Neal F
authors.initials: NF
authors.lastname: Kassell
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia 22908 and Institut Langevin, ESPCI ParisTech, CNRS UMR 7587, INSERM U979, Paris 75005, France.
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Aubry
mesh_terms: D004453:Echoencephalography / Q000295:instrumentation* / Q000379:methods*; D004867:Equipment Design; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D020100:Hydrogels; D008279:Magnetic Resonance Imaging / Q000379:methods; D008954:Models, Biological; D019047:Phantoms, Imaging; D013696:Temperature; D062125:Thermometry / Q000379:methods; D014057:Tomography, X-Ray Computed
chemical_list: D020100:Hydrogels