title: Characterization and evaluation of tissue-mimicking gelatin phantoms for use with MRgFUS.
abstract: BACKGROUND
  A tissue-mimicking phantom that accurately represents human-tissue properties is important for safety testing and for validating new imaging techniques. To achieve a variety of desired human-tissue properties, we have fabricated and tested several variations of gelatin phantoms. These phantoms are simple to manufacture and have properties in the same order of magnitude as those of soft tissues. This is important for quality-assurance verification as well as validation of magnetic resonance-guided focused ultrasound (MRgFUS) treatment techniques.
  
  
  METHODS
  The phantoms presented in this work were constructed from gelatin powders with three different bloom values (125, 175, and 250), each one allowing for a different mechanical stiffness of the phantom. Evaporated milk was used to replace half of the water in the recipe for the gelatin phantoms in order to achieve attenuation and speed of sound values in soft tissue ranges. These acoustic properties, along with MR (T1 and T2*), mechanical (density and Young's modulus), and thermal properties (thermal diffusivity and specific heat capacity), were obtained through independent measurements for all three bloom types to characterize the gelatin phantoms. Thermal repeatability of the phantoms was also assessed using MRgFUS and MR thermometry.
  
  
  RESULTS
  All the measured values fell within the literature-reported ranges of soft tissues. In heating tests using low-power (6.6 W) sonications, interleaved with high-power (up to 22.0 W) sonications, each of the three different bloom phantoms demonstrated repeatable temperature increases (10.4 ± 0.3 °C for 125-bloom, 10.2 ± 0.3 °C for 175-bloom, and 10.8 ± 0.2 °C for 250-bloom for all 6.6-W sonications) for heating durations of 18.1 s.
  
  
  CONCLUSIONS
  These evaporated milk-modified gelatin phantoms should serve as reliable, general soft tissue-mimicking MRgFUS phantoms.
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, UT USA ; Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA.
authors.forename: Alexis I
authors.initials: AI
authors.lastname: Farrer
authors.affiliation: Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA ; Department of Physics and Astronomy, University of Utah, Salt Lake City, UT USA.
authors.forename: Henrik
authors.initials: H
authors.lastname: Odéen
authors.affiliation: Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA ; School of Computing, University of Utah, Salt Lake City, UT USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: de Bever
authors.affiliation: Department of Mechanical Engineering, University of Utah, Salt Lake City, UT USA.
authors.forename: Brittany
authors.initials: B
authors.lastname: Coats
authors.affiliation: Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA.
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Parker
authors.affiliation: Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA.
authors.forename: Allison
authors.initials: A
authors.lastname: Payne
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, UT USA ; Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT USA.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Christensen
keywords: Gelatin; MRgFUS; Phantoms; Tissue-mimicking