title: Technical Note: Multipurpose CT, ultrasound, and MRI breast phantom for use in radiotherapy and minimally invasive interventions.
abstract: OBJECTIVE
  To develop a multipurpose gel-based breast phantom consisting of a simulated tumor with realistic imaging properties in CT, ultrasound and MRI, or a postsurgical cavity on CT. Applications for the phantom include: deformable image registration (DIR) quality assurance (QA), autosegmentation validation, and localization testing and training for minimally invasive image-guided procedures such as those involving catheter or needle insertion.
  
  
  METHODS
  A thermoplastic mask of a typical breast patient lying supine was generated and then filled to make an array of phantoms. The background simulated breast tissue consisted of 32.4 g each of ballistic gelatin (BG) powder and Metamusil™ (MM) dissolved in 800 ml of water. Simulated tumors were added using the following recipe: 12 g of barium sulfate (1.4% v/v) plus 0.000 14 g copper sulfate plus 0.7 g of MM plus 7.2 g of BG all dissolved in 75 ml of water. The phantom was evaluated quantitatively in CT by comparing Hounsfield units (HUs) with actual breast tissue. For ultrasound and MRI, the phantoms were assessed based on subjective image quality and signal-difference to noise (SDNR) ratio, respectively. The stiffness of the phantom was evaluated based on ultrasound elastography measurements to yield an average Young's modulus. In addition, subjective tactile assessment of phantom was performed under needle insertion.
  
  
  RESULTS
  The simulated breast tissue had a mean background value of 24 HU on CT imaging, which more closely resembles fibroglandular tissue (40 HU) as opposed to adipose (-100 HU). The tumor had a mean CT number of 45 HU, which yielded a qualitatively realistic image contrast relative to the background either as an intact tumor or postsurgical cavity. The tumor appeared qualitatively realistic on ultrasound images, exhibiting hypoechoic characteristics compared to background. On MRI, the tumor exhibited a SDNR of 3.7. The average Young's modulus was computed to be 15.8 ± 0.7 kPa (1 SD).
  
  
  CONCLUSIONS
  We have developed a process to efficiently and inexpensively produce multipurpose breast phantoms containing simulated tumors visible on CT, ultrasound, and MRI. The phantoms have been evaluated for image quality and elasticity and can serve as a medium for DIR QA, autosegmentation QA, and training for minimally invasive procedures.
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Ruschin
authors.affiliation: Techna Institute, University Health Network, Toronto, Ontario M5G 1P5, Canada.
authors.forename: Sean R H
authors.initials: SR
authors.lastname: Davidson
authors.affiliation: Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3, Canada.
authors.forename: William
authors.initials: W
authors.lastname: Phounsy
authors.affiliation: Institute of Health Policy, University of Toronto, Toronto, Ontario M5T 3M6, Canada.
authors.forename: Tae Sun
authors.initials: TS
authors.lastname: Yoo
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Lee
authors.initials: L
authors.lastname: Chin
authors.affiliation: Department of Radiation Oncology, Erasmus MC Cancer Institute, 3075 EA Rotterdam, Netherlands.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pignol
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Ananth
authors.initials: A
authors.lastname: Ravi
authors.affiliation: Department of Medical Physics, Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Claire
authors.initials: C
authors.lastname: McCann
mesh_terms: D001466:Barium Sulfate; D001940:Breast / Q000000981:diagnostic imaging; D001943:Breast Neoplasms / Q000000981:diagnostic imaging; D019327:Copper Sulfate; D055119:Elastic Modulus; D004867:Equipment Design; D005780:Gelatin; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D016683:Supine Position; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014463:Ultrasonography / Q000295:instrumentation*; D014867:Water
chemical_list: D014867:Water; D001466:Barium Sulfate; D005780:Gelatin; D019327:Copper Sulfate