title: X-ray phase contrast imaging of the breast: analysis of tissue simulating materials.
abstract: OBJECTIVE
  Phase contrast imaging, particularly of the breast, is being actively investigated. The purpose of this work is to investigate the x-ray phase contrast properties of breast tissues and commonly used breast tissue substitutes or phantom materials with an aim of determining the phantom materials best representative of breast tissues.
  
  
  METHODS
  Elemental compositions of breast tissues including adipose, fibroglandular, and skin were used to determine the refractive index, n = 1 - δ + i β. The real part of the refractive index, specifically the refractive index decrement (δ), over the energy range of 5-50 keV were determined using XOP software (version 2.3, European Synchrotron Radiation Facility, France). Calcium oxalate and calcium hydroxyapatite were considered to represent the material compositions of microcalcifications in vivo. Nineteen tissue substitutes were considered as possible candidates to represent adipose tissue, fibroglandular tissue and skin, and four phantom materials were considered as possible candidates to represent microcalcifications. For each material, either the molecular formula, if available, or the elemental composition based on weight fraction, was used to determine δ. At each x-ray photon energy, the absolute percent difference in δ between the breast tissue and the substitute material was determined, from which three candidates were selected. From these candidate tissue substitutes, the material that minimized the absolute percent difference in linear attenuation coefficient μ, and hence β, was considered to be best representative of that breast tissue.
  
  
  RESULTS
  Over the energy range of 5-50 keV, while the δ of CB3 and fibroglandular tissue-equivalent material were within 1% of that of fibroglandular tissue, the μ of fibroglandular tissue-equivalent material better approximated the fibroglandular tissue. While the δ of BR10 and adipose tissue-equivalent material were within 1% of that of adipose tissue, the tissue-equivalent material better approximated the adipose tissue in terms of μ. Polymethyl methacrylate, a commonly used tissue substitute, exhibited δ greater than fibroglandular tissue by ≈ 12%. The A-150 plastic closely approximated the skin. Several materials exhibited δ between that of adipose and fibroglandular tissue. However, there was an energy-dependent mismatch in terms of equivalent fibroglandular weight fraction between δ and μ for these materials. For microcalcifications, aluminum and calcium carbonate were observed to straddle the δ and μ of calcium oxalate and calcium hydroxyapatite. Aluminum oxide, commonly used to represent microcalcifications in the American College of Radiology recommended phantoms for accreditation exhibited δ greater than calcium hydroxyapatite by ≈ 23%.
  
  
  CONCLUSIONS
  A breast phantom comprising A-150 plastic to represent the skin, commercially available adipose and fibroglandular tissue-equivalent formulations to represent adipose and fibroglandular tissue, respectively, was found to be best suited for x-ray phase-sensitive imaging of the breast. Calcium carbonate or aluminum can be used to represent microcalcifications.
authors.affiliation: Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA. srinivasan.vedantham@umassmed.edu
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Vedantham
authors.forename: Andrew
authors.initials: A
authors.lastname: Karellas
mesh_terms: D032701:Biomimetics / Q000295:instrumentation*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014961:X-Ray Diffraction / Q000295:instrumentation*
references.citation: J Digit Imaging. 2004 Mar;17(1):64-70
references.pmid: 15255520
references.citation: Med Phys. 2013 Jan;40(1):011901
references.pmid: 23298092
references.citation: Radiology. 2002 Dec;225(3):801-7
references.pmid: 12461264
references.citation: Phys Med Biol. 1977 Mar;22(2):219-28
references.pmid: 857261
references.citation: Opt Express. 2011 Feb 14;19(4):3339-46
references.pmid: 21369156
references.citation: Radiology. 2011 Jun;259(3):684-94
references.pmid: 21436089
references.citation: Med Phys. 2012 Sep;39(9):5317-35
references.pmid: 22957600
references.citation: Invest Radiol. 2005 Jul;40(7):385-96
references.pmid: 15973129
references.citation: Phys Med Biol. 2013 Jan 7;58(1):R1-35
references.pmid: 23220766
references.citation: Phys Med Biol. 2010 May 7;55(9):2669-77
references.pmid: 20400806
references.citation: Med Phys. 1995 Apr;22(4):375-9
references.pmid: 7609717
references.citation: Phys Med Biol. 1997 Nov;42(11):2015-25
references.pmid: 9394394
references.citation: Phys Med Biol. 2002 Jan 7;47(1):47-63
references.pmid: 11814227
references.citation: Radiology. 2008 Apr;247(1):98-105
references.pmid: 18292479
references.citation: Br J Radiol. 1977 Nov;50(599):814-21
references.pmid: 588903
references.citation: Med Phys. 2008 Apr;35(4):1199-206
references.pmid: 18491511
references.citation: Radiology. 1999 Oct;213(1):23-37
references.pmid: 10540637
references.citation: Phys Med Biol. 1977 Sep;22(5):889-99
references.pmid: 909925
references.citation: Med Phys. 2008 Mar;35(3):1078-86
references.pmid: 18404942
references.citation: Med Phys. 2013 Mar;40(3):031913
references.pmid: 23464328
references.citation: Med Phys. 2009 Dec;36(12):5437-43
references.pmid: 20095256
references.citation: Radiology. 2000 Mar;214(3):895-901
references.pmid: 10715065
references.citation: Phys Med Biol. 2009 May 7;54(9):2747-53
references.pmid: 19369710
references.citation: Med Phys. 2012 Mar;39(3):1530-41
references.pmid: 22380385
references.citation: Med Phys. 2012 Dec;39(12):7317-28
references.pmid: 23231281
references.citation: Med Phys. 2012 Jan;39(1):424-8
references.pmid: 22225312
references.citation: Med Phys. 1982 May-Jun;9(3):436-41
references.pmid: 7110074
references.citation: Med Phys. 2003 Aug;30(8):2169-79
references.pmid: 12945983
references.citation: Br J Radiol. 1946 Feb;19:52-63
references.pmid: 21015391
references.citation: Invest Radiol. 2011 Dec;46(12):801-6
references.pmid: 21788904
references.citation: Med Phys. 2010 Nov;37(11):6047-54
references.pmid: 21158316
references.citation: Radiology. 1979 Feb;130(2):485-91
references.pmid: 760167