title: Determinants of the reliability of ultrasound tomography sound speed estimates as a surrogate for volumetric breast density.
abstract: OBJECTIVE
  High breast density, as measured by mammography, is associated with increased breast cancer risk, but standard methods of assessment have limitations including 2D representation of breast tissue, distortion due to breast compression, and use of ionizing radiation. Ultrasound tomography (UST) is a novel imaging method that averts these limitations and uses sound speed measures rather than x-ray imaging to estimate breast density. The authors evaluated the reproducibility of measures of speed of sound and changes in this parameter using UST.
  
  
  METHODS
  One experienced and five newly trained raters measured sound speed in serial UST scans for 22 women (two scans per person) to assess inter-rater reliability. Intrarater reliability was assessed for four raters. A random effects model was used to calculate the percent variation in sound speed and change in sound speed attributable to subject, scan, rater, and repeat reads. The authors estimated the intraclass correlation coefficients (ICCs) for these measures based on data from the authors' experienced rater.
  
  
  RESULTS
  Median (range) time between baseline and follow-up UST scans was five (1-13) months. Contributions of factors to sound speed variance were differences between subjects (86.0%), baseline versus follow-up scans (7.5%), inter-rater evaluations (1.1%), and intrarater reproducibility (∼0%). When evaluating change in sound speed between scans, 2.7% and ∼0% of variation were attributed to inter- and intrarater variation, respectively. For the experienced rater's repeat reads, agreement for sound speed was excellent (ICC = 93.4%) and for change in sound speed substantial (ICC = 70.4%), indicating very good reproducibility of these measures.
  
  
  CONCLUSIONS
  UST provided highly reproducible sound speed measurements, which reflect breast density, suggesting that UST has utility in sensitively assessing change in density.
authors.affiliation: Department of Health and Human Services, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive MSC 9774, Bethesda, Maryland 20892.
authors.forename: Zeina G
authors.initials: ZG
authors.lastname: Khodr
authors.affiliation: Karmanos Cancer Institute, Wayne State University, 4100 John R, Detroit, Michigan 48201.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Sak
authors.affiliation: Department of Health and Human Services, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive MSC 9774, Bethesda, Maryland 20892.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Pfeiffer
authors.affiliation: Karmanos Cancer Institute, Wayne State University, 4100 John R, Detroit, Michigan 48201 and Delphinus Medical Technologies, 46701 Commerce Center Drive, Plymouth, Michigan 48170.
authors.forename: Nebojsa
authors.initials: N
authors.lastname: Duric
authors.affiliation: Karmanos Cancer Institute, Wayne State University, 4100 John R, Detroit, Michigan 48201 and Delphinus Medical Technologies, 46701 Commerce Center Drive, Plymouth, Michigan 48170.
authors.forename: Peter
authors.initials: P
authors.lastname: Littrup
authors.affiliation: Karmanos Cancer Institute, Wayne State University, 4100 John R, Detroit, Michigan 48201.
authors.forename: Lisa
authors.initials: L
authors.lastname: Bey-Knight
authors.affiliation: Henry Ford Health System, 2799 W Grand Boulevard, Detroit, Michigan 48202.
authors.forename: Haythem
authors.initials: H
authors.lastname: Ali
authors.affiliation: Henry Ford Health System, 2799 W Grand Boulevard, Detroit, Michigan 48202.
authors.forename: Patricia
authors.initials: P
authors.lastname: Vallieres
authors.affiliation: Division of Cancer Prevention, National Cancer Institute, Department of Health and Human Services, 9609 Medical Center Drive MSC 9774, Bethesda, Maryland 20892.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Sherman
authors.affiliation: Department of Health and Human Services, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive MSC 9774, Bethesda, Maryland 20892.
authors.forename: Gretchen L
authors.initials: GL
authors.lastname: Gierach
mesh_terms: D000328:Adult; D000368:Aged; D001940:Breast / Q000166:cytology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D015203:Reproducibility of Results; D014054:Tomography / Q000379:methods*; D000069453:Ultrasonic Waves