Determinants of the reliability of ultrasound tomography sound speed estimates as a surrogate for volumetric breast density

Abstract

Purpose: 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. C 2015 American Association of Physicists in Medicine. [http://dx

Using Speed of Sound Imaging to Characterize Breast Density

“…Sound speed and density information were extracted from the images using a semi-automated method in the software package ImageJ (US National Institutes of Health, Bethesda Maryland, USA) (Rasband 1997–2012) by one reader (M. Sak). There is a demonstrated reliability in sound speed estimates when processing UST scans in this manner, with a reported ICC of 0.934 for sound speed measurements (Khodr, et al 2015). The sound speed of the surrounding water bath is intermediate to the sound speeds of the breast tissue and must therefore be segmented from each image manually.…”

Quantitative assessment of breast density using transmission ultrasound tomography

“…It may be that the value differs due to differences in the SOS images used in the segmentation. Our 3D algorithm (utilizing diffraction) appears to avoid some artifacts and volume averaging that may arise with 2D reconstruction algorithms, especially if the model is based on refraction only, as in the case of ray‐based inversions . Note that Sak et al.…”

“…4,5 The only factors associated with greater increases in breast cancer risk are age and certain genetic mutations, such as those in the BRCA genes. [6][7][8][9] In this era of precision medicine, risk models for screening based on breast density have increasingly been proposed as an alternative to risk models based on age. [10][11][12] For risk-based screening using breast density to be effective, the methods to assess breast density must be reliable, robust, accessible, and consistent.…”

Ultrasound tomography imaging with waveform sound speed: parenchymal changes in women undergoing tamoxifen therapy

“…Descriptive statistics were then calculated on the remaining voxels, including measures such as the mean value and standard deviation. This method of masking sound speed images to produce quantitative measurements has shown to be reliable between different users and repeatable 15 .…”