Dedicated breast CT: Fibroglandular volume measurements in a diagnostic population

Abstract

Purpose: To determine the mean and range of volumetric glandular fraction (VGF) of the breast in a diagnostic population using a high-resolution flat-panel cone-beam dedicated breast CT system. This information is important for Monte Carlo-based estimation of normalized glandular dose coefficients and for investigating the dependence of VGF on breast dimensions, race, and pathology. Methods: Image data from a clinical trial investigating the role of dedicated breast CT that enrolled 150 women were retrospectively analyzed to determine the VGF. The study was conducted in adherence to a protocol approved by the institutional human subjects review boards and written informed consent was obtained from all study participants. All participants in the study were assigned BI-RADS R 4 or 5 as per the American College of Radiology assessment categories after standard diagnostic work-up and underwent dedicated breast CT exam prior to biopsy. A Gaussian-kernel based fuzzy c-means algorithm was used to partition the breast CT images into adipose and fibroglandular tissue after segmenting the skin. Upon determination of the accuracy of the algorithm with a phantom, it was applied to 137 breast CT volumes from 136 women. VGF was determined for each breast and the mean and range were determined. Pathology results with classification as benign, malignant, and hyperplasia were available for 132 women, and were used to investigate if the distributions of VGF varied with pathology. Results: The algorithm was accurate to within ±1.9% in determining the volume of an irregular shaped phantom. The study mean (± inter-breast SD) for the VGF was 0.172 ± 0.142 (range: 0.012-0.719). VGF was found to be negatively correlated with age, breast dimensions (chest-wall to nipple length, pectoralis to nipple length, and effective diameter at chest-wall), and total breast volume, and positively correlated with fibroglandular volume. Based on pathology, pairwise statistical analysis (Mann-Whitney test) indicated that at the 0.05 significance level, there was no significant difference in distributions of VGF without adjustment for age between malignant and nonmalignant breasts (p = 0.41). Pairwise comparisons of the distributions of VGF in increasing order of mammographic breast density indicated all comparisons were statistically significant (p < 0.002). Conclusions: This study used a different clinical prototype breast CT system than that in previous studies to image subjects from a different geographical region, and used a different algorithm for analysis of image data. The mean VGF estimated from this study is within the range reported in previous studies, indicating that the choice of 50% glandular weight fraction to represent an average breast for Monte Carlo-based estimation of normalized glandular dose coefficients in mammography needs revising. In the study, the distributions of VGF did not differ significantly with pathology.

Technical Note: Skin thickness measurements using high‐resolution flat‐panel cone‐beam dedicated breast CTa)

“…BI-RADS R 4 and 5 assessment categories correspond to a suspicious abnormality and highly suggestive of malignancy, respectively. The clinical prototype dedicated breast CT system [15][16][17] used in this study was different from the previous study. 13 FDK reconstruction 18 that provided isotropic (0.273 mm) 3 voxels were used.…”

“…In order to describe the modifications, a synopsis of the method 13 along with the modifications is provided. The steps involved were: manually defining the breast volume used for determining the breast skin thickness; 17,19 segmenting the breast volume from the background (air), for which we used an algorithm 20,21 different from the prior study; 13 transforming each coronal slice to polar coordinates, for which we used 1 • angular steps and applied and a 3 × 3 median filter prior to polar transform; followed by applying a one-dimensional (1D) derivative filter to obtain the gradient image. For segmenting the skin layer from the gradient image, we used a search range of up to 5.5-6.8 mm (20-25 voxels of 0.273 mm size) from the outer skin layer (air-skin boundary) to determine the voxel with the minimum (negative) gradient representative of the inner skin layer (skin-fat boundary).…”

Three dimensional dose distribution comparison of simple and complex acquisition trajectories in dedicated breast CT

“…Studies have reported typical skin thickness measurements of ∼1.5 mm. 38,40 The cylindrical phantom walls were composed of 1.5 mm of acrylic (µ = 0.279 cm ). The overall attenuation caused by acrylic is comparable to the attenuation caused by skin (<3%); however, the attenuation by the polyethylene terephthalate is lower (∼2.5%), slightly overestimating of dose values in the breast phantom.…”

“…Previous studies 15,37,38 including our own have shown that the mean diameters of clinically encountered breasts range from 10 to 14 cm depending on the orientation of the measurement. 37 Although the maximum diameter encountered clinically can be as high as 20 cm, 38 selecting a range of phantom diameters that encompass the observed means is sufficient for our intended purpose of characterizing major differences in dose distribution between the two orbits.…”

“…37 Although the maximum diameter encountered clinically can be as high as 20 cm, 38 selecting a range of phantom diameters that encompass the observed means is sufficient for our intended purpose of characterizing major differences in dose distribution between the two orbits. Therefore, all the phantoms used in this study have diameters in the 10-15 cm range.…”