| The goal of this study was to characterize the image quality of a dedicated, quasi-monochromatic x-ray spectrum, cone beam breast imaging system under scatter corrected and non-scatter corrected conditions for a variety of simulated breast compositions. Computed tomography (CT) projections were acquired of a breast phantom containing two concentric sets of acrylic spheres that varied in size (1-8mm) based on their azimuthal position. A 700 ml breast phantom was filled with 3 different concentrations of methanol and water, simulating a wide range of breast densities. Acrylic yarn was sometimes included to simulate the structural components and connective tissue of a breast. For each phantom condition, 2D scatter was measured for 360° of projection angles. Scatter correction was performed and scatter-corrected and uncorrected projections were then reconstructed with an iterative ordered subsets convex (OSC) algorithm. Reconstructed image quality of various phantom configurations and (non)corrected conditions was characterized using line profiles, non-uniformity index, signal-to-noise ratio (SNR) and contrast analysis. A human observer detection task and a two alternative forced choice (2-AFC) study for the spheres in the different concentric rings were used to determine the effects of scatter correction on signal detection. Line profiles, non-uniformity calculations, and contrast results consistently show that scatter correction effectively reduces the cupping artifact and improves image contrast for the three concentrations used. SNR results indicate higher noise, and thus lower overall SNR, for the scatter corrected images in the lower density background. SNR of signals was found to be independent of scatter correction for the higher density background. Results from the observer study indicate that there was no statistical difference in the number or sizes of lesions observed in the scatter versus non-scatter corrected images for all densities. Results of the 2-AFC study indicate that for the lower density concentration, scatter correction did not play a role in the probability of detection of spheres greater than 3 mm for the inner radius and 2 mm for the outer radius, but it was effective in improving performance for spheres less than 2 mm for both the inner and outer radii. For the higher density, scatter correction was found to improve the detectability of spheres greater than 3 mm for the inner radius and greater than 2 mm for the outer radius. The statistical analysis of the 2-AFC study did however find that the overall effect of scatter correction was marginal though the combined effect of scatter correction and size was not significant except for 4 mm sphere across the densities examined.;While the results of the observer study are ambiguous as to whether scatter correction significantly improves signal detection, we believe applying scatter correction for differing breast conditions improves overall image quality and is recommended for subsequent use. |
