Asymmetric scatter kernels for software-based scatter correction of gridless mammography

Abstract

Scattered radiation remains one of the primary challenges for digital mammography, resulting in decreased image contrast and visualization of key features. While anti-scatter grids are commonly used to reduce scattered radiation in digital mammography, they are an incomplete solution that can add radiation dose, cost, and complexity. Instead, a software-based scatter correction method utilizing asymmetric scatter kernels is developed and evaluated in this work, which improves upon conventional symmetric kernels by adapting to local variations in object thickness and attenuation that result from the heterogeneous nature of breast tissue. This fast adaptive scatter kernel superposition (fASKS) method was applied to mammography by generating scatter kernels specific to the object size, x-ray energy, and system geometry of the projection data. The method was first validated with Monte Carlo simulation of a statistically-defined digital breast phantom, which was followed by initial validation on phantom studies conducted on a clinical mammography system. Results from the Monte Carlo simulation demonstrate excellent agreement between the estimated and true scatter signal, resulting in accurate scatter correction and recovery of 87% of the image contrast originally lost to scatter. Additionally, the asymmetric kernel provided more accurate scatter correction than the conventional symmetric kernel, especially at the edge of the breast. Results from the phantom studies on a clinical system further validate the ability of the asymmetric kernel correction method to accurately subtract the scatter signal and improve image quality. In conclusion, software-based scatter correction for mammography is a promising alternative to hardware-based approaches such as anti-scatter grids. Description of PurposeScattered radiation remains one of the primary challenges for digital mammography. Despite the lower energies used in mammography, the small air-gap distance leads to relatively high scatter-to-primary ratios (SPR) of ~0.2-0.7 for 2-6 cm thick breasts, respectively, that add undesirable low-frequency signal and increased noise to the projection, resulting in decreased detectability and contrast-to-noise ratio (CNR) of key features such as masses or microcalcifications. 1 Hardware-based solutions such as a Bucky anti-scatter grid can reduce scattered radiation, but are imperfect solutions due to the loss of primary radiation (~30%) and resulting radiation dose increase to compensate for the loss. Secondary considerations include the remaining transmitted scatter (~20%), mechanical complexity of a moving grid to avoid grid lines, and additional cost. 2 Alternatively, software-based scatter estimation and correction methods can be used in gridless systems to subtract the scatter signal from the measured projection to recover image contrast, improve image quality, and potentially reduce radiation dose since primary photons are no longer lost to the grid. However, conventional software-based methods typically apply symmetric kernels th...

Simple method for computing scattered radiation in breast tomosynthesis

“…Estimation of scattered radiation can lead to scatter signal reduction strategies in clinical environment; however, it can also help in the design of image simulation frameworks by enabling the addition of the correct amount of scattered radiation in simulated image data . Some of these frameworks are used within virtual clinical trials (VCTs) for lesion detection performance .…”

Breast Imaging

“…Scattered radiation remains one of the main challenges in digital mammography [1], limiting the quantitative usefulness of radiographic images. It reduces the quality of the image, degrades the contrast and the signal to noise ratio, reduces the dynamic range and therefore affects the diagnosis of low contrast lesions and small microcalcifications [2,3].…”

“…However, anti-scatter grids are an incomplete solution, adding complexity and cost to the mammography system manufacturing. Although they help to improve image quality, they also attenuate primary radiation, leading to an increase in the patient dose delivered (up to a factor of 3) to maintain a constant Detector Air Kerma (DAK) [1], [4,5].…”

Scatter reduction for grid-less mammography using the convolution-based image post-processing technique

“…Scattering reduces the quantitative usefulness of the mammogram, affecting the diagnosis of malignant lesions 1,2,3 .…”

“…Although this method helps to improve the image quality, it is not a complete solution. The grids do not block all the scattered radiation and attenuate a proportion of primary radiation, leading to an increase in the patient dose delivered, and add complexity and cost to the overall system 1,4,5 .…”