2D AND 3D breast elastography with a combined ultrasound/digital tomosynthesis mammography system

Abstract

Ultrasound elastography is a novel imaging method which acts as a surrogate to manual palpation to evaluate elastic properties of tissue. In this dissertation, elastography was conducted through a mammographic paddle in conjunction with a combined ultrasound/digital tomosynthesis mammography system to improve breast lesion characterization. Imaging through a mammographic paddle may adversely affect ultrasound image quality by reducing spatial resolution, increasing attenuation, and decreasing contrast. Thus, appropriate paddle choice is essential to create high quality through-paddle ultrasound images and strain images. Sonographic image quality through mammographic paddles of varying materials and thicknesses was compared with direct-contact (no paddle) image quality. TPX plastic paddles ≤ 2.5 mm thick performed best; when employed in vivo, 83% of cases produced image quality as good or better than their direct-contact analogues. Through-paddle 2D elastography was conducted through the best paddle using a 1D ultrasound transducer at 7.5 MHz and performance was compared with freehand elastography. For small strain step sizes (< 0.5%), through-paddle elastography produced correlation coefficients and strain SNR comparable to freehand elastography. Ultimately, the aim of elastography is to acquire high quality strain estimates in 3D to fully characterize tissue. Thus, data acquisition techniques were extended to a small 3D volume. Compared with its 2D analogue, 3D elastography created higher correlation coefficients for strain step sizes ≥ 1% and at least 35% improvement in strain SNR for all step sizes. These early successes indicate that through-paddle elastography can create high quality elastograms which might aid in breast lesion characterization. Next, through-paddle elastography was performed in 20 human subjects with varying breast masses. This dissertation introduced the elasticity characteristic “differential correlation coefficient,” which exploits the severe decorrelation observed in cysts under compression to differentiate cystic and solid masses. When applied in a clinical setting, this characteristic demonstrated potential to reduce the malignancy rating of a complicated cyst, changing management options from biopsy to imaging follow-up. Additional elastographic appearances of breast masses were evaluated, including lesion size, stiffness, margin regularity, and boundary flow. These studies suggest that elastography has potential to improve characterization of breast masses beyond x-ray tomography and sonography alone.