A Combined Regularization Method Using Prior Structural Information for Sound-Speed Image Reconstruction of Ultrasound Computed Tomography

Abstract

Ultrasound computed tomography (USCT) is a promising technique for breast imaging. It provides three modalities: echo image, sound speed image (SSI), and attenuation image. The echo image reveals structural details of the breast with high resolution but is not quantitative. The SSI is quantitative, but its resolution is generally lower than that of the echo image. The SSI reconstruction is an ill-posed problem, thus the Tikhonov or total variation (TV) regularization methods are generally used. Tikhonov regularization is stable, but it tends to smooth the SSI and results in low resolution. TV regularization can preserve the sharp edges and provide higher resolution, but it may result in staircase artifacts. To combine the advantages of Tikhonov and TV regularizations, this article proposes a combined regularization method using prior structural information from the echo image. The proposed method mainly includes three steps. First, the echo image is reconstructed using the synthetic aperture (SA) technique and then segmented into breast and water regions. The segmentation result is used as prior structural information. Second, the USCT sound propagation forward model was built. Finally, with a penalty term according to the prior structural information, the combined regularization method is used to reconstruct the SSI. Both simulation and ex vivo experiments were conducted for evaluation. In the simulation, the proposed method has a low root-mean-square-error (13.78 m/s), a high correlation coefficient (0.812), a high structural similarity (0.755), and a low standard deviation of water sound speed (2.33 m/s). In the ex vivo experiment, the method has a low standard deviation of water sound speed (1.44 and 3.13 m/s for small and large objects, respectively), a low contrast to noise ratio (3.09 and 5.08), and a high Dice coefficient (0.92 and 0.97). Thus, the proposed combined regularization method using prior structural information can improve reconstruction quality.

Ultrasound Computed Tomography Reflection Imaging with Coherence-Factor Beamforming for Breast Tumor Early Detection

“…Lastly, women often endure pain and discomfort as their breasts require compression during imaging. Prior research [5][6][7] indicates that mammography coupled with adjunctive ultrasound imaging can notably enhance sensitivity for screening in dense breasts. However, current breast ultrasound (BUS) imaging encounters hurdles like non-isotropic low resolution and a high reliance on operator skill, which restrict its effectiveness in breast cancer screening and early detection [8,9].…”

“…To overcome the limitations of current methodologies, ultrasound computed tomography (USCT) has emerged as a promising avenue for breast cancer screening and diagnosis [5][6][7]. Offering the capability to automatically generate three-dimensional (3D) breast images across sound-speed, attenuation, and reflection modalities [13], the USCT imaging system typically comprises a bed with an opening situated atop a water tank housing a ring ultrasound transducer.…”