Ultrasonic transmission tomography in refracting media: reduction of refraction artifacts by curved-ray techniques

Abstract

The present work concerns the problem of refraction artifacts in ultrasonic transmission tomography. The reconstruction is improved by curved-ray methods, combined with algebraic reconstruction techniques. The problem of acoustic ray tracing and image interpolation has been carefully studied, and different reconstruction algorithms have been developed and compared. The effect of the geometrical characteristics of the set-up and the studied medium characteristics (geometry and acoustical properties) on the reconstruction accuracy are considered. Some simulation results are presented which show an encouraging reduction of the refraction artifacts. The results have been confirmed by experiments carried out with agar-gel phantoms. The experimental device and procedure are described and straight- and curved-ray reconstructions are shown. Reconstruction quality can be improved significantly for refractive index variations of up to 10%, which seems sufficient for soft tissue imaging; yet there are some limiting factors, such as multipath propagation, if any, or the difficulty of choosing an initial value for the reconstruction.

Refraction corrected transmission ultrasound computed tomography for application in breast imaging

“…7,20,23,24 However, none of these methods have been efficient enough to be deployed in practice, and thus the more recent literature is dominated by straight ray propagation methods. But as was shown by Denis et al 25 and more recently by Li et al,26 nonlinear ray tracing can achieve substantial qualitative improvements over straight ray casting, even for moderately refracting fields. Yet that work did not offer efficient methods to accomplish this.…”

<title>Extended-Kalman-filter-based reconstruction approach to curved ray optical tomography</title>

“…As against deterministic approaches such as the algebraic reconstruction techniques (ART) or its variants like the averaged correction per projec tion (ACP) or the simultaneous ART (SART) algorithms [2], [3), in stochastic approaches such as the Kalman filter (KF) or the maximum like. lihood estimator, the reconstruction problem is considered as an estimation problem, by considering the projections as samples of a random process.…”

Time of flight ultrasonic CT based on ML-EM for wooden pillars

“…ML-EM process gives positive value for the pixels. And absorption, scattering, resolution can be corrected easily in ML-EM process [7] [8]. In this paper, we proposed an approach for wooden inspection by using ultrasonic CT based on ML-EM method.…”