Refraction-corrected ray-based inversion for three-dimensional ultrasound tomography of the breast

Ultrasound Tomography has seen a revival of interest in the past decade, especially for breast imaging, due to improvements in both ultrasound and computing hardware. In particular, three-dimensional ultrasound tomography, a fully tomographic method in which the medium to be imaged is surrounded by ultrasound transducers, has become feasible. In this paper, a comprehensive derivation and study of a robust framework for large-scale bent-ray ultrasound tomography in 3D for a hemispherical detector array is presented. Two ray-tracing approaches are derived and compared. More significantly, the problem of linking the rays between emitters and receivers, which is challenging in 3D due to the high number of degrees of freedom for the trajectory of rays, is analysed both as a minimisation and as a root-finding problem. The ray-linking problem is parameterised for a convex detection surface and three robust, accurate, and efficient ray-linking algorithms are formulated and demonstrated. To stabilise these methods, novel adaptive-smoothing approaches are proposed that control the conditioning of the update matrices to ensure accurate linking. The nonlinear UST problem of estimating the sound speed was recast as a series of linearised subproblems, each solved using the above algorithms and within a steepest descent scheme. The whole imaging algorithm was demonstrated to be robust and accurate on realistic data simulated using a full-wave acoustic model and an anatomical breast phantom, and incorporating the errors due to time-of-flight picking that would be present with measured data. This method can used to provide a low-artefact, quantitatively accurate, 3D sound speed maps. In addition to being useful in their own right, such 3D sound speed maps can be used to initialise full-wave inversion methods, or as an input to photoacoustic tomography reconstructions

Limited Angle Ultrasound Tomography of the Compressed Breast

X-ray mammography is widely accepted as the clinical standard for breast cancer screening and diagnosis. However, reflection mode ultrasound has been known to outperform x-ray in screening performance in dense breasts. With newer modes of ultrasound, acoustic properties of breast tissue, such as the speed of sound and attenuation coefficient distributions, can be extracted from captured ultrasound signals and used to characterize breast tissue types and contribute to detection and diagnosis of malignancy. The same is possibly true for optical absorption via photoacoustic imaging. Recently, we have developed a dual-sided ultrasound scanner that can be integrated with existing x-ray mammographic systems and acquire images in the mammographic view and compression. Transmission imaging for speed of sound and attenuation coefficient in this geometry is termed limited angle tomography, as the beams at frequencies yielding high resolution cannot transit the long axis of the compressed breast. This approach, ideally, should facilitate the co-registration and comparisons between images from three modalities discussed here (x-ray, ultrasound and photoacoustic) and increase diagnostic detection confidence. However, potential limitations inherent in limited angle tomography have received minimal exploration up to this study, and existing imaging techniques developed for this approach are based on overly optimistic assumptions that hinder achievement of the desired image quality. This investigation of these problems should contribute valuable information to the validation and translation of the mammographically-configured, dual-sided ultrasound, or ultrasound and photoacoustic, scanner to the clinic. This dissertation first aims to extensively identify possible sources of error resulting from imaging in the limited angle tomography approach. Simulation findings mapping parametric conditions reveal that image artifacts arising in reflection mode (B-mode) can be modulated or mitigated by ultrasound gels with adequate acoustic properties. In addition, sound speed imaging was performed determining the level of significance for several key sources of error. Results suggest that imaging in transmission mode is the most sensitive to transducer misplacement in the signal propagation direction. This misplacement, however, could be minimized easily by routinely calibrating transducer positions. Next, this dissertation aims to advance speed of sound, attenuation, and photoacoustic image reconstruction algorithms for the limited angle tomography approach. This was done by utilizing both structural information of the imaged objects/tissues by means of the corresponding reflection mode images taken from the same imaging location, and a full acoustic modeling framework to account for complex acoustic interactions within the field of view. We have shown through simulations that both a priori information from reflection mode images and full acoustic modeling contribute to a noticeable improvement in the reconstructed images. Work done throughout the course of this dissertation should provide a foundation and insight necessary for improvements upon the existing dual-sided ultrasound scanner towards breast imaging in the clinic.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143944/1/rungroj_1.pd

Three-dimensional view of out-of-plane artifacts in photoacoustic imaging using a laser-integrated linear-transducer-array probe

Research on photoacoustic imaging (PAI) using a handheld integrated photoacoustic probe has been a recent focus of clinical translation of this imaging technique. One of the remaining challenges is the occurrence of out-of-plane artifacts (OPAs) in such a probe. Previously, we proposed a method to identify and remove OPAs by axially displacing the transducer array. Here we show that besides the benefit of removing OPAs from the imaging plane, the proposed method can provide a three-dimensional (3D) view of the OPAs. In this work, we present a 3D reconstruction method using axial transducer array displacement. By axially displacing the transducer array, out-of-plane absorbers can be three-dimensionally visualized at an elevation distance of up to the acquired imaging depth. Additionally, OPAs in the in-plane image are significantly reduced. We experimentally demonstrate the method with phantom and in vivo experiments using an integrated PAI probe. We also compare the method with elevational transducer array displacement and take into account the sensitivity of the transducer array in the 3D reconstruction.</p

Vascular Complexity Evaluation Using a Skeletonization Approach and 3D LED-Based Photoacoustic Images

Vasculature analysis is a fundamental aspect in the diagnosis, treatment, outcome evaluation and follow-up of several diseases. The quantitative characterization of the vascular network can be a powerful means for earlier pathologies revealing and for their monitoring. For this reason, non-invasive and quantitative methods for the evaluation of blood vessels complexity is a very important issue. Many imaging techniques can be used for visualizing blood vessels, but many modalities are limited by high costs, the need of exogenous contrast agents, the use of ionizing radiation, a very limited acquisition depth, and/or long acquisition times. Photoacoustic imaging has recently been the focus of much research and is now emerging in clinical applications. This imaging modality combines the qualities of good contrast and the spectral specificity of optical imaging and the high penetration depth and the spatial resolution of acoustic imaging. The optical absorption properties of blood also make it an endogenous contrast agent, allowing a completely non-invasive visualization of blood vessels. Moreover, more recent LED-based photoacoustic imaging systems are more affordable, safe and portable when compared to a laser-based systems. In this chapter we will confront the issue of vessel extraction techniques and how quantitative vascular parameters can be computed on 3D LED-based photoacoustic images using an in vitro vessel phantom model

PreFlap: From Photoacoustic Tomography Images to Vascular Mapping Sheets for Improved Preoperative Flap Evaluation

Objective: Advancements in technology have improved image acquisition and processing in the field of medical imaging, giving medical doctors the tools to implement effective medical care. In plastic surgery, despite advances in anatomical knowledge and technology, problems in preoperative planning for flap surgery remain. Methods: In this study, we propose a new protocol to analyze three-dimensional (3D) photoacoustic tomography images and generate two-dimensional (2D) mapping sheets that can help surgeons identify perforators and the perfusion territory during preoperative planning. The core of this protocol is PreFlap, a new algorithm that converts 3D photoacoustic tomography images into 2D vascular mapping images. Conclusion: Experimental results demonstrate that PreFlap can improve preoperative flap evaluation, thus can greatly saving surgeons' time and improving surgical outcomes

A Spatial-Domain Factor for Sparse-Sampling Circular-View Photoacoustic Tomography

Circular full-view configuration of photoacoustic imaging systems (C-PAI) has many applications in biomedicine (e.g., breast and brain imaging). To obtain a high-quality reconstructed image, dense spatial sampling (a large number of acoustic detectors) is needed, which makes the system expensive and challenging. Unfortunately, by reducing the number of spatial samples, streak artifacts appear, which degrade the quality of the reconstructed image. In this article, we propose a spatial-domain factor to suppress the streak artifacts and enhance the reconstructed image quality in a sparse sampling C-PAI system. Numerical and experimental studies are conducted to evaluate the proposed method. The results show that by reducing the number of spatial samples by one-fifth of the minimum required value to meet the Nyquist criteria, the proposed method provides a higher quality reconstructed image in terms of artifacts suppression and resolution improvement compared to the conventional method with dense spatial sampling. The proposed method improves the structural similarity index measure (SSIM), generalized contrast-to-noise ratio (gCNR), CNR, and tangential resolution values up to 100%, 9%, 38.6 dB, and ∼45%, respectively. Based on the advantages of the proposed method, a low-cost version of a C-PAI system for clinical applications can be developed.This is a manuscript of the article published as Hakakzadeh, Soheil, Praveenbalaji Rajendran, Vahid Amin Nili, Zahra Kavehvash, and Manojit Pramanik. "A spatial-domain factor for sparse-sampling circular-view photoacoustic tomography." IEEE Journal of Selected Topics in Quantum Electronics 29, no. 4: Biophotonics (2022): 1-9. doi: https://doi.org/10.1109/JSTQE.2022.3229622. Copyright 2022 Institute of Electrical and Electronics Engineers. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Posted with permission

Mathematics and Algorithms in Tomography

This is the eighth Oberwolfach conference on the mathematics of tomography. Modalities represented at the workshop included X-ray tomography, sonar, radar, seismic imaging, ultrasound, electron microscopy, impedance imaging, photoacoustic tomography, elastography, vector tomography, and texture analysis