Abstract
Photoacoustic computed tomography (PACT), also known as optoacoustic tomography, is an emerging imaging technique that holds great promise for biomedical imaging. PACT is a hybrid imaging method that can exploit the strong endogenous contrast of optical methods along with the high spatial resolution of ultrasound methods. In its canonical form that is addressed in this article, PACT seeks to estimate the photoacoustically-induced initial pressure distribution within the object. Image reconstruction methods are employed to solve the acoustic inverse problem associated with the image formation process. When an idealized imaging scenario is considered, analytic solutions to the PACT inverse problem are available; however, in practice, numerous challenges exist that are more readily addressed within an optimization-based, or iterative, image reconstruction framework. In this article, the PACT image reconstruction problem is reviewed within the context of modern optimization-based image reconstruction methodologies. Imaging models that relate the measured photoacoustic wavefields to the sought-after object function are described in their continuous and discrete forms. The basic principles of optimization-based image reconstruction from discrete PACT measurement data are presented, which includes a review of methods for modeling the PACT measurement system response and other important physical factors. Non-conventional formulations of the PACT image reconstruction problem, in which acoustic parameters of the medium are concurrently estimated along with the PACT image, are also introduced and reviewed.
Highlights
Introduction to PACTPhotoacoustic computed tomography (PACT), known as optoacoustic tomography, is a rapidly emerging imaging technique that holds great promise for biomedical imaging (Kruger et al, 1995; Kruger et al, 1999; Xu and Wang, 2002; Xu and Wang, 2003b; Oraevsky and Karabutov, 2003)
A sufficiently short (Diebold, 2009b) laser pulse is employed to irradiate an object at time t = 0 and the photoacoustic effect results in the generation of internal pressure distribution inside of the object, which is denoted as p0(r), r ∈ R3
The PACT image reconstruction problem of estimating the photoacoustically-induced initial pressure distribution has been reviewed within the context of modern optimization-based image reconstruction methodologies
Summary
Photoacoustic computed tomography (PACT), known as optoacoustic tomography, is a rapidly emerging imaging technique that holds great promise for biomedical imaging (Kruger et al, 1995; Kruger et al, 1999; Xu and Wang, 2002; Xu and Wang, 2003b; Oraevsky and Karabutov, 2003). The goal of PACT in its canonical formulation is to reconstruct an image that represents a map of the initial pressure distribution within the object from knowledge of the measured photoacoustically-induced acoustic signals. Optimization-based, or iterative, image reconstruction methods for PACT provide the opportunity to enhance image quality by compensating for physical factors, noise, and data-incompleteness. While such approaches are routinely employed in the broader image reconstruction community, relatively few research groups have explored such modern reconstruction methods for PACT. Imaging models that relate the measured photoacoustic wavefields to the sought-after object function are described in their continuous and discrete forms These models will describe physical nonidealities in the data such as those introduced by acoustic inhomogeneity, attenuation, and the response of the imaging system.
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