Practical photoacoustic tomography: Realistic limitations and technical solutions

Abstract

This article offers a perspective on photoacoustic tomography (PAT) under realistic scenarios. While PAT has gained much attention in preclinical and clinical research, most early works used image reconstruction techniques based on ideal assumptions, and thus these techniques may not be fully effective in real environments. In this work, we consider such non-ideal conditions as a limited view, limited bandwidth, lossy medium, or heterogeneous medium. More importantly, we use k-Wave simulation to numerically evaluate the effects of these limiting factors on various image reconstruction algorithms. Then, to enable more reliable PAT image reconstruction, we introduce recent techniques for mitigating each of the limiting conditions. We seek to emphasize the importance of working within these realistic limitations, and we encourage researchers to develop compensating solutions that advance PAT’s translation to real clinical environments.

Integrating photoacoustic tomography into a multimodal automated breast ultrasound scanner

“…44 Further, the inclusion of an elevational acoustic lens on the SonixEmbrace transducer limits the acceptance angle of the detection elements, leading to imaging artifacts and decreased sensitivity. 23 Capacitive micromachined ultrasound transducers (CMUTs) have proven very promising in terms of frequency response and angular sensitivity, 45,46 but they suffer from expensive and complex fabrication and are known to be delicate and therefore prone to degradation with use. Recent developments in fabrication techniques may alleviate or eliminate some of these issues, facilitating rapid prototyping of thin, flexible, transparent CMUT arrays.…”

“…While these optics offer flexibility in terms of the light delivery, this spatial non-uniformity of the fluence must be accounted for during data reconstruction. [21][22][23] Spatial fluence modeling is commonly used in photoacoustic simulations to provide an accurate ground truth for experimental validation, 20,22 and this is usually accomplished via a Monte Carlo simulation of the radiative transfer equation (RTE). It is also often necessary in quantitative photoacoustic tomography to fully model the fluence such that the optical parameters of the tissue can be recovered absolutely, for example, in the recent work of Hänninen et al 24 In motivating their work, the authors highlight that a significant shortcoming of the standard Monte Carlo method is the necessary computation time, which can be prohibitive for large tomographic problems such as ours.…”

Nonlinear mechanisms in photoacoustics—Powerful tools in photoacoustic imaging

“…As mentioned in the introduction, this review focuses on the above-mentioned six types of nonlinearity as the representative examples, but it is worth mentioning there exist other nonlinear effects in PA imaging, including nano-/microbubble generations [ 45 , 46 ], photochemical reactions [ 47 ], the photoacoustic resonance [ [48] , [49] , [50] , [51] ], unsatisfied stress and thermal confinement [ 52 ]. In addition, the nonlinear beamforming (BF) technique [ [53] , [54] , [55] , [56] , [57] , [58] , [59] ] is another one used in photoacoustic tomography (PAT), which will be briefly discussed here. In PAT, delay and sum (DAS) is the most common beamforming algorithm owing to its straightforward implementation, however, it suffers from strong noises and sidelobes [ 59 , 125 ].…”

A photoacoustic finder fully integrated with a solid-state dye laser and transparent ultrasound transducer

“…Advantageously, PA imaging can delineate SLNs in deep tissue with high resolution and high contrast. However, PA SLN imaging based on blue (methylene blue, MB) or green (indocyanine green, ICG) dyes requires expensive and bulky laser systems such as Q-switched Nd:Yag pumped optical parametric oscillators, Ti: Sapphire lasers, or liquid dye lasers [ [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] ]. Thus, these systems are not yet widespread in clinical settings.…”