Visualization of photoacoustic images in a limited-View measuring system using eigenvalues of a photoacoustic transmission matrix

Abstract

Photoacoustic imaging is a unique imaging method that involves extracting information from points at different depths, an advantage of ultrasound imaging, while maintaining functional information, a key feature of conventional photo imaging. This makes it easy to add functional images to ultrasound images by adding a laser pulse source to the conventional ultrasound imaging device and detecting a photo-ultrasound signal via a conventional ultrasound probe. One challenge when using normal one-dimensional (1D) probes and generating photoacoustic images is the limited-view problem, in which artefacts are observed due to the positions of the ultrasound transducers. In this study, we used a photoacoustic transmission matrix (PA-TM) for simulation and performed a verification test using a 1D probe and a phantom. The results confirmed that the eigenvalues of the PA-TM visualized the light absorber itself in the limited-view measurement system, which eliminates reconstruction artefacts and further scattering artefacts, and that visualization is possible by signal intensity amplification through further phase modulation.

Breaking Acoustic Limit of Optical Focusing Using Photoacoustic‐Guided Wavefront Shaping

“…Meanwhile, WFS based on the photoacoustic (PA) effect [ 55,56 ] offers an alternative approach for controlling the scattered light distribution. The PA‐based guide star approach has raised a lot of interest [ 53,54,57–66 ] since its first application in WFS by Kong et al. [ 67 ] Unlike ultrasound tagging based on the acousto–optical effect, which delivers ultrasound and receives signals of frequency‐modulated light, PA‐guided strategies send in light and detect ultrasound.…”

Wavefront Shaping and Its Application to Enhance Photoacoustic Imaging

“…However, recently, researchers began to notice that the seemingly random scattering events and the resultant speckles are actually deterministic within a certain temporal window [37,38], and it is possible to reverse [39][40][41] or compensate for [42] the scattering-induced phase scrambling. To do so, researchers have developed several wavefront shaping (sometimes also referred to wavefront engineering) techniques, such as iterative wavefront optimization [23][24][25][26]28,[42][43][44][45][46][47][48][49][50][51], measuring the transmission matrix of the scattering medium [21,22,[52][53][54][55][56], and optical time reversal via phase conjugation [39,40,[57][58][59][60][61][62][63][64][65]. Nevertheless, the goals of these implementations are identical, i.e., to make light wavelets traveling along different optical paths interfere coherently at a region of interest (ROI) and form a bright optical spot (focus) out of the much darker background.…”

“…For that purpose, researchers have proposed injected or embedded probes, such as small optical sensors [66,67], fluorescence particles [68,69], and nonlinear beads [57], ultrasound mediation [40,58,61,70,71], as well as absorption perturbation [22,25,46,48,[72][73][74][75][76]. Among them, PA signal has been proved very attractive [22,25,28,47,48,53,55,73,74,76], as it is noninvasive, relatively deeply-penetrating, and it can pinpoint the focal spot accurately (the acoustic and optical foci overlap). Furthermore, with linear [22,25,28,53,73,74] or nonlinear [48] PA signals as the guide star, acousticand optical-diffraction limited optical focal spot can be achieved, respectively, benefiting from the nature of PA signal generation.…”