Speed-of-sound compensated photoacoustic tomography for accurate imaging

TL;DR

This paper introduces new methods for accurately reconstructing photoacoustic images by accounting for spatial variations in the speed-of-sound within biological tissues, significantly reducing artifacts.

Contribution

The authors develop and validate novel iterative reconstruction algorithms that incorporate SOS inhomogeneities and refraction effects for improved photoacoustic tomography accuracy.

Findings

Refractive modeling reduces image artifacts.

SOS inhomogeneity correction enhances image clarity.

Experimental validation confirms improved reconstruction quality.

Abstract

In most photoacoustic (PA) measurements, variations in speed-of-sound (SOS) of the subject are neglected under the assumption of acoustic homogeneity. Biological tissue with spatially heterogeneous SOS cannot be accurately reconstructed under this assumption. We present experimental and image reconstruction methods with which 2-D SOS distributions can be accurately acquired and reconstructed, and with which the SOS map can be used subsequently to reconstruct highly accurate PA tomograms. We begin with a 2-D iterative reconstruction approach in an ultrasound transmission tomography (UTT) setting, which uses ray refracted paths instead of straight ray paths to recover accurate SOS images of the subject. Subsequently, we use the SOS distribution in a new 2-D iterative approach, where refraction of rays originating from PA sources are accounted for in accurately retrieving the distribution of these sources. Both the SOS reconstruction and SOS-compensated PA reconstruction methods utilize the Eikonal equation to model acoustic wavefront propagation, which is solved using a high accuracy fast marching method (HAFMM). We validate the new reconstruction algorithms using numerical phantoms. For experiments we use the PER-PACT method which can be used to simultaneously acquire SOS and PA data from subjects. We test the reconstruction algorithms using experimental data acquired with the PER-PACT setup from challenging physical phantoms. The results show that it is important to take SOS inhomogeneities into account. The iterative reconstruction algorithms, that model acoustic refractive effects, yield artifact-free highly accurate images. Our approach of using the hybrid measurement method and the new reconstruction algorithms, is successful in substantially improving the quality of PA images with a minimization of blurring and artefacts.