In Vivo Three-Dimensional Raster Scan Optoacoustic Mesoscopy Using Frequency Domain Inversion.

Qutaiba Mustafa,Christian Zakian,Vasilis Ntziachristos,Ludwig Prade,Antonios Stylogiannis,Murad Omar,Pouyan Mohajerani

doi:10.1109/tmi.2021.3084356

Abstract

Optoacoustic signals are typically reconstructed into images using inversion algorithms applied in the time-domain. However, time-domain reconstructions can be computationally intensive and therefore slow when large amounts of raw data are collected from an optoacoustic scan. Here we considered a fast weighted ω-k (FWOK) algorithm operating in the frequency domain to accelerate the inversion in raster-scan optoacoustic mesoscopy (RSOM), while seamlessly incorporating impulse response correction with minimum computational burden. We investigated the FWOK performance with RSOM measurements from phantoms and mice in vivo and obtained 360-fold speed improvement over inversions based on the back-projection algorithm in the time-domain. This previously unexplored inversion of in vivo optoacoustic data with impulse response correction in frequency domain reconstructions points to a promising strategy of accelerating optoacoustic imaging computations, toward video-rate tomography.

Highlights

U NDERSTANDING organismal growth and development, as well as analyzing physiology and disease in intact tissues requires imaging tools that can penetrate deeper than optical microscopy
We focused on the inversion problem in raster-scan optoacoustic mesoscopy (RSOM) and aimed for a novel implementation of the ω − k algorithm, namely fast weighted ω − k (FWOK), with improved image quality by integrating the transfer function of the detector, while capitalizing on the computational speed of the Fourier domain
To enable a comparative visualization of the relative mean separation and standard deviation of each pixel value distribution, we first normalized the corresponding reconstructed image to the maximum pixel value within the three regions combined, and normalized the histogram obtained for each region to its maximum count, thereby adjusting for the different areas enclosed by each region

Summary

Introduction

U NDERSTANDING organismal growth and development, as well as analyzing physiology and disease in intact tissues requires imaging tools that can penetrate deeper than optical microscopy. While optical microscopy is limited to depths of a few hundred micrometers due to photon scatter in tissue [1], optoacoustic imaging can go beyond the depth limit set by diffusion. Optoacoustics achieve improved depth when generating images based on acoustic wave propagation (acoustic diffraction), i.e. wave propagation that experiences 102- to 103-fold less scattering in tissues compared to light. Raster scan optoacoustic mesoscopy (RSOM), for example, provides up to sub-10 micron resolution of tissues within several millimetres depth [2], [3]. It has been used to image model organisms [4], angiogenesis in tumor development [5], [6], and skin vasculature in healthy individuals and those with skin conditions [7]

Methods

Results

Conclusion