Quantitative photoacoustic estimates of intervascular blood oxygenation differences using linear unmixing

C Bench,B Cox

doi:10.1088/1742-6596/1761/1/012001

Abstract

The linear unmixing technique is an appealing method for estimating blood oxygen saturation (sO2) from multiwavelength photoacoustic tomography images, as estimates can be acquired with a straightforward matrix inversion. However, the technique can only rarely provide accurate estimates in vivo, as it requires that the light fluence at the voxels of interest is constant with wavelength. One way to extend the set of cases where accurate information related to sO2 can be acquired with the technique is by taking the difference in sO2 estimates between vessels. Assuming images are perfectly reconstructed, the intervascular difference in sO2 estimates is accurate if the error in the estimates due to the wavelength dependence of the fluence is identical for both. An in silico study was performed to uncover what kinds of conditions may give rise to accurate sO2 differences for a vessel pair. Basic criteria were formulated in simple tissue models consisting of a pair of vessels immersed in two-layer skin models. To assess whether these criteria might still be valid in more realistic imaging scenarios, the sO2 difference was estimated for vessels in more complex tissue models.

Highlights

Photoacoustic (PA) tomography is a hybrid modality that can produce images of tissue with the specificity of optical techniques and the high spatial resolution of ultrasound [1]
The linear unmixing technique is an appealing method for estimating blood oxygen saturation from multiwavelength photoacoustic tomography images, as estimates can be acquired with a straightforward matrix inversion
Basic criteria were formulated in simple tissue models consisting of a pair of vessels immersed in two-layer skin models

Summary

Introduction

Photoacoustic (PA) tomography is a hybrid modality that can produce images of tissue with the specificity of optical techniques and the high spatial resolution of ultrasound [1]. Xia et al [16] used the assumption that the fluence remains unchanged for two different oxygenation states to estimate blood sO2, but this is unlikely to be the case in vivo as the oxygenation of neighbouring capillaries change in tandem with the target vessel and the optical properties of the tissue, and the fluence will vary Another approach has been to use 1D analytical fluence models (e.g. Beer-Lambert Law) to estimate the wavelength-dependence of the fluence, either by fitting to the data or using values reported in the literature [17,18,19,20,21,22]. This involves finding situations in which the fluence is approximately independent of the wavelength

Spectroscopic Linear Unmixing

Findings

Conclusions