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Effect of wavelength selection on the accuracy of blood oxygen saturation estimates obtained from photoacoustic images

Hochuli, R; Beard, PC; Cox, B; (2015) Effect of wavelength selection on the accuracy of blood oxygen saturation estimates obtained from photoacoustic images. In: Oraevsky, AA and Wang, LV, (eds.) Photons Plus Ultrasound: Imaging and Sensing 2015. SPIE Green open access

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Abstract

In photoacoustic tomography (PAT) the image contrast is due to optical absorption, and because of this PAT images are sensitive to changes in blood oxygen saturation (sO2). However, this is not a linear relationship due to the presence of a non-uniform light fluence distribution. In this paper we systematically evaluate the conditions in which an approximate linear inversion scheme–which assumes the internal fluence distribution is unchanged when the absorption coefficient changes–can give accurate estimates of sO2. A numerical phantom of highly vascularised tissue is used to test this assumption. It is shown that using multiple wavelengths over a broad range of the near-infrared spectrum yields inaccurate estimates of oxygenation, while a careful selection of wavelengths in the 620-920nm range is likely to yield more accurate oxygenation values. We demonstrate that a 1D fluence correction obtained by fitting a linear function to the average decay rate in the image can further improve the estimates. However, opting to use these longer wavelengths involves sacrificing signal-to-noise ratio in the image, as the absorption of blood is low in this range. This results in an inherent trade-off between error in the sO2 estimates due to fluence variation and error due to noise. This study shows that the depth to which sO2 can be estimated accurately using a linear approximation is limited in vivo, even with idealised measurements, to at most 3mm. In practice, there will be even greater uncertainties affecting the estimates, e.g., due to bandlimited or partial-view acoustic detection.

Type: Proceedings paper
Title: Effect of wavelength selection on the accuracy of blood oxygen saturation estimates obtained from photoacoustic images
Event: Conference on Photons Plus Ultrasound - Imaging and Sensing
Location: San Francisco, CA
Dates: 08 February 2015 - 10 February 2015
Open access status: An open access version is available from UCL Discovery
DOI: 10.1117/12.2081429
Publisher version: https://doi.org/10.1117/12.2081429
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10113889
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