Abstract
Significance: Quantitative optoacoustic (OA) imaging has the potential to provide blood oxygen saturation () estimates due to the proportionality between the measured signal and the blood’s absorption coefficient. However, due to the wavelength-dependent attenuation of light in tissue, a spectral correction of the OA signals is required, and a prime challenge is the validation of both the optical characterization of the tissue and the .Aim: We propose to assess the reliability of levels retrieved from spectral fitting by measuring the similarity of OA spectra to the fitted blood absorption spectra.Approach: We introduce a metric that quantifies the trends of blood spectra by assigning a pair of spectral slopes to each spectrum. The applicability of the metric is illustrated with in vivo measurements on a human forearm.Results: We show that physiologically sound values do not necessarily imply a successful spectral correction and demonstrate how the metric can be used to distinguish values that are trustworthy from unreliable ones.Conclusions: The metric is independent of the methods used for the OA data acquisition, image reconstruction, and spectral correction, thus it can be readily combined with existing approaches, in order to monitor the accuracy of quantitative OA imaging.
Highlights
The metric is independent of the methods used for the OA data acquisition, image reconstruction, and spectral correction, it can be readily combined with existing approaches, in order to monitor the accuracy of quantitative OA imaging
Quantitative optoacoustic (OA) imaging is an emerging technique that allows the determination of blood oxygen saturation (SO2) by exploiting the distinct absorption spectra of oxy- and deoxyhemoglobin[9,10] while providing a higher spatial resolution in deep tissue than diffuse optical tomography.[11,12]
The estimation of SO2 levels can be achieved by performing spectral fits of blood absorption spectra to measured OA spectra, after correcting them for spectral distortions induced by the wavelengthdependent attenuation of light in tissue.[9,13,14]
Summary
Estimating oxygen levels in blood is of paramount importance in various preclinical and clinical applications, e.g., for the study of tumor characteristics,[1,2] personalized cancer treatment,[3,4,5,6] or the detection and monitoring of cerebral ischemia in newborns.[7,8] Quantitative optoacoustic (OA) imaging is an emerging technique that allows the determination of blood oxygen saturation (SO2) by exploiting the distinct absorption spectra of oxy- and deoxyhemoglobin[9,10] while providing a higher spatial resolution in deep tissue than diffuse optical tomography.[11,12] The estimation of SO2 levels can be achieved by performing spectral fits of blood absorption spectra to measured OA spectra, after correcting them for spectral distortions induced by the wavelengthdependent attenuation of light in tissue.[9,13,14] One major aspect that has recently gained increasing attention is assessing the reliability of the quantitative results.[15,16] In this paper, we focus on estimating the uncertainty of the SO2 levels retrieved from spectral fitting, independently of the methods used for OA data acquisition, image reconstruction, or for the correction of spectral distortions. We dwell on the fact that fitted SO2 values that are physiologically
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