Abstract
Tissue hypoxia is associated with tumor and inflammatory diseases, and detection of hypoxia is potentially useful for their detailed diagnosis. An endoscope system that can optically observe hemoglobin oxygen saturation (StO2) would enable minimally invasive, real-time detection of lesion hypoxia in vivo. Currently, point measurement of tissue StO2 via endoscopy is possible using the commercial fiber-optic oximeter T-Stat, which is based on visible light spectroscopy at many wavelengths. For clinical use, however, imaging of StO2 is desirable to assess the distribution of tissue oxygenation around a lesion. Here, we describe our StO2 imaging technique based on a small number of wavelength ranges in the visible range. By assuming a homogeneous tissue, we demonstrated that tissue StO2 can be obtained independently from the scattering property and blood concentration of tissue using four spectral bands. We developed a prototype endoscope system and used it to observe tissue-simulating phantoms. The StO2 (%) values obtained using our technique agreed with those from the T-Stat within 10%. We also showed that tissue StO2 can be derived using three spectral band if the scattering property is fixed at preliminarily measured values.
Highlights
An imbalance in oxygen supply and demand causes hypoxia in solid tumor tissues, and tumor cells in chronic hypoxia show resistance to radiotherapy and chemotherapy, which leads to a poor prognosis for cancer patients.[1,2,3,4]
Since the hemoglobin oxygen saturation (StO2) varies with the dissolved oxygen concentration in a tissue, and the absorption spectrum of the hemoglobin varies with its StO2, hemoglobin has often been used for optical measurements of tissue oxygen level
spatial frequency domain imaging (SFDI) needs spatially modulated illumination in principle, and it is impractical to apply the technique to common forward-viewing endoscopes
Summary
An imbalance in oxygen supply and demand causes hypoxia in solid tumor tissues, and tumor cells in chronic hypoxia show resistance to radiotherapy and chemotherapy, which leads to a poor prognosis for cancer patients.[1,2,3,4] The treatment-resistant property of the tumor cells is a result of their adaptive response to the hypoxic environment by regulating oxygen-dependent gene expression. The performance of T-Stat has been validated by tissue-simulating phantom and animal experiments, and by some human studies.[7,8,9] Measurement of tissue oxygenation may provide useful information for endoscopic diagnosis, and Several studies have used the hyperspectral imaging method for in vivo optical imaging of StO2 distribution, using multiple images corresponding to different light wavelengths.[13,14] very few studies have reported on StO2 imaging using a small number of wavelengths. As an application for a fundus camera, Nakamura et al.[15] presented an StO2 imaging technique for human retinal vessels using only two wavelengths: 545 and 560 nm. SFDI needs spatially modulated illumination in principle, and it is impractical to apply the technique to common forward-viewing endoscopes
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