Abstract
Review of the existing studies on the contact pressure-induced changes in the optical properties of biological tissues showed that the reported changes in transmittance, reflectance, absorption, and scattering coefficient are vastly inconsistent. In order to gain more insight into the contact pressure-induced changes observed in biomedical applications involving common probe-spectrometer diffuse reflectance measurement setups and provide a set of practical guidelines minimizing the influence of the changes on the analysis of acquired spectra, we conducted a series of in vivo measurements, where the contact pressure was precisely controlled, and the spectral and contact pressure information were acquired simultaneously. Classification of three measurement sites on a human hand, representing the natural variability in the perfusion and structure of the underlying tissue, was assessed by training and evaluating classifiers at different contact pressure levels and for different probe operators. Based on the results, three practical guidelines have been proposed to avoid classification performance degradation. First, the most suitable pressure level should be identified. Second, the pressure level should be kept in a narrow range during the acquisition of spectra. Third, applications utilizing probes equipped with a calibrated spring can use several classifiers trained at different contact pressure levels to improve classification performance.
Highlights
IntroductionDiffuse reflectance spectroscopy (DRS) is a rapid noninvasive technique that is gaining increasing importance in numerous biomedical applications, such as cancer diagnosis and treatment,[1,2,3] burn depth assessment,[4] monitoring tissue oxygenation,[5,6] classification of healthy and pathological dental tissues,[7] monitoring blood glucose,[8,9] and other blood metabolites or drugs.[10,11,12] In general, DRS spectra can be acquired in two ways, namely by point spectroscopy or by hyperspectral imaging.[13,14] Many practical applications utilize a spectrometer and a fiber-optic probe
Based on the obtained results, we proposed several practical guidelines minimizing the influence of contact pressure–induced effects on the classification performance of existing Diffuse reflectance spectroscopy (DRS) fiber optic probe–based systems
It is evident that the classification performance is on average independent of the applied contact pressure; it depends on the measurement site
Summary
Diffuse reflectance spectroscopy (DRS) is a rapid noninvasive technique that is gaining increasing importance in numerous biomedical applications, such as cancer diagnosis and treatment,[1,2,3] burn depth assessment,[4] monitoring tissue oxygenation,[5,6] classification of healthy and pathological dental tissues,[7] monitoring blood glucose,[8,9] and other blood metabolites or drugs.[10,11,12] In general, DRS spectra can be acquired in two ways, namely by point spectroscopy or by hyperspectral imaging.[13,14] Many practical applications utilize a spectrometer and a fiber-optic probe. The acquired DRS spectra are formed by the reflected or transmitted, partially absorbed and scattered light. A fiber-optic probe pressed against the studied tissue is usually used to acquire diffuse reflectance spectra. Even a light contact pressure can significantly affect the tissue optical properties and the light coupling into the fiber-optic probe. There are several studies on the contact pressure-induced spectral changes in the visible and near-infrared DRS,[15,16,17,18,19,20,21,22,23,24,25] as well as similar studies involving other spectroscopic and imaging
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