Pressure-induced near infrared spectra response as a valuable source of information for soft tissue classification

Abstract

Abstract. Acquiring near infrared spectra in vivo usually requires a fiber-optic probe to be pressed against the tissue. The applied pressure can significantly affect the optical properties of the underlying tissue, and thereby the acquired spectra. The existing studies consider these effects to be distortions. In contrast, we hypothesize that the pressureinduced spectral response is site-and tissue-specific, providing additional information for the tissue classification. For the purpose of this study, a custom system was designed for dynamic pressure control and rapid acquisition of spectra. The pressure-induced spectral response was studied at three proximate skin sites of the human hand. The diffuse reflectance and scattering were found to decrease with the applied contact pressure. In contrast, the concentrations of chromophores, and consequently the absorption, increased with the applied contact pressure. The pressure-induced changes in the tissue optical properties were found to be site-specific and were modeled as a polynomial function of the applied contact pressure. A quadratic discriminant analysis classification of the tissue spectra acquired at the three proximate skin sites, based on the proposed pressure-induced spectral response model, resulted in a high (90%) average classification sensitivity and specificity, clearly supporting the working hypothesis.

Impact of contact pressure–induced spectral changes on soft-tissue classification in diffuse reflectance spectroscopy: problems and solutions

“…16,21 The full contact pressure range was employed only by one study. 25 The effects of the applied contact pressure on the tissue optical properties in terms of transmittance, reflectance, absorption, and scattering coefficients were found to be governed by the local concentrations of water, hemoglobin, and lipids. 25 The observed increase in the tissue transmittance with the applied pressure 15,24 was explained by the reduction in the specimen thickness.…”

“…The resulting changes can substantially degrade the performance of the subsequent quantitative or qualitative spectral analysis. 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 techniques. [26][27][28][29] Initial studies were focused on ex vivo measurements and utilized a so-called spring-loaded compression apparatus [ Fig.…”

“…1(b)], which measured additional force on the sample. 24,30 Several studies focused on in vivo measurements of human and animal skin at different sites, 18,21,23,25,29 including abdomen, 28 breast, 16,19,22 and mouse muscle. 20 Some simple measurement setups [ Fig.…”

“…2(c)]. 18,19,25 Two studies on the pressure-induced changes in breast tissue's optical properties employed experimental setups enhanced by additional force sensors. 16,22 However, the location of the force sensors did not correspond with the position of the probe, rendering the measured contact pressure inaccurate.…”

Comparison of a near-infrared reflectance spectroscopy system and skin conductance measurements for in vivo estimation of skin hydration: a clinical study

“…Compared to the experimental setup we used in our previous study [7], in this setup the fiber probe end touched the surface of skin during the measurement. It is known that the compression of skin changes its optical properties [14][15][16][17][18]. As we were not able to include a pressure sensor in our experimental setup to determine the applied pressure for each measurement, the operator doing the measurements trained to apply approximately the same pressure for each measurement by just lightly touching the skin surface.…”