Effect of probe pressure on skin tissue optical properties measurement using multi-diameter single fiber reflectance spectroscopy

Abstract

Multi-Diameter Single Fiber Reflectance spectroscopy (MDSFR) allows rapid and noninvasive extraction of tissue optical properties that requires the fiberoptic to be placed in contact with the tissue. To ensure a good optical contact, the application of probe pressure is inevitable and usually not well controlled. In this study, we investigated the effect of probe pressure by performing in vivo MDSFR measurements (400–1600 nm) on human inner forearm skin with controlled probe indentation and continuous pressure monitoring. For the probe pressures up to 28.4 s mm−2 (213 mmHg), the reduced scattering coefficient pivoted around 800 nm (increasing scattering slope) while the phase function related parameter decreased (up to 20%, depending on the wavelength). A significant decrease of hemoglobin concentration (∼81%), oxygen saturation (∼86%), apparent vessel diameter (∼100%) as well as the displacement of extracellular water (∼24%) was observed with increasing probe pressure. A correlation was observed between the changes in water volume fraction and phase function related parameter gamma . We theorize that the latter changes in phase function may be due to the induced deformation of the tissue structure and the displacement of extracellular water. The extensive analysis of the pressure induced changes in the measured MDSFR spectra and the related changes in optical properties demonstrate that the effects of probe pressure must be minimized to avoid bias in the results.