Algorithm for automated selection of application-specific fiber-optic reflectance probes

Abstract

Abstract. Several optical techniques and fiber-optic probe systems have been designed to measure the optical properties of tissue. While a wide range of options is often beneficial, it poses a problem to investigators selecting which method to use for their biomedical application of interest. We present a methodology to optimally select a probe that matches the application requirements. Our method is based both on matching a probe's mean sampling depth with the optimal diagnostic depth of the clinical application and on choosing a probe whose interrogation depth and path length is the least sensitive to alterations in the target medium's optical properties. Satisfying these requirements ensures that the selected probe consistently assesses the relevant tissue volume with minimum variability. To aid in probe selection, we have developed a publicly available graphical user interface that takes the desired sampling depth and optical properties of the medium as its inputs and automatically ranks different techniques in their ability to robustly target the desired depth. Techniques investigated include single fiber spectroscopy, differential path length spectroscopy, polarization-gating, elastic light scattering spectroscopy, and diffuse reflectance. The software has been applied to biological case studies.

Review of diverse optical fibers used in biomedical research and clinical practice

“…The shape of the tip determines how the light emerging from the fiber is distributed on a tissue sample and also determines the light collection efficiency for viewing the irradiated tissue sample or examining scattered or fluorescing light emitted from the sample. [84][85][86][87][88][89][90][91][92][93][94][95][96] When deciding on the geometry of an optical fiber tip, parameters that need to be evaluated include the sizes of the illumination and light-collection areas, the collection angle (related to the fiber NA), and the fiber diameter. Another important factor to keep in mind is that biological tissue has a multilayered characteristic from both compositional and functional viewpoints.…”

Effect of probe geometry and optical properties on the sampling depth for diffuse reflectance spectroscopy

“…12 Because of this, the depth sampling of a DRS probe can be tuned by adjusting the probe geometry, allowing for the design of application specific probes. 13 Many studies have investigated the sampling depth in scattering media both experimentally and numerically. [12][13][14][15][16] Most of these studies rely on the diffusion approximation, which is not valid for short SDSs and highly absorbing media.…”

“…13 Many studies have investigated the sampling depth in scattering media both experimentally and numerically. [12][13][14][15][16] Most of these studies rely on the diffusion approximation, which is not valid for short SDSs and highly absorbing media. Others investigated the sampling depth only for reflectance probes with specific geometries, such as single-fiber reflectance, 16 overlapping illumination and collection areas, 17,18 large SDSs (SDS > 1∕μ 0 s ), 19 and diffuse reflectance spectroscopy probes only at specific SDSs and fiber diameters.…”

“…Others investigated the sampling depth only for reflectance probes with specific geometries, such as single-fiber reflectance, 16 overlapping illumination and collection areas, 17,18 large SDSs (SDS > 1∕μ 0 s ), 19 and diffuse reflectance spectroscopy probes only at specific SDSs and fiber diameters. 13,20 Backman and Gomes recently developed an empirical model to describe sampling depth for a DRS probe. This model is based on a previous study on the sampling depth of single-fiber spectroscopy probes and is only valid for DRS probes with fiber diameters of 200 μm and an SDS of 250 μm.…”

“…This model is based on a previous study on the sampling depth of single-fiber spectroscopy probes and is only valid for DRS probes with fiber diameters of 200 μm and an SDS of 250 μm. 13 A model that can accurately determine sampling depth for any given SDSs and tissue optical properties will allow the development of application specific probes where light sampling from a specific depth is necessary. Additionally, knowledge of the sampling depth can be used to determine wavelength-dependent differences in the sampling depth due to the difference in optical properties across wavelengths.…”