Abstract
Recent focused Monte Carlo and experimental studies on steady-state single-fiber reflectance spectroscopy (SfRS) from a biologically relevant scattering medium have revealed that, as the dimensionless reduced scattering of the medium increases, the SfRS intensity increases monotonically until reaching a plateau. The SfRS signal is semi-empirically decomposed to the product of three contributing factors, including a ratio-of-remission (RoR) term that refers to the ratio of photons remitting from the medium and crossing the fiber-medium interface over the total number of photons launched into the medium. The RoR is expressed with respect to the dimensionless reduced scattering parameter , where is the reduced scattering coefficient of the medium and is the diameter of the probing fiber. We develop in this work, under the assumption of an isotropic-scattering medium, a method of analytical treatment that will indicate the pattern of RoR as a function of the dimensionless reduced scattering of the medium. The RoR is derived in four cases, corresponding to in-medium (applied to interstitial probing of biological tissue) or surface-based (applied to contact-probing of biological tissue) SfRS measurements using straight-polished or angle-polished fiber. The analytically arrived surface-probing RoR corresponding to single-fiber probing using a 15° angle-polished fiber over the range of agrees with previously reported similarly configured experimental measurement from a scattering medium that has a Henyey–Greenstein scattering phase function with an anisotropy factor of 0.8. In cases of a medium scattering light anisotropically, we propose how the treatment may be furthered to account for the scattering anisotropy using the result of a study of light scattering close to the point-of-entry by Vitkin et al. (Nat. Commun. 2011, doi:10.1038/ncomms1599).
Highlights
Reflectance spectroscopy [1,2] is simple to setup, and the machinery is relatively low cost.Reflectance spectroscopy instrumented by using single-fiber probe, which is generally referred to as single-fiber reflectance spectroscopy (SfRS) [3,4,5,6], delivers light to a turbid medium and detects the light returning to the collection aperture of the same fiber after the photons have experienced some scattering/attenuation events in the medium
Some earlier studies have examined the fiber-optical aspect of the SfRS signal, necessitating removing the internal specular reflections from the collected signal [18] and accounting for the collection efficiency of a single fiber [19] as being limited by the numerical aperture
This work has presented an isotropic-scattering-based analytical treatment to the ratio-of-remission (RoR) factor that quantifies the ratio of photons remitting from the medium and crossing the fiber face over the total number of photons launched into the medium in steady-state SfRS
Summary
Reflectance spectroscopy [1,2] is simple to setup, and the machinery is relatively low cost.Reflectance spectroscopy instrumented by using single-fiber probe, which is generally referred to as single-fiber reflectance spectroscopy (SfRS) [3,4,5,6], delivers light to a turbid medium and detects the light returning to the collection aperture of the same fiber after the photons have experienced some scattering/attenuation events in the medium. To quantitate the measurement by SfRS as the endpoint is to estimate tissue optical properties based on the measurements, it is imperative to have a working model of the dependence of SfRS signal intensity (which is spectrally resolved) upon tissue optical properties ( spectrally resolved). A series of studies, based on extensive Monte Carlo (MC) simulations and experimental validations, have quantitated the effect of optical properties on SfRS measurement [20,21,22,23,24,25,26] Among these studies, Kanick et al investigated the dependence of the effective photon path length, as well as sampling depth [20,21] on the optical properties of the sampled medium. Kanick et al and Gamm et al further studied the relationship between SfRS signal intensity and the scattering properties of the medium [22,23]
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