Subdiffuse scattering model for single fiber reflectance spectroscopy.

Anouk L Post,Henricus J C M Sterenborg,Dirk J Faber,Ton G Van Leeuwen,Fransien G Woltjer

doi:10.1117/1.jbo.25.1.015001

Abstract

.To detect small-scale changes in tissue with optical techniques, small sampling volumes are required. Single fiber reflectance (SFR) spectroscopy has a sampling depth of a few hundred micrometers. SFR spectroscopy uses a single fiber to emit and collect light. The only available model to determine optical properties with SFR spectroscopy was derived for tissues with modified Henyey–Greenstein phase functions. Previously, we demonstrated that this model is inadequate for other tissue phase functions. We develop a model to relate SFR measurements to scattering properties for a range of phase functions, in the absence of absorption. Since the source and detector overlap, the reflectance cannot be accurately described by diffusion theory alone: SFR measurements are subdiffuse. Therefore, we describe the reflectance as a combination of a diffuse and a semiballistic component. We use the model of Farrell et al. for the diffuse component, solved for an overlapping source and detector fiber. For the semiballistic component, we derive a new parameter, , which incorporates the integrals of the phase function over 1 deg in the backward direction and 23 deg in the forward direction. Our model predicts the reflectance with a median error of 2.1%, compared to 9.0% for the currently available model.

Highlights

Reflectance spectroscopy techniques are used to relate tissue optical properties to various types of diseases
Single fiber reflectance (SFR) measurements, a model that is valid for the wide range of phase functions that can be encountered in tissue is essential
Based on Monte Carlo (MC) simulations with modified Henyey–Greenstein (MHG), two-term Henyey–Greenstein (TTHG), and RMC phase functions, we show that our model predicts the reflectance more accurately, compared to the currently used model from Kanick et al.[7] for a range of phase functions, μs0d values and numerical aperture (NA)

Summary

Introduction

Reflectance spectroscopy techniques are used to relate tissue optical properties to various types of diseases. Depending on the clinical question, an important consideration in choosing a spectroscopic technique is its sampling volume. Since optical properties are averaged over this volume, techniques with small sampling volumes are required to detect local, small-scale changes in tissue. Single fiber reflectance (SFR) spectroscopy is a technique with a sampling depth in the order of a few hundred micrometers and has been used in a number of studies in the field of oncology.[1,2,3,4,5,6] SFR spectroscopy uses a single fiber, in contact with tissue, to emit and collect light, connected to a broadband light source and a spectrograph to detect the steady-state reflectance versus wavelength. Tissue optical properties can be derived and related to the disease state of tissue

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Conclusion