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.
Polarization-gated spectroscopy is an established method to depth-selectively interrogate the structural properties of biological tissue. We employ this method in vivo in the azoxymethane (AOM)-treated rat model to monitor the morphological changes that occur in the field of a tumor during early carcinogenesis. The results demonstrate a statistically significant change in the shape of the refractive-index correlation function for AOM-treated rats versus saline-treated controls. Since refractive index is linearly proportional to mass density, these refractive-index changes can be directly linked to alterations in the spatial distribution patterns of macromolecular density. Furthermore, we found that alterations in the shape of the refractive-index correlation function shape were an indicator of both present and future risk of tumor development. These results suggest that noninvasive measurement of the shape of the refractive-index correlation function could be a promising marker of early cancer development.
A modified polarized Monte Carlo code is developed that allows heterogeneous structure to be modeled.
The code is validated with existent polarized Monte Carlo code. Heterogeneous structure simulating colon tissue is
simulated to understand the difference between simulations of homogeneous vs heterogeneous tissue structure.
Reflectance measurements from simulations containing increased blood vessel size and increased blood volume fraction, both markers for potential cancerous tissue, are studied in order to better interpret reflectance measurement from diagnostic probes.
Noninvasive and real-time analysis of tissue properties, in particular, the quantitative assessment of blood content and
light scattering properties of mucosa is useful in a wide variety of applications. However, the nature of interactions
between contact fiber-optic probes and the tissue surface presents a challenging problem with respect to the variability of
in vivo measurements, for example affects due to variations in the pressure and angle of the probe tip on the tissue
surface. Previously, pressure and angle effects have been investigated for other modalities (i.e. diffuse reflectance and
Raman spectroscopy). We present an evaluation of this variability, as well as the length of time in contact with tissue for
polarization-gated spectroscopy. The evaluation is based on the quantification of mucosal blood content at superficial
depths (within 100 to 200 microns of tissue surface) for in vivo measurements of oral mucosa. Measurements are
presented for different pressures, angles and time scales and the variability due to these factors is assessed.
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