Accurate extraction of optical properties and top layer thickness of two-layered mucosal tissue phantoms from spatially resolved reflectance spectra

Abstract

We are reporting on an experimental investigation of a movable diffuse reflectance spectroscopy system to extract diagnostically relevant optical properties of two-layered tissue phantoms simulating mucosae that are covered with stratified squamous epithelium. The reflectance spectra were measured at multiple sourcedetector separations using two imaging fiber bundles in contact with the phantoms, one with its optical axis perpendicular to the sample surface (perpendicular probe) and the other with its distal end beveled and optical axis tilted at 45 deg (oblique probe). Polystyrene microspheres and purified human hemoglobin were used to make tissue phantoms whose scattering and absorption properties could be well controlled and theoretically predicted. Monte Carlo simulations were used to predict the reflectance spectra for system calibration and an iterative curve fitting that simultaneously extracted the top layer reduced scattering coefficient, thickness, bottom layer reduced scattering coefficient, and hemoglobin concentration of the phantoms. The errors of the recovered parameters ranged from 7% to 20%. The oblique probe showed higher accuracy in the extracted top layer reduced scattering coefficient and thickness than the perpendicular probe. The developed system and data analysis methods provide a feasible tool to quantify the optical properties in vivo.

Investigation of optical properties of dissected and homogenized biological tissue

“…36 Shredding the tissue causes most of its internal structures to be destroyed or more evenly distributed, 10 thus creating a macroscopic volume with rather uniform optical properties. Although studies concerning the comparison of different measurement techniques are available and a lot of investigations into tissue mimicking phantoms (layered and homogenous) are performed, [37][38][39][40] the influence of the structure of tissue sample on the optical properties has not been investigated systematically on biological samples so far. Thus, the objective of this investigation is the comparison of the optical properties measured on dissected, sliced tissue samples and their corresponding homogenized versions using the IS technique and a dual-step reflectance method (DSR).…”

Precancerous esophageal epithelia are associated with significantly increased scattering coefficients

“…Knowing approximately the difference in scattering coefficients between normal and precancerous epithelia is very helpful in developing non-invasive diagnostic tools focused on quantifying the scattering coefficients of the epithelium in vivo. For example, for developing diffuse reflectance spectroscopy techniques, an error similar to 20% in the estimated epithelial scattering coefficient [22] would be sufficient to distinguish precancerous tissue from normal tissue. The observed high interpatient variability suggests a strategy of quantifying the epithelial scattering coefficients of normal regions on the same patient and identifying suspect lesions based on the relative change in scattering coefficients rather than using a fixed cut-off scattering coefficient for distinguishing precancerous tissue in all patients.…”

“…Another group of techniques rely on detecting multiply scattered light which is also known as diffuse reflectance to estimate an average scattering coefficient of the tissue based on the radiative transport equation or Monte Carlo simulations for photon migration [19][20][21]. There have been recent efforts to estimate the scattering coefficient of the relatively thin epithelial layer in addition to the conventional estimation of the scattering and absorption coefficients of the semi-infinitely thick stromal layer [22][23][24][25]. Although promising, the methods have not achieved accurate extraction of the scattering coefficient of the epithelium in vivo.…”

Development of a movable diffuse reflectance spectroscopy system for clinical study of esophageal precancer

“…To improve the discrimination of precancerous tissue from normal tissue, we have developed a Monte-Carlo two-layer forward model to predict reflectance with the parallel computing power of graphics processing units (GPU). Accurate extraction of optical properties of two-layer mucosal tissue phantoms has been achieved with an iterative curve fitting method [2]. We constructed a movable imaging spectrograph-based system, validated the system with two-layer phantoms, and demonstrated the quantification of two-layer tissue properties of buccal mucosa in vivo.…”