We have a toolbox to quantify tissue optical properties that is composed of specialized fiberoptic probes for UV-visible diffuse reflectance spectroscopy and a fast, scalable inverse Monte Carlo (MC) model. In this paper, we assess the robustness of the toolbox for quantifying physiologically relevant parameters from turbid tissue-like media. In particular, we consider the effects of using different instruments, fiberoptic probes, and instrument-specific settings for a wide range of optical properties. Additionally, we test the quantitative accuracy of the inverse MC model for extracting the biologically relevant parameters of hemoglobin saturation and total hemoglobin concentration. We also test the effect of double-absorber phantoms (hemoglobin and crocin to model the absorption of hemoglobin and beta carotene, respectively, in the breast) for a range of absorption and scattering properties. We include an assessment on which reference phantom serves as the best calibration standard to enable accurate extraction of the absorption and scattering properties of the target sample. We found the best reference-target phantom combinations to be ones with similar scattering levels. The results from these phantom studies provide a set of guidelines for extracting optical parameters from clinical studies.

Abstract.A hybrid optical device that uses a multimode fiber coupled to a tunable light source for illumination and a 2.4-mm photodiode for detection in contact with the tissue surface is developed as a first step toward our goal of developing a cost-effective, miniature spectral imaging device to map tissue optical properties in vivo. This device coupled with an inverse Monte Carlo model of reflectance is demonstrated to accurately quantify tissue absorption and scattering in tissue-like turbid synthetic phantoms with a wide range of optical properties. The overall errors for quantifying the absorption and scattering coefficients are 6.0± 5.6 and 6.1± 4.7%, respectively. Compared with fiber-based detection, having the detector right at the tissue surface can significantly improve light collection efficiency, thus reducing the requirement for sophisticated detectors with high sensitivity, and this design can be easily expanded into a quantitative spectral imaging system for mapping tissue optical properties in vivo. © UV-visible diffuse reflectance spectroscopy ͑UV-VIS DRS͒ is sensitive to the absorption and scattering properties of biological molecules in tissue and thus can be used as a tool for quantitative tissue physiology in vivo. One major absorber of light in mucosal tissue in the visible range is hemoglobin ͑Hb͒, which shows distinctive, wavelength-dependent absorbance characteristics depending on its concentration and oxygenation. Tissue scattering is sensitive to the size and density of cellular structures such as nuclei and mitochondria. Thus, DRS of tissues can quantify changes in oxygenation, blood volume and alterations in cellular density and morphology. Some potential clinical applications of UV-VIS DRS include monitoring of tissue oxygenation, 1 precancer and cancer detection, 2,3 intraoperative tumor margin assessment, 4 and assessing tumor response to cancer therapy. 1Our group has developed a fiber optic DRS system 5 and a fast inverse Monte Carlo ͑MC͒ model of reflectance 6 to nondestructively and rapidly quantify tissue absorption and scattering properties. The system consists of a 450-W xenon lamp, a monochromator, a fiber optic probe, an imaging spectrograph, and a CCD camera. Previously published studies by our group 7 show that this technology is capable of quantifying breast tissue physiological and morphological properties, and that these quantities can be used to discern between malignant and non-malignant tissues with sensitivities and specificities exceeding 80%. Although this technology coupled with the MC model is a robust toolbox for quantifying tissue optical properties, this system suffers from several drawbacks similar to other spectrometers. First, optical fibers when used for detection, collect a relatively small portion of the remitted signal, thus high-quantum-efficiency, low-noise detectors are required to detect the signal, particularly in the UV-blue spectral region. Optical-fiber-based detection, while reasonable for single-point sampling, is unwieldy and expensive...

A diffuse reflectance spectroscopy system was modified as a step towards miniaturization and spectral imaging of tissue absorption and scattering. The modified system uses a tunable source and an optical fiber for illumination and a photodiode in contact with tissue for detection. Compared to the previous system, it is smaller, less costly, and has comparable performance in extracting optical properties in tissue phantoms. Wavelength reduction simulations show the feasibility of replacing the source with LEDs to further decrease system size and cost. Simulated crosstalk analysis indicates that this evolving system can be multiplexed for spectral imaging in the future.

Abstract. We describe the potential of 5-aminolevulinic acid ͑ALA͒-induced protoporphyrin IX ͑PpIX͒ fluorescence as a source of contrast for margin detection in commonly diagnosed breast cancer subtypes. Fluorescence intensity of PpIX in untreated and ALA-treated normal mammary epithelial and breast cancer cell lines of varying estrogen receptor expression were quantitatively imaged with confocal microscopy. Percentage change in fluorescence intensity integrated over 610-700 nm ͑attributed to PpIX͒ of posttreated compared to pretreated cells showed statistically significant differences between four breast cancer and two normal mammary epithelial cell lines. However, a direct comparison of post-treatment PpIX fluorescence intensities showed no differences between breast cancer and normal mammary epithelial cell lines due to confounding effects by endogenous fluorescence from flavin adenine dinucleotide ͑FAD͒. Clinically, it is impractical to obtain pre-and post-treatment images. Thus, spectral imaging was demonstrated as a means to remove the effects of endogenous FAD fluorescence allowing for discrimination between posttreatment PpIX fluorescence of four breast cancer and two normal mammary epithelial cell lines. Fluorescence spectral imaging of ALAtreated breast cancer cells showed preferential PpIX accumulation regardless of malignant phenotype and suggests a useful contrast mechanism for discrimination of residual cancer at the surface of breast tumor margins.

Neutron stimulated emission computed tomography (NSECT) is presented as a new technique for in vivo tomographic spectroscopic imaging. A full implementation of NSECT is intended to provide an elemental spectrum of the body or part of the body being interrogated at each voxel of a three-dimensional computed tomographic image. An external neutron beam illuminates the sample and some of these neutrons scatter inelastically, producing characteristic gamma emission from the scattering nuclei. These characteristic gamma rays are acquired by a gamma spectrometer and the emitting nucleus is identified by the emitted gamma energy. The neutron beam is scanned over the body in a geometry that allows for tomographic reconstruction. Tomographic images of each element in the spectrum can be reconstructed to represent the spatial distribution of elements within the sample. Here we offer proof of concept for the NSECT method, present the first single projection spectra acquired from multi-element phantoms, and discuss potential biomedical applications.