Guillermo Marquez

Anisotropy in the absorption and scattering spectra of chicken breast tissue.

Oblique incidence reflectometry is a simple and accurate method for measuring the absorption and the reduced-scattering coefficients of turbid media. We used this technique to deduce absorption and reduced-scattering spectra from wavelength-resolved measurements of the relative diffuse reflectance profile of white light as a function of source-detector distance. In this study, we measured the absorption and the reduced-scattering coefficients of chicken breast tissue in the visible range (400-800 nm) with the oblique incidence probe oriented at 0 degrees and 90 degrees relative to the muscle fibers. We found that the deduced optical properties varied with the probe orientation. Measurements on homogenized chicken breast tissue yielded an absorption spectrum comparable with the average of the absorption spectra for 0 degrees and 90 degrees probe orientations measured on the unhomogenized tissue. The reduced-scattering spectrum for homogeneous tissue was greater than that acquired for unhomogenized tissue taken at either probe orientation. This experiment demonstrated the application of oblique-incidence, fiber-optic reflectometry to measurements on biological tissues and the effect of tissue structural anisotropy on optical properties.

White light oblique incidence reflectometer for measuring absorption and reduced scattering spectra of tissue-like turbid media

We designed a quick and inexpensive system for spectral measurements of optical properties including absorption coefficient and reduced scattering coefficient. The system was based on oblique incidence reflectometry.[1] A broad band light source was coupled into an optic fiber to deliver light obliquely to turbid media. Nine detection optic fibers were used to collect the diffuse reflectance as a function of source-detector distance. The relative diffuse reflectance profile was used to deduce the absorption and reduced scattering spectra. The system was able to acquire data in a wavelength range of 256 nm within a fraction of a second.

Development of tissue-simulating optical phantoms: poly-N-isopropylacrylamide solution entrapped inside a hydrogel.

The average turbid optical properties of the N-isopropylacrylamide (NIPA) polymer solution entrapped inside a polyacrylamide hydrogel (called an NIPA/PAAM gel system) were studied using a multiwavelength oblique-incidence reflectometer. The turbidity of such a system can be drastically changed by simply switching the temperature from below the low critical solution temperature of the NIPA, around 33 degrees C, to above. The absorption coefficient and the reduced scattering coefficient were obtained as a function of wavelength for samples with selected NIPA and blue dextran concentrations. It is found that the scattering of the optical phantom comes from the NIPA polymer chains and the absorption from the blue dextran. The turbid optical properties of an NIPA/PAAM gel system can be tuned to simulate biological tissues at a specific wavelength by varying compositions of NIPA and blue dextran and further modified by controlling the temperature.

Skin lesion classification using oblique-incidence diffuse reflectance spectroscopic imaging

We discuss the use of a noninvasive in vivo optical technique, diffuse reflectance spectroscopic imaging with oblique incidence, to distinguish between benign and cancer-prone skin lesions. Various image features were examined to classify the images from lesions into benign and cancerous categories. Two groups of lesions were processed separately: Group 1 includes keratoses, warts versus carcinomas; and group 2 includes common nevi versus dysplastic nevi. A region search algorithm was developed to extract both one- and two-dimensional spectral information. A bootstrap-based Bayes classifier was used for classification. A computer-assisted tool was then devised to act as an electronic second opinion to the dermatologist. Our approach generated only one false-positive misclassification out of 23 cases collected for group 1 and two misclassifications out of 34 cases collected for group 2 under the worst estimation condition.

Particle sizing in concentrated suspensions by use of steady-state, continuous-wave photon-migration techniques

We demonstrate a new approach for determining particle-size distribution in concentrated suspensions from spectral measurement of isotropic scattering coefficients by use of steady-state, continuous-wave photon-migration techniques. Successful recovery of particle-size distribution for TiO(2) suspensions in the form of log-normal functions is achieved through a regularized inverse algorithm, into which a synthesized scheme of Marquardt and Tikhonov regularizations has been incorporated. Our results for dense TiO(2) suspensions with three different particle concentrations are in excellent agreement with the size distribution as measured with x-ray sedimentation.

Characterization of skin lesion texture in diffuse reflectance spectroscopic images

This paper examines various texture features extracted from skin lesion images obtained by using diffuse reflectance spectroscopic imaging. Different image texture features have been applied to such images to separate precancerous from benign cases. These features are extracted based on the co-occurrence matrix, wavelet decomposition , fractal signature, and granulometric approaches. The results so far indicate that fractal and wavelet-based features are effective in distinguishing precancerous from benign cases.

Measurement of absorption and scattering spectra of chicken breast with oblique incidence reflectometry

Oblique incidence relfectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients of turbid media. We used this technique to deduce absorption and reduced scattering spectra from wavelength resolved measurements of the relative diffuse reflectance profile of white light. In this study we measured the absorption and reduced scattering coefficients of chicken breast in the visible with the oblique incidence probe oriented at 0, 30, 60, and 90 degrees relative to the muscle fibers. We found that the reconstructed optical properties varied with probe orientation. This experiment demonstrates (1) the application of oblique-incidence fiber- optic reflectometry to measurements on biological tissue and (2) the effect of structural anisotropy on optical properties.

Anisotropic absorption and reduced scattering spectra of chicken breast tissue measured using oblique incidence reflectometry

Oblique incidence reflectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients of turbid media. We used this technique to deduce absorption and reduced scattering spectra form wavelength-resolved measurements of the relative diffuse reflectance profile of white light as a function of source- detector distance. In this study we measured the absorption and reduced scattering coefficients of chicken breast tissue in the visible range with the oblique incidence probe oriented at 0 to 90 degrees relative to the muscle fibers. We found that the deduced optical properties varied with the probe orientation. This experiment demonstrated the application of oblique-incidence, fiber-optic reflectometry to measurements on biological tissues and the effect of tissue structural anisotropy on optical properties.

Skin cancer detection using spectroscopic oblique-incidence reflectometry

This paper presents a technique for classifying skin abnormalities using oblique-incidence diffuse reflectance spectroscopy. The objective is to provide a non-invasive computer-assisted tool to dermatologists for lowering the number of unnecessary biopsies. A high accuracy of detection (95%) has been obtained.

Measurement of tissue optical properties and modeling of optimal light delivery for tumor treatment

Oblique-incidence reflectometry was used to measure the optical properties of rat tumors with injected absorption- enhancement dye. The measured optical properties were used to model light delivery into the tissues for optimal therapeutic effects. The goal was to efficiently deliver the maximum amount of optical power into buried tumors being treated while avoiding potential damage to normal tissue caused by strong optical power deposition underneath the tissue surface illuminated by the laser beam. The distribution of power deposition was simulated for single beam delivery and multiple beam delivery as well. The simulated results showed that with an appropriate dye enhancement and an optimal laser delivery configuration, a high selectivity for laser treatment of tumors could be achieved.