A need exists for the continued development of diagnostic tools and methods capable of distinguishing and characterizing slight differences in the optical properties of tissues. We present a method to estimate the scattering coefficient contribution as a function of particle size in complex mixtures of polystyrene spheres. The experimental method we used is a Mueller matrix imaging approach. The Mueller matrix encodes the polarization-dependent properties of the sample and describes how a given sample will transform an incident light polarization state. A partial least-squares approach is used to form a model around a set of Mueller matrix image-based measurements to accurately predict the individual scattering coefficient contributions in phantoms containing 0.2, 0.5, 1, and 2 µm-diameter polystyrene spheres. The results show individual scattering coefficient contribution errors as low as 0.1585 cm–1 can be achieved. In addition, it is shown how the scattering type (i.e., Rayleigh and Mie) is encoded within the Mueller matrix. Such methods may eventually lead to the development of improved diagnostic tools capable of characterizing and distinguishing between tissue abnormalities, such as superficial cancerous lesions from their benign counterparts.
Recently, polarization based optical approaches have received considerable interest due to their potential medical applications. Glucose, a chiral molecule, has the ability to rotate the plane of linearly polarized light, commonly referred to as optical activity, as well as affecting the refractive index of the media which is therefore affects the overall scattering coefficient in a given media. The magnitude of each effect is related to the concentration of glucose. Based on these effects, it would be expected that a change in glucose concentration would alter the diffuse reflectance polarization patterns from turbid media. In this study, we investigate how each of these effects is correlated to glucose concentration in a physiological range for highly scattering biological media. Furthermore, it is shown how diffusely polarized imaging when coupled with chemometrics techniques can be used to quantify glucose concentration.
The development of a rapid, inexpensive, and accurate in vivo phenotyping methodology for characterizing drug-metabolizing phenotypes with reference to the cytochrome P450 (CYP450) enzymes would be very beneficial. In terms of application, in the wake of the human genome project, considerable interest is focused on the development of new drugs whose uses will be tailored to specific genetic polymorphisms, and on the individualization of dosing regimens that are also tailored to meet individual patient needs depending upon genotype. In this investigation, chemical probes for CYP450 enzymes were characterized and identified with Raman spectroscopy. Furthermore, gold-based metal colloid clusters were utilized to generate surface enhanced Raman spectra for each of the chemical probes. Results will be presented demonstrating the ability of SERS to identify minute quantities of these probes on the order needed for in vivo application.
In this paper we present experimental results demonstrating processing techniques developed in our laboratory that can be utilized to decode or extract useful information from two-dimensional Mueller matrices of turbid media. Through the use of these methods, involving the partial least squares technique, it is shown how scattering coefficient contributions as a function of particle size can be estimated for a given sample. Furthermore, we demonstrate how a spatial selection algorithm known as "chain select" can be used to help facilitate the interpretation of the measured Mueller matrix images. The samples utilized in this investigation were comprised of polystyrene spheres with diameters ranging from 200 nm to 2000 nm and analyzed with 514 nm light. At this wavelength, both Rayleigh and Mie-types of scattering are observed.
In the recent past, optical polarimetry has been shown as a potential method for noninvasive physiologic glucose sensing in the eye. Although the necessary sensitivity and accuracy have been demonstrated experimentally through in vitro studies using a range of media from simplistic glucose doped-water to more complex media such as aqueous humor, the main problem currently hindering long-term in vivo measurements is corneal birefringence coupled with motion artifact. This is due to the inability to distinguish E-field rotation due to glucose from the effects of time varying corneal birefringence. In this investigation, the effect of corneal birefringence will be discussed and a potential method to overcome this problem will be presented with supporting results.
In this investigation, a polarization-based imaging system is developed and described that measures the two-dimensional effective backscattering Mueller matrix of a sample in near real-time. As is well known, a Mueller matrix can provide considerable information on the makeup and optical characteristics of a sample and also directly describes how the sample transforms an incident light beam. The ability to measure the two-dimensional Mueller matrix of a biological sample, therefore, can provide considerable information on the sample composition as well as the potential to reveal significant structural information that normally would not be visible through standard imaging techniques. Additional information can also be obtained through the application of image-processing, decomposition, and reconstruction techniques that operate directly on the 2D Mueller matrix. Using the developed system, it is shown how the induction of internal strain within the sample coupled with image reconstruction and decomposition techniques can further improve image contrast and aid in the detection of boundaries between tissues of different biomechanical and structural properties. The studies presented were performed with both rat tissue and a melanoma-based tissue culture. The results demonstrate how these techniques could provide information that may be of diagnostic value in the physical detection of malignant lesion boundaries.
Optical Coherence Tomography (OCT) is a relatively new type of imaging system for medical diagnosis. Because most current OCT systems use a sharply focused beam in tissues, they have a short depth of field (high image resolution is near the focus only). In this paper, limited diffraction beams of different orders are used to increase depth of field and to reduce sidelobes in OCT. Results show that the proposed OCT system has a lateral resolution of about 4.4 wavelengths (the central wavelength of the source is about 940 nm with a bandwidth of about 70 nm) and lower than -60 dB sidelobes over an entire depth of field of 4.5 mm with the diameter of the objective lens of 1 mm.
An optical fiber sensing system for biomedical and biochemical sensing was developed. The system was designed for multiparameter sensing to pH, SO2, NH3/NH4+. In the developed system, two light emitting diodes are used as light sources, a silicon photo-diode is used as light signal detector, a multimold stepped bifurcate optical fiber bundle with great aperture is used as light transmissive medium, the dyestuff is coupled to fiber by different methods. The new design idea is double beam compensation. The system is small, cheap but stable and sensitive, its response for pH is about 0.01 pH, the detective limits are 2 micrometers ol/L for NH+4 in water, 2 X 10-4 mol/L for SO32- in water, respectively. The system is powered with battery, so can be used for fieldwork.
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