Effect of thermal damage on the in vitro optical and fluorescence characteristics of liver tissues

Thermal energy generated by radio-frequency current or other means may be employed in treating liver tumors by means of thermal coagulation when conventional resection is impossible. Currently, these thermal energy-based therapeutic procedures suffer from the lack of an adequate feedback control system, making it difficult to determine the optimal therapeutic endpoint. In this study, the potential of optical spectroscopy to provide such an objective endpoint for these procedures is presented. Freshly harvested canine liver samples were exposed to 50/spl deg/C, 60/spl deg/C, and 70/spl deg/C water baths for times ranging from 0 to 60 min. Transmission and reflectance were measured from each sample using an integrating sphere and the optical properties of each sample were accordingly derived. Excitation-emission matrices were recorded from the samples using a spectrofluorometer to identify the intrinsic fluorescence characteristics of native and thermally coagulated liver tissues. In addition, fluorescence and diffuse reflectance spectra were separately obtained from the samples prepared using a portable spectroscopic system. Results of this study show that fluorescence and optical properties of liver tissues exhibit clear and consistent changes through the thermal coagulation process. Specifically, the primary peak in the fluorescence spectra from liver tissues shifts from 480 nm in the native state to 510 nm in the fully coagulated state. In addition, a three- to fourfold increase in the absolute intensity of the diffuse reflectance spectra is observed upon complete coagulation of liver tissues. These dynamic spectral features indicate that fluorescence and diffuse reflectance spectroscopy may provide a direct measure of the biochemical and structural changes associated with tissue thermal damage in the liver.     

In Vivo Detection of Gold Nanoshells in Tumors Using Diffuse Optical Spectroscopy

This study demonstrates the use of diffuse optical spectroscopy (DOS) for the noninvasive measurement of gold nanoshell concentrations in tumors of live mice. We measured the diffuse optical spectra (500-800 nm) using an optical fiber probe placed in contact with the tissue surface. We performed in vitro studies on tissue phantoms illustrating an accurate measurement of gold-silica nanoshell concentration within 12.6% of the known concentration. In vivo studies were performed on a mouse xenograft tumor model. DOS spectra were measured at preinjection, immediately postinjection, 1 and 24 h postinjection times, and the nanoshell concentrations were verified using neutron activation analysis.     

In vivo intermolecular zero-quantum coherence MR spectroscopy in the rat spinal cord at 17.6 T: a feasibility study

Objective: The feasibility of in vivo magnetic resonance spectroscopy of the healthy rat spinal cord at 17.6 T using conventional methods and intermolecular zero-quantum coherence (iZQC) spectroscopy is explored and the performance of both approaches is compared. Methods: Localised spectra were acquired at 17.6 T from three healthy Fisher rats and phantoms with injected iron-oxide particles using the PRESS and a modified HOMOGENIZED sequence. Results: Well-resolved in vivo spectra showing the four singlet resonances of creatine, choline, and N-acetyl aspartate were obtained with both approaches. iZQC spectra were acquired from larger voxels, but did not provide higher sensitivity or resolution in the healthy spinal cord. In the presence of paramagnetic iron-oxide particles, the quality of in vitro spectra acquired with PRESS declined and was strongly dependent on the quality of the local shim. iZQC spectra were not affected by the presence of iron-oxide particles and provided narrow lines (9 Hz) independent of the shim. Conclusion: In vivo iZQC spectroscopy of the rat spinal cord is possible. The robustness in presence of local field distortions makes iZQC methods a promising alternative for the investigation of tissue containing labelled cells, implants, or clotted blood. New application of MRS to tissue inaccessible using conventional methods may thus become possible.     

Stokes shift emission spectroscopy of human tissue and key biomolecules

The Stokes-shifted emission spectra were measured for various photoactive biomolecules in aqueous solution and tissue such as tryptophan, collagen, nicotinamide adenine dinucleotide, and flavin. Information is obtained on the molecular activity in the tissue. This new approach allows for the extraction of some new information not obtained from excitation and/or fluorescence spectroscopy for a single spectral scan.     

In situ monitoring and control for MBE growth of optoelectronicdevices

Improved control over layer thickness has been realized using optical interference techniques such as reflectance spectroscopy. It is now common to observe spectra of distributed-Bragg-reflector (DBR) mirrors during growth to make corrections for growth rate drifts. Real-time optical flux monitoring (OFM) by atomic absorption allows precise layer control by measuring group III fluxes continuously during growth. The flux information can be used to operate growth shutters and to control effusion cell heaters in a feedback loop. Improved substrate temperature measurement by diffuse reflectance spectroscopy (DRS) allows precise measurement of substrate temperature. DRS is not subject to the same errors encountered in pyrometer or thermocouple measurements of substrate temperature     

Light propagation in tissue during fluorescence spectroscopy withsingle-fiber probes

Fluorescence spectroscopy systems designed for clinical use commonly employ fiberoptic probes to deliver excitation light to a tissue site and collect remitted fluorescence. Although a wide variety of probes have been implemented, there is little known about the influence of probe design on light propagation and the origin of detected signals. In this study, we examined the effect of optical fiber diameter, probe-tissue spacing and numerical aperture on light propagation during fluorescence spectroscopy with a single-fiber probe. A Monte Carlo model was used to simulate light transport in tissue. Two distinct sets of excitation-emission wavelength pairs were studied (337/450 nm and 400/630 nm). Simulation results indicated that increasing fiber diameter or fiber-tissue spacing increased the mean excitation-emission photon pair pathlength and produced a transition from high selectivity for superficial fluorophores to a more homogeneous probing with depth. Increasing numerical aperture caused an increase in signal intensity, but axial emission profiles and pathlengths were not significantly affected for numerical aperture values less than 0.8. Tissue optics mechanisms and implications for probe design are discussed. This study indicates that single-fiber probe parameters can strongly affect fluorescence detection and should be considered in the design of optical diagnostic devices     

Effects of compression on soft tissue optical properties

Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this paper, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400-1800 mm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of a Hispanic donor and two Caucasian donors were obtained from the tissue bank. Bovine aorta and sclera, and porcine sclera came from a local slaughter house. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1, 1, and 2 kgf/cm². Under compression, tissue thicknesses were reduced up to 78%. Generally speaking, the reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in absorption and scattering coefficients among most of the compressed specimens     

Inverse method 3-D reconstruction of localized in vivofluorescence-application to Sjogren syndrome

The development of specific fluorescently labeled cell surface markers have opened the possibility of specific and quantitative noninvasive diagnosis of tissue changes. We are developing a fluorescence scanning imaging system that can perform a “noninvasive optical biopsy” of the Sjogren syndrome (SS) which may replace the currently used histological biopsy. The diagnosis of SS is based on the quantification of the number of topical preadministered fluorescent antibodies which specifically bind to the lymphocytes infiltrating the minor salivary glands. We intend to scan the lower lip, and for each position of the scan, generate a two-dimensional (2-D) image of fluorescence using a charge-coupled device (CCD) camera. We have shown previously that our diffuse fluorescent photon migration theory predicts adequately the positions and strengths of one and two fluorescent targets embedded at different depths in tissue-like phantoms. An inverse reconstruction algorithm based on our theoretical findings has been written in C⁺⁺ and uses 2-D images to predict the strength and location of embedded fluorophores. However, due to large numbers of variables, which include the optical properties of the tissue at the excitation and emission wavelengths, and the positions and strengths of an unknown number of fluorophore targets, the validity of the final result depends on assumptions (such as the number of targets) and the input values for the optical parameters. Our results show that the number of fluorophore targets reconstructed for each scan is limited to two, and at least the scattering coefficient at the excitation wavelength is needed a priori to obtain good results. The latter can be obtained by measurements of spatially resolved diffuse reflectance at the excitation wavelength that provides the product of the absorption and scattering coefficients     

On-off laser delivery into a precise tissue area using smart tissue-activated fiber probes

A novel and simple concept for on-off switching laser radiation delivery into a precise tissue area using tissue-activated optical fiber probes is demonstrated. The authors present the operating principle and general optical features of the fiber-optic-based delivery technique. The basic idea includes the use of a single delivery fiber with a specially shaped angled tip. Because of the frustrated-total-internal reflectance caused by the refractive-index change of the surrounding medium, the angled fiber tip acts as a smart tissue-activated probe. It provides a safe way for laser delivery that includes only two states of tissue illumination: 1) off-state (no tissue illumination), when the fiber tip is out of the tissue area and the laser emission is backreflected due to total-internal-reflection and 2) on-state (maximum tissue illumination), when the fiber tip is on the absorbing tissue area and becomes "transparent" because of the frustrated-total-internal reflectance. Here, optical properties of tissue-activated fiber probes used for precise laser delivery are investigated both experimentally and theoretically by analyzing the backreflectance signal power. Optical fibers working in the visible and mid-infrared spectral regions with various geometrical parameters are used and a spatial resolution of 2 /spl mu/m is achieved when the fiber tip is moved toward the absorption tissue surface.     

A hyperspectral imaging system for in vivo optical diagnostics

This paper details the basic principles and instrumental systems as well as applications of hyperspectral imaging system in the biomedical field. The development of an HSI system that combines recent advances in several photonic technologies, including an AOTF, a 2-D CCD detector, and imaging fiber optics. The integration of these technologies leads to a versatile and powerful imaging system that can rapidly record spectral images of samples. This imaging system could find useful applications in medical diagnostics applications where rapid in vivo detection of complex samples is required. The HSI technique has the potential for in site optical diagnosis on tissue and it can be use for guidance of surgical intervention and treatment. The optical diagnostic approaches may either be an imaging modality or a spectroscopic modality. The spectroscopic diagnostics may also provide real-time assessment of tissue response to therapy.     

Noninvasive blood glucose assay using a newly developed near-infrared system

This paper reports in vivo near-infrared (NIR) noninvasive blood glucose assay using dermis tissue spectra. We assume that the glucose content in dermis tissue traces the variations in blood glucose. For dermis spectra measurements, epidermis, especially stratum corneum, acts as an interference in skin tissue. Thus, we have developed a method for the selective measurement of dermis tissue spectra, enabling us to obtain better quality spectra for an accurate blood glucose assay. The selective measurement of the dermis spectra realized by using a newly developed fiber-optic probe that consists of source and detector optical fibers separated by 0.65 mm on a skin surface. The light path in the skin tissue for this geometry has been simulated by a Monte Carlo method. The simulation results show that detected light mainly interrogates dermis tissue. As the absorbance signal of glucose in human tissue is extremely small, the quality of the measured spectra is critical for the reliable assay. The present method for blood glucose assay has been applied to one Type 1 diabetic. The correlation coefficient between the blood glucose content predicted by NIR spectra and those measured by finger-prick was 0.928 and the standard error of prediction was 32.2 mg/dL. These results demonstrate the potential of our methodology for noninvasive NIR blood glucose assay.     

d/0条件光谱漫反射比的测定方法探讨

应用积分球理论，通过积分推导的方法，对积分球法光谱漫反射比的测量进行了理论论证，并对积分球开口误差进行了修正，提出了新的d/0条件光谱漫反射比测量装置的结构。     

The effect of light losses in double integrating spheres on opticalproperties estimation

The double integrating sphere setup (DIS) measures diffuse reflectance, diffuse transmittance and collimated transmittance, from which the optical properties of tissue (the absorption coefficient μ _a, the scattering coefficient μ_s and the anisotropy of scattering g) are estimated. The effect of light losses in the DIS and optical thickness on optical properties estimation by the inverse adding doubling algorithm (IAD) and uniqueness of measurement have been investigated using a Monte Carlo method. Results were obtained for optical properties in turbid tissues (0.80⩽albedo⩽0.99, 0.80⩽anisotropy⩽ 0.99, 1.5⩽optical thickness⩽7.5) sandwiched between glass slides. At optical thickness=6.0 the loss of light through the glass slides is ranging from 13%±0.5% (at albedo=0.80) to 15%±0.5% (at albedo=0.98) of the incident power. The loss of light at the exit port in the transmittance sphere is increasing up to 50% of the incident power at highly forward scattering. These losses result in a dependency on optical thickness of the optical properties estimation by the IAD algorithm. Furthermore, because of these losses, the DIS setup measurement is found to be fundamentally nonunique, when simultaneously measuring the diffuse reflectance, diffuse transmittance and collimated transmittance     

Determination of epithelial tissue scattering coefficient using confocal microscopy

Most models of light propagation through tissue assume the scattering properties of the various tissue layers are the same. The authors present evidence that the scattering coefficient of normal cervical epithelium is significantly lower than values previously reported for bulk epithelial tissue. They estimated the scattering coefficient of normal and precancerous cervical epithelium using measurements of the reflectance as a function of depth from confocal images. Reflectance measurements were taken from ex vivo cervical biopsies and fit to an exponential function based upon Beer's law attenuation. The mean scattering coefficients derived were 22 cm/sup -1/ for normal tissue and 69 cm/sup -1/ for precancerous tissue. These values are significantly lower than previously reported for bulk epithelial tissues and suggest that scattering of bulk tissue is dominated by the stroma. They also suggest that computational models to describe light propagation in epithelial tissue must incorporate different scattering coefficients for the epithelium and stroma. Further, the lower scattering of the epithelium suggests greater probing depths for fiber optic probes used by optical diagnostic devices which measure reflectance and fluorescence in epithelial tissue. The difference in scattering between normal and precancerous tissue is attributed to increased nuclear size, optical density, and chromatin texture. The scattering coefficients measured here are consistent with predictions of numerical solutions to Maxwell's equations for epithelial cell scattering.     

Amplified spontaneous emission spectroscopy in strainedquantum-well lasers

Amplified spontaneous emission spectroscopy is used to extract the gain and refractive index spectra systematically. We obtain the gain and differential gain spectra using the Hakki-Paoli method. The refractive index profile, the induced change in refractive index by an incremental current, and the linewidth enhancement factor are measured from the Fabry-Perot peaks and the current-induced peak shifts in the amplified spontaneous emission spectra. The measured optical gain and refractive index are then compared with our theoretical model for strained quantum-well lasers. We show that a complete theoretical model for calculating the electronic band structure, the optical constant, and the linewidth enhancement factor agrees very well with the experiment. Our approach demonstrates that amplified spontaneous emission spectroscopy can be a good diagnostic tool to characterize laser diodes, extract the optical gain and index profiles, and confirm material parameters such as the strained quantum-well band structure parameters for a semiconductor structure under carrier injection     

An overview of activities at the Laser Biomedical Research Center

Research projects on laser heating and ablation and on spectroscopy of biological tissues are described. The discussion focuses on studies regarding microscopic laser light scattering of biological cells and structures, ablation of calcific tissue using pulsed HF laser radiation, and fluorescence and its use in diagnosing atherosclerosis. A specifically designed multifiber laser catheter constructed to collect tissue fluorescence spectra using fiber optics is described.     

Investigation of optical clearing of gastric tissue immersed with hyperosmotic agents

In order to understand the role of water desorption and the mass transport process in the optical clearing effect on gastric tissues with the application of hyperosmotic agents, the porcine stomach tissues (pyloric mucosa) applied topically with glycerol and dimethyl sulfoxide (DMSO) are investigated with optical coherence tomography (OCT) and the near infrared reflectance spectroscopy. Three solutions of 80% and 50% glycerol, and 50% DMSO are studied, each of which shows significant improvement in light transmittance and, thus, reduction of the light scattering of tissue. It is found that, among the solutions investigated, 80% glycerol achieves the best clearing effect on improvement of both the light penetration and imaging contrast. More detailed microstructures of the mucosal layer can be observed for glycerol treatment, while these structures are not resolvable by the conventional OCT. Light transmittance is increased by approximately 23% and diffuse reflectance decreased by approximately 24% at 30 min after the topical application of 80% glycerol. 50% DMSO is more effective than 50% glycerol only at the beginning stage; thereafter the rate of optical clearing is slowed down with time. Although DMSO can enhance the light transmittance and thus reduce the scattering, it has a negligible effect on the imaging contrast improvement. The mass transport process of agent to tissue accounts for the different clearing effects for glycerol and DMSO, respectively. It is concluded that the optical clearing by the hyperosmotic agent is strongly correlated with the water desorption kinetics induced by agent and the agent mass transport process within tissue. In other words, the tissue dehydration induced by agent and the refractive index matching between the agent and the main scattering components within tissue facilitated by the agent mass transport are responsible for optical clearing effects.     

Coulomb enhancement in InGaAs-GaAs quantum-well lasers

It is shown that Coulomb enhancement (CE) has a significant influence on the spectral characteristics of optical gain and spontaneous emission in strained InGaAs quantum wells. CE-modified gain spectra are utilized to make an accurate prediction of the dependence of lasing wavelength on cavity length, Threshold-current predictions using the CE-modified gain-current relation show improved agreement with experiment     

Fitting interrelated datasets: metabolite diffusion and general lineshapes

Objective

Simultaneous modeling of true 2-D spectroscopy data, or more generally, interrelated spectral datasets has been described previously and is useful for quantitative magnetic resonance spectroscopy applications. In this study, a combined method of reference-lineshape enhanced model fitting and two-dimensional prior-knowledge fitting for the case of diffusion weighted MR spectroscopy is presented.

Materials and methods

Time-dependent field distortions determined from a water reference are applied to the spectral bases used in linear-combination modeling of interrelated spectra. This was implemented together with a simultaneous spectral and diffusion model fitting in the previously described Fitting Tool for Arrays of Interrelated Datasets (FiTAID), where prior knowledge conditions and restraints can be enforced in two dimensions.

Results

The benefit in terms of increased accuracy and precision of parameters is illustrated with examples from Monte Carlo simulations, in vitro and in vivo human brain scans for one- and two-dimensional datasets from 2-D separation, inversion recovery and diffusion-weighted spectroscopy (DWS). For DWS, it was found that acquisitions could be substantially shortened.

Conclusion

It is shown that inclusion of a measured lineshape into modeling of interrelated MR spectra is beneficial and can be combined also with simultaneous spectral and diffusion modeling.

     

Highly luminescent CdSe nanoparticles embedded in silica thin films

Thin films of luminescent CdSe nanoparticles with and without silica capping were prepared using sol-gel method. The blue shift observed in the optical absorption spectra suggested quantum confinement effect in the prepared films. The films showed photoluminescence emission in the range of 510–590 nm depending upon the particle size of CdSe particles. The emission intensity increased when CdSe particles were embedded in silica matrix. The emission intensity was found to decrease with aging for the films containing CdSe particles without silica capping when they were exposed in relatively humid air (relative humidity 80%). The films containing CdSe nanoparticles embedded in silica matrix showed more stable behavior. The emission intensity practically remained constant with aging in humid atmosphere.