Confocal microscopy [detecting and diagnosing cancers]

Optical technologies, such as reflectance and fluorescence microscopy, may help detect and diagnose cancers that originate in the epithelium. The epithelium is the layer of tissue that is exposed to the environment and lines the body's cavities. Cancers that originate in the epithelium include cervical, oral, colon, lung, stomach, bladder and skin cancers. The curable precursors to cervical cancer are cervical epithelial lesions that have larger and more densely spaced nuclei. A fiber-optic confocal microscope (FOCM) has been developed at the Optical Spectroscopy Lab, University of Texas at Austin, to help detect and diagnose these lesions in vivo. With the aid of acetic acid as a contrast agent, the FOCM shows nuclear size and density information throughout the epithelium, presenting the same information as histology but without removing, staining and slicing cervical epithelial tissue. (There are also spatial resolution requirements for showing cell nuclei.) The Optical Spectroscopy Lab continues to develop confocal microscopic instrumentation, new contrast agents, and image processing techniques to improve early detection of precancerous cervical lesions.     

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the objective lens) and multiple scattering substantially limit the accuracy of the measurement with the OCT technique. We studied the influence of the confocal function and multiple scattering on the accuracy of the measurement and proposed methods that provide measurement of the total attenuation coefficient with a significantly reduced systematic error. Experiments were performed in tissue phantoms and porcine and human skin in vitro and in vivo. Our data indicate that the tissue total attenuation coefficient can noninvasively be measured in vivo with the accuracy of 5%-10% in the range from 0.5 to 17 mm/sup -1/ and about 20% in the range up to 40 mm/sup -1/. These results suggest that the proper correction of the OCT-based measurement for the confocal function and multiple scattering provides absolute values of tissue total attenuation coefficient with high accuracy and resolution that may not be achievable by other optical techniques in vivo.     

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     

Sized-fiber reflectometry for measuring local optical properties

Sized-fiber spectroscopy describes a device and method for measuring absorption and reduced scattering properties of tissue using optical fibers with different diameters. The device used in this paper consists of two fibers with diameters of 200 and 600 μm. Each fiber emits and collects its own backscattered light. Backscattered light measurements for solutions with absorption coefficients of 0.1-2.0 cm ^-1 and reduced scattering coefficients of 5-50 cm^-1 demonstrate that the device is most sensitive for the highest scattering materials. Monte Carlo simulations suggest the device is insensitive to the fiber illumination characteristics and that the light returning to the fiber is nearly uniform over all directions. Finally, experiments and Monte Carlo simulations of the sized-fiber device indicate that 50% of the signal arises from roughly 1.2 and 1.9 reduced mean-free paths for the 200- and 600-μm fibers, respectively     

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     

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     

High-speed InSb photodetectors on GaAs for mid-IR applications

We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06/spl times/10/sup -6/ cm/sup 2/ to 2.25/spl times/10/sup -4/ cm/sup 2/ measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 /spl Omega/ cm/sup 2/. At 77 K, spectral measurements yielded high responsivity between 3 and 5 /spl mu/m with the cutoff wavelength of 5.33 /spl mu/m. The maximum responsivity for 80-/spl mu/m diameter detectors was 1.00/spl times/10/sup 5/ V/W at 4.35 /spl mu/m while the detectivity was 3.41/spl times/10/sup 9/ cm Hz/sup 1/2//W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 /spl mu/m with the pump at 780 nm. 30-/spl mu/m diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.     

Near-infrared (NIR) tomography breast image reconstruction with a priori structural information from MRI: algorithm development for reconstructing heterogeneities

A combined magnetic resonance and near-infrared (MRI-NIR) imaging modality can potentially yield high resolution maps of optical properties from noninvasive simultaneous measurement. The main disadvantage of near-infrared (NIR) tomography lies in the low spatial resolution resulting from the highly scattering nature of tissue for these wavelengths. MRI has achieved high resolution, but suffers from low specificity. In this study, NIR image reconstruction algorithms that incorporate a priori structural information provided by MRI are investigated in an attempt to optimize recovery of a simulated optical property distribution. The effect of high levels of tissue heterogeneity are evaluated to determine the limitations of incorporating prior information into a realistic set of patient breast images. We assume absorption coefficient (/spl mu//sub a/) variations near /spl plusmn/40%, and transport scattering coefficient (/spl mu//sub s//sup //) variations near /spl plusmn/20%, in a coronal breast MRI geometry. Changes in tissue pathology due to tumor growth can be observed with NIR tompgraphy, and so the goal here is to determine how best to quantify these tumor-based contrast regions within the presence of high tissue heterogeneity. By applying knowledge of tissue's layered structure in reconstruction through various constraints in the iterative algorithm, quantitative recovery of the tumor optical properties improves from 69% to 74%, and localization improves as well. However, only when the true heterogeneity of the tissue distribution was included was accurate quantification of the tumor region possible. Using a good initial guess of /spl mu//sub a/ and /spl mu//sub s//sup //, derived from the regional structure of the model, quantification of the region reaches 99% of the true value, and spatial resolution retains a similar value to the original MRI image.     

Determination of piezoelectric and pyroelectric coefficients and thermal diffusivity of 1-3 PZT/epoxy composites

PZT/epoxy composites with 1-3 connectivity were prepared using the dice-and-fill technique. The samples were poled with an electric field of 10 MV/m for 30 minutes at room temperature. The piezoelectric and pyroelectric coefficients for the composites were measured. From the laser interferometric measurements, it was found that the piezoelectric d/sub 33/ coefficients for the composites were independent of the volume fraction and averaged (190 /spl mnplus/ 10) pm/V, which was about half of the measured value of lead zirconate titanate (PZT) ceramic. Measurements of the pyroelectric coefficient showed that the coefficients increased with the ceramic content and reached values as large as 54 /spl mu/C/m/sup 2/ /spl deg/C. The thermal diffusivity of the composites was also determined using a technique based on the measurement of the phase retardation of a thermal wave passing through the material. The average value for the composites was (2.15/spl mnplus/ 0.05) /spl times/ 10/sup -7/ m/sup 2//s.     

In Vivo Molecular Imaging of Cervical Neoplasia Using Acetic Acid as Biomarker

In this paper, a molecular imaging method employing acetic acid dilute solution as a biomarker is described. An interpretation of the biophysical processes that are involved in the biomarker-tissue interaction and are determining the in vivo measured dynamic scattering characteristics is presented. On the basis of this interpretation, a compartmental model of the epithelium is developed for predicting the epithelial transport phenomena that are expected to be correlated with the dynamic characteristics of the backscattered light. The model predictions have been compared with the experimental data obtained from patients with cervical neoplasia of different grade, with the aid of a specially developed imaging system. Comparisons confirmed the validity of the interpretation of the phenomenon, and particularly, the fact that dynamic scattering characteristics are largely determined by the intracellular proton concentration kinetics. In addition, the correlation of the latter with both structural and functional alterations, associated with cervical neoplasia development, has been predicted theoretically and confirmed experimentally. The established correlation enables the derivation of quantitative indices expressing disease-specific microstructural and functional alterations, from the in vivo measured dynamic optical characteristics. This highlights the potential of the developed imaging method and technology for the noninvasive diagnosis, guided therapeutics, and screening of cervical neoplasia.     

Quantitative optical biopsy of liver tissue ex vivo

The intensity of the intrinsic autofluorescence of the reduced form of nicotineamide adenine dinucleotid (NADH) of biological tissue depends on the local, cellular concentration of this coenzyme. It plays a dominant role in the Krebs cycle and, therefore, serves as an indicator for the vitality of the observed cells. Due to the individually and locally varying boundary conditions and optical tissue properties, which are scattering coefficients, absorption coefficients and an anisotropy factor g, the fluorescence signal needs to be rescaled. Rescaling methods use for instance the Kubelka-Munk theory or the photon migration theory. Our rescaling method is partly based on measurements and partly theoretically derived. By combining four methods, i.e., laser-induced fluorescence (LIF) of the time-resolved signal, biochemical concentration measurements. Monte Carlo simulations with typical optical parameters and microscopic investigations, we demonstrate that simultaneous detection of the fluorescence and backscattering signal can easily and accurately provide rescaled, quantitative values for the NADH concentrations     

Characteristics of a saturated 18.9-nm tabletop laser operating at 5-Hz repetition rate

We report the characteristics of a saturated high-repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft X-ray laser was pumped at a 5-Hz repetition rate by 8-ps 1-J optical laser pulses impinging at grazing incidence into a precreated Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser output intensity was observed for an angle of 20/spl deg/, at which we measured a small signal gain of 65 cm/sup -1/ and a gain-length product g/spl times/l>15. Spatial coherence measurements resulting from a Young's double-slit interference experiment show the equivalent incoherent source diameter is about 11 /spl mu/m. The peak spectral brightness is estimated to be of the order of 1/spl times/10/sup 24/ photons s/sup -1/ mm/sup -2/ mrad/sup -2/ within 0.01% spectral bandwidth. This type of practical, small scale, high-repetition soft X-ray laser is of interest for many applications.     

Intraoperative application of optical spectroscopy in the presenceof blood

A simple but effective method of spectral processing was developed to minimize or remove the effects of the presence of superficial blood on tissue optical spectra and, hence, enhance the performance of optical-spectroscopic-based in vivo tissue diagnosis and surgical guidance. This spectral-processing algorithm was developed using the principles of absorption-induced light attenuation wherein the ratio of fluorescence intensity (F) and the hth power of diffuse reflectance intensity (Rd) at a given emission wavelength λ_m is immune to spectral distortions induced by the presence of blood on the tissue surface. Here, the exponent h is determined by the absorption coefficients of whole blood at the excitation and emission wavelengths. The theoretical basis of this spectral processing was verified using simulations and was experimentally validated. Furthermore, the optical spectra of brain tissues collected in vivo was processed using this algorithm to evaluate its impact on brain tissue differentiation using combined fluorescence and diffuse reflectance spectroscopy. Based on the simulation, as well as experimental results, it was observed that using F/Rd^h h can effectively reduce or remove spectral distortions induced by superficial blood contamination on tissue optical spectra. Thus, optical spectroscopy can also be used intraoperatively for applications such as surgical guidance of tumor resection     

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.     

Recent progress in high-power blue-violet lasers

The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm/sup 2/. This is thought to be due to the large transparency current density Jt and the large optical internal loss /spl alpha//sub i/. Recently, the internal loss was successfully reduced to 13.6 cm/sup -1/ by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70/spl deg/C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use.     

Endoscopic OCT Approaches Toward Cancer Diagnosis

A majority of human cancers originate in the epithelial tissues of the body. These include cancers in the oral cavity and pharynx, the digestive system, the respiratory system, the genital system, and the urinary system. It has been shown that early detection of these cancers can significantly improve the prognosis of affected patients. These cancers are currently diagnosed using endoscopic methods during which video imaging systems are inserted to visualize the tissue surface and guide tissue biopsies. Endoscopic optical coherence tomography (EOCT) has the potential to improve the early detection of epithelial cancers by providing high resolution, subsurface images of epithelial tissues. These subsurface images can assist the surgeon in selecting biopsy locations, and may also provide diagnostic information including the presence of cancerous and precancerous conditions in these tissues. This paper reviews current EOCT approaches toward imaging and evaluating internal epithelial tissues for various pathologies.     

An Optical Imaging Technique Using Deep Illumination in the Angular Domain

This paper describes a novel optical imaging method, deep illumination angular domain imaging (ADI), for detecting micron-scale objects within highly scattering media. The new optical imaging is a much simpler and less expensive solution as compared to other available optical imaging techniques. In principle, deep illumination ADI uses collimation detection capabilities of small acceptance angle devices to extract photons emitted from the scattered light created by a laser source, aimed deep beneath the turbid medium surface. The laser source forms an illumination ball within the medium that emits scattered light in all directions and illuminates objects near the surface from behind. Consequently, when photons from this illumination ball pass an object and reach the angular filter, light that is not subsequently scattered passes through to a camera detector, whereas scattered photons are rejected by the filter. Image results obtained are recorded for different phantom locations, phantom sizes, and medium scattering levels. Our images clearly display sub-204 m phantoms when placed 3 mm deep within a test scattering medium with total effective attenuation coefficient (mu'_eff) up to 5.8^-1 cm or 2.5 mm deep in chicken tissue tests. Preliminary digital image processing shows the image contrast enhancement and the definition improvement.     

Electron injection in "electron-only" devices based on a symmetric metal/silole/metal structure

We report on electron injection from two different metal electrodes into three silole derivatives, namely 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP), 1,2-bis(1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl) ethane (2PSP) and 2,5-bis-(2', 2'-bipyridin-6-yl)-1, 1-dimethyl-3,4-diphenylsilacyclopentadiene (PyPySPyPy), previously employed as emissive and electron transport materials in molecular organic light-emitting diodes (MOLEDs). Silole films were sandwiched between symmetric Mg:Ag or bilayer CsF-Al electrodes. The steady-state current density-voltage characteristics were measured as a function of the silole layer thickness for the two cathodes. The trap-free space-charge-limited current based on time-of-flight measurements compared with the injected electron current for PyPySPyPy indicated that Mg:Ag contacts limit the injected current, while CsF-Al contacts behave as quasi-ohmic contacts. Similar findings were obtained for 2PSP and PPSPP allowing steady-state derived electron mobility parameters to be extracted. Based on space-charge-limited conduction analysis of the measured current-voltage characteristics, PyPySPyPy is found to be a superior electron transporting silole with approximately an order of magnitude higher electron mobility (2.0/spl times/10/sup -4/ cm/sup 2//Vs) compared with those of 2PSP (2.4/spl times/10/sup -5/ cm/sup 2//Vs) and PPSPP (5.2/spl times/10/sup -5/ cm/sup 2//Vs), which is significantly higher than that of the prototype electron transport material tris (8-hydroxyquinolinolato) aluminum (III) (Alq/sub 3/) (6.5/spl times/10/sup -7/ cm/sup 2//Vs) at 0.6 MV/cm.     

Quantitative reflectometry of the ocular fundus

This review shows that quantitative measurements of fundus reflectance can be described by models that explicitly incorporate anatomical and physical properties of the fundus tissue. Newer techniques examine the fundus in ways fundamentally different from conventional optics, and must be included in this approach of measurement and modeling. The importance of the “inner surface reflector” (ISR) for tomographic imaging warrants more study of its optical properties, particularly its directional reflectance. For example, because the surface of a glaucomatous optic disc can slope steeply into the cup, the directional reflectance of the ISR may affect its apparent topography and thus the reproducibility of measurements of cup size     

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.