Abstract : The general goal of the program was to demonstrate that the fluid flow measurement technique known as the Vorticity Optical Probe (VOP) could be used to measure the vorticity vectors within a volume of a flow field at many distinguishable locations simultaneously. The spatial resolution of the measurements would be small enough for them to be sensitive to the fine-scale fluctuations of the flow, yet the overall sampling volume large enough to enable study of the interactions between fine-scale features and large-scale structures. The specific objectives of the program were to demonstrate that: 1) The VOP provides sufficient information to allow rapid measurement of all three components of the vorticity vector at a single well-defined point within the flow field; 2) The vorticity vectors at several spatially distinct but unknown positions can be measured concurrently; and 3) A method could be developed for determining where in the sampling volume the vorticity is being measured. These three specific goals have been met using simulations of both the VOP and rotational flow. A data analysis technique has been developed which demonstrates the three-component measurement capability and indicates the inherent limits on its precision. (JHD)
We demonstrate for the first time the integration of two technologies, Spectral Domain Optical Coherence Tomography (SDOCT) and Line-Scanning Laser Ophthalmoscopy (LSLO) into a single compact instrument that shares the same imaging optics and line scan camera for both OCT and LSLO imaging. Co-registered high contrast wide-field en face retinal LSLO and SDOCT images are obtained non-mydriatically with less than 600 microwatts of broadband illumination at 15 frames/sec. The LSLO/SDOCT hybrid instrument could have important applications in clinical ophthalmic diagnostics and emergency medicine.
Abstract : In the period of fall 1983/spring 1984 the authors were predominantly concerned with the design, construction and testing of a new large scale flow system. It appears from preliminary examination that this flow system generates a turbulent boundary layer suitable for wide ranging study of vorticity dynamics. Verification that the flow exhibits normal boundary layer characteristics with both flow visualization and hot-film anemometry is under way. The Vorticity Optical Probe provides a measure of local vorticity fluctuations. It is based upon the tendency of small spherical particles to rotate with angular velocity, omega, as omega = W/2 determined by the local fluid vorticity W. To measure the particle rotation, plane mirrors (15 micron lead carbonate platelets) imbedded in about 25 micron Lucite (PMMA) spheres are the vorticity problem particles. Laser light reflected from the rotating particles allows the local vorticity to be deduced. Clearly, the refractive index of the working fluid must be matched to that of the polymethyl methacrolate particles (n=1.49) to eliminate refraction at their spherical surfaces. The choice of working fluid to match the particle refractive index has a direct effect on the flow system construction design and materials selection: the authors selected a 60 wt.% aqueous solution of ZnI2 (zinc iodide) with n=1.49, density rhonu=0.01 sq cm/sec. This fluid is moderately corrosive, perhaps comparable with sea water, but it does appear practicable for use in moderate scale flow systems and thus extends the usefulness of the vorticity probe. These along with other physical considerations are discussed in part II.
We demonstrate in vivo measurements in human retinal vessels of an experimental parameter, the slope of the low coherence interferometry (LCI) depth reflectivity profile, which strongly correlates with the real value of blood hematocrit. A novel instrument that combines two technologies, spectral domain low coherence interferometry (SDLCI) and retinal tracking, has been developed and used for these measurements. Retinal tracking allows a light beam to be stabilized on retinal vessels, while SDLCI is used for obtaining depth-reflectivity profiles within the investigated vessel. SDLCI backscatter extinction rates are obtained from the initial slope of the A-scan profile within the vessel lumen. The differences in the slopes of the depth reflectivity profiles for different subjects are interpreted as the difference in the scattering coefficient, which is correlated with the number density of red blood cells (RBC) in blood. With proper calibration, it is possible to determine hematocrit in retinal vessels. Ex vivo measurements at various RBC concentrations were performed to calibrate the instrument. Preliminary measurements on several healthy volunteers show estimated hematocrit values within the normal clinical range.
We have developed a compact, multimodal instrument for simultaneous acquisition of en face quasi-confocal fundus images and adaptive-optics (AO) spectral-domain optical coherence tomography (SDOCT) cross-sectional images. The optical system including all AO and SDOCT components occupies a 60×60 cm breadboard that can be readily transported for clinical applications. The AO component combines a Hartmann-Shack wavefront sensor and a microelectromechanical systems-based deformable mirror to sense and correct ocular aberrations at 15 Hz with a maximum stroke of 4 μm. A broadband superluminescent diode source provides 4 μm depth resolution for SDOCT imaging. In human volunteer testing, we observed up to an 8 dB increase in OCT signal and a corresponding lateral resolution of <10 μm as a result of AO correction.
Aim: The goal of this research was to develop and preliminarily test a novel technology and instrumentation that could help to significantly increase the diagnostic yield of current colon cancer screening procedures. This technology is based on a combined fluorescence–optical coherence tomography (OCT) imaging, and topical delivery of a cancer-targeting agent. Materials & methods: Gold colloid-adsorbed poly(ε-caprolactone) microparticles were labeled with a near-infrared dye, and functionalized with argentine–glycine–aspartic acid (RGD peptide) to effectively target cancer tissue, and enhance fluorescence-imaging contrast. The RGD peptide recognizes the αvβ3-integrin receptor, which is overexpressed by epithelial cancer cells. OCT was used under fluorescence guidance to visualize tissue morphology and, thus, to serve as a confirmatory tool for cancer presence. Results: A preliminary testing of this technology on human colon cancer cell lines, a mouse model of colon cancer, as well as human colon tissue specimens, was performed. Strong binding of microparticles to cancer cells and no binding to cells that do not significantly express integrins, such as mouse fibroblasts, was observed. Preferential binding to cancer tissue was also observed. Strong fluorescence signals were obtained from cancer tissue, owing to the efficient binding of the contrast agent. OCT imaging was capable of revealing clear differences between normal and cancer tissue. Conclusion: A dual-modality imaging approach combined with topical delivery of a cancer-targeting contrast agent has been preliminarily tested for colon cancer diagnosis. Preferential binding of the contrast agent to cancer tissue allowed the cancer-suspicious locations to be highlighted and, thus, guided OCT imaging to visualize tissue morphology and determine tissue type. If successful, this multimodal approach might help to increase the sensitivity and the specificity of current colon cancer-screening procedures in the future.
An active, hardware-based retinal tracker is integrated with a clinical optical coherence tomography (OCT) system to investigate the effects of stabilization on acquisition of high-resolution retinal sections. The prototype retinal tracker locks onto common fundus features, detects transverse eye motion via changes in feature reflectance, and positions the OCT diagnostic beam to fixed coordinates on the retina with mirrors driven by a feedback control loop. The system is tested in a full clinical protocol on subjects with normal and glaucomatous eyes. Experimental analysis software is developed to coalign and coadd multiple fundus and OCT images and to extract quantitative information on the location of structures in the images. Tracking is highly accurate and reproducible on all but one subject, resulting in the ability to scan the same retinal location continually over long periods of time. The results show qualitative improvement in 97% of coadded OCT scans and a reduction in the variance of the position of the optic disc cup edge to less than 1 pixel (<60 µm). The tracking system can be easily configured for use in research on ultra-high-resolution OCT systems for advanced image modalities. For example, tracking will enable very high density 3-D scans of the retina, which are susceptible to eye motion artifacts even for new high-speed systems.
A novel technology and instrumentation for fine needle aspiration (FNA) breast biopsy guidance is presented. This technology is based on spectral-domain low coherence interferometry (SD-LCI). The method, apparatus, and preliminary in vitro/in vivo results proving the viability of the method and apparatus are presented in detail. An advanced tissue classification algorithm, preliminarily tested on breast tissue specimens and a mouse model of breast cancer is presented as well. Over 80% sensitivity and specificity in differentiating all tissue types and 93% accuracy in differentiating fatty tissue from fibrous or tumor tissue was obtained with this technology and apparatus. These results suggest that SD-LCI could help for more precise needle placement during the FNA biopsy and therefore could substantially reduce the number of the nondiagnostic aspirates and improve the sensitivity and specificity of the FNA procedures.
