A colonoscopy's near-blind navigation process frequently causes disorientation for the scope operator, leading to harm for the patient. Navigation can be improved if real-time colonoscope shape, location, and orientation information is provided by a shape-tracking aid, such as a fiber optic bend sensor. Fiber optic bend sensors provide advantages over conventional electromechanical shape-trackers, including low cost and ease of integration. However, current fiber optic bend sensors lack either the ability to detect both bending direction and curvature, or the ability to detect multiple localized bends. An inexpensive multifiber bend sensor was developed to aid users in navigation during colonoscopy. The bend sensor employs active-cladding optical fibers modified with fluorescent quantum dots, bandpass filters, and a complementary metal-oxide-semiconductor imager as key components. Results from three-fiber sensors demonstrate the bend sensor's ability to measure curvature (error of 0.01 mm), direction (100% accuracy), and location (predetermined distance) of a bend in the fiber bundle. Comparison with spectroscopy data further confirmed the accuracy of the bending direction measurement for a three-fiber sensor. Future work includes improvements in fiber manufacturing to increase sensor sensitivity and consistency. An expanded 31 fiber bundle would be needed to track the full length of a colonoscope.
We present the design and fabrication of a novel fiber optic multiparameter bend sensor. Unlike current intrinsic fiber optic multiparameter bend sensors that depend on multiple cores or multiple fibers, the new sensor is based on three circumferential active-cladding point modifications on a single optical fiber at specific axial locations along the length of the fiber. A commercial 30-W CO2 laser is used to cut three point modifications in the plastic cladding of the fiber. Each of the three defects is filled with fluorophores (quantum dots) with different peak emission wavelengths. A 405-nm laser (operating at 10-mW) is used to excite the quantum dots, while a spectrometer, coupled to the fiber, measures the emission signals of each of the three fluorophores simultaneously. Results show that bending direction and degree of curvature at a single localized modification region can be expressed as a function of the three fluorescence intensities.
Colonoscopy is the current gold standard for colon cancer screening and diagnosis. However, the near-blind navigation
process employed during colonoscopy results in endoscopist disorientation and scope looping, leading to missed
detection of tumors, incorrect localization, and pain for the patient. A fiber optic bend sensor, which would fit into the
working channel of a colonoscope, is developed to aid navigation through the colon during colonoscopy. The bend
sensor is comprised of a bundle of seven fibers doped with quantum dots (QDs). Each fiber within the bundle contains a
unique region made up of three zones with differently-colored QDs, spaced 120° apart circumferentially on the fiber.
During bending at the QD region, light lost from the fiber's core is coupled into one of the QD zones, inducing
fluorescence of the corresponding color whose intensity is proportional to the degree of bending. A complementary
metal oxide semiconductor camera is used to obtain an image of the fluorescing end faces of the fiber bundle. The
location of the fiber within the bundle, the color of fluorescence, and the fluorescence intensity are used to determine the
bundle's bending location, direction, and degree of curvature, respectively. Preliminary results obtained using a single
fiber with three QD zones and a seven-fiber bundle containing one active fiber with two QDs (180° apart) demonstrate
the feasibility of the concept. Further developments on fiber orientation during bundling and the design of a graphical
user interface to communicate bending information are also discussed.
Colonoscopy is the gold standard for screening for inflammatory bowel disease and colorectal cancer. Flexible
endoscopes are difficult to manipulate, especially in the distensible and tortuous colon, sometimes leading to
disorientation during the procedure and missed diagnosis of lesions. Our goal is to design a navigational aid to guide
colonoscopies, presenting a three dimensional representation of the endoscope in real-time. Therefore, a flexible sensor
that can track the position and shape of the entire length of the endoscope is needed. We describe a novel shape-tracking
technology utilizing a single modified optical fiber. By embedding fluorophores in the buffer of the fiber, we
demonstrated a relationship between fluorescence intensity and fiber curvature. As much as a 40% increase in
fluorescence intensity was achieved when the fiber's local bend radius decreased from 58 mm to 11 mm. This approach
allows for the construction of a three-dimensional shape tracker that is small enough to be easily inserted into the biopsy
channel of current endoscopes.
Many studies on thermal processing of thin-film structures assume an incoherent thermal emission with an emissivity value that is constant or varies according to bulk properties. However, thermal radiation has a coherence length that varies with temperature. Thus, coherent thin-film interference affects the radiative properties of heterostructures when the wavelengths of radiation are of the same order of magnitude as the film thicknesses. For semiconducting and dielectric thin films on optically thick substrates, there are distinct trends in these microscale radiative effects. Numerical simulations of the temperature-dependent optical characteristics of multilayer thin-film structures were conducted to evaluate the thin-film interference effects. These results can be applied to thermal processes of thin-film structures where a spatial or temporal temperature distribution exists. An example of these effects is shown for radiative cooling of silicon-on-insulator wafers.
Thermal processing, a necessary step in the fabrication of most microelectronic devices, is used to improve the material quality of thin films. One example of thermal processing of thin films is Zone- Melting Recrystallization with a radiant line heat source. A line heater, situated above the film, heats a narrow region beyond its melt point creating a molten zone. As the line heater is moved slowly over the film, the material in the wake of the moving molten zone freezes in the form of a single crystal. The morphology of the solid/liquid interface strongly influences the resultant quality of the crystal. A planar morphology, in fact, produces a poor quality film which contains branching dislocations. A cellular morphology produces the highest quality films with limited point of line defects. In-situ observations of the crystalline quality can be made by examining the solid/liquid interface morphology. The real-time image analysis of the interface and the closed-loop control of the process are described in this paper.
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