With 332,000 operations carried out every year, the implantation of an artificial hip joint is one of the most common
surgical operations performed in the US. According to prognosis which takes the demographical change into account, the
number of these operations will increase in the coming years.
One of the essential requirements is the perfect reconstruction of the biomechanical functions, especially the knowledge
about the center of the hip rotation and the length of the leg. Based on this information it is possible to ensure the right
position of the newly set leg during surgery.
The aim of this work is to present and evaluate an optical measurement method in order to gather information about the
center of the hip joint and the leg length. An appropriate laboratory setup has been designed and implemented in order to
evaluate two different approaches: a structured light-method consisting of a DLP-Beamer or a laser source which
projects defined patterns onto the patient and a marker-based system. Together with this both methods are combined
with custom software to determine the hip joint center and the leg length with an accuracy of around +/- 0.2 inches. The
clinical use of the tested approaches would give the surgeon the opportunity to reset the implant-parameters in the course
of the surgery. In this way subsequent illnesses such as scoliotic pelvis can be prevented.
The production of complex titanium components for various industries using laser welding processes has received growing attention in recent years. It is important to know whether the result of the cohesive joint meets the quality requirements of standardization and ultimately the customer requirements. Erroneous weld seams can have fatal consequences especially in the field of car manufacturing and medicine technology. To meet these requirements, a real-time process control system has been developed which determines the welding quality through a locally resolved temperature profile. By analyzing the resulting weld plasma received data is used to verify the stability of the laser welding process. The determination of the temperature profile is done by the detection of the emitted electromagnetic radiation from the material in a range of 500 nm to 1100 nm. As detectors, special high dynamic range CMOS cameras are used. As the emissivity of titanium depends on the wavelength, the surface and the angle of radiation, measuring the temperature is a problem. To solve these a special pyrometer setting with two cameras is used. That enables the compensation of these effects by calculating the difference between the respective pixels on simultaneously recorded images. Two spectral regions with the same emissivity are detected. Therefore the degree of emission and surface effects are compensated and canceled out of the calculation. Using the spatially resolved temperature distribution the weld geometry can be determined and the laser process can be controlled. The active readjustment of parameters such as laser power, feed rate and inert gas injection increases the quality of the welding process and decreases the number of defective goods.
Minimal invasive surgery methods have received growing attention in recent years. In vital important areas, it is crucial for the surgeon to have a precise knowledge of the tissue structure. Especially the visualization of arteries is desirable, as the destruction of the same can be lethal to the patient. In order to meet this requirement, the study presents a novel assistance system for endoscopic surgery. While state-of-the art systems rely on pre-operational data like computer-tomographic maps and require the use of radiation, the goal of the presented approach is to provide the clarification of subjacent blood vessels on live images of the endoscope camera system. Based on the transmission and reflection spectra of various human tissues, a prototype system with a NIR illumination unit working at 808 nm was established. Several image filtering, processing and enhancement techniques have been investigated and evaluated on the raw pictures in order to obtain high quality results. The most important were increasing contrast and thresholding by difference of Gaussian method. Based on that, it is possible to rectify a fragmented artery pattern and extract geometrical information about the structure in terms of position and orientation. By superposing the original image and the extracted segment, the surgeon is assisted with valuable live pictures of the region of interest. The whole system has been tested on a laboratory scale. An outlook on the integration of such a system in a clinical environment and obvious benefits are discussed.
Optical fibers are used in various applications, e. g. optical communication, material processing, as a laser medium
or to generate efficient supercontinua. For most of these applications the knowledge of the dispersion is an
essential prerequisite. The dispersion and modal properties of photonic crystal fibers (PCF) strongly depend
on the hole diameter and pitch. Since fabrication tolerances affect the structure of the photonic lattice, the
dispersion behavior as well as the number of guided transverse modes can differ from numerical calculations.
Dispersion measurement of singlemode photonic crystal fibers has been well described in recent papers. However,
the determination of dispersion in the presence of higher-order modes is much more difficult.
To measure the dispersion of optical fibers with high accuracy, a time-domain white-light interferometer based
on a Mach-Zehnder interferometer is presented. The experimental setup allows to determine the wavelength-dependent
differential group delay of light travelling through conventional fibers and PCFs within the wavelength
range from VIS to NIR. Interferences appear due to superposition of two laser beams, one propagating through
the tested fiber and the other travelling through air. Measuring the different group delays of a step-index fiber
shows the sufficient accuracy of the interferometer.
This paper demonstrates a simple yet effective way to suppress higher-order modes, making it possible to
measure the chromatic dispersion of singlemode as well as multimode fibers.
Precise optical loss measurements are a prerequisite for the development of new optical materials and complex optical
multilayers. A flat supercontinuum (400 nm - 1650 nm), generated by a photonic crystal fiber pumped with a train of
kHz nanosecond Q-switched microchip laser pulses at 1064 nm is used for high sensitive cavity ring down (CRD) loss
measurements. The supercontinuum based CRD-technique enables the precise determination of the reflectivity of highreflective
coatings from R = 0.995 to R = 0.99995 or of the transmission loss of optical materials from τ = 0.005 to
τ = 0.00005 with an accuracy better than 2 • 10-6, and covers an extreme wide spectral range of more than 1000 nm.
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