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  • 1.
    Paulsen, Martin
    KTH, School of Technology and Health (STH), Medical Engineering.
    Simulation driven pre-operative planning for the treatment of hallux rigidus: A novel concept of implant assessment2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The present study utilizes finite element analysis in order to simulate a surgical operation in the treatment of a hallux rigidus case, as designed and developed by Episurf Medical AB (Stockholm, Sweden). The surgical intervention includes an initial cheilectomy as well as an insertion of an orthopedic implant.

    The goal of the study was to evaluate the current concept of the medical intervention as it is manifested today, as well as to give design suggestions as how to further improve the pre-planning of the surgery. MRI-images of the first metatarsophalangeal joint in the hallux was collected from a patient suffering from hallux rigidus, and used in order to build case-specific geometrical images to be used in the FE analysis. The simulation was setup as to simulate a normal motion in the first metatarsophalangeal joint during a normal gait pattern.

    The first simulation was conducted without any intervention, while the second was conducted after a pre-determined operation plan in accordance with the surgical operation that Episurf Medical AB wants to perform. The results was then compared and analyzed in order to determine the post-surgical effects that such an operation could have on the patient. A third and final simulation was then performed, by using optimization algorithms in order to make suggestions to the pre-planned cheilectomy shape, as well as orientation of the implant.

    Two parameters were being investigated in order to assess the surgical intervention as designed by Episurf Medical AB; the contact stress on the articular side of the metatarsal head, and the strain on the implant shaft.

    The current manifestation of the cheilectomy did not reduce the contact stress compared to the untreated condition, as the implant failed to be a load baring surface due to the two dimensional nature of which it is conceived. Instead, the contact surface area is reduced and positioned medial and lateral to the implant head. The optimization algorithm could reduce the maximum contact stress significantly, from 295MPa and 400MPa in the treated and untreated conditons respectively, to 160MPa after the optimization algorithm.

    It became clear that the angle of the cheilectomy as well as the orientation of the implant angle has an incriminating effect on the post-operative results. However, the shape of the cheilectomy as well as the design of the implant would need to be revised in future embodiments, as the current concept failed to provide joint with a new articulating surface. Further development of the models formulated in this thesis is advised, as well as validating the findings with clinical data.

  • 2.
    Zheng, Miaomiao
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Ultrasound Contrast Agents: Fabrication, size distribution and visualization2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Ultrasound contrast agents composed of micro-bubble filled with gas are introduced to increase the backscattered power from blood. Their intravenously injection results in the improved contrast in the images.

    The aim of this master thesis project is to manufacture MB suspension at varied temperature and shear forces and to inspect the size distribution and concentration of the PVA-shelled micro-bubble with standard methods according to the developed protocol. A pulser-receiver (Panametrics PR 5072) setup combined with two transducers (2.25 MHz and 5 MHz) was used to investigate the backscattered enhancement of the micro-bubble suspension.

    Images were collected with transmission optical microscope (OLYMPUS IX71) with the aid of counting chamber. The diameter and concentration of the micro-bubbles were analyzed by Image J. The pulser-receiver setup was used to test the acoustic response.

    The mean diameter of micro-bubbles was from 2.03 to 4.38 µm with a standard deviation between 0.40 and 1.12 µm and the micro-bubble concentration varied from 0.07× to 5.22× MBs/ml. The enhancement of the ultrasound backscattered power was greater than 20 dB or even reached 30 dB when the energy was increased. 

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