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Has files: YesSubject: search.filters.subject.400304 Biomedical imaging

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    Sub-pixel registration for low cost, low dosage, x-ray phase contrast imaging : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Electronic and Computer Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2021) Bradley, Hamish
    X-ray phase contrast imaging is an imaging modality that measures the phase shift of the X-ray wavefronts as they travel through different materials. This gives a higher contrast between regions of similar X-ray attenuation, in a medical sense this corresponds to a higher contrast of soft tissues. A new area of research for X-ray phase contrast imaging is to use shadow-based intensity modulation to generate these images. This thesis explores a range of different registration techniques, and their suitability for phase contrast imaging using shadow based intensity modulation. Image registration is a key step in generating the phase contrast images as it is related to the x and y differential phase. These are then integrated to generate the phase contrast image. Therefor a high accuracy sub-pixel registration technique will provide high quality phase contrast images. The registration techniques explored are 1D curve 2-D surface fitting to a correlation map, phase registration, Newton-Raphson method, and optimal interpolation filtering. These registration techniques were tested with images that are noise free, as well as images corrupted by Poisson noise. The Newton-Raphson, and the optimal interpolation filters show the most promise due to low errors in the noise free environment. In the presence of noise, the Newton-Raphson method performs poorly, and hence requires a good denoising method, while the optimal interpolation filters do not get any improvement from any denoising techniques. Currently the Newton-Raphson based method are used widely in digital image correlation, however the optimal interpolation filtering has the benefit of not being limited by the choice of interpolation technique, and it removes the iterative process, and depending on the size of the optimal interpolation filter it performs better than, or only marginally worse than the Newton-Raphson method.
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    A portable multi-modal micro-imaging system for automated scanning and image stitching applications : a thesis submitted to Massey University in accordance with the requirements of the degree of Master of Engineering in the School of Engineering and Advanced Technology
    (Massey University, 2019) Naqvi, Adam
    Microscopic imaging is an important element in many fields like biology, medicine, diagnostics, engineering, and materials research. Muti-modal microscopes are ideal for imaging samples that reveal unseen structures that could not otherwise be seen with normal bright-field microscopes. Point-of-care micro-imaging devices are ones that can deliver the features of a microscope in areas where access to a laboratory or medical facilities are scarce. This thesis presents the development of a portable micro-imaging system that uses multi-modal illumination to image samples in bright-field, fluorescence, ambient and laser diffraction modes. A systematic design method has been used to develop the system from the conceptual phase to a working prototype. The system incorporates variable magnification through an inverted turret system and a GUI application for live image view, automatic scanning, auto-focusing and image processing. The utility of the system is demonstrated through imaging stained biological samples for a local industry application. The acquired images are measured against sharpness and noise. It is observed that the sharpness and noise of the images produced vary with the type of sample: samples with higher contrast generally produce sharper images with less noise. It has also been found that diffused ambient illumination produces the most consistent sharpness and noise scores between magnifications. Performance of algorithms used is discussed and improvements are suggested for building a more compact and stable platform including a method to calibrate measurements for particle size estimation.