| After a period of popularity in the 1950's and '60's, interest in point-projection x-ray microscopy waned for several reasons: The abundant information superimposed in the projection complicated image interpretation. Serial-section reconstruction from light and electron micrographs produced three-dimensional images, though the investment in time and the problems of registration and distortion were considerable. Brilliant, low-energy synchrotron sources provided ten-nanometer resolution for very thin sections, though at extremely high cost. Computed tomography drew attention from scientists and mathematicians while revolutionizing diagnostic medicine.;In 1984, Feldkamp first demonstrated direct volume reconstruction from planar conebeam projections. Simultaneously, solid state and other digital x-ray detectors made it possible to record high-resolution images with reasonable speed and efficiency. Low-cost, fanbeam scanners became accessible to the average institution.;My research goal was to demonstrate the feasibility of low-cost, high-resolution, volume reconstruction from conebeam x-ray projections. Capitalizing on recent developments in detectors, algorithms and computational power, I overcame the primary disadvantage of point-projection microscopy: superimposition of information. Using a modified scanning electron microscope as a micro-focal x-ray source and storage phosphor plate detectors, I reconstructed the guinea pig cochlea at 40-micron resolution. Experimental results and computational models prove the method has the potential to provide isotropic resolution at the cellular level in small specimens. I showed the theoretical predictions to be in good agreement with experiment, so that the model can be used in design development and performance evaluation of future instruments.;Continued improvements in x-ray sources and detectors and in volume reconstruction algorithms will increase the spatial resolution and utility of the method, and multispectral analysis will provide quantitation of specimen constituents. The advantages of the technique include its dose-efficiency and ability to image specimens opaque to optical and charged-particle illumination. Since samples are imaged in air, living specimens may be studied. The results of research described in this dissertation indicate that conebeam microtomography can be routinely and cost-effectively applied in the fields of biology, microelectronics and materials science. |
