Bent Laue Crystals in Biomedical X-ray Imaging Applications
This dissertation presents several synchrotron-based biomedical X-ray imaging projects involving bent Laue silicon (Si) crystals. Log-spiral bent Laue analyzers (BLA) were made from 20 micron thick Si crystals to map manganese (Mn) fluorescence in the X-ray fluorescence (XRF) imaging of the human brain with Parkinson's disease (PD). The BLA improved Mn specificity in XRF imaging and achieved a Mn detection limit of 0.5 mM concentration and an energy resolution of 34.5 eV. A novel method of three dimensional (3D) confocal XRF imaging of iodine was designed based on the one dimensional (1D) focusing ability of a log-spiral BLA made from 175 micron thick Si crystals. Combined with a pencil beam or a two dimensional (2D) focused beam, a 3D voxel of 100 × 100 × 124 cubic micron could be used to probe the 3D elemental mapping of a sample. A cylindrical bent Laue monochromator (BLM) was made from 600 micron thick Si crystals to simultaneously prepare three beams for the three-energy K-Edge Subtraction (KES) imaging and KES Computed Tomography (CT). A novel three-beam chopper was made as the first beam chopper for fast switching among the three beams. The three-energy KES imaging was successfully used to track uptake of injected iodine with time in a live mouse. The first simultaneous dual-energy KES imaging and the first KES CT imaging were successfully performed in Canada at the Biomedical Imaging and Therapy (BMIT) beamline. A novel rat head restraint and its corresponding field flatteners were constructed using a rapid-prototyping machine for the KES project based on CT scan data of a rat. This type of animal restraint worked well to immobilize the animal and holds great promise in improving the image quality and repeatability while reducing stress on experimental animals. The field flattener improved the signal-to-noise ratio (SNR) of the image at a cost of raised maximum exposure to some regions of the subject and reduced anatomical information in the images. In animal imaging applications, this method holds great promise to visualize low concentrations of contrast agents. Another cylindrical BLM was made to perform the novel Near Edge Spectral Imaging (NESI) and NESI CT. It showed high sensitivity for iodine with a measured detection limit of 2 microgram/centimetre square and a slightly better SNR performance than conventional KES imaging. The overwhelming impact of NESI is that it will bring together contrast imaging and elemental speciation imaging through X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) analysis which have been totally different realms.
Bent Laue Crystal, Near Edge Spectral Imaging (NESI), K-Edge Subtraction (KES) imaging, X-Ray Fluorescence (XRF) imaging, Confocal XRF imaging, Animal Restraint, Field Flattener
Doctor of Philosophy (Ph.D.)