DEVELOPMENT OF A MULTIPLE ENERGY SYNCHROTRON BIOMEDICAL IMAGING SYSTEM

Abstract

A multiple energy imaging (MEI) system that can extract multiple endogenous or induced contrast materials as well as water and bone images would be ideal for imaging of biological subjects. The continuous spectrum available from synchrotron light facilities provides a nearly perfect source for MEI. This dissertation is on a novel MEI imaging system developed for biomedical imaging applications at the BioMedical Imaging and Therapy bend magnet beamline, Canadian Light Source. The developed MEI system prepares a horizontally focused polychromatic x-ray imaging beam. Its components are: a cylindrically bent Laue single silicon (5, 1, 1) crystal monochromator, scanning and positioning stages for the subjects, flat panel (area) detector, and a data acquisition and control system. The Si crystal is bent by means of a frame bender and has a bent radius of 0.5 m. Depending on the horizontal beam width of filtered synchrotron radiation (20 to 50 keV) incident on the monochromator; the size and spectral energy range of the focused beam prepared vary, and can be up to 15 keV. The spectral energy range covers the K-edges of iodine (33.17 keV), xenon (34.56 keV), cesium (35.99 keV), and barium (37.44 keV). Iodine, xenon and barium are commonly used biomedical and clinical contrast agents. A phantom composed of six materials: iodine, xenon, cesium, barium, water, and bone was imaged using the MEI system and their projected concentrations successfully extracted. For quantification of iodine, cesium and barium, the minimum detection limit of the MEI system is about 1.0 mg/ml for iodine and barium, and 0.5 mg/ml for cesium. The estimated dose rate to the phantom imaged at a ring current of 200 mA is 8.7 mGy/s, corresponding to a cumulative dose of 1.3 Gy. A crossover correction algorithm has also been developed to suppress crossover artifacts associated with the MEI system, dual-beam KES and spectral KES systems. Potential biomedical applications of the imaging system will include projection imaging that requires any of the extracted K-edges as a contrast agent and multi-contrast K-edge imaging.