Pseudo-monoenergetic x-ray diffraction measurements using balanced filters for coherent-scatter computed tomography
Date of Award
Master of Science
Dr. Ian A. Cunningham
Dr. David Holdsworth
Dr. Deidre L. Batchelar
In the treatment of kidney stones, knowing stone composition has been established as an important aid to the understanding of stone formation and in preventing recurrences, particularly the composition of the initial “core” of the stone. Traditionally, stone composition has come from laboratory techniques such as infrared spectroscopy and x-ray diffraction. These methods require taking multiple samples of excised stone fragments and powdering them - losing structural information in the process, and therefore the specific core composition. Coherent-scatter computed tomography (CSCT) is a method of non-destructive “composition” imaging based on measurements of diffraction patterns from tissues. Use of an x-ray tube degrades scatter-pattern angular resolution due to the x-ray spectral width, making it difficult to uniquely identify some materials. The use of two transmission filters with similar atomic numbers (balanced “Ross filters”) to generate pseudo-monoenergetic scatter patterns of common kidney stone components is described as it applies to CSCT. We show that an analysis of angular-blur mechanisms reveals that focal spot size and beam width are the most important factors determining Bragg-peak width when erbium and thulium balanced filters are used. A Bragg-peak RMS angular width of approximately 0.14° (relative width of 3% at 5° scatter angle) can be achieved, reducing peak-overlap in the scatter functions of common kidney stone constituents. CSCT is capable of producing 3-D material-distribution maps. In previous studies, such maps were of relative material density. We describe a theoretical method to generate absolute (g/cm3) mass-density distributions. Balanced-filter CSCT improves scatter-function angular resolution and allows for the measurement of common kidney-stone constituents with non-overlapping peaks.
Beath, Stephen R., "Pseudo-monoenergetic x-ray diffraction measurements using balanced filters for coherent-scatter computed tomography" (2009). Digitized Theses. 3875.