Dr. Christopher Dydula Profile

Dr. Christopher Dydula

PhD student at Toronto Metropolitan Univ

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Proceedings Article | 18 May 2020 Presentation + Paper

Design and development of a rotating-anode x-ray tube coherent scatter projection imaging system

Christopher Dydula, Tong Xu, Paul Johns

Proceedings Volume 11404, 1140408 (2020) https://doi.org/10.1117/12.2554209

KEYWORDS: X-rays, Imaging systems, X-ray imaging, X-ray detectors, Scattering, Collimators, Data acquisition, Rayleigh scattering, X-ray diffraction, X-ray medical imaging, X-ray sources, Prototyping

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Coherent x-ray scatter is material specific, and imaging systems utilizing information from coherently scattered x rays are promising for security and medical applications requiring material identification with high sensitivity. A persistent challenge for practical implementation of these systems has been slow image acquisition. Our approach to reducing acquisition time is to develop a multibeam projection imaging system rather than a volumetric (CT or otherwise) imaging system. Previously we implemented a synchrotron-based system with five coplanar pencil beams and continuous motion of the object. Now we present a tabletop x-ray scatter imaging system built using a rotating-anode x-ray tube and a scintillating, energy-integrating flat-panel detector. A conventional source is more challenging to use than a synchrotron beam due to polychromaticity, low intensity, beam divergence, and x-ray tube thermal considerations. Simulations were performed to determine the system layout that optimized the intensity and angular resolution of scatter signals. The tube is inclined 6.1° to reduce apparent focal spot size. The primary collimation allows for an array of up to three rows by five columns of pencil beams, 3mm diameter and 2 cm apart at the object midplane 35 cm from the source, to irradiate the object simultaneously. There is no scatter collimation and the multiplexed scatter signals are disentangled using a maximum-likelihood expectation maximization algorithm. Motorized translation stages scan the object through the beams. The system can image objects up to 10 × 10 × 10 cm³ and 1 kg. Post-object primary beam attenuators allow for the same detector to measure transmitted and scattered x rays simultaneously. Initial images acquired with the system are presented. Using 15 beams, a 6000-pixel scatter image of a 6 cm × 10 cm region was acquired in 4.6 min.

Proceedings Article | 9 March 2017 Paper

Accelerated x-ray scatter projection imaging using multiple continuously moving pencil beams

Christopher Dydula, George Belev, Paul Johns

Proceedings Volume 10132, 101324J (2017) https://doi.org/10.1117/12.2253720

KEYWORDS: X-rays, X-ray imaging, Scattering, Synchrotrons, Prototyping, Data acquisition, Algorithm development, Image system modeling, Rayleigh scattering, Radiology, Sensors, Motion models, Statistical modeling

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Coherent x-ray scatter varies with angle and photon energy in a manner dependent on the chemical composition of the scattering material, even for amorphous materials. Therefore, images generated from scattered photons can have much higher contrast than conventional projection radiographs. We are developing a scatter projection imaging prototype at the BioMedical Imaging and Therapy (BMIT) facility of the Canadian Light Source (CLS) synchrotron in Saskatoon, Canada. The best images are obtained using step-and-shoot scanning with a single pencil beam and area detector to capture sequentially the scatter pattern for each primary beam location on the sample. Primary x-ray transmission is recorded simultaneously using photodiodes. The technological challenge is to acquire the scatter data in a reasonable time. Using multiple pencil beams producing partially-overlapping scatter patterns reduces acquisition time but increases complexity due to the need for a disentangling algorithm to extract the data. Continuous sample motion, rather than step-and-shoot, also reduces acquisition time at the expense of introducing motion blur. With a five-beam (33.2 keV, 3.5 mm2 beam area) continuous sample motion configuration, a rectangular array of 12 x 100 pixels with 1 mm sampling width has been acquired in 0.4 minutes (3000 pixels per minute). The acquisition speed is 38 times the speed for single beam step-and-shoot. A system model has been developed to calculate detected scatter patterns given the material composition of the object to be imaged. Our prototype development, image acquisition of a plastic phantom and modelling are described.

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