Mercedes Martinson

Development of a bent Laue beam-expanding double-crystal monochromator for biomedical X-ray imaging

A bent Laue beam-expanding double-crystal monochromator was developed and tested at the Biomedical Imaging and Therapy beamline at the Canadian Light Source. The expander will reduce scanning time for micro-computed tomography and allow dynamic imaging that has not previously been possible at this beamline.

Phase-preserving beam expander for biomedical X-ray imaging

Building on previous work, a phase-preserving bent Laue beam-expanding monochromator was developed with the capability of performing live animal phase contrast dynamic imaging at the Biomedical Imaging and Therapy beamline at the Canadian Light Source.

Respiratory-gated KES imaging of a rat model of acute lung injury at the Canadian Light Source

A K-edge subtraction imaging approach for respiratory-gated lung imaging using iodine and xenon contrast agents in a rodent model is presented.

Multiple energy synchrotron biomedical imaging system.

A multiple energy imaging 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 multiple energy x-ray imaging. A novel multiple energy x-ray imaging system, which prepares a horizontally focused polychromatic x-ray beam, has been developed at the BioMedical Imaging and Therapy bend magnet beamline at the Canadian Light Source. The imaging system is made up of 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. Depending on the crystals bent radius, reflection type, and the horizontal beam width of the filtered synchrotron radiation (20-50 keV) used, the size and spectral energy range of the focused beam prepared varied. For example, with a bent radius of 95 cm, a (1,1,1) type reflection and a 50 mm wide beam, a 0.5 mm wide focused beam of spectral energy range 27 keV-43 keV was obtained. This 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); some of these elements are used as biomedical and clinical contrast agents. Using the developed imaging system, a test subject composed of iodine, xenon, cesium, and barium along with water and bone were imaged and their projected concentrations successfully extracted. The estimated dose rate to test subjects imaged at a ring current of 200 mA is 8.7 mGy s-1, corresponding to a cumulative dose of 1.3 Gy and a dose of 26.1 mGy per image. Potential biomedical applications of the imaging system will include projection imaging that requires any of the extracted elements as a contrast agent and multi-contrast K-edge imaging.

Biomedical Imaging Using Synchrotron Radiation: Experience at the Biomedical Imaging and Therapy (BMIT) Facility at the Canadian Light Source

The Biomedical Imaging and Therapy (BMIT) beamlines at the Canadian Light Source (CLS) comprise a multi-modality synchrotron imaging facility capable of imaging objects with 2–200 μm resolution with beam sizes up to ~200 mm wide and ~10 mm high in the experimental hutches [1–3]. BMIT hosts two beamlines, a bend magnet 05B1-1 and an insertion device 05ID-2, with capabilities to apply absorption imaging, in-line phase contrast imaging (PCI), analyzer-based imaging (ABI) or diffraction-enhanced imaging (DEI), and K-Edge Subtraction (KES) imaging. Talbot or grating interferometry is under development.

Characterization of a bent Laue double-crystal beam-expanding monochromator

A previously reported bent Laue double-crystal monochromator was found to have areas of missing intensity in the final X-ray beam. Measurements of the shape of the bent crystal wafers have been made using mechanical and diffraction methods to evaluate the crystal system and provide insight into potential methods of mitigating the non-uniformities in the beam.

An energy dispersive bent Laue monochromator for K-edge subtraction imaging

K-Edge Subtraction (KES) is a powerful synchrotron imaging method that allows the quantifiable determination of a contrast element (e.g. iodine) and matrix material (usually represented as water) in both projection imaging and computed tomography. A bent Laue monochromator has been developed that has very good focal and energy dispersive properties for KES. Approximately 5% of the vertical beam profile is involved in “edge crossing” energies, thus no splitter is employed as has been done with previous implementations where approximately 33% of the beam size was blocked. The beam can be narrowed vertically allowing a smaller crossover angle than a splitter based system which minimizes artifacts. The combination of good spatial resolution, energy dispersive properties, flux and a unique approach to data analysis make this system nearly ideal for KES.

Measuring the criticality of the `magic condition' for a beam-expanding monochromator

The effect of minor mismatch between the geometric and single-ray foci for a cylindrically bent Laue double-crystal monochromator is examined and found to be less detrimental than previously believed. Even without exact matching, the transverse coherence of the X-ray beam is not deteriorated by the system, enabling the phase-based imaging techniques critical to modern biomedical imaging experiments.

Indirect measurement of average alveolar dimension using dynamic phase-contrast imaging

For some lung diseases, assessment of alveolar dimension could add critical information to inform patient care and disease progression. However, current clinical imaging techniques, such as computed tomography, lack the resolution required to measure these small structures in patients. While the gold standard imaging modality for measuring alveoli is micro-CT, this technique is not possible in clinical use due to the size of the patients and the radiation dose. An alternative imaging modality is phase-based contrast imaging, which would deliver a lower dose to patients and increase the size limit. Phase contrast X-ray imaging has previously been combined with particle image velocimetry (PIV) to measure lung motion, another indicator of lung disease. Thus it was hypothesized that average alveolar size could also be measured indirectly using PIV. In the work reported here, we show that average alveolar size shows a high correlation to the mathematical divergence of the velocity vector field that results from the speckle pattern produced by phase imaging of mouse lungs. This correlation is linear with p<0.006. If this correlation holds in human lungs, it could potentially be calibrated to indirectly measure average alveolar size in human patients using some of the grating-based phase-contrast imaging methods that are showing great promise in clinical use.

Design of a mouse restraint for synchrotron-based computed tomography imaging

High-resolution computed tomography (CT) imaging of a live animal within a lead-lined synchrotron light hutch presents several unique challenges. In order to confirm that the animal is under a stable plane of anaesthesia, several physiological parameters (e.g. heart rate, arterial oxygen saturation, core body temperature and respiratory rate) must be remotely monitored from outside the imaging hutch. In addition, to properly scan the thoracic region using CT, the animal needs to be held in a vertical position perpendicular to the fixed angle of the X-ray beam and free to rotate 180°-360°. A new X-ray transparent mouse restraint designed and fabricated using computer-aided design software and three-dimensional rapid prototype printing has been successfully tested at the Biomedical Imaging and Therapy bending-magnet (BMIT-BM) beamline at the Canadian Light Source.