A fiducial subject pre-alignment system for the Biomedical Imaging and Therapy beamlines at the Canadian Light Source

Positioning, immobilization, and organ motion are some of the major concerns in all imaging modalities. With synchrotron X-ray imaging, alignment of the region of interest to the beam is usually done inside the experimental hutch. However, because specimen alignment can be time consuming; such a system is wasteful of valuable beam time. For the purposes of the Biomedical Imaging and Therapy (BMIT) beamlines at the Canadian Light Source, we propose an effective and versatile means of positioning a wide range of subjects (human and animal) with a wide range of sizes using a laser-based fiducial system to define the region of interest (ROI) before imaging; i.e., outside the experimental hutch. This system will allow the beam path through a specific region of interest to be modeled outside the imaging hutch in a way that it can be reproduced relative to the fixed X-ray beamline inside the hutch. The model will include an indication of the center of the beam and a rectangular area around the target delineating the limits of the area to be imaged (i.e., encompassing the “region of interest”). The rectangular field of view would be projected on the incoming (entrance) side of the subject as well as the outgoing (exit) side of the subject, and these projections must be coaxial with each other and parallel with the X-ray beam. This method is user friendly, allows mistake to be corrected before experiment and most importantly saves time

Application of a High‑Resolution Computed Radiography System in Detecting an Iodinated X‑ray Contrast Agent: Small Animal Phantom Study

Tumor angiogenesis, the creation of new blood vessels, is the characteristic of solid tumors and crucial for their development. Iodinated contrast agents are used to increase the X‑ray detectability of zone of angiogenesis, and thus providing a means for tracking tumor growth. The overall objective of this project was to evaluate the performance of Kodak CR 7400, a high‑resolution compact computed radiography (CR) system in detection of Omnipaque‑240, an iodinated contrast agent, in a phantom mimicking small animal tumor model. The first phase of the project was dedicated to a comprehensive assessment of CR image quality by measuring presampled Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), Relative Standard Deviation of Noise (RSD), Noise Equivalent Quanta (NEQ), and Detective Quantum Efficiency (DQE). Next, dual‑energy and temporal subtraction techniques were implemented to enhance the contrast of iodinated regions and suppress soft tissue background in the phantom. The underlying physics of each technique was discussed, including the design of the phantoms, the simulation and measurement of the Signal‑to‑Noise Ratio (SNR) in the final subtracted iodine image, and dose assessment. In the end, the results of both techniques were compared along with discussions about the advantages and limitations of implementing each technique. Overall, the study supported the potential of low‑cost CR 7400 in small animal study, particularly detecting iodinated contrast agents implementing temporal subtraction technique and provided a background for similar small animal studies using a CR system

The design and implementation of a CT and MRI compatible multipurpose phantom: testing the effectiveness of multiple contrast material concentrations for CTA

Thesis (M.A.)--Boston UniversityThe purpose of our study was to determine if it is possible to acquire CTA images of small vessels using lower concentrations of iodinated contrast material without substantially diminishing image quality. A custom designed multi-purpose phantom was used to test multiple concentrations of iodinated contrast material using low x-ray tube voltage experimental CTA protocols. A single scan using 120 kVp and Noise Index at a setting of 23 was compared to scans using 100 kVp and 80 kVp tube voltages and Noise Index settings of 23, 21, and 19. Lower tube voltages did produce increased attenuation in contrast material regions of interest, however, increased image noise caused the CNR and FOM for the currently established imaging protocol to be superior to the experimental protocols tested. Despite minor decreases in image quality, the experimental imaging protocols were able to produce images utilizing significantly decrease levels of radiation dose. Given minor changes in imaging quality, the ability to substantially reduce dose while maintaining a satisfactory level of image quality was positive. Further experimentation with low kVp CTA imaging utilizing additional NI settings is warranted to measure possible further improvements in image quality while still maintaining low radiation dose

Imaging Stroke Evolution after Middle Cerebral Artery Occlusion in Non-human Primates

This article reviews imaging approaches applied to the study of stroke in nonhuman primates. We briefly survey the various surgical and minimally invasive experimental stroke models in nonhuman primates, followed by a summary of studies using computed tomography, positron emission tomography and magnetic resonance imaging and spectroscopy to monitor stroke from the hyperacute phase (within minutes of the onset of cerebral ischemia) to the chronic phase (1 month and beyond)

Applications of CT Perfusion-Based Triaging and Prognostication in Acute Ischemic Stroke

CT Perfusion (CTP) is a minimally invasive imaging technique that aids acute ischemic stroke (AIS) triage and prognostication by determining tissue viability based on hemodynamic parameters. The goals of this research are to determine: 1) CTP thresholds for estimation of infarct and penumbra volume, 2) how CTP scan duration impacts infarct and penumbra volume estimates, and 3) reliability of CTP for predicting functional outcomes following intra-arterial therapy (IAT). Chapter 2 introduced an experimental study for determining ischemia-time dependent thresholds for brain infarction using multimodal imaging in a porcine stroke model that is easier to implement than previous large animal stroke models. CTP determined an absolute cerebral blood flow (CBF) threshold of 12.6±2.8mL∙min-1∙100g-1 for brain infarction after 3h of ischemia, which was close to that derived using hydrogen clearance in a previous study by Jones et al (Journal of Neurosurgery, 1981;54(6):773-782). Chapter 3 retrospectively investigated the impact of CTP scan duration on cerebral blood volume (CBV), CBF, and time-to-maximum (Tmax) and found optimal scan durations that minimized radiation dose while not under- or over-estimating infarct volumes measured using two previously derived CBF thresholds for infarction. We found that CBV and Tmax decreased at shorter scan durations, whereas CBF was independent of scan duration, consequently, infarct volume estimated by both CBF thresholds was independent of scan duration. Chapter 4 compared reperfusion seen on follow-up CTP to reperfusion predicted by post-IAT digital subtraction angiography (DSA) and the ability of the two modalities to predict good 90-day functional outcome in a retrospective study. We found that patients with ‘complete reperfusion’ grades on DSA often had ischemic tissue on follow-up CTP and that follow-up CTP had superior specificity and accuracy for predicting functional outcome compared to DSA. In summary, this research has shown that CBF thresholds can reliably detect infarct in AIS and are independent of scan duration, allowing radiation dose to be minimized by limiting scans to 40s without compromising accuracy of infarct volume estimates. Finally, CTP is a more specific and accurate predictor of functional outcome than the commonly used post-procedural DSA, this could help select patients for neuroprotective therapy

Curved array photoacoustic tomographic system for small animal imaging

We present systematic characterization of a photoacoustic imaging system optimized for rapid, high-resolution tomographic imaging of small animals. The system is based on a 128-element ultrasonic transducer array with a 5-MHz center frequency and 80% bandwidth shaped to a quarter circle of 25mm radius. A 16-channel data-acquisition module and dedicated channel detection electronics enable capture of a 90-deg field-of-view image in less than 1s and a complete 360-deg scan using sample rotation within 15s. Measurements on cylindrical phantom targets demonstrate a resolution of better than 200μm and high-sensitivity detection of 580-μm blood tubing to depths greater than 3cm in a turbid medium with reduced scattering coefficient μ′s =7.8cm^(−1). The system is used to systematically investigate the effects of target size, orientation, and geometry on tomographic imaging. As a demonstration of these effects and the system imaging capabilities, we present tomographic photoacoustic images of the brain vasculature of an ex vivo mouse with varying measurement aperture. For the first time, according to our knowledge, resolution of sub-200-μm vessels with an overlying turbid medium of greater than 2cm depth is demonstrated using only intrinsic biological contrast