Physics Commons^™

Magnetic Resonance Systems Development For Point-Of-Care Mri Platforms, Eric J. Lessard

Electronic Thesis and Dissertation Repository

Magnetic resonance imaging utilizes electromagnets to produce anatomical images in both clinical and research settings. In the race towards increasing performance head-optimized scanners have begun playing a significant role in providing high quality imaging of the head. However, they are implemented using smaller geometries and as such fail to allow entrance of the patient past their shoulders. This is overcome by designing asymmetric gradient coils which have their imaging region located towards one end of the gradient coil, as opposed to the geometric center, allowing brain imaging. There exists interest in compact configurations which allow imaging further into the cervical …

Improving Hydrid Pet/Mri Cardiovascular Imaging With Improved Hardware Design And Attenuation Correction Coefficient, Adam Helmy Farag

Electronic Thesis and Dissertation Repository

According to the World Health Organization (WHO) report in 2019, cardiovascular diseases (CVD) cause 52% of all illness-related deaths globally and are considered to be the second most common cause of death in Canada. CVD is also estimated to cost the Canadian economy about $21.2 billion in direct and indirect costs. With these figures, it is vital to develop the most effective and accurate methods and tools to diagnose accurately CVD and their causes. One of the promising tools for accurate diagnostic and therapeutic of CVD is the integrated Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) PET/MRI technology, …

Optimization Of Design Procedures For Delta Relaxation Enhanced Magnetic Resonance, Daniel J. Martire

Electronic Thesis and Dissertation Repository

Delta relaxation enhanced magnetic resonance (dreMR) is a magnetic resonance imaging (MRI) method that produces contrast based on longitudinal relaxation dispersion. Through modulation of the magnetic field using an actively-shielded, field-cycling insert coil, this technique increases probe specificity and suppresses remaining signal. However, significant improvements are needed. This thesis addresses two advancements in dreMR with a focus on optimizing design procedures. A general procedure was developed to design split power solenoid magnets. The procedure was then applied to the design of a switched-field exposure system. A coil was constructed and the method was validated. This procedure can be used for …

Developments In Pet-Mri For Radiotherapy Planning Applications, John Christian Patrick

Electronic Thesis and Dissertation Repository

The hybridization of magnetic resonance imaging (MRI) and positron emission tomography (PET) provides the benefit of soft-tissue contrast and specific molecular information in a simultaneous acquisition. The applications of PET-MRI in radiotherapy are only starting to be realised. However, quantitative accuracy of PET relies on accurate attenuation correction (AC) of, not only the patient anatomy but also MRI hardware and current methods, which are prone to artefacts caused by dense materials. Quantitative accuracy of PET also relies on full characterization of patient motion during the scan. The simultaneity of PET-MRI makes it especially suited for motion correction. However, quality assurance …

Digging Deeper With Diffuse Correlation Spectroscopy, Kyle J. Verdecchia

Electronic Thesis and Dissertation Repository

Patients with neurological diseases are vulnerable to cerebral ischemia, which can lead to brain injury. In the intensive care unit (ICU), neuromonitoring techniques that can detect flow reductions would enable timely administration of therapies aimed at restoring adequate cerebral perfusion, thereby avoiding damage to the brain. However, suitable bedside neuromonitoring methods sensitive to changes of blood flow and/or oxygen metabolism have yet to be established.

Near-infrared spectroscopy (NIRS) is a promising technique capable of non-invasively monitoring flow and oxygenation. Specifically, diffuse correlation spectroscopy (DCS) and time-resolved (TR) NIRS can be used to monitor blood flow and tissue oxygenation, respectively, and …

Optimizing Respiratory Gated Intensity Modulated Radiation Therapy Planning And Delivery Of Early-Stage Non-Small Cell Lung Cancer, Ilma Xhaferllari

Electronic Thesis and Dissertation Repository

Stereotactic ablative body radiotherapy (SABR) is the standard of care for inoperable early-stage non-small cell lung cancer (NSCLC) patients. However, thoracic tumours are susceptible to respiratory motion and, if unaccounted for, can potentially lead to dosimetric uncertainties. Respiratory gating is one method that limits treatment delivery to portions of the respiratory cycle, but when combined with intensity-modulated radiotherapy (IMRT), requires rigorous verification. The goal of this thesis is to optimize respiratory gated IMRT treatment planning and develop image-guided strategies to verify the dose delivery for future early-stage NSCLC patients.

Retrospective treatment plans were generated for various IMRT delivery techniques, including …

Hyperpolarized 129xe Magnetic Resonance Imaging Of Radiation-Induced Lung Injury, Ozkan Doganay

Electronic Thesis and Dissertation Repository

Lung cancer is the largest contributor to cancer-related mortality worldwide. Only 20% of stage III non-small cell lung cancer patients survive after 5-years post radiation therapy (RT). Although RT is an important treatment modality for lung cancer, it is limited by Radiation-Induced Lung Injury (RILI). RILI develops in two phases: (i) the early phase (days-weeks) referred to radiation pneumonitis (RP), and (ii) the late phase (months). There is a strong interest in early detection of RP using imaging to improve outcomes of RT for lung cancer. This thesis describes a promising approach based on ¹²⁹Xe gas as a contrast …

Development Of A Small Animal Conformal Irradiator With Dual Energy X-Ray Computed Tomography Imaging For Kilovoltage Dosimetry, Michael D. Jensen

Electronic Thesis and Dissertation Repository

External beam radiotherapy has become technically sophisticated with image guided radiation therapy (IGRT) and intensity modulated radiation therapy (IMRT). These technologies allow for precise delivery of radiation to geometric targets in cancer patients. However, many questions remain on how to best define targets based on biological information, such as functional imaging, and how to combine radiation with other cancer therapies. To help answer these questions, small animal preclinical studies are needed to generate data to inform clinical trials. However, the precise radiation delivery capabilities of IGRT and IMRT have not been available in the preclinical labs. To enable translational experiments …

A Non-Contrast Magnetic Resonance Imaging Technique To Assess Blood-Brain Barrier Permeability, Harini Pandithasekera

Electronic Thesis and Dissertation Repository

The Blood-brain barrier (BBB) regulates the entry of compounds between the blood and the brain, thus plays an important role in brain homeostasis. Studies indicate in disease states such as Alzheimer’s the BBB integrity is compromised. The motive of this project is to investigate the sensitivity of the diffusion-weighted arterial spin labeling (DW-ASL) technique to detect water exchange. Testing the sensitivity requires a reliable method of opening the barrier at specific locations of the brain. Here, a unique technology named focused ultrasound (FUS) has been used to mimic a compromised BBB environment.

A series of experiments were conducted in a …

Resting State Functional Magnetic Resonance And Diffusion Tensor Imaging Of Hemiplegic Cerebral Palsy Patients Treated With Constraint-Induced Movement Therapy: Predictors And Clinically Correlated Evidence Of Neuroplasticity, Kathryn Y. Manning

Electronic Thesis and Dissertation Repository

Hemiplegic cerebral palsy is characterized by unilateral upper limb impairment and patients often compensate by performing most tasks with their unaffected arm. Constraint-induced movement therapy (CIMT) directly combats this learned non-use by casting the unaffected arm and forcing the patient to repetitively practice skills with the hemiplegic limb. Subjects with hemiplegic cerebral palsy were recruited from Holland Bloorview Kids Rehabilitation Hospital, Thames Valley Children’s Centre and McMaster Children’s Hospital. MRI acquisitions and clinical evaluations were collected at baseline, 1 and 6-months later. The case group participated in a CIMT camp after baseline evaluations and was compared to an untreated control …

The Impact Of Lateral Electron Disequilibrium On Stereotactic Body Radiation Therapy Of Lung Cancer, Brandon Disher

Electronic Thesis and Dissertation Repository

Stereotactic Body Radiation Therapy (SBRT) is an effective treatment option for patients with inoperable early-stage lung cancer. SBRT uses online image-guidance technology [e.g. cone-beam CT (CBCT)] to focus small-fields of high energy x-rays onto a tumour to deliver ablative levels of radiation dose (e.g. 54 Gy) in a few treatment fractions (e.g. 3). For the combination of these treatment parameters and a low density lung, lateral electron disequilibrium (LED) can potentially occur, reducing lung and tumour doses. The goal of this thesis was to determine the impact of LED on stereotactic body radiation therapy for lung cancer.

The effect of …

Mri-Based Attenuation Correction In Emission Computed Tomography, Harry R. Marshall

Electronic Thesis and Dissertation Repository

The hybridization of magnetic resonance imaging (MRI) with positron emission tomography (PET) or single photon emission computed tomography (SPECT) enables the collection of an assortment of biological data in spatial and temporal register. However, both PET and SPECT are subject to photon attenuation, a process that degrades image quality and precludes quantification. To correct for the effects of attenuation, the spatial distribution of linear attenuation coefficients (μ-coefficients) within and about the patient must be available. Unfortunately, extracting μ-coefficients from MRI is non-trivial. In this thesis, I explore the problem of MRI-based attenuation correction (AC) in emission tomography.

In particular, I …

Hemodynamics In The Stenosed Carotid Bifurcation With Plaque Ulceration, Emily Y. Wong

Electronic Thesis and Dissertation Repository

The presence of irregular plaque surface morphology or ulceration of the atherosclerotic lesion has been identified as an independent risk factor for ischemic stroke. Doppler ultrasound (DUS) is the most commonly performed non-invasive technique used to assess patients suspected of having carotid artery disease, but currently does not incorporate the diagnosis of plaque ulceration. Advanced Doppler analyses incorporating quantitative estimates of flow disturbances may result in diagnostic indices that identify plaque ulcerative conditions. A technique for the fabrication of DUS-compatible flow phantoms was developed, using a direct-machining method that is amenable to comprehensive DUS investigations. In vitro flow studies in …