Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Physics

Supervisor

Chronik, Blaine A.

Abstract

Magnetic Resonance Imaging (MRI) is a non-invasive imaging modality with excellent soft tissue contrast and sensitivity to tissue temperature. MRI use is growing in Canada with expectation that this is expected to continue in the medium term, with more wide adoption of MRI and in particular a renewed focus on MR systems which deviate from the most commonly used 1.5T field strength system. By implementing systems which do not use as strong magnets and instead operate

Generally, as the field strength of an MR system decreases, the signal received when imaging also decreases, which makes it difficult to implement some applications which are standard at higher field. One such application is temperature mapping on a these <1T >systems, which can be used to monitor thermal therapies interventionally.

This thesis addresses the potentials for implementing temperature mapping at 0.5T, both in the creation of a tissue mimicking phantom which can be used to compare temperature mapping methods and implementing temperature maps both in vivo and in the custom phantom. As well, motivated by the sensitivity that thermal mapping has to external disturbances, the challenges that these accessible MR systems face when being in non-specialized environments is addressed, as this can potentially limit the efficacy of temperature mapping.

This work ultimately demonstrates the acceptable capabilities of a 0.5T system to map temperatures with an adequate temporal resolution, along with presenting practical solutions to operating a system in non-traditional locations.

Summary for Lay Audience

Magnetic Resonance Imaging, or MRI, is a medical imaging technique that helps doctors non-invasively probe the body. It's excellent at showing details of the tissues and organs inside the body and is sensitive to a variety of changes in the body, including changes to the temperature of tissues. Because of this, clinicians have been using standard MRIs to create maps of temperature, which can be used when treating a patient using tumor ablation or other thermal therapies. The use of these maps helps to track the amount of thermal dose being applied to a patient and can ensure that we are not applying too much or too little treatment. In Canada, the use of MRI is growing, and this trend is expected to continue.

Now, there's a new focus on making MRI machines that are different from the ones we usually see. These new MR systems use weaker magnets, which can make them less expensive and easier to install in places that aren’t hospitals or other specialized imaging facilities. However, the tradeoff when using these magnets in places where they are less isolated from their environment is the images we get from MRI are not as clear, although using state of the art components can close much of the quality gap between these lower field systems and the standard counterparts.

This thesis is about finding ways to implement temperature mapping techniques on these lower field MRI systems, particularly at a field strength of 0.5T. We're creating models which accurately mimick properties of human tissue, we test how well temperatures can be measured, and figure out what challenges are faced when placing these MR systems in non-traditional settings like in remote areas or smaller clinics. This research is helping to make MRI more accessible and useful for everyone, while showing the capabilities of imaging on a lower field system can approach what is currently done at higher field strengths.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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