Transmit array concepts for improved safety in magnetic resonance imaging
Abstract/Contents
- Abstract
- Magnetic resonance imaging (MRI) is a powerful medical imaging modality that can generate high-resolution diagnostic images with excellent soft-tissue contrast. Unlike x-ray and CT, MRI does not use any ionizing radiation and consequently is considered a safe imaging modality for most patients. However, for patients with implanted medical devices, MRI presents significant safety hazards. The transmit radiofrequency (RF) fields used in MRI can induce current in elongated conductors, such as neurostimulator and cardiac pacemaker leads, potentially causing dangerous heating of surrounding tissues. This safety hazard prevents many patients with implanted medical devices from receiving MRI exams, and it also presents challenges for MRI-guided interventional procedures. Much of the RF safety work to date has focused on modifying implanted devices to be safer in the MRI environment. This dissertation presents a different approach to the RF safety problem. Instead of modifying devices for the MRI environment, this work explores how transmit array technology can be used to make the MRI environment itself safer for existing devices by controlling the induced RF current levels that are responsible for heating. A novel toroidal transmit-receive coil for safely visualizing conductive interventional guidewires is presented. This coil transforms conductive guidewires and catheters into controllable elements of a transmit array and allows device visualization using only milliwatts of transmit power. Successful device visualization is demonstrated at 1.5T and 3T. Fluoroptic temperature probe measurements indicate that the low power levels required for device visualization are orders of magnitude below the levels that induce heating in a tissue-mimicking phantom. It is then shown that an array of independently-controllable transmit coils (parallel transmit) can be used to induce minimal RF current in elongated conductors, thereby reducing the RF heating risk, while still allowing visualization of the surrounding volume. Feasibility is demonstrated on a four-channel parallel transmit system at 1.5T, and the current reduction performance is quantified with current sensor measurements and image-based current estimates. Fluoroptic temperature probe measurements confirm that the reduction in current results in the reduction of wire tip heating.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2014 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Etezadi-Amoli, Maryam |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering. |
| Primary advisor | Pauly, John (John M.) |
| Thesis advisor | Pauly, John (John M.) |
| Thesis advisor | Scott, Greig Cameron, 1962- |
| Thesis advisor | Nishimura, Dwight George |
| Advisor | Scott, Greig Cameron, 1962- |
| Advisor | Nishimura, Dwight George |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Maryam Etezadi-Amoli. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2014. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Maryam Etezadi-Amoli
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