Academic Journal
Phase imaging for reducing macrovascular signal contributions in high-resolution fMRI
| العنوان: | Phase imaging for reducing macrovascular signal contributions in high-resolution fMRI |
|---|---|
| المؤلفون: | Stanley, Olivia W |
| المصدر: | Electronic Thesis and Dissertation Repository |
| بيانات النشر: | Scholarship@Western |
| سنة النشر: | 2021 |
| المجموعة: | The University of Western Ontario: Scholarship@Western |
| مصطلحات موضوعية: | Functional MRI, High resolution fMRI, Gradient echo, Coil Combination, Phase regression, Macrovasculature, Biophysics |
| الوصف: | High resolution functional MRI allows for the investigation of neural activity within the cortical sheet. One consideration in high resolution fMRI is the choice of which sequence to use during imaging, as all methods come with sensitivity and specificity tradeoffs. The most used fMRI sequence is gradient-echo echo planar imaging (GE-EPI) which has the highest sensitivity but is not specific to microvasculature. GE-EPI results in a signal with pial vessel bias which increases complexity of performing studies targeted at structures within the cortex. This work seeks to explore the use of MRI phase signal as a macrovascular filter to correct this bias. First, an in-house phase combination method was designed and tested on the 7T MRI system. This method, the fitted SVD method, uses a low-resolution singular value decomposition and fitting to a polynomial basis to provide computationally efficient, phase sensitive, coil combination that is insensitive to motion. Second, a direct comparison of GE-EPI, GE-EPI with phase regression (GE-EPI-PR), and spin echo EPI (SE-EPI) was performed in humans completing a visual task. The GE-EPI-PR activation showed higher spatial similarity with SE-EPI than GE-EPI across the cortical surface. GE-EPI-PR produced a similar laminar profile to SE-EPI while maintaining a higher contrast-to-noise ratio across layers, making it a useful method in low SNR studies such as high-resolution fMRI. The final study extended this work to a resting state macaque experiment. Macaques are a common model for laminar fMRI as they allow for simultaneous imaging and electrophysiology. We hypothesized that phase regression could improve spatial specificity of the resting state data. Further analysis showed the phase data contained both system and respiratory artifacts which prevented the technique performing as expected under two physiological cleaning strategies. Future work will have to examine on-scanner physiology correction to obtain a phase timeseries without artifacts to allow for the phase ... |
| نوع الوثيقة: | text |
| وصف الملف: | application/pdf |
| اللغة: | English |
| Relation: | https://ir.lib.uwo.ca/etd/8167; https://ir.lib.uwo.ca/context/etd/article/10800/viewcontent/auto_convert.pdf |
| الاتاحة: | https://ir.lib.uwo.ca/etd/8167 https://ir.lib.uwo.ca/context/etd/article/10800/viewcontent/auto_convert.pdf |
| Rights: | http://creativecommons.org/licenses/by/4.0/ |
| رقم الانضمام: | edsbas.ABFE8B19 |
| قاعدة البيانات: | BASE |
| الوصف غير متاح. |