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NEW METHODS FOR CAROTID MRI
by
Mahender K. Makhijani
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
August 2012
Copyright 2012 Mahender K. Makhijani
Object Description
| Title | New methods for carotid MRI |
| Author | Makhijani, Mahender K. |
| Author email | mahendermakhijani@gmail.com;mahendermakhijani@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Electrical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2012-08-02 |
| Date submitted | 2012-08-02 |
| Date approved | 2012-08-02 |
| Restricted until | 2012-08-02 |
| Date published | 2012-08-02 |
| Advisor (committee chair) | Nayak, Krishna S. |
| Advisor (committee member) |
Ortega, Antonio Hsiai, Tzung |
| Abstract | Magnetic resonance imaging (MRI) is a promising modality for assessment and analysis of arterial plaque because of its inherent 3D nature, excellent soft tissue discrimination, and lack of ionizing radiation. Recently, clinicians have used non-invasive MRI measurements of carotid artery plaque for diagnosis and management of carotid atherosclerosis. However, the development of vessel wall imaging (VWI) in MRI is currently restricted due to low signal-to-noise ratio (SNR), limited resolution and motion artifacts due to long scan times. In addition the standard VWI technique used in MRI relies on suppression of signal from flowing blood in the artery lumen to provide necessary contrast between the plaque and surrounding tissue/blood. In this thesis, I present new methods for imaging of the carotid arteries to improve on some of the current limitations in carotid MRI. ❧ First, I introduce a new technique for improving blood suppression in carotid MRI. In standard carotid MRI approaches a preparatory sequence is used for suppression of flowing blood in order to improve plaque contrast with respect to the lumen. However, the complicated and cyclic flow patterns at the carotid bifurcation result in slow and stagnant blood flow. MR carotid artery images frequently suffer from plaque mimicking artifacts, which may result in incorrect diagnosis. In addition these artifacts are exacerbated in 3D imaging, which might alleviate some SNR limitations. The proposed method utilizes a hybrid preparation for blood suppression that is more robust to stagnant or re-circulant flow with 3D imaging. ❧ Second, I present a new anisotropic 3D cones sampling trajectory for accelerating data acquisition. In carotid MRI a highly anisotropic field-of-view (FOV) is sufficient to cover the anatomy of interest (carotid bifurcation). The proposed trajectory is an extension of Gurney's design to anisotropic FOVs. The resulting FOV is shaped like a flat cylinder while spatial resolution remains isotropic. 3D carotid imaging with a 73.2% reduction in scan time compared to isotropic FOV cones is demonstrated. ❧ Finally, I present a new method for image reconstruction from undersampled data using compressed sensing (CS) theory. CS is a relatively new theory that allows for acceleration and de-noising, and is independent of the traditional MR acceleration techniques. The proposed method utilizes a variant of CS known as model-based CS which allows for higher and more robust acceleration. Preliminary studies have verified the feasibility of CS for achieving modest acceleration rates (<3) in carotid imaging. The proposed method improves on this rate by exploiting correlations and dependencies by imposing a data-driven statistical model. The signal model is trained on an application/anatomy specific training database. A modified recovery algorithm is used to encourage sparse solutions that comply with the learnt model while maintaining robustness of recovery. 3D carotid imaging with rate 4.5 fold acceleration was successfully demonstrated in patients without compromising clinically relevant quantitative endpoints or image quality. |
| Keyword | acceleration; carotid; CS; MRI |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Rights | Makhijani, Mahender K. |
| Access conditions | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@usc.edu |
| Archival file | uscthesesreloadpub_Volume4/etd-MakhijaniM-1116.pdf |
Description
| Title | Page 1 |
| Full text | NEW METHODS FOR CAROTID MRI by Mahender K. Makhijani A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ELECTRICAL ENGINEERING) August 2012 Copyright 2012 Mahender K. Makhijani |
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