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Optimal design of gradient waveforms for magnetic resonance imaging

Simonetti, Orlando Paul
http://rave.ohiolink.edu/etdc/view?acc_num=case1056482554

Abstract Details

1992, Doctor of Philosophy, Case Western Reserve University, Biomedical Engineering.
Fourier transform magnetic resonance imaging utilizes temporally varying linear magnetic field gradients to encode spatial information. These gradient waveforms influence image properties such as resolution, signal-to-noise ratio, and sensitivity to motion. This thesis presents a general formalism for the design of gradient waveforms using non-linear constrained optimization. Methods of formulating and solving the optimal waveform design problem are described, and example waveforms and images are displayed for a variety of design objectives and constraint sets. Artificial constraints on waveform shape imposed by multi-lobe waveform designs are eliminated by defining the waveform as a set of discrete amplitudes. These amplitudes are determined subject to the constraints defined by imaging conditions and the specific gradient hardware system of interest. Most waveform design objectives are expressed as linear or quadratic functions of the discrete parameter set, and most constraints as linear functions. Linear and quadratic programming techniques are thus utilized to solve the optimization problem and generate physically realizable waveforms which optimally achieve specific imaging and motion artifact reduction goals. Another important aspect of gradient waveform design explored in this thesis is the relationship between gradient wavefor m time moments and motion sensitivity. Theoretical analysis, computer simulations, and experiments with a computer controlled linear motion phantom reveal several key points. In general, waveform time moments define sensitivity to the time derivatives of position of moving material only at a single point in time: the time about which the moments are computed. A Taylor's Series description of instantaneous position is expanded about this same point in time to compute the phase acquired due to specific derivatives of position. A moment is representative of the phase sensitivity to a particular derivative of position throughout the waveform only when sensitivity to all lower order derivatives is zero. The choice of the moment center or point of expansion adds a degree of freedom which may be used advantageously in the design of motion compensating and motion phase encoding gradient waveforms. These concepts are demonstrated by human imaging examples, and may prove useful in MR angiography and echo planar imaging.
Jeffrey Duerk (Advisor)
294 p.
Engineering, Biomedical
Optimal design gradient waveforms magnetic resonance imaging

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Citations

  • Simonetti, O. P. (1992). Optimal design of gradient waveforms for magnetic resonance imaging [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1056482554

    APA Style (7th edition)

  • Simonetti, Orlando. Optimal design of gradient waveforms for magnetic resonance imaging. 1992. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1056482554.

    MLA Style (8th edition)

  • Simonetti, Orlando. "Optimal design of gradient waveforms for magnetic resonance imaging." Doctoral dissertation, Case Western Reserve University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056482554

    Chicago Manual of Style (17th edition)

case1056482554
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© 1992, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.