Technical innovations in gradient array systems for MRI applications

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buir.advisorAtalar, Ergin
dc.contributor.authorBabaloo, Reza
dc.date.accessioned2023-04-07T11:15:59Z
dc.date.available2023-04-07T11:15:59Z
dc.date.copyright2023-02
dc.date.issued2023-02
dc.date.submitted2023-04-06
dc.descriptionCataloged from PDF version of article.en_US
dc.descriptionThesis (Ph.D.): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2023.en_US
dc.descriptionIncludes bibliographical references (leaves 65-75).en_US
dc.description.abstractIn Magnetic Resonance Imaging, gradient array coils have lately been employed in a variety of applications, such as field profiling. This capability of array technology can be used to minimize electric fields induced by gradient waveforms. For this purpose, a whole-body gradient array with all three gradients is being investigated. Gradient current amplitudes are optimized to produce a target magnetic field within a desired region of linearity (ROL) while minimizing induced electric fields. By reducing the diameter of ROL, generating a target gradient within a slice, and relaxing the linearity error, array coil electric fields are significantly reduced compared to a conventional coil. When a linear gradient is required in a small region, higher gradient strengths and slew rates can be achieved without exceeding peripheral nerve stimulation thresholds. Because of a high number of channels in the array design, feedback controllers significantly raise the system cost due to the expensive current sensors used for gradient current measurements. Thus, a nonlinear second-order feed-forward controller is introduced for the gradient array chain. The feed-forward controller is then modified to update the controller coefficients based on thermal behavior prediction to deal with time-varying parameters caused by temperature-dependent resistances. Gradient current measurements and MRI experiments are conducted to show the effectiveness of the proposed method. In the scope of this thesis, novel applications and hardware solutions are proposed to make array technology valuable and feasible.en_US
dc.description.provenanceSubmitted by Betül Özen (ozen@bilkent.edu.tr) on 2023-04-07T11:15:59Z No. of bitstreams: 1 B161929.pdf: 31672824 bytes, checksum: 234b9f68c329e30ca9e77f50caa17df8 (MD5)en
dc.description.provenanceMade available in DSpace on 2023-04-07T11:15:59Z (GMT). No. of bitstreams: 1 B161929.pdf: 31672824 bytes, checksum: 234b9f68c329e30ca9e77f50caa17df8 (MD5) Previous issue date: 2023-02en
dc.description.statementofresponsibilityby Reza Babalooen_US
dc.format.extentxv, 87 leaves : illustrations ; 30 cm.en_US
dc.identifier.itemidB161929
dc.identifier.urihttp://hdl.handle.net/11693/112323
dc.language.isoEnglishen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectGradient arrayen_US
dc.subjectNonlinear characterizationen_US
dc.subjectFeed-forward controlleren_US
dc.subjectDroop compensationen_US
dc.subjectField optimizationen_US
dc.subjectAdjustable region of linearityen_US
dc.subjectMinimum electric fielden_US
dc.subjectPeripheral nerve stimulationen_US
dc.titleTechnical innovations in gradient array systems for MRI applicationsen_US
dc.title.alternativeMR uygulamaları için gradyan dizi sistemlerindeki teknik yenilikleren_US
dc.typeThesisen_US
thesis.degree.disciplineElectrical and Electronic Engineering
thesis.degree.grantorBilkent University
thesis.degree.levelDoctoral
thesis.degree.namePh.D. (Doctor of Philosophy)

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