{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/81072"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/81072","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Design of Multidimensional Large -Tip -Angle Radiofrequency Pulses for Parallel Transmission in Magnetic Resonance Imaging","abstract":"To address the second issue, the difficulty of directly applying the variable-rate selective excitation principle to multidimensional RF pulses (including both single-channel and parallel transmission) is first identified. Then, an alternative approach using a new class of spiral trajectories, termed the variable slew-rate spirals, is proposed to locally reduce B 1 amplitude of 2D RF pulses. The peak B1 reduction is achieved by changing the gradient slew-rate profile, and hardware constraints such as gradient amplitude and slew-rate constraints are inherently satisfied by the design of variable slew-rate spiral gradient waveforms. The governing differential equations for a variable slew-rate spiral are derived, and both numeric and analytic solutions to the equations are given. The variable slew-rate spiral design is applicable to peak B 1 amplitude reduction of both single-channel and parallel transmission RF pulses. The localized manipulation of gradient waveforms empowers variable slew-rate spirals to generate shorter RF pulses than conventional constant slew-rate spiral-based pulses under the same hardware constraints. These shorter RF pulses are in general less sensitive to resonance frequency offsets.","abstract_html":"To address the second issue, the difficulty of directly applying the variable-rate selective excitation principle to multidimensional RF pulses (including both single-channel and parallel transmission) is first identified. Then, an alternative approach using a new class of spiral trajectories, termed the variable slew-rate spirals, is proposed to locally reduce B 1 amplitude of 2D RF pulses. The peak B1 reduction is achieved by changing the gradient slew-rate profile, and hardware constraints such as gradient amplitude and slew-rate constraints are inherently satisfied by the design of variable slew-rate spiral gradient waveforms. The governing differential equations for a variable slew-rate spiral are derived, and both numeric and analytic solutions to the equations are given. The variable slew-rate spiral design is applicable to peak B 1 amplitude reduction of both single-channel and parallel transmission RF pulses. The localized manipulation of gradient waveforms empowers variable slew-rate spirals to generate shorter RF pulses than conventional constant slew-rate spiral-based pulses under the same hardware constraints. These shorter RF pulses are in general less sensitive to resonance frequency offsets.","abstract_has_math":false,"creators":["Xu, Dan"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Electrical and Computer Engineering","degree_department":null,"school":null,"contributors":["Liang, Zhi-Pei"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-09-25T20:09:29Z","date_published":"2015-09-25T20:09:29Z","updated_at":"2026-07-22T22:26:15Z","subjects":["Engineering, Biomedical"],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(MiAaPQ)AAI3301253"],"render_values":[{"text":"(MiAaPQ)AAI3301253","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/81072","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Liang, Zhi-Pei"]},{"key":"dc:creator","label":"Author","values":["Xu, Dan"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2015-09-25T20:09:29Z","10000-01-01","2007"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Electrical and Computer Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Engineering, Biomedical"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/81072","(MiAaPQ)AAI3301253"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["To address the second issue, the difficulty of directly applying the variable-rate selective excitation principle to multidimensional RF pulses (including both single-channel and parallel transmission) is first identified. Then, an alternative approach using a new class of spiral trajectories, termed the variable slew-rate spirals, is proposed to locally reduce B 1 amplitude of 2D RF pulses. The peak B1 reduction is achieved by changing the gradient slew-rate profile, and hardware constraints such as gradient amplitude and slew-rate constraints are inherently satisfied by the design of variable slew-rate spiral gradient waveforms. The governing differential equations for a variable slew-rate spiral are derived, and both numeric and analytic solutions to the equations are given. The variable slew-rate spiral design is applicable to peak B 1 amplitude reduction of both single-channel and parallel transmission RF pulses. The localized manipulation of gradient waveforms empowers variable slew-rate spirals to generate shorter RF pulses than conventional constant slew-rate spiral-based pulses under the same hardware constraints. These shorter RF pulses are in general less sensitive to resonance frequency offsets.","Made available in DSpace on 2015-09-25T20:09:29Z (GMT). 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Then, an alternative approach using a new class of spiral trajectories, termed the variable slew-rate spirals, is proposed to locally reduce B 1 amplitude of 2D RF pulses. The peak B1 reduction is achieved by changing the gradient slew-rate profile, and hardware constraints such as gradient amplitude and slew-rate constraints are inherently satisfied by the design of variable slew-rate spiral gradient waveforms. The governing differential equations for a variable slew-rate spiral are derived, and both numeric and analytic solutions to the equations are given. The variable slew-rate spiral design is applicable to peak B 1 amplitude reduction of both single-channel and parallel transmission RF pulses. The localized manipulation of gradient waveforms empowers variable slew-rate spirals to generate shorter RF pulses than conventional constant slew-rate spiral-based pulses under the same hardware constraints. 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