2026-09-22T08:04:36Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/81072 2023-07-11 col_2142_5131 col_2142_8888 com_2142_5130 com_2142_8887 com_2142_234

Liang, Zhi-Pei Xu, Dan 2015-09-25T20:09:29Z 2015-09-25T20:09:29Z 10000-01-01 2007 2007 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). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 3301253.pdf: 5565494 bytes, checksum: 6f6718bef04d6b29040acf473d41d220 (MD5) Previous issue date: 2007 Embargo set by: Seth Robbins for item 82354 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs U of I Only 171 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. http://hdl.handle.net/2142/81072 (MiAaPQ)AAI3301253 eng Engineering, Biomedical Design of Multidimensional Large -Tip -Angle Radiofrequency Pulses for Parallel Transmission in Magnetic Resonance Imaging text Electrical and Computer Engineering Electrical and Computer Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.