Broadband RF‐amplitude‐dependent flip angle pulses with linear phase slope

• Published in: Magnetic resonance in chemistry 2017-09, Vol.55 (9), p.797-803
• Main Authors: Koos, Martin R. M., Feyrer, Hannes, Luy, Burkhard
• Format: Article
• Language: English
• Subjects: Broadband; broadband pulse; Ernst angle; Excitation; excitation pulse; ICEBERG; Linear phase; Medicin och hälsovetenskap; NMR spectroscopy; optimal control theory; RADFA; variable flip angle
• ISSN: 0749-1581; 1097-458X; 1097-458X
• DOI: 10.1002/mrc.4593

Pulse sequences in NMR spectroscopy sometimes require the application of pulses with effective flip angles different from 90° and 180°. Previously (Magn. Reson. Chem. 2015, 53, 886‐893), offset‐compensated broadband excitation pulses with RF‐amplitude‐dependent effective flip angles (RADFA) were introduced that are applicable in such cases. However, especially RF‐amplitude‐restricted RADFA pulses turned out to perform not as good as desired in terms of achievable bandwidths. Here, a class of RF‐amplitude‐restricted RADFA pulses with linear phase slope is introduced that allows excitation over much larger bandwidths with better performance. In this theoretical work, the basic principle of the pulse class is explained, their physical limits explored, and their properties, also compared with other pulse classes, discussed in detail. Copyright © 2017 John Wiley & Sons, Ltd. Many nuclear magnetic resonance pulse sequences require flip angles different from 90° or 180°, which can be achieved by RF‐amplitude variation with previously published rf‐amplitude‐dependent effective flip angle pulses. We present here a novel class of RF‐amplitude‐dependent effective flip angle pulses for excitation of very wide bandwidths at arbitrary flip angles that can be obtained by introducing a linear phase slope in the excitation profile. In this theoretical work, the basic principle is explained, properties are discussed, and physical limits are explored.