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Self‐refocused adiabatic pulse for spin echo imaging at 7 T
Author(s) -
Balchandani Priti,
Khalighi Mohammad Mehdi,
Glover Gary,
Pauly John,
Spielman Daniel
Publication year - 2012
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.23089
Subject(s) - adiabatic process , pulse (music) , spin echo , nuclear magnetic resonance , phase (matter) , physics , signal (programming language) , pulse sequence , imaging phantom , optics , atomic physics , materials science , magnetic resonance imaging , computer science , quantum mechanics , medicine , detector , radiology , programming language
Spin echo pulse sequences are used to produce clinically important T 2 contrast. However, conventional 180° radiofrequency pulses required to generate a spin echo are highly susceptible to the B 1 inhomogeneity at high magnetic fields such as 7 Tesla (7 T), resulting in varying signal and contrast over the region of interest. Adiabatic 180° pulses may be used to replace conventional 180° pulses in spin echo sequences to provide greater immunity to the inhomogeneous B 1 field at 7 T. However, because the spectral profile of an adiabatic 180° pulse has nonlinear phase, pairs of these pulses are needed for proper refocusing, resulting in increased radiofrequency power deposition and long minimum echo times. We used the adiabatic Shinnar Le‐Roux method to generate a matched‐phase adiabatic 90°–180° pulse pair to obviate the need for a second adiabatic 180° pulse for phase refocusing. The pulse pair was then reformulated into a single self‐refocused pulse to minimize the echo time, and phantom and in vivo experiments were performed to validate pulse performance. The self‐refocused adiabatic pulse produced transmit profiles that were substantially more uniform than those achieved using a conventional spin echo sequence. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.