Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7 T

Department of Radiology, Stanford University, Stanford, CA, USA.
Magnetic Resonance in Medicine (Impact Factor: 3.57). 04/2012; 67(4):1077-85. DOI: 10.1002/mrm.23089
Source: PubMed


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.

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