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Ultrahigh field single‐refocused diffusion weighted imaging using a matched‐phase adiabatic spin echo (MASE)
Author(s) -
Dyvorne Hadrien,
O'Halloran Rafael,
Balchandani Priti
Publication year - 2016
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.25790
Subject(s) - adiabatic process , nuclear magnetic resonance , spin echo , physics , fast spin echo , specific absorption rate , phase (matter) , materials science , optics , nuclear medicine , magnetic resonance imaging , medicine , computer science , telecommunications , radiology , antenna (radio) , quantum mechanics , thermodynamics
Purpose To improve ultrahigh field diffusion‐weighted imaging (DWI) in the presence of inhomogeneous transmit B 1 field by designing a novel semi‐adiabatic single‐refocused DWI technique. Methods A 180° slice‐selective, adiabatic radiofrequency (RF) pulse of 4 ms duration was designed using the adiabatic Shinnar‐Le Roux algorithm. A matched‐phase slice‐selective 90° RF pulse of 8 ms duration was designed to compensate the nonlinear phase of the adiabatic 180° RF pulse. The resulting RF pulse combination, matched‐phase adiabatic spin echo (MASE), was integrated into a single‐shot echo planar DWI sequence. The performance of this sequence was compared with single‐refocused Stejskal‐Tanner (ST), twice‐refocused spin echo (TRSE) and twice‐refocused adiabatic spin echo (TRASE) in simulations, phantoms, and healthy volunteers at 7 Tesla (T). Results In regions with inhomogeneous B 1 , MASE resulted in increased signal intensity compared with ST (up to 64%). Moderate increase in specific absorption rate (35–39%) was observed for adiabatic RF pulses. MASE resulted in higher signal homogeneity at 7T, leading to improved visualization of measures derived from diffusion‐weighted images such as white matter tractography and track density images. Conclusion Efficient adiabatic SLR pulses can be adapted to single‐refocused DWI, leading to substantially improved signal uniformity when compared with conventional acquisitions. Magn Reson Med 75:1949–1957, 2016. © 2015 Wiley Periodicals, Inc.