Abstract:
PURPOSE:To improve ultrahigh field diffusion-weighted imaging (DWI) in the presence of inhomogeneous transmit B1 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 B1 , 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.
journal_name
Magn Reson Medjournal_title
Magnetic resonance in medicineauthors
Dyvorne H,O'Halloran R,Balchandani Pdoi
10.1002/mrm.25790subject
Has Abstractpub_date
2016-05-01 00:00:00pages
1949-57issue
5eissn
0740-3194issn
1522-2594journal_volume
75pub_type
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