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Reduced field of view MRI with rapid, B 1 ‐robust outer volume suppression
Author(s) -
Smith Travis B.,
Nayak Krishna S.
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.23116
Subject(s) - spiral (railway) , imaging phantom , pulse sequence , flip angle , pulse (music) , multislice , nuclear magnetic resonance , physics , materials science , signal (programming language) , field of view , optics , magnetic resonance imaging , mathematics , computer science , medicine , radiology , mathematical analysis , detector , programming language
MRI scans are inefficient when the size of the anatomy under investigation is small relative to the subject's full extent. The field of view must be expanded, and acquisition times accordingly prolonged. Shorter scans are feasible with reduced field of view imaging (rFOV) using outer volume suppression (OVS), a magnetization preparation sequence that attenuates signal outside a region of interest (ROI). This work presents a new OVS sequence with a cylindrical ROI, short duration, and improved tolerance for B 1 +inhomogeneity. The sequence consists of a nonselective adiabatic tipdown pulse, which provides B 1 + ‐robust signal suppression, and a fast 2D spiral cylindrical tipback pulse. Analysis of the Bloch equations with transverse initial magnetization reveals a conjugate symmetric constraint for tipback pulses with small flip angles. This property is exploited to achieve two‐shot performance from the single‐shot tipback pulse. The OVS sequence is validated in phantoms and in vivo with multislice spiral imaging at 3 T. The relative signal‐to‐noise ratio efficiency of the proposed sequence was 98% in a phantom and 75–90% in vivo. The effectiveness is demonstrated with cardiovascular rFOV imaging, which exhibits improved resolution and reduced artifacts compared to conventional, full field of view imaging. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.