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Ramped hybrid encoding for improved ultrashort echo time imaging
Author(s) -
Jang Hyungseok,
Wiens Curtis N.,
McMillan Alan B.
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.25977
Subject(s) - encoding (memory) , imaging phantom , ultrashort pulse , temporal resolution , excitation , optics , computer science , materials science , nuclear magnetic resonance , physics , artificial intelligence , laser , quantum mechanics
Purpose We propose a new acquisition to minimize the per‐excitation encoding duration and improve the imaging capability for short T 2 * species. Methods In the proposed ramped hybrid encoding (RHE) technique, gradients are applied before the radiofrequency (RF) pulse as in pointwise encoding time reduction with radial acquisition (PETRA) and zero echo time (ZTE) imaging. However, in RHE, gradients are rapidly ramped after RF excitation to the maximum amplitude to minimize encoding duration. To acquire central k‐space data not measured during RF deadtime, RHE uses a hybrid encoding scheme similar to PETRA. A new gradient calibration method based on single‐point imaging was developed to estimate the k‐space trajectory and enable robust and high quality reconstruction. Results RHE enables a shorter per‐excitation encoding time and provides the highest spatial resolution among ultrashort T 2 * imaging methods. In phantom and in vivo experiments, RHE exhibited robust imaging with negligible chemical shift or blurriness caused by T 2 * decay and unwanted slice selection. Conclusion RHE allows the shortest per‐excitation encoding time for ultrashort T 2 * imaging, which alleviates the impact of fast T 2 * decay occurring during encoding, and enables improved spatial resolution. Magn Reson Med 76:814–825, 2016. © 2015 Wiley Periodicals, Inc.