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Snapshot‐CEST: Optimizing spiral‐centric‐reordered gradient echo acquisition for fast and robust 3D CEST MRI at 9.4 T
Author(s) -
Zaiss Moritz,
Ehses Philipp,
Scheffler Klaus
Publication year - 2018
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.3879
Subject(s) - k space , snapshot (computer storage) , flip angle , nuclear magnetic resonance , fast spin echo , physics , image quality , point spread function , magnetic resonance imaging , imaging phantom , computer science , algorithm , optics , artificial intelligence , fourier transform , medicine , quantum mechanics , image (mathematics) , radiology , operating system
Gradient echo (GRE)‐based acquisition provides a robust readout method for chemical exchange saturation transfer (CEST) at ultrahigh field (UHF). To develop a snapshot‐CEST approach, the transient GRE signal and point spread function were investigated in detail, leading to optimized measurement parameters and reordering schemes for fast and robust volumetric CEST imaging. Simulation of the transient GRE signal was used to determine the optimal sequence parameters and the maximum feasible number of k ‐space lines. Point spread function analysis provided an insight into the induced k ‐space filtering and the performance of different rectangular reordering schemes in terms of blurring, signal‐to‐noise ratio (SNR) and relaxation dependence. Simulation results were confirmed in magnetic resonance imaging (MRI) measurements of healthy subjects. Minimal repetition time (TR) is beneficial for snapshot‐GRE readout. At 9.4 T, for TR = 4 ms and optimal flip angle close to the Ernst angle, a maximum of 562 k ‐space lines can be acquired after a single presaturation, providing decent SNR with high image quality. For spiral‐centric reordered k ‐space acquisition, the image quality can be further improved using a rectangular spiral reordering scheme adjusted to the field of view. Application of the derived snapshot‐CEST sequence for fast imaging acquisition in the human brain at 9.4 T shows excellent image quality in amide and nuclear Overhauser enhancement (NOE), and enables guanidyl CEST detection. The proposed snapshot‐CEST establishes a fast and robust volumetric CEST approach ready for the imaging of known and novel exchange‐weighted contrasts at UHF.