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Respiration resolved imaging with continuous stable state 2D acquisition using linear frequency SWEEP
Author(s) -
Jackson L. H.,
Price A. N.,
Hutter J.,
Ho A.,
Roberts T. A.,
Slator P. J.,
Clough J. R.,
Deprez M.,
McCabe L.,
Malik S. J.,
Chappell L.,
Rutherford M. A.,
Hajnal J. V.
Publication year - 2019
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.27834
Subject(s) - sweep frequency response analysis , breathing , signal (programming language) , materials science , excitation , computer science , acoustics , nuclear magnetic resonance , physics , biomedical engineering , biological system , medicine , quantum mechanics , biology , anatomy , programming language
Purpose To investigate the potential of continuous radiofrequency (RF) shifting (SWEEP) as a technique for creating densely sampled data while maintaining a stable signal state for dynamic imaging. Methods We present a method where a continuous stable state of magnetization is swept smoothly across the anatomy of interest, creating an efficient approach to dense multiple 2D slice imaging. This is achieved by introducing a linear frequency offset to successive RF pulses shifting the excited slice by a fraction of the slice thickness with each successive repeat times (TR). Simulations and in vivo imaging were performed to assess how this affects the measured signal. Free breathing, respiration resolved 4D volumes in fetal/placental imaging is explored as potential application of this method. Results The SWEEP method maintained a stable signal state over a full acquisition reducing artifacts from unstable magnetization. Simulations demonstrated that the effects of SWEEP on slice profiles was of the same order as that produced by physiological motion observed with conventional methods. Respiration resolved 4D data acquired with this method shows reduced respiration artifacts and resilience to non‐rigid and non‐cyclic motion. Conclusions The SWEEP method is presented as a technique for improved acquisition efficiency of densely sampled short‐TR 2D sequences. Using conventional slice excitation the number of RF pulses required to enter a true steady state is excessively high when using short‐TR 2D acquisitions, SWEEP circumvents this limitation by creating a stable signal state that is preserved between slices.