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Chemical shift encoding using asymmetric readout waveforms
Author(s) -
Rydén Henric,
Norbeck Ola,
Avventi Enrico,
Skorpil Mikael,
Niekerk Adam,
Skare Stefan,
Berglund Johan
Publication year - 2021
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.28529
Subject(s) - waveform , pulse sequence , sampling (signal processing) , sequence (biology) , encoding (memory) , computer science , pulse (music) , nuclear magnetic resonance , physics , chemistry , artificial intelligence , telecommunications , radar , biochemistry , detector
Purpose To describe a new method for encoding chemical shift using asymmetric readout waveforms that enables more SNR‐efficient fat/water imaging. Methods Chemical shift was encoded using asymmetric readout waveforms, rather than conventional shifted trapezoid readouts. Two asymmetric waveforms are described: a triangle and a spline. The concept was applied to a fat/water separated RARE sequence to increase sampling efficiency. The benefits were investigated through comparisons to shifted trapezoid readouts. Using asymmetric readout waveforms, the scan time was either shortened or maintained to increase SNR. A matched in‐phase waveform is also described that aims to improve the SNR transfer function of the fat and water estimates. The sequence was demonstrated for cervical spine, musculoskeletal (MSK), and optic nerve applications at 3T and compared with conventional shifted readouts. Results By removing sequence dead times, scan times were shortened by 30% with maintained SNR. The shorter echo spacing also reduced T 2 blurring. Maintaining the scan times and using asymmetric readout waveforms achieved an SNR improvement in agreement with the prolonged sampling duration. Conclusions Asymmetric readout waveforms offer an additional degree of freedom in pulse sequence designs where chemical shift encoding is desired. This can be used to significantly shorten scan times or to increase SNR with maintained scan time.