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Effects of imaging gradients in sequences with varying longitudinal storage time—Case of diffusion exchange imaging
Author(s) -
Lasič Samo,
Lundell Henrik,
Topgaard Daniel,
Dyrby Tim B.
Publication year - 2018
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.26856
Subject(s) - magnetic resonance imaging , diffusion , nuclear magnetic resonance , diffusion mri , signal (programming language) , materials science , physics , computer science , medicine , radiology , programming language , thermodynamics
Purpose To illustrate the potential bias caused by imaging gradients in correlation MRI sequences using longitudinal magnetization storage (LS) and examine the case of filter exchange imaging (FEXI) yielding maps of the apparent exchange rate (AXR). Methods The effects of imaging gradients in FEXI were observed on yeast cells. To analyze the AXR bias, signal evolution was calculated by applying matrix exponential operators. Results A sharp threshold for the slice thickness was identified, below which the AXR is increasingly underestimated. The bias can be understood in terms of an extended low‐pass diffusion filtering during the LS interval, which is more pronounced at lower exchange rates. For a total exchange rate constant larger than 1 s −1 , the AXR bias is expected to be negligible when slices thicker than 2.5 mm are used. Conclusion In correlation experiments like FEXI, relying on LS with variable duration, imaging gradients may cause disrupting effects that cannot be easily mitigated and should be carefully considered for unbiased results. In typical clinical applications of FEXI, the imaging gradients are expected to cause a negligible AXR bias. However, the AXR bias may be significant in preclinical settings or whenever thin imaging slices are used. Magn Reson Med 79:2228–2235, 2018. © 2017 International Society for Magnetic Resonance in Medicine.