Effects of imaging gradients in sequences with varying longitudinal storage time-Case of diffusion exchange imaging

Samo Lasic, Henrik Lundell, Daniel Topgaard, Tim Bjørn Dyrby

Research output: Contribution to journalJournal articlepeer-review

236 Downloads (Pure)


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 2.5mm 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.
Original languageEnglish
JournalMagnetic Resonance in Medicine
Issue number4
Pages (from-to)2228-2235
Publication statusPublished - 2017


  • Radiology, Nuclear Medicine and Imaging
  • Crusher
  • Double diffusion encoding
  • FEXI
  • Longitudinal storage
  • Mixing time
  • Slice
  • crusher
  • double diffusion encoding
  • longitudinal storage
  • mixing time
  • slice


Dive into the research topics of 'Effects of imaging gradients in sequences with varying longitudinal storage time-Case of diffusion exchange imaging'. Together they form a unique fingerprint.

Cite this