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Linda Knutsson

Professor

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Diffusion MRI with pulsed and free gradient waveforms : effects of restricted diffusion and exchange

Författare

  • Arthur Chakwizira
  • Carl-Fredrik Westin
  • Jan Brabec
  • Samo Lasič
  • Linda Knutsson
  • Filip Szczepankiewicz
  • Markus Nilsson

Summary, in English

Monitoring time-dependence with diffusion MRI yields observables sensitive to compartment sizes (restricted diffusion) and membrane permeability (water exchange). However, restricted diffusion and exchange have opposite effects on the diffusion-weighted signal, which can lead to errors in parameter estimates. In this work, we propose a signal representation that incorporates the effects of both restricted diffusion and exchange up to second order in b-value and is compatible with gradient waveforms of arbitrary shape. The representation features mappings from a gradient waveform to two scalars that separately control the sensitivity to restriction and exchange. We demonstrate that these scalars span a two-dimensional space that can be used to choose waveforms that selectively probe restricted diffusion or exchange, eliminating the correlation between the two phenomena. We found that waveforms with specific but unconventional shapes provide an advantage over conventional pulsed and oscillating gradient acquisitions. We also show that parametrisation of waveforms into a two-dimensional space can be used to understand protocols from other approaches that probe restricted diffusion and exchange. For example, we found that the variation of mixing time in filter-exchange imaging corresponds to variation of our exchange-weighting scalar at a fixed value of the restriction-weighting scalar. The proposed signal representation was evaluated using Monte Carlo simulations in identical parallel cylinders with hexagonal and random packing as well as parallel cylinders with gamma-distributed radii. Results showed that the approach is sensitive to sizes in the interval 4 - 12

μm
and exchange rates in the simulated range of 0 to 20 s
-1 , but also that there is a sensitivity to the extracellular geometry. The presented theory constitutes a simple and intuitive description of how restricted diffusion and exchange influence the signal as well as a guide to protocol design capable of separating the two effects.

Avdelning/ar

  • Medicinsk strålningsfysik, Lund
  • MR Physics
  • eSSENCE: The e-Science Collaboration
  • Multidimensional microstructure imaging
  • Diagnostisk radiologi, Lund
  • MultiPark: Multidisciplinary research focused on Parkinson´s disease
  • Neuroradiologi

Publiceringsår

2023

Språk

Engelska

Publikation/Tidskrift/Serie

NMR in Biomedicine

Volym

36

Issue

1

Dokumenttyp

Artikel i tidskrift

Förlag

John Wiley & Sons Inc.

Ämne

  • Other Natural Sciences not elsewhere specified
  • Radiology, Nuclear Medicine and Medical Imaging

Status

Published

Forskningsgrupp

  • MR Physics
  • Multidimensional microstructure imaging
  • Neuroradiology

ISBN/ISSN/Övrigt

  • ISSN: 0952-3480