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

Chakwizira, Arthur LU ; Westin, Carl-Fredrik ; Brabec, Jan LU ; Lasič, Samo ; Knutsson, Linda LU orcid ; Szczepankiewicz, Filip LU orcid and Nilsson, Markus LU (2023) In NMR in Biomedicine 36(1).
Abstract

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... (More)

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.

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Please use this url to cite or link to this publication:
author
; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
NMR in Biomedicine
volume
36
issue
1
article number
e4827
publisher
John Wiley & Sons Inc.
external identifiers
  • pmid:36075110
  • scopus:85138689243
ISSN
0952-3480
DOI
10.1002/nbm.4827
language
English
LU publication?
yes
id
991b2a2c-34a8-4349-91a2-b7fb3ef09a87
date added to LUP
2022-09-11 15:53:28
date last changed
2024-06-27 20:35:21
@article{991b2a2c-34a8-4349-91a2-b7fb3ef09a87,
  abstract     = {{<p>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<br>
 <br>
 μm<br>
 and exchange rates in the simulated range of 0 to 20 s<br>
 -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.<br>
 </p>}},
  author       = {{Chakwizira, Arthur and Westin, Carl-Fredrik and Brabec, Jan and Lasič, Samo and Knutsson, Linda and Szczepankiewicz, Filip and Nilsson, Markus}},
  issn         = {{0952-3480}},
  language     = {{eng}},
  number       = {{1}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{NMR in Biomedicine}},
  title        = {{Diffusion MRI with pulsed and free gradient waveforms : effects of restricted diffusion and exchange}},
  url          = {{http://dx.doi.org/10.1002/nbm.4827}},
  doi          = {{10.1002/nbm.4827}},
  volume       = {{36}},
  year         = {{2023}},
}