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

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...

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Autores principales: Chakwizira, Arthur, Westin, Carl‐Fredrik, Brabec, Jan, Lasič, Samo, Knutsson, Linda, Szczepankiewicz, Filip, Nilsson, Markus
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10078514/
https://www.ncbi.nlm.nih.gov/pubmed/36075110
http://dx.doi.org/10.1002/nbm.4827
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author Chakwizira, Arthur
Westin, Carl‐Fredrik
Brabec, Jan
Lasič, Samo
Knutsson, Linda
Szczepankiewicz, Filip
Nilsson, Markus
author_facet Chakwizira, Arthur
Westin, Carl‐Fredrik
Brabec, Jan
Lasič, Samo
Knutsson, Linda
Szczepankiewicz, Filip
Nilsson, Markus
author_sort Chakwizira, Arthur
collection PubMed
description 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 parametrization 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 [Formula: see text] and exchange rates in the simulated range of 0 to 20 [Formula: see text] , 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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spelling pubmed-100785142023-04-07 Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange Chakwizira, Arthur Westin, Carl‐Fredrik Brabec, Jan Lasič, Samo Knutsson, Linda Szczepankiewicz, Filip Nilsson, Markus NMR Biomed Research Articles 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 parametrization 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 [Formula: see text] and exchange rates in the simulated range of 0 to 20 [Formula: see text] , 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. John Wiley and Sons Inc. 2022-09-27 2023-01 /pmc/articles/PMC10078514/ /pubmed/36075110 http://dx.doi.org/10.1002/nbm.4827 Text en © 2022 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd. https://creativecommons.org/licenses/by/4.0/This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ (https://creativecommons.org/licenses/by/4.0/) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research Articles
Chakwizira, Arthur
Westin, Carl‐Fredrik
Brabec, Jan
Lasič, Samo
Knutsson, Linda
Szczepankiewicz, Filip
Nilsson, Markus
Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title_full Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title_fullStr Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title_full_unstemmed Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title_short Diffusion MRI with pulsed and free gradient waveforms: Effects of restricted diffusion and exchange
title_sort diffusion mri with pulsed and free gradient waveforms: effects of restricted diffusion and exchange
topic Research Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10078514/
https://www.ncbi.nlm.nih.gov/pubmed/36075110
http://dx.doi.org/10.1002/nbm.4827
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