Milotta, Giorgia;
Corbin, Nadège;
Lambert, Christian;
Lutti, Antoine;
Mohammadi, Siawoosh;
Callaghan, Martina F;
(2022)
Mitigating the impact of flip angle and orientation dependence in single compartment R2* estimates via 2-pool modeling.
Magnetic Resonance in Medicine
10.1002/mrm.29428.
(In press).
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Abstract
Purpose: The effective transverse relaxation rate (R∗ 2) is influenced by biological features that make it a useful means of probing brain microstructure. However, confounding factors such as dependence on flip angle (α) and fiber orientation with respect to the main field (θ) complicate interpretation. The α- and θ-dependence stem from the existence of multiple sub-voxel micro-environments (e.g., myelin and non-myelin water compartments). Ordinarily, it is challenging to quantify these sub-compartments; therefore, neuroscientific studies commonly make the simplifying assumption of a mono-exponential decay obtaining a single R∗ 2 estimate per voxel. In this work, we investigated how the multi-compartment nature of tissue microstructure affects single compartment R∗ 2 estimates. / Methods: We used 2-pool (myelin and non-myelin water) simulations to characterize the bias in single compartment R∗ 2 estimates. Based on our numeric observations, we introduced a linear model that partitions R∗ 2 into α-dependent and α-independent components and validated this in vivo at 7T. We investigated the dependence of both components on the sub-compartment properties and assessed their robustness, orientation dependence, and reproducibility empirically. / Results: R∗ 2 increased with myelin water fraction and residency time leading to a linear dependence on α. We observed excellent agreement between our numeric and empirical results. Furthermore, the α-independent component of the proposed linear model was robust to the choice of α and reduced dependence on fiber orientation, although it suffered from marginally higher noise sensitivity. / Conclusion: We have demonstrated and validated a simple approach that mitigates flip angle and orientation biases in single-compartment R∗ 2 estimates
| Type: | Article |
|---|---|
| Title: | Mitigating the impact of flip angle and orientation dependence in single compartment R2* estimates via 2-pool modeling |
| Location: | United States |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1002/mrm.29428 |
| Publisher version: | https://doi.org/10.1002/mrm.29428 |
| Language: | English |
| Additional information: | Copyright © 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | R2* mapping, T2*, VFA, mono-exponential, multi-compartment, single compartment |
| UCL classification: | UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Imaging Neuroscience UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10156568 |
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