A fast calculation method for magnetic field inhomogeneity due to an arbitrary distribution of bulk susceptibility

Salomir, Rarès; Senneville, Baudouin Denis de; Moonen, Chrit

doi:10.1002/cmr.b.10083

Cited by 351 publications

(398 citation statements)

References 16 publications

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“…Phase imaging is known to depend not only on the shape of the different structures with different susceptibilities (Marques and Bowtell, 2005;Salomir et al, 2003;Schafer et al, 2009) but also on local microstructure (He and Yablonskiy, 2009), on local anisotropy of the magnetic susceptibility (Lee et al, 2010b;Liu, 2010) and even on nonsusceptibility mechanisms such as water exchange mechanisms (Luo et al, 2010;Shmueli et al, 2011;Zhong et al, 2011). In this study the phase shift observed locally between adjacent structures that remain geometrically unchanged during development was used to estimate myelination.…”

Section: Discussionmentioning

confidence: 99%

“…While phase imaging offers an improved contrast between tissues, it should be taken into account that this information is non-local. It represents, at least to a large extent, the convolution of a magnetic susceptibility distribution with the magnetic field generated by magnetic dipole (Marques and Bowtell, 2005;Salomir et al, 2003). Such property makes the contrast observed between two tissues dependent on their orientation relatively to the main magnetic field and to extend beyond their boundaries (Schafer et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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In vivo assessment of myelination by phase imaging at high magnetic field

et al. 2012

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The present study evaluated the potential of using the phase of T 2 * weighted MR images to characterize myelination during brain development and pathology in rodents at 9.4 T. Phase contrast correlated with myelin content assessed by histology and suggests that most contrast between white and cortical gray matter is modulated by myelin. Ex vivo experiments showed that gray-white matter phase contrast remains unchanged after iron extraction. In dysmyelinated shiverer mice, phase imaging correlated strongly with myelin staining, showing reduced contrast between white and gray matter when compared to healthy controls. We conclude that highresolution phase images, acquired at high field, allow assessment of myelination and dysmyelination.© 2011 Elsevier Inc. All rights reserved. IntroductionThe assessment of myelination in healthy subjects and following injury in humans and in animal models is one of the ways to determine the degree of cerebral integrity or the degree of injury in case of white matter disease like multiple sclerosis. In newborns, myelination of the posterior limb of the internal capsule, when assessed at term equivalent, has been shown to be a very robust predictor of motor impairment (Cowan and de Vries, 2005). A simple technique that would access the degree of myelination of white matter would be very useful in mature animal models of white matter injury such as multiple sclerosis and in immature animal models of white matter injury such as periventricular leukomalacia as well as in human studies. There are various methods available: one approach consists of quantification of myelin bond and free water fractions by a multiexponential analysis of the T 2 decay (Beaulieu et al., 1998;MacKay et al., 1994;Whittall and MacKay, 1989;Lancaster et al., 2003). This is generally performed using a CarrPurcell-Meiboom-Gill (CPMG) or a Turbo Spin-Echo sequences with multiple echo times (Beaulieu et al., 1998). Due to specific absorption rate (SAR) (especially at high fields) and timing constraints, the T 2 decay curve is often not fully sampled for an accurate quantification. Recently, it has been shown that myelin water fraction can also be measured using a multi-exponential analysis of the T 2 * decay in multislice multiple echo gradient echo sequence (Du et al., 2007;Hwang et al., 2010). The resulting myelin water fractions are highly dependent on the constraints introduced on the multi-exponential fitting procedure (Hwang et al., 2010) and suffer from significant inaccuracies in regions close to air-tissue interfaces. An alternative approach of a multicomponent relaxation analysis using multicomponent driven equilibrium single pulse observation of T1 and T2 (mcDESPOT) (Deoni et al., 2008) was applied successfully on infants from 3 to 11 months to quantify myelination (Deoni et al., 2011). Magnetization transfer represents an alternative approach to quantify myelin with new approaches refining its modelization by characterizing individually the relaxation and exchange rates of the free water and macromolec...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

In vivo assessment of myelination by phase imaging at high magnetic field

et al. 2012

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“…The frequency shift map was calculated (Fig. 1b) using a method described in the context of MRI (14,15), in which the 3D fast Fourier transform (3DFFT) of the frequency offset is given by:…”

Section: Methodsmentioning

confidence: 99%

Using forward calculations of the magnetic field perturbation due to a realistic vascular model to explore the BOLD effect

Marques

Bowtell

2007

NMR in Biomedicine

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This paper assesses the reliability of the infinite cylinder model used previously in the literature to simulate blood oxygenation level dependent (BOLD) signal changes. A three-dimensional finite element method was applied to a realistic model of the cortical vasculature, and the results compared with those generated from a simple model of the vasculature as a set of independent, randomly oriented, infinite cylinders. The realistic model is based on scanning electron microscopy measurements of the terminal vascular bed in the superficial cortex of the rat. Good agreement is found between the two models with regard to the extravascular R 2 Ã and R 2 dependence on the cerebral blood volume and blood oxygenation fraction. Using the realistic model, it is also possible to gain further understanding of the relative importance of intravascular and extravascular BOLD contrast. A simple parameterisation of the dependence of the relaxation rates on relative cerebral blood volume and blood-tissue susceptibility difference was carried out, allowing discussion of the variation in the form of the haemodynamic response with field strength.

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“…More theoretical work would need to be done for the complex geometry of the GP before an accurate quantification of iron spatial distribution and focal concentration could be made. Work describing a method that uses a first-order perturbation approach to Maxwell's magnetostatic equations, combined with the Fourier transformation technique for calculating magnetic field in the presence of an arbitrary distribution of bulk susceptibility, offers promise that such a complex task could indeed be accomplished (38).…”

Section: Discussionmentioning

confidence: 99%

Measurement of brain iron distribution in Hallevorden‐Spatz syndrome

Szumowski

Bas

Gaarder

et al. 2010

Magnetic Resonance Imaging

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Purpose: To investigate spatial distribution of iron accumulation in the globus pallidus (GP) in patients with Hallevorden-Spatz syndrome (HSS) using phase imaging. We compared sensitivity of a phase imaging technique to relaxation rate measurement methods (R1,R2,R2*) for iron quantification.Materials and Methods: R1, R2, and R2* were measured in GP structure of the brain of eight pantothenate kinaseassociated neurodegeneration (PKAN) patients and a healthy volunteer using a 3T magnetic resonance imaging (MRI) scanner. The phase of gradient-echo images was preprocessed to eliminate phase 2p wrapping and filtered to remove phase background variations. Phase gap across GP structure was used as a metric for iron effects quantification.Results: Among the relaxation rates the most sensitive to iron accumulation was the R2* rate. The R1 and R2 rates demonstrated only small variations in this group of subjects. Up to an order of magnitude phase gap changes were measured between one PKAN patient and an agematched healthy volunteer. Assuming that phase gap differences scale linearly with iron concentration we estimate that up to 2 mg Fe/g ww accumulates in GP of these patients.Conclusion: Our results demonstrate significantly higher sensitivity of the phase measurements for quantitative assessment of iron concentration compared to the relaxation rate measurements. Phase measurements could potentially be used for monitoring a progression and a response to therapy in PKAN.

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A fast calculation method for magnetic field inhomogeneity due to an arbitrary distribution of bulk susceptibility

Cited by 351 publications

References 16 publications

In vivo assessment of myelination by phase imaging at high magnetic field

In vivo assessment of myelination by phase imaging at high magnetic field

Using forward calculations of the magnetic field perturbation due to a realistic vascular model to explore the BOLD effect

Measurement of brain iron distribution in Hallevorden‐Spatz syndrome

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