Recommendations and guidelines from the ISMRM Diffusion Study Group for preclinical diffusion MRI: Part 1 -- In vivo small-animal imaging

The value of in vivo preclinical diffusion MRI (dMRI) is substantial. Small-animal dMRI has been used for methodological development and validation, characterizing the biological basis of diffusion phenomena, and comparative anatomy. Many of the influential works in this field were first performed in small animals or ex vivo samples. The steps from animal setup and monitoring, to acquisition, analysis, and interpretation are complex, with many decisions that may ultimately affect what questions can be answered using the data. This work aims to serve as a reference, presenting selected recommendations and guidelines from the diffusion community, on best practices for preclinical dMRI of in vivo animals. In each section, we also highlight areas for which no guidelines exist (and why), and where future work should focus. We first describe the value that small animal imaging adds to the field of dMRI, followed by general considerations and foundational knowledge that must be considered when designing experiments. We briefly describe differences in animal species and disease models and discuss how they are appropriate for different studies. We then give guidelines for in vivo acquisition protocols, including decisions on hardware, animal preparation, imaging sequences and data processing, including pre-processing, model-fitting, and tractography. Finally, we provide an online resource which lists publicly available preclinical dMRI datasets and software packages, to promote responsible and reproducible research. An overarching goal herein is to enhance the rigor and reproducibility of small animal dMRI acquisitions and analyses, and thereby advance biomedical knowledge.Comment: 69 pages, 6 figures, 1 tabl

Imagerie ihMT filtrée par T1D : caractérisation théorique, validation expérimentale et application sur la pathologie de la myéline

L'imagerie de la myéline par résonance magnétique est challengée par le temps de relaxation transversale très court des protons de la gaine de myéline. Sa structure en multicouches lipidique induit des propriétés magnétiques particulières des protons méthylènes des longues chaines lipidiques, et notamment un non-moyennage des interactions dipolaires. Une saturation radiofréquence hors-résonance provoque un arrangement particulier de ces interactions, appelé ordre dipolaire. Le transfert d’aimantation inhomogène (ihMT) permet d’isoler le signal des protons associés à un ordre dipolaire détectable, offrant ainsi, dans le cadre de l’imagerie du Système Nerveux Central (SNC), une sélectivité accrue aux tissus myélinisés. Le signal ihMT est pondérée par T1D, le temps de relaxation de l'ordre dipolaire, lui-même lié à la dynamique moléculaire lente et la microstructure tissulaire. Dans ce contexte, cette thèse a évalué la possibilité d'isoler les différentes composantes T1D caractérisant les tissus du SNC par filtrage du signal ihMT. La spécificité du signal des différents filtres ihMT-T1D pour la myéline a été évaluée par comparaison à deux références histologiques, et a été comparée à celle de métriques IRM reconnues. En outre, la sensibilité des filtres ihMT-T1D aux altérations de la myéline a été démontrée dans deux modèles de souris : le modèle cuprizone de démyélinisation aiguë et le modèle LPC de démyélinisation focale médullaire. Enfin, dans le but d'obtenir des paramètres quantitatifs plus informatifs de l'état de la myéline, une approche quantitative d’ihMT a été développée et utilisée dans des expériences réalisées sur un fantôme de myéline synthétique.Myelin specific Magnetic Resonance Imaging (MRI) is challenged by the very short transverse relaxation time characteristic of the myelin sheath. The highly organized lipid multi-layered stack ultrastructure of the myelin membrane results in peculiar magnetic properties of the methylene protons along lipid chains, including unaveraged dipolar interactions. Off-resonance radiofrequency saturation can induce a particular arrangement of these dipolar interactions, called dipolar order. Inhomogeneous Magnetization Transfer (ihMT) allows the isolation of signal arising from protons with a detectable dipolar order, thus providing in the context of Central Nervous System (CNS) imaging enhanced selectivity to myelinated tissues. The ihMT signal is weighted by T1D, the dipolar order relaxation time, itself driven by slow molecular dynamics and tissue microstructure. In this context, this thesis investigated the possibility to isolate the various T1D components encountered in CNS tissues by filtering the ihMT signal. Then, the specificity to myelination of various ihMT T1D-filters was assessed by employing histological references for myelin imaging, and was compared with other quantitative MR metrics. Furthermore, the sensitivity of ihMT T1D-filters to myelin alteration was demonstrated in two mouse models: the acute cuprizone model, and the lysophosphatidylcholine focal demyelination model in the spinal cord. Finally, with the objective of obtaining quantitative parameters more informative of the myelin membrane status, a quantitative ihMT framework using a matrix exponential approach was developed and used in experiments performed on a surrogate of the myelin membrane

Caractérisation par transfert d’aimantation inhomogène (ihMT) du réseau de Purkinje dans le cœur par IRM à 7 Teslas

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Caractérisation par transfert d’aimantation inhomogène (ihMT) du réseau de Purkinje dans le cœur par IRM à 7 Teslas

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Evaluation of Inhomogeneous Magnetization Transfer ihMT at 9.4T for the visualization of the Purkinje Network in the heart

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Toward quantitative inhomogeneous magnetization transfer (qihMT) using a general Matrix Exponential Model

International audienceInhomogeneous magnetization transfer is becoming an important tool in the detection of demyelinating pathologies, as well as in the understanding of the molecular mechanisms engaged in demyelinating/remyelinating processes. Although ihMT ratio delivers a reproducible index sensitive to the dipolar order underpinning the ihMT effect, advanced approaches analogous to quantitative MT could allow estimation of quantitative parameters directly related to the underlying biophysical model of myelin. This study proposes a general framework based on the Matrix Exponential Model allowing fast fitting of ihMT data. Demonstration of qihMT is performed ex-vivo on rat spinal cord specimen and in-vivo on mouse brain

Toward quantitative inhomogeneous magnetization transfer (qihMT) using a general Matrix Exponential Model

International audienceInhomogeneous magnetization transfer is becoming an important tool in the detection of demyelinating pathologies, as well as in the understanding of the molecular mechanisms engaged in demyelinating/remyelinating processes. Although ihMT ratio delivers a reproducible index sensitive to the dipolar order underpinning the ihMT effect, advanced approaches analogous to quantitative MT could allow estimation of quantitative parameters directly related to the underlying biophysical model of myelin. This study proposes a general framework based on the Matrix Exponential Model allowing fast fitting of ihMT data. Demonstration of qihMT is performed ex-vivo on rat spinal cord specimen and in-vivo on mouse brain

Modèle exponential matriciel general pour la quantification des paramètres biophysiques tissulaires par transfert d’aimantation inhomogène (ihMT)

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On the dipolar order underlying broad macromolecular lines

International audienceDipolar order has recently regained attention in MRI to analyze dipolar broadened lines in CEST and inhomogeneous Magnetization Transfer (ihMT), leading to new frequency irradiation patterns for enhanced saturation and access to an unexplored degree of freedom. A better understanding of dipolar order is of great interest to guide intuition and may lead to fundamental optimization of the ihMT technique, which is a promising tool providing new tissue contrasts. In this contribution we propose to review this concept, considering a simplified model of isolated proton pairs and the general Provotorov theory of RF saturation which applies to an ensemble of coupled spin

Modèle exponential matriciel general pour la quantification des paramètres biophysiques tissulaires par transfert d’aimantation inhomogène (ihMT)

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