ASL lexicon and reporting recommendations: A consensus report from the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI)

The 2015 consensus statement published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group and the European Cooperation in Science and Technology ( COST) Action ASL in Dementia aimed to encourage the implementation of robust arterial spin labeling (ASL) perfusion MRI for clinical applications and promote consistency across scanner types, sites, and studies. Subsequently, the recommended 3D pseudo-continuous ASL sequence has been implemented by most major MRI manufacturers. However, ASL remains a rapidly and widely developing field, leading inevitably to further divergence of the technique and its associated terminology, which could cause confusion and hamper research reproducibility. On behalf of the ISMRM Perfusion Study Group, and as part of the ISMRM Open Science Initiative for Perfusion Imaging (OSIPI), the ASL Lexicon Task Force has been working on the development of an ASL Lexicon and Reporting Recommendations for perfusion imaging and analysis, aiming to (1) develop standardized, consensus nomenclature and terminology for the broad range of ASL imaging techniques and parameters, as well as for the physiological constants required for quantitative analysis; and (2) provide a community-endorsed recommendation of the imaging parameters that we encourage authors to include when describing ASL methods in scientific reports/papers. In this paper, the sequences and parameters in (pseudo-)continuous ASL, pulsed ASL, velocity-selective ASL, and multi-timepoint ASL for brain perfusion imaging are included. However, the content of the lexicon is not intended to be limited to these techniques, and this paper provides the foundation for a growing online inventory that will be extended by the community as further methods and improvements are developed and established

Consensus-based technical recommendations for clinical translation of renal ASL MRI

Objectives: To develop technical recommendations for the acquisition, processing and analysis of renal ASL data in the human kidney at 1.5T and 3T field strengths that can promote standardization of renal perfusion measurements and facilitate the comparability of results across scanners and in multi-center clinical studies.Methods: An international panel of 23 renal ASL experts followed a modified Delphi process, including on-line surveys and two in-person meetings, to formulate a series of consensus statements regarding patient preparation, hardware, acquisition protocol, analysis steps and data reporting.Results: Fifty-nine statements achieved consensus, while agreement could not be reached on two statements related to patient preparation. As a default protocol, the panel recommends pseudo-continuous (PCASL) or flow-sensitive alternating inversion recovery (FAIR) labeling with a single-slice spin-echo EPI readout with background suppression, and a simple but robust quantification model.Discussion: This approach is considered robust and reproducible and can provide renal perfusion images of adequate quality and SNR for most applications. If extended kidney coverage is desirable, a 2D multislice readout is recommended. These recommendations are based on current available evidence and expert opinion. Nonetheless they are expected to be updated as more data becomes available, since the renal ASL literature is rapidly expanding

Towards multi-physic characterization of spinal cord human pathologies : coupling between multi-parametric MRI and biomechanical finite element modeling

La myélopathie cervicale est une maladie chronique dégénérative de la moelle épinière dont la fréquence augmente avec l’âge. Elle est caractérisée par une compression mécanique menant à un endommagement de la structure médullaire et peut être source de handicaps sévères dégradant la qualité de vie. Néanmoins, la prise en charge clinique reste délicate.C’est pourquoi les travaux conduits dans le cadre de cette thèse se sont focalisés sur la compréhension des phénomènes biomécaniques à l’origine de cet endommagement (via des méthodes de simulation par éléments finis) et les conséquences microstructurelles pouvant être observées par IRM multi-paramétrique. Plus précisément, le but était d’établir un lien entre la cause mécanique et les conséquences structurelles menant aux déficits cliniques afin de mieux comprendre et prédire l’évolution de ces pathologies.Pour atteindre cela, une caractérisation de la morphologie et microstructure de la moelle épinière saine a été conduite par IRM, procurant à la fois une source de données normatives pour évaluer les atteintes chez patients mais aussi des données d’entrée pour raffiner les modèles numériques utilisés. D’un point de vue biomécanique, les phénomènes mécaniques observés lors d’une compression médullaire telle que pouvant être rencontrée dans une myélopathie cervicale ont été étudiés. Bien qu’à confirmer, les résultats obtenus au cours de ces travaux sont encourageants et posent une première pierre vers l’établissement de nouvelles méthodes permettant de mieux comprendre l’origine des déficits observés chez des patients souffrant de lésions médullaires en étudiant le lien entre mécanique, microstructure et fonction.Cervical myelopathy is a chronic degenerative spinal cord pathology whose incidence increases with age. It is characterized by a mechanical compression leading to structural spinal cord damage. It can be at the origin of severe handicap hampering the quality of life. However, the clinical management remains challenging.This is why the work conducted in this thesis was focused on the comprehension of the biomechanics of the spinal cord damage (through numerical simulation finite element methods) and microstructural consequences that can be observed with multi-parametric MR imaging. More specifically, the final goal was to link the mechanical cause to the structural consequences at the origin of the clinical deficits in order to better understand and predict the pathology’s evolution.To reach that end, a characterization of the morphology and microstructure of the spinal cord was achieved using MRI, procuring on one side a normative database useful to study the alterations encountered in patients, and on another side to refine the numerical models employed. From a biomechanical perspective, the mechanisms of spinal cord compression as encountered in cervical myelopathy were studied using finite element analysis. The results obtained, which should be confirmed, are encouraging and represent a first stone towards the establishment of new methods in order to help in the clinical management of patients with spinal cord lesions by linking the mechanics, microstructure and function of the spinal cord

Segmentation of the human spinal cord

International audienceSegmenting the spinal cord contour is a necessary step for quantifying spinal cord atrophy in various diseases. Delineating gray matter (GM) and white matter (WM) is also useful for quantifying GM atrophy or for extracting multiparametric MRI metrics into specific WM tracts. Spinal cord segmentation in clinical research is not as developed as brain segmentation, however with the substantial improvement of MR sequences adapted to spinal cord MR investigations, the field of spinal cord MR segmentation has advanced greatly within the last decade. Segmentation techniques with variable accuracy and degree of complexity have been developed and reported in the literature. In this paper, we review some of the existing methods for cord and WM/GM segmentation, including intensity-based, surface-based, and image-based methods. We also provide recommendations for validating spinal cord segmentation techniques, as it is important to understand the intrinsic characteristics of the methods and to evaluate their performance and limitations. Lastly, we illustrate some applications in the healthy and pathological spinal cord. One conclusion of this review is that robust and automatic segmentation is clinically relevant, as it would allow for longitudinal and group studies free from user bias as well as reproducible multicentric studies in large populations, thereby helping to further our understanding of the spinal cord pathophysiology and to develop new criteria for early detection of subclinical evolution for prognosis prediction and for patient management. Another conclusion is that at the present time, no single method adequately segments the cord and its substructure in all the cases encountered (abnormal intensities, loss of contrast, deformation of the cord, etc.). A combination of different approaches is thus advised for future developments, along with the introduction of probabilistic shape models. Maturation of standardized frameworks, multiplatform availability, inclusion in large suite and data sharing would also ultimately benefit to the community

Fast‐spin‐echo versus rapid gradient‐echo for 3D magnetization‐prepared acquisitions: Application to inhomogeneous magnetization transfer

International audienceTo evaluate the benefits of Fast Spin Echo (FSE) imaging over Rapid Gradient-Echo (RAGE) for Magnetization-prepared inhomogeneous Magnetization Transfer (ihMT) imaging. Methods: A 3D FSE sequence was modified to include an ihMT preparation (ihMT-FSE) with an optional CSF suppression based on an Inversion-Recovery (ihMT-FLAIR). After numerical simulations assessing SNR benefits of FSE and the potential impact of an additional inversion-recovery, ihMT-RAGE, ihMT-FSE and ihMT-FLAIR sequences were compared in a group of 6 healthy volunteers, evaluating image quality, thermal and physiological noise as well as quantification using an ihMTsat approach. A preliminary exploration in the cervical spinal cord was also conducted in a group of 3 healthy volunteers. Results: Several fold improvement in thermal SNR was observed with ihMT-FSE in agreement with numerical simulations. However, we observed significantly higher physiological noise in ihMT-FSE compared to ihMT-RAGE that was mitigated in ihMT-FLAIR, which provided the best total SNR (+74% and 49% compared to ihMT-RAGE in the white and gray matter, p0.004). IhMTsat quantification was successful in all cases with strong correlation between all sequences (r 2 >0.75). Early experiments showed potential for spinal cord imaging. Conclusions: FSE generally offers higher SNR compared to gradient-echo based acquisitions for magnetization-prepared contrasts as illustrated here in the case of ihMT. However, physiological noise has a significant effect, but an IR-based CSF suppression was shown to be efficient in mitigating effects of CSF motion

High-resolution multi-parametric quantitative magnetic resonance imaging of the human cervical spinal cord at 7T

International audienceQuantitative MRI techniques have the potential to characterize spinal cord tissue impairments occurring in various pathologies, from both microstructural and functional perspectives. By enabling very high image resolution and enhanced tissue contrast, ultra-high field imaging may offer further opportunities for such characterization. In this study, a multi-parametric high-resolution quantitative MRI protocol is proposed to characterize in vivo the human cervical spinal cord at 7T. Multi-parametric quantitative MRI acquizitions including T1, T2(*) relaxometry mapping and axial diffusion MRI were performed on ten healthy volunteers with a whole-body 7T system using a commercial prototype coil-array dedicated to cervical spinal cord imaging. Automatic cord segmentation and multi-parametric data registration to spinal cord templates enabled robust regional studies within atlas-based WM tracts and GM horns at the C3 cervical level. T1 value, cross-sectional area and GM/WM ratio evolutions along the cervical cord were also reported. An original correction method for B1(+)-biased T1 mapping sequence was additionally proposed and validated on phantom. As a result, relaxometry and diffusion parameters derived from high-resolution quantitative MRI acquizitions were reported at 7T for the first time. Obtained images, with unmatched resolutions compared to lower field investigations, provided exquisite anatomical details and clear delineation of the spinal cord substructures within an acquisition time of 30min, compatible with clinical investigations. Regional statistically significant differences were highlighted between WM and GM based on T1 and T2* maps (p\textless10(-3)), as well as between sensory and motor tracts based on diffusion tensor imaging maps (p\textless0.05). The proposed protocol demonstrates that ultra-high field spinal cord high-resolution quantitative MRI is feasible and lays the groundwork for future clinical investigations of degenerative spinal cord pathologies

Variable-density Fast-Spin-Echo (FSE) for volumetric inhomogeneous Magnetization Transfer (ihMT) imaging

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Improved volumetric inhomogeneous magnetization transfer (ihMT) using a CSF-suppressed FSE sequence (FLAIR-ihMT)

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Feasibility of single-shot multi-level multi-angle diffusion tensor imaging of the human cervical spinal cord at 7T

International audiencePurposeDiffusion tensor imaging (DTI), which is frequently used to characterize microstructure impairments in many spinal cord diseases at clinical fields, may benefit from 7T investigations. Yet, it presents specific technical challenges, such as increased magnetic susceptibility‐induced image distortions.MethodsEight healthy volunteers were scanned at 7T using a prototype diffusion multi‐slice multi‐angle (MSMA) single‐shot spin‐echo echo planar imaging (EPI) sequence developed to explore the whole cervical spinal cord while limiting the partial volume effects related to the cord curvature. To mitigate the increased susceptibility‐induced distortions encountered at 7T, a reverse phase‐encoding strategy was also used. Images acquired from C1‐to‐C7 were registered to the AMU40 template to automatically extract DTI metrics in gray matter/white matter regions of interest. Effects of urn:x-wiley:07403194:media:mrm27087:mrm27087-math-0001 inhomogeneities on the DTI metrics and repeatability of the measurements were also investigated. Lastly, a DTI acquisition with a 400‐µm in‐plane resolution was acquired on one volunteer to push forward 7T potentialities.ResultsThe MSMA sequence allowed accessing to high‐resolution axial diffusion images sampling the whole cord within a single acquisition. DTI metrics were found in agreement with literature at lower field, stable along a 50–120% relative urn:x-wiley:07403194:media:mrm27087:mrm27087-math-0002 variation range, with a mean inter‐scan coefficient of variation of 8%. The two‐‐fold spatial‐resolution increase of the additional DTI acquisition enabled main white matter tracts visualization on a single‐subject basis.ConclusionAlthough C7‐level imaging needs some improvement, this preliminary study shows that transverse 7T DTI of the whole cervical spinal cord is feasible, laying the groundwork for improved multi‐parametric MR investigations and microstructure characterization of the spinal cord. Magn Reson Med 80:947–957, 2018. © 2018 International Society for Magnetic Resonance in Medicine

Changes of cortical gray matter myelin and microstructure in multiple sclerosis (MS) assessed with quantitative ihMT and MT

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