23 research outputs found
Off-resonance saturation as an MRI method to quantify mineral- iron in the post-mortem brain
PURPOSE: To employ an offâresonance saturation method to measure the mineralâiron pool in the postmortem brain, which is an endogenous contrast agent that can give information on cellular iron status. METHODS: An offâresonance saturation acquisition protocol was implemented on a 7 Tesla preclinical scanner, and the contrast maps were fitted to an established analytical model. The method was validated by correlation and BlandâAltman analysis on a ferritinâcontaining phantom. Mineralâiron maps were obtained from postmortem tissue of patients with neurological diseases characterized by brain iron accumulation, that is, Alzheimer disease, Huntington disease, and aceruloplasminemia, and validated with histology. Transverse relaxation rate and magnetic susceptibility values were used for comparison. RESULTS: In postmortem tissue, the mineralâiron contrast colocalizes with histological iron staining in all the cases. Iron concentrations obtained via the offâresonance saturation method are in agreement with literature. CONCLUSIONS: Offâresonance saturation is an effective way to detect iron in gray matter structures and partially mitigate for the presence of myelin. If a reference region with little iron is available in the tissue, the method can produce quantitative iron maps. This method is applicable in the study of diseases characterized by brain iron accumulation and can complement existing ironâsensitive parametric methods
Current Understanding of the Anatomy, Physiology, and Magnetic Resonance Imaging of Neurofluids: Update From the 2022 "ISMRM Imaging Neurofluids Study group" Workshop in Rome
Neurofluids is a term introduced to define all fluids in the brain and spine such as blood, cerebrospinal fluid, and interstitial fluid. Neuroscientists in the past millennium have steadily identified the several different fluid environments in the brain and spine that interact in a synchronized harmonious manner to assure a healthy microenvironment required for optimal neuroglial function. Neuroanatomists and biochemists have provided an incredible wealth of evidence revealing the anatomy of perivascular spaces, meninges and glia and their role in drainage of neuronal waste products. Human studies have been limited due to the restricted availability of noninvasive imaging modalities that can provide a high spatiotemporal depiction of the brain neurofluids. Therefore, animal studies have been key in advancing our knowledge of the temporal and spatial dynamics of fluids, for example, by injecting tracers with different molecular weights. Such studies have sparked interest to identify possible disruptions to neurofluids dynamics in human diseases such as small vessel disease, cerebral amyloid angiopathy, and dementia. However, key differences between rodent and human physiology should be considered when extrapolating these findings to understand the human brain. An increasing armamentarium of noninvasive MRI techniques is being built to identify markers of altered drainage pathways. During the three-day workshop organized by the International Society of Magnetic Resonance in Medicine that was held in Rome in September 2022, several of these concepts were discussed by a distinguished international faculty to lay the basis of what is known and where we still lack evidence. We envision that in the next decade, MRI will allow imaging of the physiology of neurofluid dynamics and drainage pathways in the human brain to identify true pathological processes underlying disease and to discover new avenues for early diagnoses and treatments including drug delivery. Evidence level: 1. Technical Efficacy: Stage 3
Current Understanding of the Anatomy, Physiology, and Magnetic Resonance Imaging of Neurofluids: Update From the 2022 â<scp>ISMRM</scp> Imaging Neurofluids Study groupâ Workshop in Rome
Neurofluids is a term introduced to define all fluids in the brain and spine such as blood, cerebrospinal fluid, and interstitial fluid. Neuroscientists in the past millennium have steadily identified the several different fluid environments in the brain and spine that interact in a synchronized harmonious manner to assure a healthy microenvironment required for optimal neuroglial function. Neuroanatomists and biochemists have provided an incredible wealth of evidence revealing the anatomy of perivascular spaces, meninges and glia and their role in drainage of neuronal waste products. Human studies have been limited due to the restricted availability of noninvasive imaging modalities that can provide a high spatiotemporal depiction of the brain neurofluids. Therefore, animal studies have been key in advancing our knowledge of the temporal and spatial dynamics of fluids, for example, by injecting tracers with different molecular weights. Such studies have sparked interest to identify possible disruptions to neurofluids dynamics in human diseases such as small vessel disease, cerebral amyloid angiopathy, and dementia. However, key differences between rodent and human physiology should be considered when extrapolating these findings to understand the human brain. An increasing armamentarium of noninvasive MRI techniques is being built to identify markers of altered drainage pathways. During the threeâday workshop organized by the International Society of Magnetic Resonance in Medicine that was held in Rome in September 2022, several of these concepts were discussed by a distinguished international faculty to lay the basis of what is known and where we still lack evidence. We envision that in the next decade, MRI will allow imaging of the physiology of neurofluid dynamics and drainage pathways in the human brain to identify true pathological processes underlying disease and to discover new avenues for early diagnoses and treatments including drug delivery.Evidence level: 1Technical Efficacy: Stage
ISMRM Open Science Initiative for Perfusion Imaging (OSIPI): ASL pipeline inventory
Purpose: To create an inventory of image processing pipelines of arterial spin labeling (ASL) and list their main features, and to evaluate the capability, flexibility, and ease of use of publicly available pipelines to guide novice ASL users in selecting their optimal pipeline. Methods: Developers selfâassessed their pipelines using a questionnaire developed by the Task Force 1.1 of the ISMRM Open Science Initiative for Perfusion Imaging. Additionally, each publicly available pipeline was evaluated by two independent testers with basic ASL experience using a scoring system created for this purpose. Results: The developers of 21 pipelines filled the questionnaire. Most pipelines are free for noncommercial use (n = 18) and work with the standard NIfTI (Neuroimaging Informatics Technology Initiative) data format (n = 15). All pipelines can process standard 3D single postlabeling delay pseudoâcontinuous ASL images and primarily differ in their support of advanced sequences and features. The publicly available pipelines (n = 9) were included in the independent testing, all of them being free for noncommercial use. The pipelines, in general, provided a tradeâoff between ease of use and flexibility for configuring advanced processing options. Conclusion: Although most ASL pipelines can process the common ASL data types, only some (namely, ASLPrep, ASLtbx, BASIL/Quantiphyse, ExploreASL, and MRICloud) are wellâdocumented, publicly available, support multiple ASL types, have a userâfriendly interface, and can provide a useful starting point for ASL processing. The choice of an optimal pipeline should be driven by specific data to be processed and user experience, and can be guided by the information provided in this ASL inventory
Développements en marquage de spins artériels préclinique
Cerebral blood flow (CBF) characterizes the blood supply to brain tissue. This perfusion-related parameter contributes in diagnosis and therapeutic follow-up in many diseases. The least invasive technique to measure CBF is arterial spin labeling (ASL), where arterial water is used as tracer. The aim of this PhD project, conducted within a CIFRE agreement (Convention Industrielle de Formation par la REcherche), was to increase the performance and to facilitate the use of continuous and pseudo-continuous arterial spin labeling (CASL, pCASL) tools in preclinical studies. CBF quantification by means of ASL is one of the most challenging MRI modalities in terms of the workflow, since additional adjustments, acquisitions and post-processing steps are required. First, to render the workflow smoother for the user, a CASL package has been developed in collaboration with Bruker. This workflow allows easier relative and absolute CBF measurements, thanks to the integration of automated adjustments and reconstruction steps. In a second step, problems arising at high magnetic field were addressed. A strategy to optimize the pCASL labeling sequence in order to obtain robust results was developed and its robustness towards suboptimal shim conditions was demonstrated at 9.4 T in rats. The developed pCASL-package, consisting of three sequences, was shared with ten other institutes worldwide. Another issue encountered at high magnetic fields is heating due to RF power deposition, which was assessed locally in the brain and in the carotids, as well as globally, for the CASL and pCASL sequences and for two different transmit coil configurations. In a third step, time-encoded pCASL was developed in mice in collaboration with teams of the Leiden University Medical Center. This tool enables the simultaneous mapping of CBF and arterial transit time, a parameter that can reflect underlying pathologies such as increased vessel tortuosity or occlusion.Le flux sanguin cĂ©rĂ©bral (CBF) caractĂ©rise la micro-circulation et l'irrigation des tissus. Cette information de perfusion cĂ©rĂ©brale est utilisĂ© en clinique pour le diagnostic et le suivi thĂ©rapeutique de nombreuses maladies. La technique de mesure de CBF la moins invasive est celle par marquage de spins artĂ©riels (ASL) oĂč l'eau du sang fait office de traceur. L'objectif de cette thĂšse, menĂ©e dans le cadre d'une convention CIFRE, consistait Ă faciliter l'utilisation de sĂ©quences ASL continues et pseudo-continues (CASL, pCASL) ainsi qu'Ă amĂ©liorer leur performance en prĂ©-clinique. En effet, la mesure quantitative de CBF par ASL est un protocole complexe qui nĂ©cessite plusieurs Ă©tapes d'ajustements, d'acquisitions et de traitement de donnĂ©es. Dans le but d'allĂ©ger ce protocole, un package CASL a Ă©tĂ© dĂ©veloppĂ© en collaboration avec Bruker. Plusieurs Ă©tapes d'ajustements et de post-processing ont Ă©tĂ© automatisĂ©es, rendant la gĂ©nĂ©ration de cartes CBF relatives et absolues plus aisĂ©e. Le champ magnĂ©tique Ă©levĂ© des scanners IRM prĂ©-cliniques prĂ©sente de nombreux avantages mais est Ă©galement une source de problĂšmes en ASL. Nous nous sommes intĂ©ressĂ©s plus particuliĂšrement Ă deux d'entre eux : l'instabilitĂ© du marquage de spins et l'Ă©chauffement induit par les sĂ©quences ASL. Pour stabiliser le marquage ASL, une stratĂ©gie d'optimisation de la sĂ©quence pCASL a Ă©tĂ© dĂ©veloppĂ©e et testĂ©e chez le rat Ă 9.4 T. Ceci a permis l'obtention d'un marquage robuste, mĂȘme en situations de shim dĂ©gradĂ©. Le package pCASL a Ă©tĂ© partagĂ© avec dix autres instituts dans le monde. L'Ă©chauffement induit lors de sĂ©quences CASL et pCASL par le dĂ©pĂŽt d'Ă©nergie radiofrĂ©quence a Ă©tĂ© caractĂ©risĂ© globalement et localement, dans le cerveau et au niveau des carotides, pour deux configurations d'antenne d'Ă©mission. Pour finir, une sĂ©quence pCASL encodĂ©e en temps a Ă©tĂ© dĂ©veloppĂ©e et appliquĂ©e Ă la souris, dans le cadre d'une collaboration avec des Ă©quipes nĂ©erlandaises du Leiden University Medical Center. Cet outil permet la mesure simultanĂ©e de CBF et du temps de transit artĂ©riel, un paramĂštre pouvant reflĂ©ter des pathologies vasculaires sous-jacentes
Preclinical Spinal Cord Perfusion Imaging with Pseudo-Continuous Arterial Spin Labeling
International audiencePseudo-continuous arterial spin labeling (pCASL) to monitor spinal cord perfusion and hemodynamics has the potential to inform the clinical care of spinal cord injury and other disorders. This work demonstrates successful implementation and application of pCASL of the rodent cervical spinal cord at high field
SAR comparison between CASL and pCASL at high magnetic field and evaluation of the benefit of a dedicated labeling coil
International audienceTo investigate the heating induced by (pseudo)-continuous arterial spin labeling ((p)CASL) sequences in vivo at 9.4T and to evaluate the benefit of a dedicated labeling coil
SAR comparison between CASL and pCASL at high magnetic field and evaluation of the benefit of a dedicated labeling coil
International audienceTo investigate the heating induced by (pseudo)-continuous arterial spin labeling ((p)CASL) sequences in vivo at 9.4T and to evaluate the benefit of a dedicated labeling coil