Optimization of sample preparation for MRI of formaldehyde-fixed brains

International audienceMagnetic resonance imaging of post-mortem brains allows long acquisition times up to several days and can be used to obtain high-resolution images at high field (7 T) which can be readily correlated with histological examination of the tissue. However, death and formaldehyde fixation are known to modify severely the relaxivity and diffusion properties of brain tissue. In particular, formaldehyde is known to shorten T2, which drastically reduces SNR.In order to counteract this effect and recover better SNR, free fixative can be washed out by soaking the sample in isotonic saline solution. This has been demonstrated in small biopsy-sized tissue samples, but little data is available concerning whole brain specimens.This study was designed to describe the kinetics of the change of relaxivity and diffusion properties of whole brain specimen at 7 T, during fixation, and during soaking in saline solution, in order to determine optimal soaking times.In the ewe brain, the fixation was found to stabilize after approximately 8 weeks, and the optimal duration of saline soaking is found to be around 3 weeks. These durations can be expected to be longer for larger specimen, such as human brains, which require longer penetration times

Angiographie par résonance magnétique (validation et optimisation pour la surveillance des anévrismes intracrâniens traités par coils GDC (Guglielmi Detachable Coils))

Dans notre travail, l'angiographie par résonance magnétique a été une méthode sensible et très spécifique pour la surveillance d'un reliquat ou la recherche d'une recanalisation d'un anévrisme intracrânien traité par coils GDC. Nos résultats, obtenus avec la technique en temps de vol, n'ont pas été améliorés par l'adjonction de gadolinium, sauf dans un cas d'anévrisme géant. Cette technique d'utilisation du gadolinium à l'état d'équilibre avait été préférée à la technique d'écho de gradient pondéré en T1 avec injection en bolus du gadolinium car, si cette dernière méthode permettait un excellent contraste, sa résolution spatiale était moins bonne avec les paramètres testés. L'angiographie par résonance magnétique présentait de meilleurs résultats que l'analyse radiographique du maillage des coils pour la recherche d'une recanalisation de l'anévrisme embolisé. Les artefacts importants observés lors de l'utilisation du coil Trispan ont été confirmés par une étude in vitro.In our study, MR angiography was a sensitive and very specific method to access the stability of an incomplete occlusion or to diagnose recanalization of the intracranial aneurysm. The use of gadolinium did not improve the ability of 3D time of flight MR angiography to detect the presence of residual or recurrent aneurysm. In one giant aneurysm, the use of intravenous medium contrast did result in improved visualization of a residual aneurysm. With the parameters used, first-pass dynamic contrast-enhanced MR angiography images had a good resolution but its spatial resolution were lower than those on enhanced 3D time of flight MR angiography images performed in the steady state. MR angiography results was better than the analyse of the coil-ball appearance on plain radiographic to predict the instability of angiographic occlusion. The artifact due to the use of a GDC Trispan coil has been confirmed by an in vitro study.TOURS-BU Médecine (372612103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Application of chemical exchange saturation transfer (CEST) in neuroimaging

International audienceSince the early eighties MRI has become the most powerful technic for in-vivo imaging particularly in the field of brain research. This non-invasive method allows acute anatomical observations of the living brain similar to post-mortem dissected tissues. However, one of the main limitation of MRI is that it does not make possible the neurochemical identification of the tissues conversely to positron emission tomography scanner which can provide a specific molecular characterization of tissue, in spite of poor anatomical definition. To gain neurochemical information using MRI, new categories of contrast agents were developed from the beginning of the 2000’s, particularly using the chemical-exchange saturation transfer (CEST) method. This method induces a significant change in the magnitude of the water proton signal and allows the detection of specific molecules within the tissues like sugars, amino acids, transmitters, and nucleosides. This short review presents several CEST contrast agents and their recent developments for in vivo detection of metabolites and neurotransmitters in the brain for research and clinical purposes

Is mri suitable to study the central effect of gonadal steroids during the oestrus cycle in ewes ?

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Impact de l'allaitement artificiel sur la maturation neuroendocrinienne évaluée par analyse de texture d'IRM

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Maternal deprivation and milk replacement affect the integrity of gray and white matter in the developing lamb brain

The psychoendocrine evaluation of lamb development has demonstrated that maternal deprivation and milk replacement alters health, behavior and endocrine profiles. While lambs are able to discriminate familiar and non-familiar conspecifics (mother or lamb), only lambs reared with their mother develop such clear social discrimination or preference. Lambs reared without mother display no preference for a specific lamb from its own group. Differences in exploratory and emotional behaviours between mother-reared and mother deprived lambs have also been reported. As these behavioural abilities are supported by the brain, we hypothesize that rearing with maternal deprivation and milk replacement leads to altered brain development and maturation. To test this hypothesis, we examined brain morphometric and microstructural variables extracted from in-vivo T1-weighted and diffusion-weighted magnetic resonance images acquired longitudinally (1 week, 1.5 months and 4.5 months of age) in mother-reared and mother-deprived lambs. From the morphometric variables the caudate nuclei volume was found to be smaller for mother-deprived than for mother-reared lambs. T1-weighted signal intensity and radial diffusivity were higher for mother-deprived than for mother-reared lambs in both the white and gray matters. The fractional anisotropy of the white matter was lower for mother-deprived than for mother-reared lambs. Based on these morphometric and microstructural characteristics we conclude that maternal deprivation delays and affects lamb brain growth and maturation. This article is protected by copyright. All rights reserved

MRI and luminescence detection of Zn{2+}with a lanthanide complex-zinc finger peptide conjugate.

International audienceA bioinspired probe based on a zinc finger peptide functionalized by a lanthanide(iii)-DOTA monoamide complex turns out to be active for both luminescence and MRI detection of $Zn^{2+}$, depending on the lanthanide cation. A mechanism for MRI-based detection is proposed

MRI contrast agents for quantitative zinc detection

International audienc

MRI contrast agents for quantitative zinc detection

International audienc