Detection of Multiple Pathways in the Spinal Cord White Matter Using Q-Ball Imaging

International audienceHigh angular resolution MRI such as q-ball imaging (QBI) allows to recover complex white matter architecture. We applied this technique to an ex vivo spinal cord of one cat using a 3T scanner, 100 directions and b-values varying from 1000 to 3000 s/mm2. As a result, QBI can retrieve crossing fibre information, where the diffusion tensor imaging approach is constrained to a single diffusion direction. To our knowledge, this is the first study demonstrating the benefits of QBI in observing longitudinal, commissural and dorso-ventral fibres in the spinal cord. It is a first step towards in vivo characterization of the healthy and injured spinal cord using high angular resolution diffusion imaging (HARDI) and QBI

Preparation of pure Tl2Ba2CuO6+x: the contribution of phase equilibrium studies

International audienceThe formation of the pure thallium-based cuprate Tl2Ba2CuO6+x (2201) using a convenient process in the ternary TIO1.5-BaO-CuO phase diagram is described. This process is based on the congruent formation of the oxide Tl2Ba2O5 to which CuO is mixed, constituting a quasi-binary system. In the resulting 2201 compound no trace of the main poisoning magnetic impurity BaCuO2 could be detected by AC susceptibility measurements. The orthorhombic to tetragonal transformation is asserted to be due to thallium deficiency which occurs during the heat treatments at a temperature depending on the oxygen partial pressure

Evidence of distributed subpial T2* signal changes at 7T in multiple sclerosis : an histogram based approach

Subpial lesions are the most frequent type of cortical lesion in multiple sclerosis (MS), and are thought to be closely associated with poor clinical outcome. Neuropathological studies report that subpial lesions may come in two major types: they may appear as circumscribed, focal lesions, or extend across multiple adjacent gyri leading to a phenomenon termed “general subpial demyelination” [1]. The in vivo evaluation of diffuse subpial disease is challenging – signal changes may be subtle, and extend across large regions where signal inhomogeneities due to B1 and RF receive coil non-uniformities become more pronounced. Here, we investigate whether a histogram-based analysis of T2* signal intensity in the cortex, at 7T MRI, can show evidence of distributed subpial cortical changes in patients with MS, as described histopathologically. We hypothesized that this phenomenon would be associated with significantly increased T2* signal intensity in patients compared to age-matched controls.Center Algoritm

Comparison of cervical cord results from a quantitative 3D multi-parameter mapping (MPM) protocol of the whole brain with a dedicated cervical cord protocol

We present a comparison of cervical cord metrics obtained using both a whole brain and dedicated cord implementation of a recently introduced quantitative multi-parametric MRI protocol which provides apparent proton density, R1, magnetisation transfer saturation (MTsat) and R2* maps sensitive to microstructural tissue changes in brain and spinal cord. Similar whole cervical cord (levels C1-C5) parameters were obtained using either protocol, and inter-subject variation was low, however in order to investigate tissue-specific cord parameters the dedicated cord protocol with higher in-plane resolution would be desirable

The current state-of-the-art of spinal cord imaging: methods.

A first-ever spinal cord imaging meeting was sponsored by the International Spinal Research Trust and the Wings for Life Foundation with the aim of identifying the current state-of-the-art of spinal cord imaging, the current greatest challenges, and greatest needs for future development. This meeting was attended by a small group of invited experts spanning all aspects of spinal cord imaging from basic research to clinical practice. The greatest current challenges for spinal cord imaging were identified as arising from the imaging environment itself; difficult imaging environment created by the bone surrounding the spinal canal, physiological motion of the cord and adjacent tissues, and small cross-sectional dimensions of the spinal cord, exacerbated by metallic implants often present in injured patients. Challenges were also identified as a result of a lack of "critical mass" of researchers taking on the development of spinal cord imaging, affecting both the rate of progress in the field, and the demand for equipment and software to manufacturers to produce the necessary tools. Here we define the current state-of-the-art of spinal cord imaging, discuss the underlying theory and challenges, and present the evidence for the current and potential power of these methods. In two review papers (part I and part II), we propose that the challenges can be overcome with advances in methods, improving availability and effectiveness of methods, and linking existing researchers to create the necessary scientific and clinical network to advance the rate of progress and impact of the research

Fully automated segmentation of the cervical cord from T1-weighted MRI using PropSeg: Application to multiple sclerosis.

Spinal cord (SC) atrophy, i.e. a reduction in the SC cross-sectional area (CSA) over time, can be measured by means of image segmentation using magnetic resonance imaging (MRI). However, segmentation methods have been limited by factors relating to reproducibility or sensitivity to change. The purpose of this study was to evaluate a fully automated SC segmentation method (PropSeg), and compare this to a semi-automated active surface (AS) method, in healthy controls (HC) and people with multiple sclerosis (MS). MRI data from 120 people were retrospectively analysed; 26 HC, 21 with clinically isolated syndrome, 26 relapsing remitting MS, 26 primary and 21 secondary progressive MS. MRI data from 40 people returning after one year were also analysed. CSA measurements were obtained within the cervical SC. Reproducibility of the measurements was assessed using the intraclass correlation coefficient (ICC). A comparison between mean CSA changes obtained with the two methods over time was performed using multivariate structural equation regression models. Associations between CSA measures and clinical scores were investigated using linear regression models. Compared to the AS method, the reproducibility of CSA measurements obtained with PropSeg was high, both in patients and in HC, with ICC > 0.98 in all cases. There was no significant difference between PropSeg and AS in terms of detecting change over time. Furthermore, PropSeg provided measures that correlated with physical disability, similar to the AS method. PropSeg is a time-efficient and reliable segmentation method, which requires no manual intervention, and may facilitate large multi-centre neuroprotective trials in progressive MS

Microscopy-BIDS: An extension to the brain imaging data structure for microscopy data

The Brain Imaging Data Structure (BIDS) is a specification for organizing, sharing, and archiving neuroimaging data and metadata in a reusable way. First developed for magnetic resonance imaging (MRI) datasets, the community-led specification evolved rapidly to include other modalities such as magnetoencephalography, positron emission tomography, and quantitative MRI (qMRI). In this work, we present an extension to BIDS for microscopy imaging data, along with example datasets. Microscopy-BIDS supports common imaging methods, including 2D/3D, ex/in vivo, micro-CT, and optical and electron microscopy. Microscopy-BIDS also includes comprehensible metadata definitions for hardware, image acquisition, and sample properties. This extension will facilitate future harmonization efforts in the context of multi-modal, multi-scale imaging such as the characterization of tissue microstructure with qMRI

Histological basis of laminar MRI patterns in high resolution images of fixed human auditory cortex

Functional magnetic resonance imaging (fMRI) studies of the auditory region of the temporal lobe would benefit from the availability of image contrast that allowed direct identification of the primary auditory cortex, as this region cannot be accurately located using gyral landmarks alone. Previous work has suggested that the primary area can be identified in magnetic resonance (MR) images because of its relatively high myelin content. However, MR images are also affected by the iron content of the tissue and in this study we sought to confirm that different MR image contrasts did correlate with the myelin content in the grey matter and were not primarily affected by iron content as is the case in the primary visual and somatosensory areas. By imaging blocks of fixed post-mortem cortex in a 7 Tesla scanner and then sectioning them for histological staining we sought to assess the relative contribution of myelin and iron to the grey matter contrast in the auditory region. Evaluating the image contrast in T2*-weighted images and quantitative R2* maps showed a reasonably high correlation between the myelin density of the grey matter and the intensity of the MR images. The correlation with T1-weighted phase sensitive inversion recovery (PSIR) images was better than with the previous two image types, and there were clearly differentiated borders between adjacent cortical areas in these images. A significant amount of iron was present in the auditory region, but did not seem to contribute to the laminar pattern of the cortical grey matter in MR images. Similar levels of iron were present in the grey and white matter and although iron was present in fibres within the grey matter, these fibres were fairly uniformly distributed across the cortex. Thus we conclude that T1- and T2*-weighted imaging sequences do demonstrate the relatively high myelin levels that are characteristic of the deep layers in primary auditory cortex and allow it and some of the surrounding areas to be reliably distinguished

A new elaboration process of the superconducting Tl2Ba2Cu1O6 phase with Tc=90K

International audienceWe have synthesized high quality ceramic Tl2Ba2Cu1O6+δ (2201) samples using the high pressure, high temperature route. At high oxygen content, the structure is orthorhombic and the samples are metallic but non-superconducting. Upon lowering the oxygen content, the symmetry changes from orthorhombic to tetragonal or pseudo-tetragonal. In the latter phase, the maximum superconducting critical temperature reaches 92 K. Optical micrographs show large 2201 grains and some traces of impurity phases like Tl2Ba2O5, Ba2Cu3Ox and CuO. X-ray diffraction shows only the 2201 phase. Plasma emission spectroscopy indicates that the global sample stoichiometry is Tl:Ba:Cu=2:2:1. This analysis proves that the high pressure route effectively prevents the thallium evaporation. HREM investigations exclude the possibility of cation vacancies. Microprobe analyses (EDAX) show no variation of the cation stoichiometry between the 2201 grains. X-ray diffraction on a superconducting single crystal yields a refined composition Tl1.94Ba2Cu1.06O6