Fuzzy Fibers: Uncertainty in dMRI Tractography

Fiber tracking based on diffusion weighted Magnetic Resonance Imaging (dMRI) allows for noninvasive reconstruction of fiber bundles in the human brain. In this chapter, we discuss sources of error and uncertainty in this technique, and review strategies that afford a more reliable interpretation of the results. This includes methods for computing and rendering probabilistic tractograms, which estimate precision in the face of measurement noise and artifacts. However, we also address aspects that have received less attention so far, such as model selection, partial voluming, and the impact of parameters, both in preprocessing and in fiber tracking itself. We conclude by giving impulses for future research

The effect of spaceflight and microgravity on the human brain

peer reviewedMicrogravity, confinement, isolation, and immobilization are just some of the features astronauts have to cope with during space missions. Consequently, long-duration space travel can have detrimental effects on human physiology. Although research has focused on the cardiovascular and musculoskeletal system in particular, the exact impact of spaceflight on the human central nervous system remains to be determined. Previous studies have reported psychological problems, cephalic fluid shifts, neurovestibular problems, and cognitive alterations, but there is paucity in the knowledge of the underlying neural substrates. Previous space analogue studies and preliminary spaceflight studies have shown an involvement of the cerebellum, cortical sensorimotor, and somatosensory areas and the vestibular pathways. Extending this knowledge is crucial, especially in view of long-duration interplanetary missions (e.g., Mars missions) and space tourism. In addition, the acquired insight could be relevant for vestibular patients, patients with neurodegenerative disorders, as well as the elderly population, coping with multisensory deficit syndromes, immobilization, and inactivity

Voxel-wise comparisons of cellular microstructure and diffusion-MRI in mouse hippocampus using 3D Bridging of Optically-clear histology with Neuroimaging Data (3D-BOND)

A key challenge in medical imaging is determining a precise correspondence between image properties and tissue microstructure. This comparison is hindered by disparate scales and resolutions between medical imaging and histology. We present a new technique, 3D Bridging of Optically-clear histology with Neuroimaging Data (3D-BOND), for registering medical images with 3D histology to overcome these limitations. Ex vivo 120 × 120 × 200 μm resolution diffusion-MRI (dMRI) data was acquired at 7 T from adult C57Bl/6 mouse hippocampus. Tissue was then optically cleared using CLARITY and stained with cellular markers and confocal microscopy used to produce high-resolution images of the 3D-tissue microstructure. For each sample, a dense array of hippocampal landmarks was used to drive registration between upsampled dMRI data and the corresponding confocal images. The cell population in each MRI voxel was determined within hippocampal subregions and compared to MRI-derived metrics. 3D-BOND provided robust voxel-wise, cellular correlates of dMRI data. CA1 pyramidal and dentate gyrus granular layers had significantly different mean diffusivity (p > 0.001), which was related to microstructural features. Overall, mean and radial diffusivity correlated with cell and axon density and fractional anisotropy with astrocyte density, while apparent fibre density correlated negatively with axon density. Astrocytes, axons and blood vessels correlated to tensor orientation

Sticky bubbles

We discuss the physical forces that are required to remove an air bubble immersed in a liquid from a corner. This is relevant for inkjet printing technology, as the presence of air bubbles in the channels of a printhead perturbs the jetting of droplets. A simple strategy to remove the bubble is to ush the ink past the bubble by providing a high pressure pulse. In this report we rst compute the viscous drag forces that such a ow exerts on the bubble. Then, we compare this to the \sticking forces" on the bubble, due to the capillary interaction with the wall. From this we can estimate the required ow velocities for bubble removal, as a function of channel geometry, contact angle and ink properties. Finally, we investigate other ways to exert a force on a trapped bubble. In particular we focus on forces induced by electric elds which can alter the contact angle of the drop, or by locally applying thermal gradients. Once again, these forces are compared to the sticking forces to identify the parameters where the bubble can be removed

DeepTract: A Probabilistic Deep Learning Framework for White Matter Fiber Tractography

We present DeepTract, a deep-learning framework for estimating white matter fibers orientation and streamline tractography. We adopt a data-driven approach for fiber reconstruction from diffusion weighted images (DWI), which does not assume a specific diffusion model. We use a recurrent neural network for mapping sequences of DWI values into probabilistic fiber orientation distributions. Based on these estimations, our model facilitates both deterministic and probabilistic streamline tractography. We quantitatively evaluate our method using the Tractometer tool, demonstrating competitive performance with state-of-the art classical and machine learning based tractography algorithms. We further present qualitative results of bundle-specific probabilistic tractography obtained using our method. The code is publicly available at: https://github.com/itaybenou/DeepTract.git

Pre-service teachers linking their metalinguistic knowledge to their practice: A functional approach

Existing work in Anglophone countries has raised concerns regarding teachers’ knowledge about language (KAL); this may well be an issue in other countries also, with notable exceptions such as Finland. In Australia, with the introduction of the new Australian Curriculum, the question of teacher KAL has become crucial. Teachers, both practising and pre-service, generally have some knowledge about language as an object, usually including the text structures of particular school genres and information about sentence structure and word classes. This knowledge may be based on traditional grammar and may not be well applied above the sentence level. Teachers may also have an intuitive knowledge of discourse structures and are beginning to reflect on their own discourse using understandings of dialogic teaching. This paper provides an example of how first-year pre-service teachers (PSTs) were introduced to KAL at both the grammatical and the discourse levels, as part of an introductory unit on spoken language. A range of approaches was used, including a functional view of discourse. The PSTs then applied their KAL by putting it into a context that was meaningful for them: discussing their own practice. The paper gives an illustration of some of the work they produced that demonstrates their emerging understandings

Heritability Estimation of Reliable Connectomic Features*

Brain imaging genetics is an emerging research field to explore the underlying genetic architecture of brain structure and function measured by different imaging modalities. However, not all the changes in the brain are a consequential result of genetic effect and it is usually unknown which imaging phenotypes are promising for genetic analyses. In this paper, we focus on identifying highly heritable measures of structural brain networks derived from diffusion weighted imaging data. Using the twin data from the Human Connectome Project (HCP), we evaluated the reliability of fractional anisotropy measure, fiber length and fiber number of each edge in the structural connectome and seven network level measures using intraclass correlation coefficients. We then estimated the heritability of those reliable network measures using SOLAR-Eclipse software. Across all 64,620 network edges between 360 brain regions in the Glasser parcellation, we observed ~5% of them with significantly high heritability in fractional anisotropy, fiber length or fiber number. All the tested network level measures, capturing the network integrality, segregation or resilience, are highly heritable, with variance explained by the additive genetic effect ranging from 59% to 77%

Mesures visant à freiner la hausse des coûts dans l’assurance obligatoire des soins : rapport du groupe d'experts

La santé est un des ingrédients fondamentaux du bien-être humain. On peut escompter que l’élévation du niveau de vie, la multiplication des maladies chroniques et le risque croissant de multimorbidité dû à l’évolution démographique entraînent une hausse des coûts de la santé imputable à plusieurs facteurs. Au total, ces coûts sont passés de 37,5 milliards de francs en 1996 à 77,8 milliards en 2015, tandis que ceux de l'AOS ont grimpé de 10,8 à 27,5 milliards de francs. Notons qu'au cours de cette période en question, l’importance économique a augmenté non seulement en termes absolus mais également rapporté au produit intérieur brut (PIB), indice qui mesure la performance économique d’un pays. Alors que les coûts globaux de la santé représentaient, en 1996, 9,2 % du PIB par année, ce pourcentage était supérieur à 12 en 2015. En comparaison avec la croissance démographique, les coûts des soins de santé ont également augmenté de façon disproportionnée: la progression des prestations nettes dans l’AOS est en effet de 4 % environ par assuré en moyenne, soit 3,5 % déduction faite de l’inflation. Certes, les bases de données ne sont pas parfaites, mais le faisceau d’indices pointant une tendance à l’accélération de la hausse des coûts est incontestable. Pour tenter de la freiner, une intervention politique s’impose de plus en plus, si bien que les mesures de nature à permettre au système de santé de rester financièrement viable sur la durée, tant pour les payeurs de primes que les pouvoirs publics, gagnent en importance. Les mesures envisagées dans le présent rapport visent en particulier à éviter que des prestations médicales inutiles et évitables soient fournies et, partant, à contribuer à freiner la hausse des coûts. (Contexte