Ultra-high Field (7 T) MRI and a Novel Robust Segmentation of Thalamic Nuclei on DWI for Gamma Knife Surgery Purposes: The Targeting of the Ventrointermediate Nucleus

Introduction: Gamma Knife surgery (GKS) is a noninvasive neurosurgical stereotactic procedure, increasingly used as an alternative to open functional procedures. This includes the targeting of the ventrointermediate nucleus of the thalamus (e.g., Vim) for tremor. Objective: To enhance anatomic imaging for Vim GKS using high-field (7 T) MRI and Diffusion Weighted Imaging (DWI). Methods: Five young healthy subjects and two patients were scanned both on 3 and 7 T MRI. The protocol was the same in all cases, and included: T1-weighted (T1w) and DWI at 3T; susceptibility weighted images (SWI) at 7T for the visualization of thalamic subparts. SWI was further integrated into the Gamma Plan Software® (LGP, Elekta Instruments, AB, Sweden) and co-registered with 3T images. A simulation of targeting of the Vim was done using the quadrilatere of Guyot. Furthermore, a correlation with the position of the found target on SWI and also on DWI (after clustering of the different thalamic nuclei) was performed. Results: For the 5 healthy subjects, there was a good correlation between the position of the Vim on SWI, DWI and the GKS targeting. For the patients, on the pretherapeutic acquisitions, SWI helped in positioning the target. For posttherapeutic sequences, SWI supposed position of the Vim matched the corresponding contrast enhancement seen at follow-up MRI. Additionally, on the patient's follow-up T1w images, we could observe a small area of contrast-enhancement corresponding to the target used in GKS (e.g., Vim), which belongs to the Ventral-Lateral-Ventral (VLV) nuclei group. Our clustering method resulted in seven thalamic groups. Conclusion: The use of SWI provided us with a superior resolution and an improved image contrast within the central gray matter, enabling us to directly visualize the Vim. We additionally propose a novel robust method for segmenting the thalamus in seven anatomical groups based on DWI. The localization of the GKS target on the follow-up T1w images, as well as the position of the Vim on 7 T, have been used as a gold standard for the validation of VLV cluster's emplacement. The contrast enhancement corresponding to the targeted area was always localized inside the expected cluster, providing strong evidence of the VLV segmentation accuracy. The anatomical correlation between the direct visualization on 7T and the current targeting methods on 3T (e.g., quadrilatere of Guyot, histological atlases, DWI) seems to show a very good anatomical matching.

Uncertainties in 4pi-gamma coincidence counting

The 4πβ-γ coincidence counting method and its close relatives are widely used for the primary standardization of radioactivity. Both the general formalism and specific implementation of these methods have been well-documented. In particular, previous papers contain the extrapolation equations used for various decay schemes, methods for determining model parameters and, in some cases, tabulated uncertainty budgets. Two things often lacking from experimental reports are both the rationale for estimating uncertainties in a specific way and the details of exactly how a specific component of uncertainty was estimated. Furthermore, correlations among the components of uncertainty are rarely mentioned. To fill in these gaps, the present article shares the best-practices from a few practitioners of this craft. We explain and demonstrate with examples of how these approaches can be used to estimate the uncertainty of the reported massic activity. We describe uncertainties due to measurement variability, extrapolation functions, dead-time and resolving-time effects, gravimetric links, and nuclear and atomic data. Most importantly, a thorough understanding of the measurement system and its response to the decay under study can be used to derive a robust estimate of the measurement uncertainty.

Gamma oscillations in V1 are correlated with GABAA receptor density: A multi-modal MEG and Flumazenil-PET study.

High-frequency oscillations in the gamma-band reflect rhythmic synchronization of spike timing in active neural networks. The modulation of gamma oscillations is a widely established mechanism in a variety of neurobiological processes, yet its neurochemical basis is not fully understood. Modeling, in-vitro and in-vivo animal studies suggest that gamma oscillation properties depend on GABAergic inhibition. In humans, search for evidence linking total GABA concentration to gamma oscillations has led to promising -but also to partly diverging- observations. Here, we provide the first evidence of a direct relationship between the density of GABAA receptors and gamma oscillatory gamma responses in human primary visual cortex (V1). By combining Flumazenil-PET (to measure resting-levels of GABAA receptor density) and MEG (to measure visually-induced gamma oscillations), we found that GABAA receptor densities correlated positively with the frequency and negatively with amplitude of visually-induced gamma oscillations in V1. Our findings demonstrate that gamma-band response profiles of primary visual cortex across healthy individuals are shaped by GABAA-receptor-mediated inhibitory neurotransmission. These results bridge the gap with in-vitro and animal studies and may have future clinical implications given that altered GABAergic function, including dysregulation of GABAA receptors, has been related to psychiatric disorders including schizophrenia and depression.

Aux sources de l'orthopédie clinique : l'histoire revisitée de Jean-André Venel, "père de l'orthopédie" (fin XVIIIe-début XIXe siècle)

(ENGLISH VERSION BELOW) En 1780, le médecin Jean-André Venel fonde à Orbe, dans le canton de Vaud, le premier institut orthopédique connu dans le monde, proposant une version clinique d'un savoir-faire médical ancestral. A travers des sources qui réactualisent les travaux consacrés à Venel, cet article retrace les origines de son institution et de sa pensée médicale, dans un contexte de production et de diffusion d'un savoir particulier en termes de technique du corps et de médecine de l'enfant. Revisitant la figure légendaire - ou mythique ? - de ce que l'histoire de la médecine a retenu comme étant le « père de l'orthopédie », l'article s'interroge par la même occasion sur les conditions d'émergence d'une spécialité médicale au sortir de l'Ancien Régime, et de son impact dans les premières décennies du XIXe siècle. In 1780, the physician Jean-André Venel creates in Orbe (canton of Vaud) the first orthopedic institute of the world, offering a clinical version of an ancient medical savoir-faire. By using sources that enable us to update the scholarship on Venel, this article traces the origins of his institute and of his medical thought, in the context of the production and diffusion of a specialized knowledge on the body and on children. With this new perspective on the legendary, if not mythical, figure, whom the history of medicine has canonized as the "father of orthopedia", this article also examines the conditions of emergence of a medical specialization at the end of the Ancien Régime and its impact in the first decades of the nineteenth century.

Barn owl feathers as biomonitors of mercury: sources of variation in sampling procedures.

Given their central role in mercury (Hg) excretion and suitability as reservoirs, bird feathers are useful Hg biomonitors. Nevertheless, the interpretation of Hg concentrations is still questioned as a result of a poor knowledge of feather physiology and mechanisms affecting Hg deposition. Given the constraints of feather availability to ecotoxicological studies, we tested the effect of intra-individual differences in Hg concentrations according to feather type (body vs. flight feathers), position in the wing and size (mass and length) in order to understand how these factors could affect Hg estimates. We measured Hg concentration of 154 feathers from 28 un-moulted barn owls (Tyto alba), collected dead on roadsides. Median Hg concentration was 0.45 (0.076-4.5) mg kg(-1) in body feathers, 0.44 (0.040-4.9) mg kg(-1) in primary and 0.60 (0.042-4.7) mg kg(-1) in secondary feathers, and we found a poor effect of feather type on intra-individual Hg levels. We also found a negative effect of wing feather mass on Hg concentration but not of feather length and of its position in the wing. We hypothesize that differences in feather growth rate may be the main driver of between-feather differences in Hg concentrations, which can have implications in the interpretation of Hg concentrations in feathers. Finally, we recommend that, whenever possible, several feathers from the same individual should be analysed. The five innermost primaries have lowest mean deviations to both between-feather and intra-individual mean Hg concentration and thus should be selected under restrictive sampling scenarios.

Synergy Sources, Target Autonomy and Integration in Acquisitions

Determining the appropriate level of integration is crucial to realizing value from acquisitions. Most prior research assumes that higher integration implies the removal of autonomy from target managers, which in turn undermines the functioning of the target firm if it entails unfamiliar elements for the acquirer. Using a survey of 86 acquisitions to obtain the richness of detail necessary to distinguish integration from autonomy, the authors argue and find that integration and autonomy are not the opposite ends of a single continuum. Certain conditions (e.g., when complementarity rather than similarity is the primary source of synergy) lead to high levels of both integration and autonomy. In addition, similarity negatively moderates the relationship between complementarity and autonomy when the target offers both synergy sources. In contrast, similarity does not moderate the link between complementarity and integration. The authors' findings advance scholarly understanding about the drivers of implementation strategy and in particular the different implementation strategies acquiring managers deploy when they attempt to leverage complementarities, similarities, or both.

Clinical and biochemical responses after Gamma Knife surgery for a dopamine-secreting paraganglioma: case report.

The efficacy of Gamma Knife surgery (GKS) in local tumor control of non-secreting paragangliomas (PGLs) has been fully described by previous studies. However, with regard to secreting PGL, only one previous case report exists advocating its efficacy at a biological level. The aims of this study were: 1) to evaluate the safety/efficacy of GKS in a dopamine-secreting PGL; 2) to investigate whether the biological concentrations of free methoxytyramine could be used as a marker of treatment efficacy during the follow-up. We describe the case of a 62-year-old man diagnosed with left PGL. He initially underwent complete surgical excision. Thirty months after, he developed recurrent biological and neuroradiological disease; the most sensitive biomarker for monitoring the disease, concentration of plasma free methoxytyramine, started to increase. GKS was performed at a maximal marginal dose of 16 Gy. During the following 30 months, concentration of free methoxytyramine gradually decreased from 0.14 nmol/l (2*URL) before GKS to 0.09 nmol/l, 6 months after GKS and 0.07 nmol/l at the last follow-up after GKS (1.1*URL), confirming the efficacy of the treatment. Additionally, at 30 months there was approximately 36.6% shrinkage from the initial target volume. The GKS treatment was safe and effective, this being confirmed clinically, neuroradiologically and biologically. The case illustrates the importance of laboratory tests taking into account methoxytyramine when analyzing biological samples to assess the biochemical activity of a PGL. In addition, the identification of methoxytyramine as a unique positive biomarker could designate it for the monitoring of tumor relapse after treatments, including Gamma Knife surgery.

Sources en flux: collecter, analyser, archiver, pérenniser. Enseignements d'une collecte de tweets sur le Centenaire de la Grande Guerre

En collectant plus de deux millions de tweets reliés au centenaire de la Grande Guerre, de nombreuses questions méthodologiques se sont posées, interrogeant par exemple la notion de corpus, les relations entre historien.ne.s et archivistes, le traitement du passé à une ère de données massives. Cette intervention se penche sur l'une de ces questions: comment fonder une recherche sur des sources primaires en flux? Comment résoudre la contradiction inhérente entre l'archive, réputée figée, et les données nées numériques qui sont émises en flux?