Collective proposal distributions for nonlinear MCMC samplers : Mean-field theory and fast implementation

Funding Information: ∗This research was conducted while A.D. was supported by an EPSRC-Roth scholarship co-funded by the Engineering and Physical Sciences Research Council and the Department of Mathematics at Imperial College London. Publisher Copyright: © 2022, Institute of Mathematical Statistics. All rights reserved.Over the last decades, various “non-linear” MCMC methods have arisen. While appealing for their convergence speed and efficiency, their practical implementation and theoretical study remain challenging. In this paper, we introduce a non-linear generalization of the Metropolis-Hastings algorithm to a proposal that depends not only on the current state, but also on its law. We propose to simulate this dynamics as the mean field limit of a system of interacting particles, that can in turn itself be understood as a generalisation of the Metropolis-Hastings algorithm to a population of particles. Under the double limit in number of iterations and number of particles we prove that this algorithm converges. Then, we propose an efficient GPU implementation and illustrate its performance on various examples. The method is particularly stable on multimodal examples and converges faster than the classical methods.Peer reviewe

Relationships between radiographic parameters and spinopelvic muscles in adult spinal deformity patients

Introduction While the clinical impact of coronal and sagittal alignment in adult spinal deformity (ASD) patients (pts) is established, there is a paucity of data in terms of axial plane deformity and potential association between muscle degenera- tion and 3D deformity. The purpose of this study was to analyze spinopelvic muscles characteristics in association with the 3D deformity of ASD patients. Methods This is a prospective cohort study; primary lumbar scoliosis patients (Cobb > 20°) were enrolled and sustained a low-dose X-rays with 3D spinal reconstructions and a fat/water separation MRI (from C7 to the knee). Volumetric 3D reconstructions and fat infiltration (FI) of 6 muscles groups were performed. Relationships between muscular data, radio- graphic parameters and health-related quality of life were investigated. Patients were stratified and compared based on the SRS classification, the odontoid-hip axis (ODHA) angle (> or 0.05). Pts with ODHA > 6.1° or pelvic incidence minus lumbar lordosis > 10° had significantly higher FI for the 6 muscular groups, patients with pelvic tilt > 20° had significantly higher FI for erector spinae, hip flexors and extensors (p < 0.05). SF36-PCS significantly correlated with the muscular volume; SRS and Oswestry disability index correlated with the erectors spinae volume (p < 0.05). Conclusion This study analyzed for the first time the relationship between 3D radiographic parameters and muscular charac- teristics in ASD. Sagittal malalignment is associated with increased FI and decreased muscle volumes with poor outcomes

Volume of spinopelvic muscles: comparison between adult spinal deformity patients and asymptomatic subjects

Purpose: Spinal muscles are a major component of posture in spinal pathologies and changes to the spine with aging. Specifically, spinopelvic muscles may compensate for underlying anomalies such as pelvic retroversion, knee flexion, and cervical or thoracic spinal balance abnormalities. To increase understanding between muscular characteristics and compensatory mechanisms, this study aimed to compare the volume of spinopelvic muscles in adults with a spinal deformity (ASD) to a control group of well-aligned adult subjects. Methods: Twenty-eight lumbar ASD patients [Cobb angle > 20°, > 40 years old (yo)] were prospectively included and compared to 35 normal subjects divided into 2 different groups: one group of young (Y) subjects (n = 23,  40 yo). All subjects had a fat/water separation MRI (from C7 to the knees). Volumetric 3D reconstructions of 30 spinopelvic muscles were performed and muscles volumes were compared. Results: Mean age was 60 ± 16 yo, without significant differences between the ASD and O groups (57 ± 11 yo). Age and BMI were smaller in the young group. Mean Cobb angle of the ASD group was 45 ± 11°. Comparing the ASD and O groups, total muscular volume was similar; however, erector spinae (0.24 ± 0.06 vs 0.68 ± 0.08 dm3, p = 0.001), iliopsoas (0.49 ± 0.09 vs 0.60 ± 0.09 dm3, p = 0.001) and obliquus (0.42 ± 0.08 vs 0.50 ± 0.08 dm3, p = 0.02) were significantly smaller in the ASD group. Comparing the Y and the ASD groups, total muscular volume was higher in the Y group than the ASD group (+ 3.3 dm3, p = 0.003) and erector spinae (0.24 ± 0.06 vs 0.74 ± 0.08, p = 0.0001), gluteus medius (0.51 ± 0.07 vs 0.62 ± 0.13, p = 0.01) and vastus lateralis (1.33 ± 0.21 vs 2.08 ± 0.29, p = 0.001) were significantly bigger in the Y group. Conclusion: This is the first study to compare volume of spinopelvic muscles between ASD patients and a control group without spinal deformity. Our results demonstrate that muscular degeneration has a double origin: aging and deformity. Erector spinae, iliopsoas, and obliquus are the muscles most affected by degeneration

Kinetic DTI of the cervical spine: diffusivity changes in healthy subjects

Introduction The study aims to assess the influence of neck extension on water diffusivity within the cervical spinal cord. Methods IRB approved the study in 22 healthy volunteers. All subjects underwent anatomical MR and diffusion tensor imaging (DTI) at 1.5 T. The cervical cord was imaged in neutral (standard) position and extension. Segmental vertebral rotations were analyzed on sagittal T2-weighted images using the SpineView® software. Spinal cord diffusivity was measured in cross-sectional regions of interests at multiple levels (C1–C5). Results As a result of non-adapted coil geometry for spinal extension, 10 subjects had to be excluded. Image quality of the remaining 12 subjects was good without any deteriorating artifacts. Quantitative measurements of vertebral rotation angles and diffusion parameters showed good intra-rater reliability (ICC= 0.84–0.99). DTI during neck extension revealed significantly decreased fractional anisotropy (FA) and increased radial diffusivity (RD) at the C3 level and increased apparent diffusion coefficients (ADC) at the C3 and C4 levels (p < 0.01 Bonferroni corrected). The C3/C4 level corresponded to the maximal absolute change in segmental vertebral rotation between the two positions. The increase in RD correlated positively with the degree of global extension, i.e., the summed vertebral rotation angle between C1 and C5 (R= 0.77, p= 0.006). Conclusion Our preliminary results suggest that DTI can quantify changes in water diffusivity during cervical spine extension. The maximal differences in segmental vertebral rotation corresponded to the levels with significant changes in diffusivity (C3/C4). Consequently, kinetic DTI measurements may open new perspectives in the assessment of neural tissue under biomechanical constraint

An Attempt of Early Detection of Poor Outcome after Whiplash

The main concern with whiplash is that a large proportion of whiplash patients experience disabling symptoms or whiplash-associated disorders (WAD) for months if not years following the accident. Therefore, identifying early prognostic factors of WAD development is important as WAD have widespread clinical and economic consequences. In order to tackle that question, our study was specifically aimed at combining several methods of investigation in the same WAD patients at the acute stage and 6 months later. Our longitudinal, open, prospective, multi-center study included 38 whiplash patients, and 13 healthy volunteers matched for age, gender, and socio-economic status with the whiplash group. Whiplash patients were evaluated 15–21 days after road accident, and 6 months later. At each appointment, patients underwent a neuropsychological evaluation, a full clinical neurological examination, neurophysiological and postural tests, oto-neurological tests, cervical spine cord magnetic resonance imaging (MRI) with tractography (DTI). At 6 months, whiplash patients were categorized into two subgroups based on the results of the Diagnostic and Statistical Manual of Mental Disorders as having either favorable or unfavorable progression [an unfavorable classification corresponding to the presence of post-concussion symptom (PCS)] and we searched retrospectively for early prognostic factors of WAD predicting the passage to chronicity. We found that patients displaying high level of catastrophizing at the acute stage and/or post-traumatic stress disorder associated with either abnormalities in head or trunk kinematics, abnormal test of the otolithic function and at the Equitest or a combination of these syndromes, turned to chronicity. This study suggests that low-grade whiplash patients should be submitted as early as possible after the trauma to neuropsychological and motor control tests in a specialized consultation. In addition, they should be evaluated by a neuro-otologist for a detailed examination of vestibular functions, which should include cervical vestibular evoked myogenic potential. Then, if diagnosed at risk of WAD, these patients should be subjected to an intensive preventive rehabilitation program, including vestibular rehabilitation if required.This study was funded by the French Fondation Sécurité Routièr

Increase in Il-31 Serum Levels Is Associated with Reduced Structural Damage in Early Axial Spondyloarthritis

In spondyloarthritis, little is known about the relation between circulating cytokines and patient phenotype. We have quantified serum levels of T helper type 1 cell (Th1), Th2 and Th17 cytokines in patients with recent-onset axial spondyloarthritis (AxSpA) from the DESIR cohort, a prospective, multicenter French cohort consisting of 708 patients with recent-onset inflammatory back pain (duration >3 months but <3 years) suggestive of AxSpA. Serum levels of Th1, Th2, and Th17 cytokines were assessed at baseline in patients from the DESIR cohort fulfilling the ASAS criteria (ASAS+) and were compared with age- and sex-matched healthy controls. At baseline, ASAS+ patients (n = 443) and healthy controls (n = 79) did not differ in levels of most of the Th1, Th2 and Th17 cytokines except for IL-31, and sCD40L, which were significantly higher for ASAS+ patients than controls (p < 0.001 and p = 0.012, respectively). On multivariable analysis of ASAS+ patients, IL-31 level was associated with sCD40L level (p < 0.0001), modified Stoke AS Spine Score (mSASSS) < 1 (p = 0.035). The multivariable analyses showed that IL-31 was an independent factor associated with mSASSS < 1 (p = 0.001) and low bone mineral density (p = 0.01). Increased level of IL-31 might protect against structural damage but is also related to low BMD

History page : leaders in MSK radiology : Jacques Forestier (1890-1978)

This history page in the series "Leaders in MSK Radiology" is dedicated to the memory and achievements of the French physician Jacques Forestier, whose name is connected with the medical eponym Forestier's disease, later referred to as diffuse idiopathic skeletal hyperostosis