On the correction of spiral trajectories on a preclinical MRI scanner with a high-performance gradient insert.

This study aimed to examine different trajectory correction methods for spiral imaging on a preclinical scanner with high-performance gradients with respect to image quality in a phantom and in vivo. The gold standard method of measuring the trajectories in a separate experiment is compared to an isotropic delay-correction, a correction using the gradient system transfer function (GSTF), and a combination of the two. Three different spiral trajectories, with 96, 16, and three interleaves, are considered. The best image quality is consistently achieved when determining the trajectory in a separate phantom measurement. However, especially for the spiral with 96 interleaves, the other correction methods lead to almost comparable results. Remaining imperfections in the corrected gradient waveforms and trajectories are attributed to asymmetrically occurring undulations in the actual, generated gradients, suggesting that the underlying assumption of linearity is violated. In conclusion, images of sufficient quality can be acquired on preclinical small-animal scanners using spiral k-space trajectories without the need to carry out separate trajectory measurements each time. Depending on the trajectory, a simple isotropic delay-correction or a GSTF-based correction can provide images of similar quality.

Gut Microbiome in Children with Congenital Heart Disease After Cardiopulmonary Bypass Surgery (GuMiBear Study).

The gut microbiome of infants with congenital heart disease (CHD) undergoing cardiopulmonary bypass surgery (CPB) is at risk of profound alteration. The aim of this study was to examine the gut microbiome pre- and post-bypass surgery to explore potential implications of altered gut biodiversity. A prospective cohort study involving infants with CHD who underwent CPB was performed. Faecal samples were collected from infants alongside the collection of demographic and clinical data in order to examine gut microbiome changes before and after surgery. 16S rRNA sequencing analysis was performed on DNA isolated from stool samples to determine changes in gut microbiome composition. Thirty-three patients were recruited, with samples from thirteen of these available for final analysis. Compared with healthy, matched controls, at a genus level, pre-operative samples for infants with CHD demonstrated a higher relative abundance of Escherichia-Shigella (31% vs 2-6%) and a lower relative abundance of Bifidobacterium (13% vs 40-60%). In post-operative samples, the relative abundance of Escherichia-Shigella (35%), Enterococcus (11%), Akkermansia (6%), and Staphylococcus (5%) were higher than pre-op samples. One infant developed post-operative necrotising-enterocolitis (NEC). They displayed a marked abundance of the Enterococcus (93%) genus pre-operatively. This study demonstrates that infants with CHD have an altered gut microbiome when compared with healthy controls and there might be a possible link between an abundance of virulent species and NEC.

Cardiac q-space trajectory imaging by motion-compensated tensor-valued diffusion encoding in human heart in vivo.

PURPOSE: Tensor-valued diffusion encoding can probe more specific features of tissue microstructure than what is available by conventional diffusion weighting. In this work, we investigate the technical feasibility of tensor-valued diffusion encoding at high b-values with q-space trajectory imaging (QTI) analysis, in the human heart in vivo. METHODS: Ten healthy volunteers were scanned on a 3T scanner. We designed time-optimal gradient waveforms for tensor-valued diffusion encoding (linear and planar) with second-order motion compensation. Data were analyzed with QTI. Normal values and repeatability were investigated for the mean diffusivity (MD), fractional anisotropy (FA), microscopic FA (µFA), isotropic, anisotropic and total mean kurtosis (MKi, MKa, and MKt), and orientation coherence (Cc ). A phantom, consisting of two fiber blocks at adjustable angles, was used to evaluate sensitivity of parameters to orientation dispersion and diffusion time. RESULTS: QTI data in the left ventricular myocardium were MD = 1.62 ± 0.07 µm2 /ms, FA = 0.31 ± 0.03, µFA = 0.43 ± 0.07, MKa = 0.20 ± 0.07, MKi = 0.13 ± 0.03, MKt = 0.33 ± 0.09, and Cc  = 0.56 ± 0.22 (mean ± SD across subjects). Phantom experiments showed that FA depends on orientation dispersion, whereas µFA was insensitive to this effect. CONCLUSION: We demonstrated the first tensor-valued diffusion encoding and QTI analysis in the heart in vivo, along with first measurements of myocardial µFA, MKi, MKa, and Cc . The methodology is technically feasible and provides promising novel biomarkers for myocardial tissue characterization.

Endothelial IGF-1 receptor mediates crosstalk with the gut wall to regulate microbiota in obesity.

Changes in composition of the intestinal microbiota are linked to the development of obesity and can lead to endothelial cell (EC) dysfunction. It is unknown whether EC can directly influence the microbiota. Insulin-like growth factor-1 (IGF-1) and its receptor (IGF-1R) are critical for coupling nutritional status and cellular growth; IGF-1R is expressed in multiple cell types including EC. The role of ECIGF-1R in the response to nutritional obesity is unexplored. To examine this, we use gene-modified mice with EC-specific overexpression of human IGF-1R (hIGFREO) and their wild-type littermates. After high-fat feeding, hIGFREO weigh less, have reduced adiposity and have improved glucose tolerance. hIGFREO show an altered gene expression and altered microbial diversity in the gut, including a relative increase in the beneficial genus Akkermansia. The depletion of gut microbiota with broad-spectrum antibiotics induces a loss of the favourable metabolic differences seen in hIGFREO mice. We show that IGF-1R facilitates crosstalk between the EC and the gut wall; this crosstalk protects against diet-induced obesity, as a result of an altered gut microbiota.

Validation of cardiac diffusion tensor imaging sequences: A multicentre test-retest phantom study.

Cardiac diffusion tensor imaging (DTI) is an emerging technique for the in vivo characterisation of myocardial microstructure, and there is a growing need for its validation and standardisation. We sought to establish the accuracy, precision, repeatability and reproducibility of state-of-the-art pulse sequences for cardiac DTI among 10 centres internationally. Phantoms comprising 0%-20% polyvinylpyrrolidone (PVP) were scanned with DTI using a product pulsed gradient spin echo (PGSE; N = 10 sites) sequence, and a custom motion-compensated spin echo (SE; N = 5) or stimulated echo acquisition mode (STEAM; N = 5) sequence suitable for cardiac DTI in vivo. A second identical scan was performed 1-9 days later, and the data were analysed centrally. The average mean diffusivities (MDs) in 0% PVP were (1.124, 1.130, 1.113) x 10-3  mm2 /s for PGSE, SE and STEAM, respectively, and accurate to within 1.5% of reference data from the literature. The coefficients of variation in MDs across sites were 2.6%, 3.1% and 2.1% for PGSE, SE and STEAM, respectively, and were similar to previous studies using only PGSE. Reproducibility in MD was excellent, with mean differences in PGSE, SE and STEAM of (0.3 ± 2.3, 0.24 ± 0.95, 0.52 ± 0.58) x 10-5  mm2 /s (mean ± 1.96 SD). We show that custom sequences for cardiac DTI provide accurate, precise, repeatable and reproducible measurements. Further work in anisotropic and/or deforming phantoms is warranted.

Effect of convergence on the horizontal VOR in normal subjects and patients with peripheral and central vestibulopathy.

BACKGROUND: Vestibular compensatory eye movements provide visual fixation stabilization during head movement. The anatomic pathways mediating a normal horizontal vestibulo-ocular reflex (h-VOR), when lesioned, cause spontaneous nystagmus. While previous reports address the effect of convergence on different spontaneous nystagmus types, to our knowledge, a study of acute vestibular nystagmus suppression viewing near targets comparing patients with peripheral or central vestibular lesions has not been previously reported. METHODS: We attempt to clarify potential vestibular and near-reflex interaction by comparing near and far h-VOR gain in 19 healthy controls, six patients with acute/subacute peripheral vestibular lesion (PVL), and one patient with unilateral vestibular nuclear lesion (VNL) in the pontine tegmentum. RESULTS: The horizontal (h)-VOR in normal subjects increased with convergence in both eyes (P = 0.027, P < 0.001). In unilateral PVL patients, gain failed to increase in either direction (P = 0.25, P = 0.47). In contrast, when fixating at 15 cm, the h-aVOR in the VNL lesion, gain did not increase, and a right h-nystagmus developed. Even though we found inability to increase gain in PVL with near target fixation, this did not interfere with h-nystagmus suppression upon converging. Our VNL patient had normal h-nystagmus suppression viewing far distance targets and lacked near target h-nystagmus suppression. CONCLUSION: We hypothesize that normal IO/flocculus pathway suppressed spontaneous nystagmus in PVL. Impaired h-VOR near adaptation in the medial vestibular nucleus was responsible for h-nystagmus direction with fixation block. Additionally, impaired viewing distance estimate contributed to near h-nystagmus suppression failure.

Protocol for a prospective cohort study exploring the gut microbiota of infants with congenital heart disease undergoing cardiopulmonary bypass (the GuMiBear study).

INTRODUCTION: The gut microbiota develops from birth and matures significantly during the first 24 months of life, playing a major role in infant health and development. The composition of the gut microbiota is influenced by several factors including mode of delivery, gestational age, feed type and treatment with antibiotics. Alterations in the pattern of gut microbiota development and composition can be associated with illness and compromised health outcomes.Infants diagnosed with 'congenital heart disease' (CHD) often require surgery involving cardiopulmonary bypass (CPB) early in life. The impact of this type of surgery on the integrity of the gut microbiome is poorly understood. In addition, these infants are at significant risk of developing the potentially devastating intestinal condition necrotising enterocolitis. METHODS AND ANALYSIS: This study will employ a prospective cohort study methodology to investigate the gut microbiota and urine metabolome of infants with CHD undergoing surgery involving CPB. Stool and urine samples, demographic and clinical data will be collected from eligible infants based at the National Centre for Paediatric Cardiac Surgery in Ireland. Shotgun metagenome sequencing will be performed on stool samples and urine metabolomic analysis will identify metabolic biomarkers. The impact of the underlying diagnosis, surgery involving CPB, and the influence of environmental factors will be explored. Data from healthy age-matched infants from the INFANTMET study will serve as a control for this study. ETHICS AND DISSEMINATION: This study has received full ethical approval from the Clinical Research Ethics Committee of Children's Health Ireland, GEN/826/20.

Macro-Scale Tread Patterns for Traction in the Intestine.

GOAL: Tread patterns are widely used to increase traction on different substrates, with the tread scale, geometry and material being tailored to the application. This work explores the efficacy of using macro-scale tread patterns for a medical application involving a colon substrate - renowned for its low friction characteristics. METHODS: Current literature was first summarized before an experimental approach was used, based on a custom test rig with ex vivo porcine colon, to assess different macro-scale tread patterns. Performance was based on increasing traction while avoiding significant trauma. Repeated testing (n = 16) was used to obtain robust results. RESULTS: A macro-scale tread pattern can increase the traction coefficient significantly, with a static traction coefficient of 0.74 ± 0.22 and a dynamic traction coefficient of 0.35 ± 0.04 compared to a smooth (on the macro-scale) Control (0.132 ± 0.055 and 0.054 ± 0.015, respectively). Decreasing the scale and spacing between the tread features reduced apparent trauma but also reduced the traction coefficient. CONCLUSION: Significant traction can be achieved on colon tissue using a macro-scale tread but a compromise between traction (large feature sizes) and trauma (small feature sizes) may have to be made. SIGNIFICANCE: This work provides greater insight into the complex frictional mechanisms of the intestine and gives suggestions for developing functional tread surfaces for a wide range of clinical applications.

Gait Modulation in C. elegans: An Integrated Neuromechanical Model.

Equipped with its 302-cell nervous system, the nematode Caenorhabditis elegans adapts its locomotion in different environments, exhibiting so-called swimming in liquids and crawling on dense gels. Recent experiments have demonstrated that the worm displays the full range of intermediate behaviors when placed in intermediate environments. The continuous nature of this transition strongly suggests that these behaviors all stem from modulation of a single underlying mechanism. We present a model of C. elegans forward locomotion that includes a neuromuscular control system that relies on a sensory feedback mechanism to generate undulations and is integrated with a physical model of the body and environment. We find that the model reproduces the entire swim-crawl transition, as well as locomotion in complex and heterogeneous environments. This is achieved with no modulatory mechanism, except via the proprioceptive response to the physical environment. Manipulations of the model are used to dissect the proposed pattern generation mechanism and its modulation. The model suggests a possible role for GABAergic D-class neurons in forward locomotion and makes a number of experimental predictions, in particular with respect to non-linearities in the model and to symmetry breaking between the neuromuscular systems on the ventral and dorsal sides of the body.

Forward locomotion of the nematode C. elegans is achieved through modulation of a single gait.

The ability of an animal to locomote through its environment depends crucially on the interplay between its active endogenous control and the physics of its interactions with the environment. The nematode worm Caenorhabditis elegans serves as an ideal model system for studying the respective roles of neural control and biomechanics, as well as the interaction between them. With only 302 neurons in a hard-wired neural circuit, the worm's apparent anatomical simplicity belies its behavioural complexity. Indeed, C. elegans exhibits a rich repertoire of complex behaviors, the majority of which are mediated by its adaptive undulatory locomotion. The conventional wisdom is that two kinematically distinct C. elegans locomotion behaviors-swimming in liquids and crawling on dense gel-like media-correspond to distinct locomotory gaits. Here we analyze the worm's motion through a series of different media and reveal a smooth transition from swimming to crawling, marked by a linear relationship between key locomotion metrics. These results point to a single locomotory gait, governed by the same underlying control mechanism. We further show that environmental forces play only a small role in determining the shape of the worm, placing conditions on the minimal pattern of internal forces driving locomotion.

Caenorhabditis elegans body wall muscles are simple actuators.

Over the past four decades, one of the simplest nervous systems across the animal kingdom, that of the nematode worm Caenorhabditis elegans, has drawn increasing attention. This system is the subject of an intensive concerted effort to understand the behaviour of an entire living animal, from the bottom up and the top down. C. elegans locomotion, in particular, has been the subject of a number of models, but there is as yet no general agreement about the key (rhythm generating) elements. In this paper we investigate the role of one component of the locomotion subsystem, namely the body wall muscles, with a focus on the role of inter-muscular gap junctions. We construct a detailed electrophysiological model which suggests that these muscles function, to a first approximation, as mere actuators and have no obvious rhythm generating role. Furthermore, we show that within our model inter-muscular coupling is too weak to have a significant electrical effect. These results rule out muscles as key generators of locomotion, pointing instead to neural activity patterns. More specifically, the results imply that the reduced locomotion velocity observed in unc-9 mutants is likely to be due to reduced neuronal rather than inter-muscular coupling.