Investigation of potential artefactual changes in measurements of impedance changes during evoked activity: implications to electrical impedance tomography of brain function.

Electrical impedance tomography (EIT) could provide images of fast neural activity in the adult human brain with a resolution of 1 ms and 1 mm by imaging impedance changes which occur as ion channels open during neuronal depolarization. The largest changes occur at dc and decrease rapidly over 100 Hz. Evoked potentials occur in this bandwidth and may cause artefactual apparent impedance changes if altered by the impedance measuring current. These were characterized during the compound action potential in the walking leg nerves of Cancer pagurus, placed on Ag/AgCl hook electrodes, to identify how to avoid artefactual changes during brain EIT. Artefact-free impedance changes (δZ) decreased with frequency from -0.045 ± 0.01% at 225 Hz to -0.02 ± 0.01% at 1025 Hz (mean ± 1 SD, n = 24 in 12 nerves) which matched changes predicted by a finite element model. Artefactual δZ reached c.300% and 50% of the genuine membrane impedance change at 225 Hz and 600 Hz respectively but decreased with frequency of the applied current and was negligible above 1 kHz. The proportional amplitude (δZ (%)) of the artefact did not vary significantly with the amplitude of injected current of 5-20 µA pp. but decreased significantly from -0.09 ± 0.024 to -0.03 ± 0.023% with phase of 0 to 45°. For fast neural EIT of evoked activity in the brain, artefacts may arise with applied current of >10 µA. Independence of δZ with respect to phase but not the amplitude of applied current controls for them; they can be minimized by randomizing the phase of the applied measuring current and excluded by recording at >1 kHz

High-throughput mechanobiology: Force modulation of ensemble biochemical and cell-based assays

Mechanobiology is focused on how the physical forces and mechanical properties of proteins, cells, and tissues contribute to physiology and disease. Although the response of proteins and cells to mechanical stimuli is critical for function, the tools to probe these activities are typically restricted to single-molecule manipulations. Here, we have developed a novel microplate reader assay to encompass mechanical measurements with ensemble biochemical and cellular assays, using a microplate lid modified with magnets. This configuration enables multiple static magnetic tweezers to function simultaneously across the microplate, thereby greatly increasing throughput. We demonstrate the broad applicability and versatility through in vitro and in cellulo approaches. Overall, our methodology allows, for the first time (to our knowledge), ensemble biochemical and cell-based assays to be performed under force in high-throughput format. This approach substantially increases the availability of mechanobiology measurements

Comparison of total variation algorithms for electrical impedance tomography

The applications of total variation (TV) algorithms for electrical impedance tomography (EIT) have been investigated. The use of the TV regularisation technique helps to preserve discontinuities in reconstruction, such as the boundaries of perturbations and sharp changes in conductivity, which are unintentionally smoothed by traditional l2 norm regularisation. However, the non-differentiability of TV regularisation has led to the use of different algorithms. Recent advances in TV algorithms such as the primal dual interior point method (PDIPM), the linearised alternating direction method of multipliers (LADMM) and the spilt Bregman (SB) method have all been demonstrated successful EIT applications, but no direct comparison of the techniques has been made. Their noise performance, spatial resolution and convergence rate applied to time difference EIT were studied in simulations on 2D cylindrical meshes with different noise levels, 2D cylindrical tank and 3D anatomically head-shaped phantoms containing vegetable material with complex conductivity. LADMM had the fastest calculation speed but worst resolution due to the exclusion of the second-derivative; PDIPM reconstructed the sharpest change in conductivity but with lower contrast than SB; SB had a faster convergence rate than PDIPM and the lowest image errors

Assessing the usability of tile-based interfaces to visually navigate 3-D parameter domains

Navigating 3-D parameter domains, such as color and orientation of an object, is a common task performed in most computer graphics applications. Although 1-D sliders are the most common interface for browsing such domains, they provide a tedious and difficult user experience that hampers finding desirable visual solutions. We present the Rhomb-i slider, a novel and visually enriching tile-based interface to navigate arbitrary 3-D parameter domains. Contrary to 1-D sliders, the Rhomb-i slider supports a sketch-based interface that gives simultaneous access to up to two parameters. We conducted a usability study to ascertain whether the proposed Rhomb-i slider is a more natural interface compared to 1-D sliders and other commonly used widgets for different 3-D parameter domains: HSV color space, super-shape curves, and rotation of a 3-D object. On the one hand, qualitative feedback and performance measures reveal that Rhomb-i sliders have similar results when compared to conventional HSV color interfaces, and are the preferred interface to efficiently explore the super-shapes parameter domain. On the other hand, Rhomb-i revealed to be a less efficient and effective interface to rotate a 3D object, thus paving the way to new design explorations regarding this tile-based interface

Stroke-based splatting: an efficient multi-resolution point cloud visualization technique

Current state-of-the-art point cloud visualization techniques have shortcomings when dealing with sparse and less accurate data or close-up interactions. In this paper, we present a visualization technique called stroke-based splatting, which applies concepts of stroke-based rendering to surface-aligned splatting, allowing for better shape perception at lower resolutions and close-ups. We create a painterly depiction of the data with an impressionistic aesthetic, which is a metaphor the user is culturally trained to recognize, thus attributing higher quality to the visualization. This is achieved by shaping each object-aligned splat as a brush stroke, and orienting it according to globally coherent tangent vectors from the Householder formula, creating a painterly depiction of the scanned cloud. Each splat is sized according to a color-based clustering analysis of the data, ensuring the consistency of brush strokes within neighborhood areas. By controlling brush shape generation parameters and blending factors between neighboring splats, the user is able to simulate different painting styles in real time. We have tested our method with data sets captured by commodity laser scanners as well as publicly available high-resolution point clouds, both having highly interactive frame rates in all cases. In addition, a user study was conducted comparing our approach to state-of-the-art point cloud visualization techniques. Users considered stroke-based splatting a valuable technique as it provides a higher or similar visual quality to current approaches

A method for reconstructing tomographic images of evoked neural activity with electrical impedance tomography using intracranial planar arrays

A method is presented for reconstructing images of fast neural evoked activity in rat cerebral cortex recorded with electrical impedance tomography (EIT) and a 6 × 5 mm(2) epicortical planar 30 electrode array. A finite element model of the rat brain and inverse solution with Tikhonov regularization were optimized in order to improve spatial resolution and accuracy. The optimized FEM mesh had 7 M tetrahedral elements, with finer resolution (0.05 mm) near the electrodes. A novel noise-based image processing technique based on t-test significance improved depth localization accuracy from 0.5 to 0.1 mm. With the improvements, a simulated perturbation 0.5 mm in diameter could be localized in a region 4 × 5 mm(2) under the centre of the array to a depth of 1.4 mm, thus covering all six layers of the cerebral cortex with an accuracy of <0.1 mm. Simulated deep brain hippocampal or thalamic activity could be localized with an accuracy of 0.5 mm with a 256 electrode array covering the brain. Parallel studies have achieved a temporal resolution of 2 ms for imaging fast neural activity by EIT during evoked activity; this encourages the view that fast neural EIT can now resolve the propagation of depolarization-related fast impedance changes in cerebral cortex and deeper in the brain with a resolution equal or greater to the dimension of a cortical column

An extragalactic supernebula confined by gravity

Little is known about the origins of the giant star clusters known as globular clusters. How can hundreds of thousands of stars form simultaneously in a volume only a few light years across the distance of the sun to its nearest neighbor? Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy, NGC 5253. The lines arise in gas heated by a cluster of an estimated million stars, so young that it is still enshrouded in gas and dust, hidden from optical view. We verify that the cluster contains 4000-6000 massive, hot "O" stars. Our discovery that the gases within the cluster are bound by gravity may explain why these windy and luminous O stars have not yet blown away the gases to allow the cluster to emerge from its birth cocoon. Young clusters in "starbursting" galaxies in the local and distant universe may be similarly gravitationally confined and cloaked from view.Comment: Letter to Natur

Adolescence and Later Life Disease Burden: Quantifying the Contribution of Adolescent Tobacco Initiation From Longitudinal Cohorts

Purpose: Adolescence is a time of initiation of behaviors leading to noncommunicable diseases (NCDs). We use tobacco to illustrate a novel method for assessing the contribution of adolescence to later burden. // Methods: Data on initiation of regular smoking during adolescence (10–19 years) and current adult smoking were obtained from the 1958 British Birth Cohort, the U.S. National Longitudinal Study of Adolescent Health (Add Health), the Pelotas 1982 Birth Cohort, and the Victorian Adolescent Health Cohort Study. We estimated an “adolescent attributable fraction” (AAF) by calculating the proportion of persisting adult daily smoking initiated 155 countries using contemporary surveillance data. // Results: In the 1958 British Birth Cohort, 81.6% of daily smokers at age 50 years initiated < age 20 years, with a risk ratio of 6.1 for adult smoking related to adolescent initiation. The adjusted AAF was 69.1. Proportions of smokers initiating <20 years, risk ratio, and AAFs were 83.3%, 7.0%, and 70.4% for Add Health; 75.5%, 3.7%, and 50.2% in Victorian Adolescent Health Cohort Study; and 70.9%, 5.8%, and 56.9% in Pelotas males and 89.9%, 6.4%, and 75.9% in females. Initiation <16 years resulted in the highest AAFs. Estimated AAFs globally ranged from 35% in China to 76% in Argentina. // Conclusions: The contribution of adolescent smoking initiation to adult smoking burden is high, suggesting a need to formulate and implement effective actions to reduce smoking initiation in adolescents. Similar trends in other NCD risks suggest that adolescents will be central to future efforts to control NCDs