Towards continuous EIT monitoring for hemorrhagic stroke patients.

The practical implementation of continuous monitoring of stroke patients by Electrical Impedance Tomography (EIT) is addressed. In a previous paper, we have demonstrated EIT sensitivity to cerebral hemodynamics, using scalp-mounted electrodes, very low-noise measurements, and a novel image reconstruction method. In the present paper, we investigate the potential to adapt that system for clinical application, by using 50% fewer electrodes and by incorporating into the measurement protocol an additional high-frequency measurement to provide an effective reference. Previously published image reconstruction methods for multi-frequency EIT are substantially improved by exploiting the forward calculations enabled by the detailed head model, particularly to make the referencing method more robust and to attempt to remove the effects of modelling error. Images are presented from simulation of a typical hemorrhagic stroke and its growth. These results are encouraging for exploration of the potential clinical benefit of the methodology in long-term monitoring of hemorrhagic stroke.

CSTNet: A Dual-Branch Convolutional Neural Network for Imaging of Reactive Flows Using Chemical Species Tomography.

Chemical species tomography (CST) has been widely used for in situ imaging of critical parameters, e.g., species concentration and temperature, in reactive flows. However, even with state-of-the-art computational algorithms, the method is limited due to the inherently ill-posed and rank-deficient tomographic data inversion and by high computational cost. These issues hinder its application for real-time flow diagnosis. To address them, we present here a novel convolutional neural network, namely CSTNet, for high-fidelity, rapid, and simultaneous imaging of species concentration and temperature using CST. CSTNet introduces a shared feature extractor that incorporates the CST measurements and sensor layout into the learning network. In addition, a dual-branch decoder with internal crosstalk, which automatically learns the naturally correlated distributions of species concentration and temperature, is proposed for image reconstructions. The proposed CSTNet is validated both with simulated datasets and with measured data from real flames in experiments using an industry-oriented sensor. Superior performance is found relative to previous approaches in terms of reconstruction accuracy and robustness to measurement noise. This is the first time, to the best of our knowledge, that a deep learning-based method for CST has been experimentally validated for simultaneous imaging of multiple critical parameters in reactive flows using a low-complexity optical sensor with a severely limited number of laser beams.

Tomographic imaging of carbon dioxide in the exhaust plume of large commercial aero-engines.

We report here the first implementation of chemically specific imaging in the exhaust plume of a gas turbine typical of those used for propulsion in commercial aircraft. The method used is chemical species tomography (CST) and the target species is CO2, absorbing in the near-infrared at 1999.4 nm. A total of 126 beams propagate transverse to the plume axis, along 7 m paths in a coplanar geometry, to probe a central region of diameter ≈1.5m. The CO2 absorption spectrum is measured using tunable diode laser spectroscopy with wavelength modulation, using the second harmonic to first harmonic (2f/1f) ratio method. The engine is operated over the full range of thrust, while data are recorded in a quasi-simultaneous mode at frame rates of 1.25 and 0.3125 Hz. Various data inversion methodologies are considered and presented for image reconstruction. At all thrust levels a persistent ring structure of high CO2 concentration is observed in the central region of the measurement plane, with a raised region in the middle of the plume assumed to be due to the engine's boat tail. With its potential to target various exhaust species, the CST method outlined here offers a new approach to turbine combustion research, turbine engine development, and aviation fuel research and development.

Scalp-Mounted Electrical Impedance Tomography of Cerebral Hemodynamics.

An Electrical Impedance Tomography (EIT) system has been developed for dynamic three-dimensional imaging of changes in conductivity distribution in the human head, using scalp-mounted electrodes. We attribute these images to changes in cerebral perfusion. At 100 frames per second (fps), voltage measurement is achieved with full-scale signal-to-noise ratio of 105 dB and common-mode rejection ratio > 90 dB. A novel nonlinear method is presented for 3-D imaging of the difference in conductivity distribution in the head, relative to a reference time. The method achieves much reduced modelling error. It successfully localizes conductivity inclusions in experimental and simulation tests, where previous methods fail. For > 50 human volunteers, the rheoencephalography (REG) waveform is observed in EIT voltage measurements for every volunteer, with peak-to-peak amplitudes up to approx. 50 µVrms. Images are presented of the change in conductivity distribution during the REG/cardiac cycle, at 50 fps, showing maximum local conductivity change of approx. 1% in grey/white matter. A total of 17 tests were performed during short (typically 5s) carotid artery occlusions on 5 volunteers, monitored by Transcranial Doppler ultrasound. From EIT measurements averaged over complete REG/cardiac cycles, 13 occlusion tests showed consistently decreased conductivity of cerebral regions on the occluded side, and increased conductivity on the opposite side. The maximum local conductivity change during occlusion was approx. 20%. The simplicity of the carotid artery intervention provides a striking validation of the scalp-mounted measurement system in imaging cerebral hemodynamics, and the REG images indicate its unique combination of sensitivity and temporal resolution.

Reconstruction of two-dimensional velocity distribution in scramjet by laser absorption spectroscopy tomography.

We propose a method to reconstruct the two-dimensional (2D) velocity distribution of flow fields by laser absorption spectroscopy tomography. A mathematic model is established to reveal the dependence of spectral absorbance on line-of-sight velocity distribution. Then, with multiple laser beams from different angular views covering the region of interest, a nonlinear equation set of 2D velocity distribution is established according to the model. The integrated absorbance coefficient distribution is reconstructed using the Landweber iteration algorithm and substituted into the nonlinear equation set for further simplification. Finally, the velocity distribution is reconstructed by solving the simplified equation group via the interior point algorithm. The proposed method is validated numerically by reconstructing the velocity distribution of water molecules, as calculated by computational fluid dynamics, over a cross section of a double-mode scramjet combustor. The method does not require adding extra tracer particles and avoids issues arising from the short lifetime of molecular tags. It is suitable for diagnosis of high-speed flow fields.

Constrained models for optical absorption tomography.

We consider the inverse problem of concentration imaging in optical absorption tomography with limited data sets. The measurement setup involves simultaneous acquisition of near-infrared wavelength-modulated spectroscopic measurements from a small number of pencil beams equally distributed among six projection angles surrounding the plume. We develop an approach for image reconstruction that involves constraining the value of the image to the conventional concentration bounds and a projection into low-dimensional subspaces to reduce the degrees of freedom in the inverse problem. Effectively, by reparameterizing the forward model, we impose, simultaneously, spatial smoothness and a choice among three types of inequality constraints, namely, positivity, boundedness, and logarithmic boundedness in a simple way that yields an unconstrained optimization problem in a new set of surrogate parameters. Testing this numerical scheme with simulated and experimental phantom data indicates that the combination of affine inequality constraints and subspace projection leads to images that are qualitatively and quantitatively superior to unconstrained regularized reconstructions. This improvement is more profound in targeting concentration profiles of small spatial variation. We present images and convergence graphs from solving these inverse problems using Gauss-Newton's algorithm to demonstrate the performance and convergence of our method.

Tackling modelling error in the application of electrical impedance tomography to the head.

In the head application of Electrical Impedance Tomography (EIT), reconstruction of voltage measurements for a conductivity distribution image using an ordinary method, the absolute imaging approach, is impossible due to the traditional ignorance of modelling error. The modelling error comes from the inaccuracy of geometry and structure, which are unable to be known accurately in practice, and are usually large in head application of EIT. Difference imaging is an alternative approach which is able to reduce the size of this error, but it introduces other kinds of error. In this work, we demonstrate that in situations like head EIT, the nonlinear difference imaging approach can reconstruct difference conductivity effectively: the reduced modelling error and the new errors arising are able to be ignored, because they are much smaller than the original modelling error. The magnitude of conductivity change in the head-like situation is also investigated, and a selection scheme for the initial guess in the reconstruction process is also proposed.

The Brady Bunch? New evidence for nominative determinism in patients' health: retrospective, population based cohort study.

OBJECTIVE: To ascertain whether a name can influence a person's health, by assessing whether people with the surname "Brady" have an increased prevalence of bradycardia. DESIGN: Retrospective, population based cohort study. SETTING: One university teaching hospital in Dublin, Ireland. PARTICIPANTS: People with the surname "Brady" in Dublin, determined through use of an online telephone directory. MAIN OUTCOME MEASURE: Prevalence of participants who had pacemakers inserted for bradycardia between 1 January 2007 and 28 February 2013. RESULTS: 579 (0.36%) of 161,967 people who were listed on the Dublin telephone listings had the surname "Brady." The proportion of pacemaker recipients was significantly higher among Bradys (n=8, 1.38%) than among non-Bradys (n=991, 0.61%; P=0.03). The unadjusted odds ratio (95% confidence interval) for pacemaker implantation among individuals with the surname Brady compared with individuals with other surnames was 2.27 (1.13 to 4.57). CONCLUSIONS: Patients named Brady are at increased risk of needing pacemaker implantation compared with the general population. This finding shows a potential role for nominative determinism in health.

Multiwavelength diode-laser absorption spectroscopy using external intensity modulation by semiconductor optical amplifiers.

A novel opto-electronic scheme for line-of-sight Near-IR gas absorption measurement based on direct absorption spectroscopy (DAS) is reported. A diode-laser-based, multiwavelength system is designed for future application in nonintrusive, high temporal resolution tomographic imaging of H2O in internal combustion engines. DAS is implemented with semiconductor optical amplifiers (SOAs) to enable wavelength multiplexing and to induce external intensity modulation for phase-sensitive detection. Two overtone water transitions in the Near-IR have been selected for ratiometric temperature compensation to enable concentration measurements, and an additional wavelength is used to account for nonabsorbing attenuation. A wavelength scanning approach was used to evaluate the new modulation technique, and showed excellent absorption line recovery. Fixed-wavelength, time-division-multiplexing operation with SOAs has also been demonstrated. To the best of our knowledge this is the first time SOAs have been used for modulation and switching in a spectroscopic application. With appropriate diode laser selection this scheme can be also used for other chemical species absorption measurements.

The Dublin cardiac arrest registry: temporal improvement in survival from out-of-hospital cardiac arrest reflects improved pre-hospital emergency care.

AIMS: Out-of-hospital cardiac arrest (OOHCA) survival remains poor, estimated at 3-7%. We aim to describe the incidence of OOHCA, survival from OOHCA, and the impact of improved pre-hospital care on survival from OOHCA. METHODS AND RESULTS: A retrospective registry was established using multi-source information to assess survival from cardiac arrest following the introduction of several improvements in pre-hospital emergency medical care from 2003. Survival from OOHCA, from asystole/pulseless electrical activity, and from ventricular tachycardia/ventricular fibrillation was estimated. Adjusted per 100 000 population annual incidence rates from national population census data were calculated. Mean and median emergency medical services (EMS) response times to OOHCA calls were assessed. A total of 962 OOHCAs occurred from 1 January 2003 until 31 December 2008. Sixty-nine per cent (69%, n = 664) were male. Seventy-two per cent (72%, n = 693) occurred at home with 28% occurring in a public venue. Of these public venues, 33.9% (91 of 268) had an automated external defibrillator available. Bystander cardiopulmonary resuscitation (CPR) was in progress when emergency services arrived in 11% (n = 106) of the cases. Nineteen per cent (19.4%, n = 187) had a known prior cardiac history or chest pain prior to circulatory collapse. Overall survival to hospital discharge improved significantly from 2.6 to 11.3%, P = 0.001. Survival from ventricular fibrillation (VF) to hospital admission, rose from 28.6 to 86.3%, P = 0.001. Survival to hospital discharge from VF improved from 21.4 to 33%, P = 0.007. Mean EMS response times to the scene of arrest decreased from 9.18 to 8.34 min. Emergency medical services scene time, reflecting acute pre-hospital medical care, rose from 14.46 to 18.12 min. The adjusted incidence of OOHCA for our catchment population declined from 109.4 to 88.2 per 100,000 population between 2003 and 2008. CONCLUSIONS: The incidence of OOHCA has declined but importantly, survival to hospital discharge has improved dramatically. Reduction in ambulance response time, resulting in earlier initiation of basic and advanced life support and earlier defibrillation, was associated with an increase in the proportion of victims found in VF rather than asystole and likely accounted for most of the improvement. Further improvements in response times and public education to improve bystander CPR rates should remain a priority.

A portable instrument for high-speed brain function imaging: FEITER.

Electrical Impedance Tomography (EIT) can resolve dynamic physiological information deep within human subjects [1], but its sensitivity is challenged in the case of imaging the head [2]. Here, we report a new system called fEITER that has been designed and built to enable functional imaging of the human brain using EIT via scalp-mounted electrodes, integrated with stimulation of evoked responses. Using Field-Programmable Gate Array (FPGA) technology, it provides excellent flexibility in terms of current-pattern excitation and signal processing. The instrument operates at 100 frames/second (fps) with noise of 1 µV on the rms voltage measurements. Clinical trials have been authorized by the UK MHRA and example data from human subjects are presented.

Contemporary management of and outcomes from cardiac device related infections.

AIMS: To describe the incidence and management of cardiac device infection. Infection is a serious, potentially fatal complication of device implantation. The numbers of device implants and infections are rising. Optimal care of device infection is not well defined. METHODS AND RESULTS: We retrospectively identified cases of device infection at our institution between 2000 and 2007 by multiple source record review, and active surveillance. Device infection was related to demographics, clinical, and procedural characteristics. Descriptive analysis was performed. From 2000 to 2007, a total of 2029 permanent pacemakers and 1076 biventricular/implantable cardioverter-defibrillators (ICDs) or ICDs were implanted. Thirty-nine cases of confirmed device infections were identified--27 pacemaker and 12 bivent/ICD or ICD infections, giving an infection rate of 1.25%. Median time from implant or revision to presentation was 150 days (range 2915 days, IQR25% 35-IQR75% 731). Ninety percent of patients presented with generator-site infections. The most common organism was methicillin-sensitive Staphylococcus aureus (30.8%), followed by coagulase negative Staphylococcus (20.5%). Complete device extraction occurred in 82%. Of these, none had relapse, and mortality was 7.4% (n = 2/27). With partial removal or conservative therapy (n = 13), relapse occurred in 67% (n = 8/12), with mortality of 8.4% (n = 1/12). Median duration of antibiotics was 42 days (range 47 days, IQR25% 28-IQR75% 42 days). Re-implantation of a new device occurred in 54%, at a median of 28 days (range 73 days, IQR25% 8.5-IQR75% 35 days). Methicillin-Resistant Staphylococcus Aureus infection predicted mortality (P < 0.004, RR 37, 95% CI 5.3-250). Median follow-up was 36 months. CONCLUSION: Cardiac device infection is a rare complication, with significant morbidity and mortality. Complete hardware removal with appropriate duration of antimicrobial therapy results in the best outcomes for patients.

Dobutamine stress echo-induced apical ballooning (Takotsubo) syndrome.

AIMS: We report a case of dobutamine stress echocardiography (DSE) resulting in transient apical ballooning syndrome to highlight this rare condition as a potential complication of DSE. BACKGROUND: Takotsubo cardiomyopathy, or transient apical ballooning syndrome, is a recently described form of left ventricular (LV) dysfunction induced by stress. Clinically it can mimic acute coronary syndrome in its presentation. It is characterized by an atypical distribution of LV dysynergy with apical ballooning and compensatory basal hyperkinesis. Coronary angiography is normal. It has preponderance in females. Although the aetiology of Takotsubo syndrome remains obscure catecholamine release appears to be the principal trigger. RESULTS: We report a case of dobutamine-induced transient LV apical ballooning in a woman without coronary disease, during a dobutamine stress echocardiogram. There was evidence of ventricular recovery by 72 h. To our knowledge, only three other case reports describe dobutamine-induced Takotsubo cardiomyopathy. CONCLUSION: Dobutamine stress echocardiography is a widely performed diagnostic test, however, it can rarely result in presumed catecholamine-induced transient apical ballooning syndrome.

Toward in-cylinder absorption tomography in a production engine.

Design requirements for an 8000 frame/s dual-wavelength ratiometric chemical species tomography system, intended for hydrocarbon vapor imaging in one cylinder of a standard automobile engine, are examined. The design process is guided by spectroscopic measurements on iso-octane and by comprehensive results from laboratory phantoms and research engines, including results on temporal resolution performance. Novel image reconstruction techniques, necessary for this application, are presented. Recent progress toward implementation, including details of the optical access arrangement employed and signal-to-noise issues, is described. We present first cross-cylinder IR absorption measurements from a reduced channel-count (nontomographic) system and discuss the prospects for imaging.

Krylov subspace iterative techniques: on the detection of brain activity with electrical impedance tomography.

In this paper, we review some numerical techniques based on the linear Krylov subspace iteration that can be used for the efficient calculation of the forward and the inverse electrical impedance tomography problems. Exploring their computational advantages in solving large-scale systems of equations, we specifically address their implementation in reconstructing localized impedance changes occurring within the human brain. If the conductivity of the head tissues is assumed to be real, the pre-conditioned conjugate gradients (PCGs) algorithm can be used to calculate efficiently the approximate forward solution to a given error tolerance. The performance and the regularizing properties of the PCG iteration for solving ill-conditioned systems of equations (PCGNs) is then explored, and a suitable preconditioning matrix is suggested in order to enhance its convergence rate. For image reconstruction, the nonlinear inverse problem is considered. Based on the Gauss-Newton method for solving nonlinear problems we have developed two algorithms that implement the PCGN iteration to calculate the linear step solution. Using an anatomically detailed model of the human head and a specific scalp electrode arrangement, images of a simulated impedance change inside brain's white matter have been reconstructed.