Weijia Lu

A computer model based on real anatomy for electrophysiology study

In order to investigate the pattern of wave propagation on atria in both sinus rhythm and arrhythmia, we constructed a computational model based on real anatomy. The original anatomic data which encompasses morphological and geometrical knowledge was created from a whole-body set of 2mm interval magnetic resonance imaging (MRI) images of a male volunteer and represented in stl format. The anatomic data was firstly discretized into spherical cells in equal size. Then the anisotropy of conduction velocity (CV) and conductivity were introduced into this model in definition of special conduction system. Nygren cell model was adopted to calculate the action potential (AP) waveform of each cell. Restitution of AP duration (APD) and it on CV were also introduced in this model. The pattern of activation propagation could be investigated on a perspective 3D scene after the excitation simulation. The isochronal map and the electrocardiograms (ECGs) were also produced. In this study, We used two experiments to verify this model as well as demonstrated its application in electrophysiological study: one was conducted under sinus rhythm, while in the other, two trains of boost pacings alternatively acted on the vena cava and the opening of the pulmonary vein. An identical excitation pattern described in previous studies was observed in first experiment. While in the second experiment, a foci triggered atrial fibrillation was seen on the epicardial surface.

Implementation of a novel interpolating method to epicardial potential mapping for atrial fibrillation study

Epicardial potential mapping is an efficient way to visualize the potential distribution on the epicardial surface. We found in our previous study, that the traditional linear interpolation used for the epicardial mapping may cause errors and distortions in reconstruction of the electric activities on the epicardial surface especially during the atrial fibrillation. In this study, we devoted on the implementation of a 3D interpolating method, and verified it in comparison with another interpolating method as well as studying of the mechanism of vagal atrial fibrillation (AF). In case studying, we analyzed the epicardial data from seven canine cardiac models using this method and found the macro-re-entry during the sustainable AF is more likely due to the dispersion of refractoriness in the myocardium and does not demonstrated the focal patterns at the beginning of AF. This indicated that the electrophysiological characteristics of myocardium might have been changed during the paroxysmal atrial fibrillation (PAF).

Development of Epicardial Mapping System for Studying Atrial Fibrillation

Epicardial mapping system is an important tool for studying electrophysiological characteristics of atrial fibrillation (AF). AF is the most common arrhythmia and is becoming more prevalent each year. Most in vivo experimental research on AF is performed by simultaneous epicardial mapping technique. An epicardial mapping system is developed to record electrical activities from 128 sites at the same time, with a spacing of 3.5-5.0 mm. The initial purpose of this research is to display the electrical signals on the whole-atrial epicardial surface and store these data for subsequent analysis. 128 unipolar electrodes arranged in eight flexible patches were adopted to detect signal on the surface of whole atrium. Each electrode patch was designed to adaptable to the corresponding epicardial surface of canine atrium. The system contained an amplifier with 128 isolated channels and a data acquisition card based on USB communication. Random acquisition duration of interested data during sinus or AF rhythm could be recorded. Animal tests were operated on four mongrel dogs, in which two were models of chronic AF. Result shows that this system can perform successfully in a surgical setting. This system may be a special and portable tool for whole-atrium epicardial mapping and therefore useful for studying AF.

Dynamic Epicardial Mapping Using 3D Emulation

Dynamic epicardial mapping is an important tool in cardiac electrophysiology. This article brings forward a method for 3D dynamic modeling used in epicardial mapping system. Firstly, 3DMAX was used to create a 3D heart model and an .ase file was stored. Secondly, OpenGL was applied to display this model in users window interface. When electrodes and amplifiers sampled new data, the electrode which had the minimum euler distance to each vertex of 3D model was calculated, thus an interpolate triangle was formed by combining another two adjacent electrodes. The voltage value of each vertex was obtained by using a new linear interpolation based on grads calculation. This method was proved to be feasible in animal experiments. Electrical activity could be investigated directly in a cardiac cycle through this 3D model. This model can also reflect the conduction process of depolarization in complex arrhythmia such as atrial fibrillation. This method is appropriate for any real-time 3D dynamic field modeling, which has an array of regular measure points.

Method to Develop Coded Excitation for Velocimetry in Downhole Drilling

Background: In this paper, the phase modulation coding/decoding technology is discussed for the application in the high attenuation medium based on the simulation and the experiment. Methods: For the decoding perspective, the matched filter and the inverse filter are compared. An extra processing is introduced right after the matched filtering to restrain the range sidelobes. Furthermore, in the latter part of this paper, the factors to cause a degeneration in signal-noise ratio are quantitatively evaluated by simulation beam pattern and Doppler signal. Results: Based on the experiments and simulation in this paper, its found that the signal amplitude get significant boosted (30dB) while the range resolution is compatible with the span of a single pulse. Its also proved that the frequency dependent phase distortion from attenuation will cause more degeneration than Doppler effect, but even this influence can be compensated by the equalization.

A Visual Expression to Show Epicardial Electrical Activity Comprehensively

This paper refers to a new design to show epicardial electrical activity visually and comprehensively. With emulation modeling technology and linear interpolation, electrical activity on the epicardial surface can be displayed directly, precisely and continuously. Simulation tests and animal tests proved that the system could describe the cardiac activation vividly, just like weather nephogram. The proposed method may make this epicardial mapping system an important tool in studying cardiac electrophysiology.

Method to Annotate Arrhythmias by Deep Network.

This study targets to automatically annotate on arrhythmia by deep network. The investigated types include sinus rhythm, asystole (Asys); supraventricular tachycardia (Tachy); ventricular flutter or fibrillation (VF/VFL); ventricular tachycardia (VT). Methods: 13s limb lead ECG chunks from MIT malignant ventricular arrhythmia database (VFDB) and MIT normal sinus rhythm database were partitioned into subsets for 5-fold cross validation. These signals were resampled to 200Hz, filtered to remove baseline wandering, projected to 2D gray spectrum and then fed into a deep network with brand-new structure. In this network, a feature vector for a single time point was retrieved by residual layers, from which latent representation was extracted by variational autoencoder (VAE). These front portions were trained to meet a certain threshold in loss function, then fixed while training procedure switched to remaining bidirectional recurrent neural network (RNN), the very portions to predict an arrhythmia category. Attention windows were polynomial lumped on RNN outputs for learning from details to outlines. And over sampling was employed for imbalanced data. The trained model was wrapped into docker image for deployment in edge or cloud. Conclusion: Promising sensitivities were achieved in four arrhythmias and good precision rates in two ventricular arrhythmias were also observed. Moreover, it was proven that latent representation by VAE, can significantly boost the speed of convergence and accuracy.

Dominant factor analysis of B-flow twinkling sign with phantom and simulation data

Background and purposeThe twinkling sign in B-flow imaging (BFI-TS) has been reported in the literature to increase both specificity and sensitivity compared to the traditional gray-scale imaging. Unfortunately, there has been no conclusive study on the mechanism of this effect.Methods In the study presented here, a comparative test on phantoms is introduced, where the variance of a phase estimator is used to quantify the motion amplitude. The statistical inference is employed later to find the dominate factor for the twinkling sign, which is proven by computer simulation.ResultsThrough the analysis, it is confirmed that the tissue viscoelasticity is closely coupled with the twinkling sign. Moreover, the acoustic radiation force caused by tissue attenuation is found to be the trigger of the twinkling sign.ConclusionBased on these findings, the BFI-TS is interpreted as a tissue movement triggering vibration of microcalcifications particle.

Computer Simulation of Cathode Ablation for Atrial Fibrillation

We performed the computer simulation of cathode ablation for a trial fibrillation based on the standard and improved Cox maze III procedure with transmural ablation or not. At first, a computational a trial model was built from MRI images of a male volunteer, and was discretized into spherical units in a spherical coordinate. Then, the anisotropy of conduction velocity and electrical conductivity were incorporated into the special conduction system of this model. The action potential of each cell was simulated based on the Nygren cell model. Furthermore, action potential and conduction velocity restitutions were also introduced to the model. The simulation results demonstrated that non-transmural maze III ablation procedure can achieve the same effect as the transmural ablation if the positions of ablation lines are reasonable. This study may provide theoretical hints and evidence for the usefulness of maze III ablation procedure in the treatment of chronic a trial fibrillation.

A Parallel Algorithm for Computer Simulation of Electrocardiogram Based on MPI

This paper presents a parallel algorithm for computer simulation of Electrocardiogram (ECG) based on a 3-dimensional (3D) whole-heart model. The computer heart model includes approximately 50,000 discrete elements (model cells) inside a torso model represented by 344 nodal points with 684 triangle meshes. The Poison question is applied to the volume conductor problem for simulation of ECG, which involves a maximum of about 50,000 electric current dipole sources and four boundaries including the torso surface and three surfaces of heart. A parallel algorithm was introduced to solve this problem based on Message Passing Interface (MPI). An implementation is conducted with a cluster computer system consisting of up to eight PCs, each of which has a dual-core processor. It was shown that the speedup is close to 2 in one PC and close to 8 with 8 processors, as compared to the serial algorithm. This study demonstrates a useful way of parallel computing in biomedical simulation study.