Zuxiang Fang

An Electromagnetic Tracking Method Using Rotating Orthogonal Coils

In this paper, an electromagnetic tracking method that uses two rotating orthogonal coils is proposed. Two cross-shaped coils can rotate together and be driven in sequence to generate a magnetic field. One of the rotating orthogonal coils is used to track the position of the three-axis sensor and the other is to help solve the orientation of the sensor. As rotation can provide a geometrical relationship between the magnetic source and the sensor, the method does not require the generated magnetic field to imitate the ideal dipole in calculation. A fast noniterative algorithm and simple 1-D mapping along the axis of one coil are used to realize six degree-of-freedom (6DOF) tracking. Thus, the complexity of the magnetic tracking method and the corresponding system can be greatly reduced. Simulation results show that the method has good tracking accuracy and speed, which can be further improved by using an adaptive step-size searching strategy. So, it is concluded that the method can be used as an effective target monitoring method in many application domains such as minimally invasive therapy.

A novel non-model-based 6-DOF electromagnetic tracking method using non-iterative algorithm

Electromagnetic tracking, a non-fluoroscopic image navigation method most often used in minimally invasive therapy, has prominent advantages and features over the traditional X-ray radioscopy. Using two rotating coils and one 3-axis magnetic sensor, a novel 6 degree of freedom (DOF) electromagnetic tracking method is proposed in this paper. Two alternate rotating magnetic fields are generated in turns by these coils and the moving-around sensor simultaneously detects the magnetic filed flux density in 3 orthogonal directions. As the magnitude of a magnetic field comes to the maximum only when the rotating coil directly points toward the sensor, the spatial position and orientation of the sensor can be determined using triangulation measurement. An embodiment and the corresponding system framework of this method are developed and a non-model-based non-iterative algorithm is presented to calculate the 6-DOF of position and orientation. Moreover, simulation experiments are performed to validate the proposed method. The obtained results show that the averaged position error is 0.2365 cm and the averaged orientation error is below 1 degree away from low resolution area.

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).

Analysis of epicardial mapping electrogram of sustained atrial fibrillation based on shannon entropy

The mechanisms of sustained atrial fibrillation (AF) are not well understood. And predicting the development of AF is a problem of great clinical interest. This paper proposed an AF analysis method by evaluating, based on Shannon entropy, the complexity of atrial activation in various AF stages. The first step was to preprocess and characterize electrograms. Then, Shannon entropy analysis and statistical analysis were applied to find the significance of interval entropy in sustained AF. Study results proved that interval entropy presented a degressive tendency in the process of sustained AF and some sites with high activation frequency but low entropy was possibly related to ectopic driver of AF.

Successive ECG telemetry monitoring for preventing sudden cardiac death

In this paper, a novel successive ECG telemetry monitoring prototype is developed to evaluate the effect of monitoring for those out-of-hospital patient who has serious arrhythmia and/or possesses the risk of sudden cardiac death (SCD). This system has such features as: real-time, continuous, telemetry monitoring, wide range, long distance, and long term etc. The developed prototype consists a pocket-size patient-side monitor and a monitoring center placed in a hospital, which continually collects every patient’s ECG through GPRS mobile network and automatically analyzes it, if any danger found, instantly send medical warning message to patient. Based on the subsequent experiments on three volunteers in daily activity situation, the preliminary results indicate three-channel ECGs of each volunteer and his localization information can be real-timely and continuously monitored in the center.

Decreasing the Defibrillation Energy by Optimizing the Pulse Duration of Electrical Shock

Low energy defibrillation can not only save the power of the device (especially the ICD) but also lighten the damage to the patients. This paper investigates the method to decrease the defibrillation energy by optimizing the pulse duration of electrical shock. The defibrillation threshold is one of the main parameter to evaluate the defibrillation dosage. In this paper, the defibrillation threshold corresponding to the pulse duration is analysed and studied through 7 animal trails by an appropriative defibrillator designed by ourselves.The defibrillation thresholds are changing along with the changing of the pulse duration and existing optimal pulse duration that corresponding to the lowest defibrillation threshold. Although this optimal pulse duration is not so steady under different conditions in our animal trails but it showed a nice possibility to decrease the defibrillation energy by optimizing the pulse duration.

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.

A New System for Whole-atrial Epicardial Mapping

Epicardial mapping system is an important tool in the study and treatment of cardiac arrhythmias. Surgical therapy has been applied to eliminate atrial fibrillation (AF) for almost two decades, but there is still little effect on the treatment of AF in respect that the mechanism of AF is still unknown. Further investigation into the electrophysiological properties in AF is required to develop an appropriate treatment, though radiofrequency ablation has opened the new era of therapies for AF. Nevertheless, the sequential epicardial mapping for whole-atrium will increase the benefit to understand electrical mechanism during AF. The purpose of our research is to detect the electrical activity on the atrial surface and therefore find the optimal technique or ablation procedures to prevent AF. Animal tests were operated on ten dogs in which chronic AF had been induced. In experiment whole-atrial electrodes were located on the atrial surface after the heart had been exposed. Fach 20-second sampling data during sinus or atrial fibrillation rhythm were recorded and stored for analysis. Three-dimensional dynamic maps are presented clearly and the activity of sinus or AF rhythm can be seen quite differently. The active isopotential map can display the dynamic electrical conduction of the atria as a movie. This study demonstrates the flexibility of the system in AF research

A Real-Time Continuous ECG Transmitting Method through GPRS with Low Power Consumption

In this paper, a novel real-time continuous electrocardiogram (ECG) transmitting method through GPRS network is presented, which is based on a packet-level forward error correction (PFEC) method with simultaneously considering low power consumption. This novel method is used on the user datagram protocol (UDP) for data transmission. Furthermore, a series of communication tests based on a developed experiment platform are carried out to validate this method. Results indicate that the transmitting protocol using the PFEC with a packet size of 450 bytes, 3 seconds of transmission interval per packet would achieve about 0.1% to 0.3% packet loss rate, which is more effective transmission and has lower power consumption, and conclusively match actually the requirement of the clinical mobile monitoring.

A Clustered Real-Time Remote Monitoring System for Out-of-Hospital Cardiac Patients

To provide more convenient and comprehensive medical monitoring, especially to the out-of-hospital patients, this paper describes the implementation of a novel clustered real-time remote monitoring system. The manufacture of portable terminal device and development of hospital monitoring center system are introduced in detail. In addition, all-around tests are made to the whole system. The experimental results indicate that the system can afford a long-term, real-time and continuous monitoring and accurate positioning to multiple patients simultaneously. An automatic diagnosis can also be undertaken. It presents a good clinical application prospect.