Fast EIT data acquisition system with active electrodes and its application to cardiac imaging

A wide-band high-speed data acquisition system for electrical impedance tomography (EIT) is described. 32 active electrodes are used in the system, half of them as receive electrodes and the other half as drive electrodes. A buffer is mounted on the back of each receive electrode and a current source on each drive electrode. A multielectrode system with active electrodes was built to make it convenient to attach all the electrodes on the human thorax. The system is suitable for both dynamic imaging and multifrequency electrical impedance tomography (MFEIT). Its operating frequency can be chosen between 25 kHz and 400 kHz. Current is injected sequentially into 16 adjacent current electrode pairs and the 16 voltages between adjacent receive electrodes are measured for each current injection. ECG is collected to determine the relationship between the reconstructed images and cardiac activity. The collection of one frame of data is completed within 25 ms. The system has been successfully used for imaging the variation of conductivity distribution of the human thorax. The beat-by-beat cardiac-related change of conductivity distribution has been imaged by our system. The quasi-periodic variation of the impedance distribution can be seen from the image sequence with breath-holding.