EBCT imaging of heart and lungs triggered by ECG and ventilation

A device has been developed to monitor both the bioimpedance across the thorax using the four-electrode method and the ECG. The transthoracic bioimpedance signal depends on the alveolar air volume. Coincidence of the ECG related trigger signal (e.g. R-wave) with a set tolerance band for this bioimpedance signal is determined and employed to trigger the electron beam computerised tomography (EBCT) imaging. The coincidence rate of the R-wave with the alveolar air volume depends on the width of the tolerance band. Furthermore, the coincidence rate depends on the position of the tolerance band between the endinspiratory and the endexpiratory volume. When the tolerance band is set to 10% of the tidal volume (approx. 50 ml) the displacement effect is estimated to be about 2 mm. Under these conditions, the total cycle time is prolonged to about 200 s. The trigger device has been successfully used to control the EBCT machine.