IMPROVEMENT OF CARDIAC IMAGING IN ELECTRICAL-IMPEDANCE TOMOGRAPHY BY MEANS OF A NEW ELECTRODE CONFIGURATION

Until now, electrical impedance tomography (EIT) has been used for car diac imaging with the electrodes attached transversally at the level o f the fourth intercostal space at the anterior side. However, the resu lts obtained with this electrode configuration have been disappointing . The aim of the present study was to improve the measurement design o f EIT for cardiac imaging. Therefore, magnetic resonance imaging (MRI) scans were analysed in two healthy subjects to determine the optimum anatomical plane in which atria and ventricles are clearly visually se parated. From these findings, we proposed a new oblique plane at the l evel of the ictus cordis anteriorly and 10 cm higher posteriorly. EIT pictures obtained in the oblique plane revealed a better visual separa tion between the ventricles and atria than with the electrodes attache d in the transverse plane. Comparison between volume changes measured by means of MRI and impedance changes in different regions of interest measured with EIT were performed with the electrodes in the proposed oblique plane. Ventricular and atrial volume changes measured by MRI s how the same pattern as do impedance changes measured by EIT. Furtherm ore, we assessed the reproducibility and validity of the oblique elect rode configuration in ten healthy male volunteers during rest and duri ng exercise compared with the currently used transverse electrode conf iguration. The reproducibility coefficient assessed from repeated meas urements with the electrodes attached in the oblique plane was 0.98 at rest and 0.85 during exercise. For the transverse plane the reproduci bility coefficient was 0.96 at rest and 0.66 during exercise. The well -known increase in stroke volume during exercise is 40% in healthy sub jects. The increase in impedance change during exercise compared with rest was 34 +/- 13% (20-59%) for the oblique plane and 68 +/- 57% (13- 140%) for the transverse plane. From these results we infer that the s troke volume is assessed more accurately by using the oblique plane. F rom these findings, we conclude that the oblique plane improved the ca rdiac measurements, because (i) a better spatial separation of the hea rt compartments is obtained, (ii) the results are more reliable and (i ii) measurements during exercise are more accurate with the electrodes attached in an oblique plane.