A comparison of neonatal and adult lung impedances derived from EIT images.

An objective method of extracting respiratory data from lung images is presented, together with a technique for automatically generating regions of interest delineating the anterior and posterior regions of the lungs. The method is used to extract data on the change in lung impedance with frequency, and on calculated Cole parameters, from 19 normal neonates (gestational age 32 to 42 weeks) and 8 normal adults (age 21 to 82 years). A comparison of the impedance properties of neonatal and adult lungs was made. The variation of lung impedance with frequency in neonates, as derived from EIT images, is significantly different from that found for adults. The implications for a model of the electrical impedance of lung tissue are discussed.

Reproducibility of electrical impedance tomographic spectroscopy (EITS) parametric images of neonatal lungs.

The reproducibility of electrical impedance tomographic spectroscopy (EITS) images of neonatal lungs have been investigated in 11 clinically stable babies. We have used the Sheffield Mark IIIa EITS system. An average inspiration frame was generated from the data frames associated with maximum inspiration. Frequency images were reconstructed from these frames. The frequency images were analysed to locate the pixel with the maximum change in the right lung field. The change was defined as the 614 kHz measurement relative to 9.6 kHz. A 3 x 3 pixel region of interest was centred at this point. The changes in impedance with frequency for this region of interest show good overall reproducibility between electrode applications for eight frequencies (95% limits of agreement +/- 28%). This reproducibility is improved (95% limits of agreement +/- 13%) by omitting the highest frequency (1.2 MHz) which is most subject to system noise. The parameters for the Cole model derived from data with the highest frequency omitted are less reproducible between electrode applications (95% limits of agreement, R/S +/- 0.83, fc +/- 81.6, RC +/- 0.52, SC +/- 0.39). We suspect that the parametric model used may have an effect on this. The signals recorded at the highest frequency (1.2 MHz) are a major source of variability. The reproducibility results are improved by omitting this frequency from the analysis.

Data processing techniques for serial EIT spectroscopy images: a review of some preliminary results.

Mutlifrequency EIT imaging should allow specific organs within the body to be identified by their impedance spectrum, and the use of parametric imaging should lead to a much greater freedom from movement artefacts. This will make EIT more attractive as a monitoring technique, but the data rate will require automated processing of the images. The application of dynamic regions of interest, generated on a frame by frame basis, is described, with examples from the imaging of neonatal lungs and adult stomach. The lung can be objectively identified on a single frame from the fRSC, SC and RC images, but the stomach could only be identified on the dynamic images.

Multifrequency and parametric EIT images of neonatal lungs.

The aims of the study were to investigate the problems involved in making multifrequency EIT measurements on neonates and to compare the images obtained with the results from a group of normal adults. The Sheffield electrical impedance tomographic spectroscopy (EITS) system acquires multifrequency data using a set of eight drive and eight receive electrodes. EITS measurements were made on an inhomogeneous group of 10 neonates admitted to the special care baby unit for observation and feeding. R/S, characteristic frequency, RC and SC parameters were generated using the Cole equation. Comparisons of the parameters were made with data collected from normal adults in another study. We have shown that it is possible to obtain EITS parametric images of neonatal lungs and that there are some differences in Cole parameters between the adult and neonatal groups.

Multi-frequency imaging and modelling of respiratory related electrical impedance changes.

Two studies concerning multi-frequency impedance measurements are presented. The first uses tetrapolar measurements made on the thorax and the second electrical impedance tomography images, also made from the thorax. The way in which the impedance and the changes in impedance with ventilation depend upon frequency are investigated using Cole-Cole modelling and also a physiological model of lung tissue. There is an excellent fit to the Cole-Cole model, and the results show that it should be possible to identify tissue on the basis of the impedance spectrum and the spectrum of the changes in impedance during breathing.