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 a verage inspiration frame was generated from the data frames associated with maximum inspiration. Frequency images were reconstructed from th ese frames. The frequency images were analysed to locate the pixel wit h the maximum change in the right lung field. The change was defined a s 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 fre quency for this region of interest show good overall reproducibility b etween electrode applications for eight frequencies (95% limits of agr eement +/-28%). This reproducibility is improved (95% limits of agreem ent +/-13%) by omitting the highest frequency (1.2 MHz) which is most subject to system noise. The parameters for the Cole model derived fro m data with the highest frequency omitted are less reproducible betwee n electrode applications (95% limits of agreement, R/S +/- 0.83, f(c) +/- 81.6, RC +/- 0.52, SC +/- 0.39). We suspect that the parametric mo del used may have an effect on this. The signals recorded at the highe st frequency (1.2 MHz) are a major source of variability. The reproduc ibility results are improved by omitting this frequency from the analy sis.