Systematic errors in multi-frequency EIT

Systematic errors have been measured with a multi-frequency data-collection system operating between 10.24 and 81.92 kHz. The errors were present even though a conventional background measurement on a uniform saline phantom h ad already been subtracted. Errors due to changes in transimpedance between the calibration and the tissue measurements, cable movement and electrode- skin contact impedance were simulated giving a total systematic error estim ate equivalent to a 9% change in tissue conductivity. It was shown that mor e than 89% of the image was above the total error magnitude, indicating tha t most of the image revealed true changes in tissue conductivity. In three human subjects, the largest conductivity changes were in two regions, locat ed posteriorly on either side of the midline, and were interpreted as due t o the erector spinae muscles. These regions showed increases in conductivit y of 73-104%. Identification of other anatomical features was difficult bec ause of the poor spatial resolution of the images.