OPTIMAL FILTERING OF EIT DATA IN SPECTRAL EXPANSION ANALYSIS

The signal-to-noise ratios for some EIT measurements are very low, and for in vivo EIT measurements these ate dependent on the electrode pos itioning and the distance from the current drive. The effect of removi ng noisy measurements to produce higher-fidelity images was investigat ed for the case of gastric emptying data. A consequence of this filter ing was the reduction in the size of the sensitivity matrix and its su bsequent singular-value decomposition. Several different filters were tested and for each of these the spectral expansion regularization fil ter was optimized using a chi(2) test. Filtering out the measurements made by the spinal electrode, where the spinal bone barrier lies direc tly in the current path to the stomach, produced improved images by re ducing the artefact content in the spinal sector of the conductivity m ap. For stomach imaging little useful information is produced by the s pinal electrode, and the benefits of filtering dominate. However artef act images may be generated. In contrast consistent small improvements were produced by filtering out some of the weakest signals.