We have designed and built an impedance camera to generate electrical impedance images of the thorax. Our instrument makes 100 spatially specific admittance measurements per frame at rates up to 32 frames per second. An on-line raster-scan display provides direct visualization while recording of data allows off-line quantitative analysis. We have found that some of the admittance measurements change 25% in humans with forced respiration. We discuss the principle of a mutually guarding electrode array and its limitations and present ideal instrument specifications and a working design. Continuing development may allow noninvasive measurement of localized ventilation and perfusion.
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