Patent ID: 7711418

Claim:
An electroimpedance tomograph comprising: a plurality of electrodes configured to be placed on a body; measuring circuits that process voltage signals recorded by the electrodes; and a control unit supplying two adjacent electrodes with an alternating current having one or more preset feed frequencies, said control unit receiving voltage signals from electrodes not directly supplied with said alternating current such that said control unit reconstructs the impedance distribution of the body in an electrode plane, wherein said control unit automatically sets one or more current frequencies such that said control unit records a frequency spectrum or a plurality of frequency spectra of a background signal based on voltage signals of electrodes received over a preset period of time, said voltage signals being stored in said control unit as a voltage time series, said control unit transforming said voltage time series into a background frequency spectrum, said control unit searching said background frequency for a feed frequency having a useful signal to background signal ratio that is greater than a threshold value, said useful signal having a useful signal frequency range, said background signal having a background frequency range, said threshold value being based on an overlap of said useful signal frequency range with said background frequency range.