A programmable DDS waveform generator for electrical impedance tomography (EIT)

New forms of investigation with EIT require that the signals used for measurement are of an arbitrary form. Both multifrequency and nonsinusoidal signal forms extend the application of EIT to encompass further tissue characteristic information. Recently, multifrequency EIT-systems have been constructed to characterise tissue on the basis of the bioimpedance spectrum. Ideally, the frequency response of tissue up to several MHz has to be obtained. A possibility is to measure simultaneously or successively the tissue impedance at different frequencies. Another approach is to use broadband signals like impulses or noise series. Maximum length sequences (MLS) area class of pseudorandom noise sequences which enable fast calculation of the impulse response by cross-correlating the system's input and output signals.