An EIT system includes a plurality of voltage sources for supplying a
corresponding plurality of voltages to a corresponding number of other
structures, voltage source calibration means for calibrating each voltage
source, and switching means for individually connecting the calibration
means to each voltage source in succession during a period when each
other structure is in an inactive condition. Calibrating respective
voltages and currents for each voltage source compensates for shunt
impedance of each voltage source. A method for calibrating the system
includes individually connecting the calibration means to each voltage
source in succession during a period when each other structure is in an
inactive condition for calibrating all of said voltage sources in the
same way.