1. A method of generating a series of tomographic images of a tissue sample, the tissue sample being part of a patient, using an imaging apparatus including a tank having a plurality of electrodes exposed around an interior surface of the tank; an electrically-conductive mediating fluid in the tank in an amount such as to contact the plurality of electrodes; a signal generating means for generating an electrical analog signal; a switching means for electrically and selectively connecting each of the plurality of electrodes individually to the signal generating means such that the electrical analog signal may be driven to the each of the plurality of the electrodes; and at least one computer arranged to perform mathematical calculations, said method comprising the steps of: (a) placing the tissue sample into the tank; (b) connecting one electrode to electrical ground, the electrode so connected being a grounded electrode; (c) adjusting the amount of mediating fluid in the tank to attain a fluid level; (d) connecting the signal generating means to an electrode that is not the grounded electrode by means of the switching means, the electrode so connected being an active electrode; (e) driving the analog signal to the active electrode while monitoring one or both of voltage and current at each of the plurality of electrodes so as to obtain measured values of the one or both of voltage and current at each of the plurality of electrodes; (f) calculating an impedance value associated with the each of the plurality of electrodes from the measured values of one or both of voltage and current; (g) repeating said steps (d) through (f) for a number of iterations such that no one electrode of the plurality of electrodes is connected to the signal generating means during more than one of the iterations and so as to generate a set of impedance values that includes the impedance values of said step (e), and associating the fluid level with the set of impedance values; (h) repeating said steps (c) through (g) for another number of iterations so as to create a group of unique fluid levels and a group of sets of impedance values, each of the sets of impedance values being associated with one of the unique fluid levels, the unique fluid levels being identifiable in an order from greater to smaller; (i) for each of the unique fluid levels, calculating an impedance map of modeled impedance values from the set of impedance values associated with the each of the unique fluid levels and associate the impedance map with the each of the unique fluid levels, the modeled impedance values being calculated by a numerical modeling algorithm and each of the modeled impedance values being mapped uniquely to a node of a Cartesian mesh, the Cartesian mesh being common to all impedance maps so calculated; and (j) for each of the unique fluid levels except the smallest unique fluid level, calculate an impedance image map by performing a matrix subtraction of the impedance map associated with the next smaller of the unique fluid levels from the impedance map associated with the each of the unique fluid levels and associate the impedance image map with the each of the unique fluid levels, wherein said steps (f), (i) and (j) are performed by means including the at least one computer.