S/m) and two agar lungs (0.24 S/m) in a saline background (0.424 S/m) filled to a depth of 1.6 cm. Trigonometric current patterns of amplitude 0.2 mA were applied at a frequency of 28.8 kHz (see \[[@Isaacson2004]\]). Results are presented in Section \[sec:results\_ACT3\]. The targets for the ACT4 data were made of agar with added graphite to simulate a chest phantom with a heart [[and two lungs]{}]{} in a saline bath of 0.3 S/m and height 2.25 cm. The admittivities of the targets, measured using the [sc SFP-7]{} bioimpedance meter sold by [Impedimed]{}, [[were as follows: heart [$0.68 +0.05i$ S/m]{} and lungs [$0.057 + 0.011i$ S/m]{}.]{}]{} The ACT4 system applies voltages and measures currents rather than vice-versa. In this experiment, trigonometric voltage patterns with maximum amplitude 0.5 V were applied at [[3]{}]{} kHz. ACT4 results are presented in Section \[sec:results\_ACT4\].

The data from the ACE1 system were taken on a chest shaped tank of perimeter 1.026 m with 32 electrodes of width 2.54 cm with bipolar adjacent current patterns applied at 3.3 mA and 125 kHz. [[A]{}]{}gar heart and lung targets (0.45 S/m and 0.09 S/m, respectively) [[were]{}]{} placed in a saline bath of 0.2 S/m filled to a height 