Abstract. We characterize the ability of electrical impedance tomography (EIT) to distinguish changes in internal conductivity distributions, and analyze it as a function of stimulation and measurement patterns. A distinguishability measure, z, is proposed which is related to the signal to noise ratio of a medium and to the probability of detection of conductivity changes in a region of interest. z is a function of the number of electrodes, the EIT stimulation and measurement protocol, the stimulation amplitude, the measurement noise, and the size and location of the contrasts. Using this measure we analyze various choices of stimulation and measurement patterns under the constraint of medical electrical safety limits (maximum current into the body). Analysis is performed for a planar placement of 16 electrodes for simulated 3D tank and chest shapes, and measurements in a saline tank. Results show that the traditional (and still most common) adjacent stimulation and measurement patterns have by far the poorest performance (by 6.9×). Good results are obtained for trigonometric patterns and for pair drive and measurement patterns separated by over 90 • . Since the possible improvement over adjacent patterns is so large, we present this result as a call to action: adjacent patterns are harmful, and should be abandoned. We recommend using pair drive and measurement patterns separated by one electrode less than 180 • . We describe an approach to modify an adjacent pattern EIT system by adjusting electrode placement.
In this paper we propose a novel formulation for the distinguishability of conductivity targets in electrical impedance tomography (EIT). It is formulated in terms of a classic hypothesis test to make it directly applicable to experimental configurations. We test to distinguish conductivity distributions σ 2 from σ 1 , from which EIT measurements are obtained with added white Gaussian noise with covariance Σ n . In order to distinguish the distributions, we must reject the null hypothesis H 0 :x = 0, which has a probability based on the z-score: z =x σx . This result shows that distinguishability is a product of the impedance change amplitude, the measurement strategy and the inverse of the noise amplitude. This approach is used to explore different current stimulation strategies.
Abstract-Conducted Energy Weapons (specifically the Taser) are being increasingly used by police in several countries, and have also been subject to significant media concern over the level of emissions and applicable safety standards. One issue has been the variability in electrical output between weapons, and of individual weapons over time. In order to address this issue, we present work to: 1) establish consensus on the appropriate electrical parameters to characterize a weapon's biomedical effects, and 2) the development and design of a portable test system to measure these parameters. A weapon is electrically connected to a calibrated dummy resistive load of 600 ohms and fired for 5s while the output voltage is measured and the parameters are subsequently calculated. This test system has been used to characterize 256 shots from 84 weapons over 8 test episodes spanning 16 months.
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