A. D. Seagar

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Applied potential tomography (APT) or electrical impedance imaging has received considerable attention during the past few years and some in vivo images have been produced. This paper reviews the current situation in terms of what in vivo results have been and are likely to be obtained in the near future. Both static and dynamic imaging are possible and(More)
Because of the intrinsically low sensitivity of any surface potential measurement to resistivity changes within a volume conductor, any data collection system for impedance imaging must be sensitive to changes in the peripheral potential profile of the order of 0.1%. For example, whilst the resistivity changes associated with lung ventilation and the(More)
In any practical impedance imaging system it is important to be able to predict the image quality which can be expected from particular measurements. It is of interest both to establish the smallest object that can be detected for a certain noise level and to determine the maximum resolution for a certain number of electrodes. In impedance imaging this is(More)
Applied potential tomography is a new, non-invasive technique that yields sequential images of the resistivity of gastric contents after subjects have ingested a liquid or semi-solid meal. This study validates the technique as a means of measuring gastric emptying. Experiments in vitro showed an excellent correlation between measurements of resistivity and(More)
Resistance imaging involves the reconstruction of the distribution of electrical resistivity within a conducting object from measurements of the voltages or voltage gradients developed on the boundary of the object while current is flowing within the object. In general, the relationship between the distribution of resistivity in the object and the voltage(More)
The collection of data suitable for impedance imaging is a well defined task. Once the number of electrodes is chosen, it is possible to specify the number of independent measurements which must be made. Having done so, a data collection system can be designed; preferably with the view to both maximising the speed of data collection and minimising the noise(More)
A model is developed to interpret changes in limb volume measured during venous occlusion plethysmography. The parameters of the model are chosen to represent, as closely as possible, physiological variables related to blood flow within the limb. These parameters are shown to be related to various parameters derived by other investigators for interpreting(More)
The existence of variations of normal human thoracic impedance, during the cardiac cycle to high frequency electrical current is well known. Since the impedance variations within the thorax are synchronous with the electrocardiogram (ECG), they are attributed to cardiac activity. They can arise from the change of either the rate of blood flow or the blood(More)
The problem of reconstructing a two-dimensional distribution of electrical conductivity from impedance measurements made on the circumference of a circle enclosing the distribution is studied. It is shown to be, in general, impossible to uniquely reconstruct such conductivity distributions when employing certain recently proposed approaches based on the(More)
A boundary method is presented and is used to calculate the electric potential throughout two-dimensional regions which represent cross-sections of the human body. The method differs from the usual boundary element method by representing both the boundaries and the voltages supported on them as smooth (i.e. infinitely differentiable). Examples are given(More)