PubMed · 14059529
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R PLONSEY. 1963. CURRENT DIPOLE IMAGES AND REFERENCE POTENTIALS.. https://doi.org/10.1109/tbmel.1963.4322774
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Implantable electronic devices such as pacemakers and neural implants are often used for electrical stimulation. The usage of microfabrication techniques to produce microelectromechanical systems (MEMS) has allowed engineers to address a wider range of clinical indications. A new direction in the area of MEMS technology is the goal of achieving pulsatile drug delivery. The digital capabilities of MEMS may allow greater temporal control over drug release compared to traditional polymer-based systems, while the batch-processing techniques used in the microelectronics industry can lead to greater device uniformity and reproducibility than is currently available to the pharmaceutical industry. A repertoire of structures, including microreservoirs, micropumps, valves, and sensors, is being developed that will provide a strong foundation for the design of integrated, responsive MEMS for drug delivery.
Electrical impedance tomography (EIT) was used to monitor the movement of a fluorinated hydrocarbon dense nonaqueous phase liquid (DNAPL) through a saturated porous medium within a laboratory column. Impedance measurements were made using a horizontal plane of 12 electrodes positioned at regular intervals around the centre of the column. A 2D inversion algorithm, which incorporated the cylindrical geometry of the column, was used to reconstruct resistivity and phase images from the measured data. Differential time-lapse images of DNAPL movement past the plane of electrodes were generated by the cell-by-cell subtraction of resistivity and phase baseline models from those associated with the DNAPL release stage of the experiment. The DNAPL pulse was clearly delineated as resistive anomalies in the differential time-lapse resistivity images. The spatial extent of the resistive anomalies indicated that in addition to vertical migration, some lateral spreading of the DNAPL had occurred. Residual contamination could be detected after quasi-static conditions were reestablished. Residual DNAPL saturation was estimated from the resistivity model data by applying Archie's second equation.Despite significant measured phase changes due to DNAPL contamination, the differential phase images revealed only weak anomalies associated with DNAPL flow; these anomalies could be seen only in the initial stages of the experiment during peak flow through the plane of electrodes.
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