ABSTRACT
A novel drive circuit, useful for medical electronics, is capable of supplying a sample of human tissue, across which there should be zero direct voltage (dc), with a well-defined test current from a source having an output impedance exceeding 16 MOmega at 100 kHz.
Subject(s)
Electric Impedance , Electronics, Medical , Humans , TomographyABSTRACT
Following the successful development of a multiple-drive electrical impedance tomography system OXPACT-II featuring a voltage-driven current method for in vitro studies, research work currently being undertaken at the EIT research group in Oxford is aimed at developing a real-time multiple-drive adaptive system, called the Oxford Brookes Adaptive Current Tomograph Mark-III (OXBACT-III) which will operate at several frequencies in between 10-160 kHz. The objective of this system development is to enable EIT clinical studies to be undertaken based on the adaptive current method. One of the most important issues addressed in the new system design is to achieve high data acquisition speed while maintaining sufficient system accuracy. This paper will describe the overall data acquisition system structure and relevant system performance specifications.
Subject(s)
Electric Impedance , Tomography/instrumentation , Data Display , Electrodes , MicrocomputersABSTRACT
A high output impedance current source was required for electrical impedance tomography (EIT) applications capable of operating up to 200 kHz. The architecture is based on operational-amplifier power-supply current sensing and produces a predominantly capacitive output impedance, which for the design presented is approximately 1.2 pF.
Subject(s)
Electric Impedance , Tomography/instrumentation , Amplifiers, Electronic , ElectronicsABSTRACT
This paper describes the development of an adaptive electric current tomography system which contains a novel front-end analog architecture. Programmable voltage sources have been used to deliver currents into the study object and to avoid the difficulties of obtaining high quality current sources. Through inverting an admittance matrix, the system is capable of achieving a desired current drive pattern by applying a computed voltage pattern. The tomograph, operating at 9.6 kHz, comprises 32 driving electrodes and 32 voltage measurement electrodes. The study of system noise performance shows high SNR in the data acquisition which is enhanced by a digital demodulation scheme. In vitro reconstruction images have been obtained with the data collected by the tomograph.
Subject(s)
Electrodes , Plethysmography, Impedance/methods , Signal Processing, Computer-Assisted , Tomography/methods , Equipment Design , Evaluation Studies as Topic , Image Processing, Computer-Assisted , Plethysmography, Impedance/instrumentation , Signal Processing, Computer-Assisted/instrumentation , Tomography/instrumentationABSTRACT
The accuracy requirements for adaptive current electrical impedance tomography (EIT) measurements exceed the capability of available current sources. A new architecture for an EIT system is described in which the electrode current is set indirectly from a voltage-drive structure. A numerically inverted admittance matrix, obtained from current measurements and driving voltages, has been used to achieve the desired current pattern from programmable voltage sources.
Subject(s)
Tomography/methods , Electric Conductivity , HumansABSTRACT
A wideband high CMRR instrumentation amplifier is described. Based on a previously reported current-mode design, the improved amplifier features excellent CMRR performance of better than 60 dB up to 200 kHz with unity differential gain.
