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Biomedical subjects

J Jossinet

Publications and source records attributed to J Jossinet.

29 records · Page 2Linked to original sources
PubMed1992

Electrical impedance tomography. An improved design of voltmeter for semi-parallel data acquisition.

The design and implementation of high performance differential voltmeters for semi-parallel data acquisition are described. The general requirements and specific conditions encountered in electrical impedance tomography (EIT) for accurate measurements are analysed. The major parameters are common-mode rejection and bandwidth. A specific implementation of the voltmeters, with separate DC supplies and independent signal references, is described. This arrangement, in which each voltmeter follows the input signal, automatically cancels any common-mode voltage present at the input. The signal is fed to the remainder of the instrumentation through a transformer. The use of a reduced number of components contributes to the minimisation of the inter-channel variations. Furthermore, the geometrical distribution of the voltmeters around the object minimises the length of electrode wires, also reducing the input capacitance. The number of modular voltmeters and DC/DC converters is 32. The common-mode rejection of these voltmeters is greater than 72 dB in the frequency range 3.6-560 kHz. In conclusion, the proposed solution ensures a minimisation of common-mode errors and enables the use of a 250 kHz frequency.

Electric Conductivity↗
PubMed1992

Optimal electrolytic chloriding of silver ink electrodes for use in electrical impedance tomography.

The electrode-electrolyte interface impedance may be simplistically modelled by an equivalent circuit comprising a resistance, RTOTAL, in series with an empirical, constant phase angle impedance, ZCPA. This pseudo-capacitance can be thought of as representing empirically the non-faradaic, double layer capacitance in the presence of specific adsorption and surface roughness effects. RTOTAL is the sum of the lead and electrolyte resistances. Depositing a thin layer of silver chloride on silver electrodes can yield improved electrical performance characteristics (potential and impedance) when used in conjunction with a chloride gel. An electrolytically deposited AgCl layer tends to have a rough surface profile thus leading to an increase in the effective interface area. This gives rise to a decrease in RTOTAL and ZCPA, both of which are desirable. Unfortunately AgCl is a relatively poor conductor. Increasing layer thickness causes RTOTAL to increase, thus adversely affecting the inter-electrode impedance at high frequencies. Electrode systems for use in electrical impedance tomography therefore require only relatively thin layers of AgCl.

Electric Conductivity↗
PubMed1992

Imaging the complex impedance in electrical impedance tomography.

Measuring the reactive component of the bio-impedance enables a full characterisation of the frequency response of a tissue. The amplitude of the reactive component is relatively small in the frequency range generally used in electrical impedance tomography (EIT). Its measurement is therefore more sensitive to errors. At higher frequencies, the amplitude of this component increases, which increases the signal-to-noise ratio. The stray capacitance, however, also increases and the front-end circuit must be designed carefully. The purpose of the present study is to show the feasibility of the collection of data at relatively high frequencies; 31.25 and 250 kHz were used. Both the real and reactive components were used to reconstruct images from capacitive targets. This study suggests that it may be possible to use multifrequency systems to determine the parameters of frequency loci and therefore tissue characterisation.

Electric Conductivity↗
PubMed1990

A computerized bioelectrical cardiac monitor.

The use of a micro-computer improves the performance of an impedance cardiograph. The impedance signals and the ECG are real-time processed and four analog signals are displayed on the screen. A beat-to-beat estimation of cardiac output and several indexes are computed and displayed. User's interface is by interactive screen menus. Some facilities permit data identification, storage and post-processing. The software has been designed in such a way as to be adaptable to each specific application and to enable the development of new routines for cardiac signal processing. The signals recorded in healthy patients are in agreement with the results of other similar studies.

Adult↗
PubMed1987

Physical study of the sensitivity distribution in multi-electrode systems.

The basic aim of bio-electrical multi-electrodes systems is to map the distribution of electrical parameters of the interior of the body by means of external measurements. Ideally, a perfect imaging system would be able to explore individually each point of the medium. In practice each recorded value results from the contributions of many points. For example, in classical tomography, each measurement is the integral along the line between source and detector. The reconstruction algorithm then extracts the individual value for each point of the image. The properties of electrical fields result in multi-path current flow in a medium: a given measurement not only involves the points on the line linking the electrodes, but also other points in the medium. The purpose of this work was to study the distribution of sensitivity in a model. The body was simulated by an insulating cylindrical tank of 19 cm diameter filled with water. Sixteen carbon electrodes of 6 mm diameter were placed regularly around the tank in a transverse plane. The frequency used was 20 kHz. The sensitivity at each point of the model was studied by means of a 21 mm diameter sphere of stainless steel plunged into the tank. Qualitatively the results confirmed that the sensitivity is high in the proximity of the electrodes and lower far from them. Furthermore, it is clear that the sensitivity out of the plane containing the electrodes is far from negligible. The data also allowed us to compare different electrode configurations and select those exhibiting the better sensitivity for interior points.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1985

Quantitative technique for bio-electrical spectroscopy.

Bio-electrical impedance measurements have been widely used for the study of body tissues. Apart from recordings of biophysical signals (respiration, perfusion, cardiac output, red cell settling, etc.) measurements of specific resistivity of a tissue provide information about its pathological state. Mapping electrical parameters will give more detailed information. The interpretation of recorded data and the design of equipment, both require a preliminary knowledge of the values encountered under normal and pathological conditions. The purpose of the technique described here is to determine the complex resistivity of breast tissue samples in vitro at frequencies between 0.5 kHz and 1 MHz. The equipment is described and the calibration procedure explained. A calculation of the final error interval is given. Characteristic spectra of modulus and phase angle recorded in normal and pathological breast tissue are shown. The technique can however be used for other body tissues, typical applications being fundamental tissue studies and a determination of the most suitable frequencies for use with impedance measuring devices. In clinical practice it could contribute to the determination of intra- and extracellular volume, the monitoring of transplanted organs and the examination of surgically treated tumours, and to any technique based on tissue characterization.

Biomedical Engineering↗
PubMed1976

Detailed description of an implantable directional Doppler flowmeter.

A Doppler flowmeter and the necessary modifications for implantation are described in detail. Since only part of the electronics was implanted a phase-locked loop had to be introduced in order to keep the flow measurement directional. The proper working of the apparatus is demonstrated in vitro and in vivo. As an example the result of flow studies in the aorta and the pulmonary artery after homotransplantation of the lung in dogs are given.

Animals↗
PubMedDate not supplied

A high frequency electrical impedance tomograph using distributed parallel input channels.

Electrical Impedance Tomography (EIT) is an imaging technique based on multiple impedance measurements using electronically multiplexed surface electrodes. The present study describes an EIT prototype tomograph which uses two frequencies of applied signal: 31.25 kHz (within the frequency range originally used in early EIT studies) and 250 kHz. The use of the latter frequency was made possible as a result of several technical innovations including the use of separate groups of electrodes for current injection and for differential voltage measurement and the use of parallel input channels distributed around the object. In vitro images were successfully obtained using the system at the above two frequencies. It is concluded from this study that Electrical Impedance Tomography can be used at sufficiently high frequencies to enable bio-electrical tissue characterisation.

Electric Conductivity↗