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J Jossinet

Publications and source records attributed to J Jossinet.

At least 19 recordsLinked to original sources
PubMed2002

Sauer's non-linear voltage division.

The non-linearity of the electrode-tissue interface impedance gives rise to harmonics and thus degrades the accuracy of impedance measurements. Also, electrodes are often driven into the non-linear range of their polarisation impedance. This is particularly true in clinical applications. Techniques to correct for electrode effects are usually based on linear electrode impedance data. However, these data can be very different from the non-linear values needed. Non-linear electrode data suggested a model based on simple assumptions. It is useful in predicting the frequency dependence of non-linear effects from linear properties. Sauer's treatment is a first attempt to provide a more general and rigorous basis for modelling the non-linear state. The paper reports Sauer's treatment of the non-linear case and points out its limitations. The paper considers Sauer's treatment of a series arrangement of two impedances. The tissue impedance is represented by a linear voltage-current characteristic. The interface impedance is represented by a Volterra expansion. The response of this network to periodic signals is calculated up to the second-order term of the series expansion. The resultant, time-dependent current is found to contain a DC term (rectification), as well as frequency-dependent terms. Sauer's treatment assumes a voltage clamp across the impedances and neglects higher-order terms in the series expansion. As a consequence, it fails adequately to represent some experimentally observed phenomena. It is therefore suggested that Sauer's expressions for the voltage divider should be combined with the non-linear treatments previously published by the co-authors. Although Sauer's work on the non-linear voltage divider was originally applied to the study of the non-linear behaviour of the electrode-electrolyte interface and biological tissues, it is stressed, however, that the work is applicable to a wide range of research areas.

Electric Impedance↗
PubMed2001

Electric current generated by ultrasonically induced Lorentz force in biological media.

The ions of solutions exposed to the propagation of ultrasound in the presence of a magnetic field experience Lorentz force. Their movement gives rise to a local electric current density, which is proportional to the electric conductivity of the medium. In vitro assessment of this current is performed using simple models of biological media. A constant magnetic field of 0.35 T and 500 kHz pulsed ultrasound are used. The sensing electrodes are exposed to neither the pressure wave nor the magnetic field, thus ensuring that the signal is not due to any undesirable electrode effect. The experimental results confirm that the current is proportional to the electrical conductivity of the medium. The changes in the measured current against the width of the measurement chamber show that the electrodes only collect a fraction of the current created within the medium. The magnitude of the measured current is 50nA in a saline solution of 0.5 S/m conductivity. The technique enabled the determination of the conductivity of a porcine blood sample against haematocrit. It is concluded that this type of measurement has the potential to allow the electrical conductivity of a medium to be determined using ultrasound.

Electric Conductivity↗
PubMed2001

Scanning electric conductivity gradients with ultrasonically-induced Lorentz force.

The ions in a fluid element oscillating under the effect of a sound wave in the presence of a magnetic field are submitted to Lorentz force. This gives rise to a bulk current density proportional to the medium's electric conductivity. In the present study, the integrality of this interaction current was collected using a pair of plane electrodes located on opposite sides of the sample. A focused transducer produced ultrasound bursts of 10 micros duration, 500 kHz frequency and 1.5 MPa peak pressure. The magnetic field was created by a purpose-built 0.35 T permanent magnet. Wiener inverse filtering was used to retrieve the system response from the recorded waveforms. The final signal was shown to be proportional to the gradient of sigma/rho along ultrasound propagation axis. Electric conductivity, sigma, predominantly controls this parameter since mass density, rho, does not vary in great proportions in biological media. Rectangular blocks of Agar gel and a layered bacon sample were used as models of biological media. The signals obtained in gel blocks had a longitudinal spatial resolution better than 1 mm. The successive layers of the bacon sample were clearly resolved. The advantages of this new modality for tissue characterization include the permeability of body tissue to magnetic field and ultrasound, the harmlessness of the applied fields and the improved spatial resolution in the measurement of a tissue's electric conductivity distribution.

Electric Conductivity↗
PubMed2000

Classification of breast tissue by electrical impedance spectroscopy.

Electrical impedance spectroscopy is a minimally invasive technique that has clear advantages for living tissue characterisation owing to its low cost and ease of use. The present paper describes how this technique can be applied to breast tissue classification and breast cancer detection. Statistical analysis is used to derive a set of rules based on features extracted from the graphical representation of electrical impedance spectra. These rules are used hierarchically to discriminate several classes of breast tissue. Results of statistical classification obtained from a data set of 106 cases representing six classes of excised breast tissue show an overall classification efficiency of approximately 92% with carcinoma discrimination > 86%.

Breast Neoplasms↗
PubMed2000

Quantitative assessment of ultrasound-induced resistance change in saline solution.

The purpose of the study was the experimental assessment of the interaction coefficient characterising the influence of pressure on the conductivity of electrolyte solutions. Pressure pulses were applied to samples of 9 gl-1 sodium chloride contained in cuboid measurement cells of identical cross-sectional dimensions but different thickness along the acoustic beam axis. The magnitude of the changes induced in cell resistance was recorded for three values of applied pressure increment (delta P = 0.94, 1.39 and 1.78 MPa) and three values of cell thickness (e = 0.58, 1.13 and 1.62 mm). A thick, focused transducer generated short (0.1 microsecond), unipolar pressure pulses. A model accounting for the characteristics of the pressure pulse and the geometry of the measurement cell was developed to predict the ultrasound-dependent changes in the measured electrical resistance. Despite some discrepancy between theoretical and experimental results, discussed in the paper, the results validated the order of magnitude of the interaction coefficient (10(-9) Pa-1). The predictions varied from about 50% (e = 1.62 mm, delta P = 0.94 MPa) to 77% (e = 0.58 mm, delta P = 1.78 MPa) of the experimental values.

Acoustics↗
PubMed2000

Nonlinear transient response of electrode-electrolyte interfaces.

The voltage transient response, V(t), of the electrode-electrolyte interface is known to be nonlinear. It has been shown by Onaral and Schwan in 1983 that the DC limit current of linearity, IAL, is proportional to t-beta were beta is the fractional power dependence of the linear, short pulse duration impedance. We now seek to explain the physical phenomena underlying this observation. We present an equivalent circuit model of the interface and highlight the major source of the observed nonlinear behaviour. Using the equivalent circuit model and associated formulae, an expression for the limit current of linearity is derived and compared with that found experimentally by Onaral and Schwan. According to this theoretical model, a current of as little as 22 nA can be sufficient to drive an electrode system into nonlinear behaviour at longer pulse durations.

Electric Impedance↗
PubMed2000

Experimental measurement of the acousto-electric interaction signal in saline solution.

Acoustic pressure alters local electrical conductivity in tissues and solutions. This work concerns the measurement of electrical conductivity in a liquid which is subjected to an acoustic pressure field created by a focused transducer. Measurements were made with four electrodes positioned in the ultrasonic focal zone, and the signal concerned is referred to as the acousto-electric interaction signal. A solution of sodium chloride in a measurement cell was subjected to ultrasound pressures of upto 1 MPa. It was shown that it is possible to quantitate the acousto-electric interaction signal once the ultrasonic vibration potential due to the Debye effect has been subtracted. The acousto-electric interaction signal was shown to be directly proportional to both the applied acoustic pressure and current. For the measurement cell used in this work, the interaction factor was found to be 5.3 microVmA(-1) MPa(-1).

Acoustics↗
PubMed1999

A review of parameters for the bioelectrical characterization of breast tissue.

In the data set collected by the authors in freshly excised breast tissue, the admittance loci generally differed from circular arcs, rendering the calculation of the usual set of parameters impossible. Alternative parameters were used for the analysis of these data. The present study consists of the definition and evaluation of a set of such parameters aimed at the characterization and differentiation of breast tissues. These parameters were defined so that their calculation does not require the fit of circular arcs to the experimental points and is independent of any equivalent circuit model. The results of the statistical analysis showed significant differences between most of the tissue groups, especially between cancerous tissue and all the other groups, which confirmed that impedance spectroscopy can be considered as potentially suitable for breast cancer detection.

Adipose Tissue↗
PubMed1998

The impedivity of freshly excised human breast tissue.

A set of 120 impedivity spectra was collected in breast tissue immediately after excision from 64 patients undergoing breast surgery. The measurements were made at 12 discrete frequencies halving from 1 MHz to 488 Hz. The spectra were sorted into three groups of normal tissue, mammary gland, connective tissue and adipose tissue, and three groups of pathological tissue, mastopathy, fibroadenoma and carcinoma. Intergroup multiple comparisons of the components of impedivity and admittivity were systematically carried out at every measurement frequency. The low-frequency-limit resistivity, the fractional power and characteristic frequencies were calculated from the experimental data. No significant correlation between impedivity and admittivity and patient's age was observed, except for mastopathy. No significant difference between groups of normal tissue and benign pathology (mammary gland, mastopathy and fibroadenoma) was found. The group of carcinoma differed from all the other groups principally by the low-frequency-limit resistivity, the fractional power and the phase angle at frequency above 125 kHz. These results indicate that impedance spectroscopy is appropriate for the detection of breast cancer.

Aging↗
PubMed1996

Variability of impedivity in normal and pathological breast tissue.

The impedivity of six groups of breast tissue is measured between 0.488 kHz and 1 MHz using a hand-held probe, ensuring a constant geometry factor, and a microcomputer-controlled impedance spectroscopy system. 120 spectra are collected in excised tissue samples from 64 patients undergoing breast surgery. Each spectrum consists of 12 frequency points. The mean m, the standard deviation s, and the 'reduced standard error' (epsilon = s/(m N)) of the magnitude and the phase angle of the impedivity are calculated at each frequency for all groups of tissues. The variability at low frequency (f < 10 kHz) is attributed to the dispersion in measurement errors. This contributed to the choice of 32 KHz as the lower limit of measurement frequency in constructed electrical impedance tomograph. The collected data also show that frequencies larger than 1 MHz are needed for the bio-electrical characterisation of breast tissue. In the frequency range used in electrical impedance tomography the reduced standard error of impedivity in breast tissue is about 0.1 or less. The lowest dispersions are observed in the adipose tissue, carcinoma and fibro-adenoma.

Adolescent↗
PubMed1996

Factors affecting electrode-gel-skin interface impedance in electrical impedance tomography.

The magnitude, mismatch and temporal variations of the electrode-gel-skin interface impedance can cause problems in electrical impedance tomography (EIT) measurement. It is shown that at the high frequencies generally encountered in EIT the capacitive properties of the electrode interface, and especially those of the skin, are of primary importance. A wide range of techniques are reviewed that could possibly be used to minimise these problems. These techniques include the use of skin preparation, penetration enhancers, temperature and electrical impulses. Although several of these techniques appear very attractive, they are not without serious potential drawbacks. A combination of some of these techniques may well hold the key to success.

Electric Impedance↗
PubMed1995

Tissue impedance: a historical overview.

Over the past 150 years the study of the electrical properties of various biological tissues has been undertaken by researchers from a wide variety of scientific backgrounds. This has, unfortunately, led to the existing range of confusing and misunderstood terminology/concepts. Some of the most important are presented and explained.

Animals↗
PubMed1994

Physical interpretation of Schwan's limit voltage of linearity.

The electrode/electrolyte interface impedance can be represented by the parallel combination of a non-faradaic pseudocapacitance and a faradaic, charge transfer resistance. The non-linearity of the overall electrode/electrolyte interface impedance is largely due to that of the faradaic resistance which is derived from the Butler-Volmer equation. As the charge transfer resistance dominates the interface impedance at low frequencies, it is in this region that non-linearities are first observed. The voltage limit of linearity has been investigated and found to increase gradually for higher frequencies. Although relatively linear compared with the charge transfer resistance, the non-faradaic impedance becomes non-linear at large applied voltage amplitudes and dominates the high-frequency non-linear behaviour of the overall interface impedance. Mid-frequencies are affected by a combination of the faradaic and non-faradaic non-linearities.

Electric Impedance↗
PubMed1994

Bioelectrical spectroscopy from multi-frequency EIT.

A method is described by which bioelectrical spectroscopy could be combined with multi-frequency electrical impedance tomography (EIT) enabling a Cole-Cole plot to be drawn for any selected pixel in the image for tissue characterization. To demonstrate the principles of the method, multi-frequency EIT measurements were simulated with a numerical model. As an example, porcine myocardium, immersed in an electrolytic tank, was simulated for a frequency range of 20 kHz to 2 MHz. The method could have an important application in transplant surgery for screening organs for viability prior to transplant.

Animals↗
PubMed1994

Active current electrodes for in vivo electrical impedance tomography.

The characterization of tissue by means of electrical impedance tomography requires accurate impedance measurements at relatively high frequencies. The present study describes the design and fabrication of broad-band, active, current electrodes for in vivo measurements. This approach eliminates the lead capacitances of the sourcing electrodes. The value of the resistors used were computed according to a protocol taking into account the constraints of a given application and the values and tolerances of the available components. Additional selection of the components further reduced the variability in circuit performance. The current sources designed according to the method described are usable at frequencies higher than 1 MHz, for differential load impedances up to 2000 omega. The parallel output conductance for each active electrode is 0.85 microS +/- 2%. The design method is valid for either adjacent or diametric drive, and can be applied to various applications by modifying the shape of the electrode.

Electric Conductivity↗
PubMed1992

A physical interpretation of Schwan's limit current of linearity.

In this the second of a series of papers on the nonlinearity of the electrode-electrolyte interface impedance, the wealth of experimental observations which exists in the literature on AC impedance nonlinearity is physically interpreted. The interface impedance is well represented by the parallel combination of a constant phase angle impedance and a charge transfer resistance. The charge transfer resistance is the major source of the observed nonlinearities. As a result, the current limit of linearity, iL, increases with frequency such that iL is proportional to omega beta. The series resistance, Rs, of the interface impedance initially increases with applied signal amplitude, reaches a maximum and then decreases. The series reactance, Xs, decreases monotonically with signal amplitude.

Electric Conductivity↗