Electrical measuring apparatus, and methods for determining the condition or identity of biological material
First Claim
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1. Apparatus for determining a measure of the admittance of biological tissue and an admittance ratio for the tissue, for assessing the condition or identity of the tissue, comprising:
- A pair of electrical conductors connectable to the respective contacts of a probe having a fixed spacing, between which contacts tissue is disposed in use of the apparatus;
means to generate a constant AC voltage at each of two distinct frequencies at which both the resistance and the capacitance of the tissue between said contacts are significant components of the impedance therebetween;
means to apply said constant AC voltage across said contacts first at one of said frequencies, then at the other;
precision voltage stabilization means coupled to said generation means to maintain the amplitude of said AC voltage at the two frequencies at the same accurately constant value;
buffer means in series with and between said voltage generation means and one of said conductors to minimize the loading effect of the impedance of the tissue on the impedance of the generating means;
amplifier means coupled to the other said conductor, in series with tissue when disposed between said contacts, to receive the current through the tissue and to generate an output AC voltage signal directly proportional to the current through the tissue and therefore to the admittance of the tissue on application of said AC voltage across a portion of the circuit which includes the tissue and the amplifier means; and
means to convert said output AC voltage signal to a DC output which is a measure of the admittance of the tissue between the probe contacts, the admittance ratio, for the two frequencies being thereby determinable from the respective DC outputs at the two frequencies.
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Abstract
This invention relates to a measurement system which applies voltage signals of different frequencies across a biological sample. The frequencies are chosen such that both resistance and capacitance are significant components of the measured impedance. The state of the biological sample is reflected in the admittance ratio for two frequencies.
72 Citations
10 Claims
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1. Apparatus for determining a measure of the admittance of biological tissue and an admittance ratio for the tissue, for assessing the condition or identity of the tissue, comprising:
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A pair of electrical conductors connectable to the respective contacts of a probe having a fixed spacing, between which contacts tissue is disposed in use of the apparatus; means to generate a constant AC voltage at each of two distinct frequencies at which both the resistance and the capacitance of the tissue between said contacts are significant components of the impedance therebetween; means to apply said constant AC voltage across said contacts first at one of said frequencies, then at the other; precision voltage stabilization means coupled to said generation means to maintain the amplitude of said AC voltage at the two frequencies at the same accurately constant value; buffer means in series with and between said voltage generation means and one of said conductors to minimize the loading effect of the impedance of the tissue on the impedance of the generating means; amplifier means coupled to the other said conductor, in series with tissue when disposed between said contacts, to receive the current through the tissue and to generate an output AC voltage signal directly proportional to the current through the tissue and therefore to the admittance of the tissue on application of said AC voltage across a portion of the circuit which includes the tissue and the amplifier means; and means to convert said output AC voltage signal to a DC output which is a measure of the admittance of the tissue between the probe contacts, the admittance ratio, for the two frequencies being thereby determinable from the respective DC outputs at the two frequencies. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of determining a measure of the admittance of biological tissue and admittance ratio for the tissue, for assessing the condition or identity of the tissue, comprising:
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applying an AC voltage maintained at accurately constant amplitude by precision voltage stabilization means across the sample at one frequency than the other, at which frequencies both the resistance and the capacitance of the sample are significant components of the impedance therebetween; directly measuring the respective currents across the sample by amplifier converter means having a virtual ground configuration in series with the tissue to receive the current through the tissue, and outputting AC voltage signals directly proportional to the respective currents and therefore to the admittance of the tissue; converting each said AC voltage signal to a DC output, which is a measure of the admittance across the sample, and determining the admittance ratio for the two frequencies from said DC outputs. - View Dependent Claims (9, 10)
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Specification