METHOD AND APPARATUS FOR MEASURING IMPEDANCE OF A CONDUCTING MEDIUM WITH A CALIBRATED PROBE

• US 3,566,233 A
• Filed: 10/21/1968
• Issued: 02/23/1971
• Est. Priority Date: 10/21/1968
• Status: Expired due to Term

• Current Assignee: Kontron Inc (Roche Holding AG)
• Original Assignee: Cosentino Louis Ciro, Kahn Alan Richard
• Inventors: KAHN ALAN RICHARD, COSENTINO LOUIS CIRO
• Application Number:
  US04/769,150
• Time in Patent Office: 855 Days
• US Class Current: 324/71.1
• CPC Class Codes: A61B 2562/0215 Silver or silver chloride containing
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: G01R 19/08 Measuring current density

Abstract

A technique and apparatus for measuring a quantity in a field associated with the transport of energy in a medium by introducing a transducer bearing probe to the medium, employing an external active energy source and externally adjusting the energy transport between relatively fixed transducers on the probe, and controlling said energy source by way of a new quantity in the field detected after the probe disturbance to restore the field to its nondisturbed condition enabling a precise measurement to be made.

Claims

1. A method for measuring a quantity such as impedance or thermal conductivity between two points spaced a such as tissue which medium is conducting energy such as electrical energy or heat energy except in a space between said probe'"'"''"'"'s points, by providing a probe bearing a pair of transducers separated by a nonconducting body adapted to occupy said space and calibrated in a environment such as a solution having known energy conducting characteristics similar to said medium to provide a probe calibration factor which matches the probe impedance or thermal conductivity to the environment impedance or thermal conductivity immersing the probe in said medium detecting a difference such as potential or temperature, of the medium disturbed by the probe between said two points defined by the transducer-medium interfaces, restoring the disturbed medium to its predisturbed state by externally controlling the probe'"'"''"'"'s impedance or thermal conductivity characteristics in a measurable manner through an active energy source, and measuring said quantity by relating said detected potential of the medium in its predisturbed state to the calibration factor.

2. Apparatus for measuring an electrical quantity such as current, impedance and potential in living tissue conducting current, comprising:

probe means having a first and second set of electrodes and calibrated in terms of the probe'"'"''"'"'s impedance characteristics in a medium such as a solution having known impedance characteristics to provide a calibration factor to match the probe impedance characteristics to the medium impedance characteristics;

means connecteD with said first set of electrodes for detecting an electrical potential in the tissue between the second set of electrodes at the probe-tissue interface, current producing means connected with said second set of electrodes;

means for controlling an output of said current producing means with the detected potential and in accordance with said calibration factor to provide the probe with an impedance characteristic matched to that of the tissue, and means for measuring said detected potential and the output of said current producing means.

3. Apparatus according to claim 2 wherein:

said detecting means includes voltage amplifier means having a high input impedance and a high common made rejection ratio, and said current producing means is connected from and adapted to be controlled by said amplifier means whereby the output of said current producing means is directly proportional to the voltage output of said amplifier means.

4. Apparatus according to claim 3 wherein:

said first set of electrodes includes a pair of infinitesimal potential electrodes connected to said amplifier means, and said second set of electrodes includes a pair of current electrodes connected with said current producing means.

5. Apparatus for measuring a quantity such as impedance or thermal conductivity between two points spaced in a medium such as tissue which medium is conducting energy such as electrical energy or heat energy comprising:

calibrated probe means bearing adapted for placement at each of said points including a nonconducting body intermediate said transducers which probe has been calibrated in an environment such as a solution in terms of known energy conducting characteristics similar to said medium to provide a probe calibration factor which matches the probe impedance or thermal conductivity to the environment impedance or thermal conductivity;

means connected with said transducers for detecting a difference such as potential or temperature in the medium disturbed by the probe between the transducers at the transducer-medium interfaces;

external energy producing means connected from said detection means and back to said transducers;

means for controlling an output of said external energy producing means with the difference from said detecting means and in accordance from said detecting means with said calibration factor to provide the probe with an impedance or thermal conductivity characteristic matched to that of the medium; and

means for measuring said detected difference and the output of said external energy producing means.

6. Apparatus for calibrating a probe for measuring a quantity such as impedance or thermal conductivity between two points spaced in a substance such as tissue which substance is conducting energy such as electrical energy or heat energy comprising:

a medium such as a solution having known energy conducting characteristics which characteristics are similar in type to the substance;

probe means bearing a transducer adapted for placement at each of said points including a nonconducting body intermediate and said transducers and adapted for immersion in said medium;

means connected with said transducers for detecting a difference such as potential or temperature in the medium disturbed the probe between the transducer-medium interfaces; and

external energy source means connected from said detecting means and back to said transducers for restoring the probe disturbed medium to its predisturbed state by generating an energy flow such as current or heat flux to match the probe energy conducting characteristics to that of the medium whereby a calibration factor is arrived at by relating said energy flow to said detected difference.