Impedance measurement process

Abstract

A method for use in performing impedance measurements on a subject. The method includes, in a processing system, determining at least one first impedance value, measured at a site using a first electrode configuration, determining at least one second impedance value, measured at the site using a second electrode configuration, and determining the presence, absence or degree of an anomaly using the first and second impedance values.

1 ) A method for use in performing impedance measurements on a subject, the method including, in a processing system:
 a) determining at least one first impedance value, measured at a site using a first electrode configuration;   b) determining at least one second impedance value, measured at the site using a second electrode configuration; and,   c) determining the presence, absence or degree of an anomaly using the first and second impedance values.   
     
     
         2 ) A method according to  claim 1 , wherein the method includes using a tetrapolar electrode arrangement, the first and second electrode configurations using a different configuration of drive and measurement electrodes. 
     
     
         3 ) A method according to  claim 2 , wherein the method includes, in the processing system, determining an impedance value for each of four electrode configurations. 
     
     
         4 ) A′ method according to any one of  claims 1  to  3 , wherein the method uses apparatus including a signal generator, a sensor, a switching device and an electrode array having a number of electrodes, and wherein the method includes in the processing system, controlling the electrode configuration by:
 a) selectively interconnecting the signal generator and electrodes using the switching device; and, 
 b) selectively interconnecting the sensor and electrodes using the switching device. 
 
     
     
         5 ) A method according to any one of  claims 1  to  4 , wherein the method includes, in the processing system:
 a) causing at least one drive signals to be applied to the subject; 
 b) measuring at least one induced signal across the subject; and, 
 c) determining at least one impedance value using an indication of the excitation signal and the induced signal. 
 
     
     
         6 ) A method according to any one of  claims 1  to  5 , wherein the method includes, in the processing system:
 a) determining impedance values at a number of different sites; and, 
 b) determining an impedance map using the impedance values at each site. 
 
     
     
         7 ) A method according to  claim 6 , wherein the method includes, in the processing system:
 a) determining the presence of an anomaly at any one of the sites; and,   b) determining the impedance map taking the anomaly into account.   
     
     
         8 ) A method according to  claim 7 , wherein the method includes, in the processing system, for a site having an anomaly, at least one of:
 a) excluding the site from the impedance map;   b) modifying the impedance value determined for the site.   
     
     
         9 ) A method according to any one of  claims 1  to  8 , wherein the method includes, in the processing system:
 a) determining a difference between the first and second impedance values; and, 
 b) determining the presence, absence or degree of an anomaly using the determined difference. 
 
     
     
         10 ) A method according to any one of  claims 1  to  9 , wherein the method includes, in the processing system:
 a) determining a difference between the first and second impedance values; 
 b) comparing the difference to a reference; and, 
 c) determining an anomaly depending on the result of the comparison. 
 
     
     
         11 ) A method according to any one of  claims 1  to  10 , wherein the method includes, in the processing system:
 a) comparing first and second impedance values; and, 
 b) determining the presence, absence or degree of a biological anomaly using the results of the comparison. 
 
     
     
         12 ) A method according to any one of  claims 1  to  11 , wherein the reference in a previously measured difference value for the subject. 
     
     
         13 ) A method according to any one of  claims 1  to  12 , wherein the impedance values are at least one of:
 a) measured impedance values; and, 
 b) impedance parameter values derived from measured impedance values. 
 
     
     
         14 ) A method according to  claim 12 , wherein the impedance parameter values include at least one of:
 a) an impedance at infinite applied frequency (R ∞ );   b) an impedance at zero applied frequency (R 0 ); and,   c) an impedance at a characteristic frequency (Z c ).   
     
     
         15 ) A method according to  claim 13 , wherein the method includes, in the processing system, determining the impedance parameter values at least in part using the equation: 
       
         
           
             
               Z 
               = 
               
                 
                   R 
                   ∞ 
                 
                 + 
                 
                   
                     
                       R 
                       0 
                     
                     - 
                     
                       R 
                       ∞ 
                     
                   
                   
                     1 
                     + 
                     
                       
                         ( 
                         jωτ 
                         ) 
                       
                       
                         ( 
                         
                           1 
                           - 
                           α 
                         
                         ) 
                       
                     
                   
                 
               
             
           
         
         where:
 R ∞ =impedance at infinite applied frequency; 
 R 0 =impedance at zero applied frequency; 
 ω=angular frequency; 
 τ is the time constant of a capacitive circuit modelling the subject response; and, 
 α has a value between 0 and 1. 
 
       
     
     
         16 ) A method according to any one of  claims 1  to  15 , wherein the method includes, in the processing system:
 a) causing at least one first impedance value to be measured at a site using a first electrode configuration; and, 
 b) causing at least one second impedance value to be measured at the site using a second electrode configuration. 
 
     
     
         17 ) A method according to any one of  claims 1  to  16 , wherein the processing system forms part of a measuring device for performing impedance measurements. 
     
     
         18 ) A method according to any one of  claims 1  to  17 , wherein the anomaly includes any one or a combination of:
 a) a tissue anomaly; and, 
 b) an erroneous measurement. 
 
     
     
         19 ) A method according to  claim 18 , wherein the tissue anomaly is a tissue lesion. 
     
     
         20 ) A method according to  claims 1  to  19 , wherein the impedance measurements are performed using apparatus including an electrode array having a number of electrodes provided thereon, and wherein the method includes, in the processing system, causing impedance measurements to be performed using different ones of the electrodes in the array. 
     
     
         21 ) A method according to  claim 20 , wherein the method includes:
 a) causing a first measurement to be performed at a site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes; and,   b) causing a second measurement to be performed at the site using first and third electrodes as drive electrodes and using second and fourth electrodes as measurement electrodes.   
     
     
         22 ) A method according to  claim 20  or  claim 21 , wherein the method includes:
 a) causing a measurement to be performed at a site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes; and, 
 b) causing a measurement to be performed at a second site using at least two of the first, second, third and fourth electrodes. 
 
     
     
         23 ) A method according to  claim 20 , wherein the method includes:
 a) causing a first measurement to be performed at a first site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes;   b) causing a second measurement to be performed at the first site using first and third electrodes as drive electrodes and using second and fourth electrodes as measurement electrodes.   c) causing a first measurement to be performed at a second site using third and fifth electrodes as drive electrodes and using fourth and sixth electrodes as measurement electrodes; and,   d) causing a second measurement to be performed at the second site using third and fourth electrodes as drive electrodes and using fifth and sixth electrodes as measurement electrodes.   
     
     
         24 ) A method according to any one of the  claims 20  to  23 , wherein the apparatus includes a signal generator for generating drive signals, a sensor for sensing measured signals, and a multiplexer, and wherein the method includes, in the processing system selectively interconnecting the signal generator and the sensor to electrodes in the array using the multiplexer. 
     
     
         25 ) Apparatus for use in analysing impedance measurements performed on a subject, the apparatus including a processing system for:
 a) determining at least one first impedance value, measured at a site using a first electrode configuration;   b) determining at least one second impedance value, measured at the site using a second electrode configuration; and,   c) determining the presence, absence or degree of an anomaly using the first and second impedance values.   
     
     
         26 ) Apparatus according to  claim 25 , wherein the apparatus includes:
 a) a signal generator for applying drive signals to the subject using drive electrodes; and,   b) a sensor for determining measured signals using measurement electrodes.   
     
     
         27 ) Apparatus according to  claim 26 , wherein the processing system is for:
 a) causing the signal generator to apply one or more drive signals to the subject; and,   b) determining an indication of the measured signals measured using the sensor.   
     
     
         28 ) Apparatus according to any one of the  claims 25  to  27 , wherein the processing system is for:
 a) determining an indication of drive signals applied to the subject; 
 b) determining an indication of measured signals determined using the sensor; and, 
 c) using the indications to determine an impedance. 
 
     
     
         29 ) Apparatus according to any one of the  claims 25  to  28 , wherein the apparatus includes an electrode array having a number of electrodes provided thereon, and wherein in use, selected ones of the electrodes are used as drive and measurement electrodes. 
     
     
         30 ) Apparatus according to  claim 29 , wherein the processing system is for:
 a) causing a first measurement to be performed at a site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes; and,   b) causing a second measurement to be performed at the site using first and third electrodes as drive electrodes and using second and fourth electrodes as measurement electrodes.   
     
     
         31 ) Apparatus according to  claim 29  or  claim 30 , wherein the method includes:
 a) causing a measurement to be performed at a site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes; and, 
 b) causing a measurement to be performed at a second site using at least two of the first, second, third and fourth electrodes. 
 
     
     
         32 ) Apparatus according to  claim 29 , wherein the method includes:
 a) causing a first measurement to be performed at a first site using first and second electrodes as drive electrodes and using third and fourth electrodes as measurement electrodes;   b) causing a second measurement to be performed at the first site using first and third electrodes as drive electrodes and using second and fourth electrodes as measurement electrodes.   c) causing a first measurement to be performed at a second site using third and fifth electrodes as drive electrodes and using fourth and sixth electrodes as measurement electrodes; and,   d) causing a second measurement to be performed at the second site using third and fourth electrodes as drive electrodes and using fifth and sixth electrodes as measurement electrodes.   
     
     
         33 ) Apparatus according to any one of the  claims 25  to  32 , wherein the apparatus includes:
 a) a signal generator for generating drive signals; 
 b) a sensor for sensing measured signals; and, 
 c) a multiplexer, and wherein the processing system is for selectively interconnecting the signal generator and the sensor to electrodes in the array using the multiplexer. 
 
     
     
         34 ) Apparatus according to any one of the  claims 25  to  33 , wherein the apparatus is for performing the method of any one of the  claims 1  to  24 . 
     
     
         35 ) A method for use diagnosing the presence, absence or degree of a biological anomaly in a subject by using impedance measurements performed on the subject, the method including, in a processing system:
 a) determining at least one first impedance value, measured at a site using a first electrode configuration;   b) determining at least one second impedance value, measured at the site using a second electrode configuration; and,   c) determining the presence, absence or degree of an anomaly using the first and second impedance values.