Device and method for measuring tissue impedance

Abstract

A micro-device and method for the measurement of impedance through a biological load simulating electrical impedance spectroscopy allows for miniaturization and use of low power direct current.

1 . A micro-device for the measurement of tissue impedance by electrical impedance spectroscopy technique, said device comprising:
 a. a low voltage direct current power supply;   b. a voltage generator with series impedance;   c. a micro-controller for selecting voltage impedance and for driving discrete current limited binary pulses;   d. at least an electrode pair for contact with biological tissue in electrical communication with said micro-controller;   e. a sampling switch operable between a closed and open position for timed sampling a charge of a discrete current limited binary pulse;   f. a capacitor for accumulating said sampled charge and for discharging said sampled charge when said sampled charge is equivalent to an accumulated charge;   g. an analog to digital converter for digitizing said discharged sampled charge;   h. switching means for reversing circuit polarity; and   i. transmission means in wireless communication with an external unit for transmitting said digitized sampled charge from said device.   
     
     
         2 . The micro device of  claim 1  wherein at least one of said electrode pair injects currant limited binary voltage pulses of known frequency into said tissue and said at least other electrode senses a potential of said. pulse flowing through said tissue. 
     
     
         3 . The micro-device of  claim 1  wherein said low voltage direct current power supply is a 3v battery. 
     
     
         4 . The micro-device of  claim 1  wherein said low voltage direct current power supply comprises two 1.5 v batteries. 
     
     
         5 . The micro-device of  claim 1  wherein said other electrode interfaces with said sampling switch. 
     
     
         6 . The micro-device of  claim 1  wherein sampling switch interfaces with said capacitor. 
     
     
         7 . The micro-device of  claim 1  comprising at least four electrodes, at least two of said electrodes inject current limited binary pulses into said tissue and at least two other electrodes sense potential of current through said tissue. 
     
     
         8 . The micro-device of  claim 3  wherein a sampling switch and capacitor are dedicated to each of said electrodes that sense potential of current through said tissue. 
     
     
         9 . A micro-device for the measurement of tissue impedance by electrical impedance spectroscopy technique, said device comprising:
 a. a low voltage direct current power supply;   b. at least three resistors for limiting current voltage;   c. a micro-controller for selectively limiting voltage and for driving discrete current limited binary pulses;   d. four electrodes for contact with biological tissue in electrical communication with said micro-controller, two of said electrodes comprising injection electrodes for injecting said current limited binary pulses into biological tissue and two said electrodes comprising sensing electrodes for sensing a potential of said current limited binary pulse flowing through said tissue;   e. a sampling switch operable between a closed position for timed sampling a charge of a discrete current limited binary pulse and an open position;   f. a capacitor for accumulating said sampled charge and for discharging said accumulated charge when. a sampled charge is equivalent to an accumulated charge;   g. an analog to digital converter for digitizing said sampled charge;   h. switching means for reversing circuit polarity; and   i. transmission means in wireless communication with an external unit for transmitting said digitized sampled charge from said device.   
     
     
         10 . A method for measuring the impedance of a biological load comprising the steps of:
 a. locating said micro-device of  claim 1  adjacent said biological load with said at least one electrode pair in contact with said biological load;   b. providing at least one resistor for producing current limited pulses of selected frequency from a low voltage direct current source;   c. one electrode of said electrode pair driving a series of said current limited pulses of a first polarity through said biological load;   d. one other electrode of said electrode pair sensing a potential produced by said pulses through said biological load;   e. sampling said potential at a given point on said pulses;   f. accumulating said sampled potential at a capacitor;   g. repeating steps b through f until maximum potential at said first polarity is accumulated;   h. digitizing said maximum potential;   i. transmitting said digitized maximum potential to computer means for calculating impedance at said first polarity;   j. reversing the polarity of said micro-device and repeating steps a through i to obtain maximum potential of a second polarity;   k. transmitting said digitized maximum potential at said second polarity to computer means for calculating impedance at said second polarity; and   l. averaging said impedance of said first and said second polarity to determine the impedance of said biological load.   
     
     
         11 . The method of  claim 10  wherein said pulses comprise micro controller driven positive and negative direct current square wave forms. 
     
     
         12 . The method of  claim 10  wherein a direct current square wave pulse has a non-zero component during a half cycle that is 66% of a full cycle of a micro-controller driven positive and negative square wave current pulse. 
     
     
         13 . The method of  claim 10  wherein a fast analog switch is controlled by said micro-controller for producing said current limited pulses. 
     
     
         14 . The method of  claim 13  wherein the frequency of said current limited binary current pulses ranges between 25 Hz and 100 KHz. 
     
     
         15 . The method of  claim 13  wherein a series of said current pulse wave forms of the same polarity are sampled for potential at the same point on the wave form and said sampled. potential accumulated at said capacitor, 
     
     
         16 . The method of  claim 15  wherein said series of said wave forms from the same biological load are sampled until said accumulated potential is substantially equal to the potential through said biological load and said accumulated potential is discharged to said micro-controller and digitized; and 
     
     
         17 . The method of  claim 10  wherein said current is limited to 1.0 K, 3.16K and 10K,