System for quantifying edema

• US 6,488,677 B1
• Filed: 05/10/2001
• Issued: 12/03/2002
• Est. Priority Date: 05/10/2001
• Status: Expired due to Fees

• Current Assignee: Thermal Technologies Incorporated
• Original Assignee: Thermal Technologies Incorporated
• Inventors: Bowman, Harry Frederick, Martin, Gregory T.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): ASTORINO, MICHAEL C
• Application Number:
  US09/854,369
• Publication Number:
  US 20020169388A1
• Time in Patent Office: 572 Days
• Field of Search: 600/301, 600/547, 600/549, 600/587, 606/27, 606/28
• US Class Current: 606/28
• CPC Class Codes: A61B 2018/00797 measured by multiple temperature sensors
• CPC Class Codes: A61B 2018/00815 measured by a thermistor
• CPC Class Codes: A61B 5/01 Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue clinical contact thermometers G01K13/20
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/4076 Diagnosing or monitoring particular conditions of the nervous system A61B5/4821, A61B5/4824 take precedence
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18

Abstract

A system is provided for monitoring edema in tissue. Thermal energy is supplied to tissue at a site where tissue water content is to be monitored to produce in the selected tissue a thermal response as a function of an intrinsic thermal property of tissue that varies with water content. Tissue water content is determined from the thermal response, the energy supplied and the relationship between tissue water content and the thermal property.

Claims

1. A method for quantifying water content of living tissue comprising the steps of:

contacting tissue with a thermistor at a site where tissue water content is to be quantified;

energizing the thermistor to cause the temperature of a volume of tissue to rise; and

calculating tissue water content of said volume of tissue as a function of the power used to heat said thermistor and the temperature rise of said thermistor, at least one of which is controlled in a predetermined manner, and a value obtained from a model relating tissue conductivity to tissue water content.

2. A method according to claim 1 wherein:

said energizing step comprises the step of energizing the thermistor cyclically to cause the temperature of a volume of tissue to rise and fall cyclically; and

said calculating step comprises the step of calculating tissue water content of said volume of tissue in each energizing cycle as a function of the power used to heat said thermistor in each energizing cycle and the temperature rise of said thermistor in each energizing cycle, at least one of which is predetermined, and a value obtained from a look-up reference relating tissue conductivity to tissue water content.

3. A method for quantifying water content in living tissue comprising the steps of:

heating a volume of tissue to produce therein a thermal response functionally related to the thermal conductivity of the tissue;

producing a signal functionally related to said thermal response and the thermal energy supplied in said heating step;

calculating the intrinsic thermal conductivity of the volume of tissue in a first time interval during said heating step;

calculating the perfusion of the volume of tissue in a subsequent time interval during said heating step using the calculated value of intrinsic thermal conductivity;

recalculating intrinsic thermal conductivity in said first time interval using the calculated value of perfusion;

recalculating values for perfusion and intrinsic thermal conductivity, in alternating fashion, until the recalculated values of intrinsic thermal conductivity converge to a substantially unchanging value, using in each recalculation of perfusion the previously calculated value of intrinsic thermal conductivity and in each recalculation of intrinsic thermal conductivity the previously calculated value of perfusion;

relating intrinsic thermal conductivity values for tissue with corresponding tissue water content values; and

computing the water content of the volume of tissue as a function of said substantially unchanging value of intrinsic thermal conductivity and a substantially equivalent value of intrinsic thermal conductivity taken from the relationship of thermal conductivity values with tissue water content values.

4. A method for quantifying the water content of living tissue comprising the steps of:

placing a thermistor in contact with tissue at a site where water content is to be quantified;

energizing during a time interval the thermistor to elevate the temperature of the thermistor and heat tissue at the site above the baseline temperature of tissue at the site;

relating the rate at which heat is transferred in tissue with tissue water content; and

quantifying the water content of tissue at the site as a function of the power supplied to the thermistor during the time interval, the rate at which heat from the thermistor is transferred in tissue at the site and the relationship established in said relating step.

5. A method for monitoring the water content of living tissue at a selected site comprising the steps of:

causing the temperature of tissue at the site to rise and fall cyclically;

producing a signal during each temperature cycle functionally related to the power used in said causing step and a thermal property of the tissue at the site, which thermal property varies as a function of tissue water content; and

using a model of the relationship of the thermal property of tissue to tissue water content, computing the water content of tissue at the site during each temperature cycle as a function of the signal resulting from said signal producing step and the modeled relationship.

6. A method for monitoring the water content of living tissue comprising the steps of:

introducing into tissue an energizable thermistor adapted for thermal contact with tissue surrounding said thermistor;

energizing and deenergizing said thermistor cyclically to cause the temperature of the surrounding tissue to rise and fall cyclically;

producing a signal during each energizing and deenergizing cycle functionally related to the power used to energize said thermistor and the thermal conductivity of the surrounding tissue;

modeling the relationship of tissue water content and the thermal conductivity of tissue;

calculating the value of the intrinsic thermal conductivity of the surrounding tissue in a first time interval during each energizing and deenergizing cycle;

calculating perfusion in a subsequent time interval during each energizing and deenergizing cycle using the calculated value of intrinsic thermal conductivity;

recalculating intrinsic thermal conductivity in said first time interval using the calculated value of perfusion;

recalculating values for perfusion and intrinsic thermal conductivity, in alternating fashion, until the recalculated values of intrinsic thermal conductivity converge to a substantially unchanging value, using in each recalculation of perfusion the previously calculated value of intrinsic thermal conductivity and in each recalculation of intrinsic thermal conductivity the previously calculated value of perfusion; and

computing the water content of the surrounding tissue during each energizing and deenergizing cycle as a function of said substantially unchanging value of intrinsic thermal conductivity and the relationship resulting from said modeling step.

7. A method for assessing water content of living tissue comprising the steps of:

supplying thermal energy to tissue to cause the temperature of tissue at a selected site to rise; and

calculating a value indicative of tissue water content of tissue at the selected site as a function of the power used in said heating step and the temperature rise of tissue at the selected site, at least one of which is predetermined, and a value provided by a model relating tissue conductivity or tissue diffusivity to tissue water content.

8. A method for assessing the water content in living tissue at a site in the body comprising the steps of:

introducing a thermistor into contact with tissue at a site where water content is to be assessed;

energizing the thermistor to elevate the temperature of the thermistor above the baseline temperature of tissue at the site;

producing a signal as a function of the energy supplied to the thermistor in said energizing step and the rate at which heat from the thermistor is transferred in tissue at the site; and

using a known relationship which correlates the rate at which heat is transferred in tissue with tissue water content and the signal resulting from said producing step, producing a signal indicative of the water content of tissue at the site.

9. A system for quantifying water content of living tissue comprising:

a thermistor for heating a volume of tissue;

means for energizing said thermistor to cause the temperature of the volume of tissue to rise;

means for relating tissue conductivity to tissue water content; and

means communicating with said energizing means and said relating means for calculating tissue water content of said volume of tissue as a function of the power used to heat said thermistor and the temperature rise of said thermistor, at least one of which is controlled in a predetermined manner, and a water content value obtained from said relating means.

10. A system according to claim 9 wherein:

said energizing means comprises means for energizing said thermistor cyclically to cause the temperature of the volume of tissue to rise and fall cyclically;

said relating means comprises a look-up reference; and

said calculating means comprises means for calculating the tissue water content of said volume of tissue in each energizing cycle as a function of the power used to heat said thermistor in each energizing cycle and the temperature rise of said thermistor in each energizing cycle, at least one of which is predetermined, and a water content value obtained from said look-up reference relating tissue conductivity to tissue water content.

11. A system for assessing water content in living tissue comprising:

thermistor means for thermally contacting tissue at a site where tissue water content is to be assessed;

means for energizing and deenergizing said thermistor means to cause the temperature of tissue at the site to rise and fall;

means for producing a signal during the energizing and deenergizing cycle as a function of the power used to energize said thermistor means and at least one thermal property of tissue at the site, which thermal property varies as a function of tissue water content;

means for modeling the relationship of tissue water content to the at least one thermal property of tissue; and

means for assessing the water content of tissue at the site during the energizing and deenergizing cycle as a function of the signal resulting from said signal producing means and the relationship modeled by said modeling means.

12. A system according to claim 11 wherein:

said energizing means comprises means for cyclically energizing and deenergizing said thermistor means to cause the temperature of tissue at the site to rise and fall cyclically;

said signal producing means comprises means for producing during each energizing and deenergizing cycle a signal as a function of the power used to energize said thermistor means during each energizing and deenergizing cycle and at least one thermal property of tissue at the site; and

said means for assessing tissue water content comprises means for assessing the water content of tissue at the site in each energizing and deenergizing cycle as a function of the signal resulting from said signal producing means in each energizing and deenergizing cycle and the relationship modeled by said modeling means.

13. A system according to claim 11 or 12 wherein said signal producing means comprises means for producing a signal as a function of the thermal conductivity of tissue at the site and the power used to energize said thermistor means.

14. A system according to claim 11 or 12 wherein said signal producing means comprises means for producing a signal as a function of the thermal diffusivity of tissue at the site and the power used to energize said thermistor.

15. A system according to claim 11 or 12 wherein said thermistor means comprises a probe adapted to be introduced invasively into tissue at a site where tissue water content is to be assessed and at least one thermistor mounted on said probe for contact with tissue at the site.

16. A system according to claim 11 or 12 wherein said thermistor means comprises a noninvasive probe adapted for thermal contact with the surface of tissue at a site where tissue water content is to be assessed and at least one thermistor mounted on said probe for contact with tissue at the site.

17. A system for monitoring water content in living tissue comprising:

a probe adapted for contact with the surface of tissue at a site where tissue water content is to be quantified;

a thermistor on said probe adapted for thermal contact with the tissue surface;

means for energizing and deenergizing said thermistor cyclically when said thermistor is in contact with the tissue surface to cause the temperature of tissue at the site to rise and fall cyclically;

means for producing a signal during each energizing and deenergizing cycle as a function of the power used to energize said thermistor;

means for correlating water content of tissue to tissue conductivity; and

means for quantifying the water content of tissue at the site in each energizing and deenergizing cycle as a function of the signal produced by said producing means in each energizing and deenergizing cycle and the correlation established by said correlating means.

18. A system for assessing the water content of tissue comprising:

means for thermally energizing tissue at a selected site;

means for relating tissue water content to a thermal property of tissue, which thermal property of tissue varies as a function of tissue water content;

means indicative of the thermal response produced in tissue at the site, which thermal response is a function of said thermal property of tissue at the site; and

means for indicating the water content of tissue at the site as a function of the relationship established by said relating means, the energy used to energize tissue at the site and the thermal response produced in the tissue at the site.

19. A system for assessing the water content of tissue comprising:

means for heating tissue to be assessed;

modeling means for relating tissue water content to an intrinsic thermal property of tissue which varies as a function of tissue water content;

means for producing a signal as a function of the power used by said heating means to heat the tissue to be assessed and the thermal response produced in the tissue to be assessed, which thermal response is a function of said intrinsic thermal property of the tissue to be assessed; and

means communicating with said producing means and said modeling means for producing a signal indicative of the tissue water content of tissue to be assessed as a function of the signal produced by said producing means and the relationship established in said modeling means.

20. A system for assessing the water content of tissue comprising:

a thermistor adapted for thermal communication with tissue to be assessed;

control means for heating said thermistor and producing a signal functionally related to the power used to heat said thermistor and the temperature rise of said thermistor;

means for relating tissue thermal conductivity to tissue water content; and

means communicating with said control means and said relating means for producing a signal indicative of the water content of tissue to be assessed as a function of the signal produced by said control means and the relationship established by said relating means.

21. A system for assessing the water content of tissue comprising:

a thermistor adapted for thermal communication with tissue to be assessed;

energizing means for heating said thermistor;

means for relating tissue thermal conductivity to tissue water content; and

means for indicating of the water content of tissue to be assessed as a function of the relationship established by said relating means, the energy used to heat said thermistor and the temperature rise of said thermistor.