System for quantifying blood flow in tissue with periodic updating of tissue baseline conditions
First Claim
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1. A method for determining perfusion in living tissue comprising the steps of:
- (1) establishing baseline criteria, comprising (A) determining an unperturbed temperature of the tissue;
(B) causing the temperature of the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and (C) determining a value or values for one or more thermal properties of tissue during a first selected portion of said time period;
(2) calculating a perfusion value for the tissue at a second selected portion of said time period using said thermal property value or values, and (3) evaluating one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1).
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Abstract
Disclosed are methods and apparatus for determining blood flow in tissue. Particularly methods and apparatus are disclosed for establishing baseline thermal properties for the tissue and providing one or more steps for periodically determining changes in the tissue thermal properties that correspond to a need for a new baseline and establishing the new baseline.
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Citations
77 Claims
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1. A method for determining perfusion in living tissue comprising the steps of:
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(1) establishing baseline criteria, comprising (A) determining an unperturbed temperature of the tissue;
(B) causing the temperature of the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and (C) determining a value or values for one or more thermal properties of tissue during a first selected portion of said time period;
(2) calculating a perfusion value for the tissue at a second selected portion of said time period using said thermal property value or values, and (3) evaluating one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1).
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2. A method for determining perfusion in living tissue comprising the steps of:
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(1) establishing thermal baseline criteria corresponding to thermal conditions of the tissue comprising determining an unperturbed tissue temperature;
(2) causing the temperature of a volume of the tissue to change from the unperturbed temperature to a second temperature different from the unperturbed temperature during a time interval;
(3) calculating at least one of an intrinsic thermal conductivity value and a thermal diffusivity value for said volume of tissue during a first selected portion of said time interval;
(4) calculating perfusion in said volume of tissue at a second selected portion of said time interval using said value;
(5) determining need for new baseline criteria for the tissue comprising evaluating one or both of physiologic and artifact conditions; and
(6) repeating step (1) when indicated by step (5).
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3. A method for the periodic recalibration of perfusion measurement in tissue comprising the steps of:
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(a) performing calibration of one or both of a perfusion sensor in thermal contact with the tissue and a perfusion monitoring instrument;
(b) measuring perfusion in tissue;
(c) automatically recognizing one or more of physiologic and artifact conditions under which the calibration is no longer valid;
(d) automatically performing a recalibration of one or both of the sensor and the instrument when the recognition of conditions indicates that the calibration is no longer valid; and
(d) repeating step (b). - View Dependent Claims (4, 5)
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6. A method for determining blood flow in tissue with automatic recalibration comprising the steps of:
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(1) providing an apparatus for determining properties of tissue, comprising;
a computer;
a display in electrical communication with the computer;
a detector circuit in electrical communication with the computer;
a power supply in electrical communication, with the display and detector circuit;
a keypad in electrical communication with the detector circuit; and
a probe in electrical communication with the detector circuit;
(2) inserting the probe into the tissue;
(3) operating the device to perform the following steps;
(A) measuring the unperturbed temperature of the tissue at a selected location;
(B) determining if the temperature at the location is stable, wherein if the temperature is not stable then repeating step (A);
(C) raising the temperature of the tissue at the location a predetermined amount;
(D) measuring the elevated temperature at the location and calculating perfusion;
(E) repeating step (D) for a period of time;
(F) determining if the temperature of the tissue at the location is stable, wherein if the temperature is not stable, then repeating step (A);
(G) determining if a function of the power required in step (C) to raise the temperature of the tissue is less than an established maximum value, wherein if not less, then repeating step (A);
(H) determining if the total time the measurements have been taken over is less than an established maximum, wherein if the total is not less than the established maximum, then repeating step (A);
(I) repeating step (D).
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7. In a method for determining flow in tissue, a method for automatic recalibration comprising the steps of:
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(1) measuring the unperturbed temperature of the tissue at a selected location;
(2) determining if the temperature at the location is stable, wherein if the temperature is not stable then repeating step 1;
(3) raising the temperature of the tissue at the location a predetermined amount;
(4) measuring the elevated temperature at the location and calculating the perfusion;
(5) determining if the temperature of the tissue at the location is stable, wherein if the temperature is not stable, then repeating step 1;
(6) determining if a function of the power required in step (3) to raise the temperature of the tissue is less than an established maximum value, wherein if not less, then repeating step 1;
(7) determining if the total time over which the measurements have been taken is less than an established maximum, wherein if the total is not less than the established maximum, then repeating step 1;
(8) repeating step 3.
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8. A method for monitoring perfusion in living tissue comprising:
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determining baseline thermal conditions for a selected tissue location and establishing baseline criteria based thereon;
raising the temperature in said tissue location to a value above said thermal baseline;
computing values associated with one or more selected thermal properties of the tissue location;
computing blood flow using a value that is a function of the power required by said raising step and one or more of the selected thermal property values;
evaluating one or more conditions that may significantly change one or more of the thermal baseline and the selected thermal property values; and
determining the need for new baseline criteria using data from said evaluating step. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. In a method for determining blood flow in tissue comprising the steps of:
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(1) causing temperature in the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature during a time period;
(2) calculating at least one of an intrinsic thermal conductivity and a diffusivity of the tissue during a first selected portion of said time period;
(3) calculating a perfusion of the tissue at, at least a second selected portion of said time period, using said calculated intrinsic thermal conductivity and/or diffusivity;
(4) recalculating the intrinsic thermal conductivity and diffusivity of the tissue using said calculated perfusion;
(5) recalculating the perfusion of the tissue using said recalculated intrinsic thermal conductivity and diffusivity; and
(6) repeating steps (4) and (5) until the recalculated intrinsic thermal conductivity and diffusivity and the recalculated perfusion each converge to a substantially non-changing value;
the improvement comprising the steps of;
(a) prior to step (1), establishing baseline criteria corresponding to baseline thermal conditions of the tissue; and
(b) periodically determining the need for and establishing new baseline criteria.
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17. A method for determining blood flow in tissue comprising the steps of:
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(1) establishing baseline criteria for the tissue, comprising;
determining the thermal conductivity of a heating means, said heating means having a predetermined resistance versus temperature relationship;
immersing said heating means in the tissue; and
determining the reference temperature of the tissue when the tissue is unheated;
(2) obtaining measurements of the tissue comprising the steps of;
applying power to said heating means sufficiently rapidly to heat said means to a temperature above said reference temperature so that the power necessary to maintain said temperature varies as a function of time;
determining the time varying relationship between the power required to maintain said heating means at said temperature after said temperature has been reached and the time during which said power is being applied thereto;
determining the temperature difference between said temperature and said reference temperature and determining the resistance of said heating means at said temperature;
determining the thermal conductivity of the tissue as a function of said temperature difference, of the resistance of said heating means at said temperature, of said applied power in accordance with said time varying power and time relationship, of said predetermined thermal conductivity of said heating means, and of at least one characteristic dimension of said heating means in accordance with a thermal model of said heating means and the tissue in which it is immersed wherein said heating means is treated as a distributed thermal mass and wherein heat conduction occurs in a coupled thermal system which comprises both the heating means and the adjacent region of the tissue which surrounds said heating means; and
(3) determining need for new baseline criteria for tissue comprising evaluating one or both of measurement artifact conditions and physiological conditions. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method for determining thermal properties of tissue comprising the steps of:
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(1) establishing a baseline criteria for the tissue, comprising (A) determining an unperturbed temperature of the tissue;
(B) causing the temperature of the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature during a time period; and
(C) calculating a thermal property value for the tissue as a function of the intrinsic thermal conductivity and a diffusivity of the tissue during a first selected portion of said time period;
(2) obtaining measurements of the tissue comprising the steps of;
(A) calculating a perfusion of the tissue during a second selected portion of said time period using said calculated intrinsic thermal conductivity and diffusivity related value;
(B) re-calculating the intrinsic thermal conductivity and diffusivity of the tissue using said calculated perfusion;
(C) re-calculating the perfusion of the tissue using said recalculated intrinsic thermal conductivity and diffusivity related value; and
(D) repeating steps (2B) and (2C) until the re-calculated intrinsic thermal conductivity and diffusivity and the re-calculated perfusion each converge to a substantially non-changing value; and
(3) evaluating one or more measurement artifact conditions and physiological conditions to determine if baseline conditions established by step (1) are materially affected by said conditions. - View Dependent Claims (28, 29, 30, 31, 32)
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33. A method for determining thermal properties of tissue comprising the steps of
establishing baseline thermal criteria corresponding to baseline thermal conditions of the tissue; -
inducing a temperature change in the tissue as a function of time;
calculating at least one selected intrinsic thermal property of the tissue using data obtained at a first time period;
calculating separately a perfusion rate of the tissue using data obtained at a second time period and said at least one calculated intrinsic thermal property, the effects of the perfusion of the tissue at said second time period being greater than the effects of the perfusion of the tissue at said first time period; and
determining the need for new baseline criteria for the tissue when baseline thermal conditions materially change. - View Dependent Claims (34, 35, 36, 37, 38)
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39. A method for determining the perfusion in live tissue with automatic recalibration comprising the steps:
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1) measuring the temperature of the tissue at a selected location;
2) determining if the temperature at the selected location is stable, wherein if the temperature is not stable then repeating step 1;
3) raising the temperature of the tissue at the selected location a predetermined amount;
4) measuring the power provided in step (3) to maintain the raised temperature;
5) measuring the temperature at the selected location and calculating the perfusion;
6) repeating step 5 for a period of time;
7) determining if the temperature of the tissue at the selected location is stable, wherein if the temperature is not stable, then repeating step 1;
8) determining if a function of the power measured in step (4) is less than an established maximum value, wherein if not less than the established maximum, then repeating step 1;
9) determining if the total time the measurements have been taken over is less than an established maximum, wherein if the total is not less than the established maximum, then repeating step 1;
10) repeating step 5.
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40. A method for determining thermal properties of tissue with automatic recalibration comprising the steps:
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1) providing an apparatus for determining properties of tissue, comprising;
a computer, a display in electrical communication with the computer, a detector circuit in electrical communication with the computer, a power supply in electrical communication with the computer, display and detector circuit;
a keypad in electrical communication with the detector circuit, and a probe in electrical communication with the detector circuit;
2) inserting the probe into the tissue;
3 having/operating the device perform the following steps;
A) measuring the temperature of the tissue at a selected location;
B) determining if the temperature at the selected location is stable, wherein if the temperature is not stable then repeating step 1;
C) raising the temperature of the tissue at the selected location a predetermined amount;
D) measuring the temperature at the selected location and calculating the perfusion;
E) repeating step D for a set period of time;
F) determining if the temperature of the tissue at the selected location is stable, wherein if the temperature is not stable, then repeating step 1;
G) determining if the rate of perfusion is less than an established maximum value, wherein if rate of perfusion is not less than the established maximum, then repeating step A;
H) determining if the total time the measurements have been taken over is less than an established maximum, wherein if the total is not less than the established maximum, then repeating step A;
I) repeating step D.
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41. A method comprising the steps:
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1) measuring T1 and T2;
2) determining if T1 and T2 are stable;
3) if T1 and T2 are not stable, then repeating step 1;
4) if T1 and T2 are stable, then setting T2 to T2+DT;
5) measuring TI and calculating P2;
6) determining if P2 data has been acquired for a selected time period;
7) if 10 seconds of P2 data not acquired, then repeat step 5;
8) if 10 seconds of P2 data has been acquired, then calculating Km;
9) calculating w;
10) determining if T1 is stable;
11) if T1 is not stable, then repeating step 1;
12) if T1 is stable, then determining if dP2/dt is less than dP/dt(max);
13) if dP2/dt is not less than dP/dt(max), then repeating step 1;
14) if dP2/dt is less than dP/dt(max), then determining if t is less than t(max);
15) if t is not less than t(max), then repeating step 1;
16) if t is less than t(max), then repeating step 5.
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42. A method for determining thermal properties of tissue comprising the steps of:
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(1) establishing baseline criteria corresponding to the baseline thermal conditions of the tissue, comprising;
contacting the tissue with a heating means having a predetermined resistance versus temperature relationship; and
determining a reference temperature for the tissue when the tissue is unheated;
(2) obtaining measurements of the tissue comprising the steps of;
applying power to said heating means sufficiently rapidly to heat said heating means to a temperature above said reference temperature so that the power necessary to maintain said temperature varies as a function of time;
determining the time varying relationship between the power required to maintain said heating means at said temperature after said temperature has been reached and the time during which said power is being applied thereto;
determining the temperature difference between said heating means temperature and said reference temperature and determining the resistance of said heating means at said temperature;
determining the thermal conductivity of the tissue as a function of said temperature difference, of the resistance of said heating means at said temperature, and of said applied power in accordance with said time varying power and time relationship; and
(3) evaluating one or more physiological and measurement artifact conditions to determine if baseline criteria established in step (1) are materially affected thereby and if so (4) repeating step (1).
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43. A method for determining thermal properties of tissue comprising the steps of:
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(1) establishing baseline criteria corresponding to the baseline thermal conditions of the tissue, comprising;
determining the thermal conductivity of a heating means as a function of temperature;
contacting the tissue with said heating means; and
determining a reference temperature of the tissue when the tissue is unheated;
(2) obtaining measurements of tissue comprising the steps of;
applying power to said heating means sufficiently rapidly to heat said heating means to a temperature above said reference temperature so that the power necessary to maintain said temperature varies as a function of time;
determining the time varying power and time relationship between the power required to maintain said temperature and the time during which said power is applied to said heating means;
determining the temperature difference between said temperature and said reference temperature;
determining the thermal conductivity of the tissue as a function of said temperature difference, and of said applied power in accordance with said time varying power and time relationship; and
(3) evaluating one or more physiological and measurement artifact conditions to determine if baseline criteria established in step (1) are materially affected thereby and if so (4) repeating step (1).
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44. A system for monitoring perfusion in living tissue comprising:
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a sensor adapted for thermal contact with tissue at a selected location;
means for determining system baseline criteria corresponding to baseline thermal conditions of the tissue;
a heater for changing the temperature of tissue at said location;
means for determining a perfusion related value for tissue at said location as a function of data from said sensor and the output of said heater; and
means for evaluating one or more conditions that may affect system baseline criteria and assessing the validity at the changed temperature of the system baseline criteria. - View Dependent Claims (45, 46, 47, 48, 49, 50)
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51. Apparatus for determining the perfusion of blood in living tissue comprising:
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means in thermal contact with the tissue for sensing the reference temperature of the tissue when the tissue is unheated;
means in thermal contact with the tissue for heating the tissue;
means for applying power to said heating means sufficiently rapidly to raise the temperature of said heating means to a temperature above said reference temperature so that the power necessary to maintain said heating means temperature varies as a function of time;
data processing means for determining the temperature difference between said heating means temperature and said reference temperature, for determining the resistance of said heating means at said heating means temperature and for determining the time varying relationship between the power required to maintain said heating means at said heating means temperature after said temperature has been reached and the time during which said power is being applied thereto;
said data processing means further being responsive to said temperature difference, said heating means resistance and said time varying power and time relationship for determining a perfusion related value;
means for evaluating conditions that affect the reference temperature of the tissue and recognizing conditions under which the reference temperature is no longer valid; and
means for providing an output in response to said evaluating and recognizing means. - View Dependent Claims (52, 53, 54, 55)
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56. Apparatus for determining thermal properties of living tissue comprising:
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means adapted to contact tissue for sensing a reference temperature of the tissue when the tissue is unheated;
means for heating tissue including tissue contacted by said heating means, said heating means having a predetermined thermal conductivity and a predetermined thermal diffusivity;
means for applying power to said heating means sufficiently rapidly to raise the temperature of said heating means above said reference temperature so that the power necessary to maintain said heating means temperature varies as a function of time;
data processing means for determining the temperature difference between said heating means temperature and said reference temperature, for determining the resistance of said heating means at said heating means temperature and for determining the time varying relationship between the power required to maintain said heating means at said temperature after said temperature has been reached and the time during which said power is being applied thereto;
said data processing means further being responsive to said temperature difference, said heating means resistance, said applied power in accordance with said time varying power and time relationship, said predetermined thermal conductivity of said heating means, and a change in said reference temperature for determining the thermal conductivity of the tissue. - View Dependent Claims (57, 58, 59, 60, 61, 62, 63, 64, 65, 66)
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67. An apparatus for determining thermal properties of living tissue, comprising:
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a computer;
a display in electrical communication with the computer;
a detector circuit in electrical communication with the computer;
a power supply in electrical communication with the detector circuit;
a keypad in electrical communication with the detector circuit; and
a probe in electrical communication with the detector circuit. - View Dependent Claims (68, 69, 70, 71, 72, 73, 74, 75)
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76. A method for determining perfusion in living tissue comprising the steps of:
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(1) establishing baseline criteria, comprising (A) determining an unperturbed temperature of the tissue;
(B) causing the temperature of the tissue to change from a first unperturbed temperature to a second temperature different from said first temperature for a time period, and (C) determining a value or values for one or more thermal properties of tissue during said time period;
(2) calculating a perfusion value for the tissue during said time period using said thermal property value or values, and (3) evaluating one or more physiological and artifactual conditions to determine if baseline criteria established by step (1) are materially affected by said conditions and if so repeating step (1). - View Dependent Claims (77)
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Specification