Method and apparatus for monitoring and controlling tissue temperature and lesion formation in radio-frequency ablation procedures

Claim 3

The method of claim 1 , wherein said electrical parameter is a phase angle between said voltages and corresponding currents, and said known correlation is between a capacitive parameter related to phase angle and tissue lesion formation for said tissue.

Claim 4

The method of claim 1 , wherein said electrical parameter is a capacitive component of tissue impedance, and said known correlation is between changes of said capacitive component and tissue lesion formation for said tissue.

Claim 5

The method of claim 3 , wherein said capacitive component is calculated from said voltages and corresponding currents measured during the procedure.

Claim 6

The method of claim 1 , wherein said ablation device is an electrode and said surgical procedure is carried out with radio-frequency electrical energy.

Claim 7

The method of claim 1 , further comprising the step of terminating said surgical procedure when said tissue lesion formation is estimated to reach a predetermined amount.

Claim 8

In a tissue-ablation surgical procedure wherein an ablating energy is administered to a tissue in contact with an ablation device immersed in a liquid, a method of estimating a ratio of tissue-to-liquid interface area with the device comprising the following steps: (a) administering electrical power at predetermined voltages and corresponding currents to the tissue in contact with said ablation device; (b) measuring an electrical parameter related to a capacitive component of the tissue; (c) calculating said capacitive component of the tissue; and (d) estimating said ratio on the basis of a change in said capacitive component.

Claim 9

In a tissue-ablation surgical procedure wherein an ablating energy is administered to a tissue in contact with an ablation device immersed in a liquid, a method of estimating a ratio of tissue-to-liquid interface area with the device comprising the following steps: (a) administering electrical power at predetermined voltages and corresponding currents to the tissue in contact with said ablation device; (b) measuring an electrical parameter related to a capacitive component of the tissue; (c) calculating said capacitive component of the tissue; and (d) estimating said ratio on the basis of a change in said capacitive component.

Claim 10

The method of claim 7 , wherein said electrical parameter is phase angle.

Claim 11

The method of claim 7 , wherein said electrical parameter is impedance and steps (c)-(d) are accomplished by the following steps: measuring said voltages and corresponding currents at a first frequency of operation and calculating corresponding first values of tissue admittance; measuring said voltages and corresponding currents at a second frequency of operation and calculating corresponding second values of tissue admittance; and estimating said ratio on the basis of a difference between said first and second values of tissue admittance.

Claim 12

The method of claim 7 , wherein said tissue is cardiac tissue.

Claim 13

The method of claim 7 , wherein said liquid is blood.

Claim 14

The method of claim 7 , wherein said ablating energy is radio-frequency electrical energy and said ablation device is an electrode.

Claim 15

In a tissue-ablation surgical procedure wherein an ablating energy is administered to a tissue in contact with an ablation device, a method for concurrently monitoring tissue temperature and tissue-lesion formation during the surgical procedure, comprising the following steps: (a) administering ablating electrical power to the tissue in contact with said ablation device at a predetermined ablating frequency; (b) concurrently with step (a), administering a low-frequency electrical power to the tissue in contact with said ablation device at a predetermined low-frequency voltage and a corresponding low-frequency current, wherein said low-frequency electrical power is administered at a low frequency below said ablating frequency; (c) concurrently with steps (a) and (b), administering a high-frequency electrical power to the tissue in contact with said ablation device at a predetermined high-frequency voltage and a corresponding high-frequency current, wherein said high-frequency electrical power is administered at a high frequency above said ablating frequency; (d) measuring said low-frequency voltage and corresponding low-frequency current and said high-frequency voltage and corresponding high-frequency current; (e) calculating a low-frequency impedance, a low-frequency admittance, and a high-frequency admittance based on data collected in step (d); (f) tracking said tissue temperature on the basis of a known correlation between temperature and said low-frequency impedance in the tissue; and (g) tracking said tissue-lesion formation on the basis of a known correlation between lesion formation in said tissue and a difference between said high-frequency admittance and low-frequency admittance in the tissue.

Claim 16

In a tissue-ablation surgical procedure wherein an ablating energy is administered to a tissue in contact with an ablation device, a method for concurrently monitoring tissue temperature and tissue-lesion formation during the surgical procedure, comprising the following steps: (a) administering ablating electrical power to the tissue in contact with said ablation device at a predetermined ablating frequency; (b) concurrently with step (a), administering a low-frequency electrical power to the tissue in contact with said ablation device at a predetermined low-frequency voltage and a corresponding low-frequency current, wherein said low-frequency electrical power is administered at a low frequency below said ablating frequency; (c) concurrently with steps (a) and (b), administering a high-frequency electrical power to the tissue in contact with said ablation device at a predetermined high-frequency voltage and a corresponding high-frequency current, wherein said high-frequency electrical power is administered at a high frequency above said ablating frequency; (d) measuring said low-frequency voltage and corresponding low-frequency current and said high-frequency voltage and corresponding high-frequency current; (e) calculating a low-frequency impedance, a low-frequency admittance, and a high-frequency admittance based on data collected in step (d); (f) tracking said tissue temperature on the basis of a known correlation between temperature and said low-frequency impedance in the tissue; and (g) tracking said tissue-lesion formation on the basis of a known correlation between lesion formation in said tissue and a difference between said high-frequency admittance and low-frequency admittance in the tissue.

Claim 17

The method of claim 13 , wherein said tissue is cardiac tissue.

Claim 18

The method of claim 13 , wherein said ablating energy is radio-frequency electrical energy and said ablation device is an electrode.

Claim 19

The method of claim 13 , wherein said ablating frequency is about 250-500 kHz, said low frequency is about 5 KHz, and said high frequency is about 1 MHz.

Claim 20

The method of claim 13 , further comprising the step of terminating said surgical procedure when the tissue temperature is estimated to reach about 95° C.

Claim 21

The method of claim 13 , further comprising the step of terminating said surgical procedure when said tissue-lesion formation is estimated to reach a predetermined amount.

Claim 22

A radio-frequency electrical apparatus for performing an ablation operation on a tissue, comprising: an electrode adapted for placement against said tissue; an ablation radio-frequency generator capable of energizing said electrode at a predetermined ablation frequency to produce ablation of the tissue; a low-frequency generator capable of administering a low-frequency electrical power to the tissue in contact with said electrode at a predetermined low-frequency voltage and a corresponding low-frequency current, said low-frequency electrical power being administered at a low frequency below said ablating frequency; a high-frequency generator capable of administering a high-frequency electrical power to the tissue in contact with said electrode at a predetermined high-frequency voltage and a corresponding high-frequency current, said high-frequency electrical power being administered at a high frequency above said ablating frequency; means for measuring said low-frequency voltage and corresponding low-frequency current and said high-frequency voltage and corresponding high-frequency current; means for calculating a low-frequency impedance, a low-frequency admittance, and a high-frequency admittance based on data collected by said measuring means; means for tracking a temperature of said tissue on the basis of a known correlation between tissue temperature and said low-frequency impedance; and means for tracking a tissue-lesion formation on the basis of a known correlation between lesion formation in said tissue and a difference between said high-frequency admittance and low-frequency admittance.

Claim 23

A radio-frequency electrical apparatus for performing an ablation operation on a tissue, comprising: an electrode adapted for placement against said tissue; an ablation radio-frequency generator capable of energizing said electrode at a predetermined ablation frequency to produce ablation of the tissue; a low-frequency generator capable of administering a low-frequency electrical power to the tissue in contact with said electrode at a predetermined low-frequency voltage and a corresponding low-frequency current, said low-frequency electrical power being administered at a low frequency below said ablating frequency; a high-frequency generator capable of administering a high-frequency electrical power to the tissue in contact with said electrode at a predetermined high-frequency voltage and a corresponding high-frequency current, said high-frequency electrical power being administered at a high frequency above said ablating frequency; means for measuring said low-frequency voltage and corresponding low-frequency current and said high-frequency voltage and corresponding high-frequency current; means for calculating a low-frequency impedance, a low-frequency admittance, and a high-frequency admittance based on data collected by said measuring means; means for tracking a temperature of said tissue on the basis of a known correlation between tissue temperature and said low-frequency impedance; and means for tracking a tissue-lesion formation on the basis of a known correlation between lesion formation in said tissue and a difference between said high-frequency admittance and low-frequency admittance.

Claim 24

The radio-frequency electrical apparatus of claim 19 , wherein said tissue is cardiac tissue, said ablating frequency is about 250-500 kHz, said low frequency is about 5 KHz, and said high frequency is about 1 MHz.

Claim 25

The radio-frequency electrical apparatus of claim 19 further comprising means for terminating said ablating operation when said tissue-lesion formation is estimated to reach a predetermined amount.

Claim 26

The radio-frequency electrical apparatus of claim 21 , wherein said means for terminating said ablating operation includes means for controlling an output of said ablation radio-frequency generator in response to a signal related to at least one of said low-frequency impedance and said difference between the high-frequency admittance and the low-frequency admittance.