US20160038229A1 - Tissue contact detection prior to and during an ablation procedure - Google Patents

Abstract

The present invention provides systems and methods for radiometrically measuring temperature and detecting tissue contact during ablation. An interface module includes a first input/output (I/O) port for receiving radiometer and thermocouple signals from an integrated catheter tip (ICT) that includes a radiometer; a second I/O port for receiving ablative energy from an electrosurgical generator; a temperature display; a patient relay; a computer-readable medium storing radiometer and thermocouple parameters and instructions for causing the processor to: calculate a temperature adjacent to the ICT based on the radiometer and thermocouple signals and the parameters; causing the temperature display to display the calculated temperature; closing the patient relay to pass ablative energy from the second to the first I/O port; determining whether the ICT is in contact with tissue based on the radiometer signal. An output device indicates whether the ICT is determined to be in contact with the tissue.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation application of U.S. patent application Ser. No. 14/274,438, filed May 9, 2014, which is a continuation application of U.S. patent application Ser. No. 13/486,889, filed on Jun. 1, 2012, the entirety of each of which is hereby incorporated by reference herein.
FIELD
• This application generally relates to systems and methods for measuring temperature and detecting tissue contact prior to and during tissue ablation.
BACKGROUND
• Tissue ablation may be used to treat a variety of clinical disorders. For example, tissue ablation may be used to treat cardiac arrhythmias by destroying aberrant pathways that would otherwise conduct abnormal electrical signals to the heart muscle. Several ablation techniques have been developed, including cryoablation, microwave ablation, radio frequency (RF) ablation, and high frequency ultrasound ablation. For cardiac applications, such techniques are typically performed by a clinician who introduces a catheter having an ablative tip to the endocardium via the venous vasculature, positions the ablative tip adjacent to what the clinician believes to be an appropriate region of the endocardium based on tactile feedback, mapping electrocardiogram (ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow of an irrigant to cool the surface of the selected region, and then actuates the ablative tip for a period of time and at a power believed sufficient to destroy tissue in the selected region.
• Although commercially available ablative tips may include thermocouples for providing temperature feedback via a digital display, such thermocouples typically do not provide meaningful temperature feedback during irrigated ablation. For example, the thermocouple only measures surface temperature, whereas the heating or cooling of the tissue that results in tissue ablation may occur at some depth below the tissue surface. Moreover, for procedures in which the surface of the tissue is cooled with an irrigant, the thermocouple will measure the temperature of the irrigant, thus further obscuring any useful information about the temperature of the tissue, particularly at depth. As such, the clinician has no useful feedback regarding the temperature of the tissue as it is being ablated or whether the time period of the ablation is sufficient.
• Moreover, during an ablation procedure it is important that the clinician position the ablative tip directly against the cardiac surface (e.g., makes good contact) before activating the ablation energy source and attempting to ablate the tissue. If the clinician does not have good tissue contact, ablation energy may heat the blood instead of the tissue, leading to the formation of an edema, e.g., a fluid-filled pocket or blister on the tissue surface. Such an edema may inhibit adequate destruction of aberrant nerve pathways in the tissue. For example, edemas may physically interfere with the clinician's ability to contact a desired region of tissue with the ablative tip, and thus may interfere with destruction of a desired nerve pathway. Additionally, partial lesions or lesions in undesired locations have been found after the clinician completes the procedure and the edema dissipates. Formation of such partial or undesired lesions are thought to be caused by reduced contact between the ablative tip and the tissue, resulting in a tissue temperature insufficient to cause tissue necrosis. Edemas and partially formed lesions also may make it more difficult to create an effective lesion in the future, for example during a touch-up ablation within the same procedure or later on during a secondary procedure.
• Accordingly, it may only be revealed after the procedure is completed—for example, if the patient continues to experience cardiac arrhythmias—that the targeted aberrant pathway was not adequately interrupted. In such a circumstance, the clinician may not know whether the procedure failed because the incorrect region of tissue was ablated, because the ablative tip was not actuated for a sufficient period of time to destroy the aberrant pathway, because the ablative tip was not touching or not sufficiently touching the tissue, because the power of the ablative energy was insufficient, or some combination of the above. Upon repeating the ablation procedure so as to again attempt to treat the arrhythmia, the clinician may have as little feedback as during the first procedure, and thus potentially may again fail to destroy the aberrant pathway. Additionally, there may be some risk that the clinician would re-treat a previously ablated region of the endocardium and not only ablate the conduction pathway, but damage adjacent tissues.
• In some circumstances, to avoid having to repeat the ablation procedure as such, the clinician may ablate a series of regions of the endocardium along which the aberrant pathway is believed to lie, so as to improve the chance of interrupting conduction along that pathway. However, there is again insufficient feedback to assist the clinician in determining whether any of those ablated regions are sufficiently destroyed.
• U.S. Pat. No. 4,190,053 to Sterzer describes a hyperthermia treatment apparatus in which a microwave source is used to deposit energy in living tissue to effect hyperthermia. The apparatus includes a radiometer for measuring temperature at depth within the tissue, and includes a controller that feeds back a control signal from the radiometer, corresponding to the measured temperature, to control the application of energy from the microwave source. The apparatus alternates between delivering microwave energy from the microwave source and measuring the radiant energy with the radiometer to measure the temperature. As a consequence of this time division multiplexing of energy application and temperature measurement, temperature values reported by the radiometer are not simultaneous with energy delivery.
• U.S. Pat. No. 7,769,469 to Carr et al. describes an integrated heating and sensing catheter apparatus for treating arrhythmias, tumors and the like, having a diplexer that permits near simultaneous heating and temperature measurement. This patent too describes that temperature measured by the radiometer may be used to control the application of energy, e.g., to maintain a selected heating profile.
• Despite the promise of precise temperature measurement sensitivity and control offered by the use of radiometry, there have been few successful commercial medical applications of this technology. One drawback of previously-known systems has been an inability to obtain highly reproducible results due to slight variations in the construction of the microwave antenna used in the radiometer, which can lead to significant differences in measured temperature from one catheter to another. Problems also have arisen with respect to orienting the radiometer antenna on the catheter to adequately capture the radiant energy emitted by the tissue, and with respect to shielding high frequency microwave components in the surgical environment so as to prevent interference between the radiometer components and other devices in the surgical field.
• Acceptance of microwave-based hyperthermia treatments and temperature measurement techniques also has been impeded by the capital costs associated with implementing radiometric temperature control schemes. Radiofrequency ablation techniques have developed a substantial following in the medical community, even though such systems can have severe limitations, such as the inability to accurately measure tissue temperature at depth, e.g., where irrigation is employed. However, the widespread acceptance of RF ablation systems, extensive knowledge base of the medical community with such systems, and the significant cost required to changeover to, and train for, newer technologies has dramatically retarded the widespread adoption of radiometry.
• In view of the foregoing, it would be desirable to provide apparatus and methods that permit radiometric measurement of temperature at depth in tissue, and permit use of such measurements to control the application of ablation energy in an ablation treatment, e.g., a hyperthermia or hypothermia treatment, particularly in which contact between the ablative tip and the tissue readily may be assessed.
• It further would be desirable to provide apparatus and methods that employ microwave radiometer components that can be readily constructed and calibrated to provide a high degree of measurement reproducibility and reliability.
• It also would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be introduced in a manner that is readily accessible to clinicians trained in the use of previously-known RF ablation catheters, with a minimum of retraining, and that provide readily understandable signals to the clinicians as to whether the ablative tip is in contact with tissue.
• It still further would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be readily employed with previously-known RF electrosurgical generators, thereby reducing the capital costs needed to implement such new techniques.
SUMMARY
• In view of the foregoing, it would be desirable to provide apparatus and methods for treating living tissue that employs a radiometer for temperature measurement and control. In accordance with one aspect of the invention, systems and methods are provided for radiometrically measuring temperature and detecting tissue contact prior to and during RF ablation, i.e., calculating temperature and detecting tissue contact based on signal(s) from a radiometer. Unlike standard thermocouple techniques used in existing commercial ablation systems, a radiometer may provide useful information about tissue temperature at depth—where the tissue ablation occurs—and thus provide feedback to the clinician about the extent of tissue damage as the clinician ablates a selected region of the tissue. Additionally, the radiometer may provide useful information about whether an ablative tip is in contact with tissue, and thus provide feedback to assist the clinician in properly contacting and ablating the tissue.
• In one embodiment, the present invention comprises an interface module (system) that may be coupled to a previously-known commercially available ablation energy generator, e.g., an electrosurgical generator, thereby enabling radiometric techniques to be employed with reduced capital outlay. In this manner, the conventional electrosurgical generator can be used to supply ablative energy to an “integrated catheter tip” (ICT) that includes an ablative tip, a thermocouple, and a radiometer for detecting the volumetric temperature of tissue subjected to ablation. The interface module is configured to be coupled between the conventional electrosurgical generator and the ICT, and to coordinate signals therebetween. The interface module thereby provides the electrosurgical generator with the information required for operation, transmits ablative energy to the ICT under the control of the clinician, displays via a temperature display the temperature at depth of tissue as it is being ablated, and outputs a visible or audible indication of tissue contact for use by the clinician. The displayed temperature and determination of tissue contact may be calculated based on signal(s) measured by the radiometer using algorithms such as discussed further below.
• In an exemplary embodiment, the interface module includes a first input/output (I/O) port that is configured to receive a digital radiometer signal and a digital thermocouple signal from the ICT, and a second I/O port that is configured to receive ablative energy from the electrosurgical generator. The interface module also includes a processor, a patient relay in communication with the processor and the first and second I/O ports, and a persistent computer-readable medium. The computer-readable medium stores operation parameters for the radiometer and the thermocouple, as well as instructions for the processor to use in coordinating operation of the ICT and the electrosurgical generator.
• The computer-readable medium preferably stores instructions that cause the processor to execute the step of calculating a temperature adjacent to the ICT based on the digital radiometer signal, the digital thermocouple signal, and the operation parameters. This temperature is expected to provide significantly more accurate information about lesion quality and temperature at depth in the tissue than would a temperature based solely on a thermocouple readout. The computer-readable medium may further store instructions for causing the processor to cause the temperature display to display the calculated temperature, for example so that the clinician may control the time period for ablation responsive to the displayed temperature. The computer-readable medium may further store instructions for causing the processor to close the patient relay, such that the patient relay passes ablative energy received on the second I/O port, from the electrosurgical generator, to the first I/O port, to the ICT. Note that the instructions may cause the processor to maintain the patient relay in a normally closed state, and to open the patient relay upon detection of unsafe conditions.
• The computer-readable medium preferably also stores instructions that cause the processor to execute the step of determining whether the ICT is in contact with tissue, based on the digital radiometer signal. For example, because blood and tissue have different dielectric constants, the digital radiometer signal may change when the ICT is brought into or out of contact with the tissue. The instructions may cause the processor to monitor the digital radiometer signal for changes. Any such changes may be compared to a predetermined threshold value (also stored on the computer-readable medium). If the change is determined to be greater than the threshold value, then the processor outputs a signal to an output device that, responsive to the signal, indicates whether the ICT is in contact with tissue. The output device may be, for example, a visual display device that visually represents the tissue contact, e.g., a light that illuminates when there is tissue contact, or an audio device that audibly represents the tissue contact, e.g., a speaker that generates a tone when there is tissue contact. Preferably, the processor determines whether the ICT is in contact with the tissue before passing ablation energy to the ICT.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1A is a schematic illustration of a first embodiment of an arrangement including an interface module with tissue contact indicator according to one aspect of the present invention, including a display of the front and back panels of, and exemplary connections between, the interface module, a previously known ablation energy generator, e.g., electrosurgical generator, and an integrated catheter tip (ICT).
• FIG. 1B is a schematic illustrating exemplary connections to and from the interface module ofFIG. 1A, as well as connections among other components that may be used with the interface module.
• FIG. 2A is a schematic illustrating internal components of the interface module ofFIGS. 1A-1B.
• FIG. 2B schematically illustrates additional internal components of the interface module ofFIG. 2A, as well as selected connections to and from the interface module.
• FIG. 3A illustrates steps in a method of using the interface module ofFIGS. 1A-2B during tissue ablation.
• FIG. 3B illustrates steps in a method of calculating radiometric temperature using digital signals from a radiometer and a thermocouple and operation parameters.
• FIG. 3C illustrates steps in a method of controlling an ablation procedure using a temperature calculated based on signal(s) from a radiometer using the interface module ofFIGS. 1A-2B.
• FIG. 4A illustrates data obtained during an exemplary tissue contact measurement procedure performed using the interface module ofFIGS. 1A-2B.
• FIGS. 4B-4E illustrate data obtained during exemplary ablation procedures performed using the interface module ofFIGS. 1A-2B.
• FIG. 5A illustrates a plan view of an exemplary patient interface module (PIM) associated with an integrated catheter tip (ICT) for use with the interface module ofFIGS. 1A-2B.
• FIG. 5B schematically illustrates selected internal components of the PIM ofFIG. 5A, according to some embodiments of the present invention.
• FIGS. 6A-6B respectively illustrate perspective and exploded views of an exemplary integrated catheter tip (ICT) for use with the interface module ofFIGS. 1A-2B and the PIM ofFIGS. 5A-5B, according to some embodiments of the present invention.
DETAILED DESCRIPTION
• Embodiments of the present invention provide systems and methods for radiometrically measuring temperature and detecting tissue contact prior to and during ablation, in particular cardiac ablation. As noted above, commercially available systems for cardiac ablation may include thermocouples for measuring temperature, but such thermocouples may not adequately provide the clinician with information about tissue temperature or tissue contact. Thus, the clinician may need to make an “educated guess” about whether an ablative tip is in contact with tissue, as well as whether a given region of tissue has been sufficiently ablated to achieve the desired effect. By comparison, calculating a temperature based on signal(s) from a radiometer is expected to provide accurate information to the clinician about the temperature of tissue at depth, even during an irrigated procedure. Moreover, the signal(s) from the radiometer may be used to determine whether the ablative tip is in sufficient contact with tissue before attempting to ablate the tissue, so as to reduce the likelihood of forming edemas such as described above and improve the likelihood of creating effective transmural lesions. The present invention provides a “retrofit” solution that includes an interface module that works with existing, commercially available ablation energy generators, such as electrosurgical generators. In accordance with one aspect of the present invention, the interface module displays a tissue temperature and provides an indication of tissue contact based on signal(s) measured by a radiometer, that a clinician may use to perform ablation procedures with significantly better accuracy than can be achieved using only a thermocouple for temperature measurement.
• First, high level overviews of the interface module, including tissue contact indicator, and connections thereto are provided. Then, further detail on the internal components of the interface module, and exemplary methods of calculating radiometric temperature, determining tissue contact, and controlling an ablation procedure based on same, are provided. Data obtained during experimental procedures also is presented. Lastly, further detail on components that may be used with the interface module is provided.
• FIG. 1A illustrates plan views offront panel111,back panel112, and connections to and fromexemplary interface module110, constructed in accordance with the principles of the present invention. As illustrated inFIG. 1A,front panel111 ofinterface module110 may be connected to acatheter120 that includes patient interface module (PIM)121 and integrated catheter tip (ICT)122.Catheter120 optionally is steerable, or may be non-steerable and used in conjunction with a robotic positioning system or a third-party steerable sheath (not shown).ICT122 is positioned by a clinician (optionally with mechanical assistance such as noted above), during a procedure, withinsubject101 lying on grounded table102.ICT122 may include, among other things, an ablative tip, a thermocouple, and a radiometer for detecting the volumetric temperature of tissue subjected to ablation. TheICT122 optionally includes one or more irrigation ports, which in one embodiment may be connected directly to a commercially available irrigant pump.
• In embodiments in which the ablation energy is radiofrequency (RF) energy, the ablative tip may include an irrigated ablation electrode, such as described in greater detail below with reference toFIGS. 6A-6B.ICT122 further may include one or more electrocardiogram (ECG) electrodes for use in monitoring electrical activity of the heart ofsubject101.Interface module110 receives signals from the thermocouple, radiometer, and optional ECG electrodes ofICT122 viaPIM121.Interface module110 provides toICT122, viaPIM121, power for the operation of the PIM and the sensors (thermocouple, radiometer, and ECG electrodes), and ablation energy to be applied to subject101 via the ablative tip.
• Front panel111 includestissue contact indicator170, which is an output device configured to indicate whetherICT122 is in contact with tissue, e.g., whichinterface module110 determines based on signal(s) from the radiometer as described in greater detail below.Tissue contact indicator170 may include a visual display device that visually representsinterface module110's determination of whetherICT122 is in contact with tissue. For example,tissue contact indicator170 may include a light that illuminates wheninterface module110 determines thatICT122 is in contact with tissue, and is dark wheninterface module110 determines thatICT122 is out of contact with tissue. Alternatively,tissue contact indicator170 may be an audio device that audibly representsinterface module110's determination of whetherICT122 is in contact with tissue. For example,tissue contact indicator170 may include a speaker that generates a tone wheninterface module110 determines thatICT122 is in contact with tissue, and is silent wheninterface module110 determines thatICT122 is out of contact with tissue.Tissue contact indicator170 may continuously generate a tone throughout the duration of the contact, and cease generating the tone when contact is lost, so as to facilitate the clinician's ability to determine whether tissue contact has been lost. Alternatively,tissue contact indicator170 may generate a brief tone at a first frequency when contact is made, and may generate a second tone at a second frequency when contact is lost. Optionally,tissue contact indicator170 includes a visual display device and an audio device for providing the clinician with both visible and audible indications of tissue contact.
• Back panel112 ofinterface module110 may be connected viaconnection cable135 to a commercially available previously-knownablation energy generator130, for example anelectrosurgical generator130, such as a Stockert EP-Shuttle100 Generator (Stockert GmbH, Freiburg Germany) orStockert70 RF Generator (Biosense Webster, Diamond Bar, Calif.). In embodiments where theelectrosurgical generator130 is a Stockert EP-Shuttle or70 RF Generator,generator130 includesdisplay device131 for displaying temperature and the impedance and time associated with application of a dose of RF ablation energy;power control knob132 for allowing a clinician to manually adjust the power of RF ablative energy delivered to subject101; and start/stop/mode input133 for allowing a clinician to initiate or terminate the delivery of RF ablation energy. Start/stop/mode input133 also may be configured to control the mode of energy delivery, e.g., whether the energy is to be cut off after a given period of time.
• Althoughgenerator130 may be configured to display temperature ondisplay device131, that temperature is based on readings from a standard thermocouple. As noted above, however, that reported temperature may be inaccurate while irrigant and ablative energy are being applied to tissue.Interface module110 provides togenerator130, viaconnection cable135, a thermocouple signal for use in displaying such a temperature, and signals from the ECG electrodes; and provides via indifferent electrode cable134 a pass-through connection toindifferent electrode140.Interface module110 receives fromgenerator130, viaconnection cable135, RF ablation energy thatmodule110 controllably provides toICT122 for use in ablating tissue ofsubject101.
• As will be familiar to those skilled in the art, for a monopolar RF ablation procedure, a clinician may position an indifferent electrode (IE)140 on the back ofsubject101 so as to provide a voltage differential that enables transmission of RF energy into the tissue of the subject. In the illustrated embodiment,IE140 is connected to interfacemodule110 via firstindifferent electrode cable141.Interface module110 passes through the IE signal to secondindifferent electrode cable134, which is connected to an indifferent electrode input port onelectrosurgical generator130. Alternatively,IE140 may be connected directly to that port of theelectrosurgical generator130 via appropriate cabling (not shown).
• It should be understood that electrosurgical generators other than the Stockert EP-Shuttle or70 RF Generator suitably may be used, e.g., other makes or models of RF electrosurgical generators. Alternatively, generators that produce other types of ablation energy, such as microwave generators, cryosurgical sources, or high frequency ultrasound generators, may be used.Ablation energy generator130 need not necessarily be commercially available, although as noted above it may be convenient to use one that is. It should also be appreciated that the connections described herein may be provided on any desired face or panel ofinterface module110, and that the functionalities of different connectors and input/output (I/O) ports may be combined or otherwise suitably modified.
• Front panel111 ofinterface module110 includestemperature display113, e.g., a digital two or three-digit display device configured to display a temperature calculated by a processor internal tointerface module110, e.g., as described in greater detail below with reference toFIGS. 2A-2B and3A. Other types of temperature displays, such multicolor liquid crystal displays (LCDs), alternatively may be used. In one embodiment, the functionalities oftemperature display113 andtissue contact indicator170 are provided by a single display device configured both to display temperature and to provide an indication ofinterface module110's determination of whetherICT122 is in contact with tissue. For example, the background oftemperature display113 may be configured to change from one color to another (e.g., from red to green) wheninterface module110 determines thatICT122 is in contact with tissue. In such an embodiment, a separate, audibletissue contact indicator170 such as described above optionally may be provided as well.Front panel111 also includes connectors (not labeled) through whichinterface module110 is connected toICT122 viaPIM121, and toIE140 viaindifferent electrode cable141.
• Back panel112 ofinterface module110 includes connectors (not labeled) through whichinterface module110 is connected toelectrosurgical generator130, viaindifferent electrode cable134 andconnection cable135.Back panel112 ofinterface module110 also includesdata ports114 configured to output one or more signals to a suitably programmed personal computer or other remote device, for example an EP monitoring/recording system such as the LABSYSTEM™ PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.). Such signals may, for example, include signals generated by the thermocouple, radiometer, and/or ECG electrodes of the ICT, the tissue temperature calculated byinterface module110, and the like.
• Referring now toFIG. 1B, exemplary connections to and frominterface module110 ofFIG. 1A, as well as connections among other components, are described. InFIG. 1B,interface module110 is in operable communication withcatheter120 having a patient interface module (PIM)121 and an integrated catheter tip (ICT)122 that includes a radiometer, ablative tip, a thermocouple (TC), and optionally also includes ECG electrodes and/or irrigation ports(s).Interface module110 is also in operable communication withelectrosurgical generator130 andindifferent electrode140.
• Electrosurgical generator130 optionally is in operable communication with electrophysiology (EP) monitoring/recording system160 viaappropriate cabling161, or alternatively viadata ports114 ofinterface module110 and appropriate cabling (not shown). EP monitoring/recording system160 may include, for example, various monitors, processors, and the like that display pertinent information about an ablation procedure to a clinician, such as the subject's heart rate and blood pressure, the temperature recorded by the thermocouple on the catheter tip, the ablation power and time period over which it is applied, fluoroscopic images, and the like. EP monitoring/recording systems are commercially available, e.g., the MEDELEC™ Synergy T-EP-EMG/EP Monitoring System (CareFusion, San Diego, Calif.), or the LABSYSTEM™ PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.).
• IfICT122 includes irrigation port(s), then one convenient means of providing irrigant to such ports isirrigation pump140 associated withelectrosurgical generator130, which pump is in operable communication with the generator and in fluidic communication with theICT122 viaconnector151. For example, theStockert70 RF Generator is designed for use with a CoolFlow™ Irrigation pump, also manufactured by Biosense Webster. Specifically, theStockert70 RF Generator and the CoolFlow™ pump may be connected to one another by a commercially available interface cable, so as to operate as an integrated system that works in substantially the same way as it would with a standard, commercially available catheter tip. For example, prior topositioning ICT122 in the body, the clinician instructs the pump to provide a low flow rate of irrigant to the ICT, as it would to a standard catheter tip; the ICT is then positioned in the body. Then, when the clinician presses the “start” button on the face ofgenerator130, the generator may instruct pump150 to provide a high flow rate of irrigant for a predetermined period (e.g., 5 seconds) before providing RF ablation energy, again as it would for a standard catheter tip. After the RF ablation energy application is terminated, then pump150 returns to a low flow rate until the clinician removes theICT122 from the body and manually turns off the pump.
• Referring now toFIGS. 2A-2B, further details of internal components ofinterface module110 ofFIGS. 1A-1B are provided.
• FIG. 2A schematically illustrates internal components of one embodiment ofinterface module110.Interface module110 includes first, second, third, and fourth ports201-204 by which it communicates with external components. Specifically,first port201 is an input/output (I/O) port configured to be connected tocatheter120 viaPIM121, as illustrated inFIG. 1A.Port201 receives as input fromcatheter120 digital radiometer and digital thermocouple (TC) signals, and optionally ECG signals, generated byICT122, and provides as output tocatheter120 RF ablation energy, as well as power for circuitry within theICT122 and thePIM121.Second port202 is also an I/O port, configured to be connected toelectrosurgical generator130 viaconnection cable135 illustrated inFIG. 1A, and receives as input fromgenerator130 RF ablation energy, and provides as output to generator130 a reconstituted analog thermocouple (TC) signal and raw ECG signal(s).Third port203 is an input port configured to be connected to indifferent electrode (IE)140 viaindifferent electrode cable134 illustrated inFIG. 1A, andfourth port204 is an output port configured to be connected togenerator130 viaindifferent electrode cable141 illustrated inFIG. 1A. As shown inFIG. 2A,interface module110 acts as a pass-through for the IE signal fromIE140 togenerator130, and simply receives IE signal onthird port203 and provides the IE signal togenerator130 onfourth port204.
• Interface module110 also includesprocessor210 coupled to non-volatile (persistent) computer-readable memory230, user interface280,load relay260, andpatient relay250.Memory230 stores programming that causesprocessor210 to perform steps described further below with respect toFIGS. 3A-3C, thereby controlling the functionality ofinterface module110.Memory230 also stores parameters used byprocessor210. For example,memory230 may store a set ofoperation parameters231 for the thermocouple and radiometer, as well as atemperature calculation module233, thatprocessor210 uses to calculate the radiometric temperature based on the digital TC and radiometer signals received on first I/O port201, as described in greater detail below with respect toFIG. 3B. Theoperation parameters231 may be obtained through calibration, or may be fixed.Memory230 also stores a set ofsafety parameters232 thatprocessor210 uses to maintain safe conditions during an ablation procedure, as described further below with respect toFIG. 3C.Memory230 furtherstores decision module234 thatprocessor210 uses to control the opening and closing ofpatient relay250 andload relay260 based on its determinations of temperature and safety conditions, as described further below with reference toFIGS. 3A-3C. When closed,patient relay250 passes ablative energy from the second I/O port202 to the first I/O port201. When closed,load relay260 returns ablative energy to theIE140 via dummy load D (resistor, e.g., of 120.OMEGA. resistance) and fourth I/O port204.Memory230 further storespredetermined threshold 235 value andtissue contact module236 thatprocessor210 uses to determine whetherICT122 is in contact with tissue, and to provide output indicative of such contact to the clinician, such as described further below with reference toFIG. 3A.
• As illustrated inFIG. 2A,interface module110 further includes user interface280 by which a user may receive information about the temperatureadjacent ICT122 as calculated byprocessor210, as well as other potentially useful information. In the illustrated embodiment, user interface280 includesdigital temperature display113, which displays the instantaneous temperature calculated byprocessor210. In other embodiments (not shown),display113 may be an LCD device that, in addition to displaying the instantaneous temperature calculated byprocessor210, also graphically display changes in the temperature over time for use by the clinician during the ablation procedure. User interface280 further may includedata ports114, which may be connected to a computer or EP monitoring/recording system by appropriate cabling as noted above, and which may output digital or analog signals being received or generated byinterface module110, e.g., radiometer signal(s), a thermocouple signal, and/or the temperature calculated byprocessor210. Preferably, user interface280 also includestissue contact indicator170, which is configured display theprocessor210's determination as to whetherICT122 is in contact with tissue based onpredetermined threshold value235 andtissue contact module236 stored inmemory230, e.g., as described in further detail below with reference toFIG. 3A.
• So as to inhibit potential degradations in the performance ofprocessor210,memory230, or user interface280 resulting from electrical contact with RF energy,interface module110 may include opto-electronics299 that communicate information to and fromprocessor210, but that substantially inhibit transmission of RF energy toprocessor210,memory230, or user interface280. This isolation is designated by the dashed line inFIG. 2A. For example, opto-electronics299 may include circuitry that is in operable communication with first I/O port201 so as to receive the digital TC and radiometer signals from first I/O port201, and that converts such digital signals into optical digital signals. Opto-electronics299 also may include an optical transmitter in operable communication with such circuitry, that transmits those optical digital signals toprocessor210 through free space. Opto-electronics299 further may include an optical receiver in operable communication withprocessor210, that receives such optical digital signals, and circuitry that converts the optical digital signals into digital signals for use byprocessor210. The opto-electronic circuitry in communication with the processor also may be in operable communication with a second optical transmitter, and may receive signals fromprocessor210 to be transmitted across free space to an optical receiver in communication with the circuitry that receives and processes the digital TC and radiometer signals. For example,processor210 may transmit to such circuitry, via an optical signal, a signal that causes the circuitry to generate an analog version of the TC signal and to provide that analog signal to the second I/O port. Because opto-electronic circuitry, transmitters, and receivers are known in the art, its specific components are not illustrated inFIG. 2A.
• With respect toFIG. 2B, additional internal components ofinterface module110 ofFIG. 2A are described, as well as selected connections to and from the interface module.FIG. 2B is an exemplary schematic for a grounding and power supply scheme suitable for usinginterface module110 with an RF electrosurgical generator, e.g., a Stockert EP-Shuttle or70 RF Generator. Other grounding and power supply schemes suitably may be used with other types, makes, or models of electrosurgical generators, as will be appreciated by those skilled in the art.
• As illustrated inFIG. 2B,interface module110 includes isolatedmain power supply205 that may be connected to standard three-prong A/C power outlet1, which is grounded to mains groundG. Interface module110 also includes several internal grounds, designated A, B, C, and I. Internal ground A is coupled to the external mains ground G via a relatively small capacitance capacitor (e.g., a 10 pF capacitor) and a relatively high resistance resistor (e.g., a20 NE/resistor) that substantially prevents internal ground A from floating. Internal ground B is coupled to internal ground A via a low resistance pathway (e.g., a pathway or resistor(s) providing less than 1000Ω resistance, e.g., about 0Ω resistance). Similarly, internal ground C is coupled to internal ground B via another low resistance pathway. Internal ground I is an isolated ground that is coupled to internal ground C via a relatively small capacitance capacitor (e.g., a 10 pF capacitor) and a relatively high resistance resistor (e.g., a 20 MΩ resistor) that substantially prevents isolated ground I from floating.
• Isolatedmain power supply205 is coupled to internal ground A via a low resistance pathway. Isolatedmain power supply205 is also coupled to, and provides power (e.g., ±12V) to, one or more internal isolated power supplies that in turn provide power to components internal tointerface module110. Such components include, but are not limited to components illustrated inFIG. 2A. For example,interface module110 may include one or moreisolated power supplies220 that provide power (e.g., ±4V) toprocessor210,memory230, andanalog circuitry240.Analog circuitry240 may include components of user interface280, includingtemperature display113 and circuitry that appropriately prepares signals for output ondata ports114.Data ports114, as well asanalog circuitry240, are coupled to internal ground B via low resistance pathways, while processor andmemory210,230 are coupled to internal ground C via low resistance pathways. Interface module also may include one or moreisolated power supplies270 that provide power (e.g., ±4V) toICT122,PIM121, andRF circuitry290.
• RF circuitry290 may include patient and load relays250,260, as well as circuitry that receives the radiometer and thermocouple signals and provides such signals to the processor via optoelectronic coupling, and circuitry that generates a clock signal to be provided to the ICT as described further below with reference toFIG. 5B.RF circuitry290,ICT122, andPIM121 are coupled to isolated internal ground I via low resistance pathways.
• As shown inFIG. 2B,power supply139 of RFelectrosurgical generator130, which may be external togenerator130 as inFIG. 2B or may be internal togenerator130, is connected to standard two- or three-prong A/C power outlet2. However,generator power supply139 is not connected to the ground of the outlet, and thus not connected to the mains ground G, as is the isolated main power supply. Instead,generator power supply139 and RFelectrosurgical generator130 are grounded to internal isolated ground I ofinterface module110 via low resistance pathways betweengenerator130 andPIM121 andICT122, and low resistance pathways betweenPIM121 andICT122 and internal isolated ground I. As such,RF circuitry290,PIM121,IE140, andgenerator130 are all “grounded” to an internal isolated ground I that has essentially the same potential as doesICT122. Thus, when RF energy is applied toICT122 fromgenerator130 throughinterface module110, the ground ofRF circuitry290,PIM121,ICT122,IE140, andgenerator130 all essentially float with the RF energy amplitude, which may be a sine wave of 50-100V at 500 kHz.
• As further illustrated inFIG. 2B, the ±12V of power that isolatedmain power supply205 provides to isolated processor/memory/analog power supply220 and to isolated ICT/RF power supply270 may be coupled by parasitic capacitance (pc, approximately 13 pF) to A/C power outlet1, as may be the ±4V of power that such power supplies provide to their respective components. Such parasitic coupling will be familiar to those skilled in the art. Note also that the particular resistances, capacitances, and voltages described with reference toFIG. 2B are purely exemplary and may be suitably varied as appropriate to different configurations.
• Referring now toFIG. 3A,method300 of usinginterface module110 ofFIGS. 1A-2B during a tissue ablation procedure is described. The clinician couples the integrated catheter tip (ICT)122 and indifferent electrode (IE)140 to respective I/O ports of interface module110 (step301). For example, as shown inFIG. 1A,ICT122 may be coupled to a first connector onfront panel111 ofinterface module110 via patient interface module (PIM)121, andIE140 may be coupled to a third connector onfront panel111 viaindifferent electrode cable141. The first connector is in operable communication with first I/O port201 (seeFIG. 2A) and the third connector is in operable communication with third I/O port203 (seeFIG. 2A).
• Inmethod300 ofFIG. 3A, the clinician may coupleelectrosurgical generator130 to I/O port(s) of interface module110 (step302). For example, as illustrated inFIG. 1A,electrosurgical generator130 may be coupled to a second connector onback panel112 ofinterface module110 viaconnection cable135, and also may be coupled to a fourth connector onback panel112 viaindifferent electrode cable134. The second connector is in operable communication with second I/O port202 (seeFIG. 2A), and the fourth connector is in operable communication with fourth I/O port204 (seeFIG. 2A).
• Inmethod300 ofFIG. 3A, the clinician initiates flow of irrigant, positionsICT122 within the subject, e.g., in the subject's heart, andpositions IE140 in contact with the subject, e.g., on the subject's back (step303). Those skilled in the art will be familiar with methods of appropriately positioning catheter tips relative to the heart of a subject in an ablation procedure, for example via the peripheral arterial or venous vasculature.
• Inmethod300 ofFIG. 3A,interface module110 receives digital radiometer, digital thermocouple, and/or analog ECG signals from the ICT, and receives ablation energy from generator130 (step304), for example using the connections, ports, and pathways described above with references toFIGS. 1A-2B. Preferably,generator130 may provide such ablation energy to the interface module responsive to the clinician pressing “start” usinginputs133 on the front face of generator130 (seeFIG. 1A).
• Inmethod300 ofFIG. 3A,interface module110 calculates and displays the temperature adjacent toICT122, based on the radiometer and thermocouple signals (step305). This calculation may be performed, for example, byprocessor210 based on instructions intemperature calculation module233 stored in memory230 (seeFIG. 2A). Exemplary methods of performing such a calculation are described in greater detail below with respect toFIG. 3B.
• Inmethod300 ofFIG. 3A,interface module110 determines whetherICT122 is in contact with tissue based on the digital radiometer signal (step306). For example,tissue contact module236 stored inmemory230 may causeprocessor210 ofinterface module110 first to identify a change in the radiometer signal. Specifically, the magnitude of the radiometer signal is a function of, among other things, the temperature of the material(s) near the radiometer and the dielectric constants of the material(s). Blood and tissue have different dielectric constants from one another. Therefore, as the clinician bringsICT122 into or out of contact with the tissue, that is, into or out of contact with a material having a different dielectric constant than the blood, the radiometer signal varies correspondingly. If the tissue and the blood are at the same temperature as one another, then any changes to the radiometer signal may be attributed toICT122 coming into or out of contact with the tissue. Such changes may be viewed as a change in the magnitude (e.g., voltage) of the radiometer signal over baseline, or as a percent change in the radiometer signal over baseline, in which baseline is the magnitude of the signal whenICT122 is in the blood and away from the tissue.
• Tissue contact module236 then may causeprocessor210 ofinterface module110 to compare the change in the radiometer signal to a predetermined threshold value, e.g.,predetermined threshold value235 stored inmemory230. The predetermined threshold value preferably is selected such that changes in the radiometer signal caused by non-contact sources such as noise fall below the threshold value, while changes in the radiometer caused by tissue contact fall above the threshold value. As such, threshold values may vary from system to system, depending on the particular noise characteristics and sensitivity of the radiometer. For example, at baseline, the radiometer signal may have a noise level of about ±0.1 V. It may be determined via calibration that the radiometer signal increases to about 0.3 V above baseline whenICT122 is brought into contact with tissue. As such,predetermined threshold value135 suitably may be set to an intermediate magnitude between the upper end of the noise level and the average value whenICT122 is in contact with tissue, e.g., a value in the range of about 0.11-0.29 V in the above example, e.g., 0.15 V, 0.2 V, or 0.25 V. Alternatively, the noise level of the radiometer is ±10% of baseline, and it may be determined via calibration that the radiometer signal increases by about 30% whenICT122 is brought into contact with tissue. As such,predetermined threshold value135 suitably may be set to an intermediate percentage between the upper end of the noise level and the average value whenICT122 is in contact with tissue, e.g., in the range of 11-29% in the above example, e.g., 15%, 20%, or 25% in the above example.
• Ifprocessor210 ofinterface module110 determines that the change in the radiometer signal is greater than storedpredetermined threshold value235, then the processor causestissue contact indicator170 to indicate that there is contact betweenICT122 and the tissue. For example,processor210 may transmit a signal totissue contact indicator170 that indicates thatICT122 is in contact with tissue. Responsive to the signal,tissue contact indicator170 generates an appropriate indicator that the clinician may perceive as meaning thatICT122 has been brought into contact with tissue. For example,tissue contact indicator170 may include a light that illuminates when there is tissue contact, and/or may include a speaker that generates a tone when there is tissue contact, or otherwise signal contact such as described above with reference toFIG. 1A.
• Inmethod300 illustrated inFIG. 3A,interface module110 also actuatespatient relay250 so as to provide ablation energy toICT122 for use in tissue ablation (step307). For example,processor210 may maintainpatient relay250 illustrated inFIG. 2A in a normally closed state during operation, such that ablation energy flows fromelectrosurgical generator130 toICT122 throughinterface module110 without delay upon the clinician's actuation of the generator, and may openpatient relay250 only upon detection of unsafe conditions such as described below with respect toFIG. 3C. In an alternative embodiment,processor210 may maintainpatient relay250 in a normally open state during operation, and may determine based on instructions indecision module234 and on the temperature calculated instep305 that it is safe to proceed with the tissue ablation, and then close patient relay so as to pass ablation energy to the ICT. In either case, after a time period defined usinginput133 on the front face ofgenerator130, the supply of ablation energy ceases or the clinician manually turns off the supply of ablation energy. Preferably,step307 is executed afterstep306. That is,processor210 preferably determines that there is tissue contact, and causes tissue contact indicator to provide an indication of such contact to the clinician, before allowing ablation energy to be provided toICT122 viapatient relay250.
• Interface module110 also generates an analog version of the thermocouple signal, and provides the ECG and analog thermocouple signals to generator130 (step308). Preferably,step308 is performed continuously by the interface module throughoutsteps303 through307, rather than just at the end of the ablation procedure. For example, as will be familiar to those skilled in the art, the Stockert EP-Shuttle or70 RF Generator may “expect” certain signals to function properly, e.g., those signals that the generator would receive during a standard ablation procedure that did not include use ofinterface module110. The Stockert EP-Shuttle or70 RF generator requires as input an analog thermocouple signal, and optionally may accept analog ECG signal(s). Theinterface module110 thus may pass through the ECG signal(s) generated by the ICT to the Stockert EP-shuttle or70 RF generator via second I/O port202. However, as described above with reference toFIG. 2A,interface module110 receives a digital thermocouple signal fromICT122. In its standard configuration, the Stockert EP-Shuttle or70 RF generator is not configured to receive or interpret a digital thermocouple signal. As such,interface module110 includes the functionality of reconstituting an analog version of the thermocouple signal, forexample using processor210 and opto-electronics299, and providing that analog signal togenerator130 via second I/O port202.
• Turning toFIG. 3B, the steps ofmethod350 of calculating radiometric temperature using digital signals from a radiometer and a thermocouple and operation parameters is described. The steps of the method may be executed byprocessor210 based ontemperature calculation module233 stored in memory230 (seeFIG. 2A). While some of the signals and operation parameters discussed below are particular to a PIM and ICT configured for use with RF ablation energy, other signals and operation parameters may be suitable for use with a PIM and ICT configured for use with other types of ablation energy. Those skilled in the art will be able to modify the systems and methods provided herein for use with other types of ablation energy.
• InFIG. 3B,processor210 obtains frommemory230 ofinterface module110 the operation parameters for the thermocouple (TC) and the radiometer (step351). These operation parameters may include, for example, TCSlope, which is the slope of the TC response with respect to temperature; TCOffset, which is the offset of the TC response with respect to temperature; RadSlope, which is the slope of the radiometer response with respect to temperature; TrefSlope, which is the slope of a reference temperature signal generated by the radiometer with respect to temperature; and F, which is a scaling factor.
• Processor210 then obtains via first I/O port201 and opto-electronics299 the raw digital signal from the thermocouple, TCRaw (step352), and calculates the thermocouple temperature, TCT, based on TCRaw using the following equation (step353):
• $TCT=\frac{\mathrm{TCRaw}}{\mathrm{TCSlope}}-\mathrm{TCOffset}$
• Then,processor210 causestemperature display113 to display TCT until both of the following conditions are satisfied: TCT is in the range of 35° C. to 39° C., and ablation energy is being provided to the ICT (e.g., untilstep307 ofFIG. 3A). There are several reasons to display only the thermocouple temperature TCT, as opposed to the temperature calculated based on signal(s) from the radiometer, until both of these conditions are satisfied. For example, if the temperature TCT measured by the thermocouple is less than 35° C., then based on instructions indecision module234 theprocessor210 interprets that temperature as meaning thatICT122 is not positioned within a living human body, which would have a temperature of approximately 37° C. IfICT122 is positioned in the body, power safely may be provided to the radiometer circuitry so as to obtain radiometer signal(s) thatprocessor210 may use to determine whetherICT122 is in contact with tissue (e.g., step306 ofFIG. 3A).
• As illustrated inFIG. 3B,processor210 then provides ablation energy toICT122, e.g., in accordance withstep307 described above, and receives via second I/O port202 two raw digital signals from the radiometer: Vrad, which is a voltage generated by the radiometer based on the temperature adjacent the ICT; and Vref, which is a reference voltage generated by the radiometer (step355). Note that Vrad and Vref also may be provided from the radiometer at times other than when ablation energy is being provided toICT122, and that Vrad and/or Vref may constitute the radiometer signal(s) used byprocessor210 to determine whetherICT122 is in contact with tissue (e.g., step306 ofFIG. 3A).
• As illustrated inFIG. 3B,processor210 calculates the reference temperature Tref based on Vref using the following equation (step356):
• $\mathrm{Tref}=\frac{\mathrm{Vref}}{\mathrm{TrefSlope}}+\mathrm{TrefOffset}$
• Processor210 also calculates the radiometric temperature Trad based on Vrad and Tref using the following equation (step357):
• $\mathrm{Trad}=\frac{\mathrm{Vrad}}{\mathrm{RadSlope}}-\mathrm{RadOffset}+\mathrm{Tref}$
• During operation ofinterface module110,processor210 may continuously calculate TCT, and also may continuously calculate Tref and Trad during times when ablation power is provided to the ICT (which is subject to several conditions discussed further herein).Processor210 may store inmemory230 these values at specific times and/or continuously, and use the stored values to perform further temperature calculations. For example,processor210 may store inmemory230 TCT, Tref, and Trad at baseline, as the respective values TCBase, TrefBase, and TradBase. The processor then re-calculates the current radiometric temperature TradCurrent based on the current Vrad received on second I/O port202, but instead with reference to the baseline reference temperature TrefBase, using the following equation (step358):
• $\mathrm{TradCurrent}=\frac{\mathrm{Vrad}}{\mathrm{RadSlope}}-\mathrm{RadOffset}+\mathrm{TrefBase}$
• Processor210 then calculates and causestemperature display113 to display a scaled radiometric temperature TSrad for use by the clinician based on the baseline thermocouple temperature TCBase, the baseline radiometer temperature TradBase, and the current radiometer temperature TradCurrent, using the following equation (step359):
• 
  TSrad=TCBase+(TradCurrent−TradBase)×F
• In this manner,interface module110 displays for the clinician's use a temperature calculated based on signal(s) from the radiometer that is based not only on voltages generated by the radiometer and its internal reference, described further below with reference toFIGS. 6A-6B, but also on temperature measured by the thermocouple.
• With respect toFIG. 3C,method360 of controlling an ablation procedure based on a temperature calculated based on signal(s) from a radiometer, e.g., as calculated usingmethod350 ofFIG. 3B, and also based onsafety parameters232 anddecision module234 stored inmemory230 is described.
• Inmethod360 ofFIG. 3C, a slow flow of irrigant is initiated through the ICT and the ICT is then positioned within the subject (step361). For example, in embodiments for use with aStockert70 RF Generator, the generator may automatically initiate slow irrigant flow to the catheter tip by sending appropriate signals to a CoolFlow irrigant pumping system associated with the generator, responsive to actuation of the generator by the clinician.
• After confirming that the ICT is in contact with tissue based on an indication bytissue contact indicator170 such as described above, the clinician presses a button on the generator to start the flow of ablation energy to the ICT; this may cause the generator to initiate a high flow of irrigant to the ICT and generation of ablation energy following a 5 second delay (step362). The interface module passes the ablation energy to the ICT via the patient relay, as described above with respect to step306 ofFIG. 3A.
• Based on the calculated and displayed radiometric temperature (seemethods300 and350 described above with respect toFIGS. 3A-3B), the clinician determines the temperature of the tissue volume that is being ablated by the ablation energy (step363). By comparison, temperature measured by a thermocouple alone would provide little to no useful information during this stage of the procedure.
• Interface module110 may use the calculated radiometric temperature to determine whether the ablation procedure is being performed within safety parameters. For example,processor210 may obtainsafety parameters232 frommemory230. Among other things, these safety parameters may include a cutoff temperature above which the ablation procedure is considered to be “unsafe” because it may result in perforation of the cardiac tissue being ablated, with potentially dire consequences. The cutoff temperature may be any suitable temperature below which one or more unsafe conditions may not occur, for example “popping” such as described below with respect toFIGS. 4D-4E, or tissue burning, but at which the tissue still may be sufficiently heated. One example of a suitable cutoff temperature is 85° C., although higher or lower cutoff temperatures may be used, e.g., 65° C., 70° C., 75° C., 80° C., 90° C., or 95° C. Instructions indecision module234, also stored inmemory230,cause processor210 to continuously compare the calculated radiometric temperature to the cutoff temperature, and if the radiometric temperature exceeds the cutoff temperature, the processor may set an alarm, open the patient relay, and close the load relay so as to return power to the IE via I/O port204, thereby cutting off flow of ablation energy to the ICT (step364 ofFIG. 3C). Otherwise, the processor may allow the ablation procedure to proceed (step364).
• The ablation procedure terminates (step365), for example, when the clinician presses the appropriate button ongenerator130, or when thegenerator130 automatically cuts of ablation energy at the end of a predetermined period of time.
• Referring now toFIGS. 4A-4E, illustrative data obtained during experiments using an interface module constructed in accordance with the present invention is described. This data was obtained using an unmodified Stockert EP Shuttle Generator with integrated irrigation pump, and a catheter including thePIM121 andICT122 described further below with reference toFIGS. 5A-6B coupled tointerface module110.
• FIG. 4A illustrates the change over time in various signals collected during a procedure in which the ablative tip ofICT122 was immersed into a tank of saline containing a tissue sample that were maintained at a constant temperature of about 49.5° C. and had dielectric constants similar to that of living blood and tissue, respectively. The ablative tip ofICT122 was manually brought into and out of contact with the tissue several times.Signal401 illustrated inFIG. 4A corresponds to radiometer signal Vrad (having units of Volts, right side y-axis of graph) signal402 corresponds to the thermocouple temperature (having units of ° C., left side y-axis of graph), and signal403 corresponds to display temperature Tdisplay (also having units of ° C., left side y-axis of graph).Signals401,402, and403 were collected without actuating the Stockert EP Shuttle Generator, so that changes in Vrad asICT122 was brought into contact with the tissue could be attributed to the difference between the dielectric constants of the saline and the tissue, rather than to changes in temperature.
• As can be seen inFIG. 4A,radiometer signal401 begins at abaseline404 around 2.95 V; the particular value of this baseline depends, among other things, on the dielectric constant and temperature of the saline in whichICT122 is immersed, and the sensitivity of the radiometer.Radiometer signal401 has anoise level405 of about ±0.05 V aboutbaseline404, which may be attributed to random noise in the radiometer electronics. During the time periods between about 20-32 seconds, 40-52 seconds, 60-72 seconds, and 80-92 seconds,radiometer signal401 may be seen to rapidly increase frombaseline404 to ahigher level406 around 3.37 V. Because the tissue is at the same temperature as the saline, the change inradiometer signal401 tolevel406 may be attributed to the different dielectric constant of the tissue as compared to the saline. As such, contact betweenICT122 and the tissue in the tank readily may be identified based on changes in radiometer signal frombaseline404 tolevel406. Additionally, based on such observations apredetermined threshold value407 may be defined that lies between the upper end ofnoise405 andlevel406 indicative of tissue contact, and that may be stored inmemory230 and used byprocessor210 ofinterface module110 at a later time to determine whetherICT122 is in contact with tissue. Thus, in essence, such a procedure calibrates theICT122 with regards to tissue contact. Preferably, the temperature and the dielectric constants of the materials used during such a calibration are selected to be relatively similar to those of blood and tissue of a human, so thatbaseline404,level406, andpredetermined threshold value407 are based on the expected temperatures and dielectric constants measured by the radiometer during an actual ablation procedure.
• FIG. 4B illustrates the change over time in various signals collected during an ablation procedure in whichICT122 was placed against exposed thigh tissue of a living dog, and the Stockert EP Shuttle generator actuated so as to apply 20 W of RF energy for 60 seconds. A Luxtron probe was also inserted at a depth of 3 mm into the dog's thigh. Luxtron probes are considered to provide accurate temperature information, but are impractical for normal use in cardiac ablation procedures because such probes cannot be placed in the heart of a living being.
• FIG. 4B illustrates the change over time in various signals collected during the ablation procedure.Signal410 corresponds to scaled radiometric temperature TSrad; signal420 corresponds to the thermocouple temperature; signal430 corresponds to a temperature measured by the Luxtron probe; and signal440 corresponds to the power generated by the Stockert EP Shuttle Generator.
• As can be seen fromFIG. 4B,power signal440 indicates that RF power was applied to the subject's tissue beginning at a time of about 40 seconds and ending at a time of about 100 seconds.Radiometric temperature signal410 indicates a sharp rise in temperature beginning at about 40 seconds, from a baseline inregion411 of about 28° C. to a maximum inregion412 of about 67° C., followed by a gradual fall inregion413 beginning around 100 seconds. The features ofradiometric temperature signal410 are similar to those ofLuxtron probe signal430, which similarly shows a temperature increase beginning around 40 seconds to a maximum value just before 100 seconds, and then a temperature decrease beginning around 100 seconds. This similarity indicates that the radiometric temperature has similar accuracy to that of the Luxtron probe. By comparison,thermocouple signal420 shows a significantly smaller temperature increase beginning around 40 seconds, followed by a low-level plateau in the 40-100 second region, and then a decrease beginning around 100 seconds. The relatively weak response of the thermocouple, and the relatively strong and accurate response of the Luxtron thermocouple, indicate that an unmodified Stockert EP Shuttle Generator successfully may be retrofit usinginterface module110 constructed in accordance with the principles of the present invention to provide a clinician with useful radiometric temperature information for use in an ablation procedure.
• FIG. 4C illustrates signals obtained during a similar experimental procedure, but in which two Luxtron probes were implanted into the animal's tissue, the first at a depth of 3 mm and the second at a depth of 7 mm. The Stockert EP Shuttle generator was activated, and the RF power was manually modulated between 5 and 50 W using the power control knob on the front panel of the generator. InFIG. 4C, the radiometer signal is designated460, the 3 mm Luxtron designated470, and the 7 mm Luxtron designated480. The radiometer and 3 mm Luxtron signals460,470 may be seen to have relatively similar changes in amplitude to one another resulting from the periodic heating of the tissue by RF energy. The 7mm Luxtron signal480 may be seen to have a slight periodicity, but far less modulation than do the radiometer and 3 mm Luxtron signals460,470. This is because the 7 mm Luxtron is sufficiently deep within the tissue that ablation energy substantially does not directly penetrate at that depth. Instead, the tissue at 7 mm may be seen to slowly warm as a function of time, as heat deposited in shallower portions of the tissue gradually diffuses to a depth of 7 mm.
• A series of cardiac ablation procedures were also performed in living humans using the experimental setup described above with respect toFIGS. 4B-4C, but omitting the Luxtron probes. The humans all suffered from atrial flutter, were scheduled for conventional cardiac ablation procedures for the treatment of same, and consented to the clinician's use of the interface box and ICT during the procedures. The procedures were performed by a clinician who introduced the ICT into the individuals' endocardia using conventional methods. During the procedures, the clinician was not allowed to view the temperature calculated by the interface module. As such, the clinician performed the procedures in the same manner as they would have done with a system including a conventional RF ablation catheter directly connected to a Stockert EP-Shuttle generator. The temperature calculated by the interface module during the various procedures was made available for the clinician to review at a later time. The clinician performed a total of 113 ablation procedures on five humans using the above-noted experimental setup.
• FIGS. 4D-4E illustrate data obtained during sequential ablation procedures performed on a single individual using the experimental setup. Specifically,FIG. 4D illustrates the change over time in thesignal415 corresponding to the scaled radiometric temperature TSrad, as well as the change over time in thesignal421 corresponding to the thermocouple temperature, during the tenth ablation procedure performed on the individual. During the procedure, about 40 W of RF power was applied to the individual's cardiac tissue for 60 seconds (between about 20 seconds and 80 seconds inFIG. 4D), and the clinician had atarget temperature445 of 55° C. to which it was desired to heat the cardiac tissue so as to sufficiently interrupt an aberrant pathway causing the individual's atrial flutter. It can be seen that the scaledradiometric temperature signal415, which was subjected to data smoothing inFIG. 4D, varied between about 40° C. and 51° C. while RF power was applied. By comparison, as expected, thethermocouple temperature421 provided essentially no useful information about the tissue temperature during the procedure. Notably, the clinician'starget temperature445 of 55° C. was never reached during the procedure, even though the clinician believed based on his or her perceptions of the procedure that such temperature had been reached. Because thetarget temperature445 was not reached, the tissue was insufficiently heated during the procedure to interrupt an aberrant pathway. The failure to reach the target temperature may be attributed to insufficient contact or force between the ablative tip of the ICT and the individual's cardiac tissue, the condition of the cardiac surface, insufficient power, and the like.
• FIG. 4E illustrates the change over time insignal416 corresponding to TSrad, as well as the change over time in thesignal422 corresponding to the thermocouple temperature, during the eleventh ablation procedure performed on the same individual as inFIG. 4D. During this procedure, again about 40 W of RF power was applied to the individual's cardiac tissue for 60 seconds (between about 20 seconds and 80 seconds inFIG. 4E), and the clinician again had atarget temperature445 of 55° C. It can be seen that the scaledradiometric signal416, again subject to data smoothing, varied between about 55° C. and 70° C. while RF power was applied, while thethermocouple temperature421 again provided essentially no useful information. Here, the clinician attributed the higher temperature tissue temperature achieved during the ablation to better contact between the ablative tip of the ICT and the individual's cardiac tissue. However, it can be seen that even while RF power was being applied to the tissue, the temperature varied relatively rapidly over time, e.g., from about 70° C. at about 35 seconds, to about 56° C. at 40 seconds, which may be attributed to variations in the quality of contact between the ICT and the individual's cardiac tissue.
• The results of the ablation procedures performed on the five individuals are summarized in the following table:

• 	Total	% of Total Ablation

  Number ofpatients	5
  Number ofablations	113
  Number of ablations that did not reach	50	44%
  target temperature of 55° C.
  Number of ablations that reached high	13	12%
  temperature cutoff of 95° C.
  Number ofpops	3	3%
  Number of successful treatments of	5	100%
  atrial flutter

• As can be seen from the above table, 44% of the ablation procedures did not reach the clinician's target tissue temperature of 55° C. As such, it is likely that this percentage of the procedures resulted in insufficient tissue heating to interrupt aberrant pathway(s). However, although many of the ablation procedures failed, the clinician repeated the ablation procedures a sufficient number of times to achieve 100% treatment of the individuals' atrial flutter. It is believed that displaying the calculated temperature to the clinician during ablation procedures would enable the clinician to far more accurately assess the quality of contact between the ablative tip of the ICT and the individual's cardiac tissue, and thus to sufficiently heat the tissue above the target temperature for a desired period of time, and thus reduce the clinicians' need to repeatedly perform numerous ablation procedures on the same subject so as to achieve the desired treatment.
• As shown in the above table, 12% of the ablation procedures triggered the high temperature cutoff such as illustrated inFIG. 3C. Here, the cutoff temperature was defined to be 95° C. However, it was observed that at this cutoff temperature, “pops” formed during three of the ablation procedures. A “pop” occurs when the blood boils because of excessive localized heating caused by ablation energy, which results in formation of a rapidly expanding bubble of hot gas that may cause catastrophic damage to the cardiac tissue. It is believed that a lower cutoff temperature, e.g., 85° C., may inhibit formation of such “pops.”
• Additional components that may be used in conjunction withinterface module110 of the present invention, e.g.,PIM121 andICT122 ofcatheter120, are now briefly described with reference toFIGS. 5A-6B.
• InFIG. 5A, patient interface module (PIM)121 that may be associated with the integrated catheter tip (ICT) described further below with respect toFIGS. 6A-6B is described.PIM121 includesinterface module connector501 that may be connected tofront panel111 ofinterface module110, as described with reference toFIG. 1A;PIM circuitry502, which will be described in greater detail below with reference toFIG. 5B;ICT connector503 that may be connected tocatheter120; andPIM cable504 that extends betweeninterface module connector501 andPIM circuitry502.PIM121 is preferably, but not necessarily, designed to remain outside the sterile field during the ablation procedure, and optionally is reusable with multiple ICT's.
• FIG. 5B schematically illustrates internal components ofPIM circuitry502, and includes first I/O port505 configured to be coupled tocatheter120, e.g., viaICT connector503, and second I/O port506 configured to be coupled tointerface module110, e.g., viaPIM cable504 andinterface module connector501.
• PIM circuitry502 receives on first I/O port505 an analog thermocouple (TC) signal, raw analog radiometer signals, and analog ECG signals fromcatheter120.PIM circuitry502 includes TC signal analog-to-digital (A/D)converter540 that is configured to convert the analog TC signal to a digital TC signal, and provide the digital TC signal tointerface module110 via second I/O port506.PIM circuitry502 includes a series of components configured to convert the raw analog radiometer signals into a usable digital form. For example, PIM circuitry may includeradiometric signal filter510 configured to filter residual RF energy from the raw analog radiometer signals;radiometric signal decoder520 configured to decode the filtered signals into analog versions of the Vref and Vrad signals mentioned above with reference toFIG. 3B; and radiometric signal A/D converter530 configured to convert the analog Vref, Vrad signals into digital Vref, Vrad signals and to provide those digital signals to second I/O port for transmission to interfacemodule110.PIM circuitry502 also passes through the ECG signals to second I/O port506 for transmission to interfacemodule110.
• On second I/O port506,PIM circuitry502 receives RF ablation energy from generator130 (e.g., a Stockert EP-Shuttle or70 RF Generator) viainterface module110.PIM circuitry502 passes that RF ablation energy through tocatheter120 via first I/O port505.PIM circuitry502 also receives on second I/O port506 a clock signal generated by RF circuitry withininterface module110, as described further above with reference toFIG. 2B, and passes through the clock signal to first I/O port505 for use in controlling microwave circuitry inICT122, as described below.
• Referring now toFIGS. 6A-6B, an exemplary integrated catheter tip (ICT)122 for use with theinterface module110 ofFIGS. 1A-2B and the PIM ofFIGS. 5A-5B is described. Further detail on components ofICT122 may be found in U.S. Pat. No. 7,769,469 to Carr, the entire contents of which are incorporated herein by reference, as well as in U.S. Patent Publication No. 2010/0076424, also to Carr (“the Carr publication”), the entire contents of which are incorporated herein by reference. The device described in the aforementioned patent and publication do not include a thermocouple or ECG electrodes, which preferably are included inICT122 configured for use withinterface module110.
• As described in the Carr publication and as depicted inFIGS. 6A-6B,ICT122 includes an inner orcenter conductor103 supported by a conductive carrier or insert104.Carrier104 may be formed from a cylindrical metal body having anaxial passage106 that receivesconductor103. Upper and lower sectors of that body extending inward from the ends may be milled away to exposepassage106 andconductor103 therein and to form upper and lower substantiallyparallel flats108aand108b. Flat108amay include coplanar rectangular areas108aaspaced on opposite sides ofconductor103 near the top thereof. Likewise, flat108bmay include two coplanar rectangular areas108bbspaced on opposite sides ofconductor103 near the bottom thereof. Thus,carrier104 may includecenter segment104acontaining the flats and distal andproximal end segments104band104c, respectively, which remain cylindrical, except that avertical groove107 may be formed in proximal segment104c.
• Center conductor103 may be fixed coaxially withinpassage106 by means of an electrically insulating collar orbushing109, e.g. of PTFE, press fit intopassage106 atdistal end segment104bof the carrier and by a weld to the passage wall or by an electrically conductive collar or bushing (not shown) at the carrier proximal segment104c. This causes a short circuit betweenconductor103 andcarrier104 at the proximal end of the carrier, while an open circuit may be present therebetween at the distal end of the carrier. In thecarrier center segment104a, thewalls106aofpassage106 may be spaced fromcenter conductor103. This forms a quarter wave stub S, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424.Conductor103 includesdistal end segment103awhich extends beyond the distal end ofcarrier104 a selected distance, and aproximal end segment103bwhich extends from the proximal end ofICT122 and connects to the center conductor ofcable105 configured to connect toPIM121.
• As illustrated inFIG. 6B, mounted to the upper andlower flats108aand108bofcarrier104 is a pair of opposed, parallel, mirror-image, generallyrectangular plates115aand115b. Eachplate115a,115bmay include a thin, e.g. 0.005 in.,substrate116 formed of an electrically insulating material having a high dielectric constant. Printed, plated or otherwise formed on the opposing or facing surfaces ofsubstrates116 are axially centered, lengthwiseconductive strips117, preferably 0.013-0.016 mm wide, which extend the entire lengths ofsubstrates116. Also, the opposite or away-facing surfaces ofsubstrates116 are plated withconductive layers118, e.g. of gold. The side edges oflayers118 wrap around the side edges of the substrates.
• When the ICT is being assembled,plate115amay be seated on the upper flat108aofcarrier104 and thelower plate115bis likewise seated on the lower flat108bso that thecenter conductor103 is contacted from above and below by theconductive strips117 of the upper and lower plates and thelayer118 side edges of those plates contactcarrier segment104a. A suitable conductive epoxy or cement may be applied between those contacting surfaces to secure the plates in place.
• At least one of the plates,e.g. plate115a, functions also as a support surface for one or more monolithic integrated circuit chips (M_MICs),e.g. chips122 and124. The chip(s) may include a coupling capacitor connected by a lead (not shown) tocenter conductor103 and the usual components of a radiometer such as a Dicke switch, a noise source to provide a reference temperature, amplifier stages, a band pass filter to establish the radiometer bandwidth, additional gain stages if needed, a detector and buffer amplifier. Due to the relatively small profile of thepresent ICT122, the above circuit components may be arranged in a string of four chips. The chip(s) may be secured to themetal layer118 ofplate115aby a suitable conductive adhesive so that that layer which, as described above, is grounded to theinsert104 may function as a ground plane for those chips. The plates also conduct heat away from the chips toconductor103 andcarrier104. Various leads (not shown) connect the chips to each other andother leads125bextend throughcarrier slot107 and connect thelast chip124 in the string, i.e. the radiometer output, to corresponding conductors ofcable105 leading toPIM121.
• A tubularouter conductor126 may be slid ontocarrier104 from an end thereof so that it snugly engages around the carrier with its proximal and distal ends coinciding with the corresponding ends of the carrier (not shown). Theconductor126 may be fixed in place by a conductive epoxy or cement applied around thecarrier segments104band104c.
• ICT122 also may include anannular dielectric spacer137, e.g. of PTFE, which is centered on the distal end ofcarrier104 and surrounds theconductor segment103a. The spacer may have a slit137aenabling it to be engaged around that conductor segment from the side thereof. Thespacer137 may be held in place by aconductive collar136 which encircles the spacer and is long enough to slidably engage over a distal end segment ofouter conductor126. Thecollar136 may be press fit around that conductor andcarrier segment104bto hold it in place and to electrically connect all those elements.
• The distal end of theICT122 may be closed off byconductive tip142 which, in axial section, may be T shaped. That is, thetip142 may havediscoid head142athat forms the distal end of the ICT and an axially extendingtubular neck142b. Theconductor segment103ais sufficiently long to extend beyond the distal end of thespacer137 into the axial passage inneck104b. The tip may be secured in place by conductive adhesive applied around the distal end ofconductor segment103aand at the distal end or edge ofcollar136. When the tip is in place, theconductor segment103aandtip104 form a radiometric receiving antenna, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424.
• ICT122 may further includedielectric sheath144 which may be engaged over the rear end ofouter conductor126 and slid forwardly until itsdistal end144ais spaced a selected distance behind the distal end oftip142. Theconductors103 and126 ofICT122 form an RF transmission line terminated by thetip104. When theICT122 is operative, the transmission line may radiate energy for heating tissue only from the uninsulated segment of the probe betweentip104 and thedistal end144aof thesheath144. That segment thus constitutes an RF ablation antenna.
• The proximal ends of thecenter conductor segment103b,outer conductor126 andsheath144 may be connected, respectively, to the inner and outer conductors and outer sheath ofcable105 that leads toPIM121. Alternatively, those elements may be extensions of the corresponding components ofcable105. In any event, thatcable105 connects thecenter conductor103 to the output of a transmitter which transmits a RF heating signal at a selected heating frequency, e.g. 500 GHz, to the RF ablation antenna.
• As illustrated inFIG. 6A,ICT122 further may include first, second, andthird ECG electrodes190 disposed on the outside ofsheath144, as well as athermocouple191 positioned so as to detect the temperature of blood or tissue in contact withICT122. Signals generated byelectrodes190 andthermocouple191 may be provided alongcable105 connected toPIM121.
• If desired,cable105 further may includeprobe steering wire145 whose leading end145amay be secured to the wall of apassage146 in carrier segment104c.
• Preferably, helical throughslot147 is provided incollar136 as shown inFIGS. 6A-6B. The collar material left between the slot turns essentially formshelical wire148 that bridgesspacer137.Wire148 is found to improve the microwave antenna pattern of the radiometric receiving antenna without materially degrading the RF heating pattern of the RF ablation antenna.
• The inner orcenter conductor103 may be a solid wire, or preferably is formed as a tube that enablesconductor103 to carry an irrigation fluid or coolant to the interior ofprobe tip142 for distribution therefrom throughradial passages155 intip head142athat communicate with the distal end of the axial passage intip neck142b.
• Whenplates115aand115bare seated on and secured to the upper andlower flats108aand108b, respectively, ofcarrier104,conductive strips117,117 of those members may be electrically connected to centerconductor103 at the top and bottom thereof so thatconductor103 forms the center conducts for of a slab-type transmission line whose ground plane includeslayers118,118.
• When ablation energy is provided toICT122, a microwave field exists within thesubstrate116 and is concentrated between thecenter conductor103 andlayers118,118. Preferably, as noted here, conductive epoxy is applied betweenconductor103 and strips117 to ensure that no air gaps exist there because such a gap would have a significant effect on the impedance of the transmission line as the highest field parts are closest toconductor103.
• Plates115a,115bandconductor103 segment together withcarrier104 form a quarter wave (λ_R/4) stub S that may be tuned to the frequency ofradiometer circuit124, e.g. 4 GHz. The quarter wave stub S may be tuned to the center frequency of the radiometer circuit along with components inchips122,124 to form a low pass filter in the signal transmitting path to the RF ablation antenna, while other components of the chips form a high pass or band pass filter in the signal receiving path from the antenna to the radiometer. The combination forms a passive diplexer D which prevents the lower frequency transmitter signals on the signal transmitting path from antenna T from reaching the radiometer, while isolating the path to the transmitter from the higher frequency signals on the signal receiving path from the antenna.
• The impedance of the quarter wave stub S depends upon the K value and thickness t ofsubstrates116 of the twoplates115a,115band the spacing ofcenter conductor103 from thewalls106a,106aofpassage106 in thecarrier center segment104a. Because thecenter conductor103 is not surrounded by a ceramic sleeve, those walls can be moved closer to the center conductor, enabling accurate tuning of the suspended substrate transmission line impedance while minimizing the overall diameter of theICT122. As noted above, the length of the stub S may also be reduced by makingsubstrate116 of a dielectric material which has a relatively high K value.
• In one working embodiment of theICT122, which is only about 0.43 in. long and about 0.08 in. in diameter, the components of the ICT have the following dimensions:

• Component	Dimension (inches)
  Conductor 103	0.020 outer diameter
  	0.016 inner diameter (if hollow)
  Substrate 116 (K = 9.8)	0.065 wide; thickness t = 0.005
  Strips 117	0.015 wide
  Air gap between 103 and each 106a	0.015

• Thus, the overall length and diameter of theICT122 may be relatively small, which is a useful feature for devices configured for percutaneous use.
• While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made herein without departing from the invention. For example, although the interface module has primarily been described with reference for use with an RF electrosurgical generator and the PIM and ICT illustrated inFIGS. 5A-6B, it should be understood that the interface module suitably may be adapted for use with other sources of ablation energy and other types of radiometers. Moreover, the radiometer may have components in the ICT and/or the PIM, and need not necessarily be located entirely in the ICT. Furthermore, the functionality of the radiometer, ICT, and/or PIM optionally may be included in the interface module. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.

Claims (16)

1. A method of using an interface module with an ablation energy generator and an integrated catheter tip (ICT), the ICT including a radiometer, an ablative tip, and a thermocouple, the method of using the interface module comprising the steps of:

(a) receiving at a first I/O port of the interface module a radiometer signal and a thermocouple signal from the ICT;

(b) receiving at a second I/O port of the interface module ablative energy from the ablation energy generator;

(c) calculating at the interface module a temperature adjacent to the ICT based on the radiometer signal, the thermocouple signal, and the operation parameters;

(d) determining at the interface module whether the ICT is in contact with tissue based on the radiometer signal;

(e) outputting with an output device an indication of the interface module's determination of whether the ICT is in contact with the tissue;

(f) displaying on a temperature display of the interface module the calculated temperature; and

(g) after step (e), passing ablative energy received on the second I/O port to the first I/O port by closing a patient relay of the ablation module.

2. The method ofclaim 1, wherein step (d) comprises:

(i) identifying a change in the radiometer signal;

(ii) comparing the change in the radiometer signal to a threshold value;

(iii) if the change is greater than the threshold value, transmitting a signal to the output device.

3. The method ofclaim 2, wherein the output device comprises a visual display device configured to visually represent tissue contact responsive to the signal.

4. The method ofclaim 2, wherein the output device comprises an audio device configured to audibly represent tissue contact responsive to the signal.

5. The method ofclaim 1, further comprising the steps of:

(h) storing at the interface module a safety cutoff temperature;

(i) at the interface module, comparing the calculated temperature to the safety cutoff temperature while the patient relay is closes; and

(j) if the calculated temperature exceeds the safety cutoff temperature, opening the patient relay and closing a load relay of the ablation module such that the load relay passes ablative energy received on the second I/O port to a dummy load of the ablation module.

6. The method ofclaim 1, wherein the patient relay is maintained in a normally closed state and opened upon detection of an unsafe condition.

7. The method ofclaim 1, further comprising the steps of:

(h) initially calculating at the interface module a temperature adjacent to the ICT based on the thermocouple signal and the operation parameters but not the radiometer signal;

(i) displaying on the temperature display the initially calculated temperature; and

(j) if the temperature calculated in step (h) is in the range of 35° C. to 39° C., and if the second I/O port is receiving ablative energy from the ablation energy generator, then performing steps (c)-(g).

8. The method ofclaim 1, further comprising the steps of:

(h) receiving at a third I/O port of the ablation energy generator a signal from an indifferent electrode; and

(i) providing at a fourth I/O port the signal from the indifferent electrode to the ablation energy generator.

9. The method ofclaim 1, wherein the ablative energy is selected from the group consisting of RF energy, microwave energy, cryoablation energy, and high frequency ultrasound energy.

10. The method ofclaim 1, wherein the ablative energy is RF energy.

11. A system for facilitating detection of contact with a target region of a subject, comprising:

a processor,

wherein the processor is configured to receive a signal from a radiometer carried by a medical instrument and to provide an output indicative of contact between a portion of the medical instrument and a target region of a subject based upon, at least in part, properties determined from the signal received from the radiometer.

12. The system ofclaim 11, wherein the processor is configured to regulate operation of an energy delivery member of the medical instrument based on the output indicative of the contact between the portion of the medical instrument and the target region of the subject.

13. The system ofclaim 11, wherein the system is configured to provide to a user of the system confirmation of contact between the portion of the medical instrument and the target region of the subject.

14. The system ofclaim 11, wherein the medical instrument comprises a catheter comprising an irrigation pump in fluid communication with a fluid passage of the catheter, wherein the irrigation pump is configured to selectively deliver irrigation fluid through the fluid passage of the catheter and at least one irrigation fluid port of the catheter in fluid communication with the fluid passage of the catheter during use.

15. The system ofclaim 11, further comprising the medical instrument, wherein the medical instrument comprises an ablation catheter configured to deliver energy sufficient to ablate the target region upon being activated by an ablation energy source after the output indicative of contact is provided by the processor.

16. The system ofclaim 11, further comprising the medical instrument, wherein the medical instrument comprises an energy delivery catheter configured to deliver energy to the target region upon being activated by an energy source after the output indicative of contact is provided by the processor.

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