Control of interelectrode current during ablation

Abstract

To provide a medical apparatus.SOLUTION: The medical apparatus includes a probe. The probe includes an insertion tube configured for insertion into a body cavity of a patient, and a distal assembly, which is connected distally to the insertion tube and includes a plurality of electrodes configured to contact tissue within the body cavity. An electrical signal generator is configured to apply radio frequency (RF) signals simultaneously to the plurality of electrodes with energy sufficient to ablate the tissue contacted by the electrodes. A controller is coupled to measure time-varying voltage differences between the electrodes and to adjust the radio frequency (RF) signals applied to the electrodes responsively to the measured time-varying voltage differences.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to medical devices, and more particularly to devices and methods for ablation of biological tissue. [Background technology]

[0002] Radiofrequency ablation (RFA) is a medical procedure that uses heat generated from high-frequency alternating current (e.g., in the 350-500 kHz frequency range) to ablate portions of the electrical pathways in the heart or other dysfunctional tissue. Ablation is performed by inserting a probe, such as a catheter, into the tissue and applying radiofrequency (RF) current to an electrode at the tip of the probe.

[0003] U.S. Patent No. 6,584,345 describes an apparatus for measuring electrical signals emanating from a patient's body, particularly the patient's heart. The apparatus preferably includes a catheter having an electrode array at its distal end. The apparatus further includes a first amplifier for measuring the voltage from a first electrode of the array, and a cascade of differential amplifiers, each measuring the voltage difference between two successive electrodes in the array.

[0004] U.S. Patent No. 10,182,742 describes a method and system for assessing electrode-tissue contact prior to delivery of ablation energy. The method may generally include a control unit programmed to determine the difference between the magnitude of the maximum impedance at low frequency for a given electrode and the magnitude of the minimum impedance at low frequency across all electrodes, determine the difference between the magnitude of the maximum impedance at high frequency for a given electrode and the magnitude of the minimum impedance at high frequency across all electrodes, and determine the difference between the phase of the maximum impedance at high frequency for a given electrode and the phase of the minimum required impedance at high frequency across all electrodes.

[0005] U.S. Patent Application Publication No. 2018 / 0042674 describes a catheter system and method for selectively and rapidly applying a DC voltage to drive irreversible electroporation. In some embodiments, the device includes a voltage pulse generator and an electrode controller. The voltage pulse generator is configured to generate a pulsed voltage waveform. The electrode controller is operably coupled to the voltage pulse generator and a medical device including a series of electrodes. The electrode controller includes a selection module and a pulse delivery module. The selection module selects a subset of electrodes from the series of electrodes and identifies at least one electrode as an anode and at least one electrode as a cathode. The pulse delivery module delivers an output signal associated with the pulsed voltage waveform to the subset of electrodes. Summary of the Invention [Means for solving the problem]

[0006] The embodiments of the present invention described below provide improved devices and methods for ablation of body tissue.

[0007] Thus, in accordance with one embodiment of the present invention, there is provided a medical device including a probe, the probe including: an insertion tube configured for insertion into a body cavity of a patient; and a distal assembly connected distally to the insertion tube, the distal assembly including a plurality of electrodes configured to contact tissue within the body cavity. An electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of electrodes with sufficient energy to ablate tissue contacted by the electrodes. A controller coupled to measure a time-varying voltage difference between the electrodes and adjust the radio frequency (RF) signal applied to the electrodes in response to the measured time-varying voltage difference.

[0008] In some embodiments, the controller is configured to adjust the radio frequency (RF) signal applied to the electrodes so that the voltage difference does not exceed a predetermined threshold at any time during application of the radio frequency (RF) signal. In one embodiment, the controller is configured to adjust the amplitude of the radio frequency (RF) signal to compensate for differences in the respective peak voltages measured at a given pair of electrodes. Additionally or alternatively, the controller is configured to adjust the phase of the radio frequency (RF) signal to compensate for phase shifts between the respective voltage waveforms measured at a given pair of electrodes.

[0009] In one disclosed embodiment, the distal assembly includes a balloon connected distally to the insertion tube and configured to be inflated within the body cavity by fluid flowing through the insertion tube and into the balloon.

[0010] In some embodiments, the device includes a common electrode configured to be fixed at a position on the patient's body such that a radio frequency (RF) signal passes through the body from multiple electrodes on the probe to the common electrode, thereby ablating tissue in monopolar mode. In one disclosed embodiment, the controller is configured to adjust the radio frequency (RF) signal applied to the electrodes to control the ratio between monopolar radio frequency (RF) current flowing from the electrodes on the probe to the common electrode and bipolar radio frequency (RF) current flowing between two or more of the electrodes on the probe, thereby ablating tissue simultaneously in monopolar and bipolar modes. In one embodiment, the controller is configured to control the ratio between monopolar radio frequency (RF) current and bipolar radio frequency (RF) current by adjusting the phase shift between respective voltage waveforms applied to two or more of the electrodes on the probe.

[0011] A method for medical treatment and diagnosis is also provided in accordance with one embodiment of the present invention. The method includes providing a probe for insertion into a body cavity of a patient, the probe including an insertion tube and a distal assembly connected distally to the insertion tube, the distal assembly including a plurality of electrodes configured to contact tissue within the body cavity. Radio frequency (RF) signals are applied simultaneously and in parallel to the plurality of electrodes with sufficient energy to ablate tissue contacted by the electrodes. A time-varying voltage difference between the electrodes is measured, and the radio frequency (RF) signal applied to the electrodes is adjusted in response to the measured time-varying voltage difference.

[0012] The present invention will be more fully understood from the following detailed description taken in conjunction with the drawings, in which: [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic, pictorial illustration of a medical device during a monopolar radiofrequency ablation (RFA) procedure, in accordance with an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic circuit diagram of an electrical signal generator used in a radio frequency ablation (RFA) procedure, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] In a radiofrequency ablation (RFA) procedure, an alternating current, typically at a frequency of 350-500 kHz, is driven through the target tissue via electrodes on a catheter inserted into the tissue.

[0015] Some radiofrequency ablation (RFA) procedures use a balloon catheter, which has a balloon located at its distal end and electrodes arranged on the surface of the balloon. The balloon is inflated within a body cavity, bringing the electrodes into contact with the tissue to be ablated. When ablating tissue in a small cavity within the body, such as the left atrium of the heart, a small-diameter balloon, e.g., having a diameter of less than 15 mm, can be used.

[0016] Radiofrequency ablation (RFA) can be performed in either bipolar or monopolar mode. In bipolar mode, ablation current flows from one ablation electrode to another on the same catheter. In monopolar mode, ablation current flows between an ablation electrode on the catheter and an external electrode or "return patch." The return patch is typically secured to the subject's body surface, such as on the skin of the subject's torso, and provides an electrical return connection to the radiofrequency (RF) signal generator.

[0017] For several reasons, including their small size, small-diameter balloons are commonly used in monopolar ablation modes. However, the small size of the balloons means that the electrodes on the balloon's surface are in close proximity to each other, and even a small voltage difference between any two electrodes can cause stray currents to flow between them, potentially preventing current from flowing from each electrode through the tissue to the return patch. This unintended change in current path can affect the outcome of the ablation procedure. Even when the amplitude (peak voltage) of the radio frequency (RF) signals on the electrodes is equal, the phases of the signals at the electrodes may differ from each other because the differences in electrical impedance of each current path cause stray currents to flow between the electrodes.

[0018] Some of the embodiments of the present invention described herein address the above problem by measuring and correcting for the time-varying voltage difference between electrodes on a probe during a radiofrequency ablation (RFA) procedure. In these embodiments, an electrical signal generator simultaneously applies radiofrequency (RF) signals to multiple electrodes on the probe in parallel with sufficient energy to ablate the tissue they contact during a monopolar ablation procedure. A controller measures the time-varying voltage difference between the electrodes and adjusts the radiofrequency (RF) signals applied to the electrodes so that the voltage difference does not exceed a predetermined threshold at any time during application of the radiofrequency (RF) signal. This approach ensures that any stray current between pairs of electrodes remains low enough so as not to affect the intended ablation of the radiofrequency ablation (RFA) procedure.

[0019] Typically, the controller separately measures and adjusts the amplitude and phase of the radio frequency (RF) signals applied to each of the different electrodes to compensate for differences in peak voltage and / or phase shifts between the respective voltage waveforms measured at any given pair of electrodes.

[0020] In other embodiments, the controller measures the time-varying voltage difference and adjusts the radio frequency (RF) signal to generate a more precisely defined range of voltage difference between one or more pairs of electrodes. This voltage difference can be controlled, for example, by adjusting the relative phase between the radio frequency (RF) signals applied to each electrode in each such pair. By appropriately setting the time-varying voltage difference, the ratio between the monopolar radio frequency (RF) current flowing from the electrode to the return patch and the bipolar radio frequency (RF) current flowing between two or more electrodes can be precisely controlled. Using this approach, monopolar and bipolar ablation can be performed simultaneously, thereby allowing for flexible control of the depth and extent of ablation modification.

[0021] System Description 1 is a schematic, pictorial illustration of a medical device 20 during a monopolar radiofrequency ablation (RFA) procedure, according to one embodiment of the present invention. A physician 22 performs a radiofrequency ablation (RFA) procedure on a patient 24 using an ablation catheter 26 (further details of the catheter are described below). The illustrated embodiment refers to an example of a radiofrequency ablation (RFA) procedure within a cardiac chamber of a heart 27 using a balloon 32. In alternative embodiments, the radiofrequency ablation (RFA) procedure may be performed using other types of catheters having multiple electrodes, and the radiofrequency ablation (RFA) procedure may be performed in other organs and tissues, as well as the heart 27, as will be apparent to those skilled in the art upon review of this specification.

[0022] As shown in inset 36, ablation catheter 26 comprises a shaft 28 and a distal assembly 30, where the shaft serves as an insertion tube for inserting the distal assembly into a body cavity of patient 24, in this case, into the cardiac chamber of heart 27. Distal assembly 30 comprises a balloon 32 having a plurality of ablation electrodes 34. Distal assembly 30 and a portion of shaft 28 are also shown in inset 38. In alternative embodiments, distal assembly 30 may comprise a structure other than a balloon.

[0023] The medical device 20 further includes a controller 42 and an electrical signal generator 44, which typically reside in a console 46. The controller and signal generator may each include one or more circuit components. The catheter 26 is connected to the console 46 via an electrical interface 48, such as a port or socket, that conducts radio frequency (RFA) signals from the signal generator 44 to the distal assembly 30.

[0024] Controller 42 receives configuration parameters for the ablation procedure from physician 22 (or other operator) before and / or during the procedure. Using one or more suitable input devices, such as a keyboard, mouse, or touchscreen (not shown), physician 22 defines the electrical and temporal parameters of the radiofrequency ablation (RFA) signal to be applied to selected segments of electrode 34. Controller 42 passes suitable control signals to signal generator 44 to perform the radiofrequency ablation (RFA).

[0025] The controller 42 can be further configured to track the position of each of the electrodes 34 during the radiofrequency ablation (RFA) procedure and during electrophysiological signal acquisition using any suitable tracking technique. For example, the distal assembly 30 can include one or more electromagnetic position sensors (not shown) that output signals that vary with the sensor's position in the presence of external magnetic fields generated by one or more magnetic field generators 50. Based on these signals, the controller 42 can determine the position of the electrode 34. The magnetic field generators 50 are connected to the console 46 via cables 52 and interfaces 54. Alternatively, for each electrode 34, the controller 42 can determine the respective impedances between the electrode and multiple external electrodes 56 coupled to the patient 24 at various different locations and then calculate the ratio between these impedances (which indicates the electrode's location). As yet another alternative, the controller can use both electromagnetic and impedance-based tracking methods, as described, for example, in U.S. Pat. No. 8,456,182, the disclosure of which is incorporated herein by reference.

[0026] In some embodiments, the controller 42 displays on the display screen 58 a relevant image 60 of the target anatomy, for example, annotated to show the current position and orientation of the distal assembly 30 .

[0027] The controller 42 and the electrical signal generator 44 may typically include both analog and digital components. Thus, the controller 42 includes an analog front end having multiple inputs with respective analog-to-digital converters (ADCs) for monitoring the radio frequency (RF) ablation signals applied by the signal generator 44 to each of the electrodes 34. The controller 42 also includes multiple digital output circuits for sending commands to the signal generator 44 to adjust the radio frequency (RF) signals, as described in more detail below in FIG. 2 .

[0028] The electrical signal generator 44 typically includes radio frequency (RF) analog circuitry for generating and amplifying ablation RF signals and digital input circuitry for receiving digital control signals from the controller 42 .

[0029] Alternatively, the control signals can be transmitted from the controller 42 to the electrical signal generator 44 in analog form, provided that the controller and signal generator are configured accordingly.

[0030] Typically, the functionality of the controller 42 described herein is implemented at least in part in software. For example, the controller 42 can comprise a programmed digital computing device having at least a central processing unit (CPU) and random access memory (RAM). Program code and / or data, including a software program, is loaded into the RAM for execution and processing by the CPU. The program code and / or data can be downloaded to the controller in electronic form, for example, over a network. Alternatively or additionally, the program code and / or data can be provided and / or stored on a non-transitory tangible medium, such as a magnetic, optical, or electronic storage device. When such program code and / or data is provided to the controller, it results in a machine or special-purpose computer configured to perform the tasks described herein.

[0031] At the start of a radiofrequency ablation (RFA) procedure, physician 22 inserts catheter 26 through sheath 62 with balloon 32 in a collapsed state. After the catheter exits the sheath, fluid flows through shaft 28 into the balloon, inflating the balloon to its intended functional shape. This functional shape is shown in insets 36 and 38. By containing balloon 32 in a collapsed state, sheath 62 also serves to minimize vascular trauma that may occur while the balloon is being delivered to the target location. Physician 22 uses manipulator 64 near the proximal end of the catheter and / or deflection from sheath 62 to manipulate the catheter 26 to guide it to the target location within heart 27 of patient 24. Physician 22 brings distal assembly 30 into contact with tissue of heart 27, such as myocardial tissue. Then, under the control of physician 22 and controller 42, signal generator 44 generates radio frequency ablation (RFA) signals that are delivered through catheter 26 via different respective channels to ablation electrode 34. Typical radio frequency (RF) energy required for radio frequency ablation (RFA) is in excess of 100 J.

[0032] In monopolar radiofrequency ablation (RFA), the ablation signal current flows between the ablation electrode 34 and an external electrode or "return patch" 66, which is connected externally to the patient 24, typically between the skin of the subject's torso, and the signal generator 44. However, if adjacent electrodes 34 are not of equal radio frequency (RF) voltage and phase, some of the radio frequency (RF) current will flow as stray current between the electrodes, preventing tissue ablation as intended by the physician 22. To prevent these stray currents, the controller 42 monitors the radio frequency (RF) voltage applied to the electrodes 34 by the signal generator 44. As described in further detail below in FIG. 2, the controller 42 adjusts the radio frequency (RF) signal applied to the electrodes 34 so that the voltage difference does not exceed a predetermined threshold at any time during application of the radio frequency (RF) signal.

[0033] Alternatively or additionally, controller 42 can adjust the radio frequency (RF) signal to apply a deliberate and well-controlled voltage difference between two or more of electrodes 34, for example, by introducing a phase shift between the signals applied to each of those electrodes. In this case, both unipolar and bipolar currents flow through the tissue of heart 27 in a ratio determined by the voltage difference. For example, in one embodiment, controller 42 controls the ratio between unipolar and bipolar RF currents by adjusting the phase shift between the respective voltage waveforms applied to two or more of electrodes 34.

[0034] It should be noted that although a particular type of ablation procedure is illustrated in FIG. 1, the embodiments described herein may nevertheless be applied to any suitable type of multi-channel radio frequency (RF) ablation procedure.

[0035] 2 is a schematic circuit diagram of an electrical signal generator 44, according to one embodiment of the present invention. The same labels are used to indicate items that are the same as or similar to corresponding items in FIG.

[0036] In Figure 2, distal assembly 30 is shown from a distal perspective along the axis of shaft 28. In the illustrated embodiment, distal assembly 30 includes balloon 32 and eight electrodes 34a-34h and is positioned within heart 27 of patient 24 (Figure 1) for radiofrequency ablation (RFA). For clarity, in Figure 2, the connections and internal circuitry of signal generator 44 are shown only for electrodes 34b and 34d, rather than for all eight electrodes. Subscripts b and d are used in this figure to identify the connections and circuitry specifically associated with each of electrodes 34b and 34d, respectively.

[0037] The signal generator 44 comprises a plurality of signal sources 80 which, in response to control signals CTRL received from the controller 42, generate radio frequency (RF) signals RFSIG for application to the patient 24 through the ablation electrodes 34. The signal paths are closed via return patches 66. In this embodiment, the signal sources 80 are voltage sources, with the amplitude and phase of the output voltage of each source being set by the external control signal CTRL. Alternatively, the signal sources 80 may comprise current sources, with the amplitude and phase of the output current being set by the external control signal.

[0038] Generally, the signal generator 44 may include any suitable number of signal sources 80 corresponding to the number of ablation electrodes 34. For example, the signal generator 44 may include between 2 and 20 signal generators 80. Each signal generator 80 may include, for example, a digital signal source coupled to a digital-to-analog (DA) converter, a stable free-running analog generator, or a direct digital synthesizer (DDS), such as the AD9854 DDS from Analog Devices, Inc. (Norwood, Massachusetts, USA). Each signal source 80 generates an analog output waveform whose amplitude and phase are adjusted according to a corresponding control signal CTRL.

[0039] Signal generator 44 further includes a plurality of controlled gain stages 88 (labeled GS) configured to adjust the amplitude of each of the composite signals during application of the composite signals to the subject. Typically, signal generator 44 includes one controlled gain stage 88 for each signal source 80. Each controlled gain stage 88 may include, for example, a digital potentiometer (an example of which is an AD5122 digital potentiometer manufactured by Analog Devices).

[0040] Typically, the signal generator 44 further comprises a plurality of amplifiers 90 configured to amplify the conditioned signals received from the controlled gain stage 88. The amplified radio frequency (RF) signals are output to the ablation electrodes 44 via respective channels 92. An output transformer OT typically provides electrical isolation between the electrodes and the signal generator 44.

[0041] The signal generator 44 further includes, for each channel 92, a voltage transformer 94 and / or a current transformer 96 configured to step down the voltage and / or current of the corresponding radio frequency (RF) signal to a measurable level and at a known step-down ratio. When the signal source 80 is configured as a voltage source, the step-down voltage (e.g., induced across each voltage transformer 94 and denoted V SD ) is input to the analog front end of the controller 42 and then converted to a digital signal by an analog-to-digital (AD) converter. In an alternative embodiment, the signal source 80 functions as a current source, providing a step-down current I SD is input to the analog front end of the controller 42 and converted to a digital signal by an analog-to-digital (AD) converter.

[0042] Each radio frequency (RF) signal produces a corresponding voltage V(t) at each corresponding electrode 34. V(t) varies sinusoidally as a function of time t and can be written in the following general form: V(t)=A sin(2πft+Φ), (where A is the amplitude of the signal, f is the frequency of the signal (e.g., in the frequency range of 350 to 500 kHz), and Φ is the phase of the signal.)

[0043] Following this notation, the radio frequency (RF) voltage of electrodes 34b and 34d is specifically given by: V b (t)=A b sin(2πft+Φ b) and V d (t)=A d sin(2πft+Φ d ) These radio frequency (RF) voltages V b (t) and V d (t) is the ablation current I b and I d from electrodes 34b and 34d through patient 24 to return patch 66. If the radio frequency (RF) voltages on electrodes 34b and 34d differ in amplitude and / or phase, a stray current I bd is driven between these two electrodes. This stray current can alter the effectiveness of radiofrequency ablation (RFA).

[0044] Potential stray current I bd To minimize this, the controller 42 regulates the received step-down voltage V SD b and V SD d and the known step-down ratios of transformers 94b and 94d, the actual voltages V on electrodes 34b and 34d, respectively, can be calculated using b (t) and V d (t). The controller 42 calculates the radio frequency (RF) signal V b (t) and V d (t) Amplitude (peak voltage) A (for a fixed timing signal) b and A d and phase Φ b and Φ d By calculating the difference between the signals, V b (t)-V d (t) is measured. From these measurements, the amplitude difference A b -A d and phase shift (phase difference) Φ b -Φ d If either or both of these differences exceed a predetermined threshold, the controller 42 switches the arrow CTRL b and CTRL dto their respective signal sources 80b and 80d. In response to these commands, signal sources 80b and 80d issue commands denoted by b , phase Φ b and amplitude A d , phase Φ d , so that the amplitude and phase differences return to values ​​below their respective predetermined thresholds. This prevents any stray current I between electrodes 34b and 34d. bd This ensures that the radiation dose remains low enough so as not to significantly alter the intended effect of radiofrequency ablation (RFA).

[0045] Although this example only concerns one pair of electrodes 34b and 34d, in practice the controller 42 measures the voltages of all electrodes using the techniques described above and adjusts all amplitudes and phases as necessary to ensure that the voltages of all electrodes are equal to values ​​within predetermined thresholds.

[0046] In one embodiment, the controller 42 uses a four-point method to calculate the amplitude A b and A d and phase Φ b and Φ d In this case, the controller 42 extracts the voltage V at four distinct times (t0, t1 = t0 + τ / 4, t2 = t0 + τ / 2, and t3 = t0 + τ / 4, where t0 is an arbitrarily chosen but fixed time point and τ = 1 / f is the period of the radio frequency (RF) signal) separated from one another by one-quarter of a period of the signal. SD b and V SD d As previously mentioned, the controller converts the sampled step-down voltage into the actual voltage V on electrodes 34b and 34d. b (t) and V d (t) where V b (t) is V b (t0), V b (t1), V b (t2), and V b(t3) are calculated for the individual values ​​corresponding to the four sampling times, and V d (t) is V d (t0), V d (t1), V d (t2), and V d From these values, the controller 42 calculates the RF signal V b (t) and V d (t) Calculate the amplitude and phase of each using the following formula:

[0047]

number

[0048] As an alternative to the four-point method described above, other methods may be used, such as three-point or six-point methods, but a minimum of three points over the period τ must be used to produce unique results.

[0049] In an alternative embodiment, as previously mentioned, the controller 42 does not necessarily have to calculate the amplitude difference A b -A d and phase shift (phase difference) Φ b -Φ d Rather, the controller 42 uses the command CTRL b and CTRL d are issued to the signal sources 80b and 80d, respectively, with amplitude A b and phase Φ b and amplitude A d and phase Φ d to generate a current I of a desired amplitude between the electrodes 34b and 34d. bd For example, the controller 42 may generate a particular phase shift Φ b -Φ d while maintaining amplitude A b and A d can be set to the same value. Then the current I bdwill be proportional to the sine of the phase shift, and the ratio between unipolar and bipolar currents can be controlled simply by varying the phase shift.

[0050] It will be understood that the above-described embodiments are given by way of example, and that the present invention is not limited to what is particularly shown and described in the foregoing specification. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described in the foregoing specification, as well as variations and modifications thereof not disclosed in the prior art that would occur to one skilled in the art upon reading the foregoing description.

[0051] [Embodiment] (1) A medical device, A probe, an insertion tube configured for insertion into a body cavity of a patient; a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; a probe comprising: an electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of electrodes with sufficient energy to ablate the tissue contacted by the electrodes; a controller coupled to the electrical signal generator to measure a time-varying voltage difference between the electrodes and to adjust the radio frequency (RF) signal applied by the generator to the electrodes in response to the measured time-varying voltage difference; A medical device comprising: (2) The device of embodiment 1, wherein the controller is configured to adjust the radio frequency (RF) signal applied by the generator to the electrodes so that the voltage difference does not exceed a predetermined threshold at any time during application of the radio frequency (RF) signal. (3) The device of embodiment 2, wherein the controller is configured to adjust the amplitude of the radio frequency (RF) signal to compensate for differences in the respective peak voltages measured at a given pair of the electrodes. (4) The device of embodiment 2, wherein the controller is configured to adjust the phase of the radio frequency (RF) signal to compensate for phase shifts between respective voltage waveforms measured at a given pair of the electrodes. (5) The device of embodiment 1, wherein the distal assembly comprises a balloon connected to the distal side of the insertion tube and configured to be inflated within the body cavity by fluid flowing through the insertion tube into the balloon.

[0052] (6) The device of embodiment 1, further comprising a common electrode configured to be fixed at a position on the patient's body, such that the radio frequency (RF) signal passes through the body from the multiple electrodes on the probe to the common electrode, thereby ablating the tissue in a monopolar mode. (7) The device of embodiment 6, wherein the controller is configured to adjust the radio frequency (RF) signal applied to the electrodes to control the ratio between monopolar radio frequency (RF) current flowing from the electrodes on the probe to the common electrode and bipolar radio frequency (RF) current flowing between two or more of the electrodes on the probe, thereby ablating the tissue simultaneously in the monopolar mode and the bipolar mode. (8) The device of embodiment 7, wherein the controller is configured to control the ratio between the monopolar radio frequency (RF) current and the bipolar radio frequency (RF) current by adjusting a phase shift between respective voltage waveforms applied to the two or more of the electrodes on the probe. (9) Methods for medical treatment and diagnosis, 1. Provide a probe for insertion into a body cavity of a patient, said probe comprising: an insertion tube, and a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; providing a probe comprising: applying radio frequency (RF) signals simultaneously and in parallel to the plurality of electrodes with sufficient energy to ablate the tissue contacted by the electrodes; measuring a time-varying voltage difference between the electrodes and adjusting the radio frequency (RF) signal applied to the electrodes in response to the measured time-varying voltage difference; A method comprising: (10) The method of embodiment 9, wherein adjusting the radio frequency (RF) signal includes adjusting the radio frequency (RF) signal so that the voltage difference does not exceed a predetermined threshold at any time during application of the radio frequency (RF) signal.

[0053] 11. The method of claim 10, wherein adjusting the radio frequency (RF) signal comprises adjusting the amplitude of the radio frequency (RF) signal to compensate for differences in the respective peak voltages measured at a given pair of the electrodes. (12) The method of embodiment 10, wherein adjusting the radio frequency (RF) signal includes adjusting the phase of the radio frequency (RF) signal to compensate for a phase shift between respective voltage waveforms measured at a given pair of the electrodes. (13) The method of embodiment 9, wherein the distal assembly comprises a balloon, the balloon being connected to the distal side of the insertion tube and being inflated within the body cavity by fluid flowing through the insertion tube into the balloon. (14) The method of embodiment 9, comprising fixing a common electrode at a location on the patient's body such that the radio frequency (RF) signal passes through the body from the multiple electrodes on the probe to the common electrode, thereby ablating the tissue in a monopolar mode. (15) The method of embodiment 14, wherein adjusting the radio frequency (RF) signal comprises controlling a ratio between a monopolar radio frequency (RF) current flowing from the electrode on the probe to the common electrode and a bipolar radio frequency (RF) current flowing between two or more of the electrodes on the probe, thereby ablating the tissue simultaneously in the monopolar mode and the bipolar mode.

[0054] (16) The method of embodiment 15, wherein controlling the ratio between the monopolar radio frequency (RF) current and the bipolar radio frequency (RF) current comprises adjusting a phase shift between respective voltage waveforms applied to the two or more of the electrodes on the probe. (17) A medical device, A probe, an insertion tube configured for insertion into a body cavity of a patient; a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; a probe comprising: an electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of ablation electrodes with sufficient energy to ablate the tissue contacted by the ablation electrodes; a controller coupled to the signal generator, (1) determining (a) an amplitude difference between at least two ablation electrodes of the plurality of ablation electrodes; or (b) a phase difference between the at least two ablation electrodes; (2) adjusting the amplitude or the phase for one or all of the at least two ablation electrodes, such that the amplitude difference or the phase difference of the at least two ablation electrodes returns to a value that is less than a predetermined respective amplitude threshold and a value that is less than a predetermined respective phase threshold; a controller configured to: A medical device comprising: (18) The medical device of embodiment 17, wherein the distal assembly comprises a balloon having an outer diameter of less than 15 mm, and the plurality of ablation electrodes are arranged radially around the longitudinal axis of the balloon. (19) The medical device of embodiment 17, further comprising an external electrode in contact with the patient in a monopolar ablation mode.

Claims

1. A medical device comprising: A probe, an insertion tube configured for insertion into a body cavity of a patient; a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; a probe comprising: an electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of electrodes with sufficient energy to ablate the tissue contacted by the electrodes; a controller coupled to the electrical signal generator to measure a time-varying voltage difference between the electrodes and to adjust the radio frequency (RF) signal applied by the electrical signal generator to the electrodes in response to the measured time-varying voltage difference; It is equipped with the controller is configured to adjust the radio frequency (RF) signal applied by the electrical signal generator to the electrodes so that the voltage difference does not exceed a predetermined threshold at any time during application of the radio frequency (RF) signal; The medical device, wherein the controller is configured to adjust the amplitude of the radio frequency (RF) signal to compensate for differences in respective peak voltages measured at a given pair of the electrodes.

2. 10. The medical device of claim 1, wherein the controller is configured to adjust the phase of the radio frequency (RF) signal to compensate for a phase shift between respective voltage waveforms measured at a given pair of the electrodes.

3. A medical device, A probe, an insertion tube configured for insertion into a body cavity of a patient; a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; a probe comprising: an electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of electrodes with sufficient energy to ablate the tissue contacted by the electrodes; a controller coupled to the electrical signal generator to measure a time-varying voltage difference between the electrodes and to adjust the radio frequency (RF) signal applied by the electrical signal generator to the electrodes in response to the measured time-varying voltage difference; It is equipped with The medical device, wherein the distal assembly includes a balloon connected distally to the insertion tube and configured to be inflated within the body cavity by fluid flowing through the insertion tube and into the balloon.

4. A medical device, A probe, an insertion tube configured for insertion into a body cavity of a patient; a distal assembly connected to a distal side of the insertion tube and comprising a plurality of electrodes configured to contact tissue within the body cavity; a probe comprising: an electrical signal generator configured to simultaneously apply radio frequency (RF) signals to the plurality of electrodes with sufficient energy to ablate the tissue contacted by the electrodes; a controller coupled to the electrical signal generator to measure a time-varying voltage difference between the electrodes and to adjust the radio frequency (RF) signal applied by the electrical signal generator to the electrodes in response to the measured time-varying voltage difference; It is equipped with the medical device further comprising a common electrode configured to be fixed at a location on the patient's body such that the radio frequency (RF) signal passes through the body from the multiple electrodes on the probe to the common electrode, thereby ablating the tissue in a monopolar mode; The medical device, wherein the controller is configured to adjust the radio frequency (RF) signals applied to the electrodes to control the ratio between monopolar radio frequency (RF) current flowing from the electrodes on the probe to the common electrode and bipolar radio frequency (RF) current flowing between two or more of the electrodes on the probe, thereby ablating the tissue simultaneously in the monopolar mode and the bipolar mode.

5. 5. The medical device of claim 4, wherein the controller is configured to control the ratio between the monopolar radio frequency (RF) current and the bipolar radio frequency (RF) current by adjusting a phase shift between respective voltage waveforms applied to the two or more of the electrodes on the probe.

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