Adjusting the phase of the multiphase ablation generator to detect contact

Abstract

The present invention is entitled "Adjusting the Phase of a Multiphase Ablation Generator to Detect Contact". The present invention discloses a radiofrequency ablation system, which includes: a single-frequency RF signal generator; a control circuit configured to set the phase and amplitude of multiple replicas of the RF signal; and multiple nonlinear amplifiers configured to amplify the multiple replicas of the RF signal and use the amplified replicas to drive corresponding multiple ablation electrodes of the patient's body. The processor is configured to receive the superposition of multiple replicas from the body surface patch electrode as a return signal, and is configured to adaptively adjust the phase and amplitude of the amplified replicas to zero crosstalk current in response to the return signal using the control circuit. In the tissue contact check operation mode, the phases of the amplified replicas are the same, while in the ablation operation mode, the phases of the amplified replicas are different from each other.

Description

[0001] Priority declaration

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 786,037, filed December 28, 2018, which is incorporated herein by reference as if fully set forth herein.

[0003] Copyright Notice - A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. Background Art 1. Technical Field

[0005] The present invention relates to internal medical examination of the body. More particularly, the present invention relates to catheters suitable for transferring non-mechanical forms of energy to or from the body for diagnostic and therapeutic purposes.

[0006] 2. Description of related technologies

[0007] The meanings of certain acronyms and abbreviations used in this article are given in Table 1.

[0008] Table 1: Acronyms and abbreviations

[0009] RF Radio Frequency ACL Active current position

[0010] Various known invasive medical device designs use multiple electrodes to apply ablative radiofrequency (RF) energy to a patient's tissue. For example, U.S. Patent Application Publication 2015 / 0272655 describes a system and method for preventing unexpected tissue damage caused by the delivery of unexpected bipolar RF energy. The system may include a multi-electrode ablation device and an RF delivery unit. The RF delivery unit may deliver monopolar energy to multiple electrodes, the energy being in phase, wherein all electrodes deliver the same voltage and are activated simultaneously to not deliver bipolar energy. Additionally or alternatively, the RF delivery unit may deliver bipolar energy to the electrodes. Here, the voltage difference between each pair of adjacent electrodes may be monitored, and the level of bipolar energy delivered may be calculated. If the amount of bipolar energy delivered exceeds a safety threshold, the voltage of the energy delivered to at least one electrode in each adjacent electrode pair may be adjusted.

[0011] The Advanced Current Location (ACL) system determines the location of electrodes on the patient's body by measuring the alternating current from the electrodes to a back patch on the patient's skin. Currently, for catheters with multiple electrodes, the current injected into the electrodes is differentiated and analyzed separately by modulating the alternating current injected into the electrodes at a certain frequency, which is selected to be unique to a given electrode. However, different alternating currents are generated by class A amplifiers, and these are inefficient. Documents describing the ACL system are shown and described in the following: U.S. Patents 7,536,218; 7,775,576; 7,848,787; 7,869,865; or 8,456,182, all of which are incorporated by reference into this application. Summary of the invention

[0012] According to the disclosed embodiment of the present invention, the multi-electrode ablation catheter has two operating modes. In the tissue contact check operating mode for determining the contact between the ablation electrode and the target tissue, the currents in the electrodes all have the same phase and the same frequency ω. In the ablation mode, the electrode currents are modulated at a common frequency ω, but the phases of the currents flowing through the electrodes are changed separately to minimize the crosstalk current.

[0013] According to an embodiment of the present invention, a radio frequency (RF) ablation system is provided, which includes: a signal generator configured to generate an RF signal of a given frequency; a control circuit configured to set the phase and amplitude of multiple replicas of the RF signal; a plurality of nonlinear amplifiers configured to amplify the multiple replicas of the RF signal and use the amplified replicas to drive corresponding multiple ablation electrodes of a patient's body; and a processor. The processor is configured to receive the superposition of the multiple replicas as a return signal sensed by a patch electrode attached to the patient's body, and is configured to adaptively adjust the phase and amplitude of the amplified replicas by controlling the control circuit in response to the return signal. In the tissue contact check operation mode, the phases of the amplified replicas are the same, while in the ablation operation mode, the phases of the amplified replicas are different from each other.

[0014] In the ablation mode of operation, the enlarged replicas are at least 3.6 degrees out of phase with each other.

[0015] According to one aspect of the system, the amplifier comprises a class D amplifier.

[0016] Yet another aspect of the system includes a measurement circuit configured to measure the replicas respectively amplified by the amplifiers, wherein the processor is configured to adjust the phase and amplitude of the replicas based on the measured replicas in the ablation mode of operation.

[0017] According to an embodiment of the present invention, there is also provided an ablation method, which is implemented by: generating multiple replicas of an RF signal of a given frequency, setting the phases and amplitudes of the multiple replicas, amplifying the multiple replicas of the RF signal, and driving the corresponding multiple ablation electrodes of the patient's body using the amplified replicas. The method is further performed by: attaching a patch electrode to the patient's body, receiving the superposition of the multiple replicas as a return signal sensed by the patch electrode, and adaptively adjusting the phase and amplitude of the amplified replicas in response to the return signal. The method is further performed as follows: in a tissue contact check operation mode in which the phases of the amplified replicas are the same, determining the presence of a contact state between the ablation electrode and the target tissue in the patient's body based on the return signal, and ablating the target tissue with the ablation electrode in an ablation operation mode in which the phases of the amplified replicas are different from each other.

[0018] According to another aspect of the method, in the ablation mode of operation, the enlarged replicas are phased at least 3.6 degrees out of phase with each other.

[0019] According to another aspect of the method, the amplifying is performed by a class D amplifier.

[0020] According to yet another aspect of the method, a measurement of the replica is also taken, and in response to the measurement, in the ablation mode of operation, the crosstalk current between the ablation electrodes is zeroed by adjusting the phase and amplitude of the replica. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a better understanding of the present invention, reference is made by way of example to the detailed description of the present invention which should be read in conjunction with the following drawings in which like elements are designated by like reference numerals, and in which:

[0022] Figure 1 is a diagrammatic representation of a system according to an embodiment of the present invention;

[0023] Figure 2 is a block diagram of an ACL system according to an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of an ACL circuit according to an embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of a catheter-based ablation system using a Class-D amplifier according to an embodiment of the present invention;

[0026] Figure 5 is a diagram showing an embodiment according to the present invention Figure 4 A schematic diagram showing certain details of the operation of the system shown;

[0027] Figure 6is a diagram showing an embodiment according to the present invention Figure 4 Schematic diagram of the two operating modes of the system shown;

[0028] Figure 7 Schematically shown as Figure 6 the resistance present in the system configured for the indicated operating mode; and

[0029] Figure 8 and Fig. 9 A flow chart showing the steps of an ablation algorithm according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In the following description, many specific details are listed in order to provide a comprehensive understanding of the various principles of the present invention. However, it will be apparent to those skilled in the art that not all of these details are necessary to practice the present invention. In this case, the details of well-known circuits, control logic components, and computer program instructions for conventional algorithms and processes are not shown in detail to avoid unnecessarily obscuring the general concepts.

[0031] The following specific embodiments should be read in conjunction with the accompanying drawings, in which the same elements in different drawings are numbered the same. The accompanying drawings (not necessarily drawn to scale) illustrate selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates the principles of the invention by way of example and not by way of limitation. This description will clearly enable those skilled in the art to prepare and use the invention, and describes several embodiments, adaptations, variations, alternative forms and uses of the invention, including the best mode currently believed to be implemented in the invention. As used herein, the term "about" or "approximately" for any numerical value or range indicates a suitable dimensional tolerance that allows a collection of parts or elements to achieve the intended purpose as described herein. More specifically, "about" or "approximately" may refer to a range of ±20% of the value of the enumerated value, for example, "about 90%" may refer to a range of values ​​from 71% to 99%. In addition, as used herein, the terms "patient", "host", "user" and "subject" refer to any human or animal subject, and are not intended to limit the system or method to human use, but the use of the subject invention in human patients represents a preferred embodiment. Documents incorporated herein by reference are to be considered an integral part of this application, except that, to the extent any term is defined in these incorporated documents in a manner that contradicts a definition explicitly or implicitly made in this specification, only the definition in this specification shall prevail.

[0032] Overview

[0033] Turning now to the drawings, first refer to Figure 1, which is a perspective illustration of a system 10 for performing diagnostic and therapeutic procedures on a heart 12 of a living subject, the system being constructed and operative in accordance with the disclosed embodiments of the present invention. The system includes a catheter 14, which is inserted percutaneously through the patient's vascular system into a chamber or vascular structure of the heart 12 by an operator 16. The operator 16, typically a physician, brings the distal tip 18 of the catheter into contact with the heart wall, for example, at an ablation target site. Electrical activity maps may be prepared according to the methods disclosed in U.S. Patents 6,226,542 and 6,301,496 and in commonly assigned U.S. Patent 6,892,091, the disclosures of which are incorporated herein by reference as if fully set forth herein.

[0034] System 10 may include a general purpose or embedded computer processor programmed with appropriate software for performing the functions described below. Thus, although portions of system 10 shown in other figures herein are shown as including several separate functional blocks, these blocks are not necessarily separate physical entities, but may represent, for example, different computing tasks or data objects stored in a memory accessible by the processor. These tasks may be performed in software running on a single processor or running on multiple processors. The software may be provided to the processor or processors on a tangible, non-transitory medium such as a CD-ROM or non-volatile memory. Alternatively or in addition, system 10 may include a digital signal processor or hard-wired logic components. A commercial product embodying elements of system 10 may be The 3 system was obtained from Biosense Webster, Inc., 33 Technology Drive, Irvine, CA 92618, USA. This system can be modified by one skilled in the art to implement the principles of the invention described herein.

[0035] Ablation can be performed by applying thermal energy to areas determined to be abnormal, for example, by evaluating electrical activation maps, for example, by conducting radiofrequency current through wires in the catheter to one or more electrodes at the distal end 18, which apply radiofrequency energy to the myocardium. The energy is absorbed in the tissue, thereby heating the tissue to a certain temperature (usually greater than 50°C) at which the tissue permanently loses its electrical excitability. When this procedure is successful, non-conductive ablation lesions are formed in the heart tissue, which can interrupt the abnormal electrical pathways that cause arrhythmias. The principles of the present invention can be applied to different chambers of the heart to diagnose and treat a variety of different arrhythmias.

[0036] The catheter 14 generally includes a handle 20 having suitable controls thereon to enable the operator 16 to steer, position and orient the distal end of the catheter as required for the ablation procedure. To assist the operator 16, the distal portion of the catheter 14 includes a position sensor (not shown) that provides a signal to a processor 22 located in a console 24. The processor 22 may perform several processing functions as described below.

[0037] The catheter 14 is a multi-electrode catheter, which may be a balloon or basket catheter or a Figure 1 In any case where there are multiple electrodes 32, these electrodes serve as sensing electrodes and have known positions on the basket or spline electrodes and in known relationship to each other. Thus, once the catheter is positioned in the heart, for example by constructing a current position map, the position of each of the electrodes 32 in the heart is known. A method for generating a current position map is described in commonly assigned U.S. Pat. No. 8,478,383 to Bar-Tal et al., which is incorporated herein by reference as if fully set forth herein.

[0038] Electrical signals may be transmitted back and forth between the heart 12 and the console 24 via the cables 34 from electrodes 32 located at or near the distal tip 18 of the catheter 14. Pacing signals and other control signals may be transmitted from the console 24 to the heart 12 via the cables 34 and electrodes 32.

[0039] Wire connections 35 couple the console 24 to an active current location (ACL) patch 30 and other components of a positioning subsystem for measuring the position and orientation coordinates of the catheter 14. The processor 22 or another processor (not shown) may be an element of the positioning subsystem. The electrodes 32 and body surface patch 30 may be used to measure tissue impedance at the ablation site as set forth in U.S. Pat. No. 7,536,218 to Govari et al., which is incorporated herein by reference as if fully set forth herein. A temperature sensor (not shown), typically a thermocouple or thermistor, may be mounted near the distal end 18 of the catheter 14.

[0040] The console 24 typically includes one or more ablation power generators 25. The catheter 14 can be adapted to conduct ablation energy to the heart using any known ablation technique, such as radiofrequency energy, ultrasound energy, and laser-generated light energy. Such methods are disclosed in commonly assigned U.S. Patents 6,814,733, 6,997,924, and 7,156,816, which are incorporated herein by reference as if fully set forth herein.

[0041] In one embodiment, the positioning subsystem includes a magnetic positioning tracking configuration that utilizes magnetic field generating coils 28 to determine the position and orientation of the catheter 14 by generating magnetic fields at a predetermined working volume and sensing these magnetic fields at the catheter. Suitable positioning subsystems are described in U.S. Patent 7,756,576 and the aforementioned U.S. Patent 7,536,218, which are incorporated herein by reference as if fully set forth herein.

[0042] As described above, the catheter 14 is coupled to a console 24, which enables the operator 16 to observe and regulate the functions of the catheter 14. The console 24 includes a processor, preferably a computer with appropriate signal processing circuitry. The processor is coupled to drive a monitor 29. The signal processing circuitry typically receives, amplifies, filters, and digitizes signals from the catheter 14, including signals generated by the sensors mentioned above and a plurality of position sensing electrodes (not shown) located distal to the catheter 14. The digitized signals are received and used by the console 24 and the positioning system to calculate the position and orientation of the catheter 14, and to analyze the electrical signals from the electrodes as described in additional detail below.

[0043] Typically, the system 10 includes other elements that are not shown in the drawings for simplicity. For example, the system 10 may include an electrocardiogram (ECG) monitor that is connected to receive signals from one or more body surface electrodes to provide ECG synchronization signals to the console 24. As mentioned above, the system 10 also typically includes a reference position sensor, which is located on an external reference patch attached to the outside of the subject's body, or on an internal catheter inserted into the heart 12 and maintained in a fixed position relative to the heart 12. The system 10 can receive image data from an external imaging modality such as an MRI unit and includes an image processor that can be incorporated into the processor 22 or called by the processor 22 for generating and displaying images.Electrical coupling is described in “Measurement of Electrical Coupling Between Cardiac Ablation Catheters and Tissue,” D. Curtis Deno, *Member IEEE, Haris J. Sih, Stephan P. Miller, Liane R. Teplitsky, and Russ Kuenzi, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 61, NO. 3, MARCH 2014; the impedance range in humans is described in “Determinants of impedance During Radiofrequency Catheter Ablation in Humans,” Mark Borganelli, MD, Rafel El-Atassi, MD, Angel Leon, MD, Steven J. Kalbfleisch, MD, Hugh Calkins, MD, Fred Morady, MD, and Jonathan J. Langberg, MD; Department of Internal Medicine, Division of Cardiology, University of Michigan Medical Center, 1500 E. Medical Center Drive, Bl F245, Ann Arbor, Michigan 48109-0022, Dec. 1991; impedance-controlled ablation models are described in “Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future” Enrique J Berjano, 18 April 2006 BioMedical Engineering OnLine 2006, all of which are incorporated herein by reference as if fully set forth herein.

[0044] ACL system.

[0045] The ACL system is one embodiment to which the principles of the present invention may be applied. For convenience, a brief description of the ACL system is given herein. More detailed information may be found in commonly assigned application serial number 15 / 681,474 filed on August 21, 2017 (attorney docket number BIO5844USNP), entitled “Advanced Current Location (ACL) Automatic Map Rotation to Detect Holes in Current Position Map (CPM) Mapping,” which is incorporated herein by reference as if fully set forth herein.

[0046] Reference now Figure 2 , Figure 2 is a block diagram of an ACL system 130 according to an embodiment of the present invention. To operate the system 130, an operator first operates the system in a calibration phase and then operates the system in a tracking phase. Details of the actions performed in both phases are described in the aforementioned application serial number 15 / 681,474.

[0047] See now Figure 3 , which is used for Figure 1 Schematic diagram of ablation and active current location (ACL) circuit 134 used with the system shown in . This configuration is similar to the arrangement described in U.S. Patent Application Publication 2006 / 0173251 to Govari et al. and U.S. Patent Application Publication 2007 / 0038078 to Osadchy, which are incorporated herein by reference as if fully set forth herein. This configuration can be modified to operate in accordance with the principles of the present invention. For ease of presentation, a brief description is provided below:

[0048] A plurality of body surface electrodes 136, which may be adhesive skin patches, are coupled to a body surface 138 (e.g., skin) of a subject 140. The body surface electrodes 136 are sometimes referred to herein as "patches." In cardiac applications, the body surface electrodes 136 are typically distributed around the heart, three on the subject's chest and three on the back. However, the number of body surface electrodes 136 is not critical, and they may be placed at convenient locations on the body surface 138 generally near the site of the medical procedure.

[0049] Usually set at the console 24 ( Figure 1) includes a control unit 142 including a current measurement circuit 144 and one or more catheter electrode transmitters 146 for driving current at a single operating frequency through one or more of the electrodes 136 to one or more of the body surface electrodes 136, as described below. The control unit 142 is coupled to a positioning processor. The control unit 142 is coupled to an ablator 148, which includes at least one ablation generator 150. The current flowing through the body surface electrodes 136 and the ablator body surface electrodes 152 flows in a circuit having the ablation generator 150 and is measured by a corresponding current measurement circuit (sometimes referred to herein as a "patch measurement circuit") disposed within a body electrode receiver 154. The body electrode receivers 154 are typically incorporated into the control unit 142. Alternatively, they may be attached to the body surface electrodes 136. The catheter electrodes in Figure 4 1 and 2 are shown as measuring electrodes 156 (circle) and dual-purpose electrodes 158 (oval). The dual-purpose electrode 158 is used as both an ablation electrode and one of the measuring electrodes.

[0050] The body surface electrodes 136 are connected to the body electrode receivers 154 via patch boxes 160, which protect the system from ablation and defibrillation currents. Typically, the system is configured with six body electrode receivers 154. The patch box parasitic impedances 162 (Z) are measured during the production process and are therefore known a priori. These impedances are discussed below.

[0051] Typically, about 80 measuring electrodes are used for impedance measurement, although only two measuring electrodes 156 are shown for convenience. Typically, there are one or two ablation electrodes. The coordinates of the catheter in the body are determined in the positioning system by passing current between the electrodes on the catheter and the surface electrodes 136.

[0052] The control unit 142 may also control an ablation circuit including an ablator 148 and a dual-purpose electrode 158. The ablator 148 is typically located external to the control unit 142 and incorporates the ablation generator 150. The ablator 148 is connected to the ablator body surface electrode 152 and to an ablation filter 164, which is shown in this example as being located within the control unit 142. However, this location is not required. A switch 166 configures the ablation circuit for different operating modes, as described below. A voltage measurement circuit is provided for determining the output of the catheter electrode transmitter 146. From the pair of Figure 4 An observer will note that the ablation circuit is connected to one of the catheter electrode transmitters 146.

[0053] Single frequency generator for multiple ablation electrodes.

[0054] Figure 42 is a schematic diagram of a catheter-based ablation system 220 using a class D amplifier 254 according to an embodiment of the present invention. Physically, as shown in the figure, the distal end 222 of the catheter is equipped with an RF ablation device including a plurality of electrodes 259, wherein the output of the amplifier 254 is respectively connected to the electrodes 259 through wires passing through the catheter, and the catheter is connected to a console including a control unit 250 at its proximal end.

[0055] For clarity only, the distal end of the catheter is shown as a linear array of electrodes. In practice, the distal end typically includes a multi-electrode geometry suitable for the ablation procedure in question. An exemplary configuration is an inflatable balloon or expandable basket assembly for performing pulmonary vein ablation.

[0056] In this example, the control unit 250 controls in parallel a number of class D amplifiers equal to the number of electrodes 259. Each of the class D amplifiers includes a phase shifter 252 and an amplifier 254. The control unit 250 includes a common signal generator 246 that generates a common RF signal 247 that is divided into replica signals (or "replicas") 248 of the RF signal 247 to drive the amplifiers 254. The control unit 250 commands each of the phase shifters 252 to assign a corresponding phase to the input current waveform of the amplifier 254, which is then amplified into an output current 255 that is injected into the patient's body 249 through the associated electrode 259.

[0057] As can be seen, the generated ablation current 266 flows locally through the ablated tissue 264, then through the patient's body 249, and is collected by the common back patch electrode 262. However, the finite resistance of the tissue between any two electrodes (e.g., through blood in the case of ablated blood vessels), as shown by coupling resistance 258, may cause a portion of the injected current 255 to follow a path from one electrode to another in the form of crosstalk current 257.

[0058] The control unit 250 includes an analyzer 260 that analyzes the return current 268 and determines the actual current amplitude of each injected ablation current 266 based on its measured instantaneous amplitude and phase (and possibly other inputs required for calculation). Based on the requirements and calculation steps implemented in the optimization algorithm, the analyzer adjusts the amplitude or phase or both of one or more of the currents 255 to optimize the amplitude and phase or both of the currents 255 according to certain requirements, some of which are described below. The control unit 250 receives the optimized amplitude and phase in real time and instructs the phase shifter 252 or the amplifier 254 or both in real time to responsively modify at least a portion of the phase and amplitude of the injected current 255. In one implementation, the optimization algorithm may utilize the instantaneous measured output voltage and current of the amplifier 254 to adjust the crosstalk current 257 in real time. For example, the algorithm may diagonalize the "current matrix" to set the crosstalk current 257 to zero. Additionally or alternatively, other optimization algorithms may be applied using given constraints and / or cost functions, such as those that incorporate the measured instantaneous amplitude and phase of the back patch electrode 262 .

[0059] Figure 5 260 is a schematic diagram showing some details of the operation of system 220 according to an embodiment of the present invention. As shown, the waveform in inset 269 generally contains different values ​​of amplitude 271 and phase 273. The voltage and current sensor 256 measures the output voltage and current of the amplifier, and the analyzer 260 measures the instantaneous amplitude and phase of the return current 268 and uses this information, among other things, to extract the actual electrode output voltage and current. Thus, Figure 5 The arrangement in isolates and measures the various current amplitudes in the currents 255 , 266 of each electrode 259 and one of the electrodes 259 , and derives the crosstalk current 257 .

[0060] By applying similar or substantially identical voltages to some or all of the electrodes 259 in real time during the ablation process, the crosstalk current 257 can be reduced or even eliminated. This arrangement is achieved by modulating the currents of all electrodes at the same frequency ω, and by selecting the individual amplitudes and phases of the currents 255 in real time, as shown in inset 269. Thus, when the voltage difference between any two electrodes (i.e., across resistor 258) is always kept to a minimum, the crosstalk current between any two electrodes is reduced or even completely eliminated in some cases.

[0061] As described above, in order to practically achieve minimization, or even elimination, of the changing crosstalk current, the return current 268 should be analyzed by the analyzer 260 at a sufficiently high rate so that the amplitude and phase selection occurs at a sufficiently high rate and with a sufficiently short response time. For example, such closed-loop fitting of the analytical modification of the current can be achieved by using appropriate electronic circuits and nonlinear amplifiers (e.g., phase shifters and class D amplifiers operating) in an operating frequency range of kilohertz to megahertz spectrum.

[0062] Further details regarding the configuration and operation of system 220 are disclosed in commonly assigned pending application Ser. No. 15 / 697,811, filed on Sep. 7, 2017, entitled “Variable Phase Generation And Detection For Radio-Frequency (RF) Ablation” (Attorney Docket No. BIO5865USNP), which is incorporated herein by reference as if fully set forth herein.

[0063] Phase adjustment.

[0064] In order for ablation to be effective, the electrode 259 ( Figure 4 ) must be in contact with the body tissue being ablated. One method of detecting contact is by using Figure 2 and Figure 3 However, although the sensitivity can be improved using the method described in commonly assigned U.S. Patent No. 9,168,004 to Govari et al., entitled "Machine Learning in Determining Catheter Electrode Contact," which is incorporated herein by reference as if fully set forth herein, the impedance change for any given electrode is small.

[0065] The inventors have devised a technique to reliably determine electrode contact with an ablation site through a tissue contact check mode of operation, in which the phases of the electrode currents at a common frequency ω are generally the same. Figure 6 is a diagram showing an exemplary system 220 ( Figure 4 ) is a set of schematic diagrams of two operating modes of the multiphase single frequency generator 275. The multiphase single frequency generator 275 generates an output current 277 that flows through the corresponding catheter electrode 279, then flows through the body tissue 281 and returns to the electrode 283. In the ablation operating mode, as Figure 6 As shown in the upper graph 285, the output current 277 and the current in the electrode 279 have different phases. The phase difference between any two electrodes should be at least 1 / 100 of the period, for example about 3.6°.

[0066] The diagram 287 at the bottom of the figure shows the tissue contact check mode of operation. The output current 277 generated by the single frequency generator 275 and the current in the electrode 279 have the same phase When the power to each electrode has a different phase, the generator 275 can operate at a relatively low voltage. Depending on the impedance of the body, the voltage for ablation can be about 27V RMS (for a tissue impedance of about 50 ohms) to 39V RMS (for a tissue impedance of about 100 ohms) and to 47V RMS (where the tissue impedance is about 150 ohms). However, for tissue contact checking, a large voltage is required to overcome the body tissue impedance. Therefore, the tissue contact checking mode of operation is impractical for ablation.

[0067] However, the inventors have devised a technique to exploit this behavior of body impedance to allow the same electrodes used in ablation to determine adequate tissue contact during the same ablation procedure. Specifically, Figure 7 Schematically illustrates a system configured according to FIG. 287 ( Figure 5 ) present in the n electrodes 279. Each of the n electrodes 279 has a resistor 289 (r), while the resistance of the return electrode 283 is a single common resistor 291 (R). If, for simplicity, a current I is assumed to flow through each of the n electrodes 279, then since the currents are in phase, the current flowing through the common resistor 291R is nI. Therefore, the voltage seen by the generator for any electrode 279 is:

[0068] V=Ir+nIR.

[0069] The voltage V is actually about n times higher than in the out-of-phase case and is the reason why the common phase state should not be used for ablation. However, the relatively large voltage in the tissue contact check configuration means that small changes in impedance occurring across the tissue contact effectively amplify changes in the measured voltage, so Figure 6 The tissue contact detection configuration shown is a good way to measure the contact between the target tissue and the ablation electrode 279.

[0070] With the help of the disclosure provided herein, we have designed the following method for ablating tissue in full contact with n ablation electrodes. Figure 8 The ablation algorithm 300 shown is implemented, and a person skilled in the art can use the algorithm to generate suitable software code in a suitable computing platform for its intended purpose of ablating tissue in contact with the ablation electrode. It should be noted that the algorithm 300 can be one of many algorithms designed for the system 134, and for the sake of brevity, any other algorithms that are auxiliary to the algorithm 300 will not be described.

[0071] exist Figure 8In the algorithm 300, the system 134 is programmed to generate multiple replicas of an RF signal of a given frequency in step 302. At step 304, the phase and amplitude of the replicas for the n ablation electrodes are set. At step 306, the system is programmed to amplify the multiple replicas and use the amplified replicas to stimulate or drive the corresponding multiple n ablation electrodes of the patient's body. At step 308, the system 134 is programmed to receive a return signal from the patch electrode 262, which return signal may include a superposition of the replicas. At step 310, the system 134 is programmed to adjust the replicas of the current injected into the n ablation electrodes to be in phase. At step 312, the system 134 is programmed to determine whether the tissue is in contact with the electrode. Steps 310 and 312 are performed in a sequential manner. Fig. 9 4 is further described as subroutine 400.

[0072] Reference Fig. 9 , the details of tissue contact determination can be understood by those skilled in the art to generate appropriate computer code. Generally, contact with tissue can be detected when the in-phase current injected into each electrode 279 requires the voltage (measured by the voltage and current sensor 256) to increase by about 3%-10% or more relative to the typical ablation voltage required for the ablation mode (for a certain amount of tissue impedance). Therefore, we have designed a technique that allows sufficient tissue contact to be checked during the ablation procedure by switching the current injected into the n electrodes 279 or replicas in phase at step 402 and applying increasing levels of voltage simultaneously and measuring the voltage and current with the analyzer 260 at step 404. At step 406, if there is no change in the form of the zero-based value, the system algorithm returns "no" and determines that the electrode is not in sufficient contact with the body tissue. Before returning to step 404, the system may mark the electrode as not in contact at step 408. On the other hand, once the system returns "yes" confirming tissue contact at step 406 (i.e., when the injected (i.e., replica) in-phase current requires a change from the zero-based value), the controller may mark the electrode as being in contact at step 410. Thereafter, the subroutine 400 returns to the ablation algorithm 300 ( Figure 8 ) to switch or change the n electrodes out of phase at step 316 to continue ablating the tissue (which is now in full contact with the electrodes). Figure 8 , changing to out-of-phase electrodes 279) between such operations (steps 402, 404 and 406) will occur at a very fast rate of multiple times per second, typically switching at a frequency of about 50 Hz. The number of n electrodes can be any number from about 2 to about 192.

[0073] It should be understood by those skilled in the art that the present invention is not limited to the contents specifically shown and described above. On the contrary, the scope of the present invention includes both the combination and sub-combination of the various features described above, as well as the variations and modifications of the various features described above that are not within the scope of the prior art that can be imagined by those skilled in the art when reading the above description.

Claims

1. A radiofrequency (RF) ablation system, comprising: a signal generator configured to generate an RF signal having a given frequency; a control circuit configured to set the phase and amplitude of the plurality of replicas of the RF signal generated by the signal generator; a plurality of non-linear amplifiers configured to amplify the plurality of replicas of the RF signal and drive a corresponding plurality of ablation electrodes of a patient's body using the amplified replicas; and A processor configured to: Analyze return signals from patch electrodes attached to the patient's body, the return signals comprising a superposition of the multiple replicas sensed by the patch electrodes, ablate target tissue with the multiple ablation electrodes in an ablation mode, and adaptively adjust the phase and amplitude of the amplified replicas based at least in part on the return signals by controlling the control circuit so that in the ablation operation mode, the phases of the amplified replicas are adjusted to be different from each other so as to reduce crosstalk between electrodes of the multiple electrodes.

2. The system of claim 1, wherein in the ablation mode of operation, the phases of the enlarged replicas differ from each other by at least 3.6 degrees.

3. The system of claim 1, wherein the amplifier comprises a Class D amplifier.

4. The system according to claim 1, further comprising: A measurement circuit is configured to measure the replicas respectively amplified by the amplifiers, wherein the processor is configured to adjust the phase and amplitude of the replicas based on the measured replicas in the ablation operation mode. 5 . The system of claim 1 , further comprising a catheter configured to be inserted into the patient's body, the plurality of electrodes being attached to the catheter.

6. The system of claim 5, wherein the catheter comprises one of an inflatable balloon and an expandable basket assembly.

7. The system of claim 1, wherein the tissue contacted in the tissue contact mode comprises a pulmonary vein.

8. The system of claim 1, wherein in the ablation mode of operation, the voltage of the RF signal is between 27 VRMS and 47 V RMS.

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