Controlling bipolar ablation in a multi-channel radiofrequency ablation device

Abstract

The present invention provides an ablation system, which includes a plurality of electrodes configured to contact a patient's body tissue, the plurality of electrodes including two or more ablation electrodes for contacting corresponding positions in a target organ and a return electrode. A signal generating unit includes a plurality of signal generators, the plurality of signal generators being configured to apply corresponding composite signals to corresponding ablation electrodes among the ablation electrodes. The composite signal includes a plurality of corresponding signal components, the corresponding signal components including corresponding ablation signals having different corresponding ablation signal amplitudes and phases at a common ablation signal frequency, and corresponding probe signals having corresponding probe signal amplitudes and different corresponding probe signal frequencies; the processor is coupled to measure the probe signal received by each of the plurality of electrodes, and to control the ablation signal amplitude and phase in response to the measured probe signal.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 786,755, filed December 31, 2018, which prior application is hereby incorporated by reference as if fully set forth herein. Technical Field

[0003] The present invention relates generally to therapeutic medical devices, and in particular to radio frequency (RF) ablation devices and their manufacture. Background Art

[0004] In a multi-channel ablation procedure, multiple ablation currents are applied simultaneously to multiple ablation electrodes.

[0005] U.S. Patent 5,383,917 describes multiphase RF ablation using a two-dimensional or three-dimensional electrode array that creates multiple current paths on the surface of the ablation zone. This results in a uniform lesion whose size is defined by the span of the electrode array. An orthogonal electrode catheter array suitable for cardiac ablation is used in conjunction with a two-phase RF power source to produce a 1.2 cm 2 A uniform square lesion of 1.4 mm in diameter is formed by placing the square lesions in a continuous adjacent pattern. A temperature sensor at the tip of the electrode allows the ablation temperature to be monitored and adjusted to minimize contamination of the electrode tip with condensation.

[0006] U.S. Patent Application Publication No. 2008 / 0281322 describes a radiofrequency tissue ablation system having a radiofrequency generator. The generator includes a radiofrequency source, at least four independently controllable radiofrequency outputs, a user interface, and a controller configured to deliver radiofrequency energy from the radiofrequency source to the radiofrequency outputs in one of at least two different output configurations in response to a configuration selection made by the user.

[0007] U.S. Patent Application Publication 2015 / 0272655 describes a system and method for preventing unexpected tissue damage caused by the delivery of unexpected bipolar radiofrequency energy. The system may include a multi-electrode ablation device and an RF delivery unit. The RF delivery unit may transmit monopolar energy to multiple electrodes, with the energy being in phase, where all electrodes deliver the same voltage and are activated simultaneously without delivering bipolar energy. In addition or alternatively, the RF delivery unit may transmit 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. Summary of the invention

[0008] The embodiments of the present invention described below provide improved RF ablation devices and methods of operating the same.

[0009] Therefore, according to an embodiment of the present invention, an ablation system is provided, which includes a plurality of electrodes configured to contact a patient's body tissue, the plurality of electrodes including two or more ablation electrodes for contacting corresponding positions in a target organ and a return electrode. A signal generating unit includes a plurality of signal generators, and the plurality of signal generators are configured to apply corresponding composite signals to corresponding ablation electrodes among the ablation electrodes. The composite signal includes a plurality of corresponding signal components, the corresponding signal components including corresponding ablation signals having different corresponding ablation signal amplitudes and phases at a common ablation signal frequency, and corresponding probe signals having corresponding probe signal amplitudes and different corresponding probe signal frequencies; the processor is coupled to measure the probe signal received by each of the plurality of electrodes, and to control the ablation signal amplitude and phase in response to the measured probe signal.

[0010] In the disclosed embodiment, each of the plurality of signal generators includes an ablation signal generator and a probe signal generator. Each of the plurality of signal generators includes a signal adder, the signal adder is coupled to the corresponding ablation signal generator and the corresponding probe signal generator, and the signal adder is configured to generate a corresponding composite signal by adding the corresponding probe signal to the corresponding ablation signal.

[0011] In some embodiments, the processor is configured to calculate an admittance matrix between the plurality of electrodes from the measured probe signals and use the admittance matrix in setting the ablation signal amplitude and phase.

[0012] Additionally or alternatively, the processor is configured to set the ablation signal amplitude and phase so that the corresponding unipolar and bipolar ablation currents flow from the electrodes into the body tissue. In some embodiments, the processor is configured to calculate the corresponding amplitude and phase of the ablation signal in response to preset unipolar and bipolar ablation currents and the admittance matrix, wherein the calculated ablation signal is applied to the electrodes so that the preset unipolar and bipolar ablation currents flow from the electrodes. In some embodiments, the processor is configured to minimize the difference between the corresponding preset unipolar and bipolar ablation currents and the unipolar and bipolar ablation currents that flow out. Additionally or alternatively, the processor may adjust the phase so as to control the ratio between the unipolar ablation current and the bipolar ablation current.

[0013] In a disclosed embodiment, the processor is configured to monitor changes in the probe signal during an ablation procedure and to update the admittance matrix during the ablation procedure in response to the changes.

[0014] In some embodiments, the ratio between the probe signal amplitude and the ablation signal amplitude is less than 1 : 15. Additionally or alternatively, the probe signal frequencies are different from each other and differ from the ablation signal frequency by at least 500 Hz.

[0015] In one embodiment, the plurality of electrodes are disposed on a catheter configured to contact a heart of the patient.

[0016] According to an embodiment of the present invention, a method for ablation is also provided, the method comprising placing a plurality of electrodes in contact with body tissue of a patient, the plurality of electrodes comprising two or more ablation electrodes contacting corresponding positions in a target organ and a return electrode. A corresponding composite signal is applied to a corresponding ablation electrode among the ablation electrodes, the composite signal comprising a plurality of corresponding signal components, the signal components comprising corresponding ablation signals having different corresponding ablation signal amplitudes and phases at a common ablation signal frequency, and corresponding probe signals having corresponding probe signal amplitudes and different corresponding probe signal frequencies. The probe signal received by each of the plurality of electrodes is measured, and the ablation signal amplitude and phase are controlled in response to the measured probe signal.

[0017] The present invention will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic illustration of a multi-channel ablation system and procedure according to an embodiment of the present invention;

[0019] Figure 2 is a circuit diagram schematically showing an equivalent circuit of an ablation circuit of n-1 ablation electrodes and an external electrode ("return patch") according to an embodiment of the present invention;

[0020] Figure 3 is a schematic circuit diagram of a signal generating unit according to an embodiment of the present invention; and

[0021] Figure 4 FIG. 4 is a flow chart schematically illustrating a feedback control loop for controlling an ablation signal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Overview

[0023] RF ablation of patient tissue requires at least two electrodes, typically an ablation electrode inside the patient's body, and a return electrode that may be located on the patient's skin. In this simplest configuration, there is only one possible path for the ablation current. This type of energy delivery is called monopolar energy delivery, and the ablation current is called a monopolar ablation current. The ablation effect of the monopolar ablation current is concentrated in the tissue, between the ablation electrode and the return electrode.

[0024] In a configuration with multiple internal ablation electrodes, there are multiple possible paths for the ablation current, namely between the ablation electrode pairs and between any one of the ablation electrodes and the return electrode. The energy transfer between the internal electrodes is called bipolar energy transfer, and the ablation current is called bipolar ablation current. The ablation effect of the bipolar ablation current is generally concentrated in the superficial tissue between the internal electrodes. Generally speaking, with multiple internal electrodes, there is the possibility of monopolar and bipolar energy transfer, and the splitting of the ablation current between monopolar current and bipolar current can be used to control the spatial distribution of ablation in the tissue.

[0025] In a multi-electrode configuration, some of the ablation currents may follow undesirable paths. In general, there may be intended and / or unintended unipolar ablation currents; there may also be intended and / or unintended bipolar ablation currents. For example, two internal electrodes may be energized to provide intended bipolar energy transfer, but their activation typically also provides unintended unipolar energy transfer. As another example, the current from a given electrode may consist of intended unipolar ablation current, intended bipolar ablation current flowing to one internal electrode, and unintended bipolar ablation current flowing to another internal electrode.

[0026] Monopolar and bipolar ablation currents can be controlled by time division multiplexing (TDM), where only one ablation electrode or a small number of electrodes are energized at a time. One disadvantage of TDM is that, in addition to being slow, the inherent switching from electrode to electrode generates parasitic frequencies that can interfere with other devices in the environment at the time (e.g., electrocardiogram (ECG) devices).

[0027] In the absence of adequate metering of ablation current and voltage, and in the absence of a device to control the ablation current, splitting the ablation current from any given electrode into the desired unipolar current and bipolar current (with minimal unwanted current components) in a smoothly controlled manner is a challenging task.

[0028] The embodiments of the invention described herein address these problems by incorporating into an electrode network and tissue-identifiable detection signals, calculating the network's admittance matrix based on the detection signals, and calculating the amplitude and phase of the ablation voltage and current for each electrode in order to achieve the desired unipolar and bipolar ablation currents.

[0029] In the disclosed embodiment, multiple ablation electrodes in contact with the patient's tissue are powered by an electrode circuit similar to the electrode circuit used in U.S. patent application document 15 / 898,052, filed on February 15, 2018 and published as US 2019 / 0247108, the prior application of which is incorporated herein by reference in its entirety as shown in the entirety of this patent application, and this is further described in detail below. The electrode circuit measures the current across each internal electrode in the multi-electrode system by driving a low-amplitude probe current through the electrode by itself or adding it to each high-amplitude ablation current. The probe current of each electrode has a different frequency that is unique to that electrode, which enables the probe current flowing through all electrodes and the corresponding voltage on all electrodes to be measured and identified. During the ablation procedure, each composite signal flows through a corresponding controlled gain stage, which is adjusted to feed a predetermined ablation signal power through the corresponding electrode.

[0030] The concept of using the phase of the ablation signal to control the relative amounts of unipolar and bipolar currents can be illustrated by a system with two internal electrodes (and a third return electrode): if the ablation voltages of the two internal electrodes have the same amplitude and frequency but are in anti-phase, there is essentially no unipolar current and 100% bipolar current. Alternatively, if the voltages of the two electrodes are in phase, there is essentially no bipolar current and 100% unipolar current. In general, the ratio between unipolar and bipolar ablation currents can be adjusted by adjusting the phase of the voltage at each electrode. The above-described admittance matrix can be used to find the appropriate adjustment.

[0031] As the electrical properties of the ablated tissue and the contact resistance between the electrodes and tissue typically change during the ablation process, the probe current and voltage are continuously monitored by a processor which calculates and updates the admittance matrix between all electrodes.

[0032] System Description

[0033] Figure 1 Schematic illustration of a multi-channel ablation system 20 and procedure according to an embodiment of the present invention. In the illustrated embodiment, a physician 27 is performing a multi-channel cardiac ablation procedure using the ablation system 20. The physician 27 is performing a procedure on a subject 25 using an ablation catheter 23, the distal end 36 of which includes a plurality of ablation electrodes 44.

[0034] To begin the procedure, a physician 27 inserts a catheter 23 into a subject 25 and then uses a control handle 32 to navigate the catheter to an appropriate location inside or outside a heart 30 of the subject 25. The physician then brings a distal end 36 into contact with tissue 33 of the heart 30, such as myocardial or epicardial tissue. Next, a signal generation unit (SIG GEN) 22 generates a plurality of signals 34, which are referred to herein as "composite signals" or "composite ablation signals," as described below with reference to FIG. Figure 3 As described. In addition, "signal" includes both current and voltage; where necessary, specific reference is made to current or voltage. Signal 34 is carried to ablation electrodes 44 through catheter 23 on different corresponding channels so that each electrode applies a different corresponding one of signal 34 to tissue 33 of subject 25.

[0035] In monopolar ablation, the current of signal 34 flows between ablation electrode 44 and an external electrode or "return patch" 51, which is external to subject 25, typically on the skin of the subject's torso, coupled to SIGGEN 22. In bipolar ablation, the current of signal 34 flows between ablation electrodes 44.

[0036] The ablation system 20 also includes a processor (PROC) 24. The processor 24 is configured to receive setup parameters 38 for the procedure from the physician 27 (or any other user) before and / or during the ablation procedure. For example, using one or more suitable input devices such as a keyboard, mouse, or touch screen, the physician 27 selects one of two ablation modes: (i) current mode, or (ii) power mode. In current mode, the physician 27 sets the total ablation current for each electrode 44, or sets the desired levels of monopolar current and bipolar current for the electrodes individually. In power mode, the physician 27 sets the total ablation power for each electrode 44, or sets the desired levels of monopolar power and bipolar power for the electrodes individually, where the ablation power is calculated from the voltage and current of the ablation signal and takes into account any phase shift between the two. Although the description herein uses these two modes, it should be understood that the modes are exemplary ablation modes and that a person of ordinary skill in the art will be able to adjust the description with necessary changes for other ablation modes.

[0037] The physician 27 may also use the above-mentioned input device to input the maximum power, maximum current amplitude, maximum voltage amplitude, signal duration and / or any other relevant parameters for each ablation signal 34 (for the total signal or individual unipolar and bipolar signals). (Typically, but not necessarily, these parameters are the same in all signals.) In response to receiving the setting parameters 38, the processor 24 communicates with the signal generation unit 22 so that the signal generation unit generates the signal 34 according to the setting parameters. In addition, the processor may display the setting parameters on the display 26 (which may include the aforementioned touch screen).

[0038] The processor 24 may also be configured to track the respective positions of the ablation electrodes 44 during the procedure using any suitable tracking technology. For example, the distal end 36 may include one or more electromagnetic position sensors (not shown) that generate output signals that vary with the position of the sensors in the presence of an external magnetic field by one or more magnetic field generators 42. Based on these signals, the processor may determine the position of the electrodes. Alternatively, for each electrode, the processor 24 may determine the respective impedances between the electrode and a plurality of external electrodes 49 coupled to the subject 25 at various different locations, and then calculate ratios between these impedances that indicate the position of the electrodes. Alternatively, the processor may use both electromagnetic-based tracking and impedance-based tracking, as described, for example, in U.S. Pat. No. 8,456,182, the disclosure of which is incorporated herein by reference.

[0039] In some embodiments, the processor determines which of the ablation electrodes 44 are in contact with the subject's tissue and causes those electrodes, but not the other electrodes, to deliver signals 34 to the tissue. In other words, the processor may select a subset of the signals of those electrodes that are in contact with the tissue and then cause signals 34 to be delivered on the selected subset of channels but not on the other channels.

[0040] In some embodiments, the processor displays on the display 26 an associated image 40 of the subject's anatomy annotated to, for example, show the current position and orientation of the distal end 36. Alternatively or additionally, the processor may track the temperature and / or impedance of the tissue 33 based on signals received from associated sensors disposed at the distal end 36 and control the signal generation unit 22 in response thereto. Alternatively or additionally, the processor may perform any other associated functions to control or otherwise facilitate the performance of the procedure.

[0041] The processor 24 and the signal generating unit 22 are usually located in the console 28, and both the processor and the signal generating unit may each include one or several units. The catheter 23 is connected to the console 28 via an electrical interface 35 (such as a port or a socket). The signal 34 is thus carried to the distal end 36 via the interface 35. Similarly, a signal for tracking the position of the distal end 36 and / or a signal for tracking the temperature and / or impedance of the tissue can be received by the processor 24 via the interface 35.

[0042] The processor 24 may generally include both analog components and digital components. Therefore, the processor 24 may include multiple analog-to-digital converters (ADCs) for receiving analog signals from the signal generation unit 22. The processor 24 may also include multiple digital-to-analog converters (DACs) for transmitting analog control signals to the signal generation unit 22. Alternatively, these control signals can be transmitted in digital form, provided that the signal generation unit 22 is configured to receive digital control signals. The processor 24 generally includes a digital filter for extracting the signal at a given frequency from the received signal. Some or all of these components may be included in a field programmable gate array (FPGA), such as the Cyclone series FPGA provided by Intel of Santa Clara, California, USA.

[0043] Typically, the functions of the processor 24 as described herein are implemented at least in part in software. For example, the processor 24 may include a programmed digital computing device, which includes at least a central processing unit (CPU) and a random access memory (RAM). Program code (including software programs and / or data) is loaded into the RAM for execution and processing by the CPU. For example, the program code and / or data can be downloaded to the processor in electronic form over a network. Alternatively or in addition thereto, 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 memory. Such program code and / or data, when provided to the processor, generates a machine or a special-purpose computer configured to perform the tasks described herein.

[0044] although Figure 1 A particular type of ablation procedure is shown in , but it should be noted that the embodiments described herein may be applied to any suitable type of multi-channel ablation procedure.

[0045] Equivalent Circuit and Admittance Matrix

[0046] Figure 2 is a schematic diagram of an equivalent circuit 60 of an ablation circuit representing n-1 ablation electrodes and an external electrode ("return patch") in accordance with an embodiment of the present invention.

[0047] The equivalent circuit 60 includes n nodes 62, numbered from 1 to n, representing n-1 ablation electrodes 44 and one external electrode 51. The index m refers to a common node 62. The current flowing through each node 62 sees an impedance to all other nodes due to the tissue 33 between the nodes and the contact resistance between the electrode and the tissue. In the equivalent circuit 60, these impedances are represented as partial impedances Z ij , where the refractive indices i and j refer to nodes i and j. Impedance Z ijTypically has a complex value, resulting in a phase difference between the current and the voltage in the equivalent circuit 60 .

[0048] The current fed into the node i of the equivalent circuit 60 is denoted by I i , and the potential (voltage) of the node is marked as V i Current I i and voltage V i can be written in vector form as formulas (1) and (2) respectively:

[0049]

[0050]

[0051] The linear relationship between the current vector and the voltage vector in equations (1) and (2) can be expressed by the n×n admittance matrix Y Expressed by formula (3):

[0052]

[0053] Admittance Matrix Y The element Y ij It can be written as formula (4):

[0054]

[0055] Admittance Matrix Y is symmetrical (Y ji =Y ij ), and the sum of its rows is zero, reflecting the fact that the sum of all currents fed into the equivalent circuit 60 is zero. ij complex value, so the admittance matrix Y is a complex-valued matrix.

[0056] One of the nodes 62 (often referred to as the return patch 51) is typically chosen to be a "ground" or reference node r at zero potential, and the Y The corresponding column in (because it is multiplied by 0 in formula (3)). Y , since the corresponding current can always be calculated by summing the currents in all other nodes.

[0057] Modified current vector is defined as the vector of currents of all nodes except the reference node r, and the modified voltage vector is similarly defined as a vector including the voltages of all nodes except the reference node r. By removing the row and column referring to the reference node r from the admittance matrix Y, a modified admittance matrix is ​​additionally defined and The linear relationship between can be written as formula (5) similar to formula (3):

[0058]

[0059] Admittance Matrix Y and A comparison between the two is presented in Table 1 below.

[0060] Table 1: Admittance matrices Y and Comparison between

[0061]

[0062] In the following calculations, only the admittance matrix will be used

[0063] To extract the admittance matrix Formal system

[0064] To measure the matrix for a given node k The value of the element with frequency f k An AC voltage source is connected between electrode k and reference electrode r, and the voltage and current on all electrodes are measured to form a measurement vector and The linear relationship of formula (5) still holds and can be written as formula (6):

[0065]

[0066] Simultaneously, n-1 different frequencies f1, f2, ..., f are applied to all n-1 electrodes. n-1 n-1 external AC voltage sources are used as detection signals to measure n-1 vectors and where index k assumes a frequency value from 1 to n-1, and the n-1 elements in each vector refer to n-1 nodes 62. These vectors are assembled into the corresponding (n-1)×(n-1) matrix V and I .matrix V and I The relationship between can now be written as formula (7):

[0067]

[0068] Formula (7) for n-1 frequencies f1, ...f n- 1 is valid, that is, the matrix does not vary with these frequencies, as long as they are confined to a sufficiently narrow frequency band (as explained in detail below). The admittance matrix can now be calculated by matrix inversion It is given by formula (8):

[0069] Y = I · V -1 (8)

[0070] Formalism for Calculating Bipolar and Monopolar Ablation Currents

[0071] For the calculations in the current section, the (n-1)×1 unit vector is defined as a vector of length n-1, where each element of the vector is equal to 1. This vector is convenient for summing the elements of a vector or matrix. (For example, is a vector The sum of the elements of is a matrix S The sum of the rows, is a matrix S The sum of all elements of is a vector whose elements are each V. )

[0072] By applying an ablation voltage (denoted by the ablation voltage vector Ablation voltage vector The elements of are the individual ablation voltages V at each node i i The corresponding vectors of all ablation currents can be calculated as formula (9):

[0073]

[0074] Ablation currents potentially flow in both monopolar and bipolar modes, except for the following two extreme cases:

[0075] 1. When all electrode voltages are equal, pure unipolar current will flow.

[0076] 2. When the sum of all ablation currents (which is the total current flowing into the outer electrode 51) is zero, a pure bipolar current will flow.

[0077] Based on these two extreme cases, the ablation voltage vector can be separated into the sum of the bipolar and monopolar parts, given by formula (10):

[0078]

[0079] The bipolar voltage is a vector quantity, and the single-pole voltage Vu is a scalar quantity. The above condition of pure bipolar current can be written as formula (11):

[0080]

[0081] Solving for Vu yields formula (12):

[0082]

[0083] Now the unipolar current can be written as formula (13):

[0084]

[0085] Based on formula (13), the unipolar admittance matrix and the bipolar admittance matrix can be written as formula (14) and (15), respectively:

[0086]

[0087]

[0088] The matrix Y U The element (i,j) of is given by formula (16):

[0089]

[0090] The unipolar and bipolar currents are now given by equations (17) and (18), respectively:

[0091]

[0092]

[0093] Now the ablation voltage vector can be obtained based on equations (17) and (18) The amplitude and phase of the elements are used to control the magnitude of the unipolar current and the bipolar current.

[0094] optimization

[0095] Based on equations (17) and (18) for unipolar current and bipolar current, respectively, a cost function can be defined to calculate the ablation current that will produce levels of unipolar current and bipolar current that are best close to the desired levels. In the optimization process, such values ​​of the optimization objectives are usually calculated, which give the cost function a minimum value and are used in the algorithm 120.

[0096] In one example, the target current vector for a single-stage current is written as And the target current vector of the bipolar current is written as Cost function cost(V abl) is defined by formula (19):

[0097]

[0098] In the above cost function, parameters a and b are the relative weights of monopolar current and bipolar current, the asterisk (*) indicates the conjugate operation, and the optimization target is the ablation vector The target vector and the relative weights are typically determined by a physician27.

[0099] Figure 3 1 is a schematic circuit diagram of a signal generating unit 22 according to an embodiment of the present invention. In the components similar to the electrode circuit described in U.S. Patent Application No. 15 / 898,052 mentioned above, the signal generating unit 22 includes a plurality of signal generators 80 configured to respectively generate signals 34 for application to the subject 25 through the ablation electrode 44, as described above with reference to Figure 1 In other words, each signal generator 80 is configured to generate a different corresponding signal 34 for transmission to the tissue 33 of the subject 25 through the corresponding electrode 44 .

[0100] After previous treatment, Figure 3 The present invention relates to an ablation catheter 23 having n-1 ablation electrodes 44, wherein the ablation electrodes are labeled E1, E2, ..., E n-1 , and is marked as E r The external electrode (return patch) 51.

[0101] Typically, each signal generator 80 includes a probe signal generator 82 configured to generate a signal at a unique probe signal frequency f k ablation signal generator 84, which is configured to generate a probe signal at an ablation signal frequency f ABL and a signal adder 86 configured to generate a signal 34 by adding the generated probe signal to the generated ablation signal (after gain control and amplification, as described below). Since signal 34 is a combination of the probe signal and the ablation signal, it is referred to herein as a "composite signal" or "composite ablation signal", as described above with reference to Figure 1 The admittance matrix is ​​calculated and updated using the probe signal independently of the ablation signal.

[0102] All probe signal generators 82 may transmit their signals simultaneously so that n-1 probe signals at n-1 different frequencies may propagate within the circuit simultaneously and be sampled at each of the n-1 nodes.

[0103] Although the probe signals have different corresponding probe signal frequencies f k, where k=1, ..., n-1, but the ablation signal usually has a single common ablation signal frequency f ABL (The index "k" refers to the kth channel among the n-1 channels, as described below.)

[0104] In general, the signal generating unit 22 may include any suitable number of signal generators 80 corresponding to the number of ablation electrodes 44. For example, the signal generating unit 22 may include two to twenty signal generators 80. Figure 3 Schematically illustrating n-1 signal generators 80 forming n-1 channels by showing both the first signal generator and the n-1th signal generator. The first ablation signal generator 84 is indicated by the symbol “ABL1”, and the n-1th ablation signal generator 84 is indicated by the symbol “ABL n-1 Similarly, the first probe signal generator 82 is indicated by the symbol "PRB1", and the n-1th probe signal generator 82 is indicated by the symbol "PRB n-1 "instruct.

[0105] In one embodiment, the ablation signal generators 84 are voltage sources, wherein the output voltage of each ablation signal generator is set by an external control signal. In an alternative embodiment, the ablation signal generators are current sources, wherein the output current is set by an external control signal.

[0106] Each ablation signal generator 84 and probe signal generator 82 may include a digital-to-analog converter, a stable mode-free operation generator, or a direct digital synthesizer (DDS), such as the AD9854 DDS from Analog Devices, Inc. (Norwood, Massachusetts, USA).

[0107] Typically, the probe signal frequency f k The minimum difference between any two of the frequencies is large enough to suppress the generation of problematic spurious frequencies. For example, the difference may be greater than 500 Hz, which is a typical bandwidth of ECG signals. Similarly, the difference between the ablation signal frequency and the nearest probe signal frequency (i.e., the probe signal frequency that is closest to the ablation signal frequency relative to the other probe signal frequencies) is typically greater than 500 Hz. However, the probe signal frequency is typically close enough to the ablation signal frequency that the probe signal and the ablation signal have similar frequency-related effects on the tissue 33.

[0108] For example, the difference between any pair of consecutive frequencies may be between 500 Hz and 1500 Hz. In other words, (i) the difference between the ablation signal frequency and the nearest probe signal frequency, and (iii) the difference between any pair of consecutive probe signal frequencies (which are both greater than or both less than the ablation signal frequency) may be between 500 Hz and 1500 Hz. (Two given frequencies are considered "continuous" if they are listed in sequence when all frequencies are listed in order of increasing or decreasing magnitude). Thus, for example, considering a difference of 1 kHz, an ablation signal frequency f of 486 kHz ABL and n-1 channels (for simplicity, assume n-1 is an even number), the probe signal frequency f k It can be composed of 486-(n-1) / 2kHz, 486-(n-1) / 2+1kHz, ..., 485kHz, 487kHz, ...486+(n-1) / 2-1kHz and 486+(n-1) / 2kHz.

[0109] Each probe signal generator is configured to generate its probe signal so that the ratio between the amplitude of the probe signal and the amplitude of the ablation signal to which the probe signal is added is typically less than 1:15, such as less than 1:20, 1:40, 1:60, 1:80, 1:100, or 1:120, so that due to the relatively small amplitude of the probe signal, relatively little intermodulation distortion is introduced and the contribution of the probe signal to the ablation power is negligible. For example, if the amplitude of the ablation signal is 90-110V after amplification of the composite signal as described below, the amplitude of the probe signal may be 1-2V. Since the frequency of the probe signal is similar to the frequency of the ablation signal, the two signals see similar admittances across the subject's tissue, so that the ratio between the voltages of the two signals is typically the same as the ratio between the currents of the two signals.

[0110] The signal generation unit 22 also includes a plurality of controlled gain stages 88 configured to adjust the respective amplitudes of the composite signal during application of the composite signal to the subject. Typically, the signal generation unit 22 includes one controlled gain stage 88 for each signal generator 80, such that the output from each signal adder 86 is passed to a different respective controlled gain stage. Figure 3 The first controlled gain stage 88 is indicated by the symbol “GS1” and the second controlled gain stage 88 is indicated by the symbol “GS N ” indicates the n-1th controlled gain stage 88. Each controlled gain stage 88 may include, for example, a digital potentiometer, such as the AD5122 digital potentiometer from Analog Devices.

[0111] Typically, the signal generation unit 22 also includes a plurality of amplifiers 90 configured to amplify the conditioned signals received from the controlled gain stage 88. Figure 2In the embodiment, the first amplifier 90 is indicated by the symbol “AMP1”, and the n-1th amplifier is indicated by the symbol “AMP n-1 ” indicates. The amplified signal 34 is output to the ablation electrode 44 through a plurality of channels 92. Typically, the output transformers OT1, . . . , OT n-1 Electrical isolation between the electrodes and the signal generating unit 22 is provided.

[0112] Signal generation unit 22 also includes circuitry for each channel 92, such as a voltage transformer 94 and a current transformer 96, which are configured to step down the voltage and current of signal 34 to measurable levels. For each channel i, the step-down voltage (e.g., the voltage induced across each voltage transformer 94 and represented by the symbol V SD i Indicated) and step-down current (eg, the current induced by each current transformer 96 and indicated by the symbol I SD i The probe signal frequencies f are then filtered by the digital filter of the processor 24 to extract the different probe signal frequencies f. k Then, the processor 24 obtains the signal components at each frequency in the channel i and the signal components at each frequency f. k The voltage V of the probe signal is calculated by filtering the signal PRB,ik and current I PRB,ik There are a total of (n-1) x (n-1) probe signals for n-1 frequencies from each of the n-1 channels. For example, processor 24 may measure the amplitude of the filtered signal and then multiply each of these amplitudes by the appropriate transformer ratio to obtain V PRB,ik and I PRB,ik .

[0113] By processor 24 from V PRB,ik and I PRB,ik The measured values ​​of the admittance matrix are calculated elements, as described above in the section entitled "For extracting the admittance matrix The formal system is described in detail in the section "Formal system".

[0114] Ablation voltages used to produce the desired levels of monopolar and bipolar currents Calculated by processor 24 as described in detail above in the section entitled "Optimization".

[0115] In the current mode, processor 24 uses the admittance matrix and the required ablation current I i To calculate the ablation voltage V iIn power mode, these updated values ​​are calculated based on the desired ablation power.

[0116] During this process, the processor 24 continuously sets n-1 sets of control parameters CTRL i is transmitted to the signal generation unit 22. For example, for each channel i, these control parameters may include the following: (i) for the ablation signal generator 84 (ABL i ) on / off command, (ii) for detecting signal generator 82 (PRB i ) on / off command, (iii) to adjust the ablation signal generator 84 (ABL i ) output (voltage output or current output, depending on whether the ablation signal generator is a voltage source or a current source) of the amplitude and phase, and (iv) a signal for adjusting the controlled gain stage 88 (GS i ) signal. Control parameter CTRL i may be transmitted directly from processor 24, or via any suitable hardware or other circuitry ( Figure 3 (not shown) transmission.

[0117] Processor 24 may monitor additional parameters relevant to the ablation procedure. For example, processor 24 may continuously (i) monitor the temperature at the interface between distal end 36 and tissue 33, (ii) calculate a target ablation signal power in response to the temperature that does not exceed a maximum power specified by physician 27, and (iii) adjust ablation voltage V i and current I i The amplitude and phase of the i The adjustments are transmitted to the signal generation unit 22 .

[0118] Alternatively or in addition to the above-described circuits (such as signal generators, controlled gain stages and amplifiers), the signal generating unit 22 may include any other suitable circuits, such as, for example, an output transformer for impedance matching, passive bandpass and / or bandstop filters, or passive overvoltage protection devices.

[0119] Figure 4 Schematically illustrating an algorithm 120 (in the form of a flow chart) for a feedback control loop for controlling an ablation signal according to an embodiment of the present invention. Algorithm 120 shows the main steps of the control loop. The main signals transmitted between the steps are shown within the ovals.

[0120] In the standby step 122, the ablation system 20 is turned on and enters the standby mode. At this step, the probe signal generator 82 is turned on and can transmit a probe signal, but an ablation signal is not yet transmitted from the ablation signal generator 84. In the probe signal transmission step 124, the frequency f kThe probe signal under the probe signal generator 82 (PRB k ) transmission. In the probe signal measurement step 126, the processor 24 receives the step-down signal V SD i and I SD i The probe signal V is measured and calculated by separating each frequency component of the probe signal through digital filtering. PRB,ik and I PRB,ik (As mentioned above Figure 3 described above).

[0121] The processor 24 further outputs the (n-1)×(n-1) probe signal (ellipse 129) to the admittance matrix calculation step 128. At this step, the processor 24 calculates and updates the admittance matrix and outputs it (ellipse 131) to query step 130. In query step 130, processor 24 checks whether physician 27 has started the ablation process. If ablation has not started, processor 24 enters a loop including steps 126, 128 and 130, where the processor keeps measuring the probe signal from the received step-down signal (ellipse 127) and updates the admittance matrix The fact that this circuit operates in the absence of any ablation signal supports the use of the probe signal (independent of the ablation signal) to calculate the admittance matrix

[0122] Once ablation begins, query step 130 converts the admittance matrix (oval 133) is transmitted to the control parameter calculation step 132. At this step, the desired level of unipolar current and / or bipolar current is received and (ellipse 135), for example as set by the physician 27 in the user setting step 134. The processor 24 calculates and updates the control parameter CTRL using the desired levels of unipolar and bipolar currents and the admittance matrix i The updated control parameters (ellipses 137 and 139) are transmitted to the signal generation unit 22 in a control parameter update / transmission step 136, and the ablation voltage V is adjusted accordingly. i amplitude and phase.

[0123] The processor 24 receives the step-down signal V again. SD i and I SD i (ovals 141 and 143) and enter two feedback loops (i) and (ii):

[0124] (i) In the long feedback loop, the step-down signal V SDi and I SD i (ellipse 141) is again received in the detection signal measurement step 126, resulting in updating the admittance matrix in the admittance matrix calculation step 128 Continue through steps 130, 132, and 136. Because both the properties of tissue 33 and the contact resistance between ablation electrode 44 and tissue 33 can change during ablation, the admittance matrix Continuous updates are available.

[0125] (ii) In the short ablator control loop 140, the processor 24 determines that the ablation parameters (voltage, current, power) do not exceed the limits preset by the physician 27 in the user setting step 134, and updates the control parameter CTRL as needed. i , without considering the admittance matrix The control loop 140 is short so as to be able to respond to possible excessive ablation parameters in a timely manner. It should be noted that a skilled software engineer in the art can utilize the algorithm 120 to generate the necessary step-by-step computer code for implementing the overall method in a computer system (e.g., a general purpose computer or a special purpose computer).

[0126] It should be understood that the above embodiments are cited by way of example, and the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications thereof, which should occur to those skilled in the art when reading the above description, and which are not disclosed in the prior art.

Claims

1. An ablation system, comprising: a plurality of electrodes configured to contact body tissue of a patient, including two or more ablation electrodes for contacting respective locations in a target organ and a return electrode; a signal generating unit, the signal generating unit comprising a plurality of signal generators, the plurality of signal generators being configured to apply respective composite signals to respective ones of the ablation electrodes, the composite signals comprising a plurality of respective signal components, the respective signal components comprising respective ablation signals having different respective ablation signal amplitudes and phases at a common ablation signal frequency, and respective probe signals having respective probe signal amplitudes and different respective probe signal frequencies; and A processor is coupled to measure the probe signal received by each of the plurality of electrodes and to control the ablation signal amplitude and phase in response to the measured probe signal. 2 . The ablation system according to claim 1 , wherein each of the plurality of signal generators comprises an ablation signal generator and a probe signal generator.

3. The ablation system according to claim 2, wherein each of the plurality of signal generators comprises a signal adder, the signal adder being coupled to a corresponding ablation signal generator and a corresponding probe signal generator, and wherein the signal adder is configured to generate a corresponding composite signal by adding the corresponding probe signal to the corresponding ablation signal. 4 . The ablation system of claim 1 , wherein the processor is configured to calculate an admittance matrix between the plurality of electrodes from the measured probe signals and to apply the admittance matrix when setting the ablation signal amplitude and phase.

5. The ablation system of claim 4, wherein the processor is configured to set the ablation signal amplitude and phase in response to the admittance matrix so as to cause corresponding monopolar and bipolar ablation currents to flow from the ablation electrodes into the body tissue.

6. An ablation system according to claim 5, wherein the processor is configured to calculate the corresponding amplitude and phase of the ablation signal in response to preset monopolar and bipolar ablation currents and the admittance matrix, wherein the calculated ablation signal is applied to the ablation electrode so that the preset monopolar and bipolar ablation currents flow out from the ablation electrode.

7. The ablation system of claim 6, wherein the processor is configured to minimize a difference between the respective preset monopolar and bipolar ablation currents and the delivered monopolar and bipolar ablation currents.

8. The ablation system of claim 5, wherein the processor is configured to adjust the phase so as to control a ratio between a unipolar ablation current and a bipolar ablation current.

9. The ablation system of claim 4, wherein the processor is configured to monitor changes in the probe signal during an ablation procedure and to update the admittance matrix during the ablation procedure in response to the changes.

10. The ablation system of claim 1, wherein a ratio between the probe signal amplitude and the ablation signal amplitude is less than 1:

15.

11. The ablation system of claim 1, wherein the probe signal frequencies are different from each other and differ from the ablation signal frequency by at least 500 Hz.

12. The ablation system of claim 1, wherein the plurality of ablation electrodes are disposed on a catheter configured to contact a heart of the patient.

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