Microwave catheter system having shorting diode for ablation and temperature measurements

Abstract

Systems and methods for measuring cable pollution to accurately measure parameters during ablation such as temperature of the target tissue for safe and efficacious ablation of target tissue are provided. For example, the systems described herein comprise a switch, e.g., a Dicke switch, a radiometer, and a reference termination positioned at a proximal side of a coaxial cable connecting a generator to a catheter comprising a microwave antenna, and a diode circuit positioned at a distal side of the coaxial cable, e.g., within a handle of the catheter. The diode circuit may be biased to a closed state to create a short circuit at the distal end of the cable to thereby isolate the contribution of the cable to the radiometric signals traveling through the cable, e.g., cable pollution, which may be used to compute the target tissue temperature.

Description

MICROWAVE CATHETER SYSTEM HAVING SHORTING DIODE FOR ABLATION ANDTEMPERATURE MEASUREMENTSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 659,736, filed June 13, 2024, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This technology generally relates to systems and methods for safe and efficacious ablation of target tissue by, for example, measuring parameters during ablation such as temperature of the target tissue.BACKGROUND

[0003] Tissue ablation may be used to treat a variety of clinical disorders and several ablation techniques have been developed, including cryoablation, microwave ablation, radio frequency (RF) ablation, and ultrasound ablation. Such techniques are typically performed by a clinician who introduces a catheter having an ablative tip to the target tissue percutaneously, or via the venous vasculature or the natural cavities, positions the ablative tip adjacent to what the clinician believes to be an appropriate region based on tactile feedback, mapping electrocardiogram (ECG) signals, anatomy, and / or fluoroscopic imaging, actuates flow of an irrigant to cool the surface of the selected region, and then actuates the ablative tip for a period of time believed sufficient to destroy tissue in the selected region.

[0004] Although commercially available ablative tips may include thermocouples for providing temperature feedback via a digital display, such thermocouples typically do not provide meaningful temperature feedback during irrigated ablation. For example, the thermocouple only measures surface temperature, whereas the heating or cooling of the tissue that results in tissue ablation may occur at some depth below the tissue surface. Moreover, forprocedures in which the surface of the tissue is cooled with an irrigant, the thermocouple will measure the temperature of the irrigant, thus further obscuring any useful information about the temperature of the tissue, particularly at depth. As such, the clinician has no useful feedback regarding the temperature of the tissue as it is being ablated or whether the time period of the ablation is sufficient.

[0005] Accordingly, it may only be revealed after the procedure is completed, that the targeted aberrant pathway was not adequately destroyed. In such a circumstance, the clinician may not know whether the procedure failed because the incorrect region of tissue was ablated, because the ablative tip was not actuated for a sufficient period of time to destroy the target tissue, because the ablative tip was not touching or insufficiently touching the tissue, because the power of the ablative energy was insufficient, or some combination of the above. Upon repeating the ablation procedure so as to again attempt to ablate the target tissue, the clinician may have as little feedback as during the first procedure and, thus, potentially may again fail to destroy the aberrant pathway. Additionally, there may be some risk that the clinician would retreat a previously ablated region of the target tissue and not only ablate the target tissue, but damage adjacent tissues.

[0006] In some circumstances, to avoid having to repeat the ablation procedure as such, the clinician may ablate a series of regions of the target tissue along which the target tissue is believed to lie, so as to improve the chance of successful ablation. However, there is again insufficient feedback to assist the clinician in determining whether any of those ablated regions are sufficiently destroyed. Despite the promise of precise temperature measurement sensitivity and control offered by the use of radiometry, there have been few successful commercial medical applications of this technology. One drawback of previously-known systems has been an inability to obtain highly reproducible results due to slight variations in the construction of the microwave antenna used in the radiometer, which can lead to significant differences in measured temperature from one catheter to another. Problems also have arisen with respect to orienting the radiometer antenna on the catheter to adequately capture the radiant energy emitted by the tissue, and with respect to shielding high frequency microwave components in the surgical environment so as to prevent interference between the radiometer components and other devices in the surgical field.

[0007] Microwave radiometric temperature sensing can be integrated into the catheter system to provide tissue temperature feedback. Unlike standard thermocouple techniques used in existing commercial ablation systems, a radiometer may provide useful information about tissue temperature at depth — where the tissue ablation occurs — and thus provide feedback to the clinician about the extent of tissue damage as the clinician ablates a selected region of the target tissue. However, acceptance of microwave-based hyperthermia treatments and temperature measurement techniques has been impeded by the capital costs associated with implementing radiometric temperature control schemes. Radiofrequency ablation techniques have developed a substantial following in the medical community, even though such systems can have severe limitations, such as the inability to accurately measure tissue temperature at depth, e.g., where irrigation is employed. However, the widespread acceptance of RF ablation systems, extensive knowledge base of the medical community with such systems, and the significant cost required to changeover to, and train for, newer technologies has dramatically impeded the widespread adoption of radiometry.

[0008] Another obstacle in accurately measuring tissue temperature is the contribution of cable pollution by the cable used to connect the antenna to the generator, e.g., for transmitting power to the antenna for energy emission as well as for transmitting radiometric signals, e.g., measured by the antenna, which have a power that is directly related to the temperature of the body that created them. The magnitude of the contribution from the cable is affected by the cable loss and temperature distribution along its length, and the cable loss is affected by materials selection, length and diameter. The temperature of the cable is generally not uniform along its length, particularly if the catheter is entering the patient’s body, cooling is applied along portions, microwave power is dissipating in the inner and outer conductor losses, and / or if other components are in the path such as a diplexer. Moreover, the cable must be of a coaxial structure with appropriate dimensions to achieve a desired characteristic impedance to efficiently deliver microwave power to the antenna. A thin catheter is desirable, however, as the size of the cable is reduces, microwave losses increase. For heating, the input power may be increased to overcome these losses, however, for temperature sensing, the problem is more complicated. Thus, a difficulty arises in dealing with microwave losses in the coaxial cable. Specifically, when a radiometric signal travels through a cable, part of the radiometric signal disappears into the cable because of the cable loss, and simultaneously, the cable emits thermal noise that mixes with theradiometric signal. Thus, long cables, such as a 2 meter cable typically used in an operating room to connect an antenna to a generator, will inevitably undesirably pollute the radiometric signals traveling through the cable.

[0009] U.S. Patent Nos. 8,926,605 and 8,932,284 to McCarthy et al., and U.S. Patent Nos. 11,337,756 and 12,064,174 to Allison and U.S. Patent Appl. Pub. No. 2025 / 0134596 to Bancel et al., the entire contents of each of which are incorporated herein by reference, describe systems for radiometrically measuring temperature during ablation, particularly where the temperature sensor of a reference termination for measuring a reference temperature and the Dicke switch of the radiometer are positioned at the antenna at the distal side of the cable.

[0010] FIG. 1 illustrates a simplified block diagram of a typical radiometer. As described in U.S. Patent Nos. 11,337,756 and 12,064,174, it is a simple receiver that amplifies the microwave noise power received from the tissue by the antenna and detects its magnitude. This magnitude is proportional to temperature which enables temperature sensing. A key feature of the radiometer is the Dicke switch, which functions to cause the radiometer to alternately measure the noise power from the tissue and the noise power from a known reference termination temperature such that the radiometer is constantly making a comparison measurement to a known reference. This feature enhances the temperature measurement accuracy immensely. The received signal at the input to the Dicke switch is compared to the signal from the reference termination. In the catheter system, the input to the switch includes the coaxial cable and other multiplexing components. The microwave losses in these components contribute their temperatures to the overall signal received. Since these components are dissipating heating power, their contribution to the sensed temperature is significant and confounding.

[0011] FIG. 2 illustrates a system described in U.S. Patent Nos. 11,337,756 and 12,064,174 designed to minimize the problems due to the microwave losses. As shown in FIG. 2, the Dicke switch has been relocated from the radiometer unit out to the distal end of the coaxial cable, such that heating in the cable is now common to both the tissue measurement and reference termination measurements and drops out of the temperature calculation. Accordingly, the reference temperature signal received at the proximal end of the cable includes the thermal noise from the reference termination (Tre / -) plus the cable pollution, and the radiometer signal receivedat the proximal end of the cable from the antenna includes the thermal noise from the tissue (^tissue) Plus the cable pollution (pollution). This effectively eliminates the confounding effect of the cable loss. The radiometric measurement comprises a differential temperature measurement: T = (TtiSSUe + pollution) - (Tref+ pollution) = Ttissue- Tref

[0012] Thus, by calculating the reference temperature, the tissue temperature may be determined. A computer simulation of the temperature field created by microwave heating is shown in FIG. 3A. FIG. 3A illustrates a cut through the switching antenna and surrounding tissue. The temperature along a radial line through the peak temperature shows the temperature within the target tissue. The temperature rises inside the tissue near the tissue surface and reaches a maximum at a depth near the target tissue. FIG. 3B illustrates the microwave power loss density pattern perceived by the switching antenna. Since the switching antenna and frequency are common to both the generator and radiometer, the patterns produced for both functions are coincident, and the radiometer may optimally monitor the heated region.

[0013] However, one must implement a Dicke switch in the antenna that is of a size that is on the order of the cable dimensions and can handle the heating power levels. As described in U.S. Patent Nos. 11,337,756 and 12,064,174, a design was implemented using microwave PIN diodes as high-power switching elements and a reference resistor. A biasing scheme was created that only requires one control signal that could be multiplexed onto the coaxial cable center conductor such that no additional wires are required by the antenna other than an extremely thin thermocouple wire providing the reference temperature value. The diameter of the switch section of the antenna is 1.25 mm, which is the largest diameter of the cable / antenna component.

[0014] However, as the reference termination is disposed at the distal side of the cable, these embodiments require a larger and heavier catheter handle, and the reference termination is subject to at least some heating due to leakage power dissipating in the resistor, which requires a calibration procedure for determining the thermal resistance between the reference termination and the thermocouple sensor. Moreover, reference temperature, which is a key component in the tissue temperature calculation, is difficult to accurately measure as the temperature sensor of the reference termination, e.g., a thermocouple, is disposed in a metal box to shield the circuit fromexternal noise. If the thermocouple is positioned outside of the metal box, upon delivery of power, a temperature gradient is created making it impossible to accurately measure the reference temperature. Even when the thermocouple is positioned inside the metal box, at least some external noise, e.g., 5G, WiFi, etc., will inevitably enter the circuit and disrupt the system.

[0015] In view of the foregoing, it would be desirable to provide systems and methods that permit a high degree of radiometric measurement of temperature at depth in tissue to achieve accurate temperature measurement with microwave heating. Particularly, there exists a need for measuring cable pollution, such that the catheter handle may be smaller and lighter as the reference termination and the Dicke switch may be disposed at the proximal side of the cable.SUMMARY

[0016] The present disclosure overcomes the drawbacks of previously-known systems and methods by providing a system for ablating target tissue as well as sensing parameters (e.g., temperature) during ablation. In a preferred embodiment, the ablation systems utilize microwave energy for ablation. In accordance with one aspect, a system for measuring tissue temperature is provided. The system may include a catheter having a proximal region and a distal region, the catheter configured to be operatively coupled to a generator via a cable, an antenna disposed at the distal region of the catheter, the antenna configured to measure a radiometer temperature of a target tissue, a diode circuit disposed at the proximal region of the catheter, the diode circuit comprising a diode configured to transition between an open state where a transmission path exists between a radiometer and the antenna, and a closed state where a short circuit is created at a distal end of the cable to block the transmission path between the radiometer and the antenna, and a reference termination disposed proximal to the cable, the reference termination comprising a temperature sensor configured to measure a reference temperature. The system further may include a controller having instructions that, when executed, cause the controller to: transition the diode to the closed state and receive, via the radiometer disposed proximal to the cable, a first radiometric signal from the cable when the diode is in the closed state, the first radiometric signal indicative of cable temperature; transition the diode to the open state and receive, via the radiometer, a second radiometric signal from the cable when the diode is in the open state, the second radiometric signal indicative of the radiometer temperature and the cable temperature;calculate a first radiometric measurement based on a comparison of the first radiometric signal and the reference temperature; calculate a second radiometric measurement based on a comparison of the second radiometric signal and the reference temperature; and calculate a target tissue temperature based on a comparison of the first and second radiometric measurements.

[0017] The antenna may comprise a switching antenna configured to switch between emitting energy to ablate the target tissue and measuring the radiometer temperature generated as a result of the energy emission. Accordingly, the controller may be configured to selectively switch between an ablation state where the switching antenna emits energy for a first time period and a measurement state where the radiometer receives radiometric signals from the cable and the reference temperature from the reference termination for a second time period. For example, the first time period may be at least 80% percent of a sum of the first and second time periods. Moreover, in the measurement state, the radiometer may receive the first radiometric signal from the cable and the reference temperature from the reference termination in an alternating manner for a third time period, and may receive the second radiometric signal from the cable and the reference temperature from the reference termination in an alternating manner for a fourth time period, wherein the second time period may be the sum of the third and fourth time periods. For example, the third and fourth time periods may each be 100 milliseconds.

[0018] The controller may be configured to selectively transition a switch operatively coupled to the radiometer between a first state where the radiometer receives radiometric signals from the cable, and a second state where the radiometer receives the reference temperature from the reference termination in an alternating manner. The diode, in the closed state, may be configured to cause radiometric signals traveling distally through the cable towards the antenna to be reflected proximally through the cable towards the radiometer. Additionally, the diode, in the closed state, may be configured to connect an inner conductor of the cable to an outer conductor of the cable. The controller may be configured to transition the diode from the open state to the closed state by injecting a bias through the cable. In addition, the diode circuit may comprise a capacitor in cascade with the diode. The capacitor may be disposed distal to the diode and configured to block the bias from entering the antenna, e.g., in both the open and closed states.

[0019] In some embodiments, the temperature sensor may comprise at least one of a thermistor configured to measure the reference temperature or an integrated circuit temperature sensor. The first radiometric signal may comprise radiometric noise generated based on a temperature of the radiometer and thermal noise generated by the cable, and may account for cable loss. In addition, the controller may be configured to perform a cable calibration to account for cable loss of the cable, such that the controller may be configured to calculate the target tissue temperature during an ablation procedure while accounting for the cable loss of the cable. For example, the cable calibration may be based on a calculation of the first and second radiometric measurements prior to the ablation procedure and a known tissue temperature. The catheter may comprise a handle at the proximal region, such that the diode circuit may be disposed in the handle. Moreover, the catheter may comprise a cooling channel extending through the handle, the cooling channel configured to receive a cooling fluid to cool the diode circuit. The system further may comprise the cable, wherein the cable is configured to couple the handle to the generator. Additionally, the generator may comprise the radiometer, the reference termination, and the controller. The system further may comprise a carrier configured to mount a substrate of the diode circuit, the carrier configured to electrically couple the diode circuit to the antenna and the cable.

[0020] In accordance with another aspect, a method for measuring tissue temperature is provided. The method may comprise: providing an antenna configured to be positioned in or adjacent to a target tissue, the antenna disposed at a distal region of a catheter and operatively coupled to a generator via a cable; transitioning a diode of a diode circuit disposed at a proximal region of the catheter to a closed state to create a short circuit at a distal end of the cable to block a transmission path between the antenna and a radiometer disposed proximal to the cable; receiving, via the radiometer, a first radiometric signal from the cable when the diode is in the closed state, the first radiometric signal indicative of cable temperature; transitioning the diode to an open state to unblock the transmission path between the radiometer and the antenna; receiving, via the radiometer, a second radiometric signal from the cable when the diode is in the open state, the second radiometric signal indicative of a radiometer temperature measured by the antenna and the cable temperature; calculating a first radiometric measurement based on a comparison of the first radiometric signal and a reference temperature measured by a temperature sensor of a reference termination disposed proximal to the cable; calculating asecond radiometric measurement based on a comparison of the second radiometric signal and the reference temperature; and calculating a target tissue temperature based on a comparison of the first and second radiometric measurements. For example, transitioning the diode from the open state to the closed state may comprise injecting a bias through the cable.

[0021] The method further may comprise selectively switching between causing the antenna to emit energy to ablate the target tissue and causing the antenna to measure the radiometer temperature generated as a result of the energy emission. In addition, the method may comprise selectively switching between an ablation state where the antenna emits energy for a first time period and a measurement state where the radiometer receives radiometric signals from the cable and the reference temperature from the reference termination for a second time period. For example, the first time period may be at least 80% percent of a sum of the first and second time periods. Moreover, the method may comprise selectively transitioning a switch operatively coupled to the radiometer between a first state where the radiometer receives radiometric signals from the cable, and a second state where the radiometer receives the reference temperature from the reference termination in an alternating manner. Additionally, the method may comprise performing a cable calibration to account for cable loss of the cable, such that calculating the target tissue temperature during an ablation procedure may comprise calculating the target tissue temperature while accounting for the cable loss of the cable.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a simplified block diagram of a microwave radiometer having a Dicke switch.

[0023] FIG. 2 is a block diagram of a microwave ablation system where the Dicke switch and reference termination are disposed at the end of the coaxial cable near the connection to the antenna.

[0024] FIG. 3A illustrates a computer simulation of the temperature field and power loss density created by the micro wave heating of the system of FIG. 2, and FIG. 3B illustrates the cut plane temperature distribution.

[0025] FIG. 4A is a block diagram of an exemplary microwave ablation and temperature measurement system constructed in accordance with some embodiments.

[0026] FIG. 4B is a block diagram of an alternative exemplary microwave ablation and temperature measurement system constructed in accordance with some embodiments.

[0027] FIGS. 5 A and 5B illustrate an exemplary diode circuit in an open state and a closed state, respectively.

[0028] FIG. 6 illustrates cable pollution of a radiometric signal traveling through a cable.

[0029] FIGS. 7A to 7D illustrate the reflection of radiometric signals through the cable when the diode is in the close state, creating a short circuit at the distal end of the cable.

[0030] FIGS. 8 A and 8B illustrate the alternating radiometric and reference temperature measurements when the diode is in the open state and the close state, respectively.

[0031] FIG. 8C illustrates the duty cycle of the ablation state and the measurement state of the system in accordance with some embodiments, and

[0032] FIGS. 9A to 9D illustrate an exemplary diode circuit substrate carrier constructed in accordance with some embodiments.

[0033] FIG. 10 illustrates an exemplary diode circuit substrate constructed in accordance with some embodiments.

[0034] FIG. 11 illustrates an alternative exemplary diode circuit substrate carrier having a cooling channel in accordance with some embodiments.DETAILED DESCRIPTION

[0035] Embodiments of this technology are directed to exemplary systems and methods for measuring cable pollution to accurately measure parameters during ablation such as temperature of the target tissue for safe and efficacious ablation of target tissue, e.g., targets in the vascular system including the renal vessels and soft tissue targets in liver, kidney, prostate, and lung. For example, the systems described herein comprise a switch, e.g., a Dicke switch, a radiometer, anda reference termination positioned at a proximal end of a coaxial cable connecting a generator to a catheter comprising a microwave antenna, and a diode circuit positioned at a distal end of the coaxial cable, e.g., within a handle of the catheter. By closing the diode of the diode circuit, the contribution of the cable to the radiometric signals traveling through the cable, e.g., cable pollution, may be isolated and used to compute the target tissue temperature, as described in further detail below. By positioning the reference termination out of the power path, e.g., between the generator and the antenna, no temperature gradient is created, thereby allowing accurate measurement of the reference temperature.

[0036] Referring now to FIG. 4A, an exemplary microwave ablation and temperature measurement system is provided. As shown in FIG. 4A, system 10 may comprise generator 12, frequency diplexer 14, antenna switching diplexer 16, and radiometer 18 comprising switch 20, e.g., a Dicke switch, and reference termination 22, e.g., an internal reference input, disposed at the proximal side of cable 24, e.g., a coaxial cable, that electrically connects the system to catheter 28 disposed at the distal side of cable 24, the proximal region of catheter 28, e.g., the handle of catheter 28, comprising diode circuit 26, and the distal region of catheter 28 comprising microwave antenna 30. Generator 12 may be any previously-known commercially available ablation energy generator, e.g., a micro wave energy generator, thereby enabling radiometric techniques to be employed with reduced capital outlay.

[0037] In some embodiments, the radiometer, Dicke switch, and reference termination may be integrated with the generator, as shown in FIG. 4B. Microwave ablation and temperature measurement system 1 O' may be constructed similar to system 10 with similar components having like-prime reference numerals. For example, generator 12', radiometer 18' comprising switch 20' and reference termination 22', cable 24', and catheter 28' having diode circuit 26' and antenna 30' corresponds with generator 12, radiometer 18 comprising switch 20 and reference termination 22, cable 24, and catheter 28 having diode circuit 26 and antenna 30. In FIG. 4B, the frequency diplexer and the antenna switching diplexer are omitted for brevity. System 10' differs from system 10 in that radiometer 18', switch 20', and reference termination 22' may be integrated with generator 12'. As shown in FIG. 4B, generator 12' may include bias T 32 configured to inject a bias current into cable 24' (e.g., forward bias) to transition diode circuit 26' from an open state to a closed state, as described in further detail below with regard to FIGS. 5 Aand 5B. As will be understood by a person having ordinary skill in the art, system 10 also may include a bias T for biasing the diode of diode circuit 26.

[0038] Referring again to FIG. 4A, a controller of system 10 comprising one or more processors operatively coupled to the electronic components of the system may cause antenna switching diplexer 16 to selectively switch system 10 between an ablation state where generator 12 delivers power to antenna 30 via cable 24 for energy emission, and a measurement state where radiometer 18 receives as an input radiometric signals transmitted via cable 24, e.g., signals indicative of radiometer temperature of the target tissue measured via antenna 30. In addition, during the measurement state, radiometer 18 also may receive reference temperature measurements from a temperature sensor of reference termination 22, e.g., a thermistor. For example, during the measurement state, the controller may cause switch 20 to selectively switch between receiving radiometric signals from cable 24 and signals indicative of the reference temperature from reference termination 22, e.g., in an alternating manner. Antenna switching diplexer 16 may switch the system between the ablation state and the measurement state in an alternating manner, as described in further detail below.

[0039] Moreover, during the measurement state, the controller may cause a diode of diode circuit 26 to transition between an open state where the diode is polarized to create an unobstructed transmission path between radiometer 18 and antenna 30, and a closed state where the diode is polarized to create a short circuit at the distal end of cable 24, e.g., in an alternating manner. For example, as described above, the controller may cause a bias T to inject a bias current into cable 24 to transition the diode from the open state to the closed state. Conversely, the controller may cause bias T to remove the bias current to thereby transition the diode from the closed state to the open state. Accordingly, during the measurement state, radiometer 18 receives radiometric signals from cable 24 when diode circuit 26 is in the open state, and radiometric signals from cable 24 when diode circuit 26 is in the closed state.

[0040] FIGS. 5A and 5B illustrate diode circuit 26 in the open state and the closed state, respectively. Diode circuit 26 includes diode 27, which is an open circuit between an inner conductor of cable 24 and a ground, e.g., an outer conductor of cable 24, in the open state, thereby providing the unobstructed transmission path between radiometer 18 and antenna 30. Inaddition, diode 27 is configured to be biased to connect the inner and outer conductors of cable 24 in the closed state, thereby shorting the circuit at the distal end of cable 24 and obstructing the transmission path between radiometer 18 and antenna 30. As shown in FIGS. 5A and 5B, diode circuit 26 further may include capacitor 34 in cascade with diode 27, e.g., between diode 27 and the antenna. Accordingly, capacitor 34 may be configured to block the bias current used to bias diode 27 from reaching the antenna, and accordingly, the patient’s body. Preferably, diode circuit 26 includes a single diode, e.g., diode 27. As will be understood by a person having ordinary skill in the art, diode circuit 26 may include more than one diode.

[0041] As described above, the temperature of cable 24, e.g., due to dissipative loss along the length of the cable, pollutes radiometric signals traveling through cable 24, e.g., cable pollution, received by radiometer 18. Radiometric signals traveling through cable 24 include radiometric signals indicative of radiometer temperature measured by antenna 30 in the measurement state, as well as radiometric signals indicative of temperature of radiometer 18, e.g., when diode 27 is biased to the closed state. While the radiometer does not actively create a radiometric signal, as would be understood by a person having ordinary skill in the art, all matters, including tissue and the components of the radiometer, passively emit black body radiation. Thus, radiometric signals passively created by the radiometer, e.g., radiometric noise at the temperature of the radiometer, also may travel from the radiometer along the coaxial cable, and when diode 27 is biased to the closed state, thereby creating a short circuit at the distal end of cable 24, these radiometric signals will be reflected back along cable 24 towards radiometer.

[0042] The temperature of every element / body before the Dicke switch is measured including the desired target tissue and any additional components with microwave loss. If the losses are known along with any impedance discontinuities and the temperatures are also known for these elements, they can be backed out of the measurement leaving the desired tissue temperature. However, it is impractical to measure the temperature all along the cable and it cannot be assumed to be constant since parts of the cable may be in air or in the body or have coolant flowing over it. Thus, by calculating the effective temperature of the cable, as described in further detail below, the cable contribution may be backed out from the total temperature measurement, revealing the target tissue temperature.

[0043] FIG. 6 illustrates cable pollution by a coaxial cable, e.g., due to dissipative losses along the length of the cable, of radiometric signals traveling through the cable. As shown in FIG. 6, cable 24 having a temperature Tcabie) pollutes a radiometric signal (Tinput), e.g., the temperature at the input of cable 24, traveling along cable 24, resulting in a polluted radiometric signal (Toutput), e.g., the temperature at the output of cable 24 received by radiometer 18.^output may be calculated using the following equation, where cableloss is the loss in the cable:

[0044] The contribution of cable 24 to the radiometric signals traveling through the cable, e.g., cable pollution, may be isolated and used to compute the target tissue temperature.Accordingly, if Tinputand Toutputare known, the cable pollution may be computed. However, during an ablation procedure, e.g., when the antenna emits energy, Tinputcannot be determined, e.g., temperature measures may not be attempted while energy is being emitted by the generator. Thus, by biasing diode 27 of diode circuit 26 at the distal end of cable 24 to the closed state during the measurement state, a short circuit is created at the distal end of cable 24, which causes noise power, e.g., the radiometric signals passively created by radiometer 18 at radiometer temperature and cable losses at cable temperature, to be reflected proximally back through cable 24 to be measured by radiometer 18, as shown in FIGS. 7A to 7D. FIG. 7A illustrates cable 24 having temperature Tcabtecoupled to the input of radiometer 18, which creates radiometric noise ^radiometer)atthe temperature of the radiometer. As shown in FIG. 7B, the radiometric noise get polluted as it travels distally through cable 24 towards the distal end of cable 24, resulting in a polluted radiometric signal with temperature (Tend_Of cableatthe distal end of the cable.Tend_of_cabie may be calculated using the following equation:wherein, the transmission coefficient Ctransmission) may be defined as: c ^transmission = (1 — cableloss)

[0045] As shown in FIG. 7C, when the diode at the distal end of cable 24, e.g., within the proximal region of the catheter, is biased to the closed state to create a short circuit at the distalend of cable 24, the short circuit causes radiometric signals that reach the distal end of cable 24 to be reflected proximally back through cable 24 towards radiometer 18. As shown in FIG. 7D, the reflected radiometric signals traveling back through cable 24 gets polluted again, resulting in a further polluted radiometric signal with temperature (Tciosed) at the proximal end of the cable, which is received by radiometer 18. Tciosedmay be calculated using the following equation:

[0046] By combining the equations above, Tciosedmay be defined as:Tcable * (1 ^transmission

[0047] Accordingly, the effective temperature of the cable Tcabtemay be calculated as:

[0048] The target tissue temperature may then be computed with the knowledge of the cable pollution. For example, when the diode is biased to the open state, thereby creating an unobstructed transmission path between radiometer 18 and antenna 30, the radiometric signals received by radiometer 18 from cable 24 during the measurement state (Topen) includes the radiometric signals indicative of radiometer temperature of the target tissue (Ttissue) measured by antenna 30, and the cable pollution thereof by cable 24 Tcabie), as described above, wherein Topenmay be defined by the following equation:

[0049] Accordingly, the radiometer temperature of the target tissue (Ttissue) may be computed as:

[0050] Based on the temperature of the cable equation defined above, the radiometer temperature of the target tissue (Ttissue) may be computed as:

[0051] Both Topen(e.g., the temperature at the proximal end of cable 24 received by radiometer 18 when diode 27 is in the open state, which includes the radiometric temperature of the tissue in addition to cable pollution) and Tciosed(e.g., the temperature at the proximal end of cable 24 received by radiometer 18 when diode 27 is in the closed state, which includes the reflected radiometric noise of the radiometer in addition to cable pollution) are radiometric measurements, which are computed by comparing the respective radiometric signals received by the radiometer (e.g., in the open state and in the closed state) with the reference temperature received by the radiometer from the reference termination. The temperature difference approach eliminates common path confounding factors downstream of the Dicke switch in the radiometer that limit radiometer measurement accuracy because they subtract to zero.

[0052] As described above, during the measurement state, radiometer 18 may receive radiometric signals from cable 24 while diode circuit 26 is in the open state and while diode circuit 26 is in the closed state. For example, radiometer 18 may receive radiometric signals from cable 24 while diode circuit 26 is in the open state for a first time period, and when diode circuit 26 is biased to the closed state, radiometer 18 may continue to receive radiometric signals from cable 24 for a second time period. Moreover, as described above, during the first time period, switch 20 may selectively switch between a first state where radiometer 18 receives radiometric signals from cable 24 while diode circuit 26 is in the open state, and a second state where radiometer 18 receives signals indicative of the reference temperature from reference termination 22, e.g., in an alternating manner, as shown in FIG. 8 A. For example, during the first time period, switch 20 may alternate between the first state and the second state every predetermined time interval, e.g., every 1 millisecond for the duration of the first time period.

[0053] Similarly, during the second time period, switch 20 may selectively switch between the first state where radiometer 18 receives radiometric signals from cable 24 while diode circuit26 is in the closed state, and the second state where radiometer 18 receives signals indicative of the reference temperature from reference termination 22, e.g., in an alternating manner, as shown in FIG. 8B. For example, during the second time period, switch 20 may alternate between the first state and the second state every predetermined time interval, e.g., every 1 millisecond for the duration of the second time period. As will be understood by a person having ordinary skill in the art, radiometer 18 may receive radiometric signals from cable 24 while diode circuit 26 is in the closed state for a first time period, and when diode circuit 26 is polarized to the open state, radiometer 18 may continue to receive radiometric signals from cable 24 for a second time period

[0054] Accordingly, the controller may compute a first radiometric measurement (Topen) by comparing the radiometric signals received by radiometer 18 while diode circuit 26 is in the open state with the reference temperature received during the first time period, and may compute a second radiometric measurement (Tciosed) by comparing the radiometric signals received by radiometer 18 while diode circuit 26 is in the closed state with the reference temperature received during the second time period. The switch bias may be the same for both the first and second radiometric measurements as the switch always does the same thing, e.g., it switches between the known temperature (e.g., the reference temperature is known as the temperature sensor of the reference temperature may be positioned within the generator) and the unknown temperature.

[0055] FIG. 8C illustrates an exemplary duty cycle of the microwave ablation and temperature measurement system. As described above, the system may alternate between the ablation state where antenna 30 emits energy to the target tissue, and the measurement state where radiometer 18 receives radiometric signals from cable 24 (e.g., when diode circuit 26 is in the open and closed states) and reference temperature measurements from reference termination 22, e.g., in an interleaving manner. For example, as shown in FIG. 8C, the controller may cause the system to be in the ablation state for a first time period, e.g., 800 milliseconds, followed by the measurement state for a second time period, e.g., 200 milliseconds, in an alternating manner. Accordingly, for a single cycle (e.g., the sum of the first and second time periods), the duration of the ablation state may be at least 80% of the sum of the first and second time periods.

[0056] As described above, during the measurement state, the first radiometric measurement may be computed while the diode circuit is in the open state for a first time period, and the second radiometric measurement may be computed while the diode circuit is in the closed state for a second time period. Accordingly, if the duration of the measurement state in a single cycle is 200 milliseconds, the first radiometric measurement may be computed while the diode circuit is in the open state for the first 100 milliseconds, and the second radiometric measurement may be computed while the diode circuit is in the closed state for the following 100 milliseconds, as shown in FIG. 8C.

[0057] As the radiometer does not return a temperature reading, but rather a voltage, to compute the temperature at the proximal end of the cable received by the radiometer based on the known reference temperature, the following radiometer equation may be used:Where Vradis the radiometer output voltage, RadOffSetis the sum of all the fixed errors, RadSiopeis the volts per degree sensitivity, Tref is the known reference temperature measured by the temperature sensor of the reference termination, and Tmeasuredis the measured temperature, e.g., (Topen) when the diode is in the open state and (Tciosed) when the diode is biased to the closed state.

[0058] The controller may further execute a calibration protocol to calibrate the radiometer and the temperature measurements of the reference termination, as the radiometer and the reference termination are both inside the generator. Specifically, the effective cable temperature equation involves one unknown parameter, e.g., the total loss in the cable path. Accordingly, the only disposable component of the system that needs to be calibrated before each ablation is the cable loss. This total loss has two parts, the permanent system part and a disposable part. The permanent system loss part can be measured at the time of manufacture, whereas the disposable loss part may slightly vary for each disposable. However, since it is mostly cable that is extremely uniform, a reasonably accurate value may be found in a data sheet. The two losses may then be added together.

[0059] As the nominal temperature of the human body is known, a refinement of the loss value may be determined just prior to starting an ablation, e.g., by adjusting the loss value until the radiometer reads that value. For example, once the antenna is positioned inside the patient, before starting the ablation, the known tissue temperature is 37 °C. In the radiometer temperature of the target tissue (Ttissue) equation above, if the radiometer is calibrated and the tissue temperature is known (e.g., 37 °C), the only unknown parameter is the transmission coefficient (Ctransmission), which may be computed to instantly calibrate the system without perturbing the clinical workflow. Accordingly, the system may be calibrated for cable loss in the operating room without any additional materials.

[0060] Referring now to FIGS. 9 A to 9D, an exemplary diode circuit substrate carrier is provided. Carrier 36 is configured to mount diode circuit 26, e.g., via substrate 40 on which diode circuit 26 is disposed on, and may be placed directly in a flexible catheter, e.g., in the proximal region of catheter 28. Accordingly, diode circuit 26 may be positioned in close proximity to antenna 30, thereby ensuring that the totality of the cable pollution is compensated for. As shown in FIGS. 9A and 9B, carrier 36 may have a cylindrical profile, a proximal end configured to be electrical connected to coaxial cable 24, e.g., via butt connection sleeve 42, and a distal end configured to be electrical connected to antenna 30, e.g., via antenna tip attachment 44. In addition, carrier 36 may include slot 38 sized and shaped to receive substrate 40 and diode circuit 26 therethrough, such that substrate 40 and diode circuit 26 are held within the interior of carrier 36. FIG. 9C is a top view of carrier 36, and FIG. 9D is a side view of carrier 36. FIG. 10 illustrates an exemplary diode circuit substrate, e.g., substrate 40. As the diode circuit is much smaller in size than a Dicke switch network, the catheter may have an overall smaller size as the Dicke switch is disposed at the proximal side of the cable, e.g., within the generator.

[0061] Referring now to FIG. 11, an alternative exemplary diode circuit substrate carrier is provided. Carrier 46 may be integrated with the handle of the catheter, e.g., in a rigid percutaneous design, such that the diode circuit may be place in the handle of the catheter. As shown in FIG. 11, substrate 40 may be disposed on carrier 46 for holding the diode circuit. Moreover, carrier 46 may include the same cooling circuit to cool the diode circuit that is used for cooling the catheter. For example, as shown in FIG. 11, carrier 46 may include coolingchannel 48 configured to receive cooling fluid therethrough for cooling both the catheter and the diode circuit.

[0062] Preferably, the microwave ablation and temperature measurement systems described herein are configured for minimally invasive introduction into the lungs for ablating target lung tissue through a bronchoscope while sensing temperature at the distal region of the catheter. The target lung tissue may be, for example, tumorous tissue such that the ablative treatment treats lung cancer. The distal region of the catheter may be inserted through the mouth, into the trachea, and into the lung(s) to target tissue(s) for a treatment session. The microwave ablation and temperature measurement systems may also be designed to ablate other tissue. For example, tissue may be ablated in other areas such as the kidney or liver, including tumorous tissue in those organs. As another example, efferent and / or afferent nerve fibers surrounding a blood vessel may be ablated for a treatment. As one example, the microwave ablation and temperature measurement systems may be intravascularly inserted into the renal artery to ablate the efferent and afferent nerve fibers that surround the renal artery and make up the renal sympathetic nervous system for Renal Denervation (RDN).

[0063] While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true scope of the invention.

Claims

WHAT IS CLAIMED:

1. A system for measuring tissue temperature, the system comprising: a catheter having a proximal region and a distal region, the catheter configured to be operatively coupled to a generator via a cable; an antenna disposed at the distal region of the catheter, the antenna configured to measure a radiometer temperature of a target tissue; a diode circuit disposed at the proximal region of the catheter, the diode circuit comprising a diode configured to transition between an open state where a transmission path exists between a radiometer and the antenna, and a closed state where a short circuit is created at a distal end of the cable to block the transmission path between the radiometer and the antenna; a reference termination disposed proximal to the cable, the reference termination comprising a temperature sensor configured to measure a reference temperature; a controller having instructions that, when executed, cause the controller to: transition the diode to the closed state and receive, via the radiometer disposed proximal to the cable, a first radiometric signal from the cable when the diode is in the closed state, the first radiometric signal indicative of cable temperature; transition the diode to the open state and receive, via the radiometer, a second radiometric signal from the cable when the diode is in the open state, the second radiometric signal indicative of the radiometer temperature and the cable temperature; calculate a first radiometric measurement based on a comparison of the first radiometric signal and the reference temperature; calculate a second radiometric measurement based on a comparison of the second radiometric signal and the reference temperature; and calculate a target tissue temperature based on a comparison of the first and second radiometric measurements.

2. The system of claim 1, wherein the antenna comprises a switching antenna configured to switch between emitting energy to ablate the target tissue and measuring the radiometer temperature generated as a result of the energy emission.

3. The system of claim 2, wherein the controller is configured to selectively switch between an ablation state where the switching antenna emits energy for a first time period and a measurement state where the radiometer receives radiometric signals from the cable and the reference temperature from the reference termination for a second time period.

4. The system of claim 3, wherein the first time period is at least 80% percent of a sum of the first and second time periods.

5. The system of claim 3, wherein, in the measurement state, the radiometer receives the first radiometric signal from the cable and the reference temperature from the reference termination in an alternating manner for a third time period, and receives the second radiometric signal from the cable and the reference temperature from the reference termination in an alternating manner for a fourth time period, and wherein the second time period is the sum of the third and fourth time periods.

6. The system of claim 5, wherein the third and fourth time periods are each 100 milliseconds.

7. The system of claim 1, wherein the controller is configured to selectively transition a switch operatively coupled to the radiometer between a first state where the radiometer receives radiometric signals from the cable, and a second state where the radiometer receives the reference temperature from the reference termination in an alternating manner.

8. The system of claim 1, wherein the diode, in the closed state, is configured to cause radiometric signals traveling distally through the cable towards the antenna to be reflected proximally through the cable towards the radiometer.

9. The system of claim 1, wherein the diode, in the closed state, is configured to connect an inner conductor of the cable to an outer conductor of the cable.

10. The system of claim 1, wherein the controller is configured to transition the diode from the open state to the closed state by injecting a bias through the cable.

11. The system of claim 10, wherein the diode circuit comprises a capacitor in cascade with the diode, the capacitor disposed distal to the diode and configured to block the bias from entering the antenna.

12. The system of claim 1, wherein the temperature sensor comprises at least one of a thermistor configured to measure the reference temperature or an integrated circuit temperature sensor.

13. The system of claim 1, wherein the first radiometric signal comprises radiometric noise generated based on a temperature of the radiometer and thermal noise generated by the cable, and accounts for cable loss.

14. The system of claim 1, wherein the controller is configured to perform a cable calibration to account for cable loss of the cable, and wherein the controller is configured to calculate the target tissue temperature during an ablation procedure while accounting for the cable loss of the cable.

15. The system of claim 14, wherein the cable calibration is based on a calculation of the first and second radiometric measurements prior to the ablation procedure and a known tissue temperature.

16. The system of claim 1, wherein the catheter comprises a handle at the proximal region, and wherein the diode circuit is disposed in the handle.

17. The system of claim 16, wherein the catheter comprises a cooling channel extending through the handle, the cooling channel configured to receive a cooling fluid to cool the diode circuit.

18. The system of claim 16, further comprising the cable, wherein the cable is configured to couple the handle to the generator, and wherein the generator comprises the radiometer, the reference termination, and the controller.

19. The system of claim 1, further comprising a carrier configured to mount a substrate of the diode circuit, the carrier configured to electrically couple the diode circuit to the antenna and the cable.

20. A method for measuring tissue temperature, the method comprising: providing an antenna configured to be positioned in or adjacent to a target tissue, the antenna disposed at a distal region of a catheter and operatively coupled to a generator via a cable; transitioning a diode of a diode circuit disposed at a proximal region of the catheter to a closed state to create a short circuit at a distal end of the cable to block a transmission path between the antenna and a radiometer disposed proximal to the cable; receiving, via the radiometer, a first radiometric signal from the cable when the diode is in the closed state, the first radiometric signal indicative of cable temperature; transitioning the diode to an open state to unblock the transmission path between the radiometer and the antenna; receiving, via the radiometer, a second radiometric signal from the cable when the diode is in the open state, the second radiometric signal indicative of a radiometer temperature measured by the antenna and the cable temperature; calculating a first radiometric measurement based on a comparison of the first radiometric signal and a reference temperature measured by a temperature sensor of a reference termination disposed proximal to the cable; calculating a second radiometric measurement based on a comparison of the second radiometric signal and the reference temperature; and calculating a target tissue temperature based on a comparison of the first and second radiometric measurements.

21. The method of claim 20, wherein transitioning the diode from the open state to the closed state comprises injecting a bias through the cable.

22. The method of claim 20, further comprising selectively switching between causing the antenna to emit energy to ablate the target tissue and causing the antenna to measure the radiometer temperature generated as a result of the energy emission.

23. The method of claim 20, further comprising selectively switching between an ablation state where the antenna emits energy for a first time period and a measurement state where the radiometer receives radiometric signals from the cable and the reference temperature from the reference termination for a second time period.

24. The method of claim 23, wherein the first time period is at least 80% percent of a sum of the first and second time periods.

25. The method of claim 20, further comprising selectively transitioning a switch operatively coupled to the radiometer between a first state where the radiometer receives radiometric signals from the cable, and a second state where the radiometer receives the reference temperature from the reference termination in an alternating manner.

26. The method of claim 20, further comprising performing a cable calibration to account for cable loss of the cable, and wherein calculating the target tissue temperature during an ablation procedure comprises calculating the target tissue temperature while accounting for the cable loss of the cable.

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