Coolant condition monitoring for microwave ablation probes

Abstract

The embodiment of the invention relates to coolant condition monitoring of a microwave ablation probe. A microwave ablation probe system includes a coolant delivery system that delivers coolant to a microwave ablation probe; a microwave generator that delivers microwave energy to the microwave ablation probe; and a computing system in communication with the thermal sensor on the microwave ablation probe to collect temperature data over time from the thermal sensor, where the computing system is configured to calculate a measured temperature over time by the thermal sensor to determine if the coolant delivery system is cooling the microwave ablation probe, and provide feedback of ablation procedure progression.

Description

BACKGROUND OF THE DISCLOSURE

[0001] Embodiments of the present disclosure generally relate to electromagnetic radiation (EMR) therapy, and more particularly to monitoring the cooling of a microwave ablation probe that is used to apply electromagnetic energy to a treatment site to heat tissue that needs to be treated at the treatment site.

[0002] It is known to use electromagnetic (EM) energy to heat tissue to treat diseases. When using microwave energy to heat tissue, an applicator or probe having a microwave radiation antenna is positioned relative to the tissue to be treated (heated) such that the microwave energy radiated from the antenna penetrates and heats / ablates the tissue. Many microwave probes are known in the art. Death or necrosis of living tissue cells occurs at temperatures above normal cell temperature for a sufficient length of time. The sufficient time generally depends on the temperature to which the cell is heated. Above a threshold temperature of about 41.5 °C, significant thermal damage occurs in most malignant cells. When the temperature is above 45 °C, most normal cells are damaged by heat. During treatment, it is desirable to create a period of high temperature within the target tissue sufficient to cause the desired cell damage while maintaining nearby healthy tissue at a safe lower temperature. For this reason, when using a treatment involving tissue heating, it is important to ensure both: (i) sufficient heating of the tumor / diseased tissue throughout the tumor / diseased tissue to the tumor / diseased tissue margin, and (ii) a reduction in the temperature of the normal / non-diseased tissue surrounding the tumor / diseased tissue.

[0003] Hyperthermia therapy is sometimes combined with other treatments, such as surgery, ionizing radiation, and chemotherapy. For example, when hyperthermia is combined with radiation, it is desirable to maintain the temperature within the diseased tissue in the range of about 42 °C to 45 °C. When using a combined treatment modality, higher temperatures are generally not desirable because higher temperatures can cause microvascular collapse, thereby creating resistance to other therapies such as radiotherapy and chemotherapy, and reducing the amount of systemic chemotherapy reaching the tumor due to vascular damage. Lower temperatures are not desirable because these temperatures do not provide sufficient heating, thereby reducing the therapeutic effect of the treatment. Therefore, it is important to control the temperature within the desired range of multimodal treatment and not allow the tissue in the tumor / diseased tissue or around the tumor to be heated to a temperature higher than about 45 °C because heating the tissue to these temperatures can damage the tissue and compromise the effectiveness of other treatments. Treatment within this controlled temperature range is generally referred to as hyperthermia.

[0004] Thermal therapy forms that solely utilize heating to kill tissue are generally referred to as coagulation or ablation. To adequately eradicate cancerous tumors / lesion tissues solely by heating, it is necessary to ensure sufficient heating is achieved throughout the tumor / tissue. In the case of malignant tumors, if viable tumor cells are left behind, the tumor can grow back rapidly, leaving the patient with the initial problem. During a process generally known as microwave coagulation or microwave ablation, the diseased tissue is heated to at least about 55 °C and typically above about 60 °C for an exposure time sufficient to kill the cells, typically exceeding about 1 minute. In microwave coagulation and ablation treatments, there is a temperature volume reduction that ranges from the high temperature in the treated tissue to the normal (healthy) tissue temperature of 37 °C outside the treated tissue.

[0005] To correctly treat the target cancer tumor volume or other tissue volumes to be treated, it becomes very important to correctly deliver the correct target heat distribution over a sufficient period of time to eradicate the tumor tissue while minimizing damage to the surrounding critical normal tissues. Fortunately, there are tumor sites resident in normal tissues that can be destroyed by heating in a limited area without affecting the patient's health, such as liver tissue. In such cases, coagulation can be applied in an aggressive manner to include a safety margin of destroying a limited amount of the surrounding normal tissue, thus ensuring that all cancerous tumors / diseased tissues are destroyed.

[0006] The process of very rapidly heating to high temperatures common in coagulation and ablation treatments can utilize a relatively short exposure time. By doing so, the resulting temperature distribution is mainly a result of the power absorption distribution within the tissue. However, if such treatments continue for several minutes, the blood flow and heat conduction in the tumor / diseased tissue and the surrounding tissue will alter the temperature distribution, resulting in a less predictable heat distribution because the changes occurring in the blood flow within such heated areas can be unpredictable. Therefore, it is important to optimize the uniformity of the absorbed tissue heating power to create a more predictable temperature distribution that better conforms to the treatment prescription. Thus, pre-treatment planning practices for calculating the power and temperature distributions generated by the power parameters and power relative phases applied to the tissue, both before and possibly during treatment, are important not only for coagulation and ablation but also for thermal therapy. Since higher temperatures are used during treatment, the discomfort and pain of the patient can be increased, so avoiding excessive temperatures helps reduce the need for patient sedation.

[0007] A minimally invasive microwave energy probe can be inserted into living tissue to place a heat source within or near a diseased tissue region. The minimally invasive probe helps overcome some of the difficulties encountered by surface applicators when the target tissue region is located beneath the skin (e.g., prone). The minimally invasive probe must be properly positioned to confine heating near the desired treatment area. However, even when properly placed, it is difficult to ensure that sufficient heat is generated in the diseased tissue without overheating the surrounding healthy tissue. Additionally, when the probe is operated at a higher power level to generate the higher temperatures required for coagulation and ablation, the microwave transmission line (coaxial cable) in the portion of the probe leading from outside the body to the location of the radiating antenna within the probe has a tendency to be heated to an undesired high temperature, which can cause thermal damage to the normal tissue through which the probe passes to reach the diseased tissue to be treated. Further, to maintain the minimally invasive nature of the probe form factor, small-profile coaxial cables are used, which cannot transmit high levels of microwave energy without cooling the cables within the probe. Accordingly, various methods of cooling the probe have been used in existing devices.

[0008] A cooled ablation probe can enhance the overall heating pattern of the antenna, prevent damage to the antenna, and prevent injury to the clinician or patient. Due to the high temperatures achievable through a microwave ablation probe and the sensitivity of cells to those temperatures, known heating patterns and precise temperature control are required to produce a more predictable temperature distribution to eradicate tumor cells while minimizing damage to the surrounding normal tissue.

[0009] A fluid-cooled microwave probe can be used in an ablation procedure. During operation of a microwave ablation device, if proper cooling is not maintained, such as when the flow of coolant within the probe is interrupted, the microwave ablation device can overheat and cause damage to the coaxial cable or radiating antenna within the device, which in turn results in a high reflected power and irreversible failure of the device. A coolant fluid with bubbles can circulate from a cooling system inside the microwave ablation probe. When bubbles filled with even a small amount of air or multiple bubbles very close to each other are introduced into the ablation probe, such as when the ablation probe is operated at a high power level, the ablation probe is prone to rapid failure due to overheating or an arc discharge condition. The time to failure depends on the power delivered to the antenna, the degree of reduction in coolant flow, and / or the duration of the interruption.

[0010] Although many microwave ablation probes are known in the art for applying microwave energy to tissue to heat the tissue, there is still a need for better thermal control for more efficient, consistent, and safe ablation. SUMMARY OF THE INVENTION

[0011] Embodiments relate to a microwave ablation probe that includes an elongate shaft; a coupler attached to the elongate shaft and a coolant reservoir; and a flexible circuit that includes a thermal sensor and is attached to the elongate shaft.

[0012] In one aspect, a flexible circuit is attached to the coupler and includes a thermocouple at the coupler.

[0013] The connector and the sensor are implemented on the same PCB. This eliminates the soldering step of conventional thermocouple wires to the connector or the printed circuit board.

[0014] Multiple sensors are implemented on the same PCB, and each sensor does not require a separate wire like a conventional thermocouple wire. This facilitates assembly and control in manufacturing.

[0015] In one embodiment, a microwave ablation probe system includes a coolant delivery system that delivers coolant to the microwave ablation probe; a microwave generator that delivers microwave energy to the microwave ablation probe; and a computing system that communicates with a thermal sensor on the microwave ablation probe to collect temperature data that varies over time, wherein the computing system is configured to calculate the slope of the temperature data over time to determine whether the coolant delivery system is cooling the microwave ablation probe.

[0016] The microwave ablation probe system may further include a flexible circuit that includes a thermal sensor.

[0017] In one aspect, the flexible circuit is attached to the microwave ablation probe.

[0018] In one aspect, the flexible circuit includes multiple thermal sensors.

[0019] In one aspect, the coolant delivery system includes a catheter that passes through the microwave ablation probe.

[0020] In one aspect, the microwave ablation probe includes a coupler to which the catheter is attached.

[0021] In another embodiment, a method for measuring the coolant status of a microwave ablation probe includes activating a coolant delivery system to deliver coolant to the microwave ablation probe; activating the microwave energy of the microwave ablation probe; measuring the temperature of the microwave ablation probe over time; calculating the slope of the temperature over time; and comparing the slope with a predetermined value.

[0022] In one aspect, if the slope is equal to or greater than the predetermined value, troubleshoot the coolant delivery system to verify that coolant is being delivered to the microwave ablation probe. If the slope is less than the predetermined value, determine whether the slope becomes negative after being positive.

[0023] In one aspect, if the slope does not become negative after being positive, troubleshoot the coolant delivery system to verify that coolant is being delivered to the microwave ablation probe, and if the slope becomes negative after being positive, use the microwave ablation probe.

[0024] As a result, such microwave ablation probes and methods of measuring the coolant status of a microwave ablation probe allow for better temperature control of the ablation zone while increasing safety for the patient and caregiver. Additional advantages include: a lower configuration cost for providing multiple thermocouples in a flexible circuit device compared to a single thermocouple circuit constructed using wires; omission of the soldering step of joining two different metals in the thermocouple wire to form the sensing tip of the thermocouple; and increased mechanical integrity since the flexible circuit is not as fragile as discrete thin thermocouple wires. These advantages result in higher yields, less labor, and more precise placement of the thermal sensor on the microwave ablation probe in manufacturing microwave ablation probes with integrated thermal sensing.

[0025] The description, objects, and advantages of the embodiments of the present invention will become apparent from the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above aspects and other features, aspects, and advantages of the present technology will now be described in connection with various embodiments with reference to the accompanying drawings. However, the illustrated embodiments are merely examples and are not intended to be limiting. In all the drawings, like reference numerals typically identify like components, unless the context otherwise indicates. It should be noted that the relative dimensions of the following drawings may not be drawn to scale.

[0027] Figure 1 Is a side view of an exemplary microwave ablation probe.

[0028] Figure 2 Is a side view of a microwave ablation probe according to an embodiment of the present disclosure.

[0029] Figure 3 Is a top view of a flexible circuit.

[0030] Figure 4 Is a side elevation of a side view of a microwave ablation probe including a flexible circuit.

[0031] Figure 5 Is a side view of a microwave ablation probe for experimentation.

[0032] Figure 6 Is a block diagram of a microwave ablation probe system according to an embodiment of the present disclosure.

[0033] Figure 7 Is a graph of time versus thermocouple temperature when no coolant is applied.

[0034] Figure 8 is Figure 6 a slope graph of the thermocouple temperature in

[0035] Figure 9 a graph of the thermocouple temperature against the time of coolant perfusion for evaluation.

[0036] Figure 10 is a flowchart of a method for monitoring the coolant state of a microwave ablation probe according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0037] It should be understood that the embodiments of the present invention described herein are not limited to the specific variations set forth herein, because various changes or modifications can be made to the described embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention, and equivalents can be substituted. As will be apparent to those skilled in the art after reading this disclosure, each individual embodiment described and illustrated herein has discrete components and features that can be easily separated from or combined with the features of any one of several other embodiments without departing from the scope or spirit of the embodiments of the present invention. In addition, many modifications can be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the (one or more) objectives, spirit or scope of the embodiments of the present invention. All such modifications are intended to be within the scope of the claims presented herein.

[0038] In addition, although methods may be depicted in the drawings in a particular order or described in the specification in a particular order, such methods do not need to be performed in the particular order or sequence shown and do not need to perform all methods to achieve the desired result. Other methods not depicted or described can be incorporated into the example methods and processes. For example, one or more additional methods can be performed before, after, simultaneously with, or between any of the described methods. In addition, in other implementations, these methods can be rearranged or reordered. Further, the separation of the various system components in the above-described embodiments should not be understood to require such separation in all embodiments, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products. In addition, other embodiments are also within the scope of this disclosure.

[0039] Conditional language, such as "can", "could", "might" or "may", unless specifically stated otherwise or otherwise understood in the context in which it is used, generally is intended to convey that a particular embodiment includes or does not include a particular feature, element, and / or step. Thus, such conditional language generally is not intended to imply that one or more embodiments in any way require a feature, element, and / or step.

[0040] References to singular items include the possibility of the presence of plural items. More specifically, as used herein and in the appended claims, unless the context clearly dictates otherwise, the singular forms "a", "an", "said", and "the" include plural referents. It should also be noted that claims may be drafted to exclude any optional elements. Thus, this statement is intended to serve as a basis for the use of exclusive terms such as "solely", "only", etc. in connection with the recitation or "negative" limitation of claim elements.

[0041] It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, if an element is referred to as being "directly connected" or "directly coupled" to another element, then no intervening elements are present.

[0042] It should also be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, without departing from the teachings of the present invention, a first element may be referred to as a second element.

[0043] Degree language used herein, such as the terms "approximately", "about", "generally", and "substantially", means a value, quantity, or property that is close to the stated value, quantity, or property and that still performs the desired function or achieves the desired result. For example, the terms "approximately", "about", "generally", and "substantially" may refer to an amount that is less than or equal to 10%, less than or equal to 5%, less than or equal to 1%, less than or equal to 0.1%, less than or equal to 0.01% of the stated amount. If the stated amount is 0 (e.g., none, no), then the above ranges may be a specific range and not within a specific percentage of that value. Additionally, numerical ranges include the values defining the range, and any single value provided herein may be used as an endpoint of a range that includes other single values provided herein. For example, a set of values such as 1, 2, 3, 8, 9, and 10 is also a disclosure of numerical ranges such as 1 - 10, 1 - 8, 3 - 9, etc.

[0044] Although multiple embodiments and variations thereof have been described in detail, other modifications and methods of using these embodiments will be apparent to those skilled in the art. Accordingly, it should be understood that various applications, modifications, materials, and substitutions of equivalents may be made without departing from the unique and inventive disclosure or the scope of the claims herein.

[0045] All existing subjects mentioned herein (e.g., publications, patents, patent applications, and hardware) are incorporated herein by reference in their entirety, unless the subject matter can conflict with the subject matter of the present invention (in which case, the content herein shall prevail).

[0046] Thermal ablation can be used to treat many conditions and diseases, including but not limited to cancerous tissues. These conditions and diseases can be treated in many organs of the human body, including but not limited to the liver, lungs, kidneys, prostate, bladder, ovaries, cervix, uterus, endometrium, breast, brain, stomach, colon, and skin. When treating certain diseases, it is necessary to ensure that the diseased tissue is removed without damaging the healthy tissue near the resection site. Accordingly, embodiments of the present disclosure are directed to microwave applicator probes having a more predictable and controlled ablation zone.

[0047] In a fluid-cooled microwave ablation probe, it is important to monitor the presence of fluid in the probe, detect sufficient flow rate, occurrence of blockage in the fluid line, and fluid status in terms of fluid temperature to obtain effective treatment results. Additionally, the probe shaft temperature must be maintained below the safety limit of the non-active part of the probe (i.e., outside the ablation zone where heat is created by the microwave). The maximum temperature ranges from 43°C to 48°C, depending on the heating duration. For example, the shaft temperature can be maintained at 43°C for about 11 minutes without damaging the tissue. On the other hand, the shaft temperature can damage the tissue at 48°C in about 1.5 minutes.

[0048] In addition, in current clinical practice, X-ray computed tomography (CT) and ultrasound (US) imaging are the most widely used modalities for guiding probe placement and are also used to evaluate the technical success of the procedure. One of the challenges currently faced by microwave ablation is the lack of a mature technology for intraoperative monitoring to determine the treatment endpoint, which remains an area of active research.

[0049] In some fluid-cooled microwave ablation probes, the fluid can circulate in a closed-loop circuit between a reservoir and the probe. The probe system can include a spike connected to a saline bag serving as a coolant reservoir. The spike has an inflow path and an outflow path integrated therein. Without a sensor, the user starts the fluid flow and observes the flow output on the spike. Initially, air bubbles appear in the saline bag from the outflow path in the spike. When no more air bubbles are observed, it is considered that there is fluid inside the probe and in all the pipes between the needle and the probe.

[0050] The disclosed embodiments utilize a thermal sensor array (i.e., thermocouples, thermistors, etc.) to monitor the temperature at different points on a microwave ablation probe assembly, including points on the probe shaft inside and outside the ablation zone, points on the surface of the RF cable, and points on the coolant inflow and outflow paths. Additionally, the positions of the thermal sensors are optimized to provide feedback to the user on the growth progress of the ablation zone.

[0051] These multiple thermal sensors can be positioned at different locations on the probe to provide temperature information that can be used to provide feedback on the operating characteristics of the probe and associated systems, such as a cooling system. For example, the temperature information can be used to determine when the probe and / or the cooling system reach predetermined operating parameters during the startup phase of the treatment. In other examples, the temperature information can be used to determine the size and / or shape of the ablation zone. In other examples, the temperature information can be used to determine if a blockage, obstruction, or other malfunction has occurred in the cooling system. In additional examples, the temperature information can be used to adjust or modify operating parameters during the ablation treatment. In other examples, the temperature information can be used to determine when the ablation treatment is complete.

[0052] Figure 1 FIG. is an example of a microwave ablation probe 10. The microwave ablation probe 10 can include a grip 12, and a substantially rigid elongate applicator body 14 extends from the grip 12, wherein an insertion tip 16 forms the insertion end portion of the probe for insertion into a target tissue region to be ablated. The grip 12 can be defined as the pistol grip shown, another suitable shape, or omitted entirely. The substantially rigid elongate applicator body 14 can include an outer sleeve 18 extending from the grip 12.

[0053] An embodiment of a microwave ablation probe for microwave coagulation and ablation treatment of diseased tissue within a living tissue is as Figure 2 shown. As shown, the microwave ablation probe 20 can include a coupler 22 and a substantially rigid elongate probe body 24 that extends to an insertion tip 26 that forms the insertion end of the probe for insertion into a target tissue region to be ablated. Although not shown, a grip can be included that covers the coupler 22. Some possible thermal sensor positions are shown at T1, T2, T3, the outflow end, and the inflow end. It is expected that the thermal sensors T1, T2, and T3 will be located within the ablation zone.

[0054] One challenge is to integrate the thermal sensors into the probe body 24 without increasing the overall diameter of the probe and / or without creating a high backpressure on the coolant flowing inside the microwave ablation probe 20. Conventionally, very thin thermocouple wires would be used to achieve such a design. When using thermocouple wires in or on the probe body 24, there are multiple drawbacks, such as high cost, difficulty in assembling the wires to fabricate the thermocouple, the wires being fragile and difficult to handle during assembly, difficulty in soldering to connectors or printed circuit boards, and each thermal sensor requiring a separate wire.

[0055] By using a flexible circuit such as Figure 3 shown, all of the above problems are alleviated. Additionally, a more precise and repeatable placement of the thermal sensors is achieved. For example, in the case of using three thermal sensors in a conventional probe, if each thermal sensor has one wire, there are at least three wires. Each wire would need to be individually secured to the probe. During manufacturing, the technician would need to repeat the step of securing the thermal sensor wires to the probe three times. In the probe according to the present disclosure, the positions of the three thermal sensors T1, T2, T3 can be, for example, one each at the 3 cm, 4 cm, and 5 cm marks on the marker tape. When using the flexible circuit 30, there is only one component, which includes the substrate and all three thermal sensors TC1, TC2, and TC3 (as Figure 3 shown). Due to the nature of the flexible circuit, all three thermal sensors TC1, TC2, TC3 are on the same substrate SUB at predetermined geometric positions. Thus, the position of each thermal sensor TC1, TC2, TC3 and the distance between adjacent thermal sensors are more precise than in a conventional assembly because the precision of flexible circuit manufacturing is higher than that of a technician securing the wires of the thermal sensors. The precision of flexible circuit manufacturing can be within a tolerance of 2 mils (0.002 inches). This means that the traces on the flexible circuit 30 can be as small as 2 mils or can be as close as 2 mils to each other.

[0056] Figure 3 An implementation of the flexible circuit 30 of the microwave ablation probe 20 is shown. The flexible circuit 30 can include a flexible substrate SUB on which metallized traces are routed to define the circuit. The flexible substrate SUB can be polyimide or another suitable material. The metallized traces can include, for example, top traces and ground traces to create each thermal sensor TC1, TC2, TC3, the inflow end TC, and the outflow end TC.

[0057] As shown, the flexible circuit 30 can include five thermal sensors TC1, TC2, TC3, an inlet TC, and an outlet TC, although other numbers are possible. For example, in some embodiments, the thermal sensors can be located on a cable / duct routed between the microwave ablation probe 20 and the associated console. In the illustrated embodiment, there are three legs in the flexible circuit 30. The longer leg contains three thermal sensors TC1, TC2, TC3, while the other two legs each have only one thermal sensor for the inlet TC and the outlet TC, respectively. If another thermal sensor needs to be added, it can be added to any of these legs, or a separate leg can be added to the substrate SUB. The first option will only slightly increase the width of the leg. The thermal sensor on the new leg will be wired and attached to the desired location.

[0058] The traces defining the thermal sensors can be wired to the terminal pads 32 for docking to a coupler or other lines leading to control electronics (not shown). Some common metals that can be used in the thermal sensors can be iron (Fe), copper (Cu), nickel (Ni), and platinum (Pt). Metal alloys or combinations of metals can also be used for the thermal sensors. Nichrome is an alloy composed of nickel and chromium (Cr). Constantan TM is a mixture of copper and nickel. Alumel TM is an alloy mainly composed of nickel and small amounts of aluminum, manganese, and silicon.

[0059] An advantage of this implementation is the integration of an array or row of connectors and / or terminal pads 32 into the flexible substrate SUB, replacing conventional soldering steps and facilitating connection to another connector or line. Another advantage is the precise and repeatable placement of the thermal sensors. Additionally, an analog-to-digital converter can be located in the grip or other suitable location to interface with the flexible circuit 30 to digitize the thermal sensor signals and reduce the wiring interface from the flexible circuit to the console to two lines.

[0060] Figure 4An exemplary probe 40 is shown. As shown, the probe 40 extends in a longitudinal direction along a central axis. The probe 40 includes a cable 41 located at the center along the central axis. The cable 41 is configured to deliver current to an antenna 42 positioned toward a tip 45, which can deliver RF energy or microwaves to target tissue during an ablation procedure. A choke 43 can be positioned along the cable 41 before the antenna 42 to limit and / or reduce the current returning along the cable 41. The probe 40 can also include a cooling tube located inside a housing 44 of the probe 40. The cooling tube can extend longitudinally above the choke 43 and the antenna 42. As shown, the flexible circuit 30 can be fixed to the housing 44 by being positioned with an adhesive at several points and then fixed along the probe body 24 by using heat shrink tubing. Optionally, a pressure sensitive adhesive can be used. In this example, the distance D between the proximal end of the choke and the flexible circuit 30 should not be less than 3.6 mm. In a design without a choke, the end of the flexible circuit can be placed closer to the tip 45.

[0061] Figure 5 FIG. 4 is an example of a microwave ablation probe 50 that is constructed with a flexible circuit 30 that includes thermocouples as thermal sensors TC1, TC2, TC3, an inflow TC, and an outflow TC. The extensions of the flexible circuit that extend from the probe shaft to the thermal sensors TC1, TC2, and TC3 have been routed under the housing and are not visible. The thermal sensors TC1, TC2, and TC3 are placed at the 3 cm, 4 cm, and 5 cm marks on the probe shaft. To integrate the flexible circuit 30 onto the probe shaft, TC1 is fixed in place with an adhesive. Then, while keeping the flexible circuit 30 straight and not twisted, heat shrink material can be slid over the probe shaft. The thermal sensor inflow TC and outflow TC can be attached to the coupler 22.

[0062] Figure 6 FIG. 8 is a functional block diagram of a microwave ablation system 600 according to an exemplary embodiment. As shown, the microwave ablation system 600 can include an ablation controller 610, an ablation computing system 620, a coolant reservoir 630, a flexible cable 640, and a microwave ablation probe 50. The ablation controller 610 can be coupled to the microwave ablation probe 50 via the flexible cable 640 to provide operation in a microwave mode. The ablation controller 610 can include a coolant delivery system 612, a thermal sensor interface circuit 614, and a microwave power generator 616.

[0063] The ablation computing system 620 may include a processor, such as a computer, server, laptop, tablet, workstation, network, etc. Additionally, the ablation computing system 620 and / or the ablation controller 610 may communicate with a memory for storing operating software, pre-treatment plan information, and data collected during processing. The memory may be part of the ablation computing system 620 and / or the ablation controller 610, a network, or the cloud. The ablation computing system 620 may also include a user interface, such as a display and / or other input / output devices, to allow the user to interact, control, observe, and otherwise configure the operation of the microwave ablation system 600. Although the ablation controller 610 and the ablation computing system 620 are shown as separate elements in Figure 6 , it should be understood that these and other features may be combined into a single structure, or further separated from the structures shown and described.

[0064] The coolant reservoir 630 may be defined as a container, tank, intravenous (IV) bag, or any other structure suitable for containing a fluid capable of cooling the microwave ablation probe 50 and operating with the coolant delivery system 612. For example, the coolant may be distilled water, saline, or carbon dioxide (CO 2 ) gas.

[0065] The flexible cable 640 may include an inflow line 642 for the coolant to flow from the coolant delivery system 612 to the microwave ablation probe 50, an outflow line 644 for the coolant to flow from the microwave ablation probe 50 to the outside, sensor wiring 646 for sending electrical signals between the thermal sensor interface 614 circuitry and the microwave ablation probe 50, and microwave wiring 648 for sending microwave energy from the microwave power generator 616 to the microwave ablation probe 50. In one embodiment, the coolant reservoir 630 is an intravenous (IV) bag containing distilled water or saline, where the inflow line 642 includes a spike for inserting into the IV bag, and the outflow line 644 returns to the IV bag. Thus, in this case, the cooling system is a closed loop. In another embodiment, CO 2 gas is used as the coolant. In this case, the coolant reservoir 630 is a gas tank, and the outflow line 644 and the coolant gas do not return to the tank. The gas from the outflow line 644 is released into the environment in an open-circuit state.

[0066] The flexible cable 640 may include connectors suitable for connecting to the ablation controller 610 and the microwave ablation probe 50.

[0067] The microwave ablation probe 50 may include a coupler 52, a coolant conduit 54, a thermal sensor circuitry 56, an analog-to-digital converter 57, and a microwave antenna 58. The coupler 52 may include connections to an inflow line 642, an outflow line 644, a sensor line 646, and a microwave line 648. The coolant conduit 54 may be configured to direct coolant through the microwave ablation probe 50 to absorb heat and cool the microwave ablation probe 50 during use. As described herein, the thermal sensor circuitry 56 may be a flexible circuit including a thermal sensor to transmit an electrical signal representative of temperature to a thermal sensor interface circuit 614. In some embodiments, the electrical signal from the thermal sensor circuitry 56 may be sent to the analog-to-digital converter 57. The analog-to-digital converter 57 may convert the electrical signal from the thermal sensor circuitry 56 into a two-wire digital signal for transmission to the thermal sensor interface circuit 614 to reduce the number of wires in the flexible cable 640 that would otherwise be required to send analog signals for multiple thermal sensors. The microwave antenna 58 may convert microwave energy from a microwave power generator 616 into an electromagnetic field that radiates to heat tissue in the ablation zone.

[0068] The coolant delivery system 612 may be configured to draw or pump coolant from a coolant reservoir 630 to the microwave ablation probe 50 via the inflow line 642 of the flexible cable 640. Although shown as part of the ablation controller 610, the coolant delivery system 612 may be separate from the ablation controller 610.

[0069] The thermal sensor interface circuit 614 may receive an electrical signal representative of temperature from the thermal sensor circuitry 56. This may be an analog or digital signal via the analog-to-digital converter 57. The ablation controller 610 may utilize the temperature information from the thermal sensor circuitry 56 to collect, analyze, store, and / or perform other operations.

[0070] The microwave power generator 616 is used to generate a microwave signal and send it to the microwave antenna 58. The microwave antenna 58 converts the fed high-power microwave current into an electromagnetic wave that radiates into its surrounding medium. In this way, microwave energy can be transferred to the target tissue and, in turn, heat the tissue at the distal end of the microwave ablation probe 50. Heat may be generated via various duty cycles and / or via various power curves to raise the temperature of the tissue to destroy the tissue or coagulate a bleeding state.

[0071] The microwave ablation probe 50 is tested under the following conditions: (i) no cooling fluid (i.e., saline) in the probe, (ii) probe perfusion, and (iii) blocked coolant flow. In each test, similar to Figure 5The microwave ablation probe 50 configured therein is connected to a microwave generator. The spikes of the probe are inserted into an intravenous injection bag containing saline, the saline is set to return in a closed system, and the probe is held in air. The microwave generator is turned on at a power of 5 W for 40 seconds and 60 seconds, at flow rates of 0 mL / min, 50 mL / min, and 100 mL / min, and the temperature is measured using a thermocouple integrated into the microwave ablation probe 50.

[0072] Figure 7 Graph of thermocouple temperature (°C) versus time (seconds) when there is no saline in the microwave ablation probe 50 at startup. As Figure 7 shown, after 40 seconds, the temperature is observed to rise from approximately room temperature to approximately 35 °C and above via thermocouples T1, T2, and T3. The slope of the temperature curve can be used to detect the presence of saline in the probe. As Figure 8 shown, for At = 4 seconds, the slopes of T1, T2, and T3 are calculated, showing that a slope greater than 0.5 can be used to determine the absence of saline in the microwave ablation probe 50. In the case of flow and the presence of saline, the slope will be very close to zero. The absence of saline can indicate a startup problem. Since the cooling system is a closed loop, if there is a leak, the intravenous injection bag will be empty. In the case of a leak, the technician will typically detect the leak before the intravenous injection bag is completely depleted.

[0073] Figure 9 Graph of thermocouple temperature (°C) versus time (seconds) in the case of determining whether the microwave ablation probe 50 is perfused with saline. In this case, the coolant pump is turned on simultaneously with the microwave generator. At the start of the test, the temperature of the thermocouple is observed to rise. However, when the saline reaches the probe after approximately 12 seconds, the thermocouple temperature drops, thus indicating that it takes approximately 12 seconds. To perfuse the microwave ablation probe 50. By monitoring the temperature slopes of thermocouples T1, T2, and T3 and looking for a negative slope after a positive slope, the presence of coolant flow in the microwave ablation probe 50 can be detected. Additionally, a sharp drop in the outflow temperature can be used to detect the presence of coolant. As shown in Figure 9 the outflow trajectory in [figure number] has a sharp temperature drop at approximately 12 seconds. This is like a temperature step change when the slopes of the TC1 to TC3 trajectories become negative. It should be noted that the temperature of the coolant reservoir and / or the flow rate of the coolant pump can be adjusted and used to control the temperature of the microwave ablation probe.

[0074] To simulate the case of blocked coolant flow, the microwave ablation probe 50 is first filled with saline and then the coolant pump is turned off. The thermocouple measures a temperature rise similar to Figure 7 [figure number]. Therefore, with this thermocouple configuration, it is possible to detect a blocked coolant flow situation.

[0075] Figure 10A flowchart of a method for monitoring the coolant state of a microwave ablation probe system according to an embodiment of the present disclosure, for example similar to Figure 6 the system 600 shown, having a probe 50 similar to Figure 5 shown. In step S10, the coolant flow can be activated to the microwave ablation probe. This can be achieved by starting a coolant pump or any other action compatible with starting the system to deliver the coolant to the microwave ablation probe. In step S20, the microwave energy can be activated to be sent to the microwave ablation probe. This can be accomplished by activating a microwave generator or any other suitable action.

[0076] In step S30, the temperature of a thermal sensor located in the microwave ablation probe system can be measured and recorded over a period of time. For example, the period of time can be on the order of several seconds to 60 seconds. For example, the period of time can be 1 second, 2 seconds, or 4 seconds. The time and temperature data can be stored in a memory that is part of the microwave ablation probe system. In step S40, the time and temperature data can be operated on by a computing system that is part of the microwave ablation probe system to calculate the slope of the temperature of each thermal sensor over time. For example, the slope can be calculated over a 4-second period. In step S50, the calculated slope of each thermal sensor is compared with a predetermined threshold. For example, the threshold can be 0.5. In step S60, it is determined whether the calculated slope exceeds the threshold. If the calculated slope is equal to or higher than the threshold, which indicates that the temperature of the thermal sensor is rising too fast, then in step S90 the operator is instructed to troubleshoot the coolant delivery system to ensure that the coolant reservoir contains coolant and the coolant is flowing correctly. The computer system can display a message indicating insufficient cooling and instruct the user to check for potential causes such as: whether the tip of the probe is correctly inserted into the intravenous injection bag, whether there are any leaks, or whether there is any blockage in the coolant path. If the calculated slope is not higher than the threshold, then in step S70 it is determined whether the calculated slope becomes negative after being positive. If the calculated slope remains positive, then in step S90 the operator is instructed to troubleshoot the coolant delivery system. Additionally, the computer system can be configured not to allow the microwave to be turned on. The user will not be able to use the probe until troubleshooting is complete. If the calculated slope is negative after being positive, indicating that the coolant delivery system is working and providing cooling at the thermal sensor location, then in step S80 the microwave ablation probe is ready for use. As a result, the computing system is configured to monitor, process, or calculate the temperature measured over time by the thermal sensors on the microwave ablation probe to determine whether the coolant delivery system is cooling the ablation probe and to provide feedback on the progress of the ablation procedure.

[0077] In accordance with the above teachings, various modifications and variations can be made to the present invention. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced in a manner different from that specifically described.

Claims

1. A microwave ablation probe system, comprising: a coolant delivery system for delivering coolant to the microwave ablation probe; A microwave generator, used for delivering microwave energy to the microwave ablation probe; as well as a computing system in communication with a thermal sensor on the microwave ablation probe to collect temperature data over time from the thermal sensor, wherein The computing system is configured to calculate a slope of the temperature data over time to determine whether the coolant delivery system is cooling the microwave ablation probe. 2 . The microwave ablation probe system according to claim 1 , further comprising a flexible circuit, wherein the flexible circuit comprises the thermal sensor. The microwave ablation probe system of claim 2 , wherein the flexible circuit is attached to the microwave ablation probe. The microwave ablation probe system according to claim 2 , wherein the flexible circuit comprises a plurality of thermal sensors. 5 . The microwave ablation probe system of claim 1 , wherein the coolant delivery system comprises a catheter passing through the microwave ablation probe. 6 . The microwave ablation probe system according to claim 5 , wherein the microwave ablation probe comprises a coupler, and the catheter is attached to the coupler.

7. The microwave ablation probe system according to claim 1, wherein the microwave ablation probe comprises: Slender shaft; a coupler attached to the elongated shaft and the coolant delivery system; as well as A flexible circuit includes the thermal sensor and is attached to the elongated shaft. 8 . The microwave ablation probe head system of claim 7 , wherein the flexible circuit is attached to the coupler and includes a thermal sensor at the coupler.

9. A method for measuring a coolant state of a microwave ablation probe, the method comprising: activating a coolant delivery system to deliver coolant to the microwave ablation probe; activating microwave energy to the microwave ablation probe; measuring the temperature of the microwave ablation probe over time; calculating the slope of the temperature over time; and The slope is compared to a predetermined value.

10. The method according to claim 9, wherein If the slope is equal to or greater than the predetermined value, troubleshooting the coolant delivery system to verify that coolant is being delivered to the microwave ablation probe, and If the slope is less than the predetermined value, it is determined whether the slope becomes negative after being positive.

11. The method according to claim 10, wherein If the slope is not negative after being positive, troubleshooting the coolant delivery system to verify that coolant is being delivered to the microwave ablation probe, and If the slope is negative after being positive, the microwave ablation probe is used.

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