Magnetic resonance guided focusing microwave brain tumor thermal ablation system and focusing adjustment method

Abstract

The invention discloses a magnetic resonance guided focusing microwave brain tumor thermal ablation system and a focusing adjustment method. According to the invention, three-dimensional data of MRI and CT are integrated, microwave frequency suitable for tumor size and depth is selected, and an appropriate antenna and cross polarized antenna phased array is designed. The output power and phase of the antenna are optimized by using a differential evolution algorithm, accurate focusing of microwave energy is realized, the tumor temperature is increased to an ablation level, and meanwhile, the safe temperature of healthy tissues is kept. The system effectively inhibits adverse effects of brain tissues including skull on microwave penetration, and realizes accurate ablation of tumors through combination of a small number of antennas and an iterative algorithm. MRI guidance and real-time temperature monitoring are combined, so that the accuracy and safety of thermal ablation are ensured, the brain tumor is radically treated in a non-invasive manner, and the problem that the medicine cannot penetrate through the blood brain barrier is solved. In addition, the technology can also be used for treating liver cancer, pancreatic cancer, thyroid cancer, breast cancer, kidney cancer, bone cancer, bladder cancer, gallbladder cancer and other diseases.

Description

Technical Field

[0001] The invention relates to a magnetic resonance-guided focused microwave brain tumor thermal ablation system and a focusing adjustment method, and belongs to the technical field of clinical medicine and medical equipment. Background Art

[0002] Brain tumors are one of the most dangerous types of cancer. Although medical technology has developed rapidly in recent years, effective treatment of brain tumors is still challenging, mainly because of their biological characteristics. Brain tumors infiltrate the brain, the most important organ of the human body, and craniotomy is extremely difficult. At the same time, these tumors are also located in the blood-brain barrier, which protects fragile neural tissue from harmful substances in the blood and lymphatic circulation throughout the body. Most drugs cannot penetrate this barrier, which hinders the efficacy of systemic chemotherapy. In addition, the unique developmental, genetic, epigenetic and microenvironmental characteristics of the brain often make these cancers resistant to traditional and novel treatments. At present, the treatment of brain tumors is still mainly based on surgery combined with radiotherapy and chemotherapy. However, due to the location of brain tumors and their invasive growth characteristics, it is difficult for surgery to completely remove tumor tissue without destroying the normal central nervous system. Therefore, the postoperative recurrence rate of brain tumors is very high, and central nervous system-related diseases such as cerebral edema or epilepsy may also occur. In addition, radiotherapy and chemotherapy have side effects on normal tissues of the human body, often accompanied by symptoms such as hair loss, nausea, and vomiting.

[0003] As a new technology for tumor treatment, hyperthermia has developed rapidly in recent years and has been applied to the clinical treatment of many tumors, including liver cancer, thyroid cancer, hemangioma, breast cancer, etc. The basic principle of hyperthermia is to inactivate tumor cells by heating the tumor and maintaining it at 42-45°C, thereby achieving the purpose of treatment. In addition, hyperthermia can also be used as a means of adjuvant radiotherapy and chemotherapy. Under the condition of meeting the same therapeutic effect, it can effectively reduce the dose of radiotherapy and chemotherapy and reduce damage to normal tissues. The heat sources of hyperthermia mainly include radiofrequency electromagnetic waves, microwaves, lasers, ultrasound, etc. At present, laser-based thermal therapy technology has been used clinically, but it requires a small hole in the skull and then inserting the optical fiber. It is essentially an invasive treatment technology and may cause adverse reactions such as cerebral edema and epilepsy. Transcranial focused ultrasound can also be used for brain tumor thermal therapy, but the severe distortion of ultrasound signals caused by the skull limits the applicable area in the brain, making it unsuitable for the treatment of superficial tumors. The overall system also requires a relatively high cost. Microwave ablation needle-based thermal therapy has also been widely used clinically, but it requires the ablation needle to be inserted into the human body, which is invasive and requires local or general anesthesia, which can easily cause infection and has limited applicable areas.

[0004] Focused microwave ablation system can treat tumors in a non-invasive, precise, economical and low-side effect manner. The huge application potential of focused microwave ablation technology has been explored in the treatment of breast cancer, neck tumors, liver and bladder cancer, etc. The basic principle of focused microwave hyperthermia is to use phased array antennas to radiate the treated area of ​​the human body (such as the head, breast, liver) in a non-invasive and non-invasive manner, optimize the excitation phase and amplitude of each antenna element, and focus the microwave energy radiated by all antennas on the target tumor, thereby achieving selective heating and destruction of tumor tissue, while ensuring that healthy tissue is basically unaffected.

[0005] However, there is currently no experimental feasibility study on MRI-guided focused microwave ablation of brain tumors, and no literature has yet addressed the guidance and monitoring techniques of focused microwave ablation. Summary of the invention

[0006] The technical problem to be solved by the present invention is: in view of the defects of traditional brain tumor treatment methods, the present invention provides a magnetic resonance-guided focused microwave brain tumor thermal ablation system and a focusing adjustment method of focused microwaves under magnetic resonance guidance.

[0007] In order to achieve the above-mentioned object, the present invention provides a magnetic resonance-guided focused microwave brain tumor thermal ablation system, which includes a magnetic resonance device, a focused microwave device, a coupling liquid circulation cooling device and a main control system, wherein:

[0008] The focused microwave device comprises a microwave source and a microwave antenna array connected by a non-magnetic coaxial cable, wherein the microwave antenna array is a cross-polarized antenna array, and the antenna is provided with a discretized metal layer and slots; the magnetic resonance device comprises an MRI imaging system, an MRI temperature measurement sequence and a plurality of MRI receiving coils;

[0009] The main control system is respectively connected to the magnetic resonance device and the focused microwave device for communication, and the main control system is provided with a signal acquisition module and a control module, the signal acquisition module is used to collect the whole brain temperature distribution data monitored by the MRI temperature measurement sequence and the excitation power and phase of the microwave antenna array, the microwave antenna array and the MRI receiving coil are designed in a staggered arrangement to reduce mutual interference between the two, and the control module is configured to control the temperature measurement sequence of the magnetic resonance device and the microwave antenna array to work alternately in time sharing;

[0010] The coupling liquid cooling system is used to provide cooling circulated coupling liquid to the antenna units in the microwave antenna array, and the coupling liquid forms an oil bag around the surface of the antenna unit.

[0011] Cross-polarized microwave antenna arrays refer to the combination of antenna units with different polarization directions in a microwave antenna array to achieve specific radiation characteristics. Cross-polarized antenna arrays enhance directivity, increase gain, and reduce beam width by adjusting the phase and amplitude of each antenna.

[0012] Preferably, the control module is configured to implement the following processing steps:

[0013] After the microwave antenna array has been heated for about 3 to 5 minutes, the microwave source is turned off and the MRI temperature measurement sequence is switched on to obtain a three-dimensional temperature distribution image of the target tumor tissue and surrounding areas. Based on the image, it is determined whether the microwave power is focused on the tumor target, whether the temperature at the tumor target reaches 42°C, and whether the temperature of the surrounding normal tissue is lower than the safe temperature threshold. This process is repeated until the temperature at the tumor target reaches above 42°C and the temperature of the surrounding normal tissue is lower than the safe temperature threshold.

[0014] Preferably, the working parameters of the microwave antenna array for heating are set to: single channel output power 1 to 5000 W, duty cycle 0.01% to 100%; heating under this parameter for about 3 to 5 minutes can produce a temperature rise of 1 to 2°C at the brain tumor, and temperature measurement and microwave heating are performed alternately, ultimately making the temperature at the tumor target reach and stabilize at above 42°C.

[0015] Preferably, the microwave antenna array is provided with a plurality of antenna units, and the microwave antenna array and the MRI receiving coil are an integrated structure (for example, an integrated helmet-type thermal therapy adapter), in which the antenna units in the microwave antenna array and the MRI receiving coil are staggered and not arranged on the same horizontal plane, and the antenna units are arranged outwardly relative to the MRI receiving coil (i.e., a certain angle is formed between the two); the surface of the antenna unit is wrapped with a coupling agent.

[0016] Preferably, the main control system is further provided with an image acquisition module for acquiring the three-dimensional distribution of the target tissue; the image acquisition module is connected to an imaging system, which is an MRI imaging system and / or a CT imaging system.

[0017] The present invention also provides a method for adjusting the focus of focused microwaves under the guidance of magnetic resonance for non-diagnosis and treatment purposes, characterized in that it comprises the following steps:

[0018] Step 1, using MRI and / or CT imaging systems to obtain the three-dimensional distribution of target tissues;

[0019] Step 2: According to the characteristics of microwave absorption frequency of brain tissue, the antenna operating frequency is set and the microwave antenna is designed;

[0020] Step 3: Design a microwave antenna array based on the brain tissue structure and tumor location;

[0021] Step 4: While the microwave antenna is radiating, use MRI equipment to monitor the temperature inside the brain in real time, so as to adjust the excitation power and phase of the antenna according to the temperature distribution of the brain tissue and guide the microwave focusing process;

[0022] Step 5: With the help of differential evolution iterative algorithm, adaptive moment estimation algorithm or other optimization algorithms, adjust the output power and phase of each antenna to gradually achieve high focusing of the microwave field at the tumor.

[0023] The present invention also provides a method for verifying the above thermal ablation system in a simulation model, comprising the following steps:

[0024] Step 1: First, build a system, which includes a microwave source, an antenna array, a coupling liquid circulation cooling device, a data acquisition device (spectrometer, temperature measurement optical fiber), a control computer, and cables;

[0025] Step 2: Scan the real skull CT to obtain a three-dimensional model in STL format, and at the same time make a brain tissue prosthesis according to the MRI data and fill it into the skull, and replace the skin and subcutaneous fat with pig skin; the skull is an ex vivo skull; the material of the prosthesis is obtained by adjusting the formula ratio of edible oil, water, glycerin, gelatin, formalin, etc. according to electromagnetic parameters.

[0026] Step 3. Use the phase and amplitude obtained from the simulation to set the microwave source, connect the microwave power probe to the spectrum analyzer, measure the absorbed power of the tumor center and 2 to 3 cm around it, and adjust the antenna parameters. After focusing, change the maximum output average power of the microwave source to 5W, heat the tumor to the ablation temperature, and then proportionally reduce the output power of all channels of the microwave source to achieve the temperature of the simulated human brain tissue and the tumor to remain stable for more than 10 minutes to meet the conditions for tumor cell apoptosis. During this period, the temperature measuring optical fiber continuously monitors the temperature of four locations: the tumor center, the tumor edge, the cerebrospinal fluid under the forehead, and the cerebrospinal fluid under the occipital region.

[0027] Preferably, the phase and amplitude obtained by simulation in step 3 are specifically realized by the following steps:

[0028] Step S1, after simulating and generating the electric field distribution of each antenna in the brain, use MATLAB software to convert the electric field into a .mat file and perform microwave focusing operation;

[0029] Step S2: setting the phase variable φ and amplitude variable A of the antenna excitation signal, and optimizing φ and A using a differential evolution algorithm so that the average microwave power (Q tumor ) than the maximum microwave power absorbed by healthy tissue (Q healthy ) as high as possible, that is, to maximize f = Qtumor / Q healthy In this step, the phase range is set to 0° to 360°, the amplitude range is set to 0 to 1, the cross factor cr is set to 0.8, the variation factor F is set to 0.6, the initial phase is 50 groups, the adaptive moment estimation algorithm is iterated 400 times (if the differential evolution iterative algorithm is used, the iteration number is set to 100 times), and the optimization goal is to make the average microwave power absorbed by the brain tumor (Q tumor ) than the maximum microwave power absorbed by healthy tissue (Q healthy ) as high as possible, that is, to maximize f = Q tumor / Q healthy ;

[0030] Step S3, import the antenna excitation amplitude and phase into the electromagnetic and thermal coupling simulation module EM-Thermal coupling of CST electromagnetic simulation software. In this step, set the antenna port output maximum average power to 5W, the initial temperature of human tissue to 37°C, and the coupling fluid to 15°C. Stop when the tumor temperature reaches the ablation temperature of 42-45°C.

[0031] In the present invention, the antenna array is a helmet-type design, which is an array containing 17 antenna units. For different patients, the number of units in the antenna array and the position of each unit can be flexibly adjusted. Edible oil is used as a coupling agent for microwave energy transmission to the human brain (the coupling agent can also be selected from liquid silica gel, vegetable fat, animal fat, oil and water mixture gel, deionized water and other materials, and the relative dielectric constant range of the coupling agent is: ε r =2.3~78, but the size of the antenna needs to be adjusted accordingly according to the different dielectric constants). All antennas are wrapped with oil bags and the antenna radiation surface is connected to the human scalp to reduce power reflection. The antenna is a bowtie patch antenna with a size of 3cm×5cm×3mm (that is, the metal patch is in the shape of a bowtie) and works at 1.3GHz. The 3mm dielectric substrate thickness effectively improves the working bandwidth of the antenna, and the high dielectric constant substrate material (ε r =10.2 or greater) and the use of slots on the surface of the antenna patch help to reduce the size of the antenna, and more antennas can be placed in the same space to improve the microwave focusing effect. It can also effectively reduce the eddy current induced in the metal layer of the antenna in the MRI equipment, thereby greatly improving the compatibility between the microwave focusing ablation technology and the MRI navigation technology, and improving the practicality of the present invention. At the same time, a non-magnetic coaxial cable is used for the coaxial line connecting the antenna and the matching microwave source. The non-magnetic coaxial cable mainly includes an internal metal shielding layer and an external metal conductor layer. The metal shielding layer can effectively shield external interference signals and ensure the transmission quality and stability of the signal. The non-magnetic design further prevents the interference of the magnetic field on the signal and improves the transmission efficiency and stability of the signal.

[0032] In the present invention, microwave hyperthermia and MRI temperature measurement are time-division multiplexed to reduce mutual interference. The microwave antenna array is heated for about 3 to 5 minutes with a single channel output power of 1 to 5000 W and a duty cycle of 0.01% to 100%, which can effectively produce a temperature rise of 1 to 2°C at the brain tumor. Then the microwave source is turned off and the MRI temperature measurement sequence is immediately turned on to obtain a temperature distribution map of the whole brain within 30 seconds to determine whether the microwave is focused, whether the temperature in the tumor reaches the treatment threshold, and whether the temperature in the normal tissue is lower than the safety threshold. The above steps are then repeated continuously. The time-division multiplexing method can effectively reduce the mutual interference between the two systems of microwave focused ablation and MRI. The antenna radiation power and duty cycle can be flexibly adjusted according to actual conditions.

[0033] In the present invention, the antenna patch and the back metal layer are discretized, and the metal layer on the back of the antenna includes a plurality of metal block units arranged in an array, and the width of each metal block unit can be set to 2.9mm. There is a gap between the metal block units, and the gap width can be 0.1mm, so as to form a discretized metal unit, and further reduce the eddy current generated on the surface. Taking a hexagonal magnetic resonance (MRI) receiving coil with a single side diameter of 7.4cm and a 1.5T operating frequency of 64MHz as an example, the antenna units in the antenna array are set at the grid gap 2cm away from the outside of the MRI receiving coil. The outside refers to the other side of a single antenna unit (the opposite side connected to the coil) 2cm away from the center height of the MRI receiving coil.

[0034] Real-time guidance and monitoring during focused thermal ablation are very necessary, and they have three main functions. First, guide the entire microwave focusing process, measure the temperature distribution in the brain through nuclear magnetic resonance, determine whether the microwave electric field is focused on the brain tumor, and assist in the optimization of the antenna excitation phase and amplitude, and finally achieve effective focusing of the microwave electric field and power at the tumor; second, monitor whether the temperature at the brain tumor can reach the threshold required for treatment and whether the purpose of destroying tumor cells can be achieved, which directly determines the effectiveness of focused microwave thermal therapy; third, monitor whether there is overheating in normal brain tissue or potential burns, which will directly affect the safety and side effects of focused microwave thermal therapy. The new system proposed in the present invention can effectively guide the microwave focusing process through magnetic resonance while achieving non-invasive, accurate, economical, and low-side effect tumor microwave ablation treatment, ensuring the effectiveness, accuracy, safety, and low side effects of ablation treatment. The microwave ablation technology of the present invention can also be combined with treatment methods such as radiotherapy and chemotherapy to further improve and optimize the tumor treatment effect.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention proposes for the first time a microwave thermal ablation system that uses microwave focused thermal ablation technology to treat brain tumors. This system innovatively solves the problem of accurately focusing microwave energy in a complex tissue environment and avoids the possible obstruction of the blood-brain barrier to treatment. The implementation of this technology can heat brain tumors to ablation temperature while ensuring the safety of healthy tissues, which has far-reaching scientific significance for brain science and brain disease research.

[0037] (2) The system of the present invention is based on microwave focusing technology and can achieve non-invasive ablation treatment, successfully solving the problems of high cost and damage to the body caused by traditional microwave ablation needles and other treatment equipment; the system can achieve microwave non-invasive ablation, which not only makes non-destructive brain tumor treatment possible, but also reduces the complexity of doctors' operations and the possible brain functional damage to patients. This breakthrough will promote the application and development of microwave ablation technology in clinical treatment and expand its application field to the treatment of brain tumors;

[0038] (3) To verify the practicality of the present invention, experiments were conducted using CT and MRI data combined with real human skulls. The experimental results show that the designed focused microwave thermal ablation system is highly flexible and can effectively overcome the adverse effects of microwave penetration caused by tissues such as the skull and blood-brain barrier, achieving the goal of accurately ablating brain tumors. At the same time, the system has the advantages of being portable, fast, and low-cost, providing a new solution for the treatment of brain tumors.

[0039] (4) Compared with the traditional focused microwave ablation antenna array, the present invention adopts a cross-polarized antenna array, which solves the problem of the size and shape limitations of the focus spot of the traditional array, and can more accurately change the size and shape of the focus spot to help cover the target tumor area; the application of cross-polarization enables the antenna array to focus the microwave power at any position in the brain without blind spots, avoiding the focus spot dispersion problem existing in the use of a single polarization method;

[0040] (5) The present invention proposes a complete system for MRI-guided microwave focused thermal ablation, which monitors the temperature of brain tumors and normal brain tissues in real time to ensure the effectiveness and safety of thermal ablation; adopts a coordinated design of microwave antenna arrays and MRI receiving coils to reduce interference between the two and improve MRI temperature measurement accuracy; and adopts a time-division multiplexing method of microwave antennas and MRI to reduce interference between the two; discretizes and slots the metal layer of the antenna to reduce interference with the MRI system;

[0041] In addition, the system of the present invention can also be used to perform non-invasive microwave thermal ablation on other parts of the human body by adjusting the antenna distribution and size and antenna array arrangement. These adjustments include but are not limited to: (1) adjusting the antenna substrate parameters according to the depth of the tumor location, (2) adjusting the antenna distribution and size according to the physical morphology and physiological structure of the treatment site, see Figure 2 (c)-(f); These sites include but are not limited to brain cancer, liver cancer, pancreatic cancer, thyroid cancer, breast cancer, kidney cancer, bone cancer, bladder cancer, gallbladder cancer, etc. It is also suitable for the treatment of other diseases, including but not limited to frozen shoulder, kidney stones, neurological diseases, rheumatic diseases, etc.; Microwave thermal ablation technology can also be combined with existing conventional radiotherapy and chemotherapy techniques to improve the efficacy, reduce the dose of radiotherapy radiation and chemotherapy drugs, and reduce the side effects of radiotherapy and chemotherapy; this wide application will provide strong support for the medical community in the treatment of various cancers and diseases. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the cross-section of human brain tissue distribution, where (a) is a cross-section of real human brain tissue, and (b) is a cross-section of experimental brain tissue combined with CT skull data. During the experiment, a prosthesis was used to fill the inside of the real skull. The spherical tissue in the figure is a brain tumor.

[0043] Figure 2 Schematic diagram of antenna design, where (a) is a schematic diagram of the antenna patch (front of the patch type antenna), (b) is a schematic diagram of the antenna substrate (back metal layer), and the antenna size is 5cm×3cm×3mm; the antenna metal layer is discretized, (c)-(d) are examples of antenna patch design based on different treatment tissues, (e) is an example of antenna substrate back design based on different treatment tissues, and (f) is an antenna arrangement method for thyroid tumor treatment as an example;

[0044] Figure 3 : (a) is a schematic diagram of the focused microwave brain tumor thermal ablation system combined with MRI guidance. The system includes: an MRI magnetic resonance imaging device, a brain tumor ablation antenna array wrapped in an oil capsule, and a microwave source with an integrated coaxial cable and a coupling liquid exchange pipe; (b) shows a close-up top view of the microwave antenna array and the MRI receiving coil in an alternating manner; (c) shows a close-up side view of the microwave antenna array and the MRI receiving coil.

[0045] Figure 4: (a) is a schematic block diagram of the overall construction of the experimental system. The system includes: a magnetic resonance scanner, a helmet-type antenna phased array, a coupling liquid circulation system, a microwave source, a data acquisition device, a non-magnetic coaxial cable and a control computer; (b) is a photo of the experimental system. The system includes: a helmet-type antenna phased array, a coupling liquid circulation system, a microwave source and a control computer, a spectrum analyzer, and a fiber optic thermometer; (c) is a 3D schematic diagram of the connection between the helmet-type antenna phased array, a coupling liquid circulation system, a microwave source and a control computer.

[0046] Figure 5 This is the production process of experimental prostheses; (a) indicates dividing the skull into two parts first for filling; (b) indicates using pig skin as skin and subcutaneous fat; (c) indicates filling with cerebrospinal fluid prosthesis with a thickness of about 1 mm; (d) indicates filling with gray matter simulation material with a thickness of about 5 mm; (e) the blue sphere is a tumor prosthesis and the white one is a white matter prosthesis; (f) indicates adding cerebellum and medulla oblongata prosthesis to the lower half of the skull; (g) indicates using white matter prosthesis to fill the remaining space in the skull; (h) shows a schematic diagram of the prosthesis production process.

[0047] Figure 6 It is a probe for measuring tissue microwave absorption power. It is a 7cm long metal needle with a tip that can sense electric field strength to measure microwave power inside experimental prostheses or biological tissues.

[0048] Figure 7 Schematic diagram of optical fiber temperature measurement.

[0049] Figure 8 This is a diagram of the temperature simulation results of focused microwave hyperthermia based on real brain tissue.

[0050] Fig. 9 This is a diagram of the temperature simulation results of focused microwave hyperthermia based on a real skull filling prosthesis combined with CT data.

[0051] Fig.10 This is the result of temperature detection of tumor and brain tissue in the focused microwave hyperthermia experiment with a prosthesis filled in a real skull.

[0052] Fig.11 This is a graph showing the temperature detection results of tumor and brain tissue in a focused microwave continuous constant temperature experiment with a prosthesis filled in a real skull.

[0053] Fig.12 This is a result diagram for detecting the effect of microwave source output phase disturbance on the temperature of focused microwave hyperthermia based on real brain tissue. DETAILED DESCRIPTION

[0054] In order to make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0055] First, if Figure 1 As shown in the figure, a simulation model is established through CT or MRI data, brain tissue is segmented using MATLAB software, and electromagnetic parameters, density, thermodynamic parameters, and biological tissue parameters such as blood perfusion rate, metabolic rate, and convective heat dissipation efficiency of the biological model are set for the tissue. The simulated head is divided into a system verification part and an experimental verification part. During system verification, a complete real human head tissue model is used and the tissue is filled according to MRI data. Multiple tumors of different sizes and depths are set as samples.

[0056] The antenna, connector and cable are made of non-magnetic metal materials to avoid MRI compatibility problems. The relative dielectric constant of the substrate is 10.2. The specific parameters of the antenna are as follows: Figure 2 As shown. Edible oil is used as a microwave coupling medium. The bracket is used to fix the human head tissue and the antenna, and holes are opened on both sides to circulate oil with hoses. In the simulation, the edible oil is set at 15℃ to cool the surface tissues such as the skin. Among them, the manufacturing process of the antenna is as follows:

[0057] (1) According to different treatment sites, determine the dielectric layer material of the antenna and the surface structure of the antenna patch in the simulation software (change the slot length, cutting angle and size of the bowtie antenna patch surface);

[0058] (2) 100% of the upper and lower surfaces of the dielectric layer are covered with copper to form a metal layer on the dielectric layer;

[0059] (3) Using electrochemical reagents to etch the metal layer according to the antenna surface shape diagram to produce the antenna patch structure and grooves, and discretize the back metal layer.

[0060] (4) After the metal feed port is drilled, the inner wall of the hole is electroplated with copper (this hole is used to connect the coaxial non-magnetic cable, which is connected to the microwave source).

[0061] In order to reduce the interference between the microwave system and the MRI system, the present embodiment adopts the cooperative design of the microwave antenna array and the MRI receiving coil, and designs a helmet-type antenna phased array according to the structural characteristics of the human brain. The MRI receiving coil and the antenna unit are staggered in the helmet. Specifically, a grid gap is provided on the MRI receiving coil, and the grid gap can be used to embed the patch antenna to form a focused microwave hyperthermia adapter, such as Figure 3As shown in bc, the yellow coil in the figure is the MRI receiving coil, and the gray one is the antenna. In this embodiment, the MRI receiving coil is actually a hexagon; in addition, the microwave excitation source is placed at least 5m away from the MRI equipment, and is connected to the antenna array in the receiving coil helmet using a non-magnetic microwave frequency band coaxial cable. Each antenna unit in the antenna array can be connected to the signal output channel of the microwave source using a non-magnetic coaxial cable. During use, the microwave source excites the antenna to irradiate the tumor and MRI temperature measurement monitoring is performed alternately. The microwave source duty cycle is set to 0.01% to 100%, and the maximum output power of a single channel is 1 to 5000W. The microwave source is turned off and MRI temperature measurement is turned on after every 3 to 5 minutes of heating. The three-dimensional temperature distribution is compared with the three-dimensional distribution of brain tissue obtained by the simulation model, and the microwave is gradually guided to focus on the target brain tumor. After confirming that the focusing is successful, focused microwave thermal therapy is performed to detect the temperature at the tumor and the temperature of normal tissue in the entire brain in real time to ensure the effectiveness and safety of thermal ablation. During the focusing process, the amplitude and phase adjustment process of the antenna is as follows:

[0062] After simulating and generating the electric field distribution of each antenna in the brain, MATLAB software was used to convert the electric field into a .mat file for microwave focusing operations.

[0063] The phase variable φ and amplitude variable A of the antenna excitation signal are set, and the differential evolution algorithm is used to optimize φ and A. The phase range is 0° to 360°, the amplitude range is 0 to 1, the cross factor cr is set to 0.8, the variation factor F is set to 0.6, the initial phase is 50 groups, and the number of iterations of the adaptive moment estimation algorithm is 400 times (if the differential evolution iterative algorithm is used, the number of iterations is set to 100 times). The optimization goal is to make the average microwave power absorbed by the brain tumor (Q tumor ) than the maximum microwave power absorbed by healthy tissue (Q healthy ) as high as possible, that is, to maximize f = Q tumor / Q healthy .

[0064] Finally, the antenna excitation amplitude and phase were imported into the electromagnetic and thermal coupling simulation module EM-Thermal coupling of CST electromagnetic simulation software. The maximum average power output of the antenna port was set to 5W, the initial temperature of the human tissue to 37°C, and the coupling fluid to 15°C. The ablation process was stopped when the tumor temperature reached the ablation temperature of 42-45°C.

[0065] The feasibility of the system was then verified using a real skull combined with a human brain tissue prosthesis.

[0066] First, build a prototype of the experimental system. Figure 4The system includes a microwave source, an antenna array, a coupling liquid circulation cooling device, a data collector (a spectrum analyzer for collecting microwave power, which is connected to a microwave power probe, and a temperature measuring optical fiber for collecting temperature), a control computer, and a non-magnetic coaxial cable for connecting the microwave source and the antenna array. In this embodiment, a temperature measuring optical fiber is used for system verification, and in actual application, an MRI temperature measurement sequence is used to monitor the temperature.

[0067] like Figure 5 As shown, a real skull CT scan was performed to obtain a three-dimensional model in STL format. At the same time, a brain tissue prosthesis was made according to the MRI data and filled into the skull. The skin and subcutaneous fat were replaced with pig skin with a thickness of 5 mm to 1 cm.

[0068] Use the simulated phase and amplitude to set the microwave source, and connect the microwave power probe to the spectrum analyzer, such as Figure 6 As shown, the absorbed power of the tumor center and the surrounding 2 to 3 cm is measured and the antenna parameters are adjusted. After focusing is completed, the maximum output average power of the microwave source is changed to 5W to heat the tumor to the ablation temperature. Then the output power of all channels of the microwave source is proportionally reduced to achieve a stable temperature in the human brain tissue and tumor for more than 10 minutes to meet the conditions for tumor cell apoptosis. During this period, the temperature measuring optical fiber continuously monitors the temperature of four locations: the tumor center, the tumor edge, the cerebrospinal fluid under the forehead, and the cerebrospinal fluid under the occipital region. Figure 7 shown.

[0069] Figure 8 This is the simulation result of a real human brain tissue model. After about 9 minutes, the tumor temperature rises to above the ablation temperature of 42°C. The tumor temperature is significantly higher than the surrounding tissue. The healthy tissue is cooled by the cooking oil and the temperature is always kept within a safe range.

[0070] Fig. 9 This is the temperature simulation result of a real human skull and prosthesis. After about 15 minutes of heating, the temperature of the tumor reaches 45°C and the healthy tissue is at a safe temperature.

[0071] Fig.10 The temperature change curves of four locations measured in the experiment are shown. The experimental prosthesis is the same as the simulation model. Since the initial temperature of the prosthesis is room temperature of 22-25°C, it takes longer to reach the tumor ablation temperature, but the practicality of the system can also be verified from the curve graph. Fig.11 It shows that when the tumor in Example 10(d) reaches the ablation temperature, the output power of all channels of the microwave source is reduced by 3.52 times, and the temperature of the tumor and human brain tissue is stabilized at the current temperature, thus achieving the control of the ablation temperature.

[0072] In addition, simulations were performed to verify the isolation of microwave source channels and output phase disturbance. After focusing in Example 10(d), a ±15° disturbance was randomly applied to the antenna phase. The temperature cross section Fig.12 It was shown that phase disturbance had little effect on the accuracy of focusing at the tumor.

[0073] The above-mentioned implementation cases are only preferred implementation cases of the present invention and are not any formal and substantial limitations of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A magnetic resonance-guided focused microwave brain tumor thermal ablation system, characterized in that: It includes magnetic resonance equipment, focused microwave equipment, coupling liquid cooling system and main control system, among which: The focused microwave device comprises a microwave source and a microwave antenna array connected by a non-magnetic coaxial cable, wherein the microwave antenna array is a cross-polarized antenna array, and the antenna is provided with a discretized metal layer and slots; the magnetic resonance device comprises an MRI imaging system, an MRI temperature measurement sequence and a plurality of MRI receiving coils; The main control system is respectively connected to the magnetic resonance device and the focused microwave device, and the main control system is provided with a signal acquisition module and a control module. The signal acquisition module is used to collect the whole brain temperature distribution data monitored by the MRI temperature measurement sequence and the excitation power and phase of the microwave antenna array. The microwave antenna array and the MRI receiving coil are designed in a staggered arrangement to reduce mutual interference between the two. The control module is configured to control the temperature measurement sequence of the magnetic resonance device and the microwave antenna array to work alternately in time sharing; The coupling liquid cooling system is used to provide cooling circulated coupling liquid to the antenna units in the microwave antenna array, and the coupling liquid forms an oil bag around the surface of the antenna unit.

2. The thermal ablation system according to claim 1, characterized in that: The control module is configured to implement the following processing steps: After the microwave antenna array has been heated for about 3 to 5 minutes, the microwave source is turned off and the MRI temperature measurement sequence is switched on to obtain a three-dimensional temperature distribution image of the target tumor tissue and surrounding areas. Based on the image, it is determined whether the microwave power is focused on the tumor target, whether the temperature at the tumor target reaches 42°C, and whether the temperature of the surrounding normal tissue is lower than the safe temperature threshold. This process is repeated until the temperature at the tumor target reaches above 42°C and the temperature of the surrounding normal tissue is lower than the safe temperature threshold.

3. The thermal ablation system according to claim 2, characterized in that: The working parameters of the microwave antenna array for heating are set to: single channel output power 1 to 5000W, duty cycle 0.01% to 100%; heating under this parameter for about 3 to 5 minutes can produce a temperature rise of 1 to 2°C at the brain tumor, and temperature measurement and microwave heating are performed alternately, ultimately making the temperature at the tumor target reach and stabilize at above 42°C.

4. The thermal ablation system according to claim 2, characterized in that: The microwave antenna array is provided with a plurality of antenna units, and the microwave antenna array and the MRI receiving coil are an integrated structure. In the integrated structure, the antenna units in the microwave antenna array and the MRI receiving coil are staggered and are not arranged on the same horizontal plane, and the antenna units are arranged outwardly relative to the MRI receiving coil.

5. The thermal ablation system according to claim 1, characterized in that: The main control system is also provided with an image acquisition module for acquiring the three-dimensional distribution of the target tissue; the image acquisition module is connected to the imaging system.

6. A method for adjusting the focus of focused microwaves under magnetic resonance guidance for non-diagnostic and non-therapeutic purposes, characterized in that: The following steps are involved: Step 1, using MRI and / or CT imaging systems to obtain the three-dimensional distribution of target tissues; Step 2: According to the characteristics of microwave absorption frequency of brain tissue, the antenna operating frequency is set and the microwave antenna is designed; Step 3: Design a microwave antenna array based on the brain tissue structure and tumor location; Step 4: While the microwave antenna is radiating, use MRI equipment to monitor the temperature inside the brain in real time, so as to adjust the excitation power and phase of the antenna according to the temperature distribution of the brain tissue and guide the microwave focusing process; Step 5: With the help of differential evolution iterative algorithm, adaptive moment estimation algorithm or other optimization algorithms, adjust the output power and phase of each antenna to gradually achieve high focusing of the microwave field at the tumor.

7. A method for verifying the magnetic resonance guided thermal ablation system of claim 1 in a simulation model, characterized in that: The following steps are involved: Step 1: First, build a system, which includes a microwave source, an antenna array, a coupling liquid circulation cooling device, a data acquisition device (spectrometer, temperature measurement optical fiber), a control computer, and cables; Step 2, perform CT scan on the real skull to obtain a three-dimensional model in STL format, and make a brain tissue prosthesis according to the MRI data and fill it into the skull, and replace the skin and subcutaneous fat with pig skin; the skull is an ex vivo skull; Step 3: Use the phase and amplitude obtained by simulation to set the microwave source, connect the microwave power probe to the spectrum analyzer, measure the absorbed power at the center of the tumor and 2 to 3 cm around it, and adjust the antenna parameters; After focusing is completed, the maximum output average power of the microwave source is changed to 5W to heat the tumor to the ablation temperature, and then the output power of all channels of the microwave source is reduced proportionally to achieve stable temperature maintenance of the simulated human brain tissue and the tumor for more than 10 minutes to meet the conditions for tumor cell apoptosis. During this period, the temperature measuring optical fiber continuously monitors the temperature of four locations: the tumor center, the tumor edge, the cerebrospinal fluid under the forehead, and the cerebrospinal fluid under the occipital region.

8. The method according to claim 7, characterized in that The phase and amplitude obtained by simulation in step 3 are specifically realized by the following steps: Step S1, after simulating and generating the electric field distribution of each antenna in the brain, use MATLAB software to convert the electric field into a .mat file and perform microwave focusing operation; Step S2: setting the phase variable φ and amplitude variable A of the antenna excitation signal, and optimizing φ and A using a differential evolution algorithm so that the average microwave power (Q tumor ) than the maximum microwave power absorbed by healthy tissue (Q healthy ) as high as possible, that is, to maximize f = Q tumor / Q healthy ; Step S3, importing the antenna excitation amplitude and phase into the electromagnetic and thermal coupling simulation module EM-Thermal coupling of the CST electromagnetic simulation software.

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