Magnetic resonance-guided focused microwave brain tumor thermal ablation system and focus adjustment method

Abstract

The present invention discloses a magnetic resonance-guided focused microwave brain tumor thermal ablation system and a focusing adjustment method. The present invention integrates the three-dimensional data of MRI and CT, selects the microwave frequency suitable for the size and depth of the tumor, and designs a suitable antenna and a cross-polarized antenna phased array. The differential evolution algorithm is used to optimize the antenna output power and phase to achieve precise focusing of microwave energy, increase the tumor temperature to the ablation level, and maintain the safe temperature of healthy tissue. The system effectively suppresses the adverse effects of brain tissue, including the skull, on microwave penetration, and achieves precise ablation of tumors through a small number of antennas combined with an iterative algorithm. Combined with MRI guidance and real-time temperature monitoring, the accuracy and safety of thermal ablation are ensured, non-invasive radical treatment of brain tumors is achieved, and the problem of drugs being unable to penetrate the blood-brain barrier is overcome. In addition, this technology can also be used to treat other diseases such as liver cancer, pancreatic cancer, thyroid cancer, breast cancer, kidney cancer, bone cancer, bladder cancer, and gallbladder cancer.

Description

Technical Field

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

[0002] Brain tumors are among the most dangerous types of cancer. Despite rapid advances in medical technology in recent years, effective treatment remains challenging, primarily due to their biological characteristics. Brain tumors infiltrate the brain, a vital organ in the human body, making craniotomy extremely challenging. Furthermore, these tumors reside within the blood-brain barrier, which protects delicate neural tissue from harmful substances circulating systemically in the blood and lymphatic system. Most drugs are unable to penetrate this barrier, hindering the efficacy of systemic chemotherapy. Furthermore, the brain's unique developmental, genetic, epigenetic, and microenvironmental characteristics often render these cancers resistant to both traditional and novel treatments. Currently, brain tumor treatment remains primarily surgical with adjunctive chemotherapy and radiotherapy. However, due to the tumor's location and invasive growth, complete surgical resection without damaging the normal central nervous system is difficult. Consequently, postoperative recurrence rates are high, and central nervous system-related disorders such as cerebral edema and epilepsy may also occur. Furthermore, chemotherapy and radiotherapy have side effects on normal tissues, often accompanied by symptoms such as hair loss, nausea, and vomiting.

[0003] Hyperthermia, a new technology for tumor treatment, has developed rapidly in recent years and has been applied to the clinical treatment of many tumors, including liver cancer, thyroid cancer, hemangiomas, and breast cancer. The basic principle of hyperthermia is to inactivate tumor cells by heating the tumor and maintaining it at 42-45°C, thereby achieving the desired therapeutic effect. Hyperthermia can also be used as an adjunct to radiotherapy and chemotherapy, effectively reducing the dose of both chemotherapy and radiotherapy while achieving the same therapeutic effect, minimizing damage to normal tissue. Heat sources for hyperthermia include radiofrequency electromagnetic waves, microwaves, lasers, and ultrasound. At present, laser-based thermal therapy technology has been used clinically, but it requires a small hole in the skull to insert 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 the ultrasound signal 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 higher cost. Microwave ablation needle-based thermal therapy has also been widely used in clinical practice, 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 systems can provide non-invasive, precise, economical, and low-side-effect tumor treatment. The huge application potential of focused microwave ablation technology has been explored in the treatment of diseases such as breast cancer, neck tumors, liver and bladder cancer. The basic principle of focused microwave hyperthermia is to use phased array antennas to irradiate 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 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] To achieve the above objectives, 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 includes a microwave source and a microwave antenna array connected by a non-magnetic coaxial cable. 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 includes an MRI imaging system, an MRI temperature measurement sequence, and multiple MRI receiving coils.

[0009] The main control system is communicatively connected to the magnetic resonance device and the focused microwave device, and 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 time-sharing alternation between the temperature measurement sequence of the magnetic resonance device and the microwave antenna array.

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

[0011] A cross-polarized microwave antenna array combines antenna elements with different polarization directions to achieve specific radiation characteristics. By adjusting the phase and amplitude of each antenna element, a cross-polarized antenna array enhances directivity, increases gain, and reduces beamwidth.

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

[0013] After the microwave antenna array heats 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 the surrounding area. 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 below 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 ensured to be below the safe temperature threshold.

[0014] Preferably, the operating 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 these parameters for about 3 to 5 minutes can produce a temperature rise of 1 to 2°C at the brain tumor site, and temperature measurement and microwave heating are performed alternately, ultimately causing the temperature at the tumor target site to 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 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 outward 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 magnetic resonance guidance for non-diagnostic and non-therapeutic purposes, which is characterized by comprising the following steps:

[0018] Step 1: Acquire the three-dimensional distribution of target tissue using MRI and / or CT imaging systems;

[0019] Step 2: Based on the characteristics of brain tissue microwave absorption frequency, set the antenna operating frequency and design the microwave antenna;

[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, MRI equipment is used to monitor the temperature inside the brain in real time. This allows the antenna's excitation power and phase to be adjusted based on the temperature distribution of the brain tissue, guiding 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: Perform a CT scan of the real skull to obtain a three-dimensional model in STL format. At the same time, a brain tissue prosthesis is made according to the MRI data and filled into the skull. The skin and subcutaneous fat are replaced with pig skin. The skull is an ex vivo skull. The prosthesis material is obtained by adjusting the formula ratio of edible oil, water, glycerin, gelatin, formalin, etc. according to electromagnetic parameters.

[0026] Step 3: Use the simulated phase and amplitude 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, change the maximum output average power of the microwave source to 5W to heat the tumor to the ablation temperature. Then, proportionally reduce the output power of all channels of the microwave source to achieve stable temperature in the simulated human brain tissue and the tumor for more than 10 minutes, meeting the conditions for tumor cell apoptosis. During this period, the temperature measurement 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, MATLAB software is used to convert the electric field into a .mat file for microwave focusing operation;

[0029] Step S2: Set the phase variable φ and amplitude variable A of the antenna excitation signal, and use the differential evolution algorithm to optimize φ and A so that the average power of microwaves absorbed by the brain tumor (Q tumor ) than the maximum microwave power absorbed by healthy tissue (Q healthy ) as high as possible, i.e., maximizing 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, i.e., maximizing f = Q tumor / Q healthy ;

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

[0031] In the present invention, the antenna array is a helmet-shaped design, which is an array containing 17 antenna units. The number of units in the antenna array and the position of each unit can be flexibly adjusted for different patients. Edible oil is used as a coupling agent for microwave energy transmission into the human brain (the coupling agent can also be liquid silicone, vegetable fat, animal fat, oil and water mixture gel, deionized water, etc. The relative dielectric constant range of the coupling agent is: ε r =2.3 to 78, but the antenna size needs to be adjusted accordingly depending on the dielectric constant). All antennas are wrapped in oil bladders and the antenna radiating surface is connected to the human scalp to reduce power reflection. The antenna is a 3cm × 5cm × 3mm bow tie patch antenna (i.e., the metal patch is in the shape of a bow tie) and operates at 1.3GHz. The 3mm dielectric substrate thickness effectively increases the antenna's operating bandwidth, and the high dielectric constant substrate material (ε r =10.2 or greater) and the grooving treatment on the surface of the antenna patch help to reduce the size of the antenna, so that more antennas can be placed in the same space to improve the microwave focusing effect. It can also effectively reduce the eddy currents induced in the metal layer of the antenna in the MRI equipment, thereby greatly improving the compatibility between the microwave focused 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 to connect the coaxial line between 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 uses a single channel output power of 1 to 5000W and a duty cycle of 0.01% to 100% to perform heating for about 3 to 5 minutes, which can effectively produce a temperature rise of 1 to 2°C at the brain tumor. The microwave source is then turned off and the MRI temperature measurement sequence is immediately turned on. Within 30 seconds, a temperature distribution map of the entire brain is obtained to determine whether the microwave is focused, whether the temperature in the tumor has reached the treatment threshold, and whether the temperature in normal tissue is below 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. The metal layer on the back of the antenna includes a number of metal block units arranged in an array. 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, thereby forming a discrete metal unit, further reducing the eddy current generated on the surface. Taking a hexagonal magnetic resonance (MRI) receiving coil with a 1.5T operating frequency, 64MHz, and a single-side diameter of 7.4cm as an example, the antenna units in the antenna array are set at a 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 extremely necessary and have three main functions. First, it guides the entire microwave focusing process, measures the temperature distribution in the brain through nuclear magnetic resonance, determines whether the microwave electric field is focused on the brain tumor, and assists in optimizing the antenna excitation phase and amplitude, ultimately achieving effective focusing of the microwave electric field and power on the tumor; second, it monitors whether the temperature at the brain tumor can reach the threshold required for treatment and whether it can achieve the purpose of destroying tumor cells. This directly determines the effectiveness of focused microwave hyperthermia; third, it monitors whether there is overheating or potential burns in normal brain tissue, which directly affects the safety and side effects of focused microwave hyperthermia. The new system proposed in this invention can not only achieve non-invasive, precise, economical, and low-side-effect tumor microwave ablation treatment, but also effectively guide the microwave focusing process through magnetic resonance, ensuring the effectiveness, precision, safety, and low-side-effect 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 enhance and optimize the effect of tumor treatment.

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

[0036] (1) This invention proposes for the first time a microwave thermal ablation system that utilizes 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 circumvents potential treatment obstacles posed by the blood-brain barrier. The implementation of this technology can heat brain tumors to ablation temperature while ensuring the safety of healthy tissues, and 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-invasive brain tumor treatment possible, but also reduces the complexity of doctors' operations and the possible damage to patients' brain function. 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 showed 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 the 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 traditional array focus spot. It 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 that exists when using 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 collaborative design of microwave antenna arrays and MRI receiving coils to reduce interference between the two and improve MRI temperature measurement accuracy; simultaneously adopts a time-sharing 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 parts 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., and are 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 technologies to improve efficacy, reduce radiotherapy radiation and chemotherapy drug doses, 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 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 designs 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 using thyroid tumor treatment as an example;

[0044] Figure 3 : (a) is a schematic diagram of the MRI-guided focused microwave brain tumor thermal ablation system, which includes: MRI magnetic resonance imaging equipment, an oil-capsulated brain tumor ablation antenna array, and a microwave source with integrated coaxial cables and coupling fluid exchange pipes; (b) shows a close-up top view of the microwave antenna array and the MRI receiving coil in an interlaced 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 spectrometer, and a fiber optic thermometer; (c) is a 3D schematic diagram of the connections between the helmet-type antenna phased array, the coupling liquid circulation system, the microwave source, and the control computer.

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

[0047] Figure 6 This 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] Figure 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] Figure 10 This is the temperature detection result of tumor and brain tissue in the focused microwave hyperthermia experiment with a prosthesis filled in a real skull.

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

[0053] Figure 12 This figure is a result diagram used to detect the effect of microwave source output phase disturbance on the temperature of focused microwave hyperthermia based on real brain tissue. DETAILED DESCRIPTION

[0054] 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, a simulation model is built using CT or MRI data. MATLAB software is used to segment brain tissue. 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. The simulated head is divided into system validation and experimental verification. System validation uses a complete, real human head tissue model and fills it with tissue based on MRI data. Multiple tumors of varying sizes and depths are used 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 in the figure, cooking oil is used as the microwave coupling medium. A bracket is used to secure the human head tissue and the antenna, with holes opened on both sides for oil circulation via hoses. In the simulation, the cooking oil temperature was set at 15°C to cool surface tissues such as the skin. The antenna fabrication process 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 bow tie 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 slots, 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 this embodiment, in order to reduce the interference between the microwave system and the MRI system, a microwave antenna array and an MRI receiving coil are co-designed. In view of the structural characteristics of the human brain, a helmet-type antenna phased array is designed. The MRI receiving coil and the antenna units are staggered in the helmet. Specifically, a grid gap is provided on the MRI receiving coil. The grid gap can be used to embed a 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 hexagonal. 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. After heating for 3 to 5 minutes, the microwave source is turned off and MRI temperature measurement is turned on. 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 hyperthermia is performed to detect the temperature of 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 adaptive moment estimation algorithm is iterated 400 times (if the differential evolution algorithm is used, the iteration number 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, i.e., maximizing f = Q tumor / Q healthy .

[0064] Finally, the antenna excitation amplitude and phase were imported into the EM-Thermal Coupling module of CST electromagnetic simulation software. The maximum average power output at the antenna port was set to 5W, the initial tissue temperature 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 the experimental system prototype, such as Figure 4The system includes a microwave source, an antenna array, a coupling fluid circulation cooling device, a data acquisition device (a spectrometer for collecting microwave power, which is connected to a microwave power probe, and a temperature measurement fiber for collecting temperature), a control computer, and a non-magnetic coaxial cable connecting the microwave source and the antenna array. In this embodiment, the temperature measurement fiber is used for system verification. In actual application, an MRI temperature measurement sequence is used for temperature monitoring.

[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 5mm to 1cm.

[0068] Use the simulated phase and amplitude to set the microwave source, and connect the microwave power probe to the spectrum analyzer, as shown in 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 ensure that the temperature of the human brain tissue and the tumor remains stable for more than 10 minutes, meeting the conditions for tumor cell apoptosis. During this period, the temperature measurement 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 rose to above the ablation temperature of 42°C. The tumor temperature was significantly higher than that of the surrounding tissue. The healthy tissue was inhibited by the cooling effect of the cooking oil, and the temperature was always kept within a safe range.

[0070] Figure 9 This is the temperature simulation result of a real human skull and a 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] Figure 10 The temperature curves at four locations measured during the experiment are shown. The experimental prosthesis and the simulation model are identical. Because the prosthesis initially reached room temperature (22-25°C), it took longer to reach the tumor ablation temperature. However, the curves still demonstrate the system's practicality. Figure 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, achieving the control of the ablation temperature.

[0072] In addition, the problem of microwave source channel isolation and output phase disturbance was simulated and verified. After the focusing of Example 10(d), the antenna phase was randomly perturbed by ±15°. The temperature cross section Figure 12 It shows that phase perturbation has 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 or 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 includes a microwave source and a microwave antenna array connected by a non-magnetic coaxial cable. The microwave antenna array is a cross-polarized antenna array and is composed of patch antennas. The antenna patch surface is grooved, and the metal layer on the back of the antenna patch is discretized. Specifically, the metal layer is provided with a plurality of metal block units arranged in an array, and gaps are provided between the metal block units to form discrete metal units. The magnetic resonance imaging device includes an MRI imaging system, an MRI temperature measurement sequence, and multiple MRI receiving coils. The main control system is communicatively connected to the magnetic resonance device and the focused microwave device, and 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 time-sharing alternation between the temperature measurement sequence of the magnetic resonance device and the microwave antenna array. The coupling liquid cooling system is used to provide cooling circulating coupling liquid to the antenna units in the microwave antenna array, and the coupling liquid forms an oil pocket around the surface of the antenna units; The microwave antenna array is provided with a plurality of antenna units. The microwave antenna array and the MRI receiving coil form an integrated structure. In the integrated structure, the antenna units in the microwave antenna array and the MRI receiving coil are staggered and not arranged on the same horizontal plane. The antenna units are arranged outward relative to the MRI receiving coil.

2. The thermal ablation system according to claim 1, wherein: The control module is configured to implement the following processing steps: After the microwave antenna array is heated for 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 the surrounding area. 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 below 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 ensured to be below the safe temperature threshold.

3. The thermal ablation system according to claim 2, wherein: The microwave antenna array's heating operating parameters are set to: single-channel output power of 1 to 5000 W, with a duty cycle of 0.01% to 100%. Heating under these parameters for 3 to 5 minutes can produce a temperature rise of 1 to 2°C at the brain tumor site. Temperature measurement and microwave heating are performed alternately, ultimately causing the temperature at the tumor target to reach and stabilize above 42°C.

4. The thermal ablation system according to claim 1, wherein: 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 the imaging system.

5. A method for adjusting the focus of focused microwaves under magnetic resonance guidance for non-diagnostic and non-therapeutic purposes, characterized in that: The method uses the magnetic resonance-guided focused microwave brain tumor thermal ablation system according to claim 1, comprising the following steps: Step 1: Obtain the three-dimensional distribution of the target tissue using an MRI or CT imaging system; Step 2: Based on the characteristics of brain tissue microwave absorption frequency, set the antenna operating frequency and design the microwave antenna; Step 3: Design a microwave antenna array based on the brain tissue structure and tumor location; Step 4: While the microwave antenna is radiating, MRI equipment is used to monitor the temperature inside the brain in real time. This allows the antenna's excitation power and phase to be adjusted based on the temperature distribution of the brain tissue, guiding 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.

6. 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, a control computer, and cables; Step 2: Scan the real skull CT to obtain a 3D model in STL format. Simultaneously, a brain tissue prosthesis is made according to the MRI data and filled into the skull. The skin and subcutaneous fat are replaced with pig skin. The skull is an isolated skull. Step 3: Use the simulated phase and amplitude 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. Then, the output power of all channels of the microwave source is reduced proportionally to ensure that the temperature in the simulated human brain tissue and the tumor remains stable for more than 10 minutes, meeting 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.

7. The method according to claim 6, wherein 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, MATLAB software is used to convert the electric field into a .mat file for microwave focusing operation; Step S2: Set the phase variable φ and amplitude variable A of the antenna excitation signal, and use the differential evolution algorithm to optimize φ and A so that the average microwave power Q absorbed by the brain tumor is tumor Higher microwave power Q than healthy tissue healthy As high as possible, that is, to maximize f = Q tumor / Q healthy ; Step S3: Import 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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