Self-adaptive tuning matching and control system of magnetic resonance radio frequency transmitting coil

Abstract

The invention provides a self-adaptive tuning matching and control system of a magnetic resonance radio frequency transmitting coil, and belongs to the technical field of magnetic resonance imaging. The system is composed of a radio frequency transmitting coil, a tuning matching circuit of the radio frequency transmitting coil, an automatic adjusting device, a scattering parameter measuring device, an upper computer interaction module, a PC and a computer processing program. During working, the system only needs to pre-store a group of optimal tuning and matching scattering parameters, after different parts of different human bodies enter the center of the body coil, tuning and matching circuits can be continuously adjusted, changes of the scattering parameters in the adjusting process are collected in real time, and the rotating direction of a tuning strip matching motor can be automatically judged; and the accurate tuning frequency and the optimal matching state are quickly obtained, so that the optimal transmitting efficiency is achieved.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging technology, specifically to an adaptive tuning matching and control system and method for a magnetic resonance radio frequency transmitting coil, which is particularly suitable for achieving rapid and accurate impedance matching under different human body loads, different scanning sites, and dynamic physiological motion conditions. Background Technology

[0002] Magnetic resonance imaging (MRI) uses radio frequency (RF) emitter coils to excite the spins of protons in the human body; the resonant frequency and the matching state directly determine the spin. Field uniformity and emission efficiency. Ideally, the coil should be at its optimal resonant point and conjugate matched with the power source before scanning to minimize reflected power and maximize signal-to-noise ratio. The nature of nuclear magnetic resonance (NMR) necessitates an externally applied radio frequency field. Only when the frequency equals the Larmor frequency can protons effectively absorb energy from the radio frequency field. ( For imaging proton gyromagnetic ratio, (Main magnetic field strength). The radio frequency transmitting coil can be equivalent to an LC resonant circuit, and its natural frequency... Must and Consistent; simultaneously, according to the maximum power transfer theorem, the equivalent impedance of the coil must be conjugate matched with the impedance of the 50 Ω system. During actual loading, the coil impedance is the sum of its own impedance and the local impedance of the human body; the dielectric properties of the human body continuously change with weight, body size, and body location, causing the equivalent capacitance and series resistance to change accordingly, resulting in… When the equivalent impedance deviates from the design value, the resonant point and matching state are disrupted. However, in clinical practice, the patient's weight, body shape, and scanning location are constantly changing. The dielectric constant and conductivity of human tissues can significantly alter the equivalent capacitance and additional series resistance of the coil, leading to resonant frequency shift, impedance mismatch, increased reflection coefficient, decreased emission efficiency, and consequently, deteriorated image quality.

[0003] Existing technologies such as CN114910852B use varactor diodes and a binary tuning method, which achieves automation, but varactor diodes have problems such as narrow tuning range, nonlinearity, and limited power tolerance; CN120405534A uses a PIN diode array for discrete adjustment, but the matching accuracy is limited by the array step and it is difficult to achieve continuous and smooth adjustment; CN107209235B involves multi-channel tuning, but it relies on forward / reflected power comparison and lookup table, and does not solve the problem of real-time direction judgment and oscillation suppression when mechanical load changes.

[0004] In general, existing technologies have the following problems: the general calibration process uses the abdomen of a subject with "standard weight" (approximately 75kg) as a benchmark, manually tuning and matching to the optimal state; this state is only effective for a single weight and a single location; during actual scanning, the patient's weight and location change randomly, the dielectric properties of the human body change the capacitance effect of the coil and introduce additional resistance, causing the resonant frequency and impedance to deviate from the preset values, reducing transmission efficiency; improved solutions require the additional introduction of pressure sensing circuits, pre-stored multiple sets of weight-scattering parameter mapping tables or coupling circuits, real-time acquisition of forward / reverse voltages and calculation of scattering parameters, and then switching the tuning / matching network; or setting multiple fixed LC topologies and selecting them through PIN diodes. Since the LC networks are all offline presets, it is still difficult to cover the continuous and large-scale changes in the subject's body shape and location in clinical applications, and true real-time continuous tuning cannot be achieved.

[0005] Therefore, there is an urgent clinical need to develop an "adaptive" radiofrequency transmitter coil matching scheme to achieve real-time continuous conjugate matching across the entire population, all positions, and the entire scanning cycle. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to adaptively adjust the frequency and matching circuit of the radio frequency transmitting coil for different human bodies and different scanning sites before magnetic resonance imaging (MRI) scans, so as to put it in the optimal tuning and matching network state and ensure that the transmitting coil is in the best transmission efficiency.

[0007] This invention provides an adaptive tuning matching and control system for a magnetic resonance radio frequency transmitting coil, comprising: The state sensing module is configured to acquire the operating state parameters of the radio frequency transmitting coil; The control decision module is configured to determine the target state corresponding to the current scanning conditions, compare the working state parameters with the target state, and output control commands. The motor drive adjustment module is configured to, in response to the control command, continuously adjust at least one adjustable reactive element in the frequency modulation circuit and / or matching circuit in a motor drive manner until the operating state parameters meet the target state.

[0008] Furthermore, the radio frequency transmitting coil is selected from birdcage coils or other transmitting coils, such as TEM coils, dipole coils, etc.

[0009] Furthermore, the state sensing module is a scattering parameter measurement module, which is configured to acquire the scattering parameters of the radio frequency transmitting coil.

[0010] Furthermore, the scattering parameter measurement module can use a vector network analyzer, spectrum analyzer, time domain reflectometer, etc. to measure the scattering parameters of the radio frequency transmitting coil, and it communicates with the PC and computer processing program via USB or serial port.

[0011] Furthermore, the state sensing module is a magnetic resonance signal acquisition module, which is configured to acquire the intensity of the magnetic resonance signal received by the magnetic resonance system during the operation of the radio frequency transmitting coil.

[0012] Furthermore, the control command includes adjustment direction information; the control decision module is further configured to: determine the adjustment direction of the motor drive adjustment module based on the changing trend of the working state parameters acquired this time and the working state parameters acquired last time.

[0013] Furthermore, the control decision module determines the adjustment direction by comparing the position changes of the matching points and / or the offset of the center frequency in the working state parameters.

[0014] Furthermore, the motor drive adjustment module includes a motor and a transmission component driven by the motor, the transmission component being mechanically connected to the adjustable reactance element.

[0015] Furthermore, the transmission component is an insulated screw.

[0016] Furthermore, the motor drive adjustment module includes a servo motor and an insulated screw driven by the servo motor; the insulated screw is mechanically connected to the adjustable reactance element to convert the rotational motion of the servo motor into continuous adjustment of the parameter value of the adjustable reactance element.

[0017] Furthermore, the matching circuit is an L-type, π-type, or T-type network that includes at least one adjustable reactance element.

[0018] Furthermore, the control decision module is also configured to: after the target state is met, record the final working state parameters and the corresponding position information of the motor drive adjustment module, and use them to optimize the preset parameters related to the scanning conditions.

[0019] The present invention also provides a magnetic resonance imaging device, comprising: a magnet system, a radio frequency system, and an adaptive tuning matching and control system for the aforementioned magnetic resonance radio frequency transmitting coil.

[0020] This invention also provides an adaptive tuning matching and control method for a magnetic resonance radio frequency transmitting coil, comprising the following steps: S1. Obtain the operating status parameters of the radio frequency transmitting coil; S2. Compare the working status parameters with the target status corresponding to the current scanning conditions; S3. Generate a control command containing the adjustment direction based on the comparison result, and adjust the adjustable reactance element in the tuning circuit and / or matching circuit of the radio frequency transmitting coil by driving the motor; Repeat the above steps until the working state parameters meet the target state.

[0021] Furthermore, the operating status parameters are the scattering parameters of the radio frequency transmitting coil obtained through an external measuring device; Alternatively, the operating state parameter is the intensity of the magnetic resonance signal acquired by the magnetic resonance system itself during the application of radio frequency excitation.

[0022] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. Single-parameter reference: Only a set of scattering parameters of the system center frequency f0 and the 50 Ω matching point are pre-stored, which can be used as the sole reference, simplifying the preset process.

[0023] 2. Fully automatic continuous adjustment: The scattering parameter measurement device collects scattering parameters under any load in real time, and the computer program drives the automatic adjustment device to continuously and steplessly adjust the tuning and matching network without manual intervention.

[0024] 3. Real-time determination and rapid convergence: The algorithm automatically determines the rotation direction of the tuning / matching motor, approaches the optimal point in one go, significantly shortens the tuning time, and ensures that the transmission efficiency is always optimal.

[0025] 4. High adaptability: The continuously adjustable network replaces the discrete LC combination, eliminating the need for pressure sensors and additional detection circuits, and can cover a wide range of body weight and scanning site variations.

[0026] 5. High precision assurance: The scattering parameter measurement device, as a metrology-grade front end, directly provides high-precision, high-real-time feedback signals to ensure the accuracy and reliability of the tuning and matching process.

[0027] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0028] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0029] Figure 1This is a block diagram of the adaptive tuning, matching, and control method for magnetic resonance radio frequency transmitting coils.

[0030] Figure 2 This is a flowchart illustrating the adaptive tuning, matching, and control method for a magnetic resonance radio frequency transmitter coil.

[0031] Figure 3 This is a specific mechanical implementation example of Example 2.

[0032] Figure 4 This is a diagram of a matching network structure based on adjustable capacitors and inductors.

[0033] Figure 5 This is a diagram of a matching network structure based on adjustable inductors and capacitors.

[0034] Figure 6 This is a schematic diagram of an adjustable inductor (the adjustable inductor is a hollow inductor wound with copper wire, and a copper core is installed in the center of the inductor's frame to change its inductance).

[0035] Figure 7 It is an adjustable capacitor servo drive structure.

[0036] Figure 8 It is an adjustable inductor servo drive structure. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that the algorithms for data acquisition, transmission, storage and processing steps not specifically described in the embodiments, as well as the hardware structures and circuit connections not specifically described, can all be implemented using content already disclosed in the prior art.

[0039] Tuning of the radio frequency transmitting coil is generally achieved by changing the capacitance value on the coil. In the embodiment of the present invention, the matching circuit is one of the L-type, T-type, and Π-type circuits.

[0040] The scattering parameter measurement apparatus in the embodiments of the present invention can be a vector network analyzer, a spectrum analyzer, a time domain reflectometer, etc., to measure the scattering parameters of the radio frequency transmitting coil.

[0041] The radio frequency transmitting coil described in the embodiments of the present invention can be a birdcage coil or other transmitting coils, such as a TEM coil, a dipole coil, etc.

[0042] The embodiment of the present invention can perform adaptive frequency and matching adjustment for the radio frequency transmitting coils of multiple ports.

[0043] The embodiment of the present invention can also eliminate the scattering parameter measurement device. During the process of adjusting the tuning and matching circuit, the system collects the magnitude of the magnetic resonance signal to determine whether it is in the optimal tuning and matching state.

[0044] Example 1: System Architecture and Hardware Composition This embodiment relates to an adaptive tuning and matching system and control system for a magnetic resonance radio frequency transmitting coil. The device comprises a radio frequency transmitting coil and its tuning and matching circuits, an automatic adjustment device, a scattering parameter testing device, a host computer interaction module, a PC, and a computer processing program. Figure 1 As shown.

[0045] The device pre-sets the scattering parameters to be achieved when any part of the device enters the center of the magnet in the PC memory. The preset scattering parameters are determined by the main magnetic field of the system adapted to the RF transmitting coil. When scanning a specific part, the part is first positioned at the center of the magnet. Before the scan begins, an adaptive tuning matching process is executed. After the adaptive tuning matching is completed, the image scan is performed.

[0046] After the scanning area moves to the center of the magnet via the patient bed, the scattering parameters of the transmitting coil are measured by the scattering parameter measuring device in this state. The scattering parameter measuring device transmits the measured scattering parameters to the PC in real time via USB or serial communication. The computer processing program compares the acquired scattering parameters with preset scattering parameters. If the comparison fails, an adaptive adjustment command is sent to the host computer. Upon receiving the command, the host computer drives the automatic adjustment device. The motor in the automatic adjustment device adjusts the adjustable capacitor or adjustable inductor in the matching circuit and tuning circuit via an insulated screw. During the adjustment process, the scattering parameter measuring device continuously collects scattering parameters and uploads them to the computer processing program for real-time comparison. After successful tuning and matching, the PC sends a command to the host computer to stop the adjustment process and then resumes the scanning process. If the comparison fails, the computer processing program determines the offset of the current adjustment frequency from the previous frequency and the change in the matching point based on the comparison of the current scattering parameter graph with the previous graph. It then determines whether the automatic adjustment device rotates the screw in the direction of increasing or decreasing the capacitance or inductance until matching is completed, thus saving adjustment time and quickly adjusting to the preset scattering parameter state. Figure 2 As shown.

[0047] Example 2: Specific Application Implementation of the System like Figure 3As shown, a high-pass birdcage coil is selected as the RF transmitting coil, and a vector network analyzer is selected as the measuring device for the scattering parameters of the RF transmitting coil. The high-pass birdcage coil consists of two end metal rings, a certain number of legs, and multiple capacitors. In practical applications, the resonant frequency of the transmitting coil is adjusted by changing the capacitance value located on the metal end ring. The matching circuits of the birdcage coil are usually divided into L-type, T-type, and Π-type. In this embodiment, the L-type matching network is selected. The tuning and matching circuits are as Figure 4 shown. In the L-type matching circuit of the embodiment, the adjustable capacitor and inductor can also be composed of an adjustable inductor and capacitor, as Figure 5 shown.

[0048] The adjustable capacitor in this embodiment can select non-magnetic adjustable capacitors such as the NMNT23-12E series of voltronics. The adjustable inductor uses an air-core inductor wound with copper wire. In the skeleton for winding the inductor, a copper core installed in the center of the skeleton can change its inductance, as Figure 6 shown. The motor in this embodiment can select a magnetic resonance compatible motor such as the Redo BLS072 servo motor.

[0049] After positioning the human body part to be scanned at the center of the RF transmitting coil, start the adaptive tuning and matching process. Control the power supply to output a positive voltage to conduct diode D1. At this time, diode D2 is in the off state. The vector network analyzer collects the S parameters at this time, and synchronizes the S parameter graph to the PC through USB or serial port at the same time. The computer program compares the obtained S parameter graph with the pre-stored S parameters to determine whether the center frequency f1 at this time is equal to the preset f0, and whether the coil equivalent impedance is equal to 50 ohms. If f1 is not equal to f0, the computer program issues an instruction to the host computer to drive the frequency adjustment motor to adjust the tuning capacitor through the frequency adjustment screw, as Figure 7 shown. The vector network analyzer and the computer program collect and compare in real time. If it is found that the current f1 < f0, the computer program issues an instruction to the host computer to control the frequency adjustment motor to rotate in the opposite direction to the previous rotation. If it is found that the current f1 > f0, the computer program issues an instruction to the host computer to control the frequency adjustment motor to rotate in the same direction as the previous rotation until f1 = f0. If the coil equivalent impedance is not equal to 50 ohms, the computer program issues an instruction to the host computer to drive the frequency adjustment motor to adjust the adjustable capacitor or adjustable inductor in the matching network through the matching adjustment screw, as Figure 7 , Figure 8As shown, the vector network analyzer and computer program acquire and compare data in real time. If the current equivalent impedance is less than 50 ohms, the computer program sends a command to the host computer to control the matching adjustment motor to rotate in the opposite direction of the previous rotation. If the current equivalent impedance is greater than 50 ohms, the computer program sends a command to the host computer to control the matching adjustment motor to rotate in the same direction as the previous rotation, until the equivalent impedance equals 50 ohms. At this point, the adaptive tuning and frequency modulation process ends. The control power supply outputs a reverse voltage to turn on diode D2. At this time, diode D1 is in the off state, and the RF transmitting coil is connected to the RF power amplifier, allowing the formal scanning to begin.

[0050] The adaptive tuning, matching, and control system for the MRI radio frequency transmitting coil provided by this invention only requires a pre-stored set of optimal tuning and matching scattering parameters. It allows different parts of the human body to enter the center of the coil, continuously adjusting the tuning and matching circuits, and collecting real-time data on changes in scattering parameters during adjustment. Furthermore, it can automatically determine the rotation direction of the tuning bar matching motor, quickly obtaining an accurate tuning frequency and optimal matching state, thereby achieving optimal transmission efficiency. This invention can be used to improve the efficiency and stability of the radio frequency transmitting link in medical or research MRI equipment, or to optimize the signal-to-noise ratio of the receiving link. This invention can also be used as an upgrade module for performance enhancement and modification of existing MRI equipment. It has broad industrial application prospects and significant market value.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An adaptive tuning and matching and control system for a magnetic resonance radio frequency transmit coil, characterized by, The application comprises: a state sensing module configured to obtain an operating state parameter of the radio frequency transmitting coil; a control decision module configured to determine a target state corresponding to a current scanning condition, compare the operating state parameter with the target state, and output a control instruction; a motor-driven adjustment module configured to continuously adjust at least one adjustable reactance element in a frequency modulation circuit and / or a matching circuit in a motor-driven manner in response to the control instruction until the operating state parameter meets the target state.

2. The adaptive tuning matching and control system of claim 1, wherein, The state sensing module is a scattering parameter measurement module configured to obtain a scattering parameter of the radio frequency transmitting coil.

3. The adaptive tuning matching and control system of claim 1, wherein, The state sensing module is a magnetic resonance signal acquisition module configured to acquire a magnetic resonance signal strength received by a magnetic resonance system during operation of the radio frequency transmitting coil.

4. The adaptive tuning matching and control system of claim 1, wherein, The control instruction comprises adjustment direction information; the control decision module is further configured to determine an adjustment direction of the motor-driven adjustment module according to a change trend of the operating state parameter obtained this time and the operating state parameter obtained last time.

5. The adaptive tuning matching and control system of claim 1, wherein, The motor-driven adjustment module comprises a motor and a transmission component driven by the motor, and the transmission component is mechanically connected to the adjustable reactance element.

6. The adaptive tuning matching and control system of claim 1, wherein, The matching circuit is an L-type, π-type or T-type network comprising the at least one adjustable reactance element.

7. A magnetic resonance imaging apparatus, characterized by The application comprises: a magnet system, a radio frequency system and the adaptive tuning and matching and control system of the magnetic resonance radio frequency transmitting coil according to any one of claims 1-4.

8. A method of adaptive tuning and matching and control of a magnetic resonance radio frequency transmit coil, characterized by, The application comprises the following steps: S1, obtaining an operating state parameter of the radio frequency transmitting coil; S2, comparing the operating state parameter with a target state corresponding to a current scanning condition; S3, generating a control instruction comprising an adjustment direction according to a comparison result, and adjusting an adjustable reactance element in a tuning circuit and / or a matching circuit of the radio frequency transmitting coil by driving a motor; The above steps are repeated until the operating state parameter meets the target state.

9. The method of claim 8, wherein, The operating state parameter is a scattering parameter of the radio frequency transmitting coil obtained by an external measuring device; or, the operating state parameter is a magnetic resonance signal strength acquired by a magnetic resonance system itself during application of a radio frequency excitation.

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