MRI radio frequency receiving coil impedance automatic matching device
By designing an automatic impedance matching device for MRI radio frequency receiving coils, and using a microcontroller to control a voltage-controlled adjustable capacitor and radio frequency switching devices, automatic impedance adjustment of the radio frequency receiving coils is achieved. This solves the problem of cumbersome manual adjustment in existing technologies and improves the imaging quality and efficiency of MRI equipment.
Patent Information
- Application Number
- CN202423200978.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-23
- Publication Date
- 2026-02-06
- Estimated Expiration
- 2034-12-23
AI Technical Summary
In existing MRI equipment, impedance matching of the radio frequency receiving coil requires manual adjustment, which is cumbersome and inefficient, making it difficult to guarantee the consistency and stability of the matching effect. In addition, network analyzers are expensive, which limits their widespread use in clinical applications.
An automatic impedance matching device for MRI radio frequency receiving coils was designed, comprising S11 and S21 measurement circuit modules, a PLL module, a mixer module, a bridge, an ADC module, a real-time display module, and a radio frequency receiving coil matching circuit. The impedance of the radio frequency receiving coil is automatically adjusted by controlling the voltage-controlled adjustable capacitor and radio frequency switching devices through a microcontroller.
Automatic matching of RF receiving coils was achieved, simplifying operation, improving the imaging quality and efficiency of MRI equipment, reducing costs, expanding the signal range, and ensuring the consistency and stability of the matching effect.
Smart Images
Figure CN223883745U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model belongs to the field of nuclear magnetic resonance technology relates to a kind of MRI radio frequency receiving coil impedance automatic matching device. BACKGROUND
[0002] Magnetic resonance imaging (MRI) as a kind of non-invasive medical imaging technology, plays an important role in disease diagnosis and treatment. In MRI equipment, radio frequency receiving coil is one of the key components, for receiving radio frequency signal from human tissue, and converting it into processable image signal. In order to obtain high-quality MRI image, radio frequency receiving coil needs to be impedance matched at the frequency point of magnetic resonance equipment. However, test sample size varies or different patients' part size varies, and size has an impact on the matching S11 curve of radio frequency receiving coil, that is, impedance and center frequency will change.
[0003] For example, the optimal impedance matching is realized on the small-size head, but it is not necessarily optimal for large-size head.
[0004] At present, the common radio frequency receiving coil impedance matching products on the market mainly rely on network analyzer for manual matching. In the prior art, CN 114910852 A discloses a self-adaptive matching circuit for magnetic resonance radio frequency coil and its matching method, the matching circuit impedance conversion device uses varactor diode, the adjusting circuit is complex and has low precision; using directional coupler as reflected voltage detection, the cost is higher; using special peak detector to measure reflected voltage and incident voltage to calculate S parameter, which depends on the performance of detection chip, and is not conducive to subsequent signal range expansion.
[0005] Network analyzer can measure the impedance and reflection coefficient of radio frequency receiving coil, but the operator needs to manually adjust the matching circuit according to the measurement results, which is tedious and inefficient, and it is difficult to ensure the consistency and stability of the matching effect. Moreover, there is no real-time display module.
[0006] In addition, the price of network analyzer is expensive, which limits its popularization in clinical application.
[0007] Therefore, it is of great significance to develop a device that can automatically adjust the impedance of radio frequency receiving coil according to the size change of test sample or patient part, for improving the imaging quality and efficiency of MRI equipment. UTILITY MODEL CONTENT
[0008] In view of the above, the utility model discloses a kind of MRI radio frequency receiving coil impedance automatic matching device. S11, S21 at the frequency point of the radio frequency receiving coil in the working of magnetic resonance equipment, i.e. center frequency, can be measured, and impedance in radio frequency receiving coil matching circuit module is automatically adjusted according to the result of measurement, to realize the automatic matching of coil. Test sample size is not identical or the size of the part of different patients is not identical, and size has influence on the matching S11 curve of radio frequency receiving coil, i.e. impedance and center frequency will change, and the product currently used for radio frequency receiving coil impedance matching is network analyzer visible on the market, but these network analyzers can only carry out impedance matching, and cannot automatically match the impedance of radio frequency receiving coil at center frequency according to test result.
[0009] To achieve the above object, the utility model provides the following technical scheme:
[0010] A kind of MRI radio frequency receiving coil impedance automatic matching device, comprising:
[0011] S11, S21 measuring circuit module, comprising:
[0012] Single-chip microcomputer unit circuit module;
[0013] PLL module;
[0014] Mixing module, including mixer and low pass filter circuit;
[0015] Bridge, consisting of resistance or capacitance network;
[0016] ADC module;
[0017] Interface circuit connected with the single-chip microcomputer unit circuit module, for connecting real-time display module;
[0018] Radio frequency receiving coil matching circuit, connected with S11, S21 measuring circuit module, comprising:
[0019] At least one capacitor;
[0020] At least one voltage-controlled adjustable capacitor;
[0021] Radio frequency switch device, for switching the connection of radio frequency receiving coil matching circuit, i.e. the measurement connection of S11, S21 measuring circuit module, the connection with magnetic resonance system preamplifier;
[0022] Radio frequency receiving coil matching circuit control circuit, connected with radio frequency receiving coil matching circuit, comprising:
[0023] At least one DAC device or digital potentiometer, for controlling voltage-controlled adjustable capacitor on radio frequency receiving coil matching circuit;
[0024] at least one MEMS or the like radio frequency switching device for controlling the capacitance array on the radio frequency receiving coil matching circuit;
[0025] The real-time display module is connected with the S11 and S21 measurement circuit module, and is used for displaying the measurement result in real time.
[0026] Further, the single-chip microcomputer unit circuit module further comprises a single-chip microcomputer.
[0027] Further, the ADC module is used for converting the mixed baseband signal into a digital signal.
[0028] Further, the interface circuit is a 485 protocol circuit or an I2C protocol circuit.
[0029] Further, the connection mode of the capacitance and the voltage-controlled adjustable capacitance in the radio frequency receiving coil matching circuit is parallel connection or series connection.
[0030] Further, the radio frequency switching device is a single-pole double-throw switch or a single-pole multi-throw switch.
[0031] Further, the real-time display module is a computer or an OLED screen matched with the single-chip microcomputer.
[0032] The matching circuit impedance converter uses the voltage-controlled adjustable capacitance, and has a wide adjustable range; the bridge is used, and the structure is simple and the cost is low; after the radio frequency signal is separated, the mixed frequency module is used to down-convert the radio frequency signal into a baseband signal with amplitude and phase, the signal frequency is reduced, the sampling rate requirement and the data amount of the subsequent ADC are reduced, the S parameter is obtained by the single-chip microcomputer after sampling and relevant calculation, and the scheme has lower cost and stronger expansibility.
[0033] Other advantages, objects and features of the present application will be apparent from the following detailed description of the application and from the claims, taken in conjunction with the accompanying drawings. The present application will be described with reference to the following drawings, in which: BRIEF DESCRIPTION OF DRAWINGS
[0034] In order to make the purpose, technical scheme and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, in which:
[0035] Figure 1 The present application is a structural schematic diagram;
[0036] Figure 2 The impedance automatic matching algorithm adopts a full search algorithm flowchart;
[0037] Figure 3 The utility model measurement process chart. DETAILED DESCRIPTION
[0038] The other advantages and effects of the utility model can be easily understood by the person skilled in the art from the content disclosed in the specification. The utility model can also be implemented or applied by another different specific implementation, and each detail in the specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the utility model. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the utility model in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.
[0039] Wherein, the drawings are only used for example description, and the representation is only a schematic diagram, not a physical diagram, and can not be understood as the limitation of the utility model; in order to better illustrate the embodiment of the utility model, some components in the drawings can be omitted, enlarged or reduced, and the size of the actual product is not represented; for the person skilled in the art, it can be understood that some known structures and their description in the drawings can be omitted.
[0040] The same or similar reference numerals in the drawings of the embodiments of the utility model correspond to the same or similar components; in the description of the utility model, it should be understood that if the orientation or position relationship indicated by the terms 'upper', 'lower', 'left', 'right', 'front', 'back' and the like is based on the orientation or position relationship shown in the drawings, only for the convenience of describing the utility model and simplifying the description, and not indicating or implying that the device or element indicated must have a specific orientation, a specific orientation and operation, therefore, the terms describing the position relationship in the drawings are only used for example description, and can not be understood as the limitation of the utility model, for the person skilled in the art, the specific meaning of the above terms can be understood according to the specific situation.
[0041] The utility model provides a kind of specific implementation of MRI radio frequency receiving coil impedance automatic matching device, and its structure block diagram is as shown in Figure 1 As shown in the figure.
[0042] 1. System composition
[0043] The utility model device is mainly composed of the following modules:
[0044] S11, S21 measurement circuit module: the module is used to measure the impedance and reflection coefficient of radio frequency receiving coil matching circuit, and automatically adjust the impedance of radio frequency receiving coil matching circuit according to the measurement result. It is mainly composed of single-chip microcomputer unit circuit module, PLL module, mixing module, bridge and ADC module.
[0045] RF receiving coil matching circuit: the circuit is connected with S11, S21 measurement circuit module, as the measured circuit, its impedance can be adjusted. It is mainly composed of capacitors, voltage-controlled adjustable capacitors and RF switch devices.
[0046] RF receiving coil matching circuit control circuit: the circuit is connected with RF receiving coil matching circuit, used to control and adjust the impedance of RF receiving coil matching circuit. It is mainly composed of DAC devices or digital potentiometers, and MEMS RF switch devices.
[0047] Real-time display module: the module is connected with S11, S21 measurement circuit module, used to display the results of measurement in real time. It can be a computer or an OLED screen matched with a single-chip microcomputer.
[0048] 2. S11, S21 measurement circuit module working principle
[0049] Single-chip microcomputer unit circuit module: this module controls the operation of the whole system, including controlling the PLL module to generate RF signals, controlling the mixing module to down-convert signals, controlling the ADC module to sample signals, processing sampling data to calculate S11 and S21 parameters, and displaying the results on the real-time display module.
[0050] PLL module: the module generates RF signals, one as an excitation signal, and the other as the local oscillator signal of the mixer in the mixing module.
[0051] Mixing module: the module converts high-frequency RF signals to baseband signals, i.e. the reference signal and the measured signal are mixed to generate baseband signals related to phase and amplitude, and then the difference frequency signal is obtained through low-pass filter circuit.
[0052] Bridge: the module is composed of resistance or capacitance network, and its working principle is that when the impedance of RF receiving coil matching circuit is completely matched, the reflected signal is cancelled, and when the impedance is not matched, the reflected signal is generated. Another function of the bridge is to separate the excitation signal output by the PLL module from the reflected signal of the RF receiving coil matching circuit.
[0053] ADC module: the module is used to convert the mixed baseband signal (analog signal) into digital signal, providing input data for subsequent digital processing of the single-chip microcomputer.
[0054] 3. RF receiving coil matching circuit working principle
[0055] The circuit uses the combination of capacitors and voltage-controlled adjustable capacitors, which can adjust the capacitance value of the voltage-controlled adjustable capacitor by changing its voltage value, thereby changing the impedance of the RF receiving coil matching circuit.
[0056] The radio frequency receiving coil matching circuit further comprises a radio frequency switch device for switching the connection of the radio frequency receiving coil matching circuit, i.e. the measurement connection with the S11, S21 measurement circuit module and the connection with the preamplifier of the magnetic resonance system.
[0057] 4. Working principle of the radio frequency receiving coil matching circuit control circuit
[0058] The circuit uses a DAC device or a digital potentiometer for controlling the voltage-controlled adjustable capacitor on the radio frequency receiving coil matching circuit.
[0059] If the radio frequency receiving coil matching circuit capacitor array is used as an impedance conversion device, the radio frequency receiving coil matching circuit control circuit can use a MEMS or other radio frequency switch device for controlling the capacitor array on the radio frequency receiving coil matching circuit.
[0060] 5. Working principle of the real-time display module
[0061] The module is used for displaying the results obtained by the S11, S21 measurement circuit module in real time, and can display parameters such as impedance and reflection coefficient.
[0062] 6. Impedance automatic matching process
[0063] After the system is powered on, the single-chip microcomputer initializes each module and sets the initial voltage value and step size of the voltage-controlled adjustable capacitor.
[0064] The single-chip microcomputer controls the PLL module to generate a radio frequency signal, one of which is used as an excitation signal and the other of which is used as the local oscillator signal of the mixer in the mixing module.
[0065] The excitation signal passes through the bridge, and part of the signal is injected into the radio frequency receiving coil matching circuit. The reflected signal generated by the radio frequency receiving coil matching circuit is separated by the bridge again, and the transmitted signal can be directly extracted from the RX end.
[0066] The three signals (reflected signal, reference signal, and transmitted signal) enter the mixing module, and are down-converted into baseband signals containing amplitude and phase information.
[0067] The baseband signal is sampled by the ADC module and converted into a digital signal.
[0068] The single-chip microcomputer reads the digital signal, performs S11, S21 calculation, and displays the results on the real-time display module.
[0069] If the impedance and reflection coefficient tested do not meet the requirements, the single-chip microcomputer controls the radio frequency receiving coil matching circuit control circuit to change the voltage value of the voltage-controlled adjustable capacitor on the radio frequency receiving coil matching circuit, changes the capacitance value, and thus changes the impedance on the radio frequency receiving coil matching circuit.
[0070] Repeat the above steps until the impedance and reflection coefficient meet the preset requirements.
[0071] When the impedance matching is completed, the single-chip microcomputer controls the radio frequency switch on the radio frequency receiving coil matching circuit to disconnect the radio frequency receiving coil matching circuit from the S11 and S21 measurement circuit module and connect it with the preamplifier of the magnetic resonance system, and MRI imaging is started.
[0072] The impedance automatic matching algorithm of the device adopts a full search method, and the algorithm flow is as shown in Figure 2
[0073] Initialization: Set the initial voltage value and step size of the voltage-controlled adjustable capacitor.
[0074] Determine the S11 value: If the S11 value meets the preset requirement, the matching is successful, and the connection of the radio frequency receiving coil matching circuit is switched to the preamplifier; otherwise, step 3 is entered.
[0075] Enumerate the CM capacitor: Change the voltage value of the CM capacitor and measure the S11 value.
[0076] Determine the S11 value: If the S11 value meets the preset requirement, the matching is successful, and the connection of the radio frequency receiving coil matching circuit is switched to the preamplifier; otherwise, continue to change the voltage value of the CM capacitor, and repeat steps 3 and 4 until the preset step termination value is reached, and if the preset step termination value is reached and the matching is not successful, step 5 is entered.
[0077] Enumerate the CT capacitor: Change the voltage value of the CT capacitor and measure the S11 value.
[0078] Determine the S11 value: If the S11 value meets the preset requirement, the matching is successful, and the connection of the radio frequency receiving coil matching circuit is switched to the preamplifier; otherwise, continue to change the voltage value of the CT capacitor, and repeat steps 5 and 6 until the preset step termination value is reached, and if the preset step termination value is reached and the matching is not successful, step 7 is entered.
[0079] Enumerate the CM and CT combination: Change the combined voltage value of the CM and CT capacitors and measure the S11 value.
[0080] Determine the S11 value: If the S11 value meets the preset requirement, the matching is successful, and the connection of the radio frequency receiving coil matching circuit is switched to the preamplifier; otherwise, reduce the step size of the CM and CT capacitors and return to step 3 to continue the matching.
[0081] As shown in Figure 3 , the measurement process is as follows:
[0082] When the impedance matching of the radio frequency receiving coil is performed, the PLL module in the S11, S21 measurement circuit module generates a radio frequency signal, one of which is used as the local oscillator signal of the mixer in the mixing module, and the other of which is used as the excitation signal, wherein part of the excitation signal is used as the reference signal, and the other part is used as the excitation signal; the excitation signal passes through the bridge, part of the signal is injected into the radio frequency receiving coil matching circuit, and the reflected signal generated by the radio frequency receiving coil matching circuit is separated by the single bridge again, and the transmitted signal can be directly extracted from the RX end; the three signals (reflected signal, reference signal, and transmitted signal) enter the mixing module, and are down-converted into baseband signals containing amplitude and phase information; the baseband signals are sampled by the ADC module and converted into digital signals; the single-chip microcomputer in the single-chip microcomputer unit circuit module reads the digital signals and calculates S11 and S21.
[0083] The calculation results are displayed in real time on the real-time display module. If the impedance and reflection coefficient tested do not meet the requirements, the radio frequency receiving coil matching circuit control circuit changes the voltage values of the two voltage-controlled adjustable capacitors in the radio frequency receiving coil matching circuit, changes the capacitance values, and thus changes the impedance of the radio frequency receiving coil matching circuit. When the impedance and reflection coefficient meet the preset requirements, stop matching, and the radio frequency receiving coil and its matching circuit are automatically disconnected from the measurement connection of the S11, S21 measurement circuit module, and are automatically connected to the preamplifier of the magnetic resonance system, realizing the automatic matching of the radio frequency receiving coil, and realizing the automatic switching of the radio frequency receiving coil matching circuit between the measurement and the connection to the preamplifier of the magnetic resonance system.
[0084] Measurement principle:
[0085] The radio frequency receiving coil is connected with the radio frequency receiving coil matching circuit, the radio frequency receiving coil matching circuit is connected with the S11, S21 measurement circuit module, the radio frequency receiving coil matching circuit is connected with the radio frequency receiving coil matching circuit control circuit, the radio frequency receiving coil matching circuit control circuit is connected with the S11, S21 measurement circuit module, and the S11, S21 measurement circuit module is connected with the real-time display module.
[0086] The S11, S21 measurement circuit module performs S11, S21 measurement on the radio frequency receiving coil matching circuit, and displays the measurement results in real time on the real-time display module. The radio frequency receiving coil matching circuit control circuit automatically adjusts the impedance of the radio frequency receiving coil matching circuit according to the measured impedance and reflection coefficient, until the preset matching requirements are met, for example, the reflection coefficient is less than -20dB.
[0087] When the impedance matching is completed, the radio frequency switch in the radio frequency receiving coil matching circuit disconnects the measurement connection of the radio frequency receiving coil matching circuit and the S11, S21 measurement circuit module, and connects with the preamplifier of the magnetic resonance system, and starts to perform MRI imaging.
[0088] The device can automatically measure the impedance and reflection coefficient of the radio frequency receiving coil matching circuit, and automatically adjust the impedance of the radio frequency receiving coil matching circuit according to the measurement result, so that the automatic matching of the coil is realized.
[0089] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the utility model and are not limiting. Although the utility model has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the utility model can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, and all should be covered in the scope of the claims of the utility model.
Claims
1. An automatic impedance matching device for MRI radio frequency receiving coils, characterized in that: include: The S11 and S21 measurement circuit modules include: Microcontroller unit circuit module; PLL module; A mixing module, including a mixer and a low-pass filter circuit; A bridge circuit consists of a network of resistors or capacitors. ADC module; The interface circuit connected to the single-chip microcomputer unit circuit module is used to connect to the real-time display module; The radio frequency receiving coil matching circuit, connected to the S11 and S21 measurement circuit modules, includes: At least one capacitor; At least one voltage-controlled adjustable capacitor; Radio frequency switching devices are used to switch the connection of the radio frequency receiving coil matching circuit, namely the measurement connection with the S11 and S21 measurement circuit modules and the connection with the preamplifier of the magnetic resonance system. A radio frequency receiving coil matching circuit control circuit, connected to the radio frequency receiving coil matching circuit, including: At least one DAC device or digital potentiometer is used to control the voltage-controlled adjustable capacitor on the RF receiver coil matching circuit; At least one MEMS radio frequency switching device is used to control the capacitor array on the radio frequency receiving coil matching circuit; The real-time display module is connected to the S11 and S21 measurement circuit modules and is used to display the measurement results in real time.
2. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The microcontroller unit circuit module further includes a microcontroller.
3. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The ADC module is used to convert the mixed baseband signal into a digital signal.
4. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The interface circuit is a 485 protocol circuit or an I2C protocol circuit.
5. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The capacitor and the voltage-controlled adjustable capacitor in the radio frequency receiving coil matching circuit are connected in parallel or in series.
6. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The radio frequency switching device is a single-pole double-throw switch or a single-pole multi-throw switch.
7. The MRI radio frequency receiving coil impedance automatic matching device according to claim 1, characterized in that: The real-time display module is a computer or an OLED screen that is paired with a microcontroller.