An adaptive matching circuit and matching method for magnetic resonance radio frequency coil

Abstract

The present invention relates to an adaptive matching circuit and a matching method for a magnetic resonance radio frequency coil, and belongs to the field of magnetic resonance imaging technology. The circuit includes a receiving coil, an adjustable matching circuit, a radio frequency switch, a return loss detection circuit, and a single-chip control circuit; the circuit uses a binary method to adjust the voltage value across the variable capacitance diode in the adjustable matching circuit, and automatically detects the adaptation of the matching circuit through the return loss detection circuit to achieve instant adaptive circuit matching, and through the joint action of the adjustable matching circuit, the radio frequency switch, and the single-chip control circuit, the return loss at the center frequency point of the receiving coil reaches the maximum value to achieve the best matching. The present invention can effectively avoid the situation where the matching circuit cannot match, and improve the transmission efficiency of high-frequency signal energy.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic resonance imaging, and relates to an adaptive matching circuit for a magnetic resonance radio frequency coil and a matching method thereof. Background Art

[0002] As one of the important medical imaging technologies, magnetic resonance imaging is widely used in many fields such as scientific research and clinical medicine due to its advantages that other imaging technologies cannot match, such as high spatial resolution and good spatial positioning. The radio frequency coil is a functional unit in the magnetic resonance imaging system that implements radio frequency pulse excitation, receives and processes radio frequency signals. The performance indicators of the radio frequency coil directly affect the performance of the magnetic resonance imaging equipment and are related to the quality of the MRI signal (image). In the magnetic resonance imaging system, if the impedance of the radio frequency coil matches the impedance of the radio frequency transmission line, that is, the interface between the radio frequency coil and the radio frequency transmission line reflects the power of the radio frequency signal emitted by the radio frequency coil to the minimum, the radio frequency signal output power of the radio frequency coil can be guaranteed to be the maximum, thereby ensuring the quality of the magnetic resonance image.

[0003] In general, the impedance of the RF transmission line between the magnetic resonance RF coil and the RF amplifier is set to 50 ohms, so the impedance of the RF coil is also set to 50 ohms to achieve impedance matching between the RF coil and the RF transmission line. When the signal source and load impedance remain unchanged, a fixed matching circuit can meet the requirements, but in many cases, the impedance of the load will change with the change of the environment. For example, when the subject enters the cavity of the magnetic resonance imaging system, the subject induces RF eddy currents and consumes RF energy. At the same time, the subject and the RF coil form mutual inductance, which changes the equivalent inductance and resistance of the RF coil, thereby changing the impedance of the RF coil and causing impedance mismatch between the RF coil and the transmission line. If the electronic components such as capacitors and resistors in the matching circuit in the circuit use constant values, the original impedance matching unit between the input and output will no longer match, thereby reducing the energy transmission efficiency. In addition, the magnetic induction intensity of the magnet also changes with the change of temperature, which in turn causes the magnetic resonance frequency to change with the change of temperature, which may also cause mismatch.

[0004] At present, adaptive matching circuits are mainly used in the communication field, such as the receiving matching circuit of the antenna, but are rarely used in the magnetic resonance field. Therefore, in the field of magnetic resonance, an adaptive matching circuit is urgently needed to solve the above problems. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide an adaptive matching circuit and matching method for a magnetic resonance radio frequency coil, so as to solve the problem of mismatch between the center frequency and impedance of the radio frequency coil in the prior art. The matching circuit of the present invention can automatically detect the circuit adaptation status and adjust the matching circuit value in real time, thereby improving the transmission efficiency of high-frequency signal energy.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] Solution 1: An adaptive matching circuit for a magnetic resonance radio frequency coil, comprising a receiving coil, an adjustable matching circuit, a radio frequency switch, a return loss detection circuit and a single chip microcomputer control circuit;

[0008] The receiving coil is used to receive radio frequency signals;

[0009] The adjustable matching circuit is connected to the receiving coil to match the output impedance of the receiving coil to 50 ohms; and is connected to the radio frequency switch;

[0010] One end of the RF switch is connected to the adjustable matching circuit, and the other end is selectively connected to the output terminal or the detection circuit according to the signal fed back by the single-chip control circuit, thereby switching the signal flow direction;

[0011] When the return loss detection circuit is electrically connected to the radio frequency switch, it is used to detect the return loss of the adjustable matching circuit and transmit the return loss to the single chip control circuit;

[0012] The single-chip control circuit is electrically connected to the radio frequency switch, the return loss detection circuit and the adjustable matching circuit, receives and analyzes the return loss detected by the return loss detection circuit, determines whether the return loss value at the center frequency point of the receiving coil is the maximum value, and if so, the best match has been achieved, and controls the radio frequency switch to switch to the output terminal to output a signal; if not, changes the capacitance value of the variable capacitance diode in the adjustable matching circuit through the single-chip control circuit, detects the return loss value again, and repeats this process until the return loss value at the center frequency point of the receiving coil reaches the maximum value, that is, the best match is achieved;

[0013] The output terminal is used to deliver the output signal to the next stage (preamplifier).

[0014] Optionally, the return loss detection circuit mainly includes a directional coupler, a digital frequency synthesizer and a peak detector;

[0015] The directional coupler comprises four ports, namely, an input port, an output port, a coupling port and an isolation port. The input port is electrically connected to a digital frequency synthesizer, the output port is electrically connected to a radio frequency switch, and the coupling port and the isolation port are electrically connected to a peak detector respectively. The directional coupler distributes the power of the signal in a certain proportion by isolation and shunting, and outputs the power to the peak detector.

[0016] The digital frequency synthesizer is electrically connected to the single-chip microcomputer control circuit, is controlled by the single-chip microcomputer control circuit, and outputs a sine wave signal to the input end of the directional coupler;

[0017] The peak detector is used to detect the ratio of the reflected voltage to the incident voltage, calculate the magnitude of the return loss, and feed it back to the single chip control circuit.

[0018] Optionally, the adjustable matching circuit is a combination of a capacitor and a varactor diode, a combination of a capacitor and an inductor, or a connection combination of a capacitor, an inductor, and a microstrip line.

[0019] Optionally, the adjustable matching circuit is provided with a varactor diode or a capacitor array as one of the impedance conversion devices, and the single chip control circuit can achieve impedance matching by changing the voltage value applied to the varactor diode.

[0020] Optionally, the single-chip microcomputer control circuit includes a DAC circuit and a microprocessor; the microprocessor controls the voltage across the varactor diode through the DAC circuit according to a program algorithm.

[0021] Solution 2: An adaptive matching method for a magnetic resonance radio frequency coil, specifically comprising: after the radio frequency signal received by the receiving coil passes through an adjustable matching circuit, the signal flow direction is controlled by the radio frequency switch, and the radio frequency switch has two switching directions, one is directly output to the next stage (preamplifier), and the other is input to the return loss detection circuit; the switching direction of the radio frequency switch is controlled by a microprocessor, and when the return loss detected by the return loss detection circuit is fed back to the microprocessor, the microprocessor obtains the return loss value and determines whether the return loss value at the center frequency point of the receiving coil is a maximum value. If so, the best match has been achieved, and the radio frequency switch is controlled to switch to the output terminal to output the signal; if not, the output voltage of the DAC circuit is adjusted by the microprocessor, the voltage value of the varactor diode is changed, and the return loss value is detected again, and this is repeated until the return loss value at the center frequency point of the receiving coil reaches a maximum value, that is, the best match is achieved.

[0022] Further, the voltage value of the varactor diode is adjusted, specifically including: if the frequency of the maximum return loss currently detected is less than or greater than the center frequency of the receiving coil, the voltage across the varactor diode (D1, D2, D3) is adjusted, the voltage value of one of the varactor diodes is first increased, and it is determined whether the moving direction of the maximum point of the return loss curve is correct. If the moving direction of the maximum point is correct, the voltage value of each varactor diode is adjusted by a binary search method. If the moving direction of the maximum point is incorrect, the voltage value of the varactor diode is reduced, and the voltage value of each varactor diode is adjusted by a binary search method again, so that the return loss value at the center frequency point of the receiving coil reaches the maximum value, thereby achieving the best match.

[0023] The beneficial effects of the present invention are as follows: the adaptive matching circuit of the present invention automatically detects the circuit adaptation status through the return loss detection circuit to realize instant adaptive circuit matching, and adjusts the matching circuit value through the joint action of the adjustable matching circuit, the radio frequency switch, and the single-chip control circuit, which can effectively avoid the situation where the matching circuit cannot match and improve the transmission efficiency of high-frequency signal energy.

[0024] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 It is a principle framework diagram of the adaptive matching circuit of the present invention;

[0027] Figure 2 4 is a circuit diagram of an adaptive matching circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0029] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0030] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] See also Figure 1-2 , which is an adaptive matching circuit for a magnetic resonance radio frequency coil. Generally, the impedance of the radio frequency transmission line between the magnetic resonance radio frequency coil and the radio frequency amplifier is set to 50 ohms, so the impedance of the radio frequency coil is also set to 50 ohms to achieve impedance matching between the radio frequency coil and the radio frequency transmission line. When the subject enters the cavity of the magnetic resonance imaging system, the center frequency of the radio frequency signal will shift (decrease or increase), resulting in impedance mismatch between the receiving coil and the load unit.

[0032] like Figure 2 As shown, this embodiment provides an adaptive matching circuit for a magnetic resonance radio frequency coil, including: a receiving coil L1, an adjustable matching circuit, a radio frequency switch, a return loss detection circuit and a single-chip control circuit (including a microprocessor and a DAC circuit). Among them, the receiving coil L1 is used to realize the reception of radio frequency signals and is connected to the adjustable matching circuit. The adjustable matching circuit is used to match the output impedance of the receiving coil to 50 ohms and is connected to the radio frequency switch. The radio frequency switch is used to switch the signal flow direction and can send signals within the transmission path. It is arranged between the output terminal and the detection circuit. The return loss detection circuit is used to detect the return loss of the matching circuit and is connected to the single-chip control circuit. The single-chip control circuit receives and analyzes the return loss detected by the detection circuit, determines whether the return loss value at the center frequency point of the receiving coil is the maximum value, controls the radio frequency switch to select the direction to achieve the best matching, and is electrically connected to the radio frequency switch and the return loss detection circuit. The output terminal is used to output the signal to the next stage (preamplifier).

[0033] The detection circuit is mainly composed of a directional coupler, a digital frequency synthesizer and a peak detector, which is used to detect the return loss of the matching circuit and transmit the return loss to the single-chip microcomputer control circuit.

[0034] As a preferred embodiment, the adjustable matching circuit is composed of capacitors C1, C2, C3 and varactor diodes D1, D2, D3 to form a capacitor array, capacitor C1 is connected in parallel with varactor diode D1, capacitor C2 is connected in parallel with varactor diode D2, capacitor C3 is connected in parallel with varactor diode D3, and each parallel unit is connected in series. The receiving coil L1 is connected in parallel at both ends of the varactor diode D2. The single-chip microcomputer control circuit can achieve impedance matching by changing the voltage value applied to the varactor diode. In other implementations, the adjustable matching circuit can also be a combination of capacitors and inductors or a connection combination of capacitors, inductors, and microstrip lines.

[0035] The directional coupler is electrically connected to the RF switch. The directional coupler is composed of a transmission line and includes four ports: input, output, coupling, and isolation. The directional coupler distributes the power of the signal in a certain proportion through isolation and shunting, and outputs it to the peak detector.

[0036] The peak detector is used to detect the difference between the reflected voltage and the incident voltage, calculate the return loss through the difference, and feed it back to the single-chip control circuit. The digital frequency synthesizer is electrically connected to the single-chip control circuit, controlled by the single-chip control circuit, and outputs a sine wave signal to the input end of the directional coupler.

[0037] After the RF signal received by the receiving coil passes through the adjustable matching circuit, the signal flow is controlled by the RF switch. The RF switch has two switching directions, one is to directly output to the next stage (preamplifier), and the other is to input to the detection circuit. The switching direction of the RF switch is controlled by the microprocessor. The return loss detected by the return loss detection circuit is fed back to the microprocessor. After the microprocessor obtains the return loss value, it determines whether the return loss value at the center frequency point of the receiving coil is the maximum value. If so, the best match has been achieved, and the RF switch is controlled to switch to the output terminal to output the signal; if not, the DAC circuit output voltage is adjusted, the capacitance value of the varactor diode is changed, and the return loss value is detected again. This is repeated until the return loss value at the center frequency point of the receiving coil reaches the maximum value, that is, the best match is achieved.

[0038] like Figure 2As shown, after the RF signal received by the receiving coil passes through the adjustable matching circuit, the signal flow direction is controlled by the RF switch. The RF switch has two switching directions, one is directly output to the next stage (preamplifier), and the other is input to the return loss detection circuit. The switching direction of the RF switch is controlled by the microprocessor. When the return loss detected by the return loss detection circuit meets the requirements, the microprocessor controls the RF switch to directly input to the next stage, otherwise the RF switch switches to the detection circuit. The microprocessor controls the digital frequency synthesizer in the detection circuit and outputs a sine wave to the directional coupler. The directional coupler is composed of a transmission line, including four ports: input, output, coupling, and isolation. The directional coupler distributes the power of the signal in a certain proportion through isolation and shunting, and outputs it to the peak detection. The peak detection detects the ratio of the reflected voltage to the incident voltage, calculates the magnitude of the return loss, and feeds it back to the microprocessor. After obtaining the return loss value, the microprocessor determines whether the return loss value at the center frequency point of the receiving coil is the maximum value. If so, the best match has been achieved, and the RF switch is controlled to switch to the output terminal to output the signal; if not, the output voltage of the DAC circuit is adjusted, and the capacitance value of the variable capacitance diode is changed. If the maximum return loss is currently detected, the microprocessor will detect the maximum return loss. If the frequency of the value is less than or greater than the center frequency of the receiving coil, the voltage across the varactor diodes D1, D2, and D3 is increased or decreased. The voltage value of one of the varactor diodes is increased or decreased first, and the direction of movement of the maximum return loss value is determined according to the return loss curve. If the direction is correct, it is determined whether the voltage value of the varactor diode is increased or decreased. If not, the voltage value is adjusted in reverse (if it was originally increased, it is now decreased, and if it was originally decreased, it is now increased). After determining whether the voltage value of the varactor diode is increased or decreased, the binary method is used to adjust the output voltage of the DAC circuit, change the capacitance value of the varactor diode, and detect the return loss value again. This is repeated until the return loss value at the center frequency point of the receiving coil reaches the maximum value, that is, the best match is achieved.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An adaptive matching circuit for a magnetic resonance radio frequency coil, characterized in that: The matching circuit includes a receiving coil, an adjustable matching circuit, a radio frequency switch, a return loss detection circuit and a single-chip microcomputer control circuit; The receiving coil is used to receive radio frequency signals; The adjustable matching circuit is connected to the receiving coil and is used to match the output impedance of the receiving coil to 50 ohms; Connect with RF switch; One end of the RF switch is connected to the adjustable matching circuit, and the other end is selectively connected to the output terminal or the detection circuit according to the signal fed back by the single-chip control circuit, thereby switching the signal flow direction; When the return loss detection circuit is electrically connected to the radio frequency switch, it is used to detect the return loss of the adjustable matching circuit and transmit the return loss to the single chip control circuit; The single-chip control circuit is electrically connected to the radio frequency switch, the return loss detection circuit and the adjustable matching circuit, receives and analyzes the return loss detected by the return loss detection circuit, determines whether the return loss value at the center frequency point of the receiving coil is the maximum value, and if so, the best match has been achieved, and controls the radio frequency switch to switch to the output terminal to output a signal; if not, changes the capacitance value of the variable capacitance diode in the adjustable matching circuit through the single-chip control circuit, detects the return loss value again, and repeats this process until the return loss value at the center frequency point of the receiving coil reaches the maximum value, that is, the best match is achieved; The output terminal is used to transmit the output signal to the next stage; The return loss detection circuit includes a directional coupler, a digital frequency synthesizer and a peak detector; The directional coupler comprises four ports, namely, an input port, an output port, a coupling port and an isolation port. The input port is electrically connected to a digital frequency synthesizer, the output port is electrically connected to a radio frequency switch, and the coupling port and the isolation port are electrically connected to a peak detector respectively. The directional coupler distributes the power of the signal in a certain proportion by isolation and shunting, and outputs the power to the peak detector. The digital frequency synthesizer is electrically connected to the single-chip microcomputer control circuit, is controlled by the single-chip microcomputer control circuit, and outputs a sine wave signal to the input end of the directional coupler; The peak detector is used to detect the ratio of the reflected voltage to the incident voltage, calculate the magnitude of the return loss, and feed it back to the single chip control circuit.

2. The adaptive matching circuit according to claim 1, characterized in that: The adjustable matching circuit is a combination of a capacitor and a varactor diode, a combination of a capacitor and an inductor, or a connection combination of a capacitor, an inductor and a microstrip line.

3. The adaptive matching circuit according to claim 1, characterized in that: The adjustable matching circuit is provided with a varactor diode or a capacitor array as one of the impedance conversion devices, and the single chip control circuit realizes impedance matching by changing the voltage value applied to the varactor diode.

4. The adaptive matching circuit according to claim 1, characterized in that: The single chip control circuit comprises a DAC circuit and a microprocessor; the microprocessor controls the voltage across the varactor diode through the DAC circuit according to a program algorithm.

5. An adaptive matching method for a magnetic resonance radio frequency coil, characterized in that: The matching method is implemented by the adaptive matching circuit described in any one of claims 1 to 4, specifically: after the radio frequency signal received by the receiving coil passes through the adjustable matching circuit, the signal flow direction is controlled by the radio frequency switch, and the radio frequency switch has two switching directions, one is directly output to the next level, and the other is input to the return loss detection circuit; the switching direction of the radio frequency switch is controlled by a microprocessor, and when the return loss detected by the return loss detection circuit is fed back to the microprocessor, the microprocessor obtains the return loss value and determines whether the return loss value at the center frequency point of the receiving coil is the maximum value. If so, the best match has been achieved, and the radio frequency switch is controlled to switch to the output terminal to output the signal; if not, the output voltage of the DAC circuit is adjusted by the microprocessor, the voltage value of the varactor diode is changed, and the return loss value is detected again, and this is repeated until the return loss value at the center frequency point of the receiving coil reaches the maximum value, that is, the best match is achieved.

6. The adaptive matching method according to claim 5, characterized in that: The voltage value of the varactor diode is adjusted, specifically including: if the frequency of the maximum return loss currently detected is less than or greater than the center frequency of the receiving coil, the voltage across the varactor diode is adjusted, the voltage value of one of the varactor diodes is first increased, and it is determined whether the moving direction of the maximum point of the return loss curve is correct. If the moving direction of the maximum point is correct, the voltage value of each varactor diode is adjusted by a binary search method. If the moving direction of the maximum point is incorrect, the voltage value of the varactor diode is reduced, and then the voltage value of each varactor diode is adjusted by a binary search method, so that the return loss value at the center frequency point of the receiving coil reaches a maximum value, thereby achieving optimal matching.

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