Dual-frequency resonance circuit for magnetic resonance multi-core coil and design method

Abstract

The invention relates to a dual-frequency resonance circuit for a magnetic resonance multi-core coil and a design method, the dual-frequency resonance circuit comprises a single-frequency resonance circuit and a frequency dividing circuit, the frequency dividing circuit comprises an inductor and a capacitor, the inductor and the capacitor are connected in parallel, and the capacitor is connected with the single-frequency resonance circuit. The design method comprises the steps that a capacitor at a proper position in the circuit is selected as a capacitor C2, the parameter of an inductor L2 in the frequency dividing circuit is calculated, the ratio of the capacitor C1 to the capacitor C2 corresponds to the distance between two resonant frequencies, and the two resonant frequencies reach design positions by adjusting the ratio of the capacitor C1 to the capacitor C2; a frequency dividing circuit is used to realize input and output impedance matching; an adjustable capacitor or an adjustable inductor is arranged to finely adjust the resonant frequency and the input and output impedance; and iteratively using the frequency dividing circuit to form the radio frequency coil with three or more resonant frequencies. According to the coil, magnetic resonance scanning and imaging of various nuclides can be completed without replacing the coil, passive devices are used, and electromagnetic noise and electromagnetic interference are avoided.

Description

Technical Field

[0001] The invention relates to the field of multi-core magnetic resonance coils, and in particular to a dual-frequency resonance circuit and a design method for a magnetic resonance multi-core coil. Background Art

[0002] Magnetic resonance imaging technology has been widely used in medical clinical and scientific research fields. In recent years, in addition to hydrogen nuclear magnetic resonance, 19 F. 31 P. 23 Na, 13 C and 129 The acquisition and analysis of magnetic resonance signals of various nuclides such as Xe are gradually being applied. Since the resonance frequencies of different nuclides are different, magnetic resonance radio frequency coils of different frequencies need to be used accordingly. At present, the main methods used in clinical and scientific research include:

[0003] 1 is to design and use different RF coils for the resonance frequency of each nuclide, and each coil has only one resonance frequency, corresponding to different nuclides. The above method has the following disadvantages: (1) In the scenario where multiple nuclides need to be scanned simultaneously, the coils need to be replaced frequently, which is very inconvenient. (2) When different nuclides need to be scanned simultaneously and the positioning coordinates of the scanned person or object remain unchanged, it cannot meet the scanning requirements.

[0004] 2 Use active devices (such as diodes) to form an electronic switch control circuit, change the capacitance or inductance connected to the resonant circuit, change the resonant frequency of the RF coil, so that one RF coil can support two or more resonant frequencies, thereby completing the simultaneous scanning and imaging of multiple nuclides without changing the coil or the scanning positioning. The above method has the following disadvantages:

[0005] (1) The introduction of active devices into the RF resonant circuit makes the coil's own electronic noise relatively large. The signal generated by magnetic resonance is very small, and the signal-to-noise ratio of the coil is very high. The noise introduced by active devices will seriously affect the quality of the magnetic resonance signal. (2) The introduction of active devices requires the addition of a switch control circuit (such as the DC bias voltage required to turn on and off the diode). In addition to introducing noise, this type of circuit is also prone to external electromagnetic interference, making the received magnetic resonance signal completely unusable. At the same time, the coupling of the control circuit with the high-power transmission signal will also cause the magnetic resonance to work abnormally, affecting the stability of the RF coil, and may even burn out some components in the magnetic resonance system, including the RF coil, making the system inoperable.

[0006] Therefore, there is an urgent need for a coil with low noise interference that can realize simultaneous scanning and imaging of multiple nuclides. Summary of the invention

[0007] In order to solve the problems that the existing equipment is inconvenient to use and is interfered by noise when realizing magnetic resonance scanning of different nuclides, the present invention proposes a dual-frequency resonance design method and design method for a magnetic resonance multi-nuclear coil, a frequency division circuit composed of passive devices is placed in a radio frequency resonant circuit, so that a single-frequency resonance radio frequency coil is converted into a dual-frequency resonance radio frequency coil, and the frequency division circuit is iteratively used to form a radio frequency coil with three or more frequency resonances, without adding an additional control circuit, so that magnetic resonance scanning and imaging of multiple nuclides can be completed without replacing the coil and changing the scanning positioning.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present invention proposes a dual-frequency resonance circuit for a magnetic resonance multi-core coil, including a single-frequency resonance circuit, the single-frequency resonance circuit is connected to a frequency division circuit, the frequency division circuit includes an inductor and a capacitor, the inductor is connected in parallel with the capacitor, and the capacitor is connected to the single-frequency resonance circuit.

[0009] A second aspect of the present invention provides a design method for a dual-frequency resonance circuit for a magnetic resonance multi-core coil, comprising:

[0010] Step 1: design a single-frequency resonant circuit, the equivalent circuit of which includes coil wiring inductance L1, capacitor C1, capacitor C2 and coil wiring internal resistance R1, and set the resonant frequency to the middle value of the target dual frequencies;

[0011] Step 2: adding a frequency division circuit, the equivalent circuit of which includes an inductor L2, a capacitor C2 and an internal resistance R2 of the inductor L2, the inductor L2 and the capacitor C2 are connected in parallel to form a dual-frequency resonant radio frequency coil;

[0012] Step 3: Select a capacitor at a suitable position in the circuit as capacitor C2, and calculate the parameters of inductor L2 in the frequency division circuit;

[0013] Step 4: The ratio of the capacitor C1 to the capacitor C2 corresponds to the distance between the two resonant frequencies, and the two resonant frequencies are adjusted to reach the designed position by adjusting the ratio of the capacitor C1 to the capacitor C2;

[0014] Step 5: Use the frequency division circuit to achieve input and output impedance matching;

[0015] Step 6: Set the adjustable capacitor or adjustable inductor for fine-tuning the resonant frequency and input and output impedance during debugging and use;

[0016] Step 7: The frequency division circuit is used iteratively to form a radio frequency coil having three or more resonance frequencies.

[0017] Furthermore, the parameter calculation of the inductor L2 in the frequency division circuit in step 3 is shown in formulas (1) to (8):

[0018] ω1=2πf1 (1);

[0019] ω2=2πf2 (2);

[0020]

[0021] Among them, the dual resonance frequencies are f1 and f2, corresponding to the circular frequencies ω1 and ω2, and ω0 is the middle value of the target dual frequencies;

[0022] Since the internal resistance R1 of the coil wiring and the internal resistance R2 of the inductor L2 are very small, for the convenience of analysis, it is assumed that the internal resistance R1 of the coil wiring is 0, the internal resistance R2 is 0, and the circuit input impedance seen from the power supply end is shown in formula (4):

[0023]

[0024] Among them, ω = 2πf, which is the circular frequency corresponding to different frequencies f;

[0025] When the circuit works in the resonant state, the imaginary part of the impedance is zero. The internal resistance of the coil wiring is assumed to be R1 = 0, and the internal resistance R2 = 0, so Z = 0, that is:

[0026] ω 2 L2C1-(1-ω 2 L1C1)(1-ω 2 L2C2)=0 (5);

[0027] According to the coil wiring inductance L1, capacitor C1 and capacitor C2 series resonance at ω0 and the resonant frequency formula, we can get:

[0028]

[0029] According to the parallel resonance of inductor L2 and capacitor C2 at ω0 and the resonant frequency formula, we can get:

[0030]

[0031] Combining the above formula (6) and formula (7), we can get:

[0032]

[0033] The inductor L2 is connected in parallel at both ends of the capacitor C2, so that the local circuit composed of the inductor L2 and the capacitor C2 is parallel resonant at ω0. The circuit resonant frequency changes from ω0 to the dual resonant frequencies of ω1 and ω2 symmetrical with respect to ω0, thereby realizing a dual-frequency resonant RF coil supporting multi-nuclear magnetic resonance scanning.

[0034] Furthermore, the step 4 is as described in formulas (9) to (13):

[0035] Substituting formula (8) into formula (5) and simplifying it, we can get:

[0036]

[0037] Solve formula (9) with respect to ω 2 The quadratic equation of one variable can be obtained:

[0038]

[0039] By transforming formula (7), we can get:

[0040]

[0041] Substituting formula (11) into formula (10), we can obtain:

[0042]

[0043] Let C2 = αC1, where α is a real number greater than 0, and formula (12) is expressed as:

[0044]

[0045] Since the coil wiring inductance L1 is the inductance generated by the coil wiring, the design needs to select appropriate inductance C1 and inductance C2 to make the coil resonate at a suitable center frequency. Adjusting the inductance C1 can achieve an overall shift of the two frequencies, and adjusting the ratio of the inductance C1 to the inductance C2 can adjust the interval between the two frequencies.

[0046] Furthermore, the radio frequency coil having three or more resonance frequencies described in step 7 includes but is not limited to a single-channel coil, an orthogonal coil, a birdcage coil, a planar coil, and a phased array coil.

[0047] The method can be used for various magnetic resonance radio frequency coils, including single-channel coils, orthogonal coils, birdcage coils, flat coils and phased array coils. The single-frequency resonance radio frequency coil can be converted into a dual-frequency resonance coil by simply adding a frequency division circuit at a suitable position in the single-frequency resonance circuit of the original coil.

[0048] Furthermore, the step 5 also includes adding a frequency division circuit to the input and output matching circuit of the radio frequency coil to achieve multi-frequency input and output matching of the radio frequency coil.

[0049] Furthermore, the radio frequency coil is used for radio frequency signal transmission, radio frequency signal reception, and radio frequency signal transmission and reception.

[0050] Through the above technical solution, the beneficial effects of the present invention are:

[0051] 1. The present invention realizes multi-nuclear magnetic resonance scanning that supports multiple nuclides with the same coil, and there is no need to replace the coil during scanning, thus ensuring that the positioning coordinates of the scanned object (sample) are consistent during multi-nuclear scanning, and supporting multi-nuclear synchronous real-time scanning. A frequency division circuit is added to the single-frequency resonance circuit, capacitor C2 is connected in series with the single-frequency resonance circuit, and inductor L2 is connected in parallel at both ends of capacitor C2. The method of the present invention enables the parameters of inductor L2 to meet the needs of the frequency division circuit to form parallel resonance, so that the overall circuit achieves a frequency division effect, and the ratio of capacitor C1 to capacitor C2 is adjusted by the method of the present invention to change the interval between the two resonant frequencies. Based on the iterative use of this method, a radio frequency coil with three or more resonance frequencies is realized, thereby simultaneously supporting multi-nuclear magnetic resonance scanning and imaging of three or more nuclides.

[0052] 2. The present invention uses passive devices (capacitor C2 and inductor L2) to achieve frequency division resonance, avoiding the problem that active devices reduce the signal-to-noise ratio of the coil and affect the quality of the magnetic resonance signal. At the same time, the present invention does not require a control circuit, avoiding the problem that the control circuit is prone to noise, electromagnetic interference, and affects the stability of the coil and the magnetic resonance system. The present invention can be used for various magnetic resonance radio frequency coils including but not limited to single-channel coils, orthogonal coils, birdcage coils, flat coils, and phased array coils. According to the antenna reciprocity theorem, the magnetic resonance radio frequency coil designed by the present invention can be used as a radio frequency transmitting coil, a radio frequency receiving coil, and a radio frequency transmitting and receiving coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A flowchart of the steps of a dual-frequency resonance design method for a magnetic resonance multi-core coil according to the present invention;

[0054] Figure 2 An equivalent circuit of a single-frequency resonance radio frequency coil for a dual-frequency resonance design method of a magnetic resonance multi-core coil according to the present invention;

[0055] Figure 3 An equivalent circuit of a dual-frequency resonance radio frequency coil for a dual-frequency resonance design method of a magnetic resonance multi-core coil according to the present invention;

[0056] Figure 4 The circuit normalized frequency response characteristic diagram of the equivalent circuit of a single-frequency resonant radio frequency coil;

[0057] Figure 5 The circuit normalized frequency response characteristic diagram of the dual-frequency resonant radio frequency coil equivalent circuit;

[0058] Figure 6 The present invention is a schematic diagram of a four-channel dual-frequency resonant radio frequency receiving phased array coil circuit designed based on the method of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0060] Example 1

[0061] like Figures 1 to 6 As shown, a dual-frequency resonance circuit for a magnetic resonance multi-core coil includes a single-frequency resonance circuit, the single-frequency resonance circuit is connected to a frequency division circuit, the frequency division circuit includes an inductor and a capacitor, the inductor is connected in parallel with the capacitor, and the capacitor is connected to the single-frequency resonance circuit.

[0062] A design method for a dual-frequency resonance circuit for a magnetic resonance multi-core coil, comprising:

[0063] Step 1: Design a single-frequency resonant circuit, the equivalent circuit of which includes coil wiring inductance L1, capacitor C1, capacitor C2 and coil wiring internal resistance R1, and set the resonant frequency to the middle value of the target dual frequencies;

[0064] Step 2: adding a frequency division circuit, the equivalent circuit of which includes an inductor L2, a capacitor C2 and an internal resistance R2 of the inductor L2, the inductor L2 and the capacitor C2 are connected in parallel to form a dual-frequency resonant radio frequency coil;

[0065] Step 3: Select a capacitor at a suitable position in the circuit as capacitor C2, and calculate the parameters of inductor L2 in the frequency division circuit;

[0066] Step 4: The ratio of the capacitor C1 to the capacitor C2 corresponds to the distance between the two resonant frequencies, and the two resonant frequencies are adjusted to reach the designed position by adjusting the ratio of the capacitor C1 to the capacitor C2;

[0067] Step 5: Use the frequency division circuit to achieve input and output impedance matching;

[0068] Step 6: Set the adjustable capacitor or adjustable inductor for fine-tuning the resonant frequency and input and output impedance during debugging and use;

[0069] Step 7: Use the frequency division circuit iteratively to form a radio frequency coil with three or more resonant frequencies. The parameter calculation of the inductor L2 in the frequency division circuit described in step 3 is shown in formulas (1) to (8):

[0070] ω1=2πf1 (1);

[0071] ω2=2πf2 (2);

[0072]

[0073] Among them, the dual resonance frequencies are f1 and f2, corresponding to the circular frequencies ω1 and ω2, and ω0 is the middle value of the target dual frequencies;

[0074] Since the internal resistance R1 of the coil wiring and the internal resistance R2 of the inductor L2 are very small, for the convenience of analysis, it is assumed that the internal resistance R1 of the coil wiring is 0, the internal resistance R2 is 0, and the circuit input impedance seen from the power supply end is shown in formula (4):

[0075]

[0076] Among them, ω = 2πf, which is the circular frequency corresponding to different frequencies f;

[0077] When the circuit works in the resonant state, the imaginary part of the impedance is zero. The internal resistance of the coil wiring is assumed to be R1 = 0, and the internal resistance R2 = 0, so Z = 0, that is:

[0078] ω 2 L2C1-(1-ω 2 L1C1)(1-ω 2 L2C2)=0 (5);

[0079] According to the coil wiring inductance L1, capacitor C1 and capacitor C2 series resonance at ω0 and the resonant frequency formula, we can get:

[0080]

[0081] According to the parallel resonance of inductor L2 and capacitor C2 at ω0 and the resonant frequency formula, we can get:

[0082]

[0083] Combining the above formula (6) and formula (7), we can get:

[0084]

[0085] Substituting formula (8) into formula (5) and simplifying it, we can get:

[0086]

[0087] Solve formula (9) with respect to ω 2 The quadratic equation of one variable can be obtained:

[0088]

[0089] By transforming formula (7), we can get:

[0090]

[0091] Substituting formula (11) into formula (10), we can obtain:

[0092]

[0093] Let C2 = αC1, where α is a real number greater than 0, and formula (12) is expressed as:

[0094]

[0095] The radio frequency coils having three or more resonance frequencies described in step 7 include but are not limited to single-channel coils, orthogonal coils, birdcage coils, planar coils, and phased array coils.

[0096] The step 5 also includes adding a frequency division circuit to the input and output matching circuit of the radio frequency coil to achieve multi-frequency input and output matching of the radio frequency coil.

[0097] The radio frequency coil is used for radio frequency signal transmission, radio frequency signal reception, and radio frequency signal transmission and reception.

[0098] In the circuit design, first, the inductor L2 is not connected, so that the series resonant circuit composed of the coil wiring inductor L1, capacitor C1 and capacitor C2 resonates at ω0. The normalized frequency response characteristics of the circuit are as follows: Figure 4 shown.

[0099] Then connect the inductor L2 in parallel across the capacitor C2, so that the circuit composed of the inductor L2 and the capacitor C2 is in parallel resonance at ω0. The normalized frequency response characteristics of the circuit are as follows: Figure 5 As shown, compared Figure 4 and 5 , the circuit resonant frequency changes from ω0 to the dual resonant frequencies of ω1 and ω2 which are symmetrical relative to ω0.

[0100] like Figure 6 As shown, a four-channel dual-frequency resonant radio frequency receiving phased array coil is manufactured according to the method of the present invention. Figure 6 As shown by L1-L4, C5-C8, C9-C 12 The four frequency division circuits composed of the phased array coil realize the dual-frequency resonance of each channel. 12 It is an adjustable capacitor, which can fine-tune the distance between the two resonant frequencies. 12 The value of C also affects the overall position of the two resonant frequencies of the coil, which can be adjusted by 13 -C 16 Make corrections. 13 -C 16 Also used to fine tune the shift of the two resonant frequencies.

[0101] like Figure 6 Through L5-L8, C 17 -C 20 , C 21 -C 24 The four frequency division circuits can realize the dual-frequency matching output of the coil, among which C 21 -C24 As an adjustable capacitor, the output impedance of each channel can be fine-tuned separately.

[0102] In this embodiment, a four-channel phased array coil with dual-frequency resonance is realized by using passive devices, and suitable capacitance values ​​can be selected for multi-nuclear magnetic resonance systems with different field strengths, such as 1.5T, 3T, 7T, 9.4T, etc.

[0103] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A dual-frequency resonance circuit for a magnetic resonance multi-core coil, comprising a single-frequency resonance circuit, characterized in that: The single-frequency resonant circuit is connected to a frequency dividing circuit, the frequency dividing circuit includes an inductor and a capacitor, the inductor and the capacitor are connected in parallel, and the capacitor is connected to the single-frequency resonant circuit.

2. A design method for a dual-frequency resonance circuit for a magnetic resonance multi-core coil, characterized in that: include: Step 1: design a single-frequency resonant circuit, the equivalent circuit of which includes coil wiring inductance L1, capacitor C1, capacitor C2 and coil wiring internal resistance R1, and set the resonant frequency to the middle value of the target dual frequencies; Step 2: adding a frequency division circuit, the equivalent circuit of which includes an inductor L2, a capacitor C2 and an internal resistance R2 of the inductor L2, the inductor L2 and the capacitor C2 are connected in parallel to form a dual-frequency resonant radio frequency coil; Step 3: Select a capacitor at a suitable position in the circuit as capacitor C2, and calculate the parameters of inductor L2 in the frequency division circuit; Step 4: The ratio of the capacitor C1 to the capacitor C2 corresponds to the distance between the two resonant frequencies, and the two resonant frequencies are adjusted to reach the designed position by adjusting the ratio of the capacitor C1 to the capacitor C2; Step 5: Use the frequency division circuit to achieve input and output impedance matching; Step 6: Set the adjustable capacitor or adjustable inductor for fine-tuning the resonant frequency and input and output impedance during debugging and use; Step 7: The frequency division circuit is used iteratively to form a radio frequency coil having three or more resonance frequencies.

3. A dual-frequency resonance design method for a magnetic resonance multi-core coil according to claim 2, characterized in that: The parameter calculation of the inductor L2 in the frequency division circuit described in step 3 is shown in formulas (1) to (8): ω1=2πf1 (1); ω2=2πf2 (2); Among them, the dual resonance frequencies are f1 and f2, corresponding to the circular frequencies ω1 and ω2, and ω0 is the middle value of the target dual frequencies; Since the internal resistance R1 of the coil wiring and the internal resistance R2 of the inductor L2 are very small, for the convenience of analysis, it is assumed that the internal resistance R1 of the coil wiring is 0, the internal resistance R2 is 0, and the circuit input impedance seen from the power supply end is shown in formula (4): Among them, ω = 2πf, which is the circular frequency corresponding to different frequencies f; When the circuit works in the resonant state, the imaginary part of the impedance is zero. The internal resistance of the coil wiring is assumed to be R1 = 0, and the internal resistance R2 = 0, so Z = 0, that is: oh 2 L2C1-(1-v 2 L1C1)(1-ω 2 L2C2)=0 (5); According to the coil wiring inductance L1, capacitor C1 and capacitor C2 series resonance at ω0 and the resonant frequency formula, we can get: According to the parallel resonance of inductor L2 and capacitor C2 at ω0 and the resonant frequency formula, we can get: Combining the above formula (6) and formula (7), we can get:

4. The dual-frequency resonance design method for a magnetic resonance multi-core coil according to claim 2, characterized in that: The step 4 is as described in formulas (9) to (13): Substituting formula (8) into formula (5) and simplifying it, we can get: Solve formula (9) with respect to ω 2 The quadratic equation of one variable can be obtained: By transforming formula (7), we can get: Substituting formula (11) into formula (10), we can obtain: Let C2 = αC1, where α is a real number greater than 0, and formula (12) is expressed as:

5. The dual-frequency resonance design method for a magnetic resonance multi-core coil according to claim 2, characterized in that: The radio frequency coils having three or more resonance frequencies described in step 7 include but are not limited to single-channel coils, orthogonal coils, birdcage coils, planar coils, and phased array coils.

6. A dual-frequency resonance design method for a magnetic resonance multi-core coil according to claim 2, characterized in that: The step 5 also includes adding a frequency division circuit to the input and output matching circuit of the radio frequency coil to achieve multi-frequency input and output matching of the radio frequency coil.

7. The dual-frequency resonance design method for a magnetic resonance multi-core coil according to claim 2, characterized in that: The radio frequency coil is used for radio frequency signal transmission, radio frequency signal reception, and radio frequency signal transmission and reception.

Images