CN115389991B - Metamaterial dynamic tuning system and method for magnetic resonance echo signal enhancement - Google Patents
Metamaterial dynamic tuning system and method for magnetic resonance echo signal enhancement Download PDFInfo
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- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
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Abstract
The invention relates to a metamaterial dynamic tuning system and method for enhancing magnetic resonance echo signals, comprising the following steps: a metamaterial formed by at least one structural unit, a transmitting coil of magnetic resonance equipment, a receiving coil of magnetic resonance equipment, a dynamic tuning device and a vector network analyzer. The invention can keep the metamaterial under the optimal resonance mode in the use process, namely the resonance frequency is consistent with the Larmor frequency, thereby realizing the highest imaging signal-to-noise ratio gain.
Description
Technical Field
The invention belongs to the technical field of magnetic resonance imaging, and relates to a metamaterial dynamic tuning system and method, in particular to a metamaterial dynamic tuning system and method for enhancing magnetic resonance echo signals.
Background
The magnetic resonance imaging is a non-invasive medical image examination technology, and has the advantages of no radioactivity, three-dimensional imaging, high spatial resolution, high soft tissue contrast and the like compared with other non-invasive medical imaging technologies (such as computed tomography, X-ray film and ultrasound). One key performance indicator of magnetic resonance imaging equipment is its imaging quality, so how to improve the imaging quality has been the focus of research in the development process of magnetic resonance imaging equipment.
One key factor of the image magnetic resonance imaging quality is the signal-to-noise ratio of the echo signal obtained during scanning, and better imaging quality can be obtained by higher signal-to-noise ratio. With the continuous development of meta-materials (meta-materials), in recent years, research has been started to try to apply the meta-materials to the enhancement of magnetic resonance imaging echo signals, and achieve a certain effect.
In 2001 Wiltshire et al used metamaterial based on swiss coil structural units for magnetic resonance echo signal enhancement. When the metamaterial is not used, the body coil cannot receive signals of the imaged palm in the imaging area, and after the metamaterial is placed under the palm, the body coil successfully receives signals which cannot be received originally. This result demonstrates the potential of metamaterials in magnetic resonance imaging signal enhancement. In 2008 Freire et al, a signal lens is realized by using a metamaterial with a negative refractive index, the result is that the metamaterial is matched with a surface coil for receiving for the first time, and a radio-frequency echo signal is focused by the signal lens with the negative refractive index, so that the signal-to-noise ratio of a received signal is improved by about 60%, and the improvement of the signal-to-noise ratio is lower. 2016 Slobozhanyuk et al designed a metamaterial matched with a high dielectric constant medium, the result was to arrange metal wires periodically into a two-layer plane, and then put them in a solution with high dielectric constant to form a loop. The magnetic field of the imaging region of the metamaterial surface is increased by about 2.5 times during imaging. Based on this effort, shchelokova et al in 2018 designed a tunable metamaterial. The metal wire is replaced by two layers of nested telescopic metal tubes, and the metal tubes can be stretched to a proper length and then placed in a solution, so that different resonance modes can be tuned in the use process, a better gain effect is realized, and the structure cannot be dynamically tuned in the imaging process. In 2019 Zhao X et al, a metamaterial based on a spiral structural unit is proposed, and the result is that a resonant ring is introduced into the metamaterial to realize a nonlinear gain effect of the metamaterial, so that the gain of the metamaterial to a signal can be automatically restrained in a transmission stage of a radio frequency signal, and the gain of the metamaterial to the signal can be automatically recovered in a receiving stage, so that the SNR of the surface area of the metamaterial is changed to 10-15 times that of the former one, and the design is more in line with the use scene of magnetic resonance imaging.
Luo Liuchun et al invent a magnetic signal enhancement device [ CN104459585A ] for magnetic resonance imaging, which employs a metamaterial having a plurality of artificial microstructures arranged in a periodic array, to enhance signals received by an antenna of a magnetic resonance imaging apparatus. Zheng Hairong et al invents a method for improving the performance of a multi-channel radio frequency coil [ CN105572612A ], by collecting the noise of each channel of the multi-channel radio frequency coil and calculating to obtain the noise coupling matrix thereof, and compensating the coupling deterioration of the multi-channel radio frequency coil by adopting the noise coupling matrix during image reconstruction, the purpose of improving the performance of the multi-channel radio frequency coil is achieved when the multi-channel radio frequency coil is added with magnetic metamaterials, and the signal to noise ratio of images is improved. A.p.s. blob et al invents a magnetic resonance imaging machine [ CN107835658A ], by spatially rearranging the magnetic and electric fields operating at radio frequencies by means of metamaterials used as electromagnetic field amplifiers made of a set of advantageously oriented conductors, in the region of the object to be examined, the radio frequency magnetic field is amplified resonantly, so that the signal-to-noise ratio in the magnetic resonance imaging increases. Liu Repeng et al invent a metamaterial [ CN102723608A ], wherein a structural unit is an open ring formed by a wiring of a conductive material, a patch inductor is connected in series with the wiring of the open ring, the structural unit is periodically attached to a nonmetallic substrate, and when the metamaterial has negative magnetic permeability, the response electromagnetic wave frequency is smaller, so that the requirement of a magnetic resonance imaging system on low frequency can be met, the receiving radio frequency magnetic field generated by magnetic resonance imaging is enhanced, and the signal-to-noise ratio of the magnetic resonance imaging is improved.
In summary, the current research results are mainly limited to the metamaterial structure, few results are explored on the characteristics of tunability, nonlinearity and the like, and no research results for dynamic tuning of the metamaterial for magnetic resonance enhancement exist. In practical application, the complex application scene can change the resonance frequency of the metamaterial, so that the metamaterial cannot work in the highest gain state in theoretical design, the signal cannot have the best enhancement effect, the image quality cannot be improved best, and therefore the metamaterial which cannot be tuned dynamically is insufficient in practical application.
No prior art patent document, which is the same as or similar to the present invention, was found after searching.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a metamaterial dynamic tuning system and method for enhancing a magnetic resonance echo signal, which can enable a metamaterial to be kept in an optimal resonance mode in the use process, namely the resonance frequency is consistent with the Larmor frequency, so that the highest imaging signal-to-noise ratio gain is realized.
The invention solves the practical problems by adopting the following technical scheme:
a metamaterial dynamic tuning system for magnetic resonance echo signal enhancement, comprising: the system comprises a metamaterial formed by at least one structural unit, a transmitting coil of magnetic resonance equipment, a receiving coil of the magnetic resonance equipment, a dynamic tuning device and a vector network analyzer;
the vector network analyzer is used for circularly and continuously measuring S parameters of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the dynamic tuning device in real time;
the output end of the dynamic tuning device is respectively connected with each structural unit in the metamaterial and is used for tuning the resonance mode of the metamaterial and tuning the system resonance frequency to be close to the larmor frequency;
the metamaterial is arranged between the object to be inspected and the receiving coil and is used for enhancing radio frequency echo signals during imaging.
Moreover, the dynamic tuning device comprises a digitally tunable capacitor and a controller; the output end of the vector network analyzer is connected with the controller, and is used for circularly and continuously measuring the S parameter of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the controller in the dynamic tuning device in real time; the output end of the controller is connected with the digital adjustable capacitor and is used for receiving the S parameter of the vector network analyzer in the scanning process of the magnetic resonance equipment imaging, and when a difference exists between the resonance frequency and the Larmor frequency during imaging, an additional state value is added according to the difference, a control signal for the digital adjustable capacitor is output, and the capacitance value of the digital adjustable capacitor is controlled; the digital adjustable capacitor is respectively connected with each structural unit in the metamaterial, and the resonance frequency of the metamaterial is tuned to the larmor frequency through adjustment of the digital adjustable capacitor.
The output of the receiving coil of the magnetic resonance system is connected to a vector network analyzer for transmitting excitation signals.
Furthermore, an input of a transmitting coil of the magnetic resonance device is connected with the vector network analyzer for receiving the response signal.
The structural unit is a solenoid type, birdcage plus medium type, conductor plus medium type structure formed by wires, or a Swiss coil type structure formed by conductor sheets.
A metamaterial dynamic tuning method for magnetic resonance echo signal enhancement, comprising the steps of:
step 1, before a scanning process of magnetic resonance imaging starts, a first port of a vector network analyzer transmits excitation signals required by measurement through a connected transmitting coil, a second port of the vector network analyzer receives response signals required by measurement through a connected receiving coil, and then the vector network analyzer obtains S parameters through the transmitted and received signals, and further calculates and obtains the resonance frequency of the system at the moment;
step 2, the vector network analyzer transmits the measurement result to a controller, and the controller calculates the control quantity by adopting a control strategy according to the difference value between the resonance frequency and the larmor frequency during imaging, and then outputs a control signal to a digital adjustable capacitor, and adjusts the capacitance value of the digital adjustable capacitor so as to reduce the difference value between the resonance frequency and the larmor frequency of the system;
and 3, repeatedly implementing the step 1, judging whether the difference value between the resonance frequency and the larmor frequency meets the requirement or not, and continuing the step 2 after the repeated step 1 if the difference value does not meet the requirement. If the requirements are met, the magnetic resonance imaging device performs the subsequent normal scanning flow.
The invention has the advantages and beneficial effects that:
1. the invention provides a metamaterial dynamic tuning system for enhancing a magnetic resonance echo signal, which can enable a metamaterial to be in an optimal resonance mode under the condition of causing resonance frequency change during scanning, realize the maximum echo signal gain effect, improve the signal-to-noise ratio of the magnetic resonance echo signal and improve the quality of magnetic resonance imaging.
2. The invention adopts the digital adjustable capacitor to realize the tuning of the metamaterial, and has the advantages of simple design, convenient adjustment and quick response compared with the mechanical type. The existing mechanical tunable metamaterial is relatively complex in metamaterial design, and the mechanical structure is adjusted through power driving, so that the metamaterial resonant mode is tuned, adjustment is inconvenient, and the response speed is low when the mechanical structure is adjusted.
3. The invention uses the vector network analyzer to measure the working state of the signal receiving and transmitting system, and can measure and obtain the system states of additional S parameters, impedance and the like besides the resonance mode, so that the controller obtains more input states when using more advanced control strategies (such as reinforcement learning control strategies) to realize more accurate, rapid and stable control.
Drawings
FIG. 1 is a schematic view of the overall structure of the device of the present invention;
FIG. 2 is an enlarged view of a portion of the metamaterial of FIG. 1;
reference numerals illustrate:
100-metamaterial; 201-a vector network analyzer; 202-a controller; 203-digitally tunable capacitance; a transmit coil of a 300-magnetic resonance apparatus; 400-receive coil of a magnetic resonance apparatus.
Detailed Description
Embodiments of the invention are described in further detail below with reference to the attached drawing figures:
a metamaterial dynamic tuning system for magnetic resonance echo signal enhancement, as shown in fig. 1 and 2, comprising: the system comprises a metamaterial formed by at least one structural unit, a transmitting coil of magnetic resonance equipment, a receiving coil of the magnetic resonance equipment, a dynamic tuning device and a vector network analyzer;
the vector network analyzer is used for circularly and continuously measuring S parameters of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the dynamic tuning device in real time;
the output end of the dynamic tuning device is respectively connected with each structural unit in the metamaterial and is used for tuning the resonance mode of the metamaterial and tuning the system resonance frequency to be close to the larmor frequency;
the metamaterial is arranged between the object to be inspected and the receiving coil and is used for enhancing radio frequency echo signals during imaging.
In this embodiment, the dynamic tuning device includes a digitally tunable capacitor and a controller; the output end of the vector network analyzer is connected with the controller, and is used for circularly and continuously measuring the S parameter of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the controller in the dynamic tuning device in real time; the output end of the controller is connected with the digital adjustable capacitor and is used for receiving the S parameter of the vector network analyzer in the scanning process of the magnetic resonance equipment imaging, and when a difference exists between the resonance frequency and the Larmor frequency during imaging, an additional state value is added according to the difference, a control signal for the digital adjustable capacitor is output, and the capacitance value of the digital adjustable capacitor is controlled; the digital adjustable capacitor is respectively connected with each structural unit in the metamaterial, and the resonance frequency of the metamaterial is tuned to the larmor frequency through adjustment of the digital adjustable capacitor.
In this embodiment, the output of the receiving coil of the magnetic resonance device is connected to a vector network analyzer for transmitting the excitation signal.
In this embodiment, an input end of a transmitting coil of the magnetic resonance apparatus is connected to the vector network analyzer, and is configured to receive the response signal.
In this embodiment, the structural units are solenoid-type, birdcage plus medium-type, conductor plus medium-type structures made of wires, or swiss coil-type structures made of conductor sheets.
A metamaterial dynamic tuning method for magnetic resonance echo signal enhancement, comprising the steps of:
step 1, before a scanning process of magnetic resonance imaging starts, a first port of a vector network analyzer transmits excitation signals required by measurement through a connected transmitting coil, a second port of the vector network analyzer receives response signals required by measurement through a connected receiving coil, and then the vector network analyzer obtains S parameters through the transmitted and received signals, and further calculates and obtains the resonance frequency of the system at the moment;
step 2, the vector network analyzer transmits the measurement result to a controller, and the controller calculates the control quantity by adopting a control strategy according to the difference value between the resonance frequency and the larmor frequency during imaging, and then outputs a control signal to a digital adjustable capacitor, and adjusts the capacitance value of the digital adjustable capacitor so as to reduce the difference value between the resonance frequency and the larmor frequency of the system;
and 3, repeatedly implementing the step 1, judging whether the difference value between the resonance frequency and the larmor frequency meets the requirement or not, and continuing the step 2 after the repeated step 1 if the difference value does not meet the requirement. If the requirements are met, the magnetic resonance imaging device performs the subsequent normal scanning flow.
The function and function of the individual components of the invention are further described below:
a dynamic metamaterial tuning system for enhancing magnetic resonance echo signals comprises a metamaterial formed by periodic or single structural units, a dynamic tuning device connected with the structural units, a vector network analyzer connected with the dynamic tuning device, a transmitting coil and a receiving coil of magnetic resonance equipment, and a controller, wherein the dynamic tuning device comprises a digital adjustable capacitor. Wherein:
the metamaterial is arranged between the object to be inspected and the receiving coil, and is used for enhancing radio frequency echo signals during imaging through resonance enhancement of radio frequency signals;
the digital adjustable capacitor is used for tuning the resonance mode of the metamaterial, each structural unit of the metamaterial is connected with one or more digital adjustable capacitors in parallel (one or more digital adjustable capacitors are connected in series with the structural unit which is not a medium), the capacitance value of the digital adjustable capacitor is changed, and the resonance mode of the metamaterial can be changed;
the vector network analyzer is used for measuring the working state of the magnetic resonance signal receiving and transmitting system, mainly measuring the S parameter of the system, and providing a feedback signal for the automatic tuning of the metamaterial by the subsequent controller, wherein the S parameter is defined in the theory of a signal transmission line;
the controller is used for executing the tuning process of the metamaterial, after the controller obtains a feedback signal provided by the vector network analyzer, the difference value between the resonance frequency and the Larmor frequency of the system at the moment is calculated, the difference value calculates a control quantity through a control algorithm, a control signal is output according to the control quantity, and the size of the digital adjustable capacitor is adjusted, so that the resonance frequency of the system changes towards the Larmor frequency until the resonance frequency of the system is tuned to be close to the Larmor frequency.
The vector network analyzer transmits an excitation signal required by measuring the S parameter to a connected transmitting coil through an excitation port, the transmitting coil converts the excitation signal into a radio frequency signal and transmits the radio frequency signal, the transmitted radio frequency signal passes through the metamaterial to obtain a regulated radio frequency signal, the radio frequency signal regulated by the metamaterial is received by a receiving coil to obtain a receiving signal, the received signal is received by the vector network analyzer as a response signal through a response port, the vector network analyzer calculates data such as the S parameter, the system impedance and the like through the excitation signal and the corresponding signal to serve as feedback data, the feedback data are transmitted to a controller, the feedback data calculate a control quantity through a control algorithm in the controller, the controller outputs the control signal to a digital adjustable capacitor according to the control quantity, the digital adjustable capacitor changes a capacitance value to a corresponding size according to the applied control signal, and the resonance mode of the metamaterial is changed by changing the capacitance value.
The working process of the invention is as follows:
before the scanning process of the magnetic resonance imaging starts, a first port of the vector network analyzer 201 transmits an excitation signal required for measurement through the connected transmitting coil 300, a second port of the vector network analyzer 201 receives a response signal required for measurement through the connected receiving coil 400, and then the vector network analyzer 201 obtains an S parameter through the transmitted and received signals, and further calculates and obtains the resonance frequency of the system at the moment.
In this embodiment, step 1 may further measure states such as impedance and gain of the system;
step 2, the vector network analyzer 201 transmits the measurement result to the controller 202, the controller 202 calculates the control quantity by adopting a control strategy according to the difference between the resonance frequency and the larmor frequency during imaging, and then outputs a control signal to the digital adjustable capacitor 203, and adjusts the capacitance value of the digital adjustable capacitor 203, so that the difference between the resonance frequency and the larmor frequency of the system is reduced.
In this embodiment, the control strategy in step 2 may use a PID controller, and only the difference between the resonance frequency and the larmor frequency is needed to control the control strategy, or a neuron controller and a reinforcement learning controller may be selected as the control strategy, and then the difference between the resonance frequency and the larmor frequency is removed, and other state values measured by the vector network analyzer 201 may be added to achieve a better control effect.
And 3, repeatedly implementing the step 1, judging whether the difference value between the resonance frequency and the larmor frequency meets the requirement or not, and continuing the step 2 after the repeated step 1 if the difference value does not meet the requirement. If the requirements are met, the magnetic resonance imaging device performs the subsequent normal scanning flow.
The working principle of the invention is as follows:
when the magnetic resonance imaging equipment scans different objects to be inspected, impedance of the objects to be inspected introduced into the radio frequency receiving and transmitting links can cause the resonance frequency of a radio frequency receiving and transmitting system comprising the metamaterial to change, so that the resonance frequency of the system is deviated from Larmor frequency, gain is greatly attenuated, and the problems can be caused by layer selection, deformation of the metamaterial and the like. The existing metamaterial cannot be dynamically tuned in the use process, so that the existing metamaterial cannot work in a resonance mode with the highest gain in the actual use process.
According to the metamaterial dynamic tuning system for enhancing the magnetic resonance echo signals, under the condition that the resonance frequency changes during scanning, the metamaterial can be in an optimal resonance mode, the maximum echo signal gain effect is achieved, the signal-to-noise ratio of the magnetic resonance echo signals is improved, and the quality of magnetic resonance imaging is improved.
It should be emphasized that the embodiments described herein are illustrative rather than limiting, and that this invention encompasses other embodiments which may be made by those skilled in the art based on the teachings herein and which fall within the scope of this invention.
Claims (4)
1. A metamaterial dynamic tuning system for magnetic resonance echo signal enhancement, characterized by: comprising the following steps: the system comprises a metamaterial formed by at least one structural unit, a transmitting coil of magnetic resonance equipment, a receiving coil of the magnetic resonance equipment, a dynamic tuning device and a vector network analyzer;
the vector network analyzer is used for circularly and continuously measuring S parameters of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the dynamic tuning device in real time;
the output end of the dynamic tuning device is respectively connected with each structural unit in the metamaterial and is used for tuning the resonance mode of the metamaterial and tuning the system resonance frequency to be close to the larmor frequency;
the metamaterial is arranged between the object to be inspected and the receiving coil and is used for enhancing radio frequency echo signals during imaging;
the dynamic tuning device comprises a digital adjustable capacitor and a controller; the output end of the vector network analyzer is connected with the controller, and is used for circularly and continuously measuring the S parameter of the system in the scanning process of the magnetic resonance equipment imaging and transmitting the measurement result to the controller in the dynamic tuning device in real time; the output end of the controller is connected with the digital adjustable capacitor and is used for receiving the S parameter of the vector network analyzer in the scanning process of the magnetic resonance equipment imaging, and when a difference exists between the resonance frequency and the Larmor frequency during imaging, an additional state value is added according to the difference, a control signal for the digital adjustable capacitor is output, and the capacitance value of the digital adjustable capacitor is controlled; the digital adjustable capacitor is respectively connected with each structural unit in the metamaterial, and the resonance frequency of the metamaterial is tuned to the larmor frequency through adjustment of the digital adjustable capacitor;
the method comprises the following steps:
step 1, before a scanning process of magnetic resonance imaging starts, a first port of a vector network analyzer transmits excitation signals required by measurement through a connected transmitting coil, a second port of the vector network analyzer receives response signals required by measurement through a connected receiving coil, and then the vector network analyzer obtains S parameters through the transmitted and received signals, and further calculates and obtains the resonance frequency of the system at the moment;
step 2, the vector network analyzer transmits the measurement result to a controller, and the controller calculates the control quantity by adopting a control strategy according to the difference value between the resonance frequency and the larmor frequency during imaging, and then outputs a control signal to a digital adjustable capacitor, and adjusts the capacitance value of the digital adjustable capacitor so as to reduce the difference value between the resonance frequency and the larmor frequency of the system;
step 3, repeatedly implementing the step 1, judging whether the difference value between the resonance frequency and the larmor frequency meets the requirement or not, if not, continuing to implement the step 2 after the repeated step 1; if the requirements are met, the magnetic resonance imaging device performs the subsequent normal scanning flow.
2. A metamaterial dynamic tuning system for magnetic resonance echo signal enhancement as in claim 1, wherein: the output end of the receiving coil of the magnetic resonance device is connected with the vector network analyzer and is used for receiving the response signals.
3. A metamaterial dynamic tuning system for magnetic resonance echo signal enhancement as in claim 1, wherein: the input end of the transmitting coil of the magnetic resonance device is connected with the vector network analyzer and is used for transmitting excitation signals.
4. A metamaterial dynamic tuning system for magnetic resonance echo signal enhancement as in claim 1, wherein: the structural units are solenoid-type, birdcage plus medium-type, conductor plus medium-type structures formed by wires or Swiss coil-type structures formed by conductor sheets.
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