WO2024108679A1

WO2024108679A1 - Magnetic particle imaging method based on active filter and related device thereof

Info

Publication number: WO2024108679A1
Application number: PCT/CN2022/138214
Authority: WO
Inventors: 王海峰; 黄康健; 李烨; 朱燕杰; 梁栋; 郑海荣
Original assignee: 深圳先进技术研究院
Priority date: 2022-11-23
Filing date: 2022-12-09
Publication date: 2024-05-30
Also published as: CN115804583A

Abstract

Disclosed in the present application are a magnetic particle imaging method based on an active filter and a related device thereof, the method comprising: receiving a first excitation signal generated by a signal generator, amplifying the first excitation signal by means of a power amplifier, and outputting same to a driving coil so as to generate a varying magnetic field, the magnetic moment of magnetic nanoparticles inside the driving coil changing under the excitation of the varying magnetic field so as to generate a magnetic particle signal; receiving a current signal sensed by a receiving coil corresponding to the driving coil, the current signal comprising a second excitation signal and the magnetic particle signal, the second excitation signal being sensed by the receiving coil on the basis of the first excitation signal and having the same frequency as the first excitation signal; and performing signal processing on the current signal by means of an active twin-T notch filter so as to filter out the second excitation signal corresponding to a stop band of the active twin-T notch filter, and, on the basis of the remaining magnetic particle signal, reconstructing an image of magnetic particle concentration distribution. That is, the signal-to-noise ratio of magnetic particle imaging is improved, thereby achieving better imaging effect.

Description

Active filter-based magnetic particle imaging method and related equipment

The

Technical Field

The present application relates to the field of medical imaging, and in particular to a magnetic particle imaging method based on an active filter and related equipment.

Background technique

MPI imaging (Magnetic Particle Imaging) mainly uses a selection field to generate a field free region (Field Free Region, FFR), uses a focusing field to quickly move the field free region, and uses an excitation field (driving field) to stimulate the magnetic orientation of magnetic nanoparticles in the field free region to reverse and generate high-frequency harmonic signals. The high-frequency harmonic signals are received by a receiving coil, and the spatial distribution image of the concentration of magnetic nanoparticles inside a living body is obtained through image reconstruction.

In the process of magnetic particle imaging, interference signals need to be removed to ensure the accuracy of the reconstructed magnetic particle concentration distribution map. The current method of removing interference signals is to suppress the excitation signal through a band-stop filter. However, the general passive band-stop filter has a large stopband. While filtering the excitation signal, it also filters part of the magnetic particle signal. How to minimize the impact of the filter on the magnetic particle signal is a challenging task.

In order to filter the excitation signal, the commonly used methods are gradient receiving coils and cancellation methods. The cancellation method adds a signal with the same frequency and amplitude as the excitation signal but a phase difference of 180 degrees to the signal receiving chain. This method requires accurate phase adjustment to achieve better results. The gradient receiving coil method is to set the geometric structure of the coil to achieve a filtering effect. This method relies on the reasonable design of the coil and can only be applied to one-dimensional imaging devices.

technical problem

Therefore, the existing magnetic particle imaging has the problem of poor signal processing effect, which leads to a low imaging signal-to-noise ratio.

In view of this, the embodiments of the present application provide a magnetic particle imaging method based on an active filter and related equipment thereof, aiming to solve the technical problem of low signal-to-noise ratio of existing magnetic particle imaging.

Technical Solutions

The embodiment of the present application provides a magnetic particle imaging method based on an active filter, which is applied to a magnetic particle imaging system based on an active filter. The magnetic particle imaging system based on an active filter includes a signal generator, a power amplifier, and an active double-T notch filter. The method includes:

Receiving a first excitation signal generated by the signal generator, the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil change their magnetic moments under the excitation of the changing magnetic field, and generate magnetic particle signals;

receiving a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

The current signal is processed by the active twin-T notch filter to filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and an imaging diagram of the magnetic particle concentration distribution is reconstructed based on the retained magnetic particle signal.

In a possible implementation manner of the present application, the active filter-based magnetic particle imaging system further includes a low noise amplifier and an analog-to-digital converter.

The step of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstructing an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal comprises:

Performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal;

The magnetic particle signal is amplified by the low noise amplifier, and the processed magnetic particle signal is converted into a digital signal by the analog-to-digital converter;

An imaging diagram of the magnetic particle concentration distribution is reconstructed based on the digital signal.

In a possible implementation manner of the present application, the step of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal includes:

Acquiring a signal frequency of the first excitation signal;

Determining resistance values and capacitance values in the active twin-T notch filter according to the signal frequency;

Adjusting the quality factor of the active twin-T notch filter based on the resistance value and the capacitance value to obtain a magnetic particle signal after the active twin-T notch filter processes the current signal and corresponds to the quality factor with the highest value;

The quality factor represents the stopband size of the active twin-T notch filter.

In a possible implementation manner of the present application, it is characterized in that the active twin-T notch filter is composed of an RC low-pass filter, an RC high-pass filter and an operational amplifier feedback circuit.

In a possible implementation of the present application, the circuit diagram of the RC low-pass filter and the RC high-pass filter includes a first resistor, a second resistor, and the first resistor is connected to the positive pole of a power supply; the first resistor is connected in series with the second resistor, a first capacitor is connected between the first resistor and the second resistor, and the other end of the first capacitor is grounded; the first resistor is connected in parallel with a second capacitor, the second capacitor is connected in series with a third resistor, the third resistor is connected in parallel with the first capacitor, and the other end of the third resistor is grounded; the second resistor is connected in parallel with a third capacitor, the third capacitor is connected in series with the second capacitor, and the other end of the third resistor is grounded.

In a possible implementation of the present application, the operational amplifier feedback circuit includes a first amplifier and a second amplifier, the positive power supply terminal of the first amplifier is electrically connected to the output terminals of the second resistor and the third capacitor, and the negative power supply terminal of the first amplifier is electrically connected to the output terminal of the first amplifier; the output terminal of the first amplifier is connected in series with a fourth resistor and a fifth resistor, and the other end of the fifth resistor is grounded; the output terminal of the second amplifier is electrically connected to the output terminals of the first capacitor and the third resistor, the negative power supply terminal of the second amplifier is electrically connected to the output terminal of the second amplifier, and the positive power supply terminal of the second amplifier is electrically connected to the output terminal of the fourth resistor.

The present application also provides a magnetic particle imaging system based on an active filter, the system comprising: a signal generating subsystem and a signal receiving subsystem, the signal generating subsystem comprising a signal generator, a power amplifier and a driving coil, the signal generating subsystem being used to receive a first excitation signal generated by the signal generator, the first excitation signal being amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil have their magnetic moments changed under the excitation of the changing magnetic field, and a magnetic particle signal is generated;

The signal receiving subsystem includes an active twin-T notch filter, a receiving coil, a low noise amplifier and an analog-to-digital converter. The signal receiving subsystem is used to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal with the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal; the current signal is processed by the active twin-T notch filter to filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and an imaging diagram of the magnetic particle concentration distribution is reconstructed based on the retained magnetic particle signal.

The signal receiving subsystem is also used to perform signal processing on the current signal through the active twin-T notch filter, filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtain a filtered magnetic particle signal; amplify the magnetic particle signal through the low-noise amplifier, and convert the processed magnetic particle signal into a digital signal through the analog-to-digital converter; and reconstruct an imaging diagram of the magnetic particle concentration distribution based on the digital signal.

The present application also provides a magnetic particle imaging device based on an active filter, the device comprising:

A signal generating module, used for receiving a first excitation signal generated by the signal generator, wherein the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, and the magnetic nanoparticles in the driving coil change their magnetic moments under the excitation of the changing magnetic field, thereby generating a magnetic particle signal;

a signal receiving module, configured to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

An imaging module is used to perform signal processing on the current signal through the active twin-T notch filter, filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstruct an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal.

The present application also provides an active filter-based magnetic particle imaging device, which is a physical node device. The active filter-based magnetic particle imaging device includes: a memory, a processor, and a program of the active filter-based magnetic particle imaging method stored in the memory and executable on the processor. When the program of the active filter-based magnetic particle imaging method is executed by the processor, the steps of the active filter-based magnetic particle imaging method described above can be implemented.

To achieve the above-mentioned purpose, a computer-readable storage medium is also provided, on which a magnetic particle imaging program based on an active filter is stored. When the magnetic particle imaging program based on an active filter is executed by a processor, the steps of any of the above-mentioned magnetic particle imaging methods based on an active filter are implemented.

Beneficial Effects

The present application provides a magnetic particle imaging method based on an active filter and related equipment thereof, receiving a first excitation signal generated by the signal generator, the first excitation signal being amplified by the power amplifier and output to the driving coil to generate a variable magnetic field, the magnetic nanoparticles in the driving coil change their magnetic moment under the excitation of the variable magnetic field, and generate a magnetic particle signal; receiving a current signal induced by a receiving coil corresponding to the driving coil, the current signal including a second excitation signal of the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal; performing signal processing on the current signal through the active double-T notch filter, filtering out the second excitation signal corresponding to the stopband of the active double-T notch filter, and reconstructing an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal. That is, in the present application, the excitation signal is processed by the active double-T notch filter, and through the narrow stopband bandwidth characteristics of the active double-T notch filter, only the frequency signal within the stopband can be filtered, and other frequencies are little affected, so the magnetic particle signal can be better restored, the imaging signal-to-noise ratio is improved, and a better imaging effect is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic flow chart of a first embodiment of a magnetic particle imaging method based on an active filter of the present application;

FIG2 is a schematic diagram of a framework of a magnetic particle imaging system based on an active filter according to an embodiment of the present application;

FIG3 is a circuit diagram of an active double-T notch filter of an embodiment of a magnetic particle imaging method based on an active filter of the present application;

4 is a comparison diagram of the amplitude-frequency characteristics of an active twin-T notch filter and a passive twin-T notch filter in an embodiment of a magnetic particle imaging method based on an active filter of the present application;

5 is a comparison diagram of signal spectrum distribution of an active twin-T notch filter and a passive twin-T notch filter in an embodiment of a magnetic particle imaging method based on an active filter of the present application;

FIG6 is a schematic diagram of the device structure of the hardware operating environment involved in the embodiment of the present application;

FIG. 7 is a schematic diagram of functional modules of a preferred embodiment of a magnetic particle imaging device based on an active filter of the present application.

Embodiments of the present invention

It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

The embodiment of the present application provides a magnetic particle imaging method based on an active filter. In one embodiment of the magnetic particle imaging method based on an active filter of the present application, the method is applied to a magnetic particle imaging device based on an active filter. Referring to FIG. 1 , the method includes:

Step S10, receiving a first excitation signal generated by the signal generator, wherein the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, and the magnetic nanoparticles in the driving coil change their magnetic moments under the excitation of the changing magnetic field, thereby generating a magnetic particle signal;

Step S20, receiving a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

Step S30, performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstructing an imaging map of the magnetic particle concentration distribution based on the retained magnetic particle signal.

The present embodiment aims to process the signal of the magnetic particle imaging system through an active twin-T notch filter. Due to the narrow stopband bandwidth characteristic of the active twin-T notch filter, only the frequency signal within the stopband can be filtered, which has little effect on the magnetic particle signal, thereby solving the problem of low signal-to-noise ratio of magnetic particle imaging.

Specifically, in the present application, the magnetic particle imaging system includes a signal generator, a power amplifier, and an active double-T notch filter. The power amplifier amplifies the excitation signal generated by the signal generator, and the amplified excitation signal is filtered through the stopband of the active double-T notch filter, retaining the magnetic particle signal and reconstructing the imaging diagram of the magnetic particle concentration distribution. Thus, the excitation signal is processed by the active double-T notch filter, and the narrow stopband bandwidth characteristics of the active double-T notch filter can only filter the frequency signal within the stopband, and the effect on other frequencies is very small, so the magnetic particle signal can be better restored, the imaging signal-to-noise ratio is improved, and a better imaging effect is achieved.

In this embodiment, the specific application scenarios are:

In view of the above reasons, the methods commonly used to filter the excitation signal at present are gradient receiving coils and cancellation methods. The cancellation method is to add a signal with the same frequency and amplitude as the excitation signal but a phase difference of 180 degrees in the signal receiving chain. This method requires accurate phase adjustment to achieve better results. The method of gradient receiving coils is to set the geometric structure of the coil to achieve the filtering effect. This method depends on the reasonable design of the coil and can only be applied to one-dimensional imaging equipment. Therefore, there is a problem of poor signal processing effect in the existing magnetic particle imaging, which leads to a low imaging signal-to-noise ratio.

As an example, the active filter-based magnetic particle imaging method can be applied to an active filter-based magnetic particle imaging system, and the active filter-based magnetic particle imaging system is applied to an active filter-based magnetic particle imaging device.

As an example, a magnetic particle imaging system based on an active filter includes a signal generating subsystem and a signal receiving subsystem. The signal generating subsystem includes a signal generator, a power amplifier and a driving coil, and the signal receiving subsystem includes an active twin-T notch filter, a receiving coil, a low noise amplifier and an analog-to-digital converter.

As an example, a signal generator is used to generate an excitation signal, which is also an input signal. It mainly works by reducing the square wave frequency and superimposing the voltage. In sequential logic circuits, it is also called the internal output signal of the combinational circuit.

As an example, a power amplifier is an amplifier that can produce maximum power output to drive a load (such as a speaker) under given distortion conditions.

As an example, an active twin-T notch filter belongs to a notch filter, which is also a type of band-stop filter. The advantage of a notch filter over a general band-stop filter is that it has very good cutoff characteristics and a small stopband. Therefore, it can filter out the excitation signal, but has less impact on the magnetic particle signal than a general band-stop filter, and can better retain the signal generated by the magnetic particles and reduce distortion, which is very important for the reconstruction method based on X-space.

As an example, a notch filter is a filter that can quickly attenuate the input signal at a certain frequency point to achieve a filtering effect that blocks the passage of this frequency signal. Notch filters are specifically used to filter special frequency signals in circuits and are widely used. For example, in the amplification circuits of weak signals such as artificial seismic signals, electrocardiogram signals, and electroencephalogram signals, notch filters are used to suppress the 50Hz power frequency interference signal of the mains. In television image signal processing circuits, notch filters are used to reduce the interference of sound signals. In magnetic particle imaging, we usually need to filter the excitation signal. The frequency of this excitation signal is usually fixed or has only a small change, which is very consistent with the characteristics of the notch filter. Moreover, the notch filter has a very narrow stopband and has very little effect on the magnetic particle signal. Therefore, the notch filter is very suitable for filtering the excitation signal in the signal receiving chain of magnetic particle imaging.

As an example, in an active filter, the frequency range in which the signal can pass is called the passband; conversely, the frequency range in which the signal is greatly attenuated or completely suppressed is called the stopband; the dividing frequency between the passband and the stopband is called the cutoff frequency.

Among them, the faster the amplitude of the excitation signal decreases, the better the cutoff characteristics. Compared with the general band-stop filter, the notch filter with good cutoff characteristics and small stopband has a better filtering effect on the excitation signal, and has less impact on the magnetic particle signal than the general band-stop filter, which can better retain the signal generated by the magnetic particles and reduce distortion.

As an example, the magnetic particle imaging system based on active filter is applied in MPI scanner, which can be used for spectrum analysis and two-dimensional imaging. Referring to FIG2, FIG2 is a schematic diagram of the framework of the magnetic particle imaging system based on active filter. The signal generator is connected to the power amplifier, which is connected to the magnetic field coil. The other end of the magnetic field coil is connected to the active twin-T notch filter, which is then connected to the ADC (Analog-to-digital converter).

As an example, the magnetic field coil includes a drive coil and a receive coil, the drive coil is connected to a power amplifier, and the receive coil is connected to an active double-T notch filter. The receive coil uses a gradient receive coil.

Specific steps are as follows:

Step S10, receiving a first excitation signal generated by the signal generator, the first excitation signal is amplified by the power amplifier and output to the drive coil to generate a changing magnetic field, the magnetic nanoparticles in the drive coil change their magnetic moment under the excitation of the changing magnetic field, and generate a magnetic particle signal.

As an example, a signal generator is a device that generates various signals. As a signal source, it provides a measurement signal with a specific frequency or spectrum and a suitable amplitude to stimulate the circuit under test. In the process of testing and adjusting electronic circuits, it is often necessary to input a signal that simulates the operation of the circuit, which requires the use of a signal generator.

As an example, a first excitation signal is generated by a signal generator, and the active filter-based magnetic particle imaging system receives the real-time first excitation signal to scan and process the first excitation signal.

As an example, according to the stop band and cut-off characteristics of the active twin-T notch filter and experiments, it is determined that the filtering effect of the excitation signal of 20 kHz is the best. Therefore, the signal generator generates a first excitation signal of 20 kHz.

Step S20: receiving a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal.

As an example, after the first excitation signal is amplified by a power amplifier, the magnetic field coil generates a current signal, which includes a second excitation signal with the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal.

Among them, the magnetic particle signal, such as the signal of ferroferric oxide, is emitted through the excitation signal of the magnetic coil, and the magnetic particles are formed in the coil to form a magnetic particle signal.

As an example, the driving coil generates an alternating magnetic field or a strong changing magnetic field. The magnetic moment of the magnetic nanoparticles in the driving coil changes under the excitation of the changing magnetic field, generating a magnetic particle signal. The change in the magnetic flux of the magnetic field coil caused by the change in the magnetic moment of the magnetic particles of the excitation signal and the magnetic particle signal will induce a current signal in the receiving coil.

As an example, compared with a passive notch filter, an active twin-T notch filter is formed by using an operational amplifier based on a twin-T network and adding appropriate feedback.

Among them, the passive notch filter is composed of an RC low-pass filter and an RC high-pass filter in parallel, but this passive twin-T network has a small input impedance and a large output impedance, is easily affected by the previous and next stages of the circuit, has poor cutoff characteristics, and has a low Q value (quality factor).

As an example, the quality factor (Q value) is a basic parameter that characterizes the characteristics of the resonant circuit in an electronic circuit. That is, the quality factor or Q factor is an electromagnetic quantity that represents the ratio of the energy stored in an energy storage device (e.g., an inductor, an inductor, a capacitor, etc.), a resonant circuit, to the energy lost in each cycle; the Q value of a reactive element in a series resonant circuit is equal to the ratio of its reactance to its equivalent series resistance; the larger the Q value of an element, the better the selectivity of the circuit or network formed with the element.

For removing interference signals, the larger the Q value, the smaller the stopband of the corresponding filter, which can filter a large number of excitation signals and better retain the magnetic particle signal, thereby improving the signal filtering effect.

As an example, the active filter-based magnetic particle imaging system further includes a low noise amplifier and an analog-to-digital converter, and the steps of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstructing an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal include:

Step S31, performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal;

Step S32, amplifying the magnetic particle signal by the low noise amplifier, and converting the processed magnetic particle signal into a digital signal by the analog-to-digital converter;

Step S33: reconstructing an imaging diagram of the magnetic particle concentration distribution based on the digital signal.

As an example, the stop band refers to a frequency range, and the frequency range in which the signal in the active twin-T notch filter is greatly attenuated or completely suppressed is the stop band of the active twin-T notch filter.

Normally, the frequency of the excitation signal in the magnetic particle imaging scanner based on the active filter is 20kHz, and the frequency of the magnetic particle signal is much greater than the excitation signal (for example, the frequency of the magnetic particle signal is 40kHz, 60kHz, 100kHz, etc.). The active double-T notch filter can filter out the excitation signal in the signal receiving chain of the magnetic particle imaging system based on the active filter, but has little effect on the magnetic particle signal, retaining more of the magnetic particle signal, thereby improving the signal-to-noise ratio of the imaging.

As an example, the active twin-T notch filter filters the current signal induced by the receiving coil, and the second excitation signal is greatly reduced, thereby filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter to obtain a filtered magnetic particle signal. The filtered signal is amplified to a preset range by a low-noise amplifier, and then converted into a digital signal by an ADC, and a magnetic particle concentration distribution map is reconstructed based on the digital signal.

The present application provides a magnetic particle imaging method based on an active filter and related equipment thereof. Compared with the current magnetic particle imaging based on an active filter having a low signal-to-noise ratio, the present application is applied to a magnetic particle imaging system based on an active filter, the magnetic particle imaging system based on an active filter comprising a signal generator, a power amplifier, and an active double-T notch filter. The method comprises: receiving a first excitation signal generated by the signal generator, the first excitation signal being amplified by the power amplifier and output to a driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil having a magnetic moment changed under the excitation of the changing magnetic field, and generating a magnetic particle signal; receiving a current signal induced by a receiving coil corresponding to the driving coil, the current signal comprising a second excitation signal with the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal; performing signal processing on the current signal through the active double-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active double-T notch filter, and reconstructing an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal. That is, in the present application, the excitation signal is processed by an active twin-T notch filter. Due to the narrow stopband bandwidth characteristics of the active twin-T notch filter, only the frequency signal within the stopband can be filtered, and other frequencies are little affected. Therefore, the magnetic particle signal can be better restored, the imaging signal-to-noise ratio is improved, and a better imaging effect is achieved.

Based on the above first embodiment of a magnetic particle imaging method based on an active filter, a second embodiment of a magnetic particle imaging method based on an active filter is proposed.

The active twin-T notch filter is composed of an RC low-pass filter, an RC high-pass filter and an operational amplifier feedback circuit.

As an example, a general passive notch filter is composed of an RC low-pass filter and an RC high-pass filter in parallel. However, this passive twin-T network has a small input impedance and a large output impedance. It is easily affected by the circuit stages before and after, has poor cutoff characteristics, and has a low Q value. Although high-order passive notch filters achieve good filtering effects and high Q values, they are difficult to apply in practice due to the complexity of the circuit and the special parameter values of the components. Usually, the excitation signal in a magnetic particle imaging scanner is around 20kHz. At this time, the center frequency of the notch filter is high and the bandwidth is large. The signal of the magnetic particles may be affected and it is not suitable for direct use. In this study, we use an operational amplifier based on a twin-T network and add appropriate feedback to form an active twin-T notch filter.

As an example, referring to Figure 3, the circuit diagram of the RC low-pass filter and the RC high-pass filter includes a first resistor R1, a second resistor R2, and the first resistor R1 is connected to the positive electrode of the signal source input; the first resistor R1 is connected in series with the second resistor R2, and a first capacitor C1 is connected between the first resistor R1 and the second resistor R2, and the other end of the first capacitor C1 is grounded; the first resistor R1 is connected in parallel with the second capacitor C2, and the second capacitor C2 is connected in series with a third resistor R3, the third resistor R3 is connected in parallel with the first capacitor C1, and the other end of the third resistor R3 is grounded; the second resistor R2 is connected in parallel with the third capacitor C3, the third capacitor C3 is connected in series with the second capacitor C2, and the other end of the third capacitor C3 is grounded.

The twin-T network of a common twin-T notch filter consists of one resistor and two capacitors (such as the circuit consisting of the third resistor R3, the second capacitor C2 and the third capacitor C3 in FIG3 ), and the other consists of two resistors and one capacitor to form another T-type filter (such as the circuit consisting of the first resistor R1, the second resistor R2 and the first capacitor C1 in FIG3 ).

The traditional symmetrical passive twin-T network can only give a 1/4 notch point of the Q value. When filtering the excitation signal for the magnetic particle imaging system, the low Q value cannot achieve the filtering effect. Therefore, on the basis of the passive twin-T notch filter, the operational amplifier (that is, the operational amplifier feedback circuit is used) forms an active twin-T notch filter to improve the Q value.

As an example, referring to Figure 3, the operational amplifier feedback circuit includes a first amplifier A1 and a second amplifier A2. The positive power supply terminal of the first amplifier A1 is electrically connected to the output terminals of the second resistor R2 and the third capacitor C3, and the negative power supply terminal of the first amplifier A1 is electrically connected to the output terminal of the first amplifier A1; the output terminal of the first amplifier A1 is connected in series with a fourth resistor Ra and a fifth resistor Rb, and the other end of the fifth resistor Rb is grounded; the output terminal of the second amplifier A2 is electrically connected to the output terminals of the first capacitor C1 and the third resistor R3, the negative power supply terminal of the second amplifier A2 is electrically connected to the output terminal of the second amplifier A2, and the positive power supply terminal of the second amplifier A2 is electrically connected to the output terminal of the fourth resistor Ra.

In this embodiment, the longitudinal arm of the twin-T network is connected to the output end of the first amplifier A1. The first amplifier A1 feeds back part of the output signal of the second amplifier A2 to the longitudinal arm of the twin-T network to form a bootstrap, thereby introducing positive feedback, and the Q value will increase with the increase of the feedback amount, so that the stop band of the notch filter becomes narrower and the Q value is improved.

When the fifth resistor Rb=0, that is, there is no positive feedback, the active trap becomes a passive trap, Q=1/4. The closer K is to 1, the greater the Q value. By adjusting the voltage divider ratio of the fourth resistor Ra and the fifth resistor Rb, the Q value can be effectively adjusted. In actual design, in order to facilitate the adjustment of the voltage divider ratio of the fourth resistor Ra and the fifth resistor Rb to achieve the purpose of adjusting the Q value, the fourth resistor Ra and the fifth resistor Rb are replaced with variable resistors, so as to achieve the purpose of continuously changing the Q value by sliding the variable resistor.

Therefore, in the circuit diagram of the active twin-T notch filter, a narrow stopband width can be achieved by increasing the Q value, but generally speaking, the Q value should not be too high, because a high Q value is prone to center frequency oscillation and abnormal phase-frequency characteristics. Therefore, the Q value takes a reasonable value, which can be obtained through experiments and is not specifically limited here.

Based on the first embodiment or the second embodiment of the magnetic particle imaging method based on an active filter, a third embodiment of the magnetic particle imaging method based on an active filter is proposed.

As an example, the step of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal includes:

Step S311, obtaining the signal frequency of the first excitation signal;

Step S312, determining the resistance value and the capacitance value in the active twin-T notch filter according to the signal frequency;

Step S313, adjusting the quality factor of the active twin-T notch filter based on the resistance value and the capacitance value, and obtaining a magnetic particle signal after the active twin-T notch filter processes the current signal and corresponds to the quality factor with the highest value;

As an example, the signal frequency of the first excitation signal generated by the signal generator is usually about 20kHz. The signal frequency of the first excitation signal is obtained, and according to the signal frequency, the resistance value and the capacitance value in the source twin-T notch filter can be determined to adjust the quality factor (i.e., Q value) in the active twin-T notch filter. The higher the Q value, the smaller the stop band of the source twin-T notch filter, so it can filter out the excitation signal, and the impact on the magnetic particle signal is smaller than that of a general band-stop filter, which can better retain the magnetic particle signal and reduce distortion.

As an example, the frequency characteristic of an active twin-T notch filter can be expressed as:

when hour, , then it is called is the resonant frequency of the twin-T notch filter. The cut-off characteristics on both sides are very good, so the filter has a good frequency The signal has good filtering ability.

In MPI, the excitation signal is usually around 20kHz. According to the above formula, we can determine the values of R and C. For convenience, we set C=10nF, R=800Ω, as shown in Figure 3. Based on the circuit diagram of the active twin-T notch filter, the value of the quality factor Q can be adjusted by adjusting the parameters of components such as resistors and capacitors.

in, .

The larger the Q value, the smaller the stopband of the active twin-T notch filter. That is, the signal of the active twin-T notch filter is less attenuated in high-order harmonics. This is because the active narrow stopband bandwidth only filters the frequency signal within the stopband and has little effect on other frequencies, so the signal of the magnetic particles can be better restored.

As an example, for the amplitude-frequency characteristics of the filter, we first used circuit drawing software (such as Multisim14 software) to perform circuit simulation, and the amplitude-frequency characteristics simulation results are shown in Figure 4. Figure 4 is the amplitude-frequency characteristics of the active twin-T notch filter. Among them, the upper line active twin-T filter in Figure 4 is the active twin-T notch filter, and the lower line passive twin-T filter is the passive twin-T notch filter.

A first difference between the middle value of the amplitude-frequency decreasing portion of the active twin-T notch filter and the middle value of the amplitude-frequency increasing portion of the active twin-T notch filter, and a second difference between the middle value of the amplitude-frequency decreasing portion of the passive twin-T notch filter and the middle value of the amplitude-frequency increasing portion of the passive twin-T notch filter, the first difference is significantly smaller than the second difference.

The experimental results show that the center frequency of the active twin-T notch filter is about 19.9kHz. Obviously, compared with the passive twin-T notch filter, the active twin-T notch filter has a narrower stopband bandwidth and better cutoff characteristics.

As an example, actual signal verification is performed in the MPI scanner, and a passive twin-T notch filter and an active twin-T notch filter are used for comparison. After the MPI scanner acquires the signal, Fourier transform is performed to obtain the spectrum distribution of the signal, and the result is shown in Figure 5. Among them, in the amplitude frequency of the same frequency signal in Figure 5, the left side is the data of the active twin-T notch filter, and the right side is the data of the passive twin-T notch filter.

The test results show that the signal using the active twin-T notch filter has less attenuation in high-order harmonics. This is because the active twin-T notch filter has a narrow stopband bandwidth. It only filters the frequency signal within the stopband and has little effect on other frequencies. Therefore, it can better restore the signal of the magnetic particles. In turn, the signal-to-noise ratio of magnetic particle imaging is improved, achieving better imaging effects.

Based on the above embodiment of a magnetic particle imaging method based on an active filter, a fourth embodiment of a magnetic particle imaging method based on an active filter is proposed.

A magnetic particle imaging system based on an active filter comprises a signal generating subsystem and a signal receiving subsystem.

The signal generation subsystem includes a signal generator, a power amplifier and a driving coil. The signal generation subsystem is used to receive a first excitation signal generated by the signal generator. The first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field. The magnetic moment of the magnetic nanoparticles in the driving coil changes under the excitation of the changing magnetic field, thereby generating a magnetic particle signal.

The signal receiving subsystem includes an active twin-T notch filter, a receiving coil, a low noise amplifier and an analog-to-digital converter. The signal receiving subsystem is used to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal with the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal; the current signal is processed by the active twin-T notch filter, the second excitation signal corresponding to the stop band of the active twin-T notch filter is filtered out, and an imaging diagram of the magnetic particle concentration distribution is reconstructed based on the retained magnetic particle signal.

The signal receiving subsystem is also used to process the current signal through an active twin-T notch filter, filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtain a filtered magnetic particle signal; amplify the magnetic particle signal through a low-noise amplifier, and convert the processed magnetic particle signal into a digital signal through an analog-to-digital converter; and reconstruct an imaging map of the magnetic particle concentration distribution based on the digital signal.

Refer to Figure 6, which is a schematic diagram of the device structure of the hardware operating environment involved in the embodiment of the present application.

As shown in FIG6 , the active filter-based magnetic particle imaging device may include: a processor 1001 , a memory 1005 , and a communication bus 1002 . The communication bus 1002 is used to realize the connection and communication between the processor 1001 and the memory 1005 .

Optionally, the active filter-based magnetic particle imaging device may further include a user interface, a network interface, a camera, an RF (Radio Frequency) circuit, a sensor, a WiFi module, etc. The user interface may include a display screen (Display), an input submodule such as a keyboard (Keyboard), and the optional user interface may also include a standard wired interface and a wireless interface. The network interface may include a standard wired interface and a wireless interface (such as a WI-FI interface).

Those skilled in the art will appreciate that the structure of the active filter-based magnetic particle imaging device shown in FIG6 does not constitute a limitation on the active filter-based magnetic particle imaging device, and may include more or fewer components than shown in the figure, or a combination of certain components, or a different arrangement of components.

As shown in FIG6 , the memory 1005 as a storage medium may include an operating system, a network communication module, and an active filter-based magnetic particle imaging program. The operating system is a program for managing and controlling the hardware and software resources of the active filter-based magnetic particle imaging device, and supports the operation of the active filter-based magnetic particle imaging program and other software and/or programs. The network communication module is used to realize the communication between the components inside the memory 1005, and to communicate with other hardware and software in the active filter-based magnetic particle imaging system.

In the active filter-based magnetic particle imaging device shown in FIG6 , the processor 1001 is used to execute the active filter-based magnetic particle imaging program stored in the memory 1005 to implement the steps of any of the above-mentioned active filter-based magnetic particle imaging methods.

The specific implementation of the active filter-based magnetic particle imaging device of the present application is basically the same as the above-mentioned embodiments of the active filter-based magnetic particle imaging method, and will not be repeated here.

The present application also provides a magnetic particle imaging device based on an active filter, referring to FIG7 , the device comprises:

The signal generating module 10 is used to receive the first excitation signal generated by the signal generator, the first excitation signal is amplified by the power amplifier, and output to the driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil change their magnetic moment under the excitation of the changing magnetic field, and generate a magnetic particle signal;

A signal receiving module 20, configured to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

The imaging module 30 is used to perform signal processing on the current signal through the active twin-T notch filter, filter out the excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstruct an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal; the active twin-T notch filter is composed of an RC low-pass filter, an RC high-pass filter and an operational amplifier feedback circuit.

And/or, the imaging module further includes:

A filtering submodule, used for performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal; the magnetic particle imaging system based on the active filter also includes a low noise amplifier and an analog-to-digital converter;

A signal processing submodule, used for amplifying the magnetic particle signal through the low noise amplifier, and converting the processed magnetic particle signal into a digital signal through the analog-to-digital converter;

The imaging submodule is used to reconstruct an imaging diagram of the magnetic particle concentration distribution based on the digital signal.

And/or, the filtering submodule block further includes:

An acquisition unit, configured to acquire a signal frequency of the first excitation signal;

A value determination unit, used to determine the resistance value and the capacitance value in the active twin-T notch filter according to the signal frequency;

A data adjustment unit, configured to adjust the quality factor of the active twin-T notch filter based on the resistance value and the capacitance value, and obtain a magnetic particle signal after the active twin-T notch filter processes the current signal, corresponding to the quality factor with the highest value;

And/or, the device further comprises:

A passive double-T network module, a circuit diagram for the RC low-pass filter and the RC high-pass filter includes a first resistor, a second resistor, the first resistor is connected to the positive input electrode of the signal source; the first resistor is connected in series with the second resistor, a first capacitor is connected between the first resistor and the second resistor, and the other end of the first capacitor is grounded; the first resistor is connected in parallel with a second capacitor, the second capacitor is connected in series with a third resistor, the third resistor is connected in parallel with the first capacitor, and the other end of the third resistor is grounded; the second resistor is connected in parallel with a third capacitor, the third capacitor is connected in series with the second capacitor, and the other end of the third resistor is grounded.

And/or, the device further comprises:

An operational amplifier feedback circuit module, used for the operational amplifier feedback circuit, includes a first amplifier and a second amplifier, the positive power supply terminal of the first amplifier is electrically connected to the output terminals of the second resistor and the third capacitor, and the negative power supply terminal of the first amplifier is electrically connected to the output terminal of the first amplifier; the output terminal of the first amplifier is connected in series with a fourth resistor and a fifth resistor, and the other end of the fifth resistor is grounded; the output terminal of the second amplifier is electrically connected to the output terminals of the first capacitor and the third resistor, the negative power supply terminal of the second amplifier is electrically connected to the output terminal of the second amplifier, and the positive power supply terminal of the second amplifier is electrically connected to the output terminal of the fourth resistor.

An embodiment of the present application provides a computer-readable storage medium, and the computer-readable storage medium stores one or more programs, and the one or more programs can also be executed by one or more processors to implement the steps of any of the above-mentioned active filter-based magnetic particle imaging methods.

The specific implementation of the storage medium of the present application is basically the same as the above-mentioned embodiments of the magnetic particle imaging method based on the active filter, and will not be repeated here.

The present application also provides a computer program product, including a computer program, which implements the steps of the above-mentioned active filter-based magnetic particle imaging method when executed by a processor.

The specific implementation of the computer program product of the present application is basically the same as the above-mentioned embodiments of the active filter-based magnetic particle imaging method, and will not be repeated here.

It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus hardware platform, or by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM/RAM, magnetic disk, optical disk), including a number of instructions for enabling a terminal device (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in each embodiment of the present invention.

The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

A magnetic particle imaging method based on an active filter, characterized in that it is applied to a magnetic particle imaging system based on an active filter, wherein the magnetic particle imaging system based on an active filter comprises a signal generator, a power amplifier and an active double-T notch filter, and the method comprises:

Receiving a first excitation signal generated by the signal generator, the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil change their magnetic moments under the excitation of the changing magnetic field, and generate magnetic particle signals;

receiving a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

The current signal is processed by the active twin-T notch filter to filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and an imaging diagram of the magnetic particle concentration distribution is reconstructed based on the retained magnetic particle signal.
The active filter-based magnetic particle imaging method according to claim 1, characterized in that the active filter-based magnetic particle imaging system further comprises a low noise amplifier and an analog-to-digital converter,

The step of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstructing an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal comprises:

Performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining a filtered magnetic particle signal;

The magnetic particle signal is amplified by the low noise amplifier, and the processed magnetic particle signal is converted into a digital signal by the analog-to-digital converter;

An imaging diagram of the magnetic particle concentration distribution is reconstructed based on the digital signal.
The active filter-based magnetic particle imaging method according to claim 2, characterized in that the step of performing signal processing on the current signal through the active twin-T notch filter, filtering out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtaining the filtered magnetic particle signal comprises:

Acquiring a signal frequency of the first excitation signal;

Determining resistance values and capacitance values in the active twin-T notch filter according to the signal frequency;

Adjusting the quality factor of the active twin-T notch filter based on the resistance value and the capacitance value to obtain a magnetic particle signal after the active twin-T notch filter processes the current signal and corresponds to the quality factor with the highest value;

The quality factor represents the stopband size of the active twin-T notch filter.
The active filter-based magnetic particle imaging method according to any one of claims 1 to 3, characterized in that the active twin-T notch filter is composed of an RC low-pass filter, an RC high-pass filter and an operational amplifier feedback circuit.
The active filter-based magnetic particle imaging method as described in claim 4 is characterized in that the circuit diagram of the RC low-pass filter and the RC high-pass filter includes a first resistor, a second resistor, and the first resistor is connected to the positive pole of the power supply; the first resistor is connected in series with the second resistor, a first capacitor is connected between the first resistor and the second resistor, and the other end of the first capacitor is grounded; the first resistor is connected in parallel with a second capacitor, the second capacitor is connected in series with a third resistor, the third resistor is connected in parallel with the first capacitor, and the other end of the third resistor is grounded; the second resistor is connected in parallel with a third capacitor, the third capacitor is connected in series with the second capacitor, and the other end of the third resistor is grounded.
The active filter-based magnetic particle imaging method as described in claim 5 is characterized in that the operational amplifier feedback circuit includes a first amplifier and a second amplifier, the positive power supply terminal of the first amplifier is electrically connected to the output terminals of the second resistor and the third capacitor, and the negative power supply terminal of the first amplifier is electrically connected to the output terminal of the first amplifier; the output terminal of the first amplifier is connected in series with a fourth resistor and a fifth resistor, and the other end of the fifth resistor is grounded; the output terminal of the second amplifier is electrically connected to the output terminals of the first capacitor and the third resistor, the negative power supply terminal of the second amplifier is electrically connected to the output terminal of the second amplifier, and the positive power supply terminal of the second amplifier is electrically connected to the output terminal of the fourth resistor.
A magnetic particle imaging system based on an active filter, characterized in that the system comprises a signal generating subsystem and a signal receiving subsystem, the signal generating subsystem comprises a signal generator, a power amplifier and a driving coil, the signal generating subsystem is used to receive a first excitation signal generated by the signal generator, the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, the magnetic nanoparticles in the driving coil have their magnetic moments changed under the excitation of the changing magnetic field, and a magnetic particle signal is generated;

The signal receiving subsystem includes an active twin-T notch filter, a receiving coil, a low noise amplifier and an analog-to-digital converter. The signal receiving subsystem is used to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal with the same frequency as the first excitation signal induced by the receiving coil based on the first excitation signal and a magnetic particle signal; the current signal is processed by the active twin-T notch filter to filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and an imaging diagram of the magnetic particle concentration distribution is reconstructed based on the retained magnetic particle signal.

The signal receiving subsystem is also used to perform signal processing on the current signal through the active twin-T notch filter, filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and obtain a filtered magnetic particle signal; amplify the magnetic particle signal through the low-noise amplifier, and convert the processed magnetic particle signal into a digital signal through the analog-to-digital converter; and reconstruct an imaging diagram of the magnetic particle concentration distribution based on the digital signal.
A magnetic particle imaging device based on an active filter, characterized in that the device comprises:

A signal generating module, used for receiving a first excitation signal generated by the signal generator, wherein the first excitation signal is amplified by the power amplifier and output to the driving coil to generate a changing magnetic field, and the magnetic nanoparticles in the driving coil change their magnetic moments under the excitation of the changing magnetic field, thereby generating a magnetic particle signal;

a signal receiving module, configured to receive a current signal induced by a receiving coil corresponding to the driving coil, wherein the current signal includes a second excitation signal having the same frequency as the first excitation signal and induced by the receiving coil based on the first excitation signal, and a magnetic particle signal;

An imaging module is used to perform signal processing on the current signal through the active twin-T notch filter, filter out the second excitation signal corresponding to the stop band of the active twin-T notch filter, and reconstruct an imaging diagram of the magnetic particle concentration distribution based on the retained magnetic particle signal.
A magnetic particle imaging device based on an active filter, characterized in that the magnetic particle imaging device based on an active filter comprises a memory, a processor and a magnetic particle imaging program based on an active filter stored in the memory and executable on the processor, wherein the processor implements the steps of the magnetic particle imaging method based on an active filter as described in any one of claims 1 to 6 when executing the magnetic particle imaging program based on an active filter.
A computer-readable storage medium, characterized in that an active filter-based magnetic particle imaging program is stored on the computer-readable storage medium, and when the active filter-based magnetic particle imaging program is executed by a processor, the steps of the active filter-based magnetic particle imaging method according to any one of claims 1 to 6 are implemented.