Method and device for determining frequency drift amount of magnetic resonance system and computer equipment

文档序号：1814683 发布日期：2021-11-09 浏览：11次中文

阅读说明：本技术 磁共振系统频率漂移量的确定方法、装置和计算机设备 (Method and device for determining frequency drift amount of magnetic resonance system and computer equipment ) 是由薛爱国刘柳于 2020-05-09 设计创作，主要内容包括：本申请涉及一种磁共振系统频率漂移量的确定方法、装置和计算机设备。所述方法包括：采用预设扫描序列进行第一扫描以获取第一组回波信号；所述预设扫描序列为梯度双回波序列；在所述第一扫描的预设时长后,采用所述预设扫描序列进行第二扫描以获取第二组回波信号；分别根据所述第一组回波信号和所述第二组回波计算,得到第一导航频率和第二导航频率；根据所述第一导航频率和所述第二导航频率确定磁共振系统频率漂移量。采用本方法能够得到准确的磁共振系统频率漂移量,从而提高系统频率的准确性,提高成像效果。(The application relates to a method and a device for determining frequency drift amount of a magnetic resonance system and computer equipment. The method comprises the following steps: performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence; after the preset duration of the first scanning, performing second scanning by adopting the preset scanning sequence to obtain a second group of echo signals; calculating according to the first group of echo signals and the second group of echoes respectively to obtain a first navigation frequency and a second navigation frequency; and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency. By adopting the method, the accurate frequency drift of the magnetic resonance system can be obtained, so that the accuracy of the system frequency is improved, and the imaging effect is improved.)

1. A method for determining an amount of frequency drift in a magnetic resonance system, the method comprising:

performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence;

after the preset duration of the first scanning, performing second scanning by adopting the preset scanning sequence to obtain a second group of echo signals;

calculating according to the first group of echo signals and the second group of echoes respectively to obtain a first navigation frequency and a second navigation frequency;

and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

2. The method of claim 1, wherein each set of echo signals comprises a first echo signal and a second echo signal, and wherein the calculating from the first set of echo signals and the second set of echoes respectively to obtain a first navigation frequency and a second navigation frequency comprises:

respectively carrying out frequency domain conversion on the first echo signal and the second echo signal aiming at each group of echo signals to obtain a third echo signal and a fourth echo signal after conversion;

and calculating navigation frequency according to the third echo signal and the fourth echo signal.

3. The method of claim 2, wherein said calculating a navigation frequency from said third echo signal and said fourth echo signal comprises:

integrating the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle;

carrying out phase fitting on the system echo signal to obtain a first phase angle;

and calculating navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

4. The method of claim 2, wherein said calculating a navigation frequency from said third echo signal and said fourth echo signal comprises:

calculating according to the third echo signal, the fourth echo signal and a preset phase angle function to obtain a second phase angle;

and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

5. The method of claim 3 or 4, wherein the correspondence between frequency and phase angle comprises a frequency proportional to phase angle and an inverse proportional to a time difference between the first echo signal and the second echo signal.

6. The method of claim 1, wherein the first set of echo signals comprises a plurality of pairs of echo signals, each pair of echo signals comprising two echo signals, and wherein the calculating from the first set of echo signals and the second set of echoes, respectively, to obtain a first navigation frequency and a second navigation frequency comprises:

aiming at the first group of echo signals, calculating navigation frequency according to the multiple pairs of echo signals to obtain multiple candidate navigation frequencies;

determining an average of a plurality of the candidate navigation frequencies as the first navigation frequency.

7. The method of claim 1, wherein determining an amount of magnetic resonance system frequency drift from the first and second navigator frequencies comprises:

calculating a frequency difference between the first navigation frequency and the second navigation frequency;

and performing unwrapping processing on the frequency difference value to obtain the frequency drift amount of the magnetic resonance system.

8. The method of claim 1, wherein after said determining an amount of magnetic resonance system frequency drift from said first and second navigator frequencies, the method further comprises:

correcting the frequency of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system; alternatively, the first and second electrodes may be,

and correcting the frequency of the transmitting coil and/or the frequency of the receiving coil according to the frequency drift amount of the magnetic resonance system.

9. An apparatus for determining an amount of frequency drift in a magnetic resonance system, the apparatus comprising:

the first sequence scanning module is used for carrying out first scanning by adopting a preset scanning sequence so as to obtain a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence;

the second sequence scanning module is used for performing second scanning by adopting the preset scanning sequence after the preset duration of the first scanning so as to obtain a second group of echo signals;

the navigation frequency calculation module is used for calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency;

and the drift amount determining module is used for determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

10. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 8.

Technical Field

The present invention relates to the field of magnetic resonance technology, and in particular, to a method, an apparatus, and a computer device for determining a frequency drift amount of a magnetic resonance system.

Background

In the magnetic resonance imaging process, the accuracy of the system frequency directly affects the image quality. When a long-time sequence scan is performed, the magnetic resonance system generates heat due to vibration caused by continuous switching of current, and the system frequency shifts.

In the related art, in order to avoid the system frequency drift from degrading the image quality, the system frequency is usually calibrated in real time. However, when scanning the breast or neck, it is often necessary for the user to manually adjust the system frequency. At this time, if the calibration is still performed according to the previous calibration method, the manual adjustment amount of the system frequency is considered as a frequency drift, thereby causing a calibration error of the system frequency.

Disclosure of Invention

In view of the above, there is a need to provide a method, an apparatus and a computer device for determining a frequency drift amount of a magnetic resonance system, which can avoid taking a manual adjustment amount of the system frequency as a frequency drift, thereby avoiding a system frequency calibration error.

A method of determining an amount of frequency drift of a magnetic resonance system, the method comprising:

performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals;

respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency;

and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

In one embodiment, each set of echo signals includes a first echo signal and a second echo signal, and the obtaining a first navigation frequency and a second navigation frequency according to the first echo signal and the second echo signal by computing includes:

and calculating the navigation frequency according to the third echo signal and the fourth echo signal.

In one embodiment, the calculating a navigation frequency according to the third echo signal and the fourth echo signal includes:

integrating the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle;

carrying out phase fitting on the system echo signal to obtain a first phase angle;

and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

In one embodiment, the calculating a navigation frequency according to the third echo signal and the fourth echo signal includes:

calculating according to the third echo signal, the fourth echo signal and a preset phase angle function to obtain a second phase angle;

and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

In one embodiment, the correspondence between the frequency and the phase angle includes that the frequency is proportional to the phase angle and inversely proportional to the time difference between the first echo signal and the second echo signal.

In one embodiment, the obtaining the first navigation frequency and the second navigation frequency according to the first echo signal and the second echo signal includes:

aiming at the first group of echo signals, calculating navigation frequency according to a plurality of pairs of echo signals to obtain a plurality of candidate navigation frequencies;

an average of the plurality of candidate navigation frequencies is determined as the first navigation frequency.

In one embodiment, the determining the magnetic resonance system frequency drift amount according to the first navigation frequency and the second navigation frequency includes:

calculating a frequency difference between the first navigation frequency and the second navigation frequency;

and performing unwrapping processing on the frequency difference to obtain the frequency drift amount of the magnetic resonance system.

In one embodiment, after determining the magnetic resonance system frequency drift amount according to the first navigator frequency and the second navigator frequency, the method further comprises:

and correcting the frequency of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system.

In one embodiment, after determining the magnetic resonance system frequency drift amount according to the first navigator frequency and the second navigator frequency, the method further comprises:

the frequency of the transmit coil and/or the frequency of the receive coil is modified based on the amount of magnetic resonance system frequency drift.

An apparatus for determining an amount of frequency drift of a magnetic resonance system, the apparatus comprising:

the first sequence scanning module is used for carrying out first scanning by adopting a preset scanning sequence so as to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

the second sequence scanning module is used for performing second scanning by adopting a preset scanning sequence after the preset duration of the first scanning so as to obtain a second group of echo signals;

In one embodiment, each set of echo signals includes a first echo signal and a second echo signal, and the navigation frequency calculation module includes:

the frequency domain conversion sub-module is used for respectively performing frequency domain conversion on the first echo signal and the second echo signal aiming at each group of echo signals to obtain a third echo signal and a fourth echo signal after conversion;

and the navigation frequency calculation sub-module is used for calculating the navigation frequency according to the third echo signal and the fourth echo signal.

In one embodiment, the navigation frequency calculation submodule is configured to integrate the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle; carrying out phase fitting on the system echo signal to obtain a first phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

In one embodiment, the navigation frequency calculation sub-module is configured to calculate according to the third echo signal, the fourth echo signal, and a preset phase angle function to obtain a second phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

In one embodiment, the first set of echo signals includes a plurality of pairs of echo signals, each pair of echo signals includes two echo signals, and the first navigation frequency calculation module is specifically configured to calculate a navigation frequency according to the plurality of pairs of echo signals, so as to obtain a plurality of candidate navigation frequencies; an average of the plurality of candidate navigation frequencies is determined as the first navigation frequency.

In one embodiment, the drift amount determining module is specifically configured to calculate a frequency difference between a first navigation frequency and a second navigation frequency; and performing unwrapping processing on the frequency difference to obtain the frequency drift amount of the magnetic resonance system.

In one embodiment, the apparatus further comprises:

and the navigation frequency correction module is used for correcting the frequency of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system.

In one embodiment, the apparatus further comprises:

and the coil frequency modifying module is used for modifying the frequency of the transmitting coil and/or the frequency of the receiving coil according to the frequency drift amount of the magnetic resonance system.

A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:

performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals;

respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency;

and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out the steps of:

performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals;

respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency;

and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

According to the method, the device and the computer equipment for determining the frequency drift amount of the magnetic resonance system, a preset scanning sequence is adopted for carrying out first scanning so as to obtain a first group of echo signals; after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency; and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency. According to the embodiment of the application, after a user manually adjusts the system frequency, a preset scanning sequence is adopted for carrying out first scanning and obtaining a first group of echo signals, after a preset duration, a preset scanning sequence is adopted for carrying out second scanning and obtaining a second group of echo signals, a first navigation frequency and a second navigation frequency are respectively calculated according to the first group of echo signals and the second group of echo signals, and because the first navigation frequency and the second navigation frequency both contain manual adjustment quantity of the system frequency, the manual adjustment quantity of the system frequency can be offset through calculation, so that the problem that the manual adjustment quantity of the system frequency is used as frequency drift to cause system frequency calibration errors is avoided.

Drawings

FIG. 1 is a diagram of an exemplary embodiment of a method for determining an amount of frequency drift in a magnetic resonance system;

FIG. 2 is a flow chart illustrating a method for determining an amount of frequency drift of a magnetic resonance system according to one embodiment;

FIG. 3 is a waveform diagram in one embodiment;

FIG. 4 is a schematic flow chart illustrating the step of calculating a navigation frequency based on an echo signal according to an embodiment;

FIG. 5 is a flow chart illustrating a method for determining an amount of frequency drift of an MR system according to another embodiment;

FIG. 6 is a multi-phase breast magnetic resonance image obtained using a prior art method;

FIG. 7 is a multi-phase breast magnetic resonance image obtained after frequency correction of the magnetic resonance system in one embodiment;

FIG. 8 is a block diagram showing an example of an apparatus for determining the amount of frequency drift of the magnetic resonance system;

FIG. 9 is a diagram illustrating an internal structure of a computer device according to an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The method for determining the frequency drift amount of the magnetic resonance system can be applied to the application environment shown in fig. 1. The application environment is a magnetic resonance system comprising at least a gradient system 101, a radio frequency system 102 and a control terminal 103. Wherein the gradient system 101 comprises devices such as gradient coils for generating gradient pulses; the radio frequency system 102 includes devices such as a radio frequency coil, the radio frequency coil includes a transmitting coil and a receiving coil, and the radio frequency system 102 is configured to generate a radio frequency pulse signal and detect a magnetic resonance signal generated by nuclear spins of the subject; the control terminal 103 communicates with the gradient system 101 and the radio frequency system 102 through a network, and is used for controlling the gradient system 101 and the radio frequency system 102. The control terminal 103 may be, but is not limited to, various personal computers, notebook computers, and tablet computers.

In one embodiment, as shown in fig. 2, a method for determining a frequency drift amount of a magnetic resonance system is provided, which is described by taking the method as an example for being applied to the control terminal in fig. 1, and includes the following steps:

step 201, performing a first scan by using a preset scan sequence to obtain a first group of echo signals; the preset scanning sequence is a gradient double echo sequence.

Since the system frequency is often manually adjusted by the user when scanning the breast or neck, the manual adjustment of the system frequency is regarded as a frequency drift in the real-time calibration, which results in an error in the calibration of the system frequency. To avoid this, the embodiment of the present application does not perform real-time frequency calibration any more, but employs dynamic frequency calibration after detecting an adjustment operation for the system frequency, that is, after a user manually adjusts the system frequency. Specifically, a preset scan sequence is first adopted to perform the first scan, wherein the preset scan sequence may be a gradient dual-echo sequence, as shown in the waveform diagram of fig. 3, RF is a radio frequency pulse, G_SSFor gradient in the direction of the selected layer, G_ROFor frequency encoding directional gradients, the ADC represents the signal received by the analog-to-digital converter. The gradient dual echo sequence shown in fig. 3 has only frequency encoding gradients and no phase encoding gradients. In addition, in order to reduce the influence of the preset scanning sequence on the magnetic field, the excitation flip angle is as small as possible under the condition of meeting the signal-to-noise ratio, and the gradient net area of each logic axis is zero.

While performing the first scan using the predetermined scan sequence, a first set of echo signals, FIG. 3, is acquired, along G_SSApplying a layer selection gradient corresponding to the radio frequency pulse in the direction and a dephasing gradient applied immediately after the layer selection gradient; along G_ROApplying a continuous frequency encoding gradient in a direction to avoid gradient eddy currents caused by frequent switching of the gradient; ADC samplingObtaining a first echo signal e₀And a second echo signal e₁G corresponding to the two echoes_ROThe gradient moments in the directions are the same; echo time TE (echo time) is the time from the midpoint of the RF pulse to the first echo signal e₀Δ TE is the first echo signal e₀And a second echo signal e₁The echo time difference of (2). In this embodiment, the predetermined scan sequence does not include a gradient in the phase encoding direction, i.e. the first echo signal e is sampled in the embodiment of the present application₀And a second echo signal e₁Is not phase encoded. In one embodiment, the value of TE is sufficient to ensure that the water signal and the fat signal of the test subject are in phase. In one embodiment, the system frequency is calibrated once before the user manually adjusts the system frequency, so that the system frequency can be corrected more accurately after the magnetic resonance system frequency drift amount is determined. Wherein the system frequency is the larmor frequency, i.e. the precession frequency of the magnetic nuclei or the main magnetic field frequency.

Step 202, after the preset duration of the first scanning, performing a second scanning by using a preset scanning sequence to obtain a second group of echo signals.

In the embodiment of the present application, after the first group of echo signals are acquired, the system frequency may drift after a period of time, so that the preset scanning sequence is adopted to perform the second scanning, and the second group of echo signals are acquired at the same time.

For example, a scan is performed once using the preset scan sequence, another scan is performed after 5 minutes using the preset scan sequence, and a second set of echo signals is acquired. The preset duration is not limited in detail in the embodiment of the application, and can be set according to actual conditions.

And 203, respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency.

In the embodiment of the application, a first navigation frequency is obtained by calculation according to a first group of echo signals, and a second navigation frequency is obtained by calculation according to a second group of echo signals. Specifically, each group of echo signals is subjected to frequency domain conversion, then a phase angle is calculated according to the converted echo signals, and then navigation frequency is calculated according to the corresponding relationship between the phase angle and the frequency. The specific calculation method is not limited in detail in the embodiment of the application, and can be set according to actual conditions.

And step 204, determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

In the embodiment of the application, the first navigation frequency includes a manual adjustment amount of the system frequency, and the second navigation frequency also includes a manual adjustment amount of the system frequency, so that after the first navigation frequency and the second navigation frequency are obtained, a frequency difference between the first navigation frequency and the second navigation frequency can be calculated, so that the manual adjustment amount of the system frequency is cancelled, and further, a frequency drift amount of the magnetic resonance system is obtained.

In the method for determining the frequency drift amount of the magnetic resonance system, a preset scanning sequence is adopted to perform first scanning so as to obtain a first group of echo signals; after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency; and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency. In the embodiment of the application, the first navigation frequency and the second navigation frequency both include the manual adjustment amount of the system frequency, so that the manual adjustment amount of the system frequency can be cancelled by calculation, and the problem that the manual adjustment amount of the system frequency is taken as frequency drift to cause system frequency calibration error is avoided.

In one embodiment, as shown in FIG. 4, an optional process involving calculating a navigation frequency from an echo signal. On the basis of the above embodiment, each set of echo signals includes a first echo signal and a second echo signal, and therefore, the following steps may be adopted to calculate the first navigation frequency and the second navigation frequency:

step 301, for each group of echo signals, performing frequency domain conversion on the first echo signal and the second echo signal respectively to obtain a third echo signal and a fourth echo signal after conversion.

In the embodiment of the application, a gradient double-echo sequence is adopted for scanning, and two echo signals, namely a first echo signal and a second echo signal, can be acquired. And then, performing frequency domain conversion on the first echo signal to obtain a third echo signal, and performing frequency domain conversion on the second echo signal to obtain a fourth echo signal. Specifically, the frequency domain transformation may employ a fourier transform, such as equation (1) (2):

E₀＝FFT(e₀)-------------------------------------------(1)

E₁＝FFT(e₁)--------------------------------------------(2)

wherein e is₀Is a first echo signal, e₁Is the second echo signal, E₀Is the third echo signal, E₁Is the fourth echo signal.

And step 302, calculating a navigation frequency according to the third echo signal and the fourth echo signal.

In the embodiment of the present application, after the third echo signal and the fourth echo signal in the frequency domain are obtained, the navigation frequency may be calculated in the following two ways.

The first method is as follows: integrating the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle; carrying out phase fitting on the system echo signal to obtain a first phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

Specifically, two echo signals are integrated into one system echo signal, wherein the system echo signal is represented by amplitude and phase angle. The integration process may be as in formula (3):

then, let E (i) be written as formula (4):

wherein E is₀(i)*E₁(i) Is the third echo signal E₀And a fourth echo signal E₁Conjugate multiplication; a. the_iThe amplitude of the system echo signal e (i),the phase angle of the system echo signal E (i) is shown, n represents the number of the acquired gradient double echoes, and n is more than or equal to 1.

After obtaining the system echo signal, the phase fitting can be performed by using the least square method, as shown in formula (5):

wherein, theta₁Is the fitted first phase angle.

Then, calculating the navigation frequency according to the corresponding relationship between the frequency and the phase angle and the first phase angle obtained by fitting, as specifically shown in formula (6):

the correspondence between the frequency and the phase angle includes: the frequency is proportional to the phase angle and inversely proportional to the time difference between the first echo signal and the second echo signal. Where f is the calculated navigation frequency and Δ TE is the time difference between the first echo signal and the second echo signal.

The second method comprises the following steps: calculating according to the third echo signal, the fourth echo signal and a preset phase angle function to obtain a second phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

Specifically, the second phase angle can be obtained by directly calculating according to the phase angle function, as shown in formula (7):

θ₂＝angle(∑_i(E₀(i)*E₁(i)))-----------------------(7)

wherein, theta₁Is the second phase angle.

Then, the navigation frequency is calculated according to the corresponding relationship between the frequency and the phase angle and the calculated second phase angle, as shown in formula (8):

In the process of calculating the navigation frequency according to the echo signals, respectively performing frequency domain conversion on the first echo signal and the second echo signal aiming at each group of echo signals to obtain a third echo signal and a fourth echo signal after conversion; and calculating the navigation frequency according to the third echo signal and the fourth echo signal. According to the embodiment of the application, the echo signal represented by the time domain is converted into the echo signal represented by the frequency domain, the phase angle can be calculated from the echo signal represented by the frequency domain, and the navigation frequency can be calculated according to the corresponding relation between the frequency and the phase angle, so that the first navigation frequency and the second navigation frequency are determined, and the frequency drift amount of the magnetic resonance system is obtained.

In one embodiment, as shown in fig. 5, a method for determining a frequency drift amount of a magnetic resonance system is provided, which is described by taking the method as an example for being applied to the control terminal in fig. 1, and includes the following steps:

step 401, performing a first scan by using a preset scan sequence to obtain a first group of echo signals; the preset scanning sequence is a gradient double echo sequence.

And 402, after the preset duration of the first scanning, performing a second scanning by using a preset scanning sequence to obtain a second group of echo signals.

And 403, respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency.

In the embodiment of the application, in order to make the first navigation frequency more accurate, for the first group of echo signals, the navigation frequency can be calculated according to a plurality of pairs of echo signals to obtain a plurality of candidate navigation frequencies; an average of the plurality of candidate navigation frequencies is determined as the first navigation frequency. Specifically, a plurality of pairs of echo signals are collected, wherein each pair of echo signals comprises two echo signals; calculating navigation frequency aiming at each pair of echo signals to obtain corresponding candidate navigation frequency, so that a plurality of candidate navigation frequencies can be obtained; and finally, calculating the average value of the candidate navigation frequencies, and taking the average value as the first navigation frequency.

In one embodiment, calculating a navigation frequency for each pair of echo signals, and obtaining a corresponding candidate navigation frequency may include: respectively carrying out frequency domain conversion on the first echo signal and the second echo signal to obtain a third echo signal and a fourth echo signal after conversion; and calculating the navigation frequency according to the third echo signal and the fourth echo signal.

In one embodiment, calculating the navigation frequency from the third echo signal and the fourth echo signal comprises: integrating the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle; carrying out phase fitting on the system echo signal to obtain a first phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

In one embodiment, calculating the navigation frequency from the third echo signal and the fourth echo signal comprises: calculating according to the third echo signal, the fourth echo signal and a preset phase angle function to obtain a second phase angle; and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

In one embodiment, the correspondence between frequency and phase angle includes that the frequency is proportional to the phase angle and inversely proportional to the time difference between the first echo signal and the second echo signal.

The second set of echo signals includes a pair of echo signals, so that the calculation of the second navigation frequency can be referred to the above embodiments, and is not described herein again.

Step 404, calculating a frequency difference between the first navigation frequency and the second navigation frequency; and performing unwrapping processing on the frequency difference to obtain the frequency drift amount of the magnetic resonance system.

In the embodiment of the application, after the first navigation frequency and the second navigation frequency are obtained, the frequency difference between the first navigation frequency and the second navigation frequency is calculated to offset the manual adjustment amount of the system frequency. However, due to the phase winding problem, the frequency difference cannot directly reflect the frequency drift amount of the magnetic resonance system, and therefore, the frequency difference needs to be subjected to unwrapping processing. Specifically, the formula (9):

wherein, Deltaf is the frequency drift amount of the magnetic resonance system, f_kIs the second navigation frequency, f_rIs a first navigation frequency. And, setting a frequency threshold value ton is a positive integer and takes an appropriate value such that

After the amount of frequency drift of the magnetic resonance system is obtained, any one of the following steps may be employed.

Step 405, the magnetic resonance system frequency is corrected according to the magnetic resonance system frequency drift amount.

In the embodiment of the present application, after the magnetic resonance system frequency drift amount is obtained, the magnetic resonance system frequency can be corrected according to the magnetic resonance system frequency drift amount.

In practical application, as shown in fig. 6, a multi-phase breast magnetic resonance image obtained by a method in the prior art is used, a breast phase 6 scan is performed, if the magnetic resonance system frequency drift amount is not calculated by adopting the above steps to perform system frequency correction, a first row in the figure sequentially corresponds to a first phase breast magnetic resonance image, a second phase breast magnetic resonance image and a third phase breast magnetic resonance image from left to right, a white artifact region (shown by an arrow in the figure) caused by uneven fat compression exists in the third phase breast magnetic resonance image, a second row sequentially corresponds to a fourth phase breast magnetic resonance image, a fifth phase breast magnetic resonance image and a sixth phase breast magnetic resonance image from left to right, and an obvious white artifact region caused by uneven fat compression exists in the three phases, that is, the fat compression effect gradually deteriorates with the increase of the phase. And as shown in fig. 7, the magnetic resonance image of the breast with multiple phases obtained after the frequency correction of the magnetic resonance system is performed by the method shown in fig. 2, which is also a 6-phase scan of the breast, and the frequency drift amount of the magnetic resonance system calculated by the above steps is used for performing the system frequency correction, so that the fat pressing effects of different phases are basically consistent. Therefore, the method for calculating the frequency drift amount of the magnetic resonance system to correct the system frequency can improve the accuracy of the system frequency and further improve the imaging effect.

The frequency of the transmit coil and/or the frequency of the receive coil is modified based on the amount of magnetic resonance system frequency drift, step 406.

In the embodiment of the application, after the frequency drift amount of the magnetic resonance system is obtained, the frequency of the transmitting coil can be corrected, or the frequency of the receiving coil can be corrected; or the frequency of the transmitting coil and the frequency of the receiving coil are simultaneously corrected, so that the effect of correcting the system frequency is achieved.

In the method for determining the frequency drift amount of the magnetic resonance system, a preset scanning sequence is adopted to perform first scanning so as to obtain a first group of echo signals; after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency; calculating a frequency difference between the first navigation frequency and the second navigation frequency; carrying out unwrapping processing on the frequency difference value to obtain the frequency drift amount of the magnetic resonance system; the navigation frequency can be corrected according to the frequency drift amount of the magnetic resonance system; the frequency of the transmit coil and/or the frequency of the receive coil may also be modified based on the amount of magnetic resonance system frequency drift. According to the embodiment of the application, the frequency drift amount of the magnetic resonance system is determined according to the first navigation frequency and the second navigation frequency, and the system frequency is corrected according to the frequency drift amount of the magnetic resonance system, so that the accuracy of the system frequency can be improved, and the imaging effect is further improved.

It should be understood that although the various steps in the flowcharts of fig. 2-5 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 2-5 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least some of the other steps or stages.

In one embodiment, as shown in fig. 8, there is provided an apparatus for determining a frequency drift amount of a magnetic resonance system, comprising:

a first sequence scanning module 501, configured to perform a first scanning with a preset scanning sequence to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

a second sequence scanning module 502, configured to perform a second scanning by using a preset scanning sequence after a preset duration of the first scanning to obtain a second group of echo signals;

a navigation frequency calculation module 503, configured to calculate according to the first group of echo signals and the second group of echoes respectively to obtain a first navigation frequency and a second navigation frequency;

and a drift amount determining module 504, configured to determine a magnetic resonance system frequency drift amount according to the first navigation frequency and the second navigation frequency.

In one embodiment, each set of echo signals includes a first echo signal and a second echo signal, and the navigation frequency calculation module 503 includes:

and the navigation frequency calculation sub-module is used for calculating the navigation frequency according to the third echo signal and the fourth echo signal.

In one embodiment, the first set of echo signals includes a plurality of pairs of echo signals, each pair of echo signals includes two echo signals, and the navigation frequency calculation module 503 is specifically configured to calculate a navigation frequency according to the plurality of pairs of echo signals, so as to obtain a plurality of candidate navigation frequencies; an average of the plurality of candidate navigation frequencies is determined as the first navigation frequency.

In one embodiment, the drift amount determining module 504 is specifically configured to calculate a frequency difference between a first navigation frequency and a second navigation frequency; and performing unwrapping processing on the frequency difference to obtain the frequency drift amount of the magnetic resonance system.

In one embodiment, the apparatus further comprises:

and the system frequency correction module is used for correcting the frequency of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system.

In one embodiment, the apparatus further comprises:

The specific definition of the determining device for the magnetic resonance system frequency drift amount can refer to the above definition of the determining method for the magnetic resonance system frequency drift amount, and is not described herein again. The modules in the device for determining the frequency drift amount of the magnetic resonance system can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.

In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 9. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless communication can be realized through WIFI, an operator network, NFC (near field communication) or other technologies. The computer program is executed by a processor to implement a method of determining an amount of frequency drift of a magnetic resonance system. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.

Those skilled in the art will appreciate that the architecture shown in fig. 9 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.

In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having a computer program stored therein, the processor implementing the following steps when executing the computer program:

performing first scanning by adopting a preset scanning sequence to obtain a first group of echo signals; presetting a scanning sequence as a gradient double-echo sequence;

after the preset duration of the first scanning, performing second scanning by adopting a preset scanning sequence to obtain a second group of echo signals;

respectively calculating according to the first group of echo signals and the second group of echoes to obtain a first navigation frequency and a second navigation frequency;

and determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.

In one embodiment, each set of echo signals includes a first echo signal and a second echo signal, and the processor, when executing the computer program, implements the following steps:

and calculating the navigation frequency according to the third echo signal and the fourth echo signal.

In one embodiment, the processor, when executing the computer program, performs the steps of:

integrating the third echo signal and the fourth echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle;

carrying out phase fitting on the system echo signal to obtain a first phase angle;

and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle.

In one embodiment, the processor, when executing the computer program, performs the steps of:

calculating according to the third echo signal, the fourth echo signal and a preset phase angle function to obtain a second phase angle;

and calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the second phase angle.

In one embodiment, the first set of echo signals comprises a plurality of pairs of echo signals, each pair of echo signals comprising two echo signals, the processor when executing the computer program performs the steps of: