CN113625209B - Method and device for determining frequency drift amount of magnetic resonance system and computer equipment - Google Patents
Method and device for determining frequency drift amount of magnetic resonance system and computer equipment Download PDFInfo
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Abstract
The application relates to a method, a device and computer equipment for determining frequency drift amount of a magnetic resonance system. The method comprises the following steps: performing first scanning by adopting a preset scanning sequence to acquire 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 a second scanning by adopting the preset scanning sequence to acquire a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echo signals 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 amount of the magnetic resonance system can be obtained, thereby improving the accuracy of the system frequency and the imaging effect.
Description
Technical Field
The present invention relates to the field of magnetic resonance technologies, and in particular, to a method, an apparatus, and a computer device for determining a frequency drift amount of a magnetic resonance system.
Background
During magnetic resonance imaging, the accuracy of the system frequency directly affects the image quality. When a long-time serial 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, a user is often required to manually adjust the system frequency. At this time, if calibration is still performed in the previous calibration manner, the manual adjustment amount of the system frequency is regarded as frequency drift, thereby causing an error in the calibration of the system frequency.
Disclosure of Invention
In view of the foregoing, it is desirable to provide a method, an apparatus and a computer device for determining a frequency drift amount of a magnetic resonance system, which can avoid a manual adjustment amount of a 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 acquire 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 a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals;
respectively calculating according to the first group of echo signals and the second group of echo signals 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 calculating according to the first set of echo signals and the second set of echo signals respectively obtains a first navigation frequency and a second navigation frequency includes:
for each group of echo signals, frequency domain conversion is carried out on the first echo signal and the second echo signal respectively 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, the calculating the 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;
performing phase fitting on the system echo signals 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 the 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 frequency and phase angle includes frequency being proportional to phase angle and time difference between the first echo signal and the second echo signal being inversely proportional.
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 calculating according to the first set of echo signals and the second set of echo signals respectively includes:
calculating navigation frequencies according to the echo signals of the plurality of pairs aiming at the first group 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, determining the frequency drift amount of the magnetic resonance system 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 (5) unwrapping the frequency difference value 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 navigation frequency and the second navigation frequency, the method further comprises:
the magnetic resonance system frequency is corrected according to the magnetic resonance system frequency drift amount.
In one embodiment, after determining the magnetic resonance system frequency drift amount according to the first navigation frequency and the second navigation frequency, the method further comprises:
the frequency of the transmitting coil and/or the frequency of the receiving coil is modified according to the frequency drift amount of the magnetic resonance system.
A device for determining the amount of frequency drift of a magnetic resonance system, the device comprising:
the first sequence scanning module is used for carrying out first scanning by adopting a preset scanning sequence to acquire a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence;
the second sequence scanning module is used for carrying out second scanning by adopting a preset scanning sequence after the preset duration of the first scanning so as to acquire 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 respectively 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.
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 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 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 sub-module 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; performing phase fitting on the system echo signals 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 calculating submodule 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 correspondence between frequency and phase angle includes frequency being proportional to phase angle and time difference between the first echo signal and the second echo signal being inversely proportional.
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 calculating 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 the first navigation frequency and the second navigation frequency; and (5) unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system.
In one embodiment, the apparatus further comprises:
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:
the coil frequency modification 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 storing a computer program and a processor which when executing the computer program performs the steps of:
performing first scanning by adopting a preset scanning sequence to acquire 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 a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals;
respectively calculating according to the first group of echo signals and the second group of echo signals 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 having stored thereon a computer program which when executed by a processor performs the steps of:
performing first scanning by adopting a preset scanning sequence to acquire 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 a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals;
respectively calculating according to the first group of echo signals and the second group of echo signals 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.
The method, the device and the computer equipment for determining the frequency drift amount of the magnetic resonance system perform first scanning by adopting a preset scanning sequence to acquire a first group of echo signals; after the preset duration of the first scanning, performing a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echo signals 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 the system frequency is manually adjusted by a user, the first scanning is performed by adopting the preset scanning sequence, the first group of echo signals are acquired, the second scanning is performed by adopting the preset scanning sequence after the preset time length, the second group of echo signals are acquired, the first navigation frequency and the second navigation frequency are calculated according to the first group of echo signals and the second group of echo signals respectively, and because the first navigation frequency and the second navigation frequency both contain the manual adjustment quantity of the system frequency, the manual adjustment quantity of the system frequency can be counteracted by calculation, so that the problem of system frequency calibration errors caused by frequency drift of the manual adjustment quantity of the system frequency is avoided.
Drawings
FIG. 1 is a diagram of an application environment of a method for determining a frequency drift amount of a magnetic resonance system in one embodiment;
FIG. 2 is a flow chart of a method for determining the 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 flowchart illustrating a navigation frequency calculation step according to an echo signal in one embodiment;
FIG. 5 is a flow chart of a method for determining the frequency drift of a magnetic resonance 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 of a device for determining the frequency drift of a magnetic resonance system in one embodiment;
fig. 9 is an internal structural diagram of a computer device in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only 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 an 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 gradient coils and other devices for generating gradient pulses; the radio frequency system 102 comprises a radio frequency coil and other devices, the radio frequency coil comprises a transmitting coil and a receiving coil, and the radio frequency system 102 is used for generating radio frequency pulse signals and detecting magnetic resonance signals generated by nuclear spins of a subject; the control terminal 103 communicates with the gradient system 101 and the radio frequency system 102 via a network 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, and the method is applied to the control terminal in fig. 1 for illustration, and includes the following steps:
step 201, performing a first scan using a preset scan sequence to obtain a first set of echo signals; the preset scanning sequence is a gradient double-echo sequence.
Since the user is often required to manually adjust the system frequency during scanning the breast or neck, the manual adjustment amount of the system frequency is regarded as the frequency drift by adopting a real-time calibration method, thereby causing the error of the system frequency calibration. To avoid this, the embodiments of the present application do not perform real-time frequency calibration after detecting an adjustment operation for the system frequency, i.e., the user manually adjusts the system frequency, but rather employ dynamic frequency calibration. Specifically, a preset scanning sequence is adopted to perform the first scanning, wherein the preset scanning sequence can be a gradient double-echo sequence, see the waveform diagram shown in fig. 3, RF is a radio frequency pulse, G SS To select the layer direction gradient G RO For frequency encoding a directional gradient, 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 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 clear area of each logic axis is zero.
While performing a first scan using a predetermined scan sequence, a first set of echo signals is acquired, see the waveform diagram shown in FIG. 3, along G SS Applying a layer selection gradient and a dephasing gradient immediately after the layer selection gradient in a direction corresponding to the radio frequency pulse; along G RO Applying continuous frequency encoding gradients in the direction to avoid gradient eddy currents caused by frequent switching of the gradients; ADC sampling to obtain a first echo signal e 0 And a second echo signal e 1 G corresponding to the two echoes RO The gradient moment in the direction is the same; echo time TE (echo ti)me) is the midpoint of the RF pulse to the first echo signal e 0 Delta TE is the first echo signal e 0 And a second echo signal e 1 Is used for the echo time difference of (a). 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 obtained by sampling in the embodiment of the present application 0 And a second echo signal e 1 Is not subjected to phase encoding processing. In an embodiment, the value of TE is such as to ensure that the water signal and the fat signal of the test object are in phase. In one embodiment, the calibration of the system frequency is performed once before the user manually adjusts the system frequency so that the system frequency can be corrected more accurately after the amount of magnetic resonance system frequency drift is determined. The system frequency is larmor frequency, namely precession frequency of magnetic atomic nuclei or main magnetic field frequency.
Step 202, after a preset duration of the first scan, performing a second scan by using a preset scan sequence to obtain a second set of echo signals.
In this embodiment, after the first set of echo signals is acquired, the system frequency may drift over a period of time, so that a preset scanning sequence is used to perform the second scanning, and at the same time, the second set of echo signals is acquired.
For example, a scan is performed using a predetermined scan sequence, and after 5 minutes, a scan is performed using a predetermined scan sequence again, and a second set of echo signals is obtained. The preset time length is not limited in detail, and the preset time length can be set according to actual conditions.
Step 203, calculating according to the first set of echo signals and the second set of echo signals, so as to obtain a first navigation frequency and a second navigation frequency.
In the embodiment of the application, the first navigation frequency is calculated according to the first group of echo signals, and the second navigation frequency is calculated according to the 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 relation between the phase angle and the frequency. The embodiment of the application does not limit the specific calculation mode in detail, and can be set according to actual conditions.
Step 204, determining the frequency drift amount of the magnetic resonance system according to the first navigation frequency and the second navigation frequency.
In this embodiment of the present application, since 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, 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 may be calculated, so that the manual adjustment amount of the system frequency is offset, 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 acquire a first group of echo signals; after the preset duration of the first scanning, performing a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echo signals 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 this embodiment, the first navigation frequency and the second navigation frequency both include manual adjustment amounts of the system frequency, so that the manual adjustment amounts of the system frequency can be counteracted by calculation, thereby avoiding the problem of error calibration of the system frequency caused by taking the manual adjustment amounts of the system frequency as frequency drift.
In one embodiment, as shown in FIG. 4, an alternative process involves calculating a navigator frequency from an echo signal. On the basis of the above embodiment, each set of echo signals includes the first echo signal and the second echo signal, so the calculation of the first navigation frequency and the second navigation frequency may each employ the following steps:
step 301, performing frequency domain conversion on the first echo signal and the second echo signal for each group of echo signals, to obtain a converted third echo signal and fourth echo signal.
In the embodiment of the application, the 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 fourier transformation, such as equation (1) (2):
E 0 ＝FFT(e 0 )-------------------------------------------(1)
E 1 ＝FFT(e 1 )--------------------------------------------(2)
wherein e 0 Is the first echo signal e 1 Is the second echo signal E 0 Is the third echo signal E 1 Is the fourth echo signal.
Step 302, calculating a navigator frequency from the third echo signal and the fourth echo signal.
In this 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.
Mode one: 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; performing phase fitting on the system echo signals 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 a system echo signal, wherein the system echo signal is represented by an amplitude and a phase angle. The integration process may be as in equation (3):
then, E (i) is expressed as formula (4):
wherein E is 0 (i)*E 1 (i) Is the third echo signal E 0 And a fourth echo signal E 1 Conjugate multiplication; a is that i For the amplitude of the system echo signal E (i),and n represents the number of acquired gradient double echoes, wherein n is more than or equal to 1.
After the system echo signal is obtained, a least squares method may be used to perform phase fitting, as in equation (5):
wherein θ 1 The resulting first phase angle is fitted.
Then, calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the first phase angle obtained by fitting, wherein the specific formula is as 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 navigator frequency and Δte is the time difference between the first echo signal and the second echo signal.
Mode two: 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 may be directly calculated according to a phase angle function, such as formula (7):
θ 2 ＝angle(∑ i (E 0 (i)*E 1 (i)))-----------------------(7)
wherein θ 1 Is a second phase angle.
Then, calculating the navigation frequency according to the corresponding relation between the frequency and the phase angle and the calculated second phase angle, specifically as shown in a formula (8):
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 navigator frequency and Δte is the time difference between the first echo signal and the second echo signal.
In the process of calculating the navigation frequency according to the echo signals, frequency domain conversion is performed on the first echo signal and the second echo signal respectively for 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 signals expressed in the time domain are converted into the echo signals expressed in the frequency domain, the phase angle can be calculated by the echo signals expressed in the frequency domain, and then 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, and the method is applied to the control terminal in fig. 1 for illustration, and includes the following steps:
step 401, performing a first scan by using a preset scan sequence to obtain a first set of echo signals; the preset scanning sequence is a gradient double-echo sequence.
Step 402, after a preset duration of the first scan, performing a second scan using a preset scan sequence to obtain a second set of echo signals.
Step 403, calculating according to the first set of echo signals and the second set of echo signals respectively 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 multiple pairs of echo signals, so as to obtain multiple 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, and each pair of echo signals comprises two echo signals; performing navigation frequency calculation on each pair of echo signals to obtain corresponding candidate navigation frequencies, so that a plurality of candidate navigation frequencies can be obtained; and finally, calculating an average value of the plurality of candidate navigation frequencies, and taking the average value as a first navigation frequency.
In one embodiment, calculating the navigation frequency for each pair of echo signals, deriving the corresponding candidate navigation frequency may include: frequency domain conversion is carried out on the first echo signal and the second echo signal respectively, so that a third echo signal and a fourth echo signal after conversion are obtained; and calculating the navigation frequency according to the third echo signal and the fourth echo signal.
In one embodiment, calculating the navigator frequency from 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; performing phase fitting on the system echo signals 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 navigator frequency from 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 frequency and phase angle includes frequency being proportional to phase angle and inversely proportional to a 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 the calculation of the second pilot frequency can refer to the above embodiment, and will not be described herein.
Step 404, calculating a frequency difference between the first navigation frequency and the second navigation frequency; and (5) unwrapping the frequency difference value 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, a frequency difference between the first navigation frequency and the second navigation frequency is calculated to offset a 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, so that the frequency difference needs to be subjected to unwrapping treatment. Specifically, the formula (9):
wherein Δf is the frequency drift amount of the magnetic resonance system, f k For the second navigation frequency, f r Is the first navigation frequency. And, setting the frequency threshold asn is a positive integer and takes on a suitable value such that +.>
After obtaining the frequency drift amount of the magnetic resonance system, any one of the following steps may be adopted.
Step 405, correcting the magnetic resonance system frequency according to the magnetic resonance system frequency drift amount.
In the embodiment of the 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, the breast magnetic resonance images of multiple phases obtained by the prior art method are scanned in the breast 6 phase, if the frequency drift amount of the magnetic resonance system is calculated without adopting the steps to correct the system frequency, the first row of the breast magnetic resonance images sequentially corresponds to the first phase, the second phase and the third phase from left to right in the figure, the white artifact area (shown by an arrow in the figure) generated by uneven fat suppression exists in the breast magnetic resonance images of the third phase, the second row sequentially corresponds to the breast magnetic resonance images of the fourth phase, the fifth phase and the sixth phase from left to right in the figure, and the apparent white artifact area generated by uneven fat suppression exists in the three phases, namely, the fat suppression effect gradually worsens with the increase of the phase. And as shown in fig. 7, the method shown in fig. 2 is adopted to correct the frequency of the magnetic resonance system to obtain multi-phase breast magnetic resonance images, and the multi-phase breast magnetic resonance images are also breast 6-phase scanning, and the frequency drift of the magnetic resonance system calculated by the steps is adopted to correct the frequency of the system, so that the fat pressing effects of different phases are basically consistent. Therefore, by adopting the method of the embodiment of the application to calculate the frequency drift amount of the magnetic resonance system to correct the system frequency, the accuracy of the system frequency can be improved, and the imaging effect can be further improved.
Step 406, 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.
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 corrected at the same time, 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 acquire a first group of echo signals; after the preset duration of the first scanning, performing a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals; respectively calculating according to the first group of echo signals and the second group of echo signals 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; unwrapping 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 steps in the flowcharts of fig. 2-5 are shown in order as indicated by the arrows, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least a portion of the steps of fig. 2-5 may include multiple steps or stages that are not necessarily performed at the same time, but may be performed at different times, nor does the order in which the steps or stages are performed necessarily occur sequentially, but may be performed alternately or alternately with at least a portion of the steps or stages in other steps or other steps.
In one embodiment, as shown in fig. 8, there is provided a device for determining a frequency drift amount of a magnetic resonance system, including:
a first sequence scanning module 501, configured to perform a first scan using a preset scanning sequence to obtain a first set of echo signals; the preset scanning sequence is a gradient double-echo sequence;
the second sequence scanning module 502 is configured to perform a second scan with a preset scanning sequence after a preset duration of the first scan to obtain a second set of echo signals;
A navigation frequency calculation module 503, configured to calculate a first navigation frequency and a second navigation frequency according to the first set of echo signals and the second set of echoes, respectively;
the drift amount determination module 504 is 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 calculating module 503 includes:
the frequency domain conversion sub-module is used for 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 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 sub-module 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; performing phase fitting on the system echo signals 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 calculating submodule 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 correspondence between frequency and phase angle includes frequency being proportional to phase angle and time difference between the first echo signal and the second echo signal being inversely proportional.
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 calculating 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 the first navigation frequency and the second navigation frequency; and (5) unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system.
In one embodiment, the apparatus further comprises:
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 coil frequency modification 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.
For a specific definition of the means for determining the frequency shift amount of the magnetic resonance system, reference may be made to the definition of the method for determining the frequency shift amount of the magnetic resonance system described above, which is not repeated here. The above-mentioned determination means of the frequency drift amount of the magnetic resonance system may be implemented in whole or in part by software, hardware or a combination thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In one embodiment, a computer device is provided, which may be a terminal, and the internal structure thereof 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 includes a non-volatile 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 the operating system and computer programs in the non-volatile storage media. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless mode 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, can also be keys, a track ball or a touch pad arranged on the shell of the computer equipment, and can also be an external keyboard, a touch pad or a mouse and the like.
It will be appreciated by those skilled in the art that the structure shown in fig. 9 is merely a block diagram of a portion of the structure associated with the present application and is not limiting of the computer device to which the present application applies, and that a particular computer device may include more or fewer components than shown, or may combine some of the 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 stored therein a computer program, the processor when executing the computer program performing the steps of:
performing first scanning by adopting a preset scanning sequence to acquire 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 a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals;
respectively calculating according to the first group of echo signals and the second group of echo signals 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 an embodiment, each set of echo signals comprises a first echo signal and a second echo signal, and the processor when executing the computer program implements the steps of:
For each group of echo signals, frequency domain conversion is carried out on the first echo signal and the second echo signal respectively 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, 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;
performing phase fitting on the system echo signals 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 correspondence between frequency and phase angle includes frequency being proportional to phase angle and time difference being inversely proportional to the first echo signal and the second echo signal.
In an 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 performing the steps of:
calculating navigation frequencies according to the echo signals of the plurality of pairs aiming at the first group 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 processor, when executing the computer program, performs the steps of:
calculating a frequency difference between the first navigation frequency and the second navigation frequency;
and (5) unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system.
In one embodiment, the processor, when executing the computer program, performs the steps of:
the magnetic resonance system frequency is corrected according to the magnetic resonance system frequency drift amount.
In one embodiment, the processor, when executing the computer program, performs the steps of:
the frequency of the transmitting coil and/or the frequency of the receiving coil is modified according to the frequency drift amount of the magnetic resonance system.
In one embodiment, a computer readable storage medium is provided having a computer program stored thereon, which when executed by a processor, performs the steps of:
Performing first scanning by adopting a preset scanning sequence to acquire 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 a second scanning by adopting a preset scanning sequence to acquire a second group of echo signals;
respectively calculating according to the first group of echo signals and the second group of echo signals 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 comprises a first echo signal and a second echo signal, and the computer program when executed by the processor performs the steps of:
for each group of echo signals, frequency domain conversion is carried out on the first echo signal and the second echo signal respectively 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, the computer program when executed by a processor 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;
Performing phase fitting on the system echo signals 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 computer program when executed by a processor 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 correspondence between frequency and phase angle includes frequency being proportional to phase angle and time difference being inversely proportional to the first echo signal and the second echo signal.
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 computer program when executed by the processor performs the steps of:
calculating navigation frequencies according to the echo signals of the plurality of pairs aiming at the first group 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 computer program when executed by a processor performs the steps of:
Calculating a frequency difference between the first navigation frequency and the second navigation frequency;
and (5) unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system.
In one embodiment, the computer program when executed by a processor performs the steps of:
the magnetic resonance system frequency is corrected according to the magnetic resonance system frequency drift amount.
In one embodiment, the computer program when executed by a processor performs the steps of:
the frequency of the transmitting coil and/or the frequency of the receiving coil is modified according to the frequency drift amount of the magnetic resonance system.
Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, or the like. Volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory. By way of illustration, and not limitation, RAM can be in the form of a variety of forms, such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), and the like.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
Claims (7)
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 acquire a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence, the first group of echo signals comprise a plurality of pairs of echo signals, and each pair of echo signals comprises two echo signals which are acquired sequentially after the same radio frequency pulse excitation;
After the preset duration of the first scanning, performing a second scanning by adopting the preset scanning sequence to obtain a second group of echo signals, wherein the second group of echo signals comprise a plurality of pairs of echo signals, and each pair of echo signals comprises two echo signals which are acquired after the same radio frequency pulse excitation;
respectively calculating according to the first group of echo signals and the second group of echo signals 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;
unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system;
each pair of echo signals comprises a first echo signal and a second echo signal, and the first navigation frequency and the second navigation frequency are obtained according to the first group of echo signals and the second group of echo calculation respectively, and the method comprises the following steps:
for each group of echo signals, frequency domain conversion is carried out on the first echo signal and the second echo signal respectively to obtain a third echo signal and a fourth echo signal after conversion;
and determining a phase angle according to the third echo signal, the fourth echo signal and a preset phase angle function, and calculating navigation frequency according to the phase angle, the time difference of the first echo signal and the second echo signal.
2. The method of claim 1, wherein frequency is proportional to phase angle and inversely proportional to a time difference between the first echo signal and the second echo signal.
3. The method of claim 1, wherein the calculating, based on the first set of echo signals and the second set of echoes, respectively, results in a first navigator frequency and a second navigator frequency, comprising:
calculating navigation frequencies according to the pairs of echo signals aiming at the first group of echo signals to obtain a plurality of candidate navigation frequencies;
and determining an average value of a plurality of candidate navigation frequencies as the first navigation frequency.
4. The method of claim 1, wherein after said determining an amount of magnetic resonance system frequency drift from said first navigation frequency and said second navigation frequency, the method further comprises:
correcting the frequency of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system; or,
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.
5. A device for determining the amount of frequency drift of a magnetic resonance system, the device comprising:
The first sequence scanning module is used for carrying out first scanning by adopting a preset scanning sequence to acquire a first group of echo signals; the preset scanning sequence is a gradient double-echo sequence, the first group of echo signals comprise a plurality of pairs of echo signals, and each pair of echo signals comprises two echo signals which are acquired sequentially after the same radio frequency pulse excitation;
the second sequence scanning module is used for carrying out second scanning by adopting the preset scanning sequence after the preset duration of the first scanning to obtain a second group of echo signals, wherein the second group of echo signals comprises a plurality of pairs of echo signals, and each pair of echo signals comprises two echo signals which are acquired sequentially after the same radio frequency pulse excitation;
the navigation frequency calculation module is used for calculating according to the first group of echo signals and the second group of echo signals respectively to obtain a first navigation frequency and a second navigation frequency;
the drift amount determining module is used for calculating a frequency difference value between the first navigation frequency and the second navigation frequency; unwrapping the frequency difference value to obtain the frequency drift amount of the magnetic resonance system;
each pair of echo signals comprises a first echo signal and a second echo signal, and the navigation frequency calculation module is specifically configured to perform frequency domain conversion on the first echo signal and the second echo signal for each group of echo signals, so as to obtain a third echo signal and a fourth echo signal after conversion;
And determining a phase angle according to the third echo signal, the fourth echo signal and a preset phase angle function, and calculating navigation frequency according to the phase angle, the time difference of the first echo signal and the second echo signal.
6. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor implements the steps of the method of any of claims 1 to 4 when the computer program is executed.
7. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the method of any of claims 1 to 4.
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