Magnetic resonance system frequency calibration method, device, equipment, storage medium and product

Abstract

The invention relates to a magnetic resonance system frequency calibration method and device, equipment, a storage medium and a product. The method comprises the following steps: carrying out first scanning on a to-be-scanned object by utilizing a selective water excitation sequence to obtain a first echo signal; performing second scanning on the to-be-scanned object by using the selective water excitation sequence to obtain a second echo signal; according to the first echo signal and the second echo signal, the frequency drift amount of the magnetic resonance system in the current time period is calculated; and calibrating the frequency of the radio frequency coil of the magnetic resonance system according to the frequency drift amount of the magnetic resonance system in the current time period. According to the method and the device, the system frequency is calibrated by the selective water excitation sequence, and the selective water excitation sequence only excites the water signal and does not excite other types of signals including metabolite signals; therefore, the stability of the metabolite signal is not influenced, the accuracy of the target metabolite signal is not influenced, and the quality of the spectrum image is not influenced.

Description

Technical Field

[0001] The present application relates to the field of magnetic resonance technology, and in particular to a method, device, equipment, storage medium and product for calibrating the frequency of a magnetic resonance system. Background Art

[0002] During the magnetic resonance spectroscopy scanning process, the system frequency will drift, and the system frequency drift will have an adverse effect on the magnetic resonance spectroscopy, such as causing the spectral line to become wider, reducing the spectral line resolution, and affecting the accuracy of metabolite spectral line fitting.

[0003] Traditionally, during magnetic resonance spectroscopy scanning, the system frequency drift is determined by applying pulses, and then the system frequency is calibrated in real time based on the system frequency drift. However, during the process of calibrating the system frequency using traditional methods, the applied pulses will affect the stability of the target metabolites, thereby reducing the accuracy of the collected target metabolite signals, resulting in poor quality of the spectral image. Summary of the invention

[0004] Based on this, it is necessary to provide a magnetic resonance system frequency calibration method, device, computer equipment, computer-readable storage medium and computer program product that can calibrate the system frequency without affecting the stability of the target metabolites in order to solve the above technical problems.

[0005] In a first aspect, the present application provides a method for calibrating the frequency of a magnetic resonance system. The method comprises:

[0006] Performing a first scan on the object to be scanned using a selective water excitation sequence to obtain a first echo signal;

[0007] Performing a second scan on the object to be scanned using a selective water excitation sequence to obtain a second echo signal;

[0008] Calculating the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal;

[0009] The radio frequency coil frequency of the magnetic resonance system is calibrated according to the frequency drift of the magnetic resonance system in the current period.

[0010] In one embodiment, if the first echo signal and the second echo signal are single echo signals, the frequency drift of the magnetic resonance system in the current period is calculated according to the first echo signal and the second echo signal, including:

[0011] Inputting the first echo signal and the second echo signal into a preset phase angle function to determine a phase angle difference between the first echo signal and the second echo signal;

[0012] The frequency drift amount of the magnetic resonance system in the current period is calculated according to the phase angle difference and the time difference between the first echo signal and the second echo signal.

[0013] In one embodiment, if the first echo signal and the second echo signal are single echo signals, the frequency drift of the magnetic resonance system in the current period is calculated according to the first echo signal and the second echo signal, including:

[0014] 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;

[0015] Performing feature analysis on the third echo signal to obtain first feature information of the third echo signal; and performing feature analysis on the fourth echo signal to obtain second feature information of the fourth echo signal;

[0016] The frequency drift of the magnetic resonance system in the current period is calculated according to the first characteristic information and the second characteristic information.

[0017] In one embodiment, calculating the frequency drift of the magnetic resonance system in the current period according to the first characteristic information and the second characteristic information includes:

[0018] Determining a first system frequency corresponding to the third echo signal according to the first characteristic information;

[0019] Determining a second system frequency corresponding to the fourth echo signal according to the second characteristic information;

[0020] The frequency drift of the magnetic resonance system in the current period is calculated according to the frequency difference between the first system frequency and the second system frequency.

[0021] In one embodiment, if the first echo signal is a first gradient double echo signal and the second echo signal is a second gradient double echo signal, the frequency drift amount of the magnetic resonance system in the current period is calculated according to the first echo signal and the second echo signal, including:

[0022] Determining a third system frequency corresponding to the first echo signal according to the first gradient double echo signal;

[0023] determining a fourth system frequency corresponding to the second echo signal according to the second gradient double echo signal;

[0024] The frequency drift amount of the magnetic resonance system in the current period is calculated according to the frequency difference between the third system frequency and the fourth system frequency.

[0025] In one embodiment, the selective water excitation sequence includes at least one of a frequency-selective excitation pulse sequence, a SpSp pulse sequence, and a water excitation pulse sequence.

[0026] In a second aspect, the present application also provides a magnetic resonance system frequency calibration device. The device comprises:

[0027] A first acquisition module, configured to perform a first scan on the object to be scanned using a selective water excitation sequence to acquire a first echo signal;

[0028] A second acquisition module, used for performing a second scan on the object to be scanned by using a selective water excitation sequence to acquire a second echo signal;

[0029] A calculation module, used for calculating the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal;

[0030] The calibration module is used to calibrate the radio frequency coil frequency of the magnetic resonance system according to the frequency drift of the magnetic resonance system in the current period.

[0031] In a third aspect, the present application further provides a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the magnetic resonance system frequency calibration method in the first aspect are implemented.

[0032] In a fourth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for calibrating the frequency of a magnetic resonance system in the first aspect.

[0033] In a fifth aspect, the present application further provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, the steps of the magnetic resonance system frequency calibration method in the first aspect are implemented.

[0034] The above-mentioned magnetic resonance system frequency calibration method, device, computer equipment, storage medium and computer program product use a selective water excitation sequence to perform a first scan on the scanned object to obtain a first echo signal; and use a selective water excitation sequence to perform a second scan on the scanned object to obtain a second echo signal; according to the first echo signal and the second echo signal, the frequency drift of the magnetic resonance system in the current period is calculated; according to the frequency drift of the magnetic resonance system in the current period, the radio frequency coil frequency of the magnetic resonance system is calibrated. Since the embodiment of the present application is to use a selective water excitation sequence to determine the frequency drift of the magnetic resonance system and realize the calibration of the system frequency, and the selective water excitation sequence only excites the water signal and does not excite other types of signals including metabolite signals; therefore, in the process of calibrating the system frequency, the stability of the metabolite signal will not be affected, and the accuracy of the collected target metabolite signal will not be affected, and thus the quality of the spectral image obtained by the spectral scanning will not be affected; in addition, since the frequency of the water signal can characterize the frequency of the system, the use of a selective water excitation sequence for frequency calibration can achieve accurate calibration of the system frequency on the basis of ensuring high-quality spectral imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A diagram showing an application environment of a method for calibrating a frequency of a magnetic resonance system in one embodiment;

[0036] Figure 2 is a schematic flow chart of a method for calibrating the frequency of a magnetic resonance system in one embodiment;

[0037] Figure 3 is a timing diagram of a water-excited free decay signal corresponding to a single echo signal in an embodiment;

[0038] Figure 4 is a flow chart of a method for calibrating the frequency of a magnetic resonance system in another embodiment;

[0039] Figure 5 is a flow chart of a method for calibrating the frequency of a magnetic resonance system in another embodiment;

[0040] Figure 6 is a timing diagram of a water excitation gradient double echo signal corresponding to a double echo signal in an embodiment;

[0041] Figure 7 is a flow chart of a method for calibrating the frequency of a magnetic resonance system in another embodiment;

[0042] FIG8( a ) is a brain spectrogram without real-time frequency calibration in one embodiment;

[0043] FIG8( b ) is a brain spectrogram with real-time frequency calibration applied in one embodiment;

[0044] Fig. 9 is a structural block diagram of a frequency calibration device for a magnetic resonance system in one embodiment;

[0045] Fig.10 FIG. 4 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0047] During the MR spectroscopy scanning process, the accuracy of the system frequency directly affects the quality of the spectrum. Especially after the system scans the echo planar imaging (EPI) sequence, the vibration caused by the continuous switching of the current generates heat, which in turn causes the system frequency to drift. When scanning the spectrum, the system frequency drift will cause the spectrum line to become wider, reduce the resolution of the spectrum line, and also affect the accuracy of the post-processing metabolite spectrum fitting. Metabolites include but are not limited to N-acetylaspartate (NAA), creatine (Cr) and other metabolites.

[0048] In the related art, in order to prevent the system frequency drift from reducing the spectral line quality, the system frequency is usually calibrated. Retrospective frequency calibration can ensure the alignment of signal frequencies, but it cannot solve the scenario of water pressure failure caused by frequency drift. When water pressure fails, the residual water signal has a greater impact on the spectral line baseline, which will affect the quantification result. Real-time frequency calibration can solve the shortcomings of retrospective frequency calibration and overcome the influence of field drift on water pressure. However, the first two schemes require additional signal acquisition, that is, the system frequency drift is determined by applying pulses, and then the system frequency is calibrated in real time based on the system frequency drift; and the additional acquisition signal will excite signals of all frequencies, thereby affecting the steady state of the metabolite signal.

[0049] For chemical shift imaging (CSI), the destruction of signal steady state will cause spatial artifacts. The low spatial resolution of CSI makes it difficult to determine whether there are spatial artifacts on the spectrum line, and the spatial artifacts on the spectrum line cannot be discovered in time. For single voxel spectroscopy (SVS), the destruction of signal steady state will affect the signal phase. When averaging multiple times, the phase is inconsistent between different averaging times, which will cause partial signal loss and the signal-to-noise ratio cannot reach the optimal level.

[0050] Based on this, an embodiment of the present application proposes a method for calibrating the frequency of a magnetic resonance system, which calibrates the system frequency in real time during magnetic resonance spectroscopy imaging, and solves the problem of system frequency drift without affecting the steady state of the metabolite signal, thereby overcoming the adverse effects of system frequency drift on magnetic resonance spectroscopy during long-term scanning.

[0051] The magnetic resonance system frequency calibration method provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown, the magnetic resonance scanning device 120 is used to perform magnetic resonance scanning on metabolites in the body of the object to be scanned, and obtain spectral images of tissue metabolism and biochemical changes corresponding to the object to be scanned, so as to realize magnetic resonance spectroscopy (MRS) imaging.

[0052] In one embodiment, Figure 2 As shown, a method for calibrating the frequency of a magnetic resonance system is provided. Figure 1 The magnetic resonance scanning device in the embodiment is used as an example to illustrate, and the method includes the following steps:

[0053] Step 201 : performing a first scan on an object to be scanned using a selective water excitation sequence to obtain a first echo signal.

[0054] Among them, the selective water excitation sequence can only excite water signals without exciting other types of signals, such as fat signals, various metabolite signals (such as NAA, Cr), etc. Exemplarily, the selective water excitation sequence can include but is not limited to at least one of a frequency-selective excitation pulse sequence, a SpSp pulse sequence, and a water excitation pulse sequence; wherein the SpSp pulse sequence can be interpreted as Spatial-spectral RF pulses, or as Spectral Spatial RFPulses, etc.; in addition, when the selective water excitation sequence is used to excite the water signal in the body of the object to be scanned, a layer selection gradient may be applied or not.

[0055] During the spectral scanning of the object to be scanned, long-term scanning may cause the system frequency of the magnetic resonance scanning device to drift. Therefore, during the spectral scanning, the system frequency needs to be calibrated in real time to ensure that the system frequency remains consistent during the entire spectral scanning process.

[0056] Exemplarily, at the beginning of the spectrum scan, the selective water excitation sequence can be used to perform a first scan on the object to be scanned, and a first echo signal corresponding to the first scan can be obtained; here, the first echo signal after the selective water excitation sequence penetrates the object to be scanned can be collected by the water signal acquisition module; the first echo signal includes but is not limited to one of a free decay signal, a spin echo signal, a stimulation echo signal, and a gradient echo signal. The type of the first echo signal can be related to the number of water excitation pulses in the selective water excitation sequence; for example: when the selective water excitation sequence includes a group of water excitation pulses, the first echo signal is a free decay signal; when the selective water excitation sequence includes two groups of water excitation pulses, the first echo signal is a spin echo signal; when the selective water excitation sequence includes three groups of water excitation pulses, the first echo signal is a stimulation echo signal. In addition, when the selective water excitation sequence includes a readout gradient, a gradient double echo signal can be collected; it should be noted that when the water signal acquisition module collects the gradient echo signal, phase encoding may not be applied, that is, the phase encoding gradient may not be included in the selective water excitation sequence.

[0057] In another implementation, when a magnetic resonance scanning device is used to perform spectral imaging on a subject to be scanned, the system frequency is relatively stable for a period of time at the beginning of the scan, and there may be no frequency drift phenomenon; in this case, after the first preset duration of the scan is started, the selective water excitation sequence may be used to perform a first scan on the subject to be scanned and obtain a first echo signal. In the embodiment of the present application, the first preset duration is not specifically limited, and the first preset duration can be flexibly adjusted during actual use.

[0058] In another implementation, the first scan may be performed multiple times during the initial scan, and multiple first echo signals may be acquired, and then a reference echo signal may be determined based on the multiple first echo signals, and the reference echo signal may be used as the final first echo signal. For example, an average echo signal of the multiple first echo signals may be used as the reference echo signal.

[0059] Step 202: Perform a second scan on the object to be scanned using a selective water excitation sequence to obtain a second echo signal.

[0060] When performing real-time frequency calibration, the system frequency of the magnetic resonance scanning device can be periodically detected and the system frequency can be calibrated in real time. For example, under high field, due to the increase in T1 relaxation value, the repetition time TR of spectral imaging is often relatively long; wherein, the repetition time TR refers to the time interval between two adjacent executions of the pulse sequence; based on this, between each TR, a selective water excitation sequence can be used to excite the water signal in the body of the object to be scanned, and the object to be scanned can be scanned, thereby determining the system frequency at each scan, and calibrating the system frequency in real time. Since the TR time is relatively long, the method in this embodiment does not increase the additional acquisition time.

[0061] Exemplarily, the first scan of the scanned object using the selective water excitation sequence can be called the first scan, and the subsequent periodic multiple scans can be called the second scan; the second echo signal obtained by each second scan can be analyzed and processed separately with the first echo signal obtained by the first scan, so as to determine whether the system frequency has drifted, and calibrate the system frequency that has drifted; that is, ensure that the system frequency during the entire scanning process is consistent with the system frequency during the initial scan.

[0062] In another example, in the periodic real-time frequency calibration process, the first scan of two adjacent scans can be used as the first scan, and the second scan adjacent to the first scan can be used as the second scan, so as to ensure that the system frequencies of the two adjacent scans are consistent to achieve the consistency of the system frequency in the entire scanning process. Of course, at least one scan can be included between the first scan and the second scan. The embodiment of the present application does not specifically limit the first scan and the second scan, as long as the first scan and the second scan are two water signal scans in the entire spectrum scanning process.

[0063] Exemplarily, when the second preset time length arrives after the first scan, the selective water excitation sequence can be used to perform a second scan on the object to be scanned, and a second echo signal corresponding to the second scan can be obtained; wherein, the second preset time length can be a calibration period of real-time frequency calibration; based on the calibration period, when the second preset time length arrives after the second scan, the selective water excitation sequence can be used to perform a new second scan on the object to be scanned, and a new second echo signal corresponding to the new second scan can be obtained, and this cycle can be repeated until the spectral scan of the object to be scanned is completed.

[0064] The type of the second echo signal may be the same as or different from the type of the first echo signal.

[0065] Step 203: Calculate the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal.

[0066] The current time period is a scanning time period between a first scanning time corresponding to the first scanning and a second scanning time corresponding to the second scanning.

[0067] Exemplarily, the first system frequency corresponding to the first scanning moment can be determined according to the first echo signal, and the second system frequency corresponding to the second scanning moment can be determined according to the second echo signal. Then, the frequency drift of the magnetic resonance system in the current time period can be calculated according to the difference between the first system frequency and the second system frequency.

[0068] In another example, the frequency drift of the magnetic resonance system in the current period can be directly determined by analyzing the first echo signal and the second echo signal.

[0069] Among them, the frequency drift amount can be used to characterize how much the second system frequency at the second scanning moment increases or decreases compared to the first system frequency at the first scanning moment; exemplarily, the frequency band drift amount can be a drift amount with positive and negative directions, for example: +A means that the second system frequency at the second scanning moment increases by a drift amount A compared to the first system frequency at the first scanning moment, that is, the second system frequency corresponding to the second scanning moment is faster than the first system frequency corresponding to the first scanning moment; -A means that the second system frequency at the second scanning moment decreases by a drift amount A compared to the first system frequency at the first scanning moment, that is, the second system frequency corresponding to the second scanning moment is slower than the first system frequency corresponding to the first scanning moment.

[0070] Step 204: calibrate the radio frequency coil frequency of the magnetic resonance system according to the frequency drift of the magnetic resonance system in the current period.

[0071] The radio frequency coil frequency includes the frequency of the transmitting coil and the frequency of the receiving coil.

[0072] Exemplarily, when the magnetic resonance scanning device determines the frequency drift of the magnetic resonance system in the current period, the RF coil frequency of the magnetic resonance system can be calibrated according to the frequency drift, so that the calibrated system frequency is consistent with the first system frequency corresponding to the first scanning moment. For example, when the frequency drift is +A, it means that the system frequency at this time is faster than the first system frequency corresponding to the first scanning moment. At this time, the current second system frequency can be reduced by A, that is, the current RF coil frequency can be reduced by A, so that the system frequency during the spectrum scanning process remains consistent.

[0073] Exemplarily, the magnetic resonance scanning device may also first determine the frequency drift. If the absolute value of the frequency drift is less than or equal to a preset drift threshold, the radio frequency coil frequency of the magnetic resonance system does not need to be calibrated; that is, when the offset between the second system frequency corresponding to the second scanning moment and the first system frequency corresponding to the first scanning moment is within a certain threshold error range, that is, the system frequencies at the two moments are relatively close and will not affect the spectral imaging, then the radio frequency coil frequency does not need to be calibrated, thereby reducing the number of calibrations and improving scanning efficiency.

[0074] On the contrary, when it is determined that the absolute value of the frequency drift is greater than the preset drift threshold, the radio frequency coil frequency of the magnetic resonance system is calibrated according to the frequency drift.

[0075] In the above-mentioned magnetic resonance system frequency calibration method, a selective water excitation sequence is used to perform a first scan on the scanned object to obtain a first echo signal; and a selective water excitation sequence is used to perform a second scan on the scanned object to obtain a second echo signal; according to the first echo signal and the second echo signal, the frequency drift of the magnetic resonance system in the current period is calculated; according to the frequency drift of the magnetic resonance system in the current period, the frequency of the radio frequency coil of the magnetic resonance system is calibrated. Since the selective water excitation sequence is used to determine the frequency drift of the magnetic resonance system in the embodiment of the present application, the system frequency is calibrated, and the selective water excitation sequence only excites the water signal and does not excite other types of signals including metabolite signals; therefore, the stability of the metabolite signal will not be affected in the process of calibrating the system frequency, and the accuracy of the target metabolite signal collected will not be affected, and the quality of the spectral image obtained by the spectral scanning will not be affected; in addition, since the frequency of the water signal can characterize the frequency of the system, the frequency calibration using the selective water excitation sequence can achieve accurate calibration of the system frequency on the basis of ensuring high-quality spectral imaging.

[0076] In one embodiment, the first echo signal and the second echo signal may be single echo signals or double echo signals. The following will describe the calculation methods for calculating the frequency drift for the single echo signal and the double echo signal respectively.

[0077] The first type: the first echo signal and the second echo signal are single echo signals.

[0078] Wherein, when neither phase encoding nor readout gradient is included in the selective water excitation sequence, the first echo signal and the second echo signal collected by the water signal acquisition module are single echo signals. Figure 3As shown, it shows a sequence diagram of a water signal free decay signal corresponding to a single echo signal. Among them, RF is a radio frequency excitation pulse, Gss is a layer selection gradient, and ADC is an analog-to-digital conversion module, that is, a free decay signal collected by a water signal acquisition module.

[0079] In one implementation, Figure 4 As shown, in the above step 203, calculating the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal may include:

[0080] Step 401: Input a first echo signal and a second echo signal into a preset phase angle function to determine a phase angle difference between the first echo signal and the second echo signal.

[0081] Exemplarily, the first echo signal collected at the first scanning time is recorded as e r [n], n is an integer between 0 and N-1, and N is the number of ADC sampling points. The second echo signal collected at the second scanning time is recorded as e t [n].

[0082] The first echo signal e r The conjugate of [n] and the second echo signal e t [n] are multiplied to obtain the multiplication result e[n], as shown in formula (1).

[0083]

[0084] Next, the multiplication result e[n] is summed and the phase is obtained, thereby obtaining the phase angle difference between the first echo signal and the second echo signal, as shown in formula (2).

[0085]

[0086] Here, the phase angle difference θ can also be solved using the least squares method.

[0087] Step 402: Calculate the frequency drift of the magnetic resonance system in the current period according to the phase angle difference and the time difference between the first echo signal and the second echo signal.

[0088] After determining the phase angle difference θ between the first echo signal and the second echo signal, the frequency drift f of the magnetic resonance system in the current period can be calculated according to the time interval ΔT between the first scanning moment and the second scanning moment and the phase angle difference θ between the first echo signal and the second echo signal, as shown in formula (3).

[0089]

[0090] In another implementation, Figure 5As shown, in the above step 203, calculating the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal may include:

[0091] Step 501: Perform frequency domain conversion on the first echo signal to obtain a third echo signal; and perform frequency domain conversion on the second echo signal to obtain a fourth echo signal.

[0092] Exemplarily, the first echo signal and the second echo signal may be subjected to Fourier transform to obtain a third echo signal in the frequency domain corresponding to the first echo signal and a fourth echo signal in the frequency domain corresponding to the second echo signal.

[0093] The first echo signal is denoted as e r In the case of [], the third echo signal can be expressed as E r []; The second echo signal is recorded as e t In the case of [], the fourth echo signal can be expressed as E t [ ].

[0094] Step 502: Perform characteristic analysis on the third echo signal to obtain first characteristic information of the third echo signal; and perform characteristic analysis on the fourth echo signal to obtain second characteristic information of the fourth echo signal.

[0095] Among them, the first characteristic information of the third echo signal may include characteristic information used to characterize the water peak frequency in the third echo signal, such as at least one of the center of gravity and the maximum value of the third echo signal; the second characteristic information of the fourth echo signal may include characteristic information used to characterize the water peak frequency in the fourth echo signal, such as at least one of the center of gravity and the maximum value of the fourth echo signal.

[0096] For example, for the third echo signal, the amplitude of the third echo signal may be calculated first, that is, the amplitude |E r []|, then, calculate the centroid of the amplitude of the third echo signal or the maximum amplitude, that is, |E r []|'s center of gravity or |E r The maximum value of []| is used as the first characteristic information of the third echo signal.

[0097] Similarly, for the fourth echo signal, the amplitude of the fourth echo signal can be calculated first, that is, the amplitude |E t []|, then, calculate the centroid of the amplitude of the fourth echo signal or the maximum amplitude, that is, |E t []|'s center of gravity or |E t The maximum value of []| is used as the second characteristic information of the fourth echo signal.

[0098] Step 503: Calculate the frequency drift of the magnetic resonance system in the current period according to the first characteristic information and the second characteristic information.

[0099] Exemplarily, the first system frequency corresponding to the third echo signal can be determined based on the first characteristic information; and the second system frequency corresponding to the fourth echo signal can be determined based on the second characteristic information; then, the frequency drift of the magnetic resonance system in the current time period is calculated based on the frequency difference between the first system frequency and the second system frequency.

[0100] Based on the above example, for the third echo signal, after determining the third echo signal |E r []|'s center of gravity or |E r In the case of the maximum value of []|, we can determine |E r []|'s center of gravity or |E r The value of k when []| is the maximum value is recorded as k0, and the frequency corresponding to k0 is calculated and recorded as the first system frequency f corresponding to the third echo signal r .

[0101] Similarly, for the fourth echo signal, after determining the fourth echo signal |E t []|'s center of gravity or |E t In the case of the maximum value of []|, we can determine |E t []|'s center of gravity or |E t The value of k when []| is the maximum value is recorded as k1, and the frequency corresponding to k1 is calculated and recorded as the second system frequency f corresponding to the fourth echo signal t .

[0102] Next, according to the second system frequency f t With the first system frequency f r The frequency drift of the magnetic resonance system in the current period is calculated by the frequency difference, that is, the frequency drift f = f t -f r .

[0103] In the case that both the first echo signal and the second echo signal are single echo signals, the frequency drift amount between the first echo signal and the second echo signal may be calculated by using any of the above two methods.

[0104] The second type: the first echo signal is a first gradient double echo signal, and the second echo signal is a second gradient double echo signal.

[0105] Wherein, when the selective water excitation sequence does not include phase encoding but includes a readout gradient, the first echo signal and the second echo signal acquired by the water signal acquisition module are gradient double echo signals. Figure 6As shown, it shows a sequence diagram of a water signal gradient double echo signal corresponding to a double echo signal. Among them, RF is a radio frequency excitation pulse, Gss is a layer selection gradient, Gro is a readout gradient, and ADC is an analog-to-digital conversion module, that is, a gradient double echo signal collected by a water signal acquisition module.

[0106] In one implementation, Figure 7 As shown, in the above step 203, calculating the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal may include:

[0107] Step 701: Determine a third system frequency corresponding to the first echo signal according to the first gradient double echo signal.

[0108] Step 702: Determine a fourth system frequency corresponding to the second echo signal according to the second gradient double echo signal.

[0109] In the above steps 701 and 702, the method of determining the corresponding system frequency according to the gradient double echo signal may be:

[0110] The gradient double echo signal includes a first sub-echo signal and a second sub-echo signal.

[0111] Step a: performing frequency domain conversion on the first sub-echo signal to obtain a third sub-echo signal in the frequency domain corresponding to the first sub-echo signal; and performing frequency domain conversion on the second sub-echo signal to obtain a fourth sub-echo signal in the frequency domain corresponding to the second sub-echo signal.

[0112] Step b: Integrate the third sub-echo signal and the fourth sub-echo signal to obtain a system echo signal; the system echo signal is represented by amplitude and phase angle.

[0113] Step c: performing phase fitting on the system echo signal to obtain a phase angle.

[0114] Step d, determining the phase angle and the time interval ΔT between the first sub-echo signal and the second sub-echo signal according to the phase angle ′ , to calculate the system frequency; refer to the above formula (3), that is, the phase angle and the time interval ΔT ′ By dividing by 2π, we can get the system frequency.

[0115] By adopting the above method, the third system frequency corresponding to the first echo signal and the fourth system frequency corresponding to the second echo signal can be calculated.

[0116] Step 703: Calculate the frequency drift of the magnetic resonance system in the current period according to the frequency difference between the third system frequency and the fourth system frequency.

[0117] Among them, the third system frequency is the system frequency corresponding to the first scanning time, and the fourth system frequency is the system frequency corresponding to the second scanning time. Then, the frequency difference between the fourth system frequency and the third system frequency can be used as the frequency drift of the magnetic resonance system in the current period.

[0118] The above describes the calculation methods of the system frequency drift corresponding to the single echo signal and the double echo signal, respectively, and provides a calculation basis for different types of echo signals.

[0119] In one embodiment, the above-mentioned magnetic resonance system frequency calibration method proposed in the embodiment of the present application is used to verify the actual brain spectral imaging. During the verification, the real-time system frequency calibration is not applied first, and the brain spectrum of the object to be scanned is collected, as shown in Figure 8(a); then, the real-time system frequency calibration is applied, and the brain spectrum of the object to be scanned under the real-time frequency calibration is collected, as shown in Figure 8(b). It can be seen that after the system frequency of the magnetic resonance scanning device is calibrated in real time by the above-mentioned magnetic resonance system frequency calibration method proposed in the embodiment of the present application, the problem of the broadening of the spectrum peak caused by the system frequency drift is solved, and the resolution of the spectrum line is improved.

[0120] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0121] Based on the same inventive concept, the embodiment of the present application also provides a magnetic resonance system frequency calibration device for implementing the magnetic resonance system frequency calibration method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more embodiments of the magnetic resonance system frequency calibration device provided below can refer to the limitations of the magnetic resonance system frequency calibration method above, and will not be repeated here.

[0122] In one embodiment, Fig. 9 As shown, a magnetic resonance system frequency calibration device is provided, comprising: a first acquisition module 901, a second acquisition module 902, a calculation module 903 and a calibration module 904, wherein:

[0123] A first acquisition module 901 is used to perform a first scan on the object to be scanned using a selective water excitation sequence to acquire a first echo signal;

[0124] A second acquisition module 902 is used to perform a second scan on the object to be scanned using a selective water excitation sequence to acquire a second echo signal;

[0125] A calculation module 903 is used to calculate the frequency drift of the magnetic resonance system in the current period according to the first echo signal and the second echo signal;

[0126] The calibration module 904 is used to calibrate the radio frequency coil frequency of the magnetic resonance system according to the frequency drift of the magnetic resonance system in the current period.

[0127] In one embodiment, if the first echo signal and the second echo signal are single echo signals, the calculation module 903 includes a first determination submodule and a first calculation submodule; wherein,

[0128] A first determination submodule, used for inputting the first echo signal and the second echo signal into a preset phase angle function to determine a phase angle difference between the first echo signal and the second echo signal;

[0129] The first calculation submodule is used to calculate the frequency drift of the magnetic resonance system in the current period according to the phase angle difference and the time difference between the first echo signal and the second echo signal.

[0130] In one embodiment, if the first echo signal and the second echo signal are single echo signals, the calculation module 903 includes a first acquisition submodule, a second acquisition submodule and a second calculation submodule; wherein,

[0131] A first acquisition submodule is used to perform frequency domain conversion on the first echo signal to obtain a third echo signal; and perform frequency domain conversion on the second echo signal to obtain a fourth echo signal;

[0132] The second acquisition submodule is used to perform characteristic analysis on the third echo signal to obtain first characteristic information of the third echo signal; and perform characteristic analysis on the fourth echo signal to obtain second characteristic information of the fourth echo signal;

[0133] The second calculation submodule is used to calculate the frequency drift of the magnetic resonance system in the current period according to the first characteristic information and the second characteristic information.

[0134] In one embodiment, the second calculation submodule includes a first determination unit, a second determination unit and a calculation unit; wherein,

[0135] A first determining unit, configured to determine a first system frequency corresponding to the third echo signal according to the first characteristic information;

[0136] A second determining unit, configured to determine a second system frequency corresponding to the fourth echo signal according to the second characteristic information;

[0137] The calculation unit is used to calculate the frequency drift of the magnetic resonance system in the current period according to the frequency difference between the first system frequency and the second system frequency.

[0138] In one embodiment, if the first echo signal is a first gradient double echo signal and the second echo signal is a second gradient double echo signal, the calculation module 903 includes a second determination submodule, a third determination submodule and a third calculation submodule; wherein,

[0139] A second determination submodule, configured to determine a third system frequency corresponding to the first echo signal according to the first gradient double echo signal;

[0140] A third determination submodule, configured to determine a fourth system frequency corresponding to the second echo signal according to the second gradient double echo signal;

[0141] The third calculation submodule is used to calculate the frequency drift of the magnetic resonance system in the current period according to the frequency difference between the third system frequency and the fourth system frequency.

[0142] In one embodiment, the selective water excitation sequence includes at least one of a frequency-selective excitation pulse sequence, a SpSp pulse sequence, and a water excitation pulse sequence.

[0143] Each module in the above-mentioned magnetic resonance system frequency calibration device can be implemented in whole or in part by software, hardware and a combination thereof. Each of the above-mentioned modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0144] In one embodiment, a computer device is provided. The computer device may be a magnetic resonance scanning device, and its internal structure diagram may be as follows: Fig.10As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used 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 the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a method for calibrating the frequency of a magnetic resonance system is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse, etc.

[0145] Those skilled in the art will understand that Fig.10 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0146] In one embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps of the magnetic resonance system frequency calibration method in the above-mentioned various embodiments when executing the computer program.

[0147] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the magnetic resonance system frequency calibration method in the above-mentioned embodiments are implemented.

[0148] In one embodiment, a computer program product is provided, comprising a computer program, wherein when the computer program is executed by a processor, the steps of the magnetic resonance system frequency calibration method in the above-mentioned embodiments are implemented.

[0149] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0150] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0151] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0152] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for calibrating the frequency of a magnetic resonance system, characterized in that: The method comprises: Performing a first scan on the object to be scanned using a selective water excitation sequence to obtain a first echo signal; Performing a second scan on the object to be scanned using the selective water excitation sequence to obtain a second echo signal; Calculating a frequency drift of the magnetic resonance system in a current period according to the first echo signal and the second echo signal; The radio frequency coil frequency of the magnetic resonance system is calibrated according to the frequency drift of the magnetic resonance system in the current period.

2. The method according to claim 1, characterized in that If the first echo signal and the second echo signal are single echo signals, then calculating the frequency drift amount of the magnetic resonance system in the current period according to the first echo signal and the second echo signal includes: Inputting the first echo signal and the second echo signal into a preset phase angle function to determine a phase angle difference between the first echo signal and the second echo signal; The frequency drift amount of the magnetic resonance system in the current period is calculated according to the phase angle difference and the time difference between the first echo signal and the second echo signal.

3. The method according to claim 1, characterized in that If the first echo signal and the second echo signal are single echo signals, then calculating the frequency drift amount of the magnetic resonance system in the current period according to the first echo signal and the second echo signal includes: 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; Performing feature analysis on the third echo signal to obtain first feature information of the third echo signal; and performing feature analysis on the fourth echo signal to obtain second feature information of the fourth echo signal; The frequency drift amount of the magnetic resonance system in the current period is calculated according to the first characteristic information and the second characteristic information.

4. The method according to claim 3, characterized in that The calculating, according to the first characteristic information and the second characteristic information, the frequency drift of the magnetic resonance system in the current period includes: Determining a first system frequency corresponding to the third echo signal according to the first characteristic information; determining, according to the second characteristic information, a second system frequency corresponding to the fourth echo signal; The frequency drift amount of the magnetic resonance system in the current period is calculated according to the frequency difference between the first system frequency and the second system frequency.

5. The method according to claim 1, characterized in that If the first echo signal is a first gradient double echo signal and the second echo signal is a second gradient double echo signal, then calculating the frequency drift amount of the magnetic resonance system in the current period according to the first echo signal and the second echo signal includes: determining a third system frequency corresponding to the first echo signal according to the first gradient double echo signal; determining a fourth system frequency corresponding to the second echo signal according to the second gradient double echo signal; The frequency drift amount of the magnetic resonance system in the current period is calculated according to the frequency difference between the third system frequency and the fourth system frequency.

6. The method according to claim 1, characterized in that The selective water excitation sequence includes at least one of a frequency-selective excitation pulse sequence, a SpSp pulse sequence and a water excitation pulse sequence.

7. A magnetic resonance system frequency calibration device, characterized in that: The device comprises: A first acquisition module, configured to perform a first scan on the object to be scanned using a selective water excitation sequence to acquire a first echo signal; A second acquisition module, configured to perform a second scan on the object to be scanned using the selective water excitation sequence to acquire a second echo signal; A calculation module, configured to calculate a frequency drift of the magnetic resonance system in a current period according to the first echo signal and the second echo signal; The calibration module is used to calibrate the radio frequency coil frequency of the magnetic resonance system according to the frequency drift of the magnetic resonance system in the current period.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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