Magnetic resonance scanning method and magnetic resonance imaging system

Abstract

This application provides a magnetic resonance scanning method and a magnetic resonance imaging system. The method includes: acquiring a signal showing the change of cold head parameters over time when the cold head is working in the magnetic resonance imaging system; and calibrating the carrier frequency of the radio frequency field generated by the magnetic resonance system based on the signal during magnetic resonance scanning.

Description

Technical Field

[0001] This application relates to the field of medical device technology, and in particular to a magnetic resonance scanning method and a magnetic resonance imaging system. Background Technology

[0002] Magnetic resonance imaging (MRI) systems are widely used in medical diagnostics. Their basic principle involves using a magnet to generate a uniform, strong magnetic field. With the assistance of a gradient coil generating a specific gradient field, hydrogen atoms within the patient's body are polarized. Then, a radio frequency (RF) coil emits radio pulses to excite the hydrogen nuclei, causing nuclear resonance and energy absorption. After the RF pulse stops, the hydrogen nuclei emit free-induction decay signals at a specific frequency, releasing the absorbed energy. This released energy is recorded by an external receiver and processed by a computer to obtain an image.

[0003] In superconducting magnetic resonance imaging (MRI) systems, the superconducting magnet is the core component. It utilizes superconducting coils made of superconducting materials to generate a high-intensity, highly stable magnetic field. A superconducting magnet typically includes a superconducting coil and a cryogenic container housing the coil. The cryogenic container contains a cooling medium that immerses the superconducting coil; common cooling media include liquid helium. Due to heat conduction and radiation between the interior and exterior of the cryogenic container, heat continuously enters the container, causing the expensive cooling medium to evaporate. To address this evaporation problem, a cold head is added to the cryogenic container to cool the interior, removing excess heat and maintaining the stability of the cooling medium, achieving zero evaporation. Summary of the Invention

[0004] The inventors discovered that the cold head undergoes piston-like motion, and the resulting mechanical vibrations cut the magnetic field lines in the magnetic resonance imaging system, causing magnetic field disturbances, which may in turn lead to a decrease in the quality of the magnetic resonance image.

[0005] To address at least one of the above-mentioned problems, embodiments of this application provide a magnetic resonance scanning method and a magnetic resonance imaging system.

[0006] According to one aspect of the embodiments of this application, a magnetic resonance scanning method is provided, the method comprising:

[0007] Acquire signals of the time-varying parameters of the cold head during operation of the cold head in a magnetic resonance imaging system;

[0008] During magnetic resonance imaging (MRI) scanning, the carrier frequency of the radio frequency field generated by the MRI system is calibrated based on the signal.

[0009] According to one aspect of the embodiments of this application, a magnetic resonance imaging system is provided, the system comprising:

[0010] Scanning unit;

[0011] A controller configured to perform the magnetic resonance scanning method described in the foregoing aspect.

[0012] One of the beneficial effects of this application embodiment is that the carrier frequency of the radio frequency field generated by the magnetic resonance system is calibrated by using the signal of the cold head parameter changing over time. Thus, the influence of magnetic field disturbance caused by the movement of the cold head on the quality of the magnetic resonance image can be avoided.

[0013] Referring to the following description and accompanying drawings, specific implementation methods of the embodiments of this application are disclosed in detail, indicating how the principles of the embodiments of this application can be adopted. It should be understood that the implementation methods of this application are not limited in scope. Within the spirit and scope of the appended claims, the implementation methods of this application include many changes, modifications, and equivalents. Attached Figure Description

[0014] The accompanying drawings, which form part of the specification, are used to provide a further understanding of the embodiments of this application and illustrate the implementation methods of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other implementation methods based on these drawings without creative effort.

[0015] In the attached diagram:

[0016] Figure 1 This is a schematic diagram of a magnetic resonance imaging system according to an embodiment of this application;

[0017] Figure 2 This is a schematic diagram of a magnetic resonance scanning method according to an embodiment of this application;

[0018] Figure 3 This is a schematic diagram of the signal of cold head parameters changing over time, collected in an embodiment of this application;

[0019] Figure 4 This is the processed signal spectrum diagram in the embodiments of this application;

[0020] Figure 5 This is a schematic diagram showing the correspondence between the cold head parameters and the main magnetic field center frequency related parameters in an embodiment of this application;

[0021] Figure 6 This is a schematic diagram showing the correspondence between the cold head parameters and the main magnetic field center frequency related parameters in an embodiment of this application;

[0022] Figure 7 This is a schematic diagram showing the correspondence between the cold head parameters and the main magnetic field center frequency related parameters in an embodiment of this application;

[0023] Figure 8This is a schematic diagram showing the correspondence between the cold head parameters and the main magnetic field center frequency related parameters in an embodiment of this application;

[0024] Figure 9 This is a schematic diagram of the magnetic resonance scanning process according to an embodiment of this application;

[0025] Figure 10 This is a schematic diagram of the magnetic resonance scanning process according to an embodiment of this application. Detailed Implementation

[0026] Referring to the accompanying drawings, the foregoing and other features of the embodiments of this application will become apparent from the following description. Specific embodiments of this application are specifically disclosed in the description and drawings, illustrating partial implementations in which the principles of the embodiments of this application can be adopted. It should be understood that this application is not limited to the described embodiments; rather, the embodiments of this application include all modifications, variations, and equivalents falling within the scope of the appended claims.

[0027] In the embodiments of this application, the terms "first," "second," etc., are used to distinguish different elements by name, but do not indicate the spatial arrangement or chronological order of these elements, and these elements should not be limited by these terms. The term "and / or" includes any one or more of the terms listed in association and all combinations thereof. The terms "comprising," "including," "having," etc., refer to the presence of the stated features, elements, components, or assemblies, but do not exclude the presence or addition of one or more other features, elements, components, or assemblies.

[0028] In the embodiments of this application, the singular forms "a," "the," etc., including the plural forms, should be broadly understood as "a kind" or "a class" rather than limited to the meaning of "an." Furthermore, the term "the" should be understood to include both the singular and plural forms, unless the context explicitly indicates otherwise. Additionally, the term "according to" should be understood as "at least partially based on…," and the term "based on" should be understood as "at least partially based on…," unless the context explicitly indicates otherwise.

[0029] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. The term "comprising / including" as used herein means the presence of a feature, integral, step, or component, but does not exclude the presence or addition of one or more other features, integrals, steps, or components.

[0030] For ease of understanding, Figure 1 A magnetic resonance imaging (MRI) system 100 according to some embodiments of the present invention is shown.

[0031] The MRI system 100 includes a scanning unit 111. The scanning unit 111 performs magnetic resonance scanning on an object (e.g., a human body) 170 to generate image data of a region of interest (ROI) of the object 170, which may be a predetermined anatomical location or tissue. A cooling head 61 is disposed on the magnet housing of the magnetic resonance imaging system; this is merely an example and is not intended to limit the scope of the embodiments described herein.

[0032] The operation of the MRI system 100 is controlled by an operator workstation 110, which includes an input device 114, a control panel 116, and a display 118. The input device 114 may be a joystick, keyboard, mouse, trackball, touch-activated screen, voice control, or any similar or equivalent input device. The control panel 116 may include a keyboard, touch-activated screen, voice control, buttons, sliders, or any similar or equivalent control device. The operator workstation 110 is coupled to and communicates with a computer system 120, which enables the operator to control the generation and viewing of images on the display 118. The computer system 120 includes multiple components that communicate with each other via an electrical and / or data connection module 122. The connection module 122 may be a direct wired connection, a fiber optic connection, a wireless communication link, etc. The computer system 120 may include a central processing unit (CPU) 124, a memory 126, and an image processor 128. In some embodiments, the image processor 128 may be replaced by image processing functions implemented in the CPU 124. Computer system 120 can be connected to archival media devices, permanent or backup storage, or a network. Computer system 120 can be coupled to and communicate with a separate MRI system controller 130.

[0033] The MRI system controller 130 includes a set of components that communicate with each other via an electrical and / or data connection module 132. The connection module 132 can be a direct wired connection, a fiber optic connection, a wireless communication link, etc. The MRI system controller 130 may include a CPU 131, a sequence pulse generator 133 communicating with an operator workstation 110, a transceiver (or RF transceiver) 135, a memory 137, and an array processor 139. In some embodiments, the sequence pulse generator 133 may be integrated into the scanning unit 111 of the MRI system 100. The MRI system controller 130 may receive commands from the operator workstation 110, coupled to the scanning unit 111, to indicate the scanning sequence to be performed during an MRI scan, for controlling the scanning unit 111 to perform the aforementioned magnetic resonance scan procedure. The aforementioned "scanning sequence" refers to a combination of pulses with specific intensity, shape, and timing applied during the performance of a magnetic resonance scan; these pulses typically include, for example, radio frequency pulses and gradient pulses. The radio frequency pulse may include radio frequency excitation pulses for exciting human tissue, and may also include radio frequency refocusing pulses, inversion recovery pulses, etc. Typically, multiple scanning sequences can be pre-set in a magnetic resonance imaging system to allow selection of sequences that meet clinical testing needs, such as imaging sites, imaging functions, and imaging effects.

[0034] Scanning unit 111 may include a superconducting magnet with a superconducting coil 144, a radio frequency coil assembly, and a gradient coil assembly 142. The superconducting coil 144 provides a static, uniform longitudinal magnetic field B0 throughout the cylindrical imaging volume 146 during operation. The radio frequency coil assembly may include a radio frequency transmitting coil and a radio frequency receiving coil, the transmitting coil including, for example, a body coil 148 or a local coil, and the receiving coil including, for example, a body coil 148 or a surface coil 149. The object 170 undergoing magnetic resonance scanning may be positioned within the cylindrical imaging volume 146 of scanning unit 111.

[0035] MRI system controller 130 provides gradient waveforms to gradient driver system 150, the gradient driver system including G x (x direction), G y (y-direction) and G z (z-direction) amplifiers, etc. Each G x G y and G z The gradient amplifiers all excite the corresponding gradient coils in the gradient coil assembly 142 to generate magnetic field gradients for spatial encoding of MR signals during MRI scans.

[0036] The x-direction can also be called the frequency coding direction or k in the K-space. x The direction, the y-direction, can be called the phase encoding direction or k in K-space. y Direction. Gx It can be used for frequency encoding or signal readout, and is often referred to as the frequency encoding gradient or readout gradient. G y It can be used for phase coding, and is often referred to as the phase coding gradient. G z It can be used for slice (layer) location selection to obtain K-space data. It should be noted that the layer selection direction, phase encoding direction, and frequency encoding direction can be modified according to actual needs.

[0037] In transmit mode, the radio frequency (RF) excitation pulse transmitted by pulse generator 133 can be generated via the transmit section of transceiver 135 (e.g., including an RF signal generator), and this RF excitation pulse is amplified by RF power amplifier 162. Specifically, the RF signal generator can generate corresponding RF excitation pulses based on a description of RF pulses in a predetermined scan sequence (e.g., including one or more of amplitude, frequency, transmit power, etc.). The amplified RF excitation pulse is provided to the RF transmit coil via transmit / receive switch (T / R switch) 164, which then provides an RF field B1 that is substantially perpendicular to B0 throughout the cylindrical imaging volume 146. This RF field B1 is used to excite stimulated nuclei within the object 170 to generate an MR signal. T / R switch 164 can be controlled by a signal from sequence pulse generator 133 to couple RF amplifier 162 to the RF transmit coil during transmit mode and decouple the RF transmit coil from RF amplifier 162 during receive mode.

[0038] In receive mode, the MR signal emitted by the excited nucleus within object 170 can be sensed and received by RF body coil 148 or other radio frequency receiving coils and amplified by preamplifier 166.

[0039] In some implementations, the amplified MR signal is demodulated, filtered, and digitized in the receiving section of transceiver 135.

[0040] As a non-limiting example, the transmitting section, RF power amplifier 162, etc., in transceiver 135 constitute at least a part of the RF transmitting link. Furthermore, the receiving section, preamplifier 166, RF signal demodulator (not shown), etc., in transceiver 135 constitute at least a part of the RF receiving link. One or more modules / components / assemblies of this RF transmitting link and RF receiving link are integrated in scanning unit 111.

[0041] The aforementioned MR signals can be stored as raw data in memory 137 within the MRI system controller 130. Reconstructed magnetic resonance images can be obtained by transforming / processing this stored raw data. For example, for each image to be reconstructed, the data is rearranged into separate k-space data arrays, and each of these separate k-space data arrays is input to an array processor 139, which is operated to perform a Fourier transform on the data into an array of image data.

[0042] The reconstructed image is transmitted to computer system 120 and stored in memory 126. In response to a command received from operator workstation 110, the image data may be stored in long-term memory, or it may be further processed by image processor 128 and transmitted to operator workstation 110 for display on monitor 118.

[0043] In various implementations, components of the computer system 120 and the MRI system controller 130 may be implemented on the same computer system or multiple computer systems. It should be understood that... Figure 10 The MRI system 100 shown is for illustrative purposes. Suitable MRI systems may include more, fewer, and / or different components.

[0044] The MRI system controller 130 and image processor 128 may each include a computer processor and a storage medium, either individually or jointly. The storage medium records a program for predetermined data processing to be executed by the computer processor. For example, the storage medium may store programs for performing scan processing (e.g., scan procedures, imaging sequences), image reconstruction, image processing, etc. For instance, it may store a program for implementing the magnetic resonance scanning method of the embodiments of the present invention. The storage medium may include, for example, a ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or a non-volatile memory card.

[0045] The following description is based on specific examples.

[0046] This application provides a magnetic resonance scanning method. Figure 2 This is a schematic diagram of a magnetic resonance scanning method according to an embodiment of this application, as shown below. Figure 2 As shown, the method includes:

[0047] 201. Obtain the signal of the change of cold head parameters over time when the cold head is working in the magnetic resonance imaging system;

[0048] 202. When the magnetic resonance imaging system performs a magnetic resonance scan, the carrier frequency of the radio frequency field generated by the magnetic resonance system is calibrated according to the signal.

[0049] Through the above embodiments, the carrier frequency of the radio frequency field generated by the magnetic resonance system is calibrated by using the signal of the cold head parameters changing over time. This avoids the impact of magnetic field disturbance caused by the movement of the cold head on the quality of the magnetic resonance image.

[0050] In some embodiments of this application, the cold head parameters are parameters characterizing the motion of the cold head (hereinafter referred to as motion parameters). For example, the motion parameter can be the cold head acceleration, and the signal of the motion parameter changing over time can be collected by an acceleration sensor installed on the cold head.

[0051] In some other embodiments of this application, the cold head parameters are parameters characterizing the sound generated when the cold head is working (hereinafter referred to as acoustic parameters). The signal of these acoustic parameters changing over time can be acquired by a sound acquisition device. For example, the sound acquisition device includes a microphone disposed within the scanning cavity of the magnetic resonance imaging system. This microphone can also be a reused microphone disposed within the scanning cavity of the magnetic resonance imaging system for communication between the patient lying on the scanning bed and the outside world. This eliminates the need for a separate dedicated sound acquisition device, saving hardware costs and avoiding the need for a specially designed architecture for the sound acquisition device, while simplifying the overall design of the superconducting magnetic resonance imaging system. However, the sound acquisition device is not limited to a microphone and can be other types of sound sensors, such as sound receiving transducers. The sound acquisition device can also be disposed in other locations within the superconducting magnetic resonance imaging system; for example, it can be disposed on or within the outer shell of the superconducting magnetic resonance imaging system, or on the outer shell of the cold head, or in other locations within the superconducting magnetic resonance imaging system near the cold head. This application does not limit the scope of the embodiments.

[0052] The following is a simplified description, using the cold head parameters as an example of acoustic parameters. The implementation methods for motion parameters are similar to those for acoustic parameters.

[0053] In some embodiments, in step 201, a signal of the cold head parameters changing over time is acquired, that is, a signal of the cold head parameters is acquired over a certain period of time, the length of which is not limited. Since the cold head piston moves approximately once per second, the acquisition time can include at least the time of multiple piston movements to reflect the periodic changes in the cold head parameters. Taking acoustic parameters as an example, the sound acquisition device can typically acquire acoustic signals over multiple cycles during the operation of the cold head, such as... Figure 3 As shown, for example, the sound signal can be collected within 8 to 12 seconds when the cold head is working. This is just an example, and the embodiments of this application are not intended to limit it.

[0054] In some embodiments, optionally, after acquiring the signal of the cold head parameters changing over time, the method may further include: processing the signal; and using the processed signal to calibrate the carrier frequency of the radio frequency field generated by the magnetic resonance system. This processing includes, but is not limited to, at least one of the following: analog-to-digital conversion, amplitude normalization, obtaining the spectrum of the normalized signal using a Fourier transform method followed by low-frequency filtering, and resampling, etc. The signal after the above processing is as follows: Figure 4 As shown, this can eliminate interference from background noise and other factors during the operation of the cold head, thereby improving the accuracy of magnetic field correction.

[0055] In some embodiments, in step 201, the signal of the cold head parameter changing over time can be acquired in real time during the magnetic resonance imaging system's magnetic resonance scanning process, or the signal of the cold head parameter changing over time can be acquired before the start of the magnetic resonance scanning. This application embodiment is not intended to be limiting; the specific process will be described in conjunction with the following. Figure 9 and Figure 10 Please provide an explanation.

[0056] For ease of understanding, the principle of carrier frequency calibration of the radio frequency field using the signal of cold head parameters changing over time in the embodiments of this application will be explained first.

[0057] The center frequency of the B0 field refers to the proton resonant frequency (i.e., Larmor frequency) determined by the main magnetic field in the MRI system. It is one of the core parameters of magnetic resonance imaging (MRI), directly determining the carrier frequency of the radio frequency (RF) field, including the carrier frequency of the RF pulse (or the excitation frequency of the RF pulse or the center frequency of the RF pulse) and the carrier frequency of the demodulation in the receiving link (or the demodulation frequency of the signal or the demodulation center frequency). Because the MRI system excites protons through the RF field, protons will only absorb RF energy and enter a resonant state when the carrier frequency of the RF pulse equals the Larmor frequency of the protons. If the center frequency of the main magnetic field changes (e.g., due to the influence of the cold head movement described later), the proton precession frequency changes, causing the RF field to fail to correctly excite anatomical tissues, thus producing image artifacts. The inventors discovered that the piston movement during cold head operation is a periodic reciprocating motion, repeatedly cutting the magnetic field lines of the B0 field in the MRI system, causing periodic fluctuations in the B0 field. Furthermore, the piston movement during cold head operation produces a periodic "clicking" sound. Therefore, the parameters characterizing the motion of the cold head (motion parameters) or the parameters characterizing the sound produced when the cold head is working (acoustic parameters) should be related to the changes in the B0 field. Figures 5 to 8 This is a schematic diagram showing the correspondence between the cold head parameters and the relevant parameters of the main magnetic field center frequency in an embodiment of this application. Taking acoustic parameters as an example, the horizontal axis represents time, and the vertical axis represents the center frequency offset of the B0 field and the amplitude of the acoustic parameters, respectively. The inventors discovered through simulation that, as... Figures 5 to 8As shown, even though the amplitude range of the acoustic parameters and the center frequency range of the B0 field are different, the acoustic parameters and the B0 field exhibit periodic fluctuations over time during cold head operation, and their periods are consistent. Based on this, this application proposes a method for calibrating the carrier frequency of the radio frequency field using a signal from the time-varying cold head parameters. This method can accurately predict magnetic field offset and adjust the carrier frequency of the radio frequency field in a timely manner, ensuring that the carrier frequency of the radio frequency field during magnetic resonance scanning matches the center frequency of the B0 field, thus achieving effective resonance, effective proton excitation, and signal detection. The method is described in detail below.

[0058] like Figures 5 to 8 As shown, the center frequency of the B0 field differs at different times. Therefore, to calibrate the carrier frequency of the radio frequency field, it is necessary to determine the timings (which can be replaced by moments or phases) at which the carrier frequency of the radio frequency field is calibrated, and to determine the magnitude of the carrier frequency at the corresponding timings. As mentioned earlier, since the cold head parameters and the B0 field have the same variation period, in step 202, the timing for calibrating the carrier frequency of the radio frequency field can be determined based on the signal of the cold head parameters changing over time. During magnetic resonance imaging (MRI) scanning, the carrier frequency of the radio frequency field is calibrated according to the aforementioned timing.

[0059] In some embodiments, the magnitude of the carrier frequency corresponding to the timing can be determined based on a predetermined correspondence between the cold head parameters and the parameters related to the center frequency of the main magnetic field. For example, during the system installation or calibration phase, a first signal showing the change of the cold head parameter amplitude over time and a second signal showing the change of the B0 field-related parameters over time can be acquired simultaneously within the same time period, and after time alignment, a correspondence between the first and second signals can be established.

[0060] In some embodiments, the method for acquiring the first signal is similar to step 201, and will not be repeated here. Regarding the second signal, in one embodiment, such as... Figures 5 to 8As shown, the relevant parameter of the main magnetic field center frequency (or the physical meaning of the amplitude of the second signal) can be the offset of the actual center frequency from the theoretical center frequency. In another embodiment, the relevant parameter of the main magnetic field center frequency (or the physical meaning of the amplitude of the second signal) can be the actual center frequency. Alternatively, the relevant parameter of the main magnetic field center frequency (or the physical meaning of the amplitude of the second signal) can also be a physical quantity (field strength) obtained by dividing the actual center frequency by the gyrometry ratio; this embodiment is not limited thereto. Taking the example that the relevant parameter of the main magnetic field center frequency (or the physical meaning of the amplitude of the second signal) is the offset of the actual center frequency from the theoretical center frequency, the method for obtaining the second signal includes: exciting the phantom with a rectangular pulse (or hard pulse) and acquiring the free induction decay (FID) signal, and acquiring the second signal based on the FID signal to obtain the center frequency offset changing over time. For example, the FID signal is acquired over a period of time to obtain the Larmor frequency (actual center frequency) at different times during that period, and the curve of the deviation between the actual center frequency and the theoretical center frequency at different times changing over time is determined, which is used as the second signal.

[0061] In some embodiments, establishing the correspondence includes: determining the phases of the first signal and the second signal at the same time, and determining the amplitude of the second signal under the phase of the second signal corresponding to the phase of the first signal, thereby obtaining the relationship between the phase in the first signal and the amplitude in the second signal, that is, establishing the relationship between the first signal and the second signal.

[0062] For example, since both the first and second signals are periodic signals, within one period, the phase of the first signal is... At the same time, find the amplitude F1 of the second signal when its phase is δ1, and the phase of the first signal is... At the same time, find the amplitude F2 of the second signal when its phase is δ2, and the phase of the first signal is... At the same time, find the amplitude F3 of the second signal when the phase of the first signal is δ3, and so on. Continue until the amplitude of the second signal corresponding to each phase of the first signal within one period is obtained.

[0063] For example, for each period in multiple cycles, the amplitude of the second signal corresponding to each phase of the first signal can be determined separately, and the average amplitude corresponding to the same phase in different cycles can be calculated, thereby obtaining the relationship between the phase of the first signal and the amplitude of the second signal. Taking two cycles as an example, within one cycle, the phase of the first signal is... At the same time, find the amplitude F1 of the second signal when its phase is δ1. In the next cycle, when the phase of the first signal is δ1... At the same time, find the amplitude F1' of the second signal when its phase is δ1. Therefore, determine the phase of the first signal as... When the amplitude of the second signal is (F1+F1') / 2, the amplitude is obtained. This continues until the amplitude of each phase within a period is obtained.

[0064] For example, assuming the second signal can be represented by a continuous function, the relationship between the phase of the first signal and the amplitude of the second signal can also be expressed by a function. For instance, assuming the second signal can be approximately represented as a trigonometric function with angular frequency ω, amplitude A, offset on the vertical axis B, and initial phase θ, for example, when the second signal is expressed as Asin(ωt+θ)+B, and assuming the phase of the first signal is... The phase of the second signal is The corresponding amplitude is Assume the phase of the first signal is The phase of the second signal is The corresponding amplitude is Thus, the phase of the first signal is established. The relationship between the amplitude F of the second signal and the following is:

[0065] In some embodiments, after obtaining the correspondence between the cold head parameters and the relevant parameters of the main magnetic field center frequency during the system calibration or installation phase, the center frequency relevant parameter value of the main magnetic field at a determined timing can be predicted based on this correspondence. For example, by substituting the determined timing (or phase) into the correspondence, the center frequency relevant parameter value corresponding to that timing can be determined.

[0066] The above are merely examples, but the embodiments of this application are not intended to limit them. For example, the center frequency related parameter values ​​for the corresponding timing can be preset based on experience, which will not be elaborated here.

[0067] In some embodiments, after determining the timing and corresponding center frequency related parameter values, the center frequency of the main magnetic field corresponding to that timing can be determined based on the center frequency related parameter values. This allows adjustment of the carrier frequency of the radio frequency field at each timing to match the center frequency of the main magnetic field at the corresponding timing. The radio frequency field includes a radio frequency transmitting field and a radio frequency receiving field. During adjustment, the envelope of the radio frequency pulse remains unchanged (i.e., the amplitude remains unchanged), and the carrier frequency (or the center frequency of the radio frequency field) of the radio frequency pulse and the demodulated frequency of the receiving link is adjusted. For example, control signals can be sent to the radio frequency generator in the radio frequency transmitting link and the radio frequency signal demodulator in the radio frequency receiving link to adjust the carrier frequency of the radio frequency pulse at each timing and the demodulated carrier frequency of the receiving link to be the same as the center frequency of the main magnetic field at the corresponding timing. At the same timing, the carrier frequency of the radio frequency pulse is the same as the center frequency of the main magnetic field, allowing protons to effectively absorb radio frequency energy and enter an excited state.

[0068] For example, at time T (phase) Based on the correspondence, the center frequency of the B0 field corresponding to this timing is determined to be F1. Then, during the scanning process, the corresponding phase... The center frequency of the RF pulse at that moment is also adjusted to F1, and the center frequency of the demodulation in the receiving link is also adjusted to F1. This ensures that the center frequency becomes 0 in the rotating coordinate system, avoiding artifacts in the image.

[0069] For example, assuming the theoretical center frequency is F, at time T (phase) Based on the correspondence, the center frequency offset of the B0 field corresponding to this timing is determined to be ΔF. Then, during the scanning process, the corresponding phase... The center frequency of the RF pulse at that moment is also adjusted to F+ΔF, and the center frequency of the demodulation in the receiving link is also adjusted to F+ΔF. This ensures that the center frequency becomes 0 in the rotating coordinate system, avoiding artifacts in the image.

[0070] As mentioned earlier, the signal of the cold head parameters changing over time can be acquired in real time during the magnetic resonance scan, or the signal of the cold head parameters changing over time can be acquired before the start of the magnetic resonance scan. The following sections will discuss these points in conjunction with... Figure 9 and Figure 10 Explain the corresponding magnetic resonance scanning procedure.

[0071] Figure 9 This is a schematic diagram of the magnetic resonance scanning process according to an embodiment of this application, as shown below. Figure 9 As shown, the signal of the cold head parameters changing over time is acquired in real time during the scanning process; in other words, the scanning process and the signal acquisition process are parallel. This scanning process includes the formal diagnostic scan and a pre-scan process preceding the diagnostic scan. The pre-scan process is used to determine the shimming data, determine the receiver gain, and calibrate the phase, etc. Specifically, step 201 is executed during the scanning process, and this process includes:

[0072] 901. During the system installation or calibration phase, establish the correspondence between the cold head parameters and the relevant parameters of the main magnetic field center frequency;

[0073] 902, Execute the scanning process and acquire the signal of the change of cold head parameters over time within a period L after the scan;

[0074] 903, the timing for calibrating the radio frequency field carrier frequency is determined based on this signal;

[0075] 904. Based on this timing and the aforementioned correspondence, predict the relevant parameter values ​​of the main magnetic field center frequency corresponding to this timing.

[0076] 905, adjusts the carrier frequency of the radio frequency field in real time to match the center frequency of each timing.

[0077] In 902, the scanning process may include a pre-scanning process or a formal diagnostic scanning process, and the embodiments of this application are not intended to limit it.

[0078] Furthermore, in 903, since the signal is acquired in real time after scanning, the relationship between the signal and the calibration timing can be directly obtained. For example, if the phase of the signal acquired at time T1 after scanning is Φ1, then the carrier frequency corresponding to time T1 is the center frequency corresponding to Φ1 determined according to the correspondence. The method for determining the carrier frequency for other times after scanning is the same as for time T1. Alternatively, when the second signal can be represented by a continuous function Asin(ωt+θ)+B, assuming that the phase Φ1 corresponds to the phase θ of the second signal, the change in center frequency over a continuous time period starting from time T1 can be expressed as Asin(ω(t-T1)+θ)+B. In 905, the carrier frequency of the radio frequency field is adjusted in real time according to Asin(ω(t-T1)+θ)+B.

[0079] Through the above embodiments, signals showing the change of cold head parameters over time can be acquired in real time during the scanning process, and the carrier frequency of the RF field can be calibrated in real time. This saves time and improves efficiency. It should be noted that steps 901 and 904 are optional, and the center frequency-related parameter values ​​corresponding to each timing step can be set based on empirical values.

[0080] Figure 10 This is a schematic diagram of the magnetic resonance scanning process according to an embodiment of this application, as shown below. Figure 10 As shown, signals of cold head parameters changing over time are acquired before the scan begins. For example, signals of cold head parameters changing over time are acquired before the pre-scan begins; in other words, the scanning process and the signal acquisition process are independent, not parallel. This process includes:

[0081] 1001. During the system installation or calibration phase, establish the correspondence between the cold head parameters and the relevant parameters of the main magnetic field center frequency;

[0082] 1002. Before the pre-scan, acquire the signal of the change of cold head parameters over time within a certain period of time L;

[0083] 1003, Execute the scanning process, determine the scan start time, and synchronize the acquired signal with the time after the scan to determine the time synchronization information;

[0084] 1004, determine the timing for calibrating the carrier frequency of the radio frequency field based on the time synchronization information;

[0085] 1005. Based on this timing and the aforementioned correspondence, predict the relevant parameter values ​​of the main magnetic field center frequency corresponding to this timing.

[0086] 1006, adjust the carrier frequency of the radio frequency field in real time to match the center frequency of each timing.

[0087] In 1003, the scanning process may include a pre-scanning process or a formal diagnostic scanning process, and this application embodiment is not limited thereto. In 1003, since the signal is acquired before the pre-scanning and the start time of the pre-scanning is determined, the relative difference between the acquired signal and the start time of the pre-scanning can be determined as time synchronization information. For example, at time T0 before the pre-scanning, the signal of the cold head parameters changing with time over a time length L is acquired, and the signal phase corresponding to time T0 is Φ2. The start time of the pre-scanning is time T3, and time synchronization is performed to determine the time synchronization information, that is, the offset value T0-T3 of T0 relative to T3 is calculated. Since the waveform of the cold head parameters changing with time does not change with the passage of time, or in other words, it does not change because the scan starts, therefore, after the pre-scanning starts, it is not necessary to acquire the signal of the cold head parameters changing with time. Based on the time synchronization information T0-T3 and the signal period, the phase of the signal at time T3 can be inferred. This allows for the estimation of the phase of the cold head parameters changing over time at various points after the pre-scan and formal diagnostic scans begin, thus determining the timing for calibrating the carrier frequency of the RF field. For example, if the signal phase at time T4 after the scan is calculated to be Φ4 based on the time synchronization information, then the carrier frequency at time T4 is the center frequency corresponding to Φ4, determined according to the correspondence. The method for determining the carrier frequency at other points after the scan is the same as at time T4. Alternatively, when the second signal can be represented by a continuous function Asin(ωt+θ)+B, assuming phase Φ4 corresponds to the phase θ of the second signal, the center frequency of the continuous time starting at time T4 can be expressed as Asin(ω(t-T4)+θ)+B. In 1006, the carrier frequency of the RF field is adjusted in real-time based on Asin(ω(t-T4)+θ)+B.

[0088] Through the above embodiments, signals showing the change of cold head parameters over time can be acquired before the scan begins, eliminating the need to acquire such signals after the scan has started. This avoids the influence of background noise and other factors on the acquired signals after the scan has begun, thus improving calibration accuracy. It should be noted that steps 1001 and 1005 are optional, and the center frequency corresponding to each timing step can be set based on empirical values.

[0089] It is worth noting that the above figures are merely illustrative of embodiments of this application, and the application is not limited thereto. For example, the execution order between various operations can be appropriately adjusted, and other operations can be added or some operations can be removed. Those skilled in the art can make appropriate modifications based on the above description, and are not limited to the description in the above figures.

[0090] The above embodiments are merely illustrative examples of embodiments of this application, but this application is not limited thereto, and appropriate modifications can be made based on the above embodiments. For example, the above embodiments can be used alone, or one or more of the above embodiments can be combined.

[0091] Through the above embodiments, the carrier frequency of the radio frequency field generated by the magnetic resonance system is calibrated by using the signal of the cold head parameters changing over time. This avoids the impact of magnetic field disturbance caused by the movement of the cold head on the quality of the magnetic resonance image.

[0092] This application also provides a magnetic resonance imaging system. The configuration of this magnetic resonance imaging system is as follows: Figure 1 As shown, repeated details will not be described again. Optionally, it may also include a sound acquisition device or an acceleration sensor (not shown), the implementation of which can be referred to the foregoing embodiments, and will not be described again here.

[0093] In some embodiments, with Figure 1 The difference between the aforementioned magnetic resonance imaging system and the controller 130 is that the controller 130 is configured to perform the aforementioned magnetic resonance scanning method.

[0094] In some embodiments, the controller 130 (which may also be a processor) includes a computer processor and a storage medium on which a program for predetermined data processing to be executed by the computer processor is recorded. For example, the storage medium may store programs for performing scan processing (e.g., waveform design / conversion, image reconstruction, image processing, etc.). For example, it may store a magnetic resonance scanning method for implementing the embodiments of this application. The controller 130 controls a sound acquisition device or an accelerometer to acquire signals of cold head parameters changing over time, and obtains the acquired signals from the sound acquisition device or the accelerometer. The calibration of the carrier frequency of the radio frequency field generated by the magnetic resonance system based on the signals includes: the controller 130 controlling the sequence pulse generator 133 to adjust the carrier frequency of the radio frequency pulses and adjusting the carrier frequency of the demodulation of the receiving link based on the signals. Specific implementations can be found in the foregoing embodiments and will not be repeated here.

[0095] The aforementioned storage media may include, for example, ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or non-volatile memory card.

[0096] This application also provides a computer-readable program, wherein when the program is executed in a device or MRI system, the program causes the computer to perform the methods described in the foregoing embodiments in the device or MRI system.

[0097] This application also provides a storage medium storing a computer-readable program, wherein the computer-readable program causes a computer to perform the methods described in the foregoing embodiments in a device or MRI system.

[0098] The apparatus and methods described above in this application can be implemented in hardware or in combination with software. This application relates to a computer-readable program that, when executed by a logic component, enables the logic component to implement the apparatus or components described above, or to implement the various methods or steps described above. This application also relates to storage media for storing the above programs, such as hard disks, magnetic disks, optical disks, DVDs, flash memory, etc.

[0099] The methods / apparatus described in conjunction with the embodiments of this application can be directly embodied in hardware, software modules executed by a processor, or a combination of both. For example, one or more and / or combinations of one or more functional block diagrams shown in the figures can correspond to various software modules in a computer program flow, or to various hardware modules. These software modules can correspond to the various steps shown in the figures, respectively. These hardware modules can be implemented, for example, using a field-programmable gate array (FPGA) to embed these software modules.

[0100] The software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. A storage medium can be coupled to the processor, enabling the processor to read information from and write information to the storage medium; or the storage medium can be an integral part of the processor. The processor and storage medium can reside in an ASIC. The software module can be stored in the memory of a mobile terminal or in a memory card that can be inserted into the mobile terminal. For example, if the device (such as a mobile terminal) uses a high-capacity MEGA-SIM card or a high-capacity flash memory device, the software module can be stored in the MEGA-SIM card or the high-capacity flash memory device.

[0101] One or more and / or one or more combinations of functional blocks described in the accompanying drawings can be implemented as a general-purpose processor, digital signal processor (DSP), application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, or any suitable combination thereof for performing the functions described herein. One or more and / or one or more combinations of functional blocks described in the accompanying drawings can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in communication with a DSP, or any other such configuration.

[0102] The present application has been described above with reference to specific embodiments. However, those skilled in the art should understand that these descriptions are exemplary and not intended to limit the scope of protection of the present application. Those skilled in the art can make various modifications and variations to the present application based on the principles thereof, and these modifications and variations are also within the scope of the present application.

Claims

1. A magnetic resonance scanning method, characterized in that, The method includes: Acquire signals of the time-varying parameters of the cold head during operation of the cold head in a magnetic resonance imaging system; During magnetic resonance imaging (MRI) scanning, the carrier frequency of the radio frequency field generated by the MRI system is calibrated based on the signal.

2. The method according to claim 1, wherein, The cold head parameters include cold head acoustic parameters or cold head motion parameters.

3. The method according to claim 2, wherein, The motion parameters of the cold head include the cold head acceleration.

4. The method according to claim 2, wherein, The signal of the cold head parameters changing over time is collected by a sound acquisition device or an acceleration sensor.

5. The method according to claim 4, wherein, The sound acquisition device includes a microphone disposed within the scanning cavity of the magnetic resonance imaging system.

6. The method according to claim 1, wherein, The method further includes: The signal is subjected to low-frequency filtering. Furthermore, the carrier frequency of the radio frequency field generated by the magnetic resonance system is calibrated based on the filtered signal.

7. The method according to claim 1, wherein, Calibrating the carrier frequency of the radio frequency field generated by the magnetic resonance system based on the signal includes: The timing for calibrating the carrier frequency of the radio frequency field is determined based on the signal. During magnetic resonance scanning in the magnetic resonance imaging system, the carrier frequency of the radio frequency field is calibrated according to the timing.

8. The method according to claim 7, wherein, The calibration of the carrier frequency of the radio frequency field according to the aforementioned timing includes: Based on the correspondence between the predetermined cold head parameters and the parameters related to the center frequency of the main magnetic field over time, the center frequency of the main magnetic field at each timing point is predicted. Adjust the carrier frequency of the radio frequency field at each timing to match the center frequency of the main magnetic field at the corresponding timing.

9. The method according to claim 7, wherein, The signal of the cold head parameters changing over time is acquired during the magnetic resonance scanning process of the magnetic resonance imaging system.

10. The method according to claim 7, wherein, The signal of the cold head parameters changing over time is acquired before the magnetic resonance imaging system performs a magnetic resonance scan.

11. The method according to claim 10, wherein, Determining the timing for calibrating the carrier frequency of the radio frequency field based on the signal includes: The acquired signal and the time after the magnetic resonance scan are synchronized to determine the time synchronization information; The timing for calibrating the carrier frequency of the radio frequency field is determined based on the time synchronization information.

12. The method according to claim 8, wherein, Adjusting the carrier frequency of the radio frequency field at each timing point to match the center frequency of the main magnetic field at the corresponding timing point includes: The carrier frequency of each timed radio frequency pulse and the carrier frequency of the receiving link demodulation are adjusted to be the same as the center frequency of the main magnetic field at the corresponding time.

13. A magnetic resonance imaging system, characterized in that, The system includes: Scanning unit; A controller configured to perform the magnetic resonance scanning method according to any one of claims 1 to 12.

Images