Magnetic resonance scanning method and system, and computer readable storage medium

Abstract

Embodiments of the present invention provide a magnetic resonance scanning method and system, and a computer-readable storage medium. The method includes: when an imaging volume of an object is at a current position, performing a current imaging scan on the imaging volume based on a predicted total B0 field map at the current position.

Description

Technical Field

[0001] The embodiments disclosed in the present invention relate to medical imaging technology, and more specifically to a method and system for magnetic resonance scanning, and a computer-readable storage medium. Background Art

[0002] Magnetic resonance imaging (MRI), as a medical imaging modality, can obtain images of the human body without the use of X-rays or other ionizing radiation. MRI uses a magnet with a strong magnetic field to generate a static magnetic field B0. When the patient's imaging site is positioned in the static magnetic field B0, the nuclear spins associated with the hydrogen nuclei (or other nuclides) in the tissue of the imaging site are polarized, causing the tissue of the imaging site to produce a longitudinal magnetization vector on a macroscopic scale. When a radio frequency field B1 that intersects with the direction of the static magnetic field B0 is applied, the direction of proton rotation changes, causing the tissue of the imaging site to produce a transverse magnetization vector on a macroscopic scale. After removing the radio frequency field B1, the transverse magnetization vector decays in a spiral shape until it returns to zero, and a free induction decay signal is generated during the decay process. The free induction decay signal can be collected as a magnetic resonance signal, and the tissue image of the imaging site can be reconstructed based on the collected signal.

[0003] In order to ensure the quality of magnetic resonance images, it is usually required that the static magnetic field B0 has good uniformity. In particular, there are many applications based on different imaging purposes, some of which are very sensitive to the uniformity of the static magnetic field B0, that is, in these applications, the non-uniformity of the static magnetic field B0 will have a greater impact on the imaging effect. These applications include, for example, EPI (Echo Planar Image).

[0004] Usually, during the installation or regular maintenance of the magnetic resonance equipment, the B0 field is calibrated uniformly. The calibrated static magnetic field B0 is considered to have high uniformity. However, during the scanning of the patient, the dielectric effect caused by the patient's body usually causes different degrees of disturbance to the static magnetic field B0, which reduces the uniformity of the B0 field and affects the image quality. Such a disturbance degree will also change due to the change of the patient's position. Therefore, during the imaging scan of the patient, it is first necessary to obtain the total B0 field map at the current scanning position through scanning. When the support bed carries the patient from the current scanning position to another scanning position, if the previously obtained total B0 field map is continued to be used, some image quality positions may be caused due to the inaccuracy of the total B0 field map. Otherwise, it is necessary to obtain the total B0 field map at the other scanning position through scanning again, which will increase the scanning time of the patient. Summary of the invention

[0005] An embodiment of the present invention provides a magnetic resonance scanning method, comprising:

[0006] When the imaging volume of the object is at the current position, a current imaging scan is performed on the imaging volume based on the predicted total B0 field map at the current position.

[0007] Optionally, the predicted total B0 field map is obtained based on a background B0 field map and a total B0 field map at a previous position of the imaging volume in a previous imaging scan.

[0008] Optionally, performing the current imaging scan includes: acquiring a shim value for the current imaging scan based on the predicted total B0 field map at the current position.

[0009] Optionally, performing the current imaging scan includes: adjusting scanning parameters of the current imaging scan based on the shim value of the previous imaging scan.

[0010] Optionally, the total B0 field map at the previous position is obtained based on a B0 field scan performed on the imaging volume in the previous imaging scan.

[0011] Optionally, the background B0 field map includes the background B0 field map at the previous position and the background B0 field map at the current position, and the predicted total B0 field map is predicted based on the background B0 field map at the current position, the perturbation B0 field map at the previous position, and the background B0 field map at the previous position, wherein the perturbation B0 field map at the previous position is obtained based on the total B0 field map at the previous position and the background B0 field map at the previous position.

[0012] Optionally, the previous position includes a first position where a preset layer of the imaging volume is located, the current position includes a second position where the preset layer is located, the predicted total B0 field map includes the total B0 field map at the second position, and the method further includes the following steps to obtain the predicted total B0 field map:

[0013] Acquire a total B0 field map at the first position and a disturbed B0 field map at the first position when a preset layer of the imaging volume is at the first position, wherein the disturbed B0 field map at the first position is a difference between the total B0 field map at the first position and the background B0 field map at the first position; and,

[0014] The total B0 field map at the second position when the preset layer is at the second position is predicted, and the prediction is performed based on the disturbance B0 field map at the first position, the background B0 field map at the first position, and the background B0 field map at the second position.

[0015] Optionally, the prediction includes:

[0016] Acquire a relationship coefficient related to the preset layer, wherein the relationship coefficient is acquired based on the disturbance B0 field map at the first position and the background B0 field map at the first position;

[0017] Associating the relationship coefficient with the background B0 field map at the second position to obtain a disturbance B0 field map at the second position;

[0018] A total B0 field map at the second position is calculated based on the disturbance B0 field map at the second position and the background B0 field map at the second position.

[0019] Optionally, the prediction comprises: adding the disturbance B0 field map at the second position and the background B0 field map at the second position to obtain a total B0 field map at the second position.

[0020] Optionally, the relationship coefficient comprises a coefficient associated with a linear relationship between the disturbance B0 field map at the first position and the background B0 field map at the first position.

[0021] Optionally, the relationship coefficient includes a slope value in the linear relationship.

[0022] Optionally, the previous position further includes a third position where a preset layer of the imaging volume is located, and the method further includes the following steps to obtain a predicted total B0 field map:

[0023] Acquire a total B0 field map and a disturbed B0 field map at a third position when the preset layer is at the third position, wherein the disturbed B0 field map at the third position is a difference between the total B0 field map at the third position and the background B0 field map at the third position; and,

[0024] Based on the disturbed B0 field map at the first position, the background B0 field map at the first position, the disturbed B0 field map at the third position, the background B0 field map at the third position and the background B0 field map at the second position, the total B0 field map at the second position when the preset layer is at the second position is predicted.

[0025] Optionally, the relationship coefficient is obtained based on the disturbance B0 field map at the first position, the background B0 field map at the first position, the disturbance B0 field map at the third position and the background B0 field map at the third position, and the relationship coefficient also includes an intercept value in the linear relationship.

[0026] Optionally, obtaining the relationship coefficient includes: obtaining multiple relationship coefficients related to multiple pixel points of the preset layer based on multiple disturbance B0 field strengths of the disturbance B0 field map at the first position and the corresponding multiple background B0 field strengths in the background B0 field map at the first position, and the prediction includes: calculating multiple disturbance B0 field strengths at the second position based on the multiple relationship coefficients and the corresponding multiple background B0 field strengths in the background B0 field map at the second position, and calculating multiple total B0 field strengths at the second position based on the multiple background B0 field strengths at the second position and the multiple disturbance B0 field strengths at the second position.

[0027] Optionally, the method further comprises:

[0028] performing low-pass filtering on the total B0 field image at the previous position to obtain a background B0 field reference image;

[0029] It is determined whether the difference between the background B0 field reference image and the background B0 field image is less than a first preset value, and if not, a warning message is issued.

[0030] Optionally, the method further comprises:

[0031] Acquire a background B0 field standard map related to the body part where the imaging volume is located;

[0032] Calibrate the background B0 field map based on the background B0 field standard map to obtain a background B0 field calibration map;

[0033] performing low-pass filtering on the total B0 field image at the previous position to obtain a background B0 field reference image;

[0034] It is determined whether the difference between the background B0 field reference map and the background B0 field calibration map is less than a second preset value, and if so, the background B0 field calibration map is used as the background B0 field map to predict the total B0 field map at the current position.

[0035] Optionally, the method further comprises: acquiring a background B0 field standard map related to the body part where the imaging volume is located based on a plurality of background B0 field reference maps related to the body part where the imaging volume is located.

[0036] Optionally, a plurality of background B0 field reference images associated with the body part where the imaging volume is located are respectively acquired during a plurality of scans performed on the body part where the imaging volume is located.

[0037] Optionally, data fusion is performed on a plurality of background B0 field reference images related to the body part where the imaging volume is located to obtain the background B0 field standard image.

[0038] Optionally, the method further comprises: updating a background B0 field standard map associated with the body part where the imaging volume is located based on a background B0 field reference map obtained by low-pass filtering the total B0 field map at the previous position.

[0039] Optionally, the background B0 field reference image, the background B0 field image, the B0 field standard image and the background B0 field calibration image obtained based on low-pass filtering of the total B0 field image at the previous position are all represented in the form of multi-order harmonic decomposition.

[0040] Optionally, performing the current imaging scan on the imaging volume of the object further comprises:

[0041] performing an imaging scan sequence on the imaging volume to acquire an image of the imaging volume; and,

[0042] The image of the imaging volume is corrected based on the predicted total B0 field map.

[0043] Another embodiment of the present invention further provides a magnetic resonance scanning system, comprising:

[0044] A scanner comprising a bed for carrying an object for movement, and having a plurality of scanning positions along a travel direction of the bed;

[0045] A controller is used to control the scanner to perform imaging scanning on the imaging volume of the object to obtain an image of the imaging volume, including: executing the magnetic resonance scanning method of any of the above embodiments.

[0046] Another embodiment of the present invention further provides a non-volatile computer-readable storage medium for storing computer-readable instructions, wherein the computer-readable instructions are used to execute the magnetic resonance scanning method of any of the above embodiments.

[0047] It should be understood that the brief description above is provided to introduce some concepts further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any section of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0049] Figure 1 A schematic structural diagram of a magnetic resonance imaging system is shown;

[0050] Figure 2A flow chart of a magnetic resonance scanning method according to a first embodiment of the present invention is shown;

[0051] Figure 3 A flow chart of a magnetic resonance scanning method according to a second embodiment of the present invention is shown;

[0052] Figure 4 A diagram showing changes in the perturbed B0 field strength at multiple locations acquired when an imaging volume is placed under different B0 field strengths is shown;

[0053] Figure 5 , Figure 6 The k-value component and the b-value component in the disturbance B0 field map in the field of view are shown;

[0054] Figure 7 A flow chart showing a magnetic resonance scanning method according to a third embodiment of the present invention;

[0055] Figure 8 A flow chart showing a magnetic resonance scanning method according to a fourth embodiment of the present invention;

[0056] Fig. 9 A flow chart showing a magnetic resonance scanning method according to a fifth embodiment of the present invention;

[0057] Fig.10 A flowchart showing an example of a magnetic resonance scanning method according to a sixth embodiment of the present invention;

[0058] Fig.11 Schematically illustrates an object during an imaging scan and two layers on its imaging volume;

[0059] Fig.12 A flowchart showing an example of a magnetic resonance scanning method according to a seventh embodiment of the present invention;

[0060] Fig.13 An EPI image acquired in conventional EPI is shown;

[0061] Fig.14 shows an image obtained after calibrating the above EPI image based on the B0 field map of the actual scan;

[0062] Fig.15 An image obtained after calibrating the above EPI image based on the B0 field map predicted by the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0063] Figure 1The structure diagram of a magnetic resonance imaging system is shown, and the magnetic resonance imaging system 100 includes a scanner 110 and a controller 120. The controller 120 is coupled to the scanner 110 to control the operation of the scanner 110, for example, to control the scanner 110 to perform a scanning process on an object 16 to obtain image data of the object 16. The object 16 may include imaging tissue of a human body (e.g., a patient).

[0064] Specifically, the controller 120 can send sequence control signals to relevant components of the scanner 110 (such as the RF generator and gradient coil driver described below) through a sequence generator (not shown in the figure), so that the scanner 110 executes a preset scanning sequence.

[0065] Those skilled in the art will appreciate that the above-mentioned "sequence" refers to a combination of pulses with specific amplitude, width, direction and timing applied when performing magnetic resonance imaging scanning, and these pulses may generally include, for example, radio frequency pulses and gradient pulses. The radio frequency pulse may include, for example, a radio frequency transmission pulse for exciting protons in the human body to resonate, and the gradient pulse may include, for example, a slice selection gradient pulse, a phase encoding gradient pulse, a frequency encoding gradient pulse, etc.

[0066] In one example, the scanner 110 may include a main magnet assembly 111 , a bed 112 , a radio frequency generator 113 , a radio frequency transmission coil 114 , a gradient coil driver 115 , a gradient coil assembly 116 , and a data acquisition unit 117 .

[0067] The main magnet assembly 111 generally includes an annular superconducting magnet defined in a housing, and the annular superconducting magnet is installed in an annular vacuum container. The annular superconducting magnet and its housing define a cylindrical space surrounding the object 16, such as Figure 1 The scanning cavity 118 is shown. The main magnet assembly 111 generates a constant magnetic field, namely, the B0 field, along the Z direction of the scanning cavity 118. Generally, a relatively uniform portion of the B0 field is formed in the central region of the main magnet.

[0068] The bed 112 is used to carry the object 16 and respond to the control of the controller 120 to move along the Z direction to enter and exit the above-mentioned scanning cavity 118. For example, in one embodiment, the imaging volume of the object 16 can be positioned in the central area of ​​the scanning cavity where the magnetic field strength is relatively uniform, so as to facilitate scanning and imaging of the imaging volume of the object 16.

[0069] The magnetic resonance imaging system uses the formed B0 field to transmit a static magnetic pulse signal to the subject 16 located in the scanning cavity, so that the precession of protons in the resonance volume in the subject 16 is ordered, and a longitudinal magnetization vector is generated.

[0070] The RF generator 113 is used to respond to the control signal of the controller 120 to generate RF pulses, such as RF excitation pulses. The RF excitation pulses are amplified (for example, by an RF power amplifier (not shown)) and then applied to the RF transmitting coil 114, so that the RF transmitting coil 114 transmits a RF field B1 orthogonal to the B0 field to the object 16 to excite the atomic nuclei in the above-mentioned resonance volume, thereby generating a transverse magnetization vector.

[0071] The radio frequency transmitting coil 114 may include, for example, a body coil arranged along the periphery of the main magnet, or a head coil dedicated to head imaging. The body coil may be connected to a transmit / receive (T / R) switch (not shown), and the body coil may be switched between a transmit mode and a receive mode by controlling the transmit / receive switch. In the receive mode, the body coil may be used to receive magnetic resonance signals from the subject 16.

[0072] When the radio frequency excitation pulse ends, a free induction decay signal is generated in the process that the transverse magnetization vector of the object 16 gradually returns to zero, that is, a magnetic resonance signal that can be collected.

[0073] The gradient coil driver 115 is used to respond to a gradient pulse control signal or a shim control signal sent by the controller 120 to provide appropriate current / power to the gradient coil assembly 116 .

[0074] The gradient coil assembly 116 forms a changing magnetic field in the imaging space to provide three-dimensional position information for the magnetic resonance signal, and is used to generate a compensation magnetic field for the B0 field to shim the B0 field.

[0075] The gradient coil assembly 116 may include three gradient coils, and the three gradient coils are used to generate magnetic field gradients tilted to three spatial axes (e.g., X-axis, Y-axis, and Z-axis) that are perpendicular to each other. More specifically, the gradient coil assembly 116 applies a magnetic field gradient in a slice selection direction (Z-direction) to select a layer in the imaging volume. Those skilled in the art understand that the layer is any one of a plurality of two-dimensional slices distributed along the Z-direction in the three-dimensional imaging volume. When the imaging is scanned, the radio frequency transmitting coil 114 transmits a radio frequency excitation pulse to the layer of the imaging volume and excites the layer. The gradient coil assembly 116 applies a magnetic field gradient in a phase encoding direction (Y-direction) to phase encode the magnetic resonance signal of the excited layer. The gradient coil assembly 116 applies a gradient field in a frequency encoding direction of the object 16 to frequency encode the magnetic resonance signal of the excited layer.

[0076] The data acquisition unit 117 is used to respond to the data acquisition control signal of the controller 120 to acquire the above-mentioned magnetic resonance signal (for example, received by the body coil or the surface coil). In one embodiment, the data acquisition unit 117 may include, for example, a radio frequency preamplifier, a phase detector and an analog / digital converter, wherein the radio frequency preamplifier is used to amplify the magnetic resonance signal, the phase detector is used to perform phase detection on the amplified magnetic resonance signal, and the analog / digital converter is used to convert the phase-detected magnetic resonance signal from an analog signal to a digital signal.

[0077] The controller 120 can communicate with the operation console 150, and the operation console 150 can include user input devices, such as a keyboard and a mouse. The controller 120 can respond to control commands generated by the user based on the operation console 150 or an operation panel / button set on the main magnet housing, to control the various components of the scanner 110 to perform corresponding operations.

[0078] The controller 120 may include an image reconstruction unit 121 and an image processing unit 122. The reconstruction unit 121 is used to reconstruct an image of an imaging volume of the object 16 based on the digitized magnetic resonance signal. The image processing unit 122 may be used to perform any required image processing, such as image correction, on the reconstructed image.

[0079] The operation console 150 is connected to a display unit 160 , which can display an operation interface and various data or images generated during data processing.

[0080] The controller 120 may include a computer and a storage medium, on which a predetermined control program and a data processing program to be executed by the computer are recorded. For example, the storage medium may store a program for implementing the main magnetic field evaluation method and the gradient field evaluation method of the embodiment of the present invention. The storage medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card.

[0081] Figure 1 The imaging system shown may also include a memory 170, which may be used to store information such as patient information, scanning protocols, system parameters, etc. The above-mentioned system parameters may include, for example, a background B0 field map. The background B0 field map may be pre-acquired by a variety of methods and pre-stored in the memory 170 before scanning and imaging the object 16. For example, during the installation, calibration or routine maintenance of the magnetic resonance imaging device, the background B0 field map may be obtained by imaging a phantom and calculating based on the imaging data, or the background B0 field may be measured by a field strength measurement device.

[0082] Since magnetic resonance imaging involves imaging the imaging volume of the human body, it is necessary to pre-store at least the background B0 field intensity distribution in the three-dimensional space where the imaging volume is located before the imaging scan, that is, the background B0 field map. The background B0 field map includes background B0 field maps at multiple positions along the Z direction (such as the previous position, the current position, the first position and the third position in the previous position, and the second position in the current position described below), that is, the B0 field intensity distribution on multiple XY planes, and the position in the Z direction where each XY plane is located can be the first position, the second position, or the third position described below. Therefore, the "first position", "second position", and "third position" described below can respectively include multiple position points distributed on the XY plane in the field of view (FOV).

[0083] Similarly, the total B0 field map, disturbed B0 field map, background B0 field reference map, background B0 field standard map, background B0 field calibration map, etc. involved in the embodiments of the present invention may also include the B0 field map in the above-mentioned three-dimensional space, which further includes the B0 field map at multiple positions along the Z direction.

[0084] In the process of performing imaging scans on the imaging volume of the object, scanning at the above-mentioned multiple positions may be involved. For example, a complete imaging scan may include a pre-scan and a formal scan. When the imaging volume of the object 16 is positioned at the initial position (e.g., the landmark position), a pre-scan can be performed to obtain a positioning image. Based on the positioning image, the FOV (Field of View) during the formal scan can be further determined, and then the precise positioning information of the imaging volume during the formal scan can be determined. Therefore, before performing the formal scan, the mobile bed is controlled to move along the Z direction based on the precise positioning information to re-position the imaging volume, such as aligning the center of the determined FOV with the scanning center. For another example, a complete imaging scan may include multiple scans of multiple positions of a body part, such as first imaging the area under the eyes of the head, and then imaging the forehead area of ​​the head. The FOVs of the two imagings are different. Therefore, after performing one scan, the mobile bed is controlled to move along the Z direction based on the FOV of the next scan.

[0085] In an embodiment of the present invention, in order to obtain better image quality in each imaging, the total B0 field map is considered in determining the B0 field instead of only the background B0 field map (i.e., the above-mentioned pre-stored B0 field map). The total B0 field map also includes a disturbed B0 field map caused by the disturbance of the background B0 field map caused by the body of the object 16, thereby obtaining a more accurate B0 field map, so as to avoid image quality problems caused by B0 field disturbance, such as image distortion, in the subsequent reconstruction or post-processing of the image.

[0086] Furthermore, in order to save scanning time, the current imaging scan is performed directly based on the predicted total B0 field map of the current position, and there is no need to perform B0 field scanning in order to obtain the total B0 field map, thereby saving scanning time.

[0087] The specific embodiments of the magnetic resonance scanning method proposed by the present invention are described in detail below.

[0088] First embodiment

[0089] Figure 2 FIG. 4 is a flow chart showing a magnetic resonance scanning method according to a first embodiment of the present invention. Figure 2 As shown, in step S21, when the imaging volume of the object is at the current position, a current imaging scan is performed on the imaging volume based on the predicted total B0 field map at the current position.

[0090] In one embodiment, the predicted total B0 field map is obtained based on the background B0 field map and the total B0 field map at the previous position of the imaging volume in the previous imaging scan. In this way, the total B0 field map at the next position or the current position is directly predicted based on the total B0 field map at the previous position obtained by scanning, and there is no need to perform B0 field scanning again to obtain the total B0 field map, thereby saving scanning time.

[0091] Those skilled in the art will appreciate that the "imaging volume" may be a three-dimensional region in the subject's body that is imaged when performing an imaging scan, and the region may generally be determined by setting scanning parameters. The imaging volume may generally include a plurality of volume layers, i.e., "layers" or "XY planes", that are sequentially distributed along the Z direction.

[0092] The above-mentioned current position may be, for example, a position range of the imaging volume when performing a formal scan, which may include the position of each layer of the imaging volume when performing a formal scan, such as the second position described below. The above-mentioned previous position may be, for example, a position range of the imaging volume when performing a pre-scan, which may include the position of each layer when performing a pre-scan, such as the first position described below.

[0093] As described above, the above-mentioned background B0 field map is pre-stored in the magnetic resonance imaging system, which includes the background B0 field map distributed in the entire three-dimensional imaging space (for example, a sphere or a space of similar shape), and the three-dimensional imaging space may include multiple positions along the Z direction, which may include the previous position, current position, first position, second position and / or third position described in the embodiment of the present invention. Therefore, it can be considered that the "background B0 field map" includes the background B0 field map at the current position and the background B0 field map at the previous position; the background B0 field map at the current position may include the background B0 field map at the second position; the background B0 field map at the previous position may include the background B0 field map at the first position and / or the background B0 field map at the third position.

[0094] In one embodiment, the total B0 field map at the previous position is obtained based on a B0 field scan performed on the imaging volume in the previous imaging scan.

[0095] The total B0 field diagram reflects the spatial distribution of the B0 field. Since the size of the total B0 field will affect the deflection angular velocity of the longitudinal magnetization vector of the proton, and thus the field strength of the total B0 field has a specific functional relationship with the phase change of the magnetic resonance signal over time, the total B0 field diagram of the same position can be obtained by taking the difference between the magnetic resonance signals collected at different times at the same position.

[0096] Based on the above principle, in one embodiment of the present invention, the total B0 field map of the previous position can be obtained in the following manner: two sets of image data of the imaging volume obtained when performing the previous imaging scan are obtained, and the two sets of image data have different phase information respectively, and the total B0 field map related to the first position is calculated based on the phase difference between the two sets of image data. For example, the components of the scanner 110 respond to the control signal of the controller 120 to execute the B0 field scanning sequence to obtain the above two sets of image data. The above B0 field scanning sequence can be executed as part of the imaging scanning sequence, or it can be executed before or after the imaging scan is completed. When the B0 field scanning sequence is executed, image data with B0 field strength information is obtained, which is usually used for determining and setting system parameters, etc. When the imaging scanning sequence is executed, magnetic resonance image data of different tissues of the human body is obtained, which is usually used for clinical diagnosis. Based on different clinical applications, there are a variety of B0 field scanning sequences and imaging scanning sequences in the prior art, which will not be repeated here.

[0097] In step S21, performing the current imaging scan may include: acquiring the shimming value of the current imaging scan based on the predicted total B0 field map at the current position, and further adjusting the scanning parameters of the current imaging scan based on the obtained shimming value. Specifically, when performing the current imaging scan, suitable scanning parameters related to the obtained shimming value may be selected, such as gradient current, center frequency, etc., which will also be described in the sixth embodiment.

[0098] Specifically, the above-mentioned predicted total B0 field map is predicted based on the background B0 field map at the current position, the perturbation B0 field map at the previous position and the background B0 field map at the previous position, wherein the perturbation B0 field map at the previous position is obtained based on the total B0 field map at the previous position and the background B0 field map at the previous position. For example, the total B0 field map at the previous position minus the background B0 field map at the previous position can obtain the perturbation B0 field map at the previous position.

[0099] It should be noted that the predicted total B0 field map at the current position may include the total B0 field map at the position of each layer, or may only include the total B0 field map at the positions of some layers.

[0100] Second embodiment

[0101] Figure 3 FIG. 4 is a flow chart showing a magnetic resonance scanning method according to a second embodiment of the present invention. Figure 3 As shown, the method further includes step S33, which is similar to step S21. The method of this embodiment further includes steps S31 and S32 to obtain the above-mentioned predicted total B0 field map.

[0102] In step S31, a total B0 field map and a disturbed B0 field map at a first position are obtained when a preset layer of an imaging volume of an object is at the first position. The disturbed B0 field map at the first position may be a disturbed B0 field map caused by the body of the object, which is the difference between the total B0 field map at the first position and the background B0 field map at the first position.

[0103] In step S31 , data at the first position may be directly acquired in the background B0 field to obtain a background B0 field map at the first position.

[0104] When the imaging volume is at the previous position, the position of the preset layer of the imaging volume is the first position, and a total B0 field map distributed in the three-dimensional space can be obtained by performing a B0 field scanning sequence on the imaging volume, which may include the total B0 field map on the entire three-dimensional imaging space, or only include the total B0 field map at one or more Z-axis positions in the entire three-dimensional imaging space. Specifically, it may include "the total B0 field map at the previous position" or "the total B0 field map at the first position". In step S21, data at the first position can be obtained in the "total B0 field map at the previous position" to obtain the total B0 field map at the first position.

[0105] Similarly, when the imaging volume is at another previous position, the position of the preset layer of the imaging volume is the third position, and the total B0 field map distributed in three-dimensional space obtained by performing a B0 field scanning sequence on the imaging volume may include the "total B0 field map at the previous position" or the "total B0 field map at the third position."

[0106] In step S32, a total B0 field map at the second position when the preset layer is at the second position is predicted based on the disturbance B0 field map at the first position, the background B0 field map at the first position and the background B0 field map at the second position.

[0107] When the imaging volume is at the current position, the position of the preset layer of the imaging volume is the second position, and the total B0 field map at one or more second positions predicted based on this embodiment can be used as the "total B0 field map at the current position".

[0108] As an example, the preset layer of the imaging volume may be a central layer determined in the imaging volume, the second position may be a position aligned with a scanning center (or a magnet center) of the magnetic resonance imaging system, and when performing a scan of the second position, the central layer may be located at the second position. The first position may be a position of the central layer relative to the scanning center (or the magnet center) along the Z direction when performing a pre-scan on the imaging volume.

[0109] Similar to acquiring the total B0 field map at the first position, in step S32, data at the second position may be directly acquired in the background B0 field to obtain the background B0 field map at the second position.

[0110] Any one of the multiple volume layers of the imaging volume may be the "preset layer" described in this embodiment. That is, when it is necessary to predict the total B0 field map of any position in a scan, it is sufficient to predetermine which volume layer is at the position in the scan. When it is necessary to obtain the total B0 field map associated with multiple layers, each of these layers may be used as the above-mentioned preset layer to perform steps S31 and S32.

[0111] Figure 4The figure shows the variation of the disturbance B0 field intensity at multiple locations when an imaging volume is placed under different B0 field intensities. The inventor of the present invention first boldly assumed that there is a specific relationship between the disturbance B0 field intensity and the background B0 field intensity at the same location, and thus conducted a large number of experiments to verify that there is a specific relationship between the two. Figure 3 The linear relationship shown in the figure can be included in such experiments: for example, placing the imaging volume in a strong magnetic field with strong uniformity for magnetic resonance scanning or magnetic resonance simulation scanning, and obtaining the total B0 field strength of multiple acquisition points by the above method, and then obtaining the disturbed B0 field strength of these acquisition points (the total B0 field strength minus the background B0 field strength at the corresponding position), and finally establishing a relationship diagram between the disturbed B0 field strength and the background B0 field strength. Figure 4 The multiple lines in correspond to multiple acquisition points (e.g., multiple voxel points of the imaging volume), although Figure 4 Only data from a small number of acquisition points are shown, and in practice data analysis may be performed on more acquisition points. Figure 4 The horizontal axis represents the background B0 field strength, and the vertical axis represents the disturbance B0 field strength. There is the following relationship between the disturbance B0 field strength and the background B0 field strength:

[0112] ΔB(x,y,z)=k(x,y,z)·B0(x,y,z)+b(x,y,z) (1),

[0113] In the above formula (1), ΔB(x,y,z) is the disturbance B0 field strength, B0(x,y,z) is the background B0 field strength. k(x,y,z) and b(x,y,z) are constants, where k(x,y,z) represents the slope, b(x,y,z) represents the intercept, and (x,y,z) represents the three-dimensional component in each data value.

[0114] The k value and b value of each pixel point can be calculated based on a known total B0 field map (eg, obtained by executing a B0 field scanning sequence) and a known background B0 field map in a field of view. Figure 5 , Figure 6 The k value component and b value component in the disturbance B0 field map in the field of view are shown. Figure 5 , Figure 6 It can be seen that the b-value component contains a large amount of background noise. The background noise has little effect on the prediction result of the total B0 field and can be ignored. Therefore, the relationship between the disturbance B0 field intensity associated with each pixel point in the disturbance B0 field map and the background B0 field intensity associated with the pixel point can be pre-defined as the linear relationship shown in the following formula (2), that is:

[0115] ΔB(x,y,z)=k(x,y,z)·B0(x,y,z) (2).

[0116] Such a relationship applies to each pixel point in the B0 field map at each position, that is, the relationship between the disturbance B0 field strength associated with each pixel point in the disturbance B0 field map at the first position and the background B0 field strength associated with the corresponding pixel point in the background B0 field map at the first position can be pre-set to the above-mentioned linear relationship.

[0117] Therefore, in step S32, predicting the total B0 field map at the second position when the preset layer is at the second position may include the following three sub-steps:

[0118] First sub-step: obtaining a relationship coefficient related to the preset layer based on the disturbance B0 field map at the first position and the background B0 field map at the first position. Optionally, the relationship coefficient may include a coefficient related to the linear relationship between the disturbance B0 field map at the first position and the background B0 field map at the first position. Further, the above relationship coefficient includes a slope value in the linear relationship, such as the above k value.

[0119] In the first sub-step, multiple relationship coefficients, such as multiple k values, related to multiple pixel points of the preset layer can be obtained based on multiple disturbance B0 field strengths of the disturbance B0 field map at the first position and the corresponding multiple background B0 field strengths in the background B0 field map at the first position. Second sub-step: associate the relationship coefficient to the background B0 field map at the second position to obtain the disturbance B0 field map at the second position. For example, the disturbance B0 field strength associated with each pixel point of the preset layer at the second position is calculated based on the background B0 field map at the second position and the relationship coefficient associated with each pixel point of the preset layer. Specifically, the field strength of each position point in the background B0 field map at the second position can be multiplied by the corresponding k value to obtain the disturbance B0 field map at the second position when the preset layer is in the second position.

[0120] The third sub-step: calculating the total B0 field map at the second position (when the preset layer is at the second position) based on the disturbance B0 field map at the second position and the background B0 field map at the second position. For example, the disturbance B0 field map at the second position and the background B0 field map at the second position are added to obtain the total B0 field map at the second position.

[0121] Specifically, a plurality of disturbance B0 field strengths at the second position can be calculated based on the plurality of relationship coefficients and the corresponding plurality of background B0 field strengths in the background B0 field map at the second position, and a plurality of total B0 field strengths at the second position can be calculated based on the plurality of background B0 field strengths at the second position and the plurality of disturbance B0 field strengths at the second position.

[0122] Under different system configurations, parameter settings or scanning environments, there may be other relationships between the disturbed B0 field and the background B0 field that are different from the linear relationship. However, based on the design concept of the present invention, when the prediction of the disturbed B0 field map or the total B0 field map can be achieved based on such a relationship, it is within the protection scope of the present invention.

[0123] Third embodiment

[0124] As described above, the background B0 field map is pre-acquired and pre-stored. As time goes by, the actual background B0 field map may drift, causing the accuracy of the total B0 field map predicted based on the background B0 field to decrease. In order to solve this problem, the third embodiment of the present invention further evaluates the accuracy of the background B0 field on the basis of any of the above embodiments to ensure the accuracy of the estimated total B0 field map.

[0125] Figure 7 FIG. 4 is a flow chart showing a magnetic resonance scanning method according to a third embodiment of the present invention. Figure 7 As shown, the third embodiment includes steps S71, S72, S73, S74 and S75, wherein steps S71, S72 and S75 are similar to the above-mentioned steps S31, S32 and S21, respectively.

[0126] In step S73, the total B0 field map at the previous position is low-pass filtered to obtain a background B0 field reference map. As described above, the total B0 field map at the previous position may include: when the imaging volume is at the previous position (or when the preset layer is at the first position), the total B0 field map in the three-dimensional space where the imaging volume is located. By low-pass filtering, the disturbance B0 field caused by the subject's body is filtered out, and a background B0 field reference map close to the actual background B0 field map is obtained.

[0127] In step S74, it is determined whether the difference between the background B0 field reference image and the background B0 field image is less than a first preset value. If not, a warning message is issued. In this step, by determining whether the background B0 field reference image and the background B0 field image are close enough, it is analyzed whether the background B0 field image has drifted. If the difference is too large, it means that the background B0 field image is not accurate enough. At this time, a warning message related to the background B0 field image can be issued. Based on the warning message, the background B0 field image can be calibrated and updated. Such an update can be performed after the scan is completed, or it can be performed in real time during the scan.

[0128] In one embodiment, when comparing the background B0 field reference image and the background B0 field image, the two can be subjected to harmonic decomposition and then compared. For example, the background B0 field reference image can be decomposed into H1=a1+b1*x+c1*y+d1*x*x+e1*x*y+f1*y*y(3), and the background B0 field image can be decomposed into H2=a2+b2*x+c2*y+d2*x*x+e2*x*y+f2*y*y(4), where x and y in equations (3) and (4) represent the components of the B0 field image in the X direction and the Y direction, respectively, a1 and a2 are fundamental wave components, and b1, b2, c1, c2, d1, d2, e1, e2, f1, and f2 are harmonic coefficients, respectively. In step S74, the difference between the components in equations (3) and (4) can be calculated to determine whether the background B0 field reference image and the background B0 field image are close enough.

[0129] In one implementation, steps S73 and S74 may be performed between step S71 and step S72.

[0130] If the background B0 field reference image is close enough to the pre-stored background B0 field image, the magnetic resonance imaging system can be controlled to operate according to a conventional procedure.

[0131] Fourth embodiment

[0132] In the fourth embodiment of the present invention, the background B0 field map can be calibrated in real time so that a more accurate total B0 field map can be estimated. Through research, it is found that the total B0 field map obtained when scanning different body parts is low-pass filtered, and the background B0 field reference map obtained after filtering is different due to different body parts. This may be because different parts of the body have different low-order terms, and these differences may be caused by different structures of the body parts, such as the head that is relatively symmetrical on the left and right and the abdomen that is asymmetrical on the left and right, and the low-order terms brought by the two are different. In this embodiment, the corresponding background B0 field standard map can be first obtained for different body parts, and based on the body part where the current imaging volume is located, the corresponding background B0 field standard map is selected to calibrate the background B0 field map.

[0133] Figure 8 FIG. 4 is a flow chart showing a magnetic resonance scanning method according to a fourth embodiment of the present invention. Figure 8As shown, the third embodiment includes steps S81, S82, S83, S84, S85, S86 and S87, wherein steps S81, S82 and S87 are similar to the above steps S31, S32 and S21, respectively. In particular, in step S81, the total B0 field map at the first position can be determined from the total B0 field map at the previous position, so as to "obtain the total B0 field map and the disturbance B0 field map at the first position when the preset layer is at the first position". In one implementation, steps S83 to S86 can be performed between steps S81 and S82.

[0134] In step S83, a background B0 field standard map related to the body part where the current imaging volume is located is obtained. The background B0 field standard map can be pre-stored in a memory (e.g., memory 170) of the magnetic resonance imaging system. In addition, in this step, the background B0 field standard map related to the body part (or any imaging volume in the body part) can be obtained based on a plurality of background B0 field reference maps related to the body part that have been pre-acquired. The plurality of background B0 field reference maps related to the body part are respectively acquired based on multiple scans performed on the body part, which can be obtained based on historical data of magnetic resonance scanning. In one embodiment, the background B0 field standard map related to the body part is acquired by performing data fusion on a plurality of background B0 field reference maps related to the body part.

[0135] Taking the head as an example, multiple total B0 field images related to the head can be obtained during multiple scans performed on the head (for example, of patients with different identities), and different imaging volumes in the head can be set in each scan. Low-pass filtering of the multiple total B0 field images related to the head can obtain a corresponding multiple background B0 field reference images related to the head. Data fusion of the multiple background B0 field reference images related to the head is performed such as averaging, median or other methods to obtain a background B0 field standard image related to the head. Therefore, in step S83, if the body part currently scanned is also the head, the above-mentioned background B0 field standard image related to the head can be retrieved to achieve real-time calibration of the background B0 field image in subsequent steps.

[0136] In step S84, the background B0 field map is calibrated based on the background B0 field standard map to obtain a background B0 field calibration map. In one embodiment, the background B0 field standard map and the background B0 field map are data fused to obtain a background B0 field calibration map. Such data fusion may include, for example, performing harmonic decomposition on the background B0 field standard map and the background B0 field map to obtain multiple components of each, and adding the corresponding components in the background B0 field standard map and the background B0 field map to obtain a background B0 field calibration map represented in the form of harmonic decomposition. Due to the B0 field variation caused by different body parts (the above multiple components can represent the variation), a large number of total B0 field maps of a body part are low-pass filtered to filter out high-order components, and then the remaining low-order components are data fused, such as averaging, to obtain low-order components of the B0 field brought only by the body part. When each of its low-order components is added to the corresponding component of the background B0 field, the obtained background B0 field calibration map is considered to be close to the above background B0 field reference map.

[0137] In step S85, the total B0 field image at the previous position is subjected to low-pass filtering to obtain a background B0 field reference image. Step S85 is similar to step S73 and will not be described in detail herein.

[0138] In step S86, it is determined whether the difference between the background B0 field reference image and the background B0 field calibration image is less than the second preset value. If so, the background B0 field calibration image is used as the background B0 field image to perform step S82, that is, based on the disturbance B0 field image at the first position and the background B0 field calibration image and the background B0 field image at the second position in the background B0 field calibration image, the total B0 field image at the second position when the preset layer is at the second position is predicted, thereby obtaining the predicted total B0 field image at the current position. The above-mentioned second preset value defines the critical value of the difference between the background B0 field reference image and the background B0 field calibration image. If it exceeds the critical value, it is considered that the obtained background B0 field calibration image is not accurate enough. On the contrary, it is considered to be reliable calibration data, and the total B0 field can be predicted based on the calibration data rather than the original background B0 field image. In this step, the difference between each component after the harmonic decomposition of the background B0 field reference image and the corresponding component of the background B0 field calibration image can be calculated respectively, and data processing based on these differences is performed and compared with the second preset value. The second preset value and the first preset value may be the same or different.

[0139] Fifth embodiment

[0140] Fig. 9 FIG. 5 is a flow chart showing a magnetic resonance scanning method according to a fifth embodiment of the present invention. Fig. 9As shown, the method includes steps S91, S92, S93 and S94, wherein step S91 is similar to step S31, and step S94 is similar to step S21. The fifth embodiment of the present invention is similar to any of the above embodiments, except that in this embodiment, a predefined linear relationship between the disturbance B0 field strength and the background B0 field strength (such as the above formula (1)) is used to predict the total B0 field map of another position by scanning the total B0 field map of two positions.

[0141] In step S92, the total B0 field map and the disturbed B0 field map at the third position are obtained when the preset layer is at the third position, wherein the disturbed B0 field map at the third position is the difference between the total B0 field map at the third position and the background B0 field map at the third position in the background B0 field map.

[0142] In step S93, the total B0 field map at the second position when the preset layer is at the second position is predicted based on the disturbed B0 field map at the first position, the background B0 field map at the first position, the disturbed B0 field map at the third position, the background B0 field map at the third position and the background B0 field map at the second position.

[0143] In this embodiment, according to the relationship described by formula (1) (or any other alternative mathematical formula), the relationship coefficient related to each pixel point, such as the k value (slope) and the b value (intercept), can be obtained through the data at the first position and the data at the third position, and the disturbance B0 field map at the second position is obtained by calculating it with the background B0 field map at the second position, and then the total B0 field map at the second position is obtained.

[0144] Specifically, “the total B0 field map at the second position when the predicted preset layer is at the second position” includes:

[0145] According to a predefined linear relationship between a disturbance B0 field value associated with each pixel of the preset layer in the disturbance B0 field map and a background B0 field intensity associated with the pixel, at least two relationship coefficients associated with each pixel of the preset layer are calculated based on the disturbance B0 field map and the background B0 field map at the first position and the disturbance B0 field map and the background B0 field map at the third position, such as the above-mentioned k value and b value;

[0146] Calculate the disturbance B0 field value associated with each pixel point of the preset layer at the second position based on the background B0 field map at the second position and two relationship coefficients associated with each pixel point of the preset layer;

[0147] A total B0 field map at the second position when the preset layer is at the second position is calculated based on the disturbance B0 field value associated with each pixel point of the preset layer at the second position and the background B0 field map at the second position.

[0148] Such an embodiment may be applied, for example, to imaging methods that are very sensitive to the b-value.

[0149] The above embodiments describe the magnetic resonance scanning method of the present invention. By obtaining the total B0 field map at the scanning position where the scan is to be performed, it is not necessary to add a B0 field scanning sequence to the imaging sequence, thereby saving scanning time. Moreover, in an embodiment of the present invention, the total B0 field map can be predicted for multiple "preset layers". The above embodiments also detect the accuracy of the background B0 field in real time to avoid prediction errors caused by inaccurate background B0 field. The present invention can further establish a background B0 field standard map for different body parts to calibrate the background B0 field map so that a high-accuracy background B0 field map can be obtained in real time.

[0150] Sixth embodiment

[0151] Fig.10 A flow chart of an imaging scanning method provided based on the sixth embodiment of the present invention is shown, which shows an example of predicting the total B0 field map using any of the above embodiments and performing imaging scanning on the imaging volume based on the predicted total B0 field map. Fig.11 The object 16 and two layers 161 and 162 of its imaging volume are schematically shown during an imaging scan, wherein Fig.10 The upper figure in FIG. 1 shows the positional relationship between the two layers and the scanning center when performing a pre-scan. Fig.10 The lower figure in the figure shows the positional relationship between the two layers and the scanning center when performing the actual scanning.

[0152] Combination Fig.10 , Fig.11 As shown, in step S101, a pre-scan is performed and the first total B0 field map in the three-dimensional space where the imaging volume is located and the images of each layer of the imaging volume are obtained. At this time, layer 162 is aligned with the scanning center, and layer 161 is located at position L1 25 mm away from the scanning center. Fig.11 In the figure, I represents the side close to the subject's feet, and S represents the side close to the subject's head. The bed can carry the subject to move toward the I side or the S side along the Z direction.

[0153] In step S102 , a new FOV is determined based on the image obtained by the pre-scan for use in the formal scan, and the center of the FOV is at layer 161 .

[0154] In step S103, the bed is controlled to move 25 mm to align the layer 161 with the scanning center. In this step, the layer 161 may not be aligned with the scanning center, and in the subsequent prediction, the total B0 field map at other positions is predicted. Therefore, the embodiment of the present invention can predict the total B0 field map at the position where the layer is located in the next scan for part or all layers of the imaging volume.

[0155] In step S104, the total B0 field map at L1 in the first total B0 field map is obtained, and the total B0 field map is subtracted from the background B0 field map at L1 to obtain a first disturbed B0 field map.

[0156] In step S105, a relationship coefficient associated with each pixel of layer 161 is calculated based on the first perturbation B0 field map and the background B0 field map at L1, and the relationship coefficient is multiplied with the background B0 field map at the scanning center to obtain a second perturbation B0 field map at the scanning center, and the second perturbation B0 field map is added to the background B0 field map at the scanning center to obtain a predicted second total B0 field map.

[0157] In step S106, the shim value of the scanning center is obtained based on the second total B0 field map. When the second total B0 field map is predicted for all positions in the three-dimensional space where the imaging volume is currently located, the total B0 field map in the entire space is obtained.

[0158] In step S107, the scanning parameters of the magnetic resonance scanning system are set based on the shimming value, and the imaging volume is formally scanned based on the set scanning parameters. The above scanning parameters may include a gradient shimming value and a center frequency. The center frequency is the resonance frequency of the protons of the tissue of interest, which changes based on the change of the B0 field map after shimming so as to better excite the tissue of interest. The gradient shimming value may include an increase or decrease in the current applied to the above gradient coil, and the current of the gradient coil is increased or decreased based on the shimming value to obtain a desired uniform B0 field value.

[0159] When a technology for automatically shimming the B0 field is used to shim the predicted total B0 field map and the actual scanned total B0 field map respectively, it is found that the shimming values ​​of the two are relatively close, which indicates that the total B0 field map predicted by the embodiment of the present invention and the actual scanned total B0 field map are close.

[0160] Based on the above examples, the magnetic resonance scanning method provided by the sixth embodiment of the present invention may include:

[0161] Based on the predicted total B0 field map, a current imaging scan (e.g., the above-mentioned formal scan) is performed on the imaging volume, including: obtaining a shim value at the current position based on the predicted total B0 field map, and adjusting the scanning parameters of the current imaging scan based on the shim value, such as parameters related to the gradient shim value, parameters related to the center frequency, etc. In this embodiment, the predicted total B0 field map is obtained based on the disturbance B0 field map and the background B0 field map at the position of the imaging volume in the previous imaging scan (e.g., the above-mentioned pre-scan) and the background B0 field map at the position of the imaging volume in the current imaging scan. For example, the total B0 field map at the position of the imaging volume in the current imaging scan can be predicted by any method in the first to fifth embodiments.

[0162] Seventh embodiment

[0163] Fig.12 A flow chart of a magnetic resonance scanning method according to a seventh embodiment of the present invention is shown, which shows an example of predicting a total B0 field map in an EPI (echo planar imaging) scan and performing distortion correction on an EPI image based on the predicted total B0 field map.

[0164] like Fig.12 As shown, in step S121, the scanning parameters of the current EPI scan are obtained, and the scanning parameters include the set positions of each layer of the imaging volume relative to the scanning center.

[0165] In step S122, the positions (previous positions) of some or all layers of the imaging volume in the previous scan are obtained. The previous scan may be a pre-scan, or other scans of other volumes adjacent to the current imaging volume.

[0166] In step S123, a first total B0 field image at a previous position is obtained, and the total B0 field image is correspondingly subtracted from the background B0 field image at the previous position to obtain a first disturbed B0 field image.

[0167] In step S124, a relationship coefficient associated with each pixel of the corresponding partial or entire layer is calculated based on the first disturbed B0 field map and the corresponding background B0 field map at the previous position, and the relationship coefficient is multiplied with the background B0 field map at the set position to obtain the second disturbed B0 field map at the current set position, and the second disturbed B0 field map is added to the background B0 field map at the set position to obtain the predicted second total B0 field map.

[0168] In step S125 , an EPI scan is performed based on the scan parameters set in step S111 to acquire an EPI image of the imaging volume.

[0169] In step S126, the EPI image is corrected based on the second total B0 field map predicted in step S114. Correcting the EPI image based on the total B0 field (or the disturbed B0 field) is a known technique in the art and will not be described in detail. It should be noted that EPI is only an example application. In other applications that are sensitive to the disturbed B0 field, similar methods can also be used to correct the image. The above step 26 can be performed during the image post-processing process.

[0170] Fig.13 The EPI image obtained in the conventional EPI is shown. The conventional EPI may have geometric deformation (distortion) due to the inaccuracy of the B0 field map obtained by scanning. For example, the contour of the imaging part changes and exceeds the frame shown in the figure. Fig.14 The B0 field map based on actual scanning is shown. Fig.10The EPI image shown is the image obtained after correction. Fig.15 The B0 field diagram based on the prediction of the embodiment of the present invention is shown. Fig.10 The EPI image shown is obtained after correction. Fig.14 and Fig.15 It can be seen that calibrating the EPI image based on the B0 field map predicted by the method of the embodiment of the present invention significantly improves the distortion problem in the EPI image, and the effect is basically equivalent to correcting the EPI image using the actually measured B0 field map.

[0171] Therefore, the magnetic resonance scanning method of the embodiment of the present invention may further include the following steps: when the preset layer is at the second position (or the imaging volume is at the current position), performing an imaging scanning sequence on the imaging volume to acquire an image of the imaging volume; and correcting the image of the preset layer based on the predicted total B0 field map at the second position.

[0172] Based on the above description, an embodiment of the present invention may also provide a magnetic resonance scanning system, which includes a scanner and a controller, wherein the scanner includes a bed for carrying an object to move, and has multiple scanning positions along the moving direction of the bed, for example, at least including the above-mentioned first position and second position. The controller is used to control the scanner to perform imaging scanning on the imaging volume of the object to obtain an image of the imaging volume, including: performing any one of the magnetic resonance scanning methods of the first to seventh embodiments above.

[0173] The structure and working principle of the magnetic resonance imaging system can be Figure 1 The system shown is similar and will not be described again here.

[0174] Based on the above description, an embodiment of the present invention may also provide a computer-readable storage medium in which computer-readable instructions are stored, and the computer-readable instructions are used to control a magnetic resonance scanning system to perform the magnetic resonance scanning method of any of the above embodiments. The computer-readable storage medium may be similar to Figure 1 Storage medium in controller 120 in the system shown.

[0175] As used herein, an element or step described in the singular and preceded by the word "one" or "an" should be understood as not excluding the plural number of the element or step, unless such exclusion is explicitly stated. In addition, reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that simultaneously incorporate the described features. Moreover, unless explicitly stated to the contrary, an embodiment "comprising", "including", "having" an element or multiple elements with a specific property may include additional such elements that do not have the property. The terms "including" and "in which" are used as the concise language equivalents of the corresponding terms "comprising" and "wherein". In addition, in the appended claims, the terms "first", "second" and "third" etc. are used only as markers and are not intended to impose numerical requirements or specific positional order on their objects.

[0176] This written description uses examples to disclose the invention, including the best mode, and also enables a person of ordinary skill in any relevant art to implement the invention, including making and using any device or system and performing any covered method. The scope of patent protection for the invention is defined by the claims and may include other examples known to those skilled in the art. If they have structural elements that are indistinguishable from the literal language of the claims, or if they include equivalent structural elements that are insubstantially different from the literal language of the claims, it is intended that such other examples fall within the scope of the claims.

Claims

1. A magnetic resonance scanning method, comprising: predicting a total B0 field map at a current location based on a background B0 field map and a total B0 field map at a previous location where an imaging volume of the object was located in a previous imaging scan; and, when the imaging volume of the object is at the current position, performing a current imaging scan on the imaging volume based on the predicted total B0 field map at the current position; in, The previous position includes a first position, the current position includes a second position, the predicted total B0 field map includes a total B0 field map at the second position, and the prediction includes: Acquire a total B0 field map of a preset layer of an imaging volume of the object at the first position and a disturbed B0 field map at the first position, wherein the disturbed B0 field map at the first position is a difference between the total B0 field map at the first position and the background B0 field map at the first position; Acquire a relationship coefficient related to the preset layer, wherein the relationship coefficient is acquired based on the disturbance B0 field map at the first position and the background B0 field map at the first position; Associating the relationship coefficient to the background B0 field map at the second position to obtain a disturbed B0 field map at the second position; and, A total B0 field map at the second position is calculated based on the disturbed B0 field map at the second position and the background B0 field map at the second position.

2. The scanning method according to claim 1, wherein: Executing the current imaging scan includes: acquiring the shim value of the current imaging scan based on the predicted total B0 field map at the current position.

3. The scanning method according to claim 2, wherein: Executing the current imaging scan includes: adjusting the scanning parameters of the current imaging scan based on the shim value of the current imaging scan.

4. The scanning method according to claim 1, wherein: The total B0 field map at the previous position is obtained based on a B0 field scan performed on the imaging volume in the previous imaging scan.

5. The method of claim 1, wherein the prediction comprises: The disturbance B0 field map at the second position and the background B0 field map at the second position are added together to obtain a total B0 field map at the second position.

6. The method of claim 1, wherein the relationship coefficient comprises a coefficient associated with a linear relationship between a disturbance B0 field map at the first position and a background B0 field map at the first position. The method of claim 6 , wherein the relationship coefficient comprises a slope value in the linear relationship.

8. The method of claim 7, wherein: The previous position also includes a third position where a preset layer of the imaging volume is located, and the method further includes the following steps to obtain a predicted total B0 field map: Acquire a total B0 field map and a disturbed B0 field map at a third position when the preset layer is at the third position, wherein the disturbed B0 field map at the third position is a difference between the total B0 field map at the third position and the background B0 field map at the third position; and, Based on the disturbed B0 field map at the first position, the background B0 field map at the first position, the disturbed B0 field map at the third position, the background B0 field map at the third position and the background B0 field map at the second position, the total B0 field map at the second position when the preset layer is at the second position is predicted.

9. The method of claim 8, wherein: The relationship coefficient is obtained based on the disturbance B0 field map at the first position, the background B0 field map at the first position, the disturbance B0 field map at the third position and the background B0 field map at the third position, and the relationship coefficient also includes the slope value and intercept value in the linear relationship.

10. The method according to claim 1, wherein obtaining the relationship coefficient comprises: Based on multiple disturbance B0 field strengths of the disturbance B0 field map at the first position and the corresponding multiple background B0 field strengths in the background B0 field map at the first position, multiple relationship coefficients related to multiple pixel points of the preset layer are obtained, and the prediction includes: calculating multiple disturbance B0 field strengths at the second position based on the multiple relationship coefficients and the corresponding multiple background B0 field strengths in the background B0 field map at the second position, and calculating multiple total B0 field strengths at the second position based on the multiple background B0 field strengths at the second position and the multiple disturbance B0 field strengths at the second position.

11. The method of claim 1, wherein: Also includes: performing low-pass filtering on the total B0 field image at the previous position to obtain a background B0 field reference image; It is determined whether the difference between the background B0 field reference image and the background B0 field image is less than a first preset value, and if not, a warning message is issued.

12. The method of claim 1, wherein: Also includes: Acquire a background B0 field standard map related to the body part where the imaging volume is located; Calibrate the background B0 field map based on the background B0 field standard map to obtain a background B0 field calibration map; performing low-pass filtering on the total B0 field image at the previous position to obtain a background B0 field reference image; It is determined whether the difference between the background B0 field reference map and the background B0 field calibration map is less than a second preset value, and if so, the background B0 field calibration map is used as the background B0 field map to predict the total B0 field map at the current position.

13. The method of claim 12, wherein: The method further includes: acquiring a background B0 field standard map related to the body part where the imaging volume is located based on a plurality of background B0 field reference maps related to the body part where the imaging volume is located.

14. The method of claim 13, wherein: The multiple background B0 field reference images related to the body part where the imaging volume is located are respectively acquired during multiple scans performed on the body part where the imaging volume is located.

15. The method of claim 13, wherein: Data fusion is performed on a plurality of background B0 field reference images related to the body part where the imaging volume is located to obtain the background B0 field standard image.

16. The method of claim 13, wherein: Also includes: The background B0 field standard map associated with the body part where the imaging volume is located is updated based on the background B0 field reference map obtained by low-pass filtering the total B0 field map at the previous position.

17. The method of claim 14, wherein: The background B0 field reference image, the background B0 field image, the B0 field standard image and the background B0 field calibration image obtained based on low-pass filtering of the total B0 field image at the previous position are all represented in the form of multi-order harmonic decomposition.

18. The method according to any one of claims 1 to 17, wherein: Performing the current imaging scan on the imaging volume of the object further includes: performing an imaging scan sequence on the imaging volume to acquire an image of the imaging volume; and correcting the image of the imaging volume based on the predicted total B0 field map.

19. A magnetic resonance scanning system, comprising: A scanner comprising a bed for carrying an object for movement, and having a plurality of scanning positions along a travel direction of the bed; A controller is used to control the scanner to perform imaging scanning on the imaging volume of the object to obtain an image of the imaging volume, including: executing the magnetic resonance scanning method according to any one of claims 1-18.

20. A computer-readable storage medium for storing computer-readable instructions, wherein the computer-readable instructions are used to execute the method of any one of claims 1-18.

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