Magnetic resonance imaging method

Abstract

The application relates to a magnetic resonance imaging method. The magnetic resonance imaging method comprises the following steps: performing forward blood flow acquisition on a 3D volume of a detection object by using a TOF 3D sequence to obtain a first group of magnetic resonance signals; the detection object is a blood vessel; performing reverse blood flow acquisition on the 3D volume of the detection object by using the TOF 3D sequence to obtain a second group of magnetic resonance signals; and reconstructing the first group of magnetic resonance signals and the second group of magnetic resonance signals to obtain a magnetic resonance image of the detection object. In the method, the blood flow signal acquisition is performed twice, the blood flow saturation effect can be effectively reduced, the blood flow signal intensity of the whole 3D volume is homogenized, and the influence of the signal intensity fluctuation in the blood vessel on the magnetic resonance imaging is reduced.

Description

[0001] This application is a divisional application of the invention patent application for "Method for Suppressing Static Tissue, Magnetic Resonance Imaging Method and System", the original application was filed on August 19, 2020, application number 202010838070.X. Technical Field

[0002] This application relates to the field of imaging, and in particular to a magnetic resonance imaging method. Background Technology

[0003] Magnetic resonance imaging (MRI) technology has been increasingly widely used in clinical diagnosis and scientific research, offering advantages such as safety, high contrast, and excellent resolution of soft tissues. In non-contrast vascular imaging, Time-of-Flight (TOF), based on GRE sequences, utilizes the inflow enhancement effect to image blood vessels, and finally displays them using Maximum Intensity Projection (MIP). However, background signals, especially bright fat signals, can interfere with MIP processing.

[0004] In traditional Time-of-Flight (TOF) sequences, the zero-order moment of the gradients for the selection and readout directions results in zero phase, as does the first-order moment, thus enabling vascular imaging. Traditional TOF sequences typically suppress fat by setting the time echo (TE) to out-of-phase, which limits the usable time echo (TE) and leads to flow signal loss due to long TE values. Summary of the Invention

[0005] Based on this, in view of the problem that traditional fat suppression techniques can lead to loss of flow signals, this application provides a method, magnetic resonance imaging method and system for suppressing static tissue.

[0006] A magnetic resonance imaging method, comprising:

[0007] Place the object to be tested in a static magnetic field;

[0008] The region of interest of the object to be detected is determined, the region of interest includes multiple layers, and each layer includes static tissue and fluid tissue;

[0009] Radio frequency pulses are emitted toward the object being detected to simultaneously excite the nuclear spins of both static and fluid tissues in the region of interest.

[0010] A target gradient field is applied, spatial encoding is performed, and the magnetic resonance signal of the region of interest is obtained, wherein the signal corresponding to the static tissue in the magnetic resonance signal of the region of interest is partially or completely suppressed;

[0011] The magnetic resonance signal is reconstructed to obtain a magnetic resonance image of the region of interest.

[0012] In one embodiment, the target gradient field includes gradients in the layer selection direction and gradients in the readout direction, and the target gradient field is determined by the following steps:

[0013] Obtain the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue;

[0014] Based on the relative velocity and the initial position, the gradient of the layer selection direction and the gradient of the readout direction are set.

[0015] In one embodiment, the step of obtaining the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue includes:

[0016] A flow rate encoding gradient is applied to obtain the initial position and the relative velocity in the layer selection direction and the relative velocity in the readout direction.

[0017] In one embodiment, the region of interest is one of a blood vessel, a ventricle, or the spinal cord.

[0018] A magnetic resonance imaging method, comprising:

[0019] Place the object to be tested in a static magnetic field;

[0020] The region of interest of the object to be detected is determined, the region of interest includes multiple layers, and each layer includes static tissue and fluid tissue;

[0021] An imaging sequence is applied to the detection object to obtain a first set of magnetic resonance signals. The imaging sequence includes a radio frequency pulse and a target gradient field. The radio frequency pulse is used to simultaneously excite the nuclear spins of static tissue and fluid tissue in the region of interest. The target gradient field is used to spatially encode the nuclear spins to obtain the first set of magnetic resonance signals. The signal corresponding to the static tissue in the first set of magnetic resonance signals is partially or completely suppressed.

[0022] Based on the first set of magnetic resonance signals, obtain a magnetic resonance image of the region of interest.

[0023] In one embodiment, the target gradient field includes gradients in the layer selection direction and gradients in the readout direction, and the target gradient field is determined by the following steps:

[0024] Obtain the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue;

[0025] Based on the relative velocity and the initial position, the gradient of the layer selection direction and the gradient of the readout direction are set.

[0026] In one embodiment, the first set of magnetic resonance signals is acquired along the flow direction of the fluid tissue.

[0027] A method for inhibiting static tissue includes:

[0028] The initial position of the flow organization, the relative velocity of the flow organization relative to the static organization in the layer selection direction, and the relative velocity of the flow organization relative to the static organization in the readout direction are obtained.

[0029] Based on the initial position, the relative velocity of the flowing tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flowing tissue relative to the static tissue in the readout direction, the gradient in the layer selection direction and the gradient in the readout direction are determined to determine the target gradient field applied to the object being detected; the target gradient field is used to partially or completely suppress the magnetic resonance signal corresponding to the static tissue.

[0030] In one embodiment, the step of obtaining the initial position of the flow tissue, the relative velocity of the flow tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flow tissue relative to the static tissue in the readout direction includes:

[0031] Send a position acquisition command, which instructs the gradient coil to apply a flow velocity encoded gradient to the detected object in order to obtain a feedback signal;

[0032] Based on the feedback signal, the initial position, the relative velocity of the flow tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flow tissue relative to the static tissue in the readout direction are obtained.

[0033] A magnetic resonance imaging system, comprising:

[0034] A scanning bed for placing at least the region of interest of the object to be detected in a scanning cavity, the region of interest comprising multiple layers, and each layer comprising static tissue and flowing tissue;

[0035] A radio frequency coil is used to emit radio frequency pulses to the object being detected, so as to simultaneously excite the nuclear spins of static and fluid tissues in the region of interest;

[0036] Gradient coils are used to apply a target gradient field, perform spatial encoding, and obtain the magnetic resonance signal of the region of interest, wherein the signal corresponding to the static tissue in the magnetic resonance signal of the region of interest is partially or completely suppressed;

[0037] Memory, used to store computer programs;

[0038] A processor, which executes the computer program to implement the steps of the method for suppressing static tissue as described in any of the above embodiments, or the steps of the magnetic resonance imaging method as described in any of the above embodiments.

[0039] The aforementioned magnetic resonance imaging method includes placing the object to be detected in a static magnetic field. A region of interest (ROI) is determined for the object. The ROI comprises multiple layers, each containing static and fluid tissue. A radio frequency pulse is emitted to the object to simultaneously excite the nuclear spins of both the static and fluid tissues within the ROI. A target gradient field is applied, and spatial encoding is performed to acquire the ROI magnetic resonance signal, wherein the signal corresponding to the static tissue in the ROI magnetic resonance signal is partially or completely suppressed. The magnetic resonance signal is reconstructed to obtain a magnetic resonance image of the ROI. In this method, by modifying the target gradient field to suppress the static tissue in the imaging region, imaging of fluid objects is achieved without requiring additional preprocessing pulses to suppress background tissue. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A flowchart of a magnetic resonance imaging method provided in one embodiment of this application;

[0042] Figure 2 This is a 2D timing diagram provided for one embodiment of this application;

[0043] Figure 3 This is a 3D timing diagram provided in one embodiment of this application;

[0044] Figure 4 This is a comparison image of imaging results provided in one embodiment of this application;

[0045] Figure 5 A flowchart of a method for suppressing static tissue provided in another embodiment of this application. Detailed Implementation

[0046] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0047] It is understood that the terms "first," "second," etc., used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, without departing from the scope of this application, a first acquiring module may be referred to as a second acquiring module, and similarly, a second acquiring module may be referred to as a first acquiring module. Both the first acquiring module and the second acquiring module are acquiring modules, but they are not the same acquiring module.

[0048] It should be noted that when a component is said to be "set on" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] Please see Figure 1 This application provides a magnetic resonance imaging method. The magnetic resonance imaging method includes steps S10-S50.

[0051] S10, Place the object to be detected in a static magnetic field.

[0052] In step S10, the object to be subjected to magnetic resonance imaging is designated as the detection object. The detection object can be a healthy subject, a patient, or an animal. The main magnet in the scanning device can generate a static magnetic field applied to the detection object. This static magnetic field can also be called the main magnetic field. The main magnet can also control the uniformity of the static magnetic field.

[0053] S20, determine the region of interest (ROI) of the object being detected. The ROI comprises multiple layers, and each layer includes static and fluid tissues.

[0054] In step S20, the region of interest (ROI) of the detection object can be any part or tissue, such as the heart, blood vessels, or other organs or tissues with pulsating areas. The ROI of the detection object can be set via computer. Each ROI can be a three-dimensional block / volume. The three-dimensional block includes multiple two-dimensional layers. The static tissue can be any stationary tissue such as fat, muscle, white matter, or gray matter. The flowing tissue can be blood or cerebrospinal fluid. In one embodiment, the ROI is one of a blood vessel, a ventricle, or the spinal cord.

[0055] S30, a radio frequency pulse is emitted toward the object being detected to simultaneously excite the nuclear spins of both static and fluid tissues in the region of interest.

[0056] In step S30, the radio frequency pulses may be perpendicular to the static magnetic field. A waveform generator can generate the radio frequency pulse sequence. The radio frequency pulse sequence can be amplified by a radio frequency power amplifier, processed by radio frequency electronics, and applied to a radio frequency transmitting coil to generate a third magnetic field in response to a strong current generated by the radio frequency electronics based on the amplified radio frequency pulses.

[0057] S40, apply a target gradient field, perform spatial encoding, and obtain the magnetic resonance signal of the region of interest, wherein the signal corresponding to the static tissue in the magnetic resonance signal of the region of interest is partially or completely suppressed.

[0058] In step S40, during magnetic resonance imaging, when the object being detected is lying prone or supine on the scanning bed, the gradient field in the front-back direction (i.e., the y-direction) can be used to perform phase encoding of the magnetic resonance signal, the gradient field in the left-right direction (i.e., the x-direction) can be used to perform layer selection (or layer selection) encoding, and the gradient field in the up-down direction (i.e., the z-direction) can be used to perform frequency encoding / frequency readout encoding.

[0059] In three-dimensional magnetic resonance imaging (MRI), layer selection is first required. Within each layer, frequency and phase encoding are performed to distribute the magnetic resonance signal to different pixel locations, thereby forming a magnetic resonance image. For example, layer selection encoding can be performed using a gradient field in the left-right direction (relative to the left-right direction of the human body), with the phase encoding direction perpendicular to the layer selection encoding direction, i.e., the phase encoding direction is the front-back direction / along the front of the human body pointing to the side. Of course, the layer selection encoding direction can also be the front-back direction, and correspondingly, the phase encoding direction is the left-right direction. Preferably, the method of performing phase encoding and frequency encoding on the magnetic resonance signal according to gradient fields in different directions to obtain the encoded data corresponding to the magnetic resonance signal is as follows: the magnetic resonance signal is phase-encoded using a gradient field relative to the front-back direction of the limb, and frequency readout encoding is performed using the direction of blood flow within the limb to obtain the encoded data corresponding to the magnetic resonance signal.

[0060] The signal corresponding to static tissue in the magnetic resonance signal of the region of interest can be partially or completely suppressed by modifying the gradient field sequence. Applying the gradient field sequence can cause the magnetic resonance signal of static tissue to be dephased, while the magnetic resonance signal of flowing tissue is converged. In one embodiment, by setting the phase of the zero-order gradient moments in the layer selection and readout directions to an odd multiple of π, and the phase of the first-order gradient moments in the layer selection and readout directions to 0, the suppression of static tissue and imaging of flowing tissue are achieved. This method can suppress static tissue without additional preparation modules. Optionally, in the TOF sequence, for the 2D sequence, the phase of the zero-order gradient moments in the layer selection and readout directions is set to an odd multiple of π, and the phase of the first-order moments is set to 0; for the 3D sequence, the phase of the zero-order gradient moments in the readout direction is set to an odd multiple of π, and the phase of the first-order moments is set to 0, resulting in modified 2D and 3D time-series plots as shown below. Figure 2 and Figure 3 As shown.

[0061] S50, Reconstruct the magnetic resonance signal to obtain a magnetic resonance image of the region of interest.

[0062] In step S50, the encoded data corresponding to the magnetic resonance signal is filled into the K-space. The K-space is then reconstructed to obtain a magnetic resonance image of the region of interest of the detected object. The magnetic resonance signal is a gradient echo signal.

[0063] The aforementioned magnetic resonance imaging method includes placing the object to be detected in a static magnetic field. A region of interest (ROI) is determined for the object. The ROI comprises multiple layers, each containing static and fluid tissue. A radio frequency pulse is emitted to the object to simultaneously excite the nuclear spins of both the static and fluid tissues within the ROI. A target gradient field is applied to acquire the magnetic resonance signal of the ROI, wherein the signal corresponding to the static tissue in the ROI is partially or completely suppressed. The magnetic resonance signal is reconstructed to acquire a magnetic resonance image of the ROI. In this method, by modifying the target gradient field, static tissue in the imaging region is suppressed, enabling imaging of fluid objects without requiring additional preprocessing pulses to suppress background tissue.

[0064] In one embodiment, the target gradient field includes a gradient in the layer selection direction and a gradient in the readout direction. The method for determining the target gradient field involves obtaining the relative velocity of the flowing tissue relative to the static tissue and the initial position of the flowing tissue. Based on the relative velocity and the initial position, the gradient in the layer selection direction and the gradient in the readout direction are set.

[0065] The relationship between phase and flow velocity is shown in the following formula:

[0066]

[0067]

[0068]

[0069]

[0070] In these formulas, Equation 1 represents the relationship between the position of the region of interest and time; Equation 2 represents the expression for the phase of the magnetic resonance signal in the region of interest; and Equation 3 represents the expression for the phase of the magnetic resonance signal in the region of interest after transformation. In these formulas, γ represents the gyrometry ratio, G represents the gradient, x represents the position, υ represents the velocity, φ represents the phase, and m... n Let μ represent the nth moment, t represent time, and μ represent the variable in the time axis direction corresponding to the gradient, and 0 ≤ μ ≤ t.

[0071] From the above equation, it can be seen that the phase introduced by the zeroth moment of the gradient in the layer selection and readout directions is an odd multiple of π, and the phase introduced by the first moment is 0, that is, γm0(t)x0=(2 p -1)π,γm1(t)v x0 =0. When the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue are determined, the gradient waveform in the layer selection direction and the gradient waveform in the readout direction can be obtained.

[0072] In one embodiment, the method for obtaining the relative velocity of the flowing tissue relative to the static tissue and the initial position of the flowing tissue can be to apply a flow velocity-encoded gradient to obtain the initial position and the relative velocity in the layer selection direction and the relative velocity in the readout direction. Specifically, a position acquisition command can be sent by a processor. After receiving the position acquisition command, the gradient coil applies a flow velocity-encoded gradient to the detection object. The receiving coil acquires the feedback signal of the detection object and sends it to the processor. By analyzing the feedback signal, the processor can obtain the relative velocity of the flowing tissue relative to the static tissue and the initial position of the flowing tissue.

[0073] Furthermore, based on the initial position and the relative velocity in the layer selection direction, the gradient in the layer selection direction must satisfy the following:

[0074] γm0(t)x0=(2 p -1)π;

[0075] γm1(t)v x0 =0 (Formula 5)

[0076] Where γ is the gyrometry ratio, m0(t) is the zeroth moment of the gradient in the selected layer direction, x0 is the initial position of the flow structure, P is a positive integer; m1(t) is the first moment of the gradient in the selected layer direction, v x0 The relative velocity of the flow tissue in the selected layer direction.

[0077] Based on the initial position and the relative velocity in the readout direction, the gradient in the readout direction must satisfy the following:

[0078] γM0(t)x0=(2 p -1)π;

[0079] γM1(t)v y0 =0 (Formula 6)

[0080] Where γ is the gyrometry ratio, M0(t) is the zeroth moment of the gradient in the readout direction, x0 is the initial position of the flow structure, P is a positive integer; M1(t) is the first moment of the gradient in the readout direction, v y0 The relative velocity of the flow tissue in the readout direction.

[0081] In this embodiment, according to the above method, the phase brought by the zeroth-order moment of the gradient in the layer selection and readout direction in the sequence is set to an odd multiple of π, and the phase brought by the first-order moment is 0. Please refer to [link to relevant documentation]. Figure 4 This is a comparison chart of the results, based on... Figure 4 It can be seen that this application achieves better suppression of static tissue and background signals, while having no impact on the imaging of flowing tissue (the vascular region in the figure).

[0082] Please see Figure 5 One embodiment of this application provides a method for suppressing static tissue. The method for suppressing static tissue includes:

[0083] S60, obtain the initial position of the flow organization, the relative velocity of the flow organization relative to the static organization in the layer selection direction, and the relative velocity of the flow organization relative to the static organization in the readout direction.

[0084] In step S60, the relationship between phase and flow velocity is shown in the following formula:

[0085]

[0086]

[0087]

[0088]

[0089] The relationship between phase and velocity is shown in the following formula, where γ represents the gyromagnetic ratio, G represents the gradient, x represents the position, υ represents the velocity, φ represents the phase, and m n It represents the nth order moment.

[0090] From the above equation, it can be seen that the phase introduced by the zeroth moment of the gradient in the layer selection and readout directions is an odd multiple of π, and the phase introduced by the first moment is 0, that is, γm0(t)x0=(2 p -1)π,γm1(t)v x0 =0. When the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue are determined, the gradient waveform in the layer selection direction and the gradient waveform in the readout direction can be obtained.

[0091] In one embodiment, the method for obtaining the initial position of the flow tissue, the relative velocity of the flow tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flow tissue relative to the static tissue in the readout direction can be achieved by sending a position acquisition command. The position acquisition command instructs a gradient coil to apply a flow velocity encoding gradient to the detection object to obtain a feedback signal. Based on the feedback signal, the initial position, the relative velocity of the flow tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flow tissue relative to the static tissue in the readout direction are obtained. Specifically, the position acquisition command can be sent by a processor. After receiving the position acquisition command, the gradient coil applies a flow velocity encoding gradient to the detection object. The receiving coil acquires the feedback signal from the detection object and sends it to the processor. The processor analyzes the feedback signal to obtain the relative velocity of the flow tissue relative to the static tissue and the initial position of the flow tissue.

[0092] S70, based on the initial position, the relative velocity of the flowing tissue relative to the static tissue in the layer selection direction, and the relative velocity of the flowing tissue relative to the static tissue in the readout direction, the gradient in the layer selection direction and the gradient in the readout direction are determined to determine the target gradient field applied to the detection object; the target gradient field is used to partially or completely suppress the magnetic resonance signal corresponding to the static tissue.

[0093] In step S70, based on the initial position and the relative velocity in the layer selection direction, the gradient in the layer selection direction needs to satisfy the following:

[0094] γm0(t)x0=(2 p -1)π;

[0095] γm1(t)v x0 =0 (Formula 11)

[0096] Where γ is the gyrometry ratio, m0(t) is the zeroth moment of the gradient in the selected layer direction, x0 is the initial position of the flow structure, P is a positive integer; m1(t) is the first moment of the gradient in the selected layer direction, v x0 The relative velocity of the flow tissue in the selected layer direction.

[0097] Based on the initial position and the relative velocity in the readout direction, the gradient in the readout direction must satisfy the following:

[0098] γM0(t)x0=(2 p -1)π;

[0099] γM1(t)v y0 =0 (Formula 12)

[0100] Where γ is the gyrometry ratio, M0(t) is the zeroth moment of the gradient in the readout direction, x0 is the initial position of the flow structure, P is a positive integer; M1(t) is the first moment of the gradient in the readout direction, v y0 The relative velocity of the flow tissue in the readout direction.

[0101] In this embodiment, according to the above method, the phase brought by the zeroth-order moment of the gradient in the layer selection and readout direction in the sequence is set to an odd multiple of π, and the phase brought by the first-order moment is 0. Please refer to [link to relevant documentation]. Figure 4 The figures show head images acquired using existing vascular imaging sequences and head images acquired using the imaging method of this application, respectively. The highlighted areas in the figures represent blood and flowing tissues, while areas with lower grayscale values ​​represent static tissues, cavities within the human body, etc. According to... Figure 4 It can be seen that this application achieves better suppression of static tissues without affecting the imaging of flowing tissues.

[0102] One embodiment of this application provides a magnetic resonance imaging system. The magnetic resonance imaging system includes a scanning bed, radio frequency coils, gradient coils, one or more processors, and a memory.

[0103] The scanning bed is used to place at least the region of interest (ROI) of the object being measured within the scanning cavity. The ROI comprises multiple layers, and each layer includes static and fluid tissue. The radio frequency (RF) coil is used to emit RF pulses to the object being measured to simultaneously excite the nuclear spins of both the static and fluid tissues within the ROI. The gradient coil is used to apply a target gradient field to acquire the magnetic resonance signal of the ROI, wherein the signal corresponding to the static tissue in the ROI's magnetic resonance signal is partially or completely suppressed. The memory is used to store one or more programs, and the processor, when executing the programs, implements the steps of the method for suppressing static tissue as described above.

[0104] Understandably, the object to be subjected to magnetic resonance imaging is referred to as the detection object. The detection object can be a healthy subject, a patient, or an animal. The main magnet in the scanning device can generate a static magnetic field applied to the detection object. This static magnetic field can also be called the main magnetic field. The main magnet can also control the uniformity of the static magnetic field.

[0105] The region of interest (ROI) of the detection object can be any part or tissue, such as the heart, blood vessels, or other organs or tissues with pulsating areas. Each ROI can be a three-dimensional block. The three-dimensional block includes multiple two-dimensional layers. The static tissue can be fat. The flowing tissue can be blood. In one embodiment, the ROI is one of a blood vessel, a ventricle, or the spinal cord.

[0106] The radio frequency (RF) pulses can be perpendicular to the static magnetic field. A waveform generator can produce the RF pulse sequence. The RF pulse sequence can be amplified by an RF power amplifier, processed by RF electronics, and applied to an RF transmitting coil to generate a third magnetic field in response to a strong current generated by the RF electronics based on the amplified RF pulses.

[0107] In magnetic resonance imaging, when the object being tested is lying prone or supine on the scanning table, the gradient field in the front-back direction (i.e., the y-direction) can be used to perform phase encoding (PE) of the magnetic resonance signal, the gradient field in the left-right direction (i.e., the x-direction) can be used to perform slice phase encoding (SPE), and the gradient field in the up-down direction (i.e., the z-direction) can be used to perform frequency encoding / readout encoding (RE).

[0108] In three-dimensional magnetic resonance imaging (MRI), layer selection is first required. Within each layer, frequency and phase encoding are performed to distribute the magnetic resonance signal to different pixel locations, thereby forming a magnetic resonance image. For example, layer selection encoding can be performed using a gradient field in the left-right direction (relative to the left-right direction of the human body), with the phase encoding direction perpendicular to the layer selection encoding direction, i.e., the phase encoding direction is the front-back direction / along the front of the human body pointing to the side. Of course, the layer selection encoding direction can also be the front-back direction, and correspondingly, the phase encoding direction is the left-right direction. Preferably, the method of performing phase encoding and frequency encoding on the magnetic resonance signal according to gradient fields in different directions to obtain the encoded data corresponding to the magnetic resonance signal is as follows: the magnetic resonance signal is phase-encoded using a gradient field relative to the front-back direction of the limb, and frequency readout encoding is performed using the direction of blood flow within the limb to obtain the encoded data corresponding to the magnetic resonance signal.

[0109] The signal corresponding to static tissue in the magnetic resonance signal of the region of interest can be partially or completely suppressed by modifying the gradient field sequence. In one embodiment, by setting the phase of the zeroth moment of the gradient in the layer selection and readout direction in the sequence to an odd multiple of π, and the phase of the phase of the first moment of the gradient in the layer selection and readout direction in the sequence to 0, the suppression of static tissue is achieved, and the imaging of flowing tissue is performed. This method can suppress static tissue without additional preparation modules. Optionally, in the TOF sequence, for the 2D sequence, the phase of the zeroth moment of the gradient in the layer selection and readout direction is set to an odd multiple of π, and the phase of the first moment is set to 0; for the 3D sequence, the phase of the zeroth moment of the gradient in the readout direction is set to an odd multiple of π, and the phase of the first moment is set to 0.

[0110] like Figure 2 This is a schematic diagram of a TOF 2D sequence according to an embodiment of this application, where RF represents the radio frequency pulse emitted by the radio frequency coil; Gss represents the gradient field in the layer selection direction; Gpe represents the gradient field in the phase encoding direction; and Gro represents the gradient field in the readout direction. In this embodiment, the TOF 2D sequence specifically involves applying a layer selection gradient 220 in the Gss direction simultaneously with the application of the RF pulse 210, followed by an out-of-phase gradient 230 along the Gss direction; subsequently, out-of-phase gradients 240 and 270 are applied sequentially along the Gpe and Gro directions, respectively; and simultaneously with the application of the out-of-phase gradient 270, a phase encoding gradient 250 is applied along the Gpe direction; and immediately following the out-of-phase gradient 270, a frequency encoding gradient 280 is applied to acquire the gradient echo signal 290. Of course, to reduce the influence of the gradient echo signal on the excitation signal of the next radio frequency pulse, an out-of-phase gradient 260 along the Gpe direction can also be applied after the gradient echo signal 290 is acquired. In this embodiment, the phase resulting from the zero-order moment of the gradient in the layer selection and readout directions is an odd multiple of π, and the phase resulting from the first-order moment of the gradient in the layer selection and readout directions is 0. This allows the signal corresponding to the static tissue in the magnetic resonance signal of the region of interest to be partially or completely suppressed. In this embodiment, the identical arrows inside the phase-delay gradients 240 and 260 applied along the Gpe direction indicate that they belong to the same type of gradient. The arrow of the phase-encoded gradient 250 is opposite to that of the phase-delay gradients 240 and 260, indicating that it belongs to a different type from the phase-delay gradients 240 and 260.

[0111] like Figure 3This is a schematic diagram of a TOF 3D sequence according to an embodiment of this application. In this embodiment, the TOF 3D sequence specifically involves applying a gradient 320 along the Gss direction while simultaneously applying an RF pulse 310. Following 320, an encoded gradient 330 and a dephase gradient 340 along the Gss direction are applied sequentially. Subsequently, dephase gradients 350 and 370 are applied sequentially along the Gpe and Gro directions, respectively. An encoded gradient 360 along the Gpe direction is applied immediately after 350, and a frequency encoded gradient 380 is applied immediately after 370 to acquire a gradient echo signal 390. To reduce the influence of the gradient echo signal on the excitation signal of the next RF pulse, dephase gradients 341 and 351 along the Gpe and Gss directions can be applied after the gradient echo signal 390 is acquired. In this embodiment, setting the phase of the zero-order moment of the gradient along the Gro direction to an odd multiple of PI and setting the phase of the first-order moment of the gradient along the Gro direction to 0 allows the signal corresponding to the static tissue in the magnetic resonance signal of the region of interest to be partially or completely suppressed. In this embodiment, three-dimensional TOF imaging can obtain images with high spatial resolution, and because the voxels are small, the flow phase loss is relatively small and the influence of turbulence is relatively small.

[0112] In one embodiment, the target of detection is a blood vessel, and the flowing tissue is blood flow. The magnetic resonance imaging method includes: first, using a TOF 3D sequence to acquire a first set of magnetic resonance signals by performing forward-flow acquisition on the 3D volume of the target object; then, using a TOF 3D sequence to acquire a second set of magnetic resonance signals by performing reverse-flow acquisition on the 3D volume of the target object; and reconstructing the first and second sets of magnetic resonance signals to obtain a magnetic resonance image of the target object. In this embodiment, forward-flow acquisition specifically involves first acquiring magnetic resonance signals at the proximal level of the blood flow, and then acquiring signals layer by layer towards the distal level of the blood flow, with the layering direction of the 3D volume consistent with the blood flow direction. Reverse-flow acquisition specifically involves first acquiring magnetic resonance signals at the distal level of the blood flow, and then acquiring signals layer by layer towards the proximal level of the blood flow, with the layering direction of the 3D volume opposite to the blood flow direction. In this embodiment, by acquiring blood flow signals twice, the blood flow saturation effect can be effectively reduced.

[0113] The encoded data corresponding to the magnetic resonance signal is filled into the K-space. The K-space is then reconstructed to obtain a 3D volumetric magnetic resonance image. The magnetic resonance signal can be a gradient echo signal.

[0114] In one embodiment, the object of detection is selected as blood vessels, the flowing tissue is blood flow, and the magnetic resonance imaging method is selected as follows: Figure 3The TOF 3D imaging sequence shown performs a scan on the detection object. As described above, the imaging sequence includes radio frequency pulses and a target gradient field. The radio frequency pulses are used to simultaneously excite the nuclear spins of static and flowing tissues in the 3D volume. The target gradient field is used to spatially encode the nuclear spins to obtain magnetic resonance signals. The signal corresponding to the static tissue in the first set of magnetic resonance signals is partially or completely suppressed. Furthermore, the TOF 3D imaging sequence adjusts the application timing of the encoding gradient 330 along the Gss direction and the encoding gradient 360 along the Gpe direction, so that during the acquisition of magnetic resonance signals, continuous acquisition is performed along the Gss direction, and interlaced scanning is performed along the Gpe direction within the slice. In this embodiment, the interlaced acquisition method helps reduce the blood flow saturation effect, making the blood flow signal intensity uniform throughout the 3D volume, reducing fluctuations in signal intensity within blood vessels, and enabling the display of slow blood flow and small vessels. In addition, the technical solution of this embodiment also changes the sensitivity to blood flow velocity and direction, improving the display rate of vascular stenosis and abnormal vessels.

[0115] Memory, as a computer-readable storage medium, can be used to store software programs, computer-executable programs, and modules, such as the program instructions / modules corresponding to the magnetic resonance imaging method in the embodiments of this application. The processor executes various functional applications and data processing of the device by running the software programs, instructions, and modules stored in the memory, thereby implementing the aforementioned magnetic resonance imaging method.

[0116] The memory may primarily comprise a program storage area and a data storage area. The program storage area may store the operating system and at least one application program required for a given function. The data storage area may store data created based on terminal usage. Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory, or other non-volatile solid-state storage device. In some instances, the memory may further include memory remotely located relative to the processor, which can be connected to the device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0117] The aforementioned magnetic resonance imaging system includes placing the object to be detected in a static magnetic field. A region of interest (ROI) is determined for the object. The ROI comprises multiple layers, each containing static and fluid tissue. A radio frequency pulse is emitted to the object to simultaneously excite the nuclear spins of both the static and fluid tissues within the ROI. A target gradient field is applied to acquire the ROI magnetic resonance signal, wherein the signal corresponding to the static tissue in the ROI magnetic resonance signal is partially or completely suppressed. The magnetic resonance signal is reconstructed to acquire a magnetic resonance image of the ROI. In this method, by modifying the target gradient field, static tissue in the imaging region is suppressed, enabling imaging of fluid objects without requiring additional preprocessing pulses to suppress background tissue.

[0118] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A magnetic resonance imaging method, characterized in that, include: A first set of magnetic resonance signals was obtained by performing flow-in-the-flow acquisition on the 3D volume of the object being tested using a TOF 3D sequence; the object being tested was a blood vessel; the phase of the gradient zero-order moment in the readout direction of the TOF 3D sequence was... An odd multiple of the first order moment results in a phase of 0. The TOF 3D sequence was used to perform reverse blood flow acquisition on the 3D volume of the object being detected, resulting in a second set of magnetic resonance signals; The first set of magnetic resonance signals and the second set of magnetic resonance signals are reconstructed to obtain a magnetic resonance image of the detected object.

2. The magnetic resonance imaging method according to claim 1, characterized in that, The blood flow acquisition method involves first acquiring magnetic resonance signals at the proximal level of the blood flow, and then acquiring signals layer by layer towards the distal level of the blood flow. The layering direction of the 3D volume is consistent with the blood flow direction.

3. The magnetic resonance imaging method according to claim 1, characterized in that, The reverse blood flow acquisition involves first acquiring magnetic resonance signals at the distal level of the blood flow, and then acquiring signals layer by layer towards the proximal side of the blood flow. The layering direction of the 3D volume is opposite to the blood flow direction.

4. The magnetic resonance imaging method according to claim 1, characterized in that, The TOF 3D sequence includes a radio frequency pulse and a target gradient field. The radio frequency pulse is used to simultaneously excite the nuclear spins of static and fluid tissues in the 3D volume. The target gradient field is used to spatially encode the nuclear spins to obtain magnetic resonance signals. The signal corresponding to the static tissue in the first set of magnetic resonance signals is partially or completely suppressed.

5. The magnetic resonance imaging method according to claim 4, characterized in that, The TOF 3D sequence adjusts the timing of the application of the encoding gradient along the Gss direction and the encoding gradient along the Gpe direction, so that the magnetic resonance signal is acquired continuously along the Gss direction and interlaced in the Gpe direction within the slice.

6. The magnetic resonance imaging method according to claim 4, characterized in that, The target gradient field is determined through the following steps: Obtain the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue; Based on the relative velocity and the initial position, the gradient of the layer selection direction and the gradient of the readout direction are set.

7. The magnetic resonance imaging method according to claim 6, characterized in that, The steps of obtaining the relative velocity of the flowing tissue with respect to the static tissue and the initial position of the flowing tissue include: A flow rate encoding gradient is applied to obtain the initial position and the relative velocity in the layer selection direction and the relative velocity in the readout direction.

8. The magnetic resonance imaging method according to claim 4, characterized in that, The TOF 3D sequence is obtained through the following steps: A gradient is applied along the Gss direction while the RF pulse is being applied; The encoding gradient and the phase-degradation gradient along the Gss direction are applied sequentially. Two phase-delay gradients are applied sequentially along the Gpe direction and the Gro direction, respectively. After one phase-delay gradient, an encoding gradient along the Gpe direction is applied immediately, and after the other phase-delay gradient, a frequency encoding gradient is applied immediately to acquire the gradient echo signal. Gss is the gradient field in the layer selection direction, Gpe is the gradient field in the phase encoding direction, and Gro is the gradient field in the readout direction.

9. The magnetic resonance imaging method according to claim 8, characterized in that, After acquiring the gradient echo signal, the process also includes: Two phase-delay gradients are applied along the Gpe direction and the Gss direction, respectively.

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