Magnetic resonance imaging system and method

Abstract

The embodiment of the invention provides a magnetic resonance imaging method and system. The method may include acquiring magnetic resonance imaging data of a target object. Magnetic resonance imaging data may be acquired by applying a magnetic resonance imaging pulse sequence to a target object. The magnetic resonance imaging pulse sequence may include a single radio frequency pulse for exciting a first substance in a target object and suppressing a second substance in the target object. The method may further include reconstructing a magnetic resonance image of the target object based on the magnetic resonance imaging data.

Description

Cross-reference

[0001] This specification claims priority to U.S. Application No. 18 / 430,594, filed on February 1, 2024, the entire content of which is incorporated herein by reference. Technical Field

[0002] This specification relates to the field of Magnetic Resonance Imaging (MRI), and more particularly to MRI systems and methods using MRI sequences including a single Radio Frequency (RF) pulse with off-resonant spin tipping effects (Monomial RF Pulse with Off-Resonant Spin Tipping Effects) (hereinafter referred to as MOST RF pulse). Background Art

[0003] Magnetic Resonance (MR) technology has been widely applied in various fields such as physics, chemistry, biology, and medicine. In some MR scans, it is necessary to specifically design RF pulses to excite a target substance (e.g., water) in a target object while suppressing other substances (e.g., fat, silicone) in the target object. Therefore, it is desirable to provide an improved RF pulse design strategy that can reliably suppress other substances while reliably exciting the target substance. Summary of the Invention

[0004] In one aspect of the embodiments of this specification, a method for MRI is provided. The method can be implemented on a computing device having at least one processor and at least one storage device. The method can include acquiring MRI data of a target object. The MRI data can be acquired by applying an MRI pulse sequence to the target object. The MRI pulse sequence can include a single RF pulse for exciting a first substance in the target object and suppressing a second substance in the target object. The method can further include reconstructing an MR image of the target object based on the MRI data. The waveform of the single RF pulse can be determined by: generating a trapezoidal wave; generating an initial waveform by performing an exponential transformation on each point in the trapezoidal wave; and determining the waveform of the single RF pulse by filtering the initial waveform.

[0005] In some embodiments, the phase of the single RF pulse can be a constant value during application.

[0006] In some embodiments, the trapezoidal wave can include a top side having a first length and a bottom side having a second length, and the first length can be greater than zero and less than the second length.

[0007] In some embodiments, the center frequency of the single radio frequency pulse can be determined in the following manner: determining the duration and radio frequency field strength of the single radio frequency pulse; based on the duration and the radio frequency field strength, determining a predicted first frequency response curve of the first substance with respect to the single radio frequency pulse and a predicted second frequency response curve of the second substance with respect to the single radio frequency pulse; and determining the center frequency of the single radio frequency pulse based on the predicted first frequency response curve and the predicted second frequency response curve.

[0008] In some embodiments, the predicted first frequency response curve and the predicted second frequency response curve can be determined in the following manner: determining peak width information based on the duration; determining peak frequency information based on the radio frequency field strength; and determining the predicted first frequency response curve and the predicted second frequency response curve based on the peak width information and the peak frequency information.

[0009] In some embodiments, determining the peak frequency information based on the radio frequency field strength may include: determining a threshold intensity related to the radio frequency field strength, the threshold intensity corresponding to a preset equivalent flip angle; and determining the peak frequency information based on the radio frequency field strength and the threshold intensity.

[0010] In some embodiments, determining the center frequency of the single radio frequency pulse based on the predicted first frequency response curve and the predicted second frequency response curve may include: determining one or more predicted passbands based on the predicted first frequency response curve, in which the first substance is excited; determining one or more predicted stopbands based on the predicted second frequency response curve, in which the second substance is suppressed; determining a predicted overlapping frequency range between the one or more predicted passbands and the one or more predicted stopbands; and determining the center frequency within the predicted overlapping frequency range.

[0011] In some embodiments, the first frequency response curve of the first substance with respect to the single radio frequency pulse may include one or more passbands, in which the first substance is excited, and each of the one or more passbands spans a locally continuous frequency range. The second frequency response curve of the second substance with respect to the single radio frequency pulse may include one or more stopbands, in which the second substance is suppressed, and at least one of the one or more stopbands is a semi-infinite frequency range. At least one of the one or more passbands and the at least one stopband may have an overlapping frequency range, and the center frequency of the single radio frequency pulse may be within the overlapping frequency range.

[0012] In some embodiments, the first substance and the second substance may be two different substances among water, fat, and silicone gel.

[0013] In another aspect of the embodiments of the present specification, an MRI method is provided. The method may be implemented on a computing device having at least one processor and at least one storage device. The method may include acquiring MRI data of a target object. The MRI data may be acquired by applying an MRI pulse sequence to the target object. The MRI pulse sequence may include a single radiofrequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object. The method may further include reconstructing an MR image of the target object based on the MRI data. The first frequency response curve of the first substance with respect to the single radiofrequency pulse may include one or more passbands in which the first substance is excited, and each of the one or more passbands spans a locally continuous frequency range. The second frequency response curve of the second substance with respect to the single radiofrequency pulse may include one or more stopbands in which the second substance is suppressed, and at least one of the one or more stopbands is a semi-infinite frequency range. At least one of the one or more passbands and the at least one stopband may have an overlapping frequency range, and the center frequency of the single radiofrequency pulse may be within the overlapping frequency range.

[0014] In yet another aspect of the embodiments of the present specification, an MRI system is provided. The system may include at least one storage device including a set of instructions; and at least one processor configured to communicate with the at least one storage device. When executing the set of instructions, the at least one processor may be configured to direct the system to perform operations. The operations may include acquiring MRI data of a target object. The MRI data may be acquired by applying an MRI pulse sequence to the target object. The MRI pulse sequence may include a single radiofrequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object. The operations may further include reconstructing an MR image of the target object based on the MRI data. The waveform of the single radiofrequency pulse may be determined by: generating a trapezoidal wave; generating an initial waveform by performing an exponential transformation on each point of the trapezoidal wave; and filtering the initial waveform to determine the waveform of the single radiofrequency pulse.

[0015] Additional features of a part of this specification can be illustrated in the following description. Through the study of the following description and the corresponding drawings, or the understanding of the production or operation of the embodiments, additional features of a part of this specification are obvious to those skilled in the art. The features of some embodiments of this specification can be achieved and attained by practicing or using various aspects of the methods, tools, and combinations described in the detailed examples discussed below. Brief Description of the Drawings

[0016] This application will be further described through exemplary embodiments. These exemplary embodiments will be described in detail through the drawings. These are non-limiting exemplary embodiments, in which the same numbers in the figures represent similar structures, where:

[0017] Figure 1 is an exemplary schematic diagram of an MRI shown according to some embodiments of this specification;

[0018] Figure 2 is an exemplary block diagram of a processing device shown according to some embodiments of this specification;

[0019] Figure 3 is an exemplary flowchart of reconstructing an MRI image shown according to some embodiments of this specification;

[0020] Figure 4A is an exemplary schematic diagram of the frequency response curves of a first substance and a second substance relative to a single radio frequency pulse shown according to some embodiments of this specification;

[0021] Figure 4B is an exemplary schematic diagram of the frequency response curves of a first substance and a second substance relative to a Binomial Off-Resonant Rectangular (BORR) pulse shown according to some embodiments of this specification;

[0022] Figure 4C is an exemplary schematic diagram of the frequency response curves of a first substance and a second substance relative to a Lipid Insensitive Binomial Off-Resonant RF Excitation (LIBRE) pulse shown according to some embodiments of this specification;

[0023] Figure 5 is an exemplary flowchart of a process for determining the waveform of a single radio frequency pulse shown according to some embodiments of this specification;

[0024] Figure 6 is an exemplary schematic diagram of determining the waveform of a single radio frequency pulse shown according to some embodiments of this specification;

[0025] Figure 7 is an exemplary flowchart of a process for determining the center frequency of a single radio frequency pulse as shown in some embodiments of this specification;

[0026] Figure 8 is an exemplary flowchart of a process for determining a predicted first frequency response curve and a predicted second frequency response curve as shown in some embodiments of this specification;

[0027] Figure 9 is an exemplary schematic diagram of a predicted first frequency response curve and a predicted second frequency response curve as shown in some embodiments of this specification;

[0028] Figure 10 is an exemplary schematic diagram of a predicted first frequency response curve and a predicted second frequency response curve as shown in some embodiments of this specification;

[0029] Figure 11 is an exemplary schematic diagram of a predicted first frequency response curve and a predicted second frequency response curve as shown in some embodiments of this specification; and

[0030] Figure 12 is an exemplary schematic diagram of a computing device as shown in some embodiments of this specification. Detailed Description of the Invention

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. However, those skilled in the art should understand that this application can be implemented without these details. In other cases, well-known methods, procedures, systems, components, and / or circuits have been described at a relatively high level without detailed description to avoid unnecessarily obscuring various aspects of this specification. For those of ordinary skill in the art, it is obvious that various changes can be made to the disclosed embodiments, and the general principles defined in this application can be applied to other embodiments and application scenarios without departing from the principles and scope of this application. Therefore, this application is not limited to the disclosed embodiments, but conforms to the broadest scope consistent with the scope of the patent application.

[0032] The terms used in this application are for the purpose of describing specific example embodiments only and are not restrictive. As used in this application, the singular forms "a", "an", and "the" may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that as used in the specification of this application, the terms "comprising", "including" merely indicate the presence of the described features, integers, steps, operations, components, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, components, parts, and / or their combinations.

[0033] It will be understood that when a unit, engine, module or block is referred to as being "on", "connected to" or "coupled to" another unit, engine, module or block, it can be directly on, connected or coupled to the other unit, engine, module or block, or communicate with the other unit, engine, module or block, or there may be an intermediate unit, engine, module or block, unless the context clearly dictates otherwise. In the present application, the term "and / or" may include any one or more of the related listed items or a combination thereof.

[0034] From the following description of the drawings, these and other features, characteristics, and the functions and operating methods of the related structural elements of the present application, as well as the component combinations and manufacturing economies, may become more apparent. These drawings all form part of the specification of the present application. However, it should be understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the scope of the present application. It should be understood that the drawings are not drawn to scale.

[0035] The terms "pixel" and "voxel" in this specification may be used interchangeably to refer to the elements in an image. In this specification, the term "image" may refer to a two-dimensional (2D) image, a three-dimensional (3D) image, or a four-dimensional (4D) image (e.g., a time series of 3D images). In some embodiments, the term "image" may refer to an image of a region of a subject (e.g., a region of interest (ROI)). In some embodiments, the image may be a medical image, an optical image, etc.

[0036] In this specification, for the sake of brevity, the representation of an object (such as an object, a patient or a part thereof) in an image may be referred to as an "object". For example, for the sake of brevity, the representation of an organ, tissue (such as the heart, liver, lungs) or ROI in an image may be referred to as an organ, tissue or ROI. In addition, for the sake of brevity, an image including the representation of an object or a part thereof may be referred to as an image of the object or a part thereof, or an image including the object or a part thereof. In addition, for the sake of brevity, an operation performed on the representation of an object or a part thereof in an image may be referred to as an operation performed on the object or a part thereof. For example, for the sake of brevity, the segmentation of a part of an image including the representation of an ROI may be referred to as the segmentation of the ROI.

[0037] In some MR scans, radiofrequency pulses need to be specifically designed to excite a first substance (such as water) in a target object while suppressing a second substance (such as fat, silicone) in the target object. Recently, BORR pulses and LIBRE pulses have been proposed. However, both BORR pulses and LIBRE pulses include two rectangular radiofrequency sub-pulses, which have certain requirements for MRI equipment. In addition, the frequency range for suppressing the second substance is relatively small (for example, the span of the frequency range is about 100 Hertz (Hz)), which reduces the applicability of the pulses. Therefore, it is desirable to provide an improved radiofrequency pulse design strategy to reliably excite the first substance while reliably suppressing other substances.

[0038] Some embodiments of this specification relate to an MRI system and method using an MRI pulse sequence that includes a monomial radio frequency pulse for exciting a first substance in a target object and suppressing a second substance in the target object. The monomial radio frequency pulse in some embodiments of this specification is referred to as a MOST pulse, and the waveform of the monomial radio frequency pulse can be determined by the following method: generating a trapezoidal wave; generating an initial waveform by performing an exponential transformation on each point in the trapezoidal wave; and determining the waveform of the monomial radio frequency pulse by filtering the initial waveform. By using the monomial radio frequency pulse specifically designed in some embodiments of this specification, the first substance in the target object can be effectively excited, and the second substance in the target object can be effectively suppressed, which can reduce noise and / or interference from the second substance, thereby improving the accuracy of MRI data and / or MR images. In addition, the specifically designed monomial radio frequency pulse is particularly suitable for applications in high-field and ultra-high-field scenarios. The monomial radio frequency pulse is not only insensitive to B0 and B1 inhomogeneities that are usually prominent in high fields but also can generate a relatively low Specific Absorption Rate (SAR) of radiofrequency energy.

[0039] In some embodiments, the first frequency response curve of the first substance with respect to the monomial radio frequency pulse may include one or more passbands in which the first substance is excited, and each of the one or more passbands may span a locally continuous frequency range. The second frequency response curve of the second substance with respect to the monomial radio frequency pulse may include one or more stopbands in which the second substance is suppressed, and at least one of the one or more stopbands may be a semi-infinite frequency range. At least one of the one or more passbands may have an overlapping frequency range with at least one of the stopbands, and the center frequency of the monomial radio frequency pulse may be within the overlapping frequency range. Since the frequency range of at least one stopband is semi-infinite, the entire passband of at least one passband may be located within at least one stopband, which can improve the length of the overlapping frequency range and enhance the selectivity of the center frequency of the monomial radio frequency pulse and the applicability of the monomial radio frequency pulse.

[0040] Figure 1 is an exemplary schematic diagram of the MRI system 100 shown according to some embodiments of this specification. As Figure 1 shown, the MRI system 100 may include an MRI device 110, a network 120, one or more terminals 130, a processing device 140, and a storage device 150. In some embodiments, the MRI device 110, the processing device 140, the storage device 150, and / or the terminal 130 may be interconnected and / or communicate with each other via a wireless connection (such as the network 120), a wired connection, or a combination thereof. The connections between the components in the MRI system 100 may be variable.

[0041] The MRI device 110 may be configured to generate or provide image data (such as MRI data) by scanning a target object or at least a part of the target object. For example, the MRI device 110 may acquire MRI data (such as MR signals) by applying an MRI pulse sequence to the target object. In some embodiments, the MRI device 110 may include a single-mode MRI device or a multi-mode MRI device. Exemplary multimodal MRI devices may include computed tomography-magnetic resonance imaging (CT-MRI) devices, positron emission tomography-magnetic resonance imaging (PET-MRI) scanners, etc., or any combination thereof. It should be noted that the MRI device described below is for illustrative purposes only and is not intended to limit the scope of this specification.

[0042] In some embodiments, the MRI device 110 may include a magnet, a gradient coil assembly, a radio frequency coil assembly, etc. The magnet may generate a first magnetic field (also referred to as the main magnetic field) for polarizing the target object to be scanned. The gradient coil assembly may generate a second magnetic field (also referred to as the gradient magnetic field). The gradient coil assembly may include an X-gradient coil, a Y-gradient coil, and a Z-gradient coil. The gradient coil assembly may generate one or more magnetic field gradient pulses in the X direction (Gx), Y direction (Gy), and Z direction (Gz) with respect to the main magnetic field to encode the spatial information of the target object. The radio frequency coil assembly may include a plurality of radio frequency coils. The radio frequency coils may include one or more radio frequency transmit coils and / or one or more radio frequency receive coils. The radio frequency transmit coil may transmit radio frequency pulses to the target object. Under the coordinated action of the main magnetic field, the gradient magnetic field, and the radio frequency pulses, the MRI pulse sequence may excite one or more MR signals related to the target object. The radio frequency receive coil may acquire MR signals from the target object based on the MRI pulse sequence.

[0043] The target object may include a patient or other experimental subject (such as an experimental mouse or other animal). In some embodiments, the target object may be a patient or a specific part, organ, and / or tissue of a patient. For example, the target object may include the head, neck, chest, heart, stomach, blood vessels, soft tissue, tumor, nodule, etc., or any combination thereof. In some embodiments, the target object may be non-biological. For example, the target object may include a phantom, an artificial object, etc. In this specification, the terms "object" and "subject" may be used interchangeably.

[0044] Network 120 may include any suitable network that can facilitate the exchange of information and / or data of MRI system 100. In some embodiments, one or more components of MRI system 100 (e.g., MRI device 110, terminal 130, processing device 140, storage device 150, etc.) may communicate information and / or data with one or more other components of MRI system 100 through network 120. In some embodiments, network 120 may include one or more network access points.

[0045] Terminal 130 may include a mobile device 130-1, a tablet computer 130-2, a laptop computer 130-3, etc., or any combination thereof. In some embodiments, mobile device 130-1 may include a smart home device, a wearable device, a smart mobile device, a virtual reality device, an augmented reality device, etc., or any combination thereof. In some embodiments, terminal 130 may be a part of processing device 140.

[0046] Processing device 140 may process data and / or information obtained from one or more components of MRI system 100 (MRI device 110, terminal 130, and / or storage device 150). For example, processing device 140 may acquire MRI data of the target object. Again, for example, processing device 140 may reconstruct an MR image of the target object based on the MRI data. In some embodiments, processing device 140 may be a single server or a server group. The server group may be centralized or distributed. In some embodiments, processing device 140 may be local or remote. In some embodiments, processing device 140 may be implemented on a cloud platform. Exemplary cloud platforms may include private clouds, public clouds, hybrid clouds, community clouds, distributed clouds, inter-clouds, multi-clouds, etc., or any combination thereof.

[0047] In some embodiments, processing device 140 may be implemented by a computing device. For example, the computing device may include a processor, a memory, an input / output (I / O), and a communication port. In some embodiments, processing device 140 or a part of processing device 140 may be implemented by a part of terminal 130.

[0048] The storage device 150 may store data / information (such as MRI pulse sequences, MRI data, MR images, etc.) obtained from the MRI device 110, the terminal 130, and / or any other components of the MRI system 100. In some embodiments, the storage device 150 may include a mass storage, a removable storage, a volatile read-write memory, a read-only memory (ROM), etc., or any combination thereof. In some embodiments, the storage device 150 may store one or more programs and / or instructions to execute the exemplary methods described in this specification.

[0049] In certain embodiments, the MRI system 100 may include one or more additional components, and / or one or more components of the above-described MRI system 100 may be omitted. Additionally or alternatively, two or more components of the MRI system 100 may be integrated into a single component. One component of the MRI system 100 may be implemented on two or more sub-components.

[0050] Figure 2 is an exemplary block diagram of a processing device according to some embodiments shown in this specification. In some embodiments, the processing device 140 may communicate with a computer-readable storage medium (such as Figure 1 the storage device 150 shown therein) and execute the instructions stored in the computer-readable storage medium. The processing device 140 may include an acquisition module 210 and a reconstruction module 220.

[0051] The acquisition module 210 may be configured to acquire MRI data of a target object. The MRI data may be acquired by applying an MRI pulse sequence to the target object. The MRI pulse sequence may include a single radiofrequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object. More descriptions regarding the acquisition of MRI data may be found in other parts of this specification. For example, operation 302 and its related descriptions.

[0052] The reconstruction module 220 may be configured to reconstruct an MR image of the target object based on the MRI data. More descriptions regarding the reconstruction of the MR image may be found in other parts of this specification. For example, operation 304 and its related descriptions.

[0053] In some embodiments, the processing device 140 may further include a waveform determination module 230. The waveform determination module 230 may be configured to determine the waveform of the single radiofrequency pulse. For example, the waveform determination module 230 may generate a trapezoidal wave, generate an initial waveform by performing an exponential transformation on each point in the trapezoidal wave, and determine the waveform of the single radiofrequency pulse by filtering the initial waveform. More descriptions regarding the determination of the waveform of the single radiofrequency pulse may be found in other parts of this specification. For example, Figure 5 and its related descriptions.

[0054] In some embodiments, the processing device 140 may include one or more other modules, and the above one or more modules may be omitted. For example, the processing device 140 may include a storage module for storing data generated by the modules in the processing device 140. In some embodiments, any two modules may be combined into one module, and any one module may be divided into two or more units.

[0055] Figure 3 is an exemplary flowchart of reconstructing an MR image according to some embodiments of the present specification. Process 300 may be implemented in Figure 1 the MRI system 100 shown. For example, process 300 may be stored in the storage device 150 in the form of instructions (such as an application program) and called and / or executed by the processing device 140.

[0056] In 302, the processing device 140 (for example, the acquisition module 210) may acquire MRI data of the target object.

[0057] The MRI data may be acquired by applying an MRI pulse sequence to the target object. The MR pulse sequence may be used to scan the target object and / or generate MRI data. For example, the MRI device (such as the MRI device 110) may be instructed to apply an MRI pulse sequence to the target object and acquire MRI data (such as MR signals).

[0058] In some embodiments, the MRI pulse sequence may be defined by imaging parameters and an arrangement associated with the image parameters in the time sequence. For example, the MRI pulse sequence may include or be associated with one or more parameters related to radio frequency pulses, such as bandwidth (or frequency range), amplitude (or intensity), application time, duration, etc. Again, for example, the MRI pulse sequence may include or be associated with one or more parameters related to the gradient field, such as application direction, field strength, application time, duration, etc. Still again, for example, the MRI pulse sequence may be defined by one or more time-related parameters, such as repetition time (TR), acquisition time (TA), echo time (TE), inversion time (TI), etc.

[0059] In some embodiments, the MRI pulse sequence may include a single radiofrequency pulse for exciting a first substance in a target object and suppressing a second substance in the target object. The first substance refers to the target substance to be excited by the single radiofrequency pulse, and the second substance refers to another substance to be suppressed. In some embodiments, the chemical shift of the first substance may be different from the chemical shift of the second substance. For example, the first substance and the second substance may be two different substances among water, fat, and silicone. By way of example, assuming that the resonance frequency of water is the same as the center frequency of the MRI device 110 (i.e., the chemical shift of water is equal to 0 parts per million (ppm)), when the radiofrequency field strength of the MRI device 110 is 3 Tesla (T), the chemical shift of fat relative to water may be -3.5 ppm, and the chemical shift of silicone relative to water may be -4.7 ppm.

[0060] In some embodiments, the single radiofrequency pulse may be a single radiofrequency pulse with an off-resonance spin flip effect (also known as a MOST RF pulse). Since the center frequency of the single radiofrequency pulse is different from the center frequency of a substance (such as water), the single radiofrequency pulse may be an off-resonance radiofrequency pulse. Accordingly, the signal of the substance excited by the single radiofrequency pulse may not be as effective as the signal of the substance excited by a resonant pulse. The off-resonance spin flip effect refers to an effect that can tilt the substance signal towards the x-y plane perpendicular to the Z direction.

[0061] In some embodiments, the phase of the single radiofrequency pulse may be a constant value during application. That is, when the single radiofrequency pulse is applied to the target object, the phase of the single radiofrequency pulse remains unchanged. For example, the phase of the single radiofrequency pulse may be any value within the range of -180 degrees to 180 degrees. It should be noted that the constant value corresponds to a single MRI pulse sequence. For example, the single radiofrequency pulse in the first MRI pulse sequence may correspond to a first phase, the single radiofrequency pulse in the second MRI pulse sequence may correspond to a second phase, and the first phase may be different from the second phase. In some embodiments, the phase of the single radiofrequency pulse in the MRI pulse sequence may be determined based on the system default settings or manually set by a user (such as a doctor, technician, etc.).

[0062] By fixing the phase of the single radiofrequency pulse to a constant value, the excitation effect corresponding to the single radiofrequency pulse can be made constant, thereby reducing the complexity of the application of the single radiofrequency pulse, and thus improving the efficiency and accuracy of MRI data acquisition.

[0063] In some embodiments, the processing device 140 may determine the waveform of the single radiofrequency pulse. For example, the processing device 140 may generate a trapezoidal wave, generate an initial waveform by performing an exponential transformation on each point in the trapezoidal wave, and determine the waveform of the single radiofrequency pulse by filtering the initial waveform. More descriptions about the determination of the single radiofrequency pulse waveform can be found in other parts of this specification (for example,Figure 5 and Figure 6 and its description).

[0064] In some embodiments, the processing device 140 may determine the center frequency of a single RF pulse. For example, the processing device 140 may determine the duration and RF field strength of a single RF pulse; based on the duration and RF field strength, determine a predicted first frequency response curve of the first substance relative to the single RF pulse and a predicted second frequency response curve of the second substance relative to the single RF pulse; and determine the center frequency of the single RF pulse based on the predicted first frequency response curve and the predicted second frequency response curve. For more descriptions on determining the center frequency of a single RF pulse, reference may be made to other parts of this specification (e.g., Figures 7 - 11 and its description).

[0065] By determining the phase, waveform, and center frequency of a single RF pulse, the processing device 140 may determine the single RF pulse. In some embodiments, the processing device 140 may determine the parameters of the single RF pulse based on information of the target object.

[0066] In some embodiments, the processing device 140 may determine an MRI pulse sequence based on the single RF pulse and a scan protocol. The scan protocol may include imaging parameters (e.g., one or more parameters related to gradient fields, time, etc.). In some embodiments, the scan protocol may be obtained from the storage device 150 or an external data source. In some embodiments, the scan protocol may be provided by a user or automatically generated, e.g., automatically generated based on the default settings of the MR scanner, a machine learning model.

[0067] In some embodiments, the first substance has a first frequency response curve relative to the single RF pulse, and the second substance has a second frequency response curve relative to the single RF pulse.

[0068] A frequency response profile can reflect the response conditions (such as excited state or inhibited state) of substances in a target object relative to a single radio frequency pulse at different frequencies. For example, a frequency response profile can be represented by a curve or a function that represents the signal intensity of the substance excited by a single radio frequency pulse at different frequencies (representing the response conditions). In some embodiments, the frequency response profile can be used to determine one or more passbands and one or more stopbands of a substance. The passband of a substance refers to the frequency range in which the substance is excited, and the stopband of a substance refers to the frequency range in which the substance is inhibited. For example, the passband of a substance can be the frequency range in which the signal intensity of the substance is excited to be greater than or equal to a first percentage of the maximum signal intensity of the substance. For example, the first percentage can be 90%, 92%, 95%, 98%, etc. In some embodiments, the first percentage is 95%. The stopband of a substance can be a frequency range in which the signal intensity of the substance is inhibited to be less than or equal to a second percentage of the maximum signal intensity of the substance. For example, the second percentage can be 10%, 8%, 5%, 2%, 1%, etc. In some embodiments, the second percentage is 5%. Taking water as an example, the passband of water is the frequency range in which the signal intensity of water is excited to be greater than or equal to 95% of the maximum signal intensity of water, and the stopband of water is the frequency range in which the signal intensity of water is inhibited to be less than or equal to 5% of the maximum signal intensity of water.

[0069] In some embodiments, the first frequency response profile of the first substance relative to a single radio frequency pulse can include one or more passbands in which the first substance is excited, and each of the one or more passbands can span a locally continuous frequency range. The locally continuous frequency range can also be referred to as a closed frequency range with a finite span. The second frequency response profile of the second substance relative to a single radio frequency pulse includes one or more stopbands in which the second substance is inhibited, and at least one of the one or more stopbands can be a semi-infinite frequency range. At least one of the one or more passbands and at least one of the stopbands can have an overlapping frequency range, and the center frequency of the single radio frequency pulse can be within the overlapping frequency range. In other words, the center frequency of the single radio frequency pulse is within the passband of the first substance and the stopband of the second substance. Therefore, the single radio frequency pulse can effectively excite the first substance while effectively inhibiting the second substance.

[0070] By way of example only, see Figure 4A , Figure 4A is an exemplary schematic diagram of the frequency response profiles of the first substance and the second substance relative to a single radio frequency pulse shown in some embodiments of this specification. As Figure 4AAs shown, the horizontal axis represents the frequency offset (ΔF) relative to the center frequency of water, and the vertical axis represents the normalized signal intensity (S Norm ), the solid curve is the frequency response curve for water, and the dashed curve is the frequency response curve for fat. The horizontal axis is in Hertz. The normalized signal intensity of a substance refers to the ratio of the signal intensity of that substance to the maximum signal intensity of that substance. If water is the first substance and fat is the second substance, the first frequency response curve 410 of water relative to a single RF pulse includes passbands 402 and 404 where water is excited, and each passband 402 and 404 spans a locally continuous frequency range. In some embodiments, two stopbands 406 and 407 with semi-infinite frequency ranges are located on either side of the passbands 402 and 404, and a narrow stopband 408 is located between the passbands 402 and 404. The center frequency of the narrow stopband 408 is the same as or substantially the same as the resonant frequency of water (e.g., 0 Hz). The second frequency response curve 420 of fat relative to a single RF pulse includes stopbands 412 and 414 where fat is suppressed, each of which has a semi-infinite frequency range. Passband 402 is within stopband 412 and has an overlapping frequency range 450 with stopband 412. The center frequency of a single RF pulse is within overlapping frequency range 450. For example, the center frequency of a single RF pulse can be set to 250 Hz to maximize water excitation and minimize fat suppression. In this case, the signal intensity corresponding to water is maximized, while the signal intensity corresponding to fat is minimized.

[0071] Similarly, if fat is the first substance and water is the second substance, then the passband 416 for fat is within the stopband 406 for water and has an overlapping frequency range 460 with the stopband 406. The center frequency of a single RF pulse is within the overlapping frequency range 460. For example, the center frequency of a single RF pulse can be set to -700 Hz to maximize fat excitation while minimizing water suppression. In this case, the signal intensity corresponding to fat is maximized, while the signal intensity corresponding to water is minimized.

[0072] Therefore, by applying an MRI pulse sequence including a single radio frequency pulse, the first substance in the target object can be effectively excited and the second substance in the target object can be effectively suppressed, thereby reducing the interference of the second substance on MRI data acquisition, thereby improving the signal-to-noise ratio (SNR) of the MRI data and the accuracy of the MRI data.

[0073] See also Figure 4B , Figure 4B FIG. 1 is an exemplary schematic diagram of a frequency response curve of a first substance and a second substance relative to a BORR pulse according to some embodiments of the present specification. Figure 4BAs shown, a part of the passband 471 in the frequency response curve of water overlaps with the stopband 474 in the frequency response curve of fat to have an overlapping frequency range 475. That is to say, the passband 471 is not located within the stopband 474. Therefore, the length of the overlapping frequency range 475 is less than that of the passband 471. Similarly, a part of the passband 473 in the frequency response curve of fat overlaps with the stopband 472 in the frequency response curve of water to have an overlapping frequency range 476. That is to say, the passband 473 is not located within the stopband 472. Therefore, the length of the overlapping frequency range 476 is less than that of the passband 473.

[0074] See Figure 4C , Figure 4C is an exemplary schematic diagram of the frequency response curves of the first substance and the second substance relative to the LIBRE pulse as shown in some embodiments of this specification. As Figure 4C shown, a part of the passband 481 in the frequency response curve of water overlaps with the stopband 484 in the frequency response curve of fat to have an overlapping frequency range 485. That is to say, the passband 481 is not located within the stopband 484. Therefore, the length of the overlapping frequency range 485 is less than that of the passband 481. Similarly, a part of the passband 483 in the frequency response curve of fat overlaps with the stopband 482 in the frequency response curve of water to have an overlapping frequency range 486. That is to say, the passband 483 is not located within the stopband 482. Therefore, the length of the overlapping frequency range 486 is less than that of the passband 483.

[0075] By comparison Figures 4A - 4C , since at least one stopband of the second substance relative to the single radio frequency pulse is a semi-infinite frequency range, the passband of the first substance usually has a larger overlapping frequency range with at least one stopband (for example, the entire passband of the first substance can be within one stopband of the second substance). Therefore, the center frequency of the single radio frequency pulse can be selected within a large overlapping frequency range, which can increase the selection range of the center frequency of the single radio frequency pulse, thereby improving the applicability of the single radio frequency pulse.

[0076] In addition, the specially designed single radio frequency pulse is particularly beneficial for applications under high field and ultra-high field. The single radio frequency pulse is not only insensitive to the B0 and B1 inhomogeneities that are usually prominent in high fields, but also has a relatively low specific absorption rate (SAR) of radio frequency energy due to the off-resonance characteristics of the specially designed single radio frequency pulse. For example, since the frequency range of one or more stopbands is semi-infinite (i.e., the frequency range of one or more stopbands is relatively wide), even if the B0 field is inhomogeneous, the frequency corresponding to the B0 field can be within one or more stopbands, so that the second substance in the target object can be effectively suppressed. That is, the specially designed single radio frequency pulse is insensitive to B0 inhomogeneity. Even if the B1 field is inhomogeneous, the frequency response curves of the substances are basically the same. That is, the specially designed single radio frequency pulse is insensitive to B1 inhomogeneity.

[0077] In some embodiments, the processing device 140 may obtain MRI data from an MRI device (such as the MRI device 110) or a storage device (such as the storage device 150, a database, or an external storage device) that stores the MRI data of the target object.

[0078] In 304, the processing device 140 (e.g., the reconstruction module 220) may reconstruct an MR image of the target object based on the MRI data.

[0079] The MR image can be used for diagnosis and / or treatment.

[0080] In some embodiments, the processing device 140 may generate an MR image of the target object by reconstructing the MRI data using an image reconstruction algorithm. For example, the processing device 140 may obtain k-space data by filling the k-space based on the MRI data using a transformation operation (such as a Fourier transform), and generate an MR image by reconstructing the k-space data using an image reconstruction algorithm. Exemplary image reconstruction algorithms may include a Fourier reconstruction algorithm, a parallel reconstruction algorithm (e.g., a sensitivity encoding algorithm, a Generalized Auto-calibrating Partially Parallel Acquisition (GRAPPA) algorithm, an iterative self-consistent parallel imaging reconstruction algorithm, a simultaneous multi-slice imaging algorithm, a three-dimensional parallel reconstruction algorithm, etc.), a Compressed Sensing (CS) reconstruction algorithm, a deep learning-based reconstruction algorithm, etc., or any combination thereof.

[0081] In some embodiments, the processing device 140 may further post-process the MR image. Exemplary post-processing operations may include image deformation, image enhancement, image denoising, image smoothing, etc., or any combination thereof.

[0082] In some embodiments, the processing device 140 may display the MR image of the target object. For example, after reconstructing the MR image, the processing device 140 may display the MR image through a display screen (e.g., the display screen of the terminal 130), and a user may perform diagnosis and / or treatment based on the MR image. Exemplary display screens may include a liquid crystal display screen, an electronic ink display screen, etc.

[0083] According to some embodiments of the present specification, the MRI data of the target object may be acquired by applying an MRI pulse sequence to the target object. A single radiofrequency pulse in the MRI pulse sequence may be used to excite a first substance in the target object and suppress a second substance in the target object. Therefore, the interference of the second substance on the MRI data acquisition may be reduced, which may improve the signal-to-noise ratio of the MRI data, thereby improving the accuracy of the MRI data and / or the MRI image.

[0084] Figure 5 is an exemplary flowchart of process 500 for determining a single radio frequency pulse waveform as shown in some embodiments of this specification. In some embodiments, process 500 may be executed to implement at least a portion of operation 302 related to Figure 3 the relevant description.

[0085] At 502, processing device 140 (e.g., waveform determination module 230) may generate a trapezoidal wave.

[0086] A trapezoidal wave refers to a waveform with a trapezoidal shape. For example, a trapezoidal wave may consist of multiple points, and each point in the trapezoidal wave may correspond to an amplitude and a phase. The trapezoidal wave may include a top side with a first length and a bottom side with a second length. The top side is parallel to the bottom side. The second length may be equal to the duration of the single radio frequency pulse. For example, the duration of the single radio frequency pulse may be in the range of 1 millisecond to 3 milliseconds.

[0087] In some embodiments, the first length may be greater than zero and less than the second length. For example, the first length may be greater than or equal to 0.1 times the second length and less than the second length. Also, for example, the first length may be greater than or equal to 0.11 times the second length and less than or equal to 0.8 times the second length. Further, for example, the first length may be greater than or equal to 0.12 times the second length and less than or equal to 0.6 times the second length. Further, for example, the first length may be greater than or equal to 0.13 times the second length and less than or equal to 0.4 times the second length. Further, for example, the first length may be greater than or equal to 0.14 times the second length and less than or equal to 0.2 times the second length. Further, for example, the first length may be equal to 0.15 times the second length.

[0088] As an example only, refer to Figure 6 , the horizontal axis may represent time, and the vertical axis may represent amplitude (or signal strength). The top side of trapezoidal wave 610 has a first length τ′, the bottom side of trapezoidal wave 610 has a second length τ, and the first length τ′ is equal to 0.15 times the second length τ.

[0089] In some embodiments, the shape of the trapezoidal wave may be a symmetric trapezoid. That is, the line connecting the center points of the top side and the bottom side is perpendicular to the top side (or the bottom side). Or, the shape of the trapezoidal wave may be an asymmetric trapezoid. That is, the line connecting the center points of the top side and the bottom side is not perpendicular to the top side (or the bottom side).

[0090] In some embodiments, processing device 140 may generate a triangular waveform instead of a trapezoidal wave. That is, the first length is equal to 0.

[0091] In 504, the processing device 140 (e.g., the waveform determination module 230) may generate an initial waveform by performing an exponential transformation on each point in the trapezoidal wave.

[0092] For example, an exponential transformation may be performed on each point in the trapezoidal wave based on formula (1): where I a refers to the amplitude (or signal strength) of a point in the trapezoidal wave; I b refers to the amplitude (or signal strength) of the corresponding point in the initial waveform; q refers to the exponent of the exponential transformation. As used herein, q is any value greater than 1, for example, 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 5.0, etc. In some embodiments, q is equal to 2.

[0093] In 506, the processing device 140 (e.g., the waveform determination module 230) may determine the waveform of a single radio frequency pulse by filtering the initial waveform.

[0094] In some embodiments, the processing device 140 may filter the initial waveform using a filtering algorithm. Exemplary filtering algorithms may include a Gaussian filtering algorithm, a median filtering algorithm, a bilateral filtering algorithm, a guided filtering algorithm, a weighted least squares filtering algorithm, a non-local means filtering algorithm, etc., or any combination thereof. For example, the processing device 140 may filter the initial waveform using a Gaussian filtering algorithm.

[0095] By way of example only, refer to Figure 6 Figure 6 is an exemplary schematic diagram of a process for determining the waveform of a single radio frequency pulse as shown in some embodiments of the present specification. As Figure 6 shown, an exponential transformation may be performed on each point in the trapezoidal wave 610 based on formula (1) to generate an initial waveform 620. q is equal to 2. Then, the waveform 630 of a single radio frequency pulse may be determined by filtering the initial waveform 620.

[0096] Figure 7 is an exemplary flowchart of a process 700 for determining the center frequency of a single radio frequency pulse as shown in some embodiments of the present specification. In some embodiments, process 700 may be executed to implement at least a portion of operation 302 described in connection with Figure 3

[0097] In 702, the processing device 140 (e.g., the acquisition module 210) may determine the duration and radio frequency field strength of a single radio frequency pulse.

[0098] As described above, the duration of the single RF pulse is equal to the second length of the trapezoidal wave. As described in operation 502, the duration of the single RF pulse can be determined when generating the trapezoidal wave. In some embodiments, the duration of the single RF pulse can be determined based on system default settings or manually set by the user. For example, the second length can be determined as any value within the range of 1 millisecond to 3 milliseconds.

[0099] The RF field strength of the single RF pulse can be less than or equal to the maximum RF field strength of the MRI device (such as MRI device 110) that applies the MRI pulse sequence including the single RF pulse. The maximum RF field strength can be related to information of the MRI device (such as power, year of use, etc.). For example, the maximum RF field strength can be 1.5T, 3T, 7T, 10T, etc.

[0100] In some embodiments, the RF field strength of the single RF pulse can be determined based on system default settings or manually set by the user. For example, the RF field strength can be determined as any value within the range from 0 to the maximum RF field strength (such as 1.5T, 3T, 7T, 10T, etc.). For more descriptions about the duration and RF field strength of the single RF pulse, reference can be made to other parts of this specification (for example, Figure 8 and its description).

[0101] In 704, the processing device 140 (for example, the acquisition module 210) can determine the estimated first frequency response curve of the first substance relative to the single RF pulse and the estimated second frequency response curve of the second substance relative to the single RF pulse based on the duration and the RF field strength.

[0102] The estimated frequency response curve refers to the frequency response curve estimated based on the duration and the RF field strength.

[0103] In some embodiments, the processing device 140 can determine the peak width information based on the duration and determine the peak frequency information based on the RF field strength. Further, the processing device 140 can determine the estimated first frequency response curve and the estimated second frequency response curve based on the peak width information and the peak frequency information. For more descriptions about determining the estimated first frequency response curve and the estimated second frequency response curve, reference can be made to other parts of this specification (for example, Figures 8 - 11 and its description).

[0104] In 706, the processing device 140 (for example, the acquisition module 210) can determine the center frequency of the single RF pulse based on the estimated first frequency response curve and the estimated second frequency response curve.

[0105] The center frequency of a single radio frequency pulse can be expressed by a frequency offset relative to the center frequency of the MRI device or the absolute center frequency of the single radio frequency pulse.

[0106] In some embodiments, the processing device 140 can determine one or more estimated passbands based on the estimated first frequency response curve, in which the first substance is excited, and determine one or more estimated stopbands based on the estimated second frequency response curve, in which the second substance is suppressed. The processing device 140 can determine an estimated overlapping frequency range between the one or more estimated passbands and the one or more estimated stopbands, and determine the center frequency within the estimated overlapping frequency range. More descriptions about the determination of the center frequency of the single radio frequency pulse can be found in other parts of this specification (e.g., Figures 8 - 11 and its description).

[0107] According to some embodiments of this specification, the estimated first frequency response curve of the first substance relative to the single radio frequency pulse and the estimated second frequency response curve of the second substance relative to the single radio frequency pulse can be determined based on the duration and the radio frequency field strength, and the center frequency of the single radio frequency pulse can be determined based on the estimated first frequency response curve and the estimated second frequency response curve. In this way, the accuracy of determining the estimated first frequency response curve and the estimated second frequency response curve can be improved, which can improve the accuracy of determining the center frequency of the single radio frequency pulse, thereby improving the quality of the MRI image.

[0108] Figure 8 is an exemplary flowchart of a process 800 for determining the estimated first frequency response curve and the estimated second frequency response curve shown in some embodiments of this specification. In some embodiments, the process 800 can be executed to implement at least a part of the operation 704 related to Figure 7 the relevant description.

[0109] In 802, the processing device 140 (e.g., the acquisition module 210) can determine the peak width information based on the duration of the single radio frequency pulse.

[0110] The peak width information can include the peak width of each peak in the estimated frequency response curve (i.e., the estimated first frequency response curve and the estimated second frequency response curve). A peak refers to the peak of the passband of the frequency response curve (i.e., the peak of the passband). In some embodiments, the peak width information can be expressed by the full width at half maximum of each peak in the estimated frequency response curve.

[0111] In some embodiments, the duration of a single radio frequency pulse may be related to the peak width information of the predicted frequency response curve. For example, if the duration of a single radio frequency pulse is relatively large, the full width at half maximum (FWHM) of each peak in the predicted frequency response curve may be relatively small. Correspondingly, the span of one or more passbands and one or more stopbands in the predicted frequency response curve may be relatively small. It should be noted that the duration of the single radio frequency pulse is related to the peak width information, but the center frequency of each peak in the predicted frequency response curve is not affected by the duration of the single radio frequency pulse. For example, when the duration of the single radio frequency pulse changes, the distance between the center frequency of each peak corresponding to one or more peaks of the first substance and the center frequency of each peak corresponding to one or more peaks of the second substance remains unchanged.

[0112] In some embodiments, the duration may be inversely proportional to the peak width information (such as the full width at half maximum) of each peak in one or more peaks. The inverse proportionality coefficient may be a fixed value of the single radio frequency pulse. Therefore, the processing device 140 may determine the peak width information based on the duration of the single radio frequency pulse and the inverse proportionality coefficient.

[0113] In 804, the processing device 140 (e.g., the acquisition module 210) may determine the peak frequency information based on the radio frequency field strength.

[0114] The peak frequency information refers to the information related to the center frequency of each peak in the predicted frequency response curve. In some embodiments, the peak frequency information may include the number of center frequencies (or passband peaks), the center frequency value of each peak, the amplitude (or signal strength) of each peak, etc., or any combination thereof.

[0115] The radio frequency field refers to the electromagnetic field generated by applying a single radio frequency pulse. As Figure 6 shown, since the amplitude (or signal strength) of the single radio frequency pulse changes during application, the intensity of the radio frequency field also changes. Therefore, the radio frequency field intensity refers to the maximum intensity of the radio frequency field. In some embodiments, the radio frequency field strength may be related to the voltage of the radio frequency amplifier (for applying the radio frequency pulse) of an MRI device (such as the MRI device 110). The higher the voltage, the greater the radio frequency field intensity may be.

[0116] In some embodiments, the radio frequency field strength of a single radio frequency pulse may be related to the shape of the predicted frequency response curve. For example, the radio frequency field strength of a single radio frequency pulse may affect the center frequency and amplitude (or signal strength) of each peak in the predicted frequency response curve.

[0117] In some embodiments, the processing device 140 may determine a threshold intensity related to the radio frequency field strength and determine the peak frequency information based on the radio frequency field strength and the threshold intensity. The threshold intensity may correspond to a preset equivalent flip angle.

[0118] The flip angle (or excitation angle) refers to the deviation angle of the macroscopic magnetization vector of a substance (such as a first substance, a second substance) from the equilibrium state (i.e., the B0 direction of the MRI device). The preset equivalent flip angle is the excitation effect that causes the macroscopic magnetization vector of the substance to deviate from the equilibrium state by a preset flip angle. For example, if the preset equivalent flip angle is 90 degrees, the excitation effect can be that the macroscopic magnetization vector of the substance deviates from the equilibrium state by 90 degrees. Since the excitation effect is the cumulative effect of the substance under a certain RF field strength for a certain duration, when the duration and the preset equivalent flip angle are determined, the threshold intensity related to the RF field strength can be determined.

[0119] In some embodiments, an RF pulse with a threshold intensity corresponding to the preset equivalent flip angle can be used to achieve an excitation effect corresponding to the equivalent flip angle. For example, when the preset equivalent flip angle is 90 degrees, an RF pulse with a threshold intensity corresponding to 90 degrees can achieve a 90-degree excitation effect.

[0120] In some embodiments, the processing device 140 can determine the peak frequency information by comparing the RF field strength and the threshold intensity. For example, if the RF field strength is less than the threshold intensity, the peak frequency information of the substance can include: the estimated frequency response curve of the substance includes a passband and a passband peak; two stopbands are located on both sides of the passband; the center frequency of the passband peak is the same as or substantially the same as the resonance frequency of the substance; when the RF field strength is less than the threshold intensity, the excitation degree of a single RF pulse on the substance is positively correlated with the RF field strength; when the RF field strength is less than the threshold intensity, the equivalent flip angle of a single RF pulse is positively correlated with the RF field strength; or any combination thereof.

[0121] Again, for example, if the RF field strength is much greater than the threshold intensity (e.g., greater than or equal to twice the threshold intensity), the peak frequency information of the substance can include: the estimated frequency response curve of the substance includes two passbands and two passband peaks; two stopbands with a semi-infinite frequency range are located on both sides of the two passbands; the center frequency of each passband peak is different from the resonance frequency of the substance; a third stopband (e.g., a narrow stopband) is located between the two passbands; the center frequency of the third stopband is the same as or substantially the same as the resonant frequency of the substance; when the RF field strength is equal to the maximum signal intensity, the equivalent flip angle of a single RF pulse remains 90 degrees; or any combination thereof.

[0122] Still, for example, if the RF field strength is greater than the threshold intensity and less than twice the threshold intensity, the peak frequency information of the substance can include: the estimated frequency response curve of the substance includes two passbands and two passband peaks; two stopbands are located on both sides of the two passbands; the center frequency of each passband peak is different from the resonance frequency of the substance; a half-stopband is located between the two passbands; the center frequency of the half-stopband is the same as or substantially the same as the resonant frequency of the substance; when the RF field strength is equal to the maximum signal intensity, the equivalent flip angle of a single RF pulse remains 90 degrees; or any combination thereof.

[0123] In 806, the processing device 140 (e.g., the acquisition module 210) may determine a predicted first frequency response curve and a predicted second frequency response curve based on the peak width information and the peak frequency information.

[0124] For example, the predicted first frequency response curve and the predicted second frequency response curve may be determined by combining the peak width information, the peak frequency information, and the resonance frequency of the first substance and the second substance. Taking water as an example, the number of center frequencies (or passband peaks) and the center frequency values of each peak may be determined based on the peak frequency information, and the full width at half maximum of each peak may be determined based on the peak width information, so as to determine the predicted frequency response curve of water.

[0125] In some embodiments, after determining the predicted first frequency response curve and the predicted second frequency response curve, the processing device 140 may determine the center frequency of a single radio frequency pulse based on the predicted first frequency response curve and the predicted second frequency response curve.

[0126] For ease of explanation, three examples of determining the predicted first frequency response curve, the predicted second frequency response curve, and the center frequency of a single radio frequency pulse are provided below.

[0127] Example 1:

[0128] Referring to Figure 9 , when the radio frequency field intensity is less than the threshold intensity, the predicted first frequency response curve 910 of water (exemplary first substance) and the predicted second frequency response curve 920 of fat (exemplary second substance) may be determined based on the peak width information and the peak frequency information.

[0129] As Figure 9 shown, the predicted first frequency response curve 910 of water includes a predicted passband 902 and two predicted stopbands 904 and 906 located on both sides of the predicted passband 902. The predicted second frequency response curve 920 of fat includes a predicted passband 912 and two predicted stopbands 914 and 916 located on both sides of the predicted passband 912. The predicted overlapping frequency range 950 between the predicted passband 902 and the predicted stopband 914 is determined, and the center frequency of the single radio frequency pulse relative to water may be within the predicted overlapping frequency range 950. For example, the center frequency of the single radio frequency pulse relative to water may be located at the center frequency of the predicted overlapping frequency range 950 (or the predicted passband 902 of water).

[0130] Similarly, if the first substance to be excited is fat and the second substance to be suppressed is water, the center frequency of the single radio frequency pulse relative to fat may be within the predicted overlapping frequency range 960. For example, the center frequency of the single radio frequency pulse relative to fat may be located at the center frequency of the predicted overlapping frequency range 960 (or the predicted passband 912 of fat).

[0131] Example 2:

[0132] See Figure 10 When the RF field strength is greater than the threshold strength and less than twice the threshold strength, the estimated first frequency response curve 1010 of water (exemplary first substance) and the estimated second frequency response curve 1020 of fat (exemplary second substance) can be determined based on the peak width information and the peak frequency information.

[0133] As Figure 10 shown, the estimated first frequency response curve 1010 of water includes two estimated passbands 1002 and 1004, and two estimated stopbands 1006 and 1008 located on both sides of the estimated passbands 1002 and 1004. The estimated second frequency response curve 1020 of fat includes two estimated passbands 1012 and 1014, and two estimated stopbands 1016 and 1018 located on both sides of the estimated passbands 1012 and 1014. The estimated overlapping frequency range 1050 between the estimated passband 1002 and the estimated stopband 1016 is determined, and the single RF pulse can be within the estimated overlapping frequency range 1050 relative to the center frequency of water. For example, the single RF pulse can be located at the center frequency of the estimated overlapping frequency range 1050 (or the estimated passband 1002 of water) relative to the center frequency of water.

[0134] Similarly, if the first substance to be excited is fat and the second substance to be suppressed is water, the single RF pulse can be within the estimated overlapping frequency range 1060 relative to the center frequency of fat. For example, the single RF pulse can be located at the center frequency of the estimated overlapping frequency range 1060 (or the estimated passband 1012 of fat) relative to the center frequency of fat.

[0135] Example 3:

[0136] See Figure 11 When the RF field strength is greater than or equal to twice the threshold strength, the estimated first frequency response curve 1110 of water (exemplary first substance) and the estimated second frequency response curve 1120 of fat (exemplary second substance) can be determined based on the peak width information and the peak frequency information.

[0137] As Figure 11As shown, the estimated first frequency response curve 1110 of water includes two estimated passbands 1102 and 1104, and two estimated stopbands 1106 and 1108 located on both sides of the estimated passbands 1102 and 1104. A narrow estimated stopband 1109 is located between the estimated passbands 1102 and 1104, and the center frequency of the narrow estimated stopband 1109 is the resonance frequency of water (e.g., 0 Hz). The estimated second frequency response curve 1120 of fat includes two estimated passbands 1112 and 1114, and two estimated stopbands 1116 and 1118 located on both sides of the estimated passbands 1112 and 1114. A narrow estimated stopband 1119 is located between the estimated passbands 1112 and 1114, and the center frequency of the narrow estimated stopband 1119 is the resonance frequency of fat (e.g., -440 Hz). An estimated overlap frequency range 1150 is determined between the estimated passband 1102 and the estimated stopband 1116, and the single RF pulse can be within the estimated overlap frequency range 1150 relative to the center frequency of water. For example, the single RF pulse can be located at the center frequency of the estimated overlap frequency range 1150 (or the estimated passband 1102 of water) relative to the center frequency of water.

[0138] Similarly, if the first substance to be excited is fat and the second substance to be suppressed is water, the single RF pulse can be within the estimated overlap frequency range 1160 relative to the center frequency of fat. For example, the single RF pulse can be located at the center frequency of the estimated overlap frequency range 1160 (or the estimated passband 1112 of fat) relative to the center frequency of fat.

[0139] It should be noted that the descriptions of processes 300, 500, 700, and 800 are provided for illustrative purposes and are not intended to limit the scope of this specification. Various changes and modifications can be made by those of ordinary skill in the art according to the teachings of this specification. For example, processes 300, 500, 700, and 800 can be completed with one or more additional operations not described and / or without one or more of the operations discussed. In addition, the order of operations of processes 300, 500, 700, and 800 is not intended to be limiting. However, these changes and modifications may not depart from the scope of protection of this specification.

[0140] Figure 12 is an exemplary schematic diagram of a computing device 1200 shown according to some embodiments of this specification.

[0141] In some embodiments, one or more components of the MRI system 100 can be implemented on the computing device 1200. For example, a processing engine can be implemented on the computing device 1200 and configured to implement the functions and / or methods disclosed in this specification.

[0142] The computing device 1200 may include any components for implementing the MRI system 100 described in this specification. For example, the processing device 140 may be implemented by hardware, software programs, firmware, or any combination thereof on the computing device 1200. For illustrative purposes, Figure 12 only one computer is described herein, but the computing functions related to the MRI system 100 described in this specification may be implemented in a distributed manner by a set of similar platforms to disperse the processing load of the MRI system 100.

[0143] The computing device 1200 may include a communication port connected to a network to enable data communication. The computing device 1200 may include a processor (e.g., a central processing unit (CPU)), a memory, a communication interface, a display unit, and an input device connected via a system bus. The processor of the computing device 1200 may be used to provide computing and control capabilities. The memory of the computing device 1200 may include a non-volatile storage medium and an internal memory. The non-volatile storage medium may store an operating system and computer programs. The internal memory may provide an environment for the execution of the operating system and computer programs in the non-volatile storage medium. The communication interface of the computing device 1200 may be used for wired or wireless communication with an external terminal. Wireless communication may be implemented via Wi-Fi, a mobile cellular network, near-field communication (NFC), etc. When the processor executes the computer program, a method for reconstructing an MRI image may be implemented. The display unit of the computing device 1200 may include a liquid crystal display screen or an electronic ink display screen. The input device of the computing device 1200 may include a touch layer covering the display unit, devices provided on the housing of the computing device 1200 (such as buttons, trackballs, touchpads, etc.), an external keyboard, an external touchpad, an external mouse, etc.

[0144] For ease of explanation, Figure 12 only one processor is described herein. However, it should be noted that the computing device 1200 in this specification may also include multiple processors. Therefore, the operations and / or method steps described herein as being performed by one processor may also be performed jointly or separately by multiple processors. For example, if the processor of the computing device 1200 in this specification performs operation A and operation B simultaneously, then it should be understood that operation A and operation B may also be performed jointly or separately by two or more different processors (e.g., the first processor performs operation A, the second processor performs operation B, or the first and second processors jointly perform operation A and operation B).

[0145] The basic concepts have been described above. Obviously, for those of ordinary skill in the art after reading this application, the above invention disclosure is only for illustration and does not constitute a limitation to this application. Various changes, improvements, and modifications may occur, and these are prepared for those skilled in the art, although not explicitly stated herein. Such modifications, improvements, and corrections are proposed in this application, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0146] At the same time, this application uses specific terms to describe the embodiments of this application. For example, the terms "one embodiment" and / or "some embodiments" refer to specific features, structures, or characteristics related to the embodiments being included in at least one embodiment of this specification. Therefore, it needs to be emphasized and should be understood that in various parts of this specification, two or more references to "one embodiment" or "another embodiment" do not necessarily all refer to the same embodiment. In addition, specific features, structures, or characteristics may be appropriately combined in one or more embodiments of this specification.

[0147] In addition, unless explicitly stated in the claims, the order of the processing elements and sequences, the use of numerical letters, or the use of other names in this application are not used to limit the order of the processes and methods of this application. Although some currently considered useful embodiments of the invention are discussed through various examples in the above disclosure, it should be understood that such details only serve the purpose of illustration, and the appended claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that conform to the essence and scope of the embodiments of this application. For example, although the implementation of the above various components can be embodied in a hardware device, it can also be implemented as a pure software solution, for example, installation on an existing server or mobile device.

[0148] Similarly, it should be noted that in order to simplify the expression of the disclosure of this application and thus help the understanding of one or more embodiments of the invention, in the previous description of the embodiments of this application, sometimes multiple features are grouped into one embodiment, drawing, or description thereof. However, this method of this application should not be construed as reflecting the intention that the claimed object substance to be scanned requires more features than those explicitly recited in each claim. On the contrary, the subject matter of the invention should have fewer features than the above single embodiment.

[0149] In certain embodiments, numbers representing quantities or properties used to describe and claim certain embodiments of the present application should be understood to be modified, in some cases, by the terms "about", "approximate" or "substantially". For example, unless otherwise stated, "about", "approximate" or "substantially" may represent a variation of ±20% of the value they describe. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximations, which may vary depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should be considered in terms of the specified significant digits and a general method of digit retention should be adopted. Although the numerical ranges and parameters used to confirm the breadth of the scope in some embodiments of the present application are approximations, in specific embodiments, such numerical settings are as precise as possible within the feasible range.

[0150] Each patent, patent application, published patent application, and other materials cited herein, such as articles, books, specifications, publications, documents, things, and / or similar materials, are hereby incorporated by reference in their entirety for all purposes, except for any application file history associated therewith, any content inconsistent or conflicting with this document, or any content that may limit the broadest scope of the present or future relevant claims of this document. For example, if there are any inconsistencies or conflicts between the use of terms in the description, definition, and / or association with any incorporated material and the terms associated with this document, the terms described, defined, and / or used in this document shall prevail.

[0151] Finally, it should be understood that the embodiments described in the present application are only used to illustrate the principles of the embodiments of the present application. Other variations may also fall within the scope of the present application. Therefore, by way of example and not limitation, alternative configurations of the embodiments of the present application may be considered consistent with the teachings of the present application. Accordingly, the embodiments of the present application are not limited to the embodiments explicitly presented and described in the present application.

Claims

1. A magnetic resonance imaging method implemented on a computing device having at least one processor and at least one storage device, the method comprising: Obtaining magnetic resonance imaging data of a target object, the magnetic resonance imaging data being acquired by applying a magnetic resonance imaging pulse sequence to the target object, the magnetic resonance imaging pulse sequence including a single radiofrequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object; And Reconstructing a magnetic resonance image of the target object based on the magnetic resonance imaging data, wherein the waveform of the single RF pulse is determined by: Generating a trapezoidal wave; Generating an initial waveform by performing an exponential transformation on each point in the trapezoidal wave; and Determining the waveform of the single radiofrequency pulse by filtering the initial waveform.

2. The method according to claim 1, wherein The phase of the single radiofrequency pulse is a constant value during application.

3. The method according to claim 1, characterized in that, The trapezoidal wave includes a top side having a first length and a bottom side having a second length, the first length being greater than zero and less than the second length.

4. The method according to claim 1, characterized in that The center frequency of the single radiofrequency pulse is determined by: Determining the duration and radiofrequency field strength of the single radiofrequency pulse; Based on the duration and the radiofrequency field strength, determining a predicted first frequency response curve of the first substance with respect to the single radiofrequency pulse and a predicted second frequency response curve of the second substance with respect to the single radiofrequency pulse; And Determining the center frequency of the single radiofrequency pulse based on the predicted first frequency response curve and the predicted second frequency response curve.

5. The method according to claim 4, characterized in that, The predicted first frequency response curve and the predicted second frequency response curve are determined by: Determining peak width information based on the duration; Determining peak frequency information based on the radiofrequency field strength; and Based on the peak width information and the peak frequency information, determining the predicted first frequency response curve and the predicted second frequency response curve.

6. The method according to claim 5, characterized in that, The determining the peak frequency information based on the radiofrequency field strength includes: Determining a threshold intensity related to the radiofrequency field strength, the threshold intensity corresponding to a preset equivalent flip angle; and Determining the peak frequency information based on the radiofrequency field strength and the threshold intensity.

7. The method according to claim 4, characterized in that The determining the center frequency of the single radiofrequency pulse based on the predicted first frequency response curve and the predicted second frequency response curve includes: Based on the predicted first frequency response curve, determining one or more predicted passbands in which the first substance is excited; Based on the predicted second frequency response curve, determining one or more predicted stopbands in which the second substance is suppressed; Determining a predicted overlapping frequency range between the one or more predicted passbands and the one or more predicted stopbands; and Determining the center frequency within the predicted overlapping frequency range.

8. The method according to claim 1, wherein The first frequency response curve of the first substance with respect to the single radiofrequency pulse includes one or more passbands in which the first substance is excited, each of the one or more passbands spanning a locally continuous frequency range, The second frequency response curve of the second substance with respect to the single radio frequency pulse includes one or more stop bands, in which the second substance is suppressed, and at least one of the one or more stop bands is a semi-infinite frequency range. At least one of the one or more pass bands has an overlapping frequency range with the at least one stop band, and The center frequency of the single radio frequency pulse is within the overlapping frequency range.

9. A magnetic resonance imaging method implemented on a computing device having at least one processor and at least one storage device, characterized in that, The method includes: Obtaining magnetic resonance imaging data of a target object, the magnetic resonance imaging data being acquired by applying a magnetic resonance imaging pulse sequence to the target object, the magnetic resonance imaging pulse sequence including a single radio frequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object; and Reconstructing a magnetic resonance image of the target object based on the magnetic resonance imaging data, where The first frequency response curve of the first substance with respect to the single radio frequency pulse includes one or more pass bands, in which the first substance is excited, and each of the one or more pass bands spans a locally continuous frequency range. The second frequency response curve of the second substance with respect to the single radio frequency pulse includes one or more stop bands, in which the second substance is suppressed, and at least one of the one or more stop bands is a semi-infinite frequency range. At least one of the one or more pass bands has an overlapping frequency range with the at least one stop band, and The center frequency of the single radio frequency pulse is within the overlapping frequency range.

10. A magnetic resonance imaging system, characterized in that, The system includes At least one storage device including a set of instructions; And At least one processor configured to communicate with the at least one storage device, where when the set of instructions is executed, the at least one processor is configured to direct the system to perform operations, the operations including: Obtaining magnetic resonance imaging data of a target object, the magnetic resonance imaging data being acquired by applying a magnetic resonance imaging pulse sequence to the target object, the magnetic resonance imaging pulse sequence including a single radio frequency pulse for exciting a first substance in the target object and suppressing a second substance in the target object; and Reconstructing a magnetic resonance image of the target object based on the magnetic resonance imaging data, where the waveform of the single radio frequency pulse is determined by: Generating a trapezoidal wave; Generating an initial waveform by performing an exponential transformation on each point in the trapezoidal wave; and Determining the waveform of the single radio frequency pulse by filtering the initial waveform.

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