Magnetic resonance signal acquisition method and system based on chemical exchange saturation transfer

Abstract

The embodiment of the invention discloses a magnetic resonance signal acquisition method and system based on chemical exchange saturation transfer. The method comprises the following steps: applying a pre-configured pulse sequence to a scanned object to acquire a magnetic resonance signal; wherein the pulse sequence comprises a saturation module, the saturation module is used for enabling chemical exchange in the scanning object to reach a steady state, the saturation module comprises a plurality of saturation pulses, and a time gap exists between each pair of adjacent saturation pulses in the plurality of saturation pulses; and each acquisition module is used for acquiring magnetic resonance signals corresponding to one or more k-space trajectories, and the application time of at least one acquisition module is in a time gap between a pair of adjacent saturation pulses. Therefore, the scanning time can be effectively shortened.

Description

Technical Field

[0001] The present specification relates to the field of medical imaging, and in particular to a magnetic resonance signal acquisition method and system based on chemical exchange saturation transfer. Background Art

[0002] Chemical Exchange Saturation Transfer (CEST) imaging is a new type of Magnetic Resonance Imaging (MRI) technology. Its imaging principle is: many biological macromolecules such as proteins, glycosaminoglycans, glycogen, etc. contain hydrogen protons. During magnetic resonance scanning, they can be saturated with hydrogen protons by applying a pre-saturation pulse. The saturated hydrogen protons chemically exchange with the hydrogen protons in the surrounding water. By measuring the changes in water molecule signals, the content of these molecules in the human body can be indirectly measured.

[0003] Traditional CEST imaging requires that the chemical exchange in the scanned object (such as a patient) reaches a steady state before starting to collect magnetic resonance signals, which makes the scanning time very long and cannot meet clinical needs. In view of this, it is hoped to reduce the scanning time of CEST imaging. Summary of the invention

[0004] The purpose of this specification is to provide a magnetic resonance signal acquisition method that can reduce the scanning time of CEST imaging.

[0005] The first aspect of the embodiments of the present specification provides a method for collecting magnetic resonance signals based on chemical exchange saturation transfer. The method includes: applying a preconfigured pulse sequence to a scanned object to collect magnetic resonance signals. The pulse sequence includes: a saturation module, the saturation module is used to make the chemical exchange in the scanned object reach a steady state, the saturation module includes a plurality of saturation pulses, and there is a time gap between each pair of adjacent saturation pulses in the plurality of saturation pulses; one or more acquisition modules, each of the acquisition modules is used to collect magnetic resonance signals corresponding to one or more k-space trajectories, and the application time of at least one of the acquisition modules is in the time gap between a pair of adjacent saturation pulses.

[0006] In some embodiments, the applying a preconfigured pulse sequence comprises applying a saturation pulse, a spoiler gradient and an acquisition module successively within each repetition time.

[0007] In some embodiments, applying the preconfigured pulse sequence further includes applying a fat suppression module before each of the acquisition modules, wherein the fat suppression module is used to suppress fat signals.

[0008] In some embodiments, at least one of the acquisition modules adopts a Cartesian acquisition mode or a spiral acquisition mode. The acquisition modules are applied such that the acquisition modules corresponding to the k-space trajectory in the edge region of the k-space are applied earlier than the acquisition modules corresponding to the k-space trajectory in the center region of the k-space.

[0009] In some embodiments, the applying a preconfigured pulse sequence: applying 1 acquisition module for every application of up to 5 saturation pulses.

[0010] In some embodiments, the applying a preconfigured pulse sequence: each time a saturation pulse is applied, one acquisition module is applied.

[0011] In some embodiments, the acquisition module includes a gradient echo sequence or an echo planar imaging sequence.

[0012] In some embodiments, the method further comprises: correcting the acquired magnetic resonance signal.

[0013] A second aspect of the embodiments of this specification provides a magnetic resonance device, comprising a processor and a storage device. The storage device stores instructions for magnetic resonance signal acquisition, and when the processor executes the instructions, the magnetic resonance signal acquisition method as described in any embodiment of this specification is implemented.

[0014] The third aspect of the embodiments of the present specification provides a magnetic resonance signal acquisition system based on chemical exchange saturation transfer, including a sequence acquisition unit and a signal acquisition unit. The sequence acquisition unit is used to acquire a pre-configured pulse sequence, and the signal acquisition unit is used to apply the pulse sequence to the scanned object to acquire magnetic resonance signals. Wherein, the pulse sequence includes: a saturation module, the saturation module is used to make the chemical exchange in the scanned object reach a steady state, the saturation module includes a plurality of saturation pulses, and there is a time gap between each pair of adjacent saturation pulses in the plurality of saturation pulses; one or more acquisition modules, each of the acquisition modules is used to acquire magnetic resonance signals corresponding to one or more k-space trajectories, and the application time of at least one of the acquisition modules is in the time gap between a pair of adjacent saturation pulses.

[0015] The embodiments of this specification provide a method and system for collecting magnetic resonance signals based on chemical exchange saturation transfer. Compared with traditional CEST imaging, the improved pulse sequence can effectively reduce the scanning time because the time gap between saturation pulses is used to collect magnetic resonance signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] This specification will be further described in the form of exemplary embodiments, which will be described in detail by the accompanying drawings. These embodiments are not restrictive, and in these embodiments, the same number represents the same structure, wherein:

[0017] Figure 1A and Figure 1B It is a schematic diagram of the composition of the traditional CEST sequence;

[0018] Figure 2 It is the timing diagram of the pre-saturation module in the traditional CEST sequence;

[0019] Figure 3 is an exemplary module diagram of a magnetic resonance signal acquisition system according to some embodiments of this specification;

[0020] Figure 4 is an exemplary flow chart of a magnetic resonance signal acquisition method according to some embodiments of the present specification;

[0021] Figure 5A to Figure 5D is a schematic diagram of the composition of the improved CEST sequence shown in some embodiments of this specification;

[0022] Figure 6 is a timing diagram of a single execution in an improved CEST sequence according to some embodiments of this specification;

[0023] Figure 7A to Figure 7C is a schematic diagram of different acquisition modes according to some embodiments of this specification;

[0024] Figures 8A to 8C is a schematic diagram of different acquisition modes shown in some embodiments of this specification;

[0025] Fig.9A and Fig. 9B is a schematic diagram of a 3D conical spiral acquisition mode according to some embodiments of this specification;

[0026] Fig. 10A and Fig. 10B is a schematic diagram of another 3D conical spiral acquisition mode according to some embodiments of this specification;

[0027] Fig.11A and Fig. 11B It is a schematic diagram of a multi-leaf 3D conical spiral acquisition mode according to some embodiments of the present specification. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of this specification. For ordinary technicians in this field, this specification can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0029] It should be understood that the "system", "device", "unit" and / or "module" used herein are a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the words can be replaced by other expressions.

[0030] As shown in this specification, unless the context clearly indicates an exception, the words "a", "an", "a kind" and / or "the" do not refer to the singular, but also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0031] Flowcharts are used in this specification to illustrate the operations performed by the system according to the embodiments of this specification. It should be understood that the preceding or following operations are not necessarily performed precisely in order. Instead, the steps may be processed in reverse order or simultaneously. At the same time, other operations may also be added to these processes, or one or more operations may be removed from these processes.

[0032] Firstly, the related concepts of magnetic resonance imaging (MRI) and chemical exchange saturation transfer (CEST) are introduced.

[0033] A pulse sequence may refer to a setting of multiple parameters such as radio frequency (RF) pulses, gradient fields, signal acquisition time, and their temporal order. By executing a pre-configured pulse sequence, magnetic resonance signal acquisition can be achieved, for example, the acquired magnetic resonance signals are filled into k-space. Then, the acquired magnetic resonance signals are subjected to inverse Fourier transformation to reconstruct a magnetic resonance image. For example, the k-space data lattice can be transformed into a magnetic resonance image lattice by inverse Fourier transformation.

[0034] Radio frequency pulses are the prerequisite for generating magnetic resonance signals. When the frequency of the radio frequency pulse is equal to the precession frequency of hydrogen protons, hydrogen protons absorb energy and produce resonance. This process is also called excitation. The RF pulse that plays an excitation role is also called an excitation pulse. There are also some RF pulses that play other roles. For example, in CEST imaging, in addition to the excitation pulse, there is also a saturation pulse.

[0035] A pulse sequence may include multiple repetitions (or the same pulse sequence / pulse sequence combination may be applied multiple times within a period of time), and the duration of each repetition may be referred to as the repetition time (TR). The process corresponding to each TR may be regarded as an acquisition or execution, that is, TR may refer to the time interval between two adjacent acquisitions or executions.

[0036] The gradient field is mainly used to spatially locate the magnetic resonance signal (or called spatial encoding). In addition, the change of the gradient field will also generate a magnetic resonance signal, which is called a gradient echo signal. The pulse sequence that generates a magnetic resonance signal by changing the gradient field is called a gradient echo (GRE) sequence. The gradient can be divided into three directions, corresponding to three spatial axes (for example, the X-axis, Y-axis and Z-axis that are orthogonal to each other). The gradients in these three directions are usually distinguished and named as the slice selection gradient (denoted as Gs), the phase gradient (denoted as Gp) and the readout gradient (denoted as Gr).

[0037] The signal acquisition time is the acquisition time of the magnetic resonance (MR) signal, which can refer to the time interval from the excitation to the formation of the maximum echo. The acquired magnetic resonance signal is also called the echo signal, and accordingly, the signal acquisition time is also called the echo time (TE). Figure 2 and Figure 6 ), the signal acquisition time can be represented by a box labeled ADC (Analog-to-Digital Converter), and the MR signal acquired (i.e., sampled) by the ADC at a certain moment can be used to fill the corresponding position point in the k-space.

[0038] Signal acquisition (sampling) can follow certain patterns or strategies. According to the sampling frequency, the sampling strategy can be divided into full sampling strategy, undersampling strategy and oversampling strategy. According to the acquisition trajectory in k-space (referred to as k-space trajectory), the acquisition mode can be divided into Cartesian acquisition mode, spiral acquisition mode, radial acquisition mode, etc.

[0039] Referring to the introduction in the background technology, CEST imaging requires contrast between different molecules (one of which is a water molecule), and this contrast is also called CEST contrast. The substance used to form CEST contrast with water molecules can be called CEST contrast agent (or CEST marker). CEST contrast agents can be divided into two categories: endogenous contrast agents and exogenous contrast agents. Endogenous contrast agents use macromolecular substances existing in the human body as natural contrast agents, while exogenous CEST contrast agents introduce substances that have a difference with the inherent frequency of water molecules to form a better CEST contrast.

[0040] For the convenience of description, this article refers to the pulse sequence used for CEST imaging as a CEST sequence, and the magnetic resonance image generated based on CEST as a CEST image.

[0041] In the clinical environment, in order to improve the detectability, tissue contrast and signal-to-noise ratio of CEST markers, traditional CEST imaging needs to wait until the chemical exchange in the scanned object (such as a patient) reaches a steady state (usually more than ten saturation pulses need to be applied) before starting to collect MR signals. In traditional CEST imaging, the module in the CEST sequence used to make the chemical exchange in the scanned object reach a steady state can be called a pre-saturation module (or a CEST preparation module), and the module in the CEST sequence used to collect MR signals can be called an acquisition module.

[0042] Figure 1A and Figure 1B This is a schematic diagram of the composition of the traditional CEST sequence.

[0043] like Figure 1A As shown, corresponding to a reconstructed single magnetic resonance image, the conventional CEST sequence 100 includes a presaturation module 110 and an acquisition module 120. During the application of the conventional CEST sequence 100, each application of a presaturation module 110 may be followed by an acquisition module 120 to reconstruct a magnetic resonance image.

[0044] Each pre-saturation module 110 may include multiple saturation pulses. Under the joint action of these saturation pulses, the chemical exchange in the scanned object (such as a patient) gradually reaches a steady state. In practical applications, the time to reach the steady state can be estimated based on relevant parameters (such as T1 value), and the pre-saturation module 110 is designed based on the estimated time.

[0045] In some embodiments, to achieve homeostasis and suppress fat signaling, e.g. Figure 1B As shown, the conventional CEST sequence 100 may further include: a T1 recovery module 105 applied before the pre-saturation module 110 ; and a fat suppression module 115 applied between the pre-saturation module 110 and the acquisition module 120 .

[0046] Figure 2 is a timing diagram of the pre-saturation module 110 in a conventional CEST sequence.

[0047] like Figure 2 As shown, in addition to the multiple saturation pulses (denoted as RF_CEST), each pre-saturation module 110 may also include multiple spoiler gradients (Spoiler Gradient, also translated as spoiler gradient) applied along each direction (such as X direction, Y direction, Z direction). Figure 2 In, τ p represents the duration of the saturation pulse, τd represents the time interval between a pair of adjacent saturation pulses, and Pi represents the duration of the pre-saturation module 110. Each pulse (such as a saturation pulse) is displayed on the waveform as a short period (for example, the duration is τ p ) ups and downs (similar to pulses), each spoiler gradient (spoiler gradient) can be displayed on the waveform as a trapezoid with the time axis as the base (actually it is a non-ideal rectangle, theoretically it cannot be 100% rectangular, but it is actually a trapezoid). Figure 2 In each pre-saturation module 110, a combination of saturation pulses and spoiler gradients (e.g., 1 saturation pulse + 1 spoiler gradient) needs to be repeatedly applied. In order to achieve a steady state, it is often necessary to apply a dozen or even dozens of combinations of saturation pulses and spoiler gradients in each pre-saturation module 110.

[0048] For the convenience of description, the duration of the pre-saturation module 110, that is, the time interval from its start time to the end time, can be referred to as the saturation time. In order to achieve a steady state, the saturation time usually needs to reach 3 to 5 times the T1 value (that is, the saturation time can be equal to the aforementioned estimated time). Taking the main magnetic field strength of 1.5T commonly used in clinical practice as an example, the T1 value of the water signal is about 4000ms, and the T1 of most human tissues such as gray matter and white matter is about 850ms. Therefore, in order to achieve a steady state, the saturation time often needs to reach 12s to 20s, and the application of other modules (such as fat suppression module 115 and acquisition module 120) also takes time, which makes the entire scanning time very long and cannot meet clinical needs (for example, some patients cannot tolerate long scanning).

[0049] In order to save time, many clinical scans start to collect MR signals before reaching steady state (for example, saturation time is less than 12s), resulting in the detection sensitivity and specificity of various quantitative results related to the CEST images (referred to as CEST results) to the markers being greatly reduced, greatly reducing the clinical diagnostic value of CEST. CEST results include but are not limited to the quantitative results of amide proton transfer (Amide Proton Transfer, APT), relay nuclear Ostwald effect (NOE-relayed exchange, rNOE), glutamate chemical exchange saturation transfer (GluCEST) and other effects. It is understandable that since the content of CEST markers that can be detected in the body is usually very low, this makes the detection sensitivity and specificity of CEST results to the markers very important.

[0050] In view of this, the embodiments of this specification provide an improved CEST sequence. By executing the CEST sequence, the scanning time can be effectively shortened while allowing the use of a better saturation time (such as 12 to 20 seconds), thereby obtaining various CEST results with high sensitivity and high specificity in a short time. In a preferred embodiment, a certain imaging quality can be guaranteed by constraining the acquisition priority of MR signals of different frequencies. For more details about the improved CEST sequence, please refer to Figures 5A to 5D and its related description.

[0051] It is understood that the sequence design method in this specification can be applied to any pulse sequence involving steady state. As an example only, the pulse sequence involving steady state can refer to a pulse sequence in which the acquisition module includes a gradient echo sequence or an echo planar imaging (EPI) sequence.

[0052] Figure 3 is an exemplary module diagram of a magnetic resonance signal acquisition system according to some embodiments of the present specification. The system 300 may be implemented in a magnetic resonance device.

[0053] like Figure 3 As shown, the system 300 may include a sequence acquisition unit 310 and a signal acquisition unit 320 .

[0054] The sequence acquisition unit 310 can be used to acquire a preconfigured pulse sequence. For example, the sequence acquisition unit 310 can be used to determine the components (such as saturation pulses, acquisition modules, spoiler gradients, etc.) included in the pulse sequence and the number, application time, and application order of each component.

[0055] The signal acquisition unit 320 may be used to apply a pre-configured pulse sequence to the scanned object to acquire MR signals. For example, the signal acquisition unit 320 may instruct the magnetic resonance device to execute a pulse sequence to acquire MR signals.

[0056] In some embodiments, the system 300 may further include a signal correction unit 330. The signal correction unit 330 may be used to correct the acquired MR signals.

[0057] For more details about the system 300 and its elements, please refer to Figure 4 and its related description.

[0058] It should be understood that Figure 3The system and its units shown can be implemented in various ways. For example, in some embodiments, the system and its units can be implemented by hardware, software or a combination of software and hardware. Among them, the hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or a dedicated design hardware. Those skilled in the art will understand that the above methods and systems can be implemented using computer executable instructions and / or included in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The system and its units of this specification can not only be implemented by hardware circuits such as ultra-large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., but can also be implemented by software such as executed by various types of processors, and can also be implemented by a combination of the above hardware circuits and software (for example, firmware).

[0059] It should be noted that the above description of the system and its units is only for convenience of description and does not limit this specification to the scope of the embodiments. It is understandable that for those skilled in the art, after understanding the principle of the system, it is possible to arbitrarily combine the various units or form a subsystem connected to other units without deviating from this principle. For example, the signal correction unit 330 can be omitted. Such variations are all within the scope of protection of this specification.

[0060] Figure 4 It is an exemplary flow chart of a magnetic resonance signal acquisition method according to some embodiments of the present specification. In some embodiments, the process 400 may be executed by a magnetic resonance device, specifically, by a magnetic resonance signal acquisition system 300 implemented in the magnetic resonance device.

[0061] like Figure 4 As shown, process 400 may include the following steps.

[0062] Step 410 , obtaining a pre-configured pulse sequence. In some embodiments, step 410 may be performed by the sequence obtaining unit 310 .

[0063] In some embodiments, the pulse sequence can be configured by the user. For example, the magnetic resonance device may include an operating console (that is, the sequence acquisition unit 310 can be implemented in the operating console) so that the user can configure the pulse sequence. Specifically, the user can configure the type, parameters, application scenarios, etc. of the pulse sequence through the operating console. The types of pulse sequences may include spin echo (Spin Echo, SE) sequence, fast spin echo (Fast Spin Echo, FSE) sequence, gradient echo (GRE) sequence, etc. Referring to the foregoing, the parameters of the pulse sequence may include one or more parameters of radio frequency pulses, gradient fields, signal acquisition time, etc. The type and parameters of the pulse sequence can be determined by a pulse sequence diagram (for example, Figure 2 and Figure 6 ) reflects that the operation console can display a pulse sequence diagram to the user so that the user can configure the pulse sequence. For another example, the user can import the configured pulse sequence into the magnetic resonance device through a certain method (e.g., a USB flash drive, a network).

[0064] In some embodiments, the magnetic resonance device may have a pre-configured pulse sequence built in. For example, the pulse sequence may be pre-configured by the device manufacturer and the configured pulse sequence may be written into the magnetic resonance device.

[0065] More details on the pulse sequences can be found elsewhere in this article, for example, Figures 5A to 5D , Figure 6 and its related description.

[0066] Step 420 , executing the pulse sequence to acquire MR signals from the scanned object. In some embodiments, step 420 may be executed by the signal acquisition unit 320 .

[0067] Figures 5A to 5D It is a schematic diagram of the composition of the improved CEST sequence (pulse sequence) shown in some embodiments of this specification.

[0068] like Figures 5A to 5C As shown, corresponding to the reconstructed single magnetic resonance image, the improved CEST sequence 500 may include multiple saturation pulses 510 applied at intervals and multiple acquisition modules 520. The multiple saturation pulses may form a saturation module (RF excitation pulse combination) for achieving a steady state of chemical exchange in the body of the scanned object (such as a patient), that is, by applying multiple RF excitation pulses to the scanned area, the protons of the corresponding substances in the scanned area are in a saturated state.

[0069] refer to Figure 2 In the conventional CEST sequence 100, there is a time gap (duration τ) between each pair of adjacent saturation pulses. dBased on this, the acquisition module 120 can be divided into multiple parts, and each part is applied between a pair of adjacent saturation pulses, wherein each part can be regarded as a new acquisition module, that is, Figures 5A to 5C The acquisition module 520 in the improved CEST sequence can effectively reduce the scanning time compared with the traditional CEST sequence because the time gap between the saturation pulses is used to acquire the MR signal.

[0070] In some embodiments, Figure 5A As shown in FIG. 5 , during the application of the improved CEST sequence 500, a collection module 520 may be applied between each pair of adjacent saturation pulses. For example, a collection module 520 may be applied each time a saturation pulse is applied. In this way, the time gap between the saturation pulses may be fully utilized. In other embodiments, such as Figure 5B As shown, during the application of the improved CEST sequence 500, one acquisition module 520 may be applied every two or more saturation pulses. For example, when more than ten saturation pulses are required to reach a steady state, Figure 5B As shown, during the application of the improved CEST sequence 500, one acquisition module 520 may be applied for every five saturation pulses applied. Of course, these two embodiments may be combined with each other. Figure 5C As shown, in the CEST sequence, the order of applying the saturation pulses and the acquisition modules may include: 2 saturation pulses→1 acquisition module→1 saturation pulse→1 acquisition module→3 saturation pulses→1 acquisition module→1 saturation pulse→1 acquisition module.

[0071] In some embodiments, if conditions permit (for example, the MR signals required to reconstruct a magnetic resonance image can be acquired within the time interval between a pair of adjacent saturation pulses), Figure 5D As shown, corresponding to a reconstructed single magnetic resonance image, the improved CEST sequence 500 may include only one acquisition module 520 , and the acquisition module 520 may be applied between a pair of adjacent saturation pulses.

[0072] In summary, corresponding to the acquisition of a single magnetic resonance image, the improved CEST sequence 500 includes a saturation module and one or more acquisition modules, wherein the application time of at least one acquisition module 520 can be in the time gap between a pair of adjacent saturation pulses in the saturation module. For the convenience of description, this article specifically records this acquisition module as acquisition module 520. It should be understood that other acquisition modules (not shown) are allowed to exist in the improved CEST sequence 500, for example, an acquisition module applied after the saturation module (i.e., after the last saturation pulse in the saturation module).

[0073] Figure 6It is a timing diagram of a single execution in the improved CEST sequence shown in some embodiments of this specification.

[0074] refer to Figure 6 During the application of the CEST sequence 500, a saturation pulse 510 (denoted as RF_CEST), a spoiler gradient (spoiler gradient) 512 and an acquisition module 520 may be applied successively within each repetition time (denoted as TR). Figure 6 In, τ p represents the duration of the saturation pulse, τ d represents the time gap between a pair of adjacent saturation pulses, and Ti represents the duration of the acquisition module 520. Specifically, during the application of the CEST sequence 500, each time a saturation pulse is applied, a spoiler gradient 512 may be applied along each direction (such as the X direction, the Y direction, and the Z direction), followed by an acquisition module 520. The acquisition module 520 may include an RF part (such as an excitation pulse, denoted as RF_image), a gradient part (such as an imaging gradient applied along each direction), and a signal acquisition part (represented as a box marked with ADC).

[0075] In some embodiments, the improved CEST sequence 500 may further include a fat suppression module applied before each acquisition module 520 to suppress fat signals. Figure 6 During the application of the CEST sequence 500, the fat suppression module 515 may be applied after the application of the spoiler gradient 512 is completed and before the application of the acquisition module 520 (ie, before the application of RF_image).

[0076] In some embodiments, during the magnetic resonance signal acquisition process, a compressed sensing method or an artificial intelligence algorithm can be used to increase the sampling speed of the k-space, thereby further speeding up the scanning.

[0077] In some embodiments, the at least one acquisition module 520 may adopt a Cartesian acquisition mode or a spiral acquisition mode, wherein each acquisition module 520 may be used to acquire MR signals corresponding to one or more k-space trajectories. It can be understood that the k-space trajectory may be formed by connecting sampling points in the k-space. Further, the application of the acquisition module 520 in the improved CEST sequence 500 satisfies: the acquisition module 520 corresponding to the k-space trajectory in the edge area of ​​the k-space is applied earlier than the acquisition module 520 corresponding to the k-space trajectory in the center area of ​​the k-space. For example, the acquisition module corresponding to the k-space trajectory in the edge area of ​​the k-space may be applied near the first few saturation pulses in the saturation module (for example, between the third pair of pulse sequences), and the acquisition module corresponding to the k-space trajectory in the center area of ​​the k-space may be applied near the last few saturation pulses in the saturation module (for example, between the latest pair of pulse sequences).

[0078] It should be understood that as the number of applied saturation pulses increases, the chemical exchange in the scanned object is getting closer to a steady state. Since the acquisition time of the k-space trajectory in the edge area of ​​the k-space is earlier, the acquisition time of the MR signal corresponding to the k-space trajectory in the center area of ​​the k-space is closer to the time point when the steady state is reached than the MR signal corresponding to the k-space trajectory in the edge area of ​​the k-space. Accordingly, the quality of the signal collected in the center area is higher than that of the signal in the edge area. Since the signal in the center area of ​​the k-space is crucial to image reconstruction, a certain imaging quality can be guaranteed by setting the acquisition priority of the signals in different areas.

[0079] Combine the following Figures 7A to 7C and Figures 8A to 8C An example is given to illustrate the specific implementation method of constraining the signal acquisition priority.

[0080] like Fig. 7A As shown in FIG. 1 , when the Cartesian acquisition mode is adopted, the MR signals corresponding to the k-space trajectory outside the dotted box (i.e., the edge area of ​​the k-space) can be acquired first, and then the MR signals corresponding to the k-space trajectory inside the dotted box (i.e., the center area of ​​the k-space) can be acquired. Furthermore, in the center area of ​​the k-space, the MR signals corresponding to the k-space trajectory closer to the center of the k-space can be acquired later. Similarly, in the edge area of ​​the k-space, the MR signals corresponding to the k-space trajectory closer to the center of the k-space can be acquired later.

[0081] like Figure 7B As shown, when the circular spiral acquisition mode is adopted, MR signals can be acquired along the direction of spiraling into the center of the k-space (hereinafter referred to as the spiraling direction). Specifically, the entire spiral trajectory can be divided along the spiraling direction, so as to obtain multiple k-space trajectories in sequence, and then the MR signals corresponding to these k-space trajectories can be acquired in the order in which they are acquired. For example, Figure 7B The spiral trajectory in the image has 8 circles in total, and each circle of the trajectory can be used as a k-space trajectory. The MR signals corresponding to these 8 k-space trajectories can be collected sequentially from the outside to the inside.

[0082] like Figure 7C As shown, when the square spiral acquisition mode is adopted, MR signals can also be acquired along the direction of spiraling into the center of the k-space (hereinafter referred to as the spiraling direction). Specifically, the entire spiral trajectory can be cut along the spiraling direction, so as to obtain multiple k-space trajectories in sequence, and then the MR signals corresponding to these k-space trajectories can be acquired in the order in which they are acquired. For example, Figure 7C The spiral trajectory in the figure can be considered to have a total of 6 circles from the outside to the inside, and each circle of the trajectory can be used as a k-space trajectory. The MR signals corresponding to these 6 k-space trajectories can be collected sequentially from the outside to the inside.

[0083] In some embodiments, the constraints on signal acquisition priority can also be applied to other acquisition modes. Fig. 7A The single-shot Cartesian acquisition mode shown in the figure is Fig. 8A In the multi-shot Cartesian acquisition mode shown in FIG. , the MR signals corresponding to the k-space trajectory in the edge area of ​​the k-space can be acquired preferentially. Figure 7B The circular spiral acquisition mode shown in the figure is Figure 8B When the variable density spiral acquisition mode (i.e., the multi-shot circular spiral acquisition mode) is used, the MR signals corresponding to the k-space trajectory in the edge area of ​​the k-space can be acquired preferentially. For another example, when the EPI acquisition mode (not limited to single excitation or multi-excitation) is used, the MR signals corresponding to the k-space trajectory in the edge area of ​​the k-space can also be acquired preferentially. For another example, for 3D acquisition, refer to Figure 8C , k-space is expanded to three dimensions (such as k x , k y and k v ), or in other words, there are multiple layers (such as the 1st layer to the Nvth layer) of two-dimensional k-space. Figure 8C In the spiral stack acquisition mode shown, the MR signals corresponding to the k-space trajectory in the edge area of ​​the k-space can be acquired preferentially, where the central area of ​​the k-space is a 3D area composed of multiple layers of 2D areas.

[0084] In some embodiments, the constraints on signal acquisition priority can be applied to more 3D acquisition modes, including but not limited to Figures 9A to 11B Three 3D conical spiral acquisition modes are shown. When the 3D conical acquisition mode is used, similar to the 2D circular spiral acquisition mode, the entire spiral trajectory can be cut along the spiral direction, so as to obtain multiple k-space trajectories in sequence, and then the MR signals corresponding to these k-space trajectories can be acquired in the order of acquisition. Fig.9A This is a schematic diagram of a 3D conical acquisition mode in a 3D perspective. Fig. 9B This is a schematic diagram of the acquisition mode in a 2D perspective (top view). Fig. 10A This is a schematic diagram of another conical acquisition mode in 3D perspective. In this mode, the k-space trajectory is distributed on multiple conical surfaces. Fig. 10B The k-space trajectory on a single cone surface is shown, along with the spacing of the k-space data (1 / FOV), where FOV represents the image field of view. Fig.11A This is a 2D schematic diagram of a multi-leaf 3D conical spiral acquisition mode in the XY plane. Fig. 11B A 3D schematic diagram of the model.

[0085] In particular, when the improved pulse sequence includes only one acquisition module 520, the acquisition module 520 can be applied near the last saturation pulse in the saturation module, for example, Figure 5D As shown, the acquisition module 520 can be applied between the last pair of saturation pulses in the saturation module.

[0086] In some embodiments, multiple saturation pulses may be applied as pre-pulses first, so that the chemical exchange in the scanned object reaches an approximate steady state, and then the at least one acquisition module 520 is applied. As an example only, when the number of pre-pulses reaches 80% (or other proportions, such as 70%, 90%) of the total number of saturation pulses in the saturation module, it can be considered that the chemical exchange in the scanned object reaches an approximate steady state. In this way, regardless of whether the signal acquisition priority is constrained, a certain imaging quality can be guaranteed.

[0087] In some embodiments, process 400 may further include step 430 .

[0088] Step 430 , correcting the acquired magnetic resonance signal. In some embodiments, step 430 may be performed by the signal correction unit 330 .

[0089] Compared with the traditional CEST sequence 100, since the application time of the acquisition module is advanced, at least part of the MR signals acquired by the improved CEST sequence 500 are acquired before reaching a steady state, and their quality is poor. It can be corrected by certain means to improve the imaging quality.

[0090] In some embodiments, the signal correction unit 330 may input the MR signal collected by the improved CEST sequence 500 into a trained correction model to obtain a corrected MR signal. The training sample of the correction model may include a first MR signal collected by the improved CEST sequence 500 (as a model input) and a second MR signal collected by the traditional CEST sequence 100 (as a sample label). The loss function of the correction model may be defined based on the difference between the predicted result of the sample (i.e., the model output) and the sample label. By way of example only, the correction model may include a neural network model, such as a deep learning model.

[0091] In some embodiments, the correction may also be achieved by a preset image correction algorithm.

[0092] It should be noted that the above description of the relevant process is only for example and explanation, and does not limit the scope of application of this specification. For those skilled in the art, various modifications and changes can be made to the process under the guidance of this specification. However, these modifications and changes are still within the scope of this specification.

[0093] The beneficial effects that may be brought about by the embodiments of this specification include but are not limited to: (1) Acquiring MR signals in the time gap between saturation pulses can effectively shorten the scanning time, thereby obtaining various CEST results with high sensitivity and high specificity in a short time; (2) By constraining the acquisition priority of MR signals of different frequencies, a certain imaging quality can be guaranteed; (3) By correcting the acquired MR signals, the imaging quality can be improved. It should be noted that different embodiments may produce different beneficial effects. In different embodiments, the beneficial effects that may be produced may be any one or a combination of the above, or any other possible beneficial effects.

[0094] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation on the embodiments of this specification. Although not explicitly stated here, those skilled in the art may make various modifications, improvements and corrections to the embodiments of this specification. Such modifications, improvements and corrections are suggested in the embodiments of this specification, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of this specification.

[0095] At the same time, this specification uses specific words to describe the embodiments of this specification. For example, "one embodiment", "an embodiment" and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of this specification. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different locations in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of this specification can be appropriately combined.

[0096] In addition, it will be appreciated by those skilled in the art that the various aspects of the embodiments of this specification may be illustrated and described by a number of patentable categories or situations, including any new and useful process, machine, product or combination of substances, or any new and useful improvements thereto. Accordingly, the various aspects of the embodiments of this specification may be performed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The above hardware or software may all be referred to as "data blocks", "modules", "engines", "units", "components" or "systems". In addition, the various aspects of the embodiments of this specification may be represented as a computer product located in one or more computer-readable media, the product including computer-readable program code.

[0097] A computer storage medium may include a propagated data signal containing computer program code, for example, in baseband or as part of a carrier wave. The propagated signal may be in a variety of forms, including electromagnetic, optical, etc., or a suitable combination. A computer storage medium may be any computer-readable medium other than a computer-readable storage medium, which can be connected to an instruction execution system, device or apparatus to communicate, propagate or transmit the program for use. The program code on the computer storage medium may be transmitted via any suitable medium, including radio, cable, fiber optic cable, RF, or similar media, or any combination of the above media.

[0098] The computer program coding required for the operation of each part of the embodiment of this specification can be written in any one or more programming languages, including object-oriented programming languages ​​such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB.NET, Python, etc., conventional procedural programming languages ​​such as C language, VisualBasic, Fortran2003, Perl, COBOL2002, PHP, ABAP, dynamic programming languages ​​such as Python, Ruby and Groovy, or other programming languages, etc. The program coding can be run completely on the user's computer, or run on the user's computer as an independent software package, or partly run on the user's computer and partly run on the remote computer, or run completely on the remote computer or processing equipment. In the latter case, the remote computer can be connected to the user's computer by any network form, such as a local area network (LAN) or a wide area network (WAN), or connected to an external computer (e.g., by the Internet), or in a cloud computing environment, or used as a service such as software as a service (SaaS).

[0099] In addition, unless explicitly stated in the claims, the order of the processing elements and sequences described in the embodiments of this specification, the use of alphanumeric characters, or the use of other names are not intended to limit the order of the processes and methods of the embodiments of this specification. Although the above disclosure discusses some invention embodiments that are currently considered useful through various examples, it should be understood that such details are only for illustrative purposes, and the attached claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that are consistent with the essence and scope of the embodiments of this specification. For example, although the system components described above can be implemented by hardware devices, they can also be implemented only by software solutions, such as installing the described system on an existing processing device or mobile device.

[0100] Similarly, it should be noted that in order to simplify the description of the embodiments disclosed in this specification, thereby helping to understand one or more embodiments of the invention, in the above description of the embodiments of this specification, multiple features are sometimes combined into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the objects of the embodiments of this specification are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0101] Each patent, patent application, patent application publication, and other materials, such as articles, books, specifications, publications, documents, etc., cited in this specification is hereby incorporated by reference in its entirety. Except for application history documents that are inconsistent with or conflicting with the contents of this specification, documents that limit the broadest scope of the claims of this application (currently or later attached to this application) are also excluded. It should be noted that if the descriptions, definitions, and / or use of terms in the materials attached to this specification are inconsistent or conflicting with the contents described in this specification, the descriptions, definitions, and / or use of terms in this specification shall prevail.

[0102] Finally, it should be understood that the embodiments described in this specification are only used to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of the embodiments of this specification. Therefore, as an example and not a limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly introduced and described in this specification.

Claims

1. A magnetic resonance signal acquisition method based on chemical exchange saturation transfer, characterized in that: include: Applying a preconfigured pulse sequence to the scanned object to acquire magnetic resonance signals; wherein the pulse sequence includes: A saturation module, the saturation module is used to make the chemical exchange in the scanned object reach a steady state, the saturation module includes a plurality of saturation pulses, and there is a time gap between each pair of adjacent saturation pulses in the plurality of saturation pulses; One or more acquisition modules, each of which is used to acquire magnetic resonance signals corresponding to one or more k-space trajectories, and the application time of at least one of the acquisition modules is in the time gap between a pair of adjacent saturation pulses.

2. The method according to claim 1, characterized in that The applying of the pre-configured pulse sequence includes: applying a saturation pulse, a spoiler gradient and a collection module successively within each repetition time.

3. The method according to claim 1, characterized in that The applying of the preconfigured pulse sequence further includes applying a fat suppression module before each of the acquisition modules, wherein the fat suppression module is used to suppress fat signals.

4. The method according to claim 1, characterized in that At least one of the acquisition modules adopts a Cartesian acquisition mode or a spiral acquisition mode; The acquisition modules are applied in such a manner that: the acquisition modules corresponding to the k-space trajectory in the edge region of the k-space are applied earlier than the acquisition modules corresponding to the k-space trajectory in the center region of the k-space.

5. The method according to claim 1, characterized in that The applying of the preconfigured pulse sequence includes: applying one acquisition module every time at most five saturation pulses are applied.

6. The method according to claim 1, characterized in that The applying of the preconfigured pulse sequence includes: applying one acquisition module each time one saturation pulse is applied.

7. The method according to claim 1, characterized in that The acquisition module includes a gradient echo sequence or a planar echo imaging sequence.

8. The method according to claim 1, characterized in that Also includes: The acquired magnetic resonance signals are corrected.

9. A magnetic resonance device, characterized in that: The system comprises a processor and a storage device, wherein the storage device stores instructions for magnetic resonance signal acquisition, and when the processor executes the instructions, the magnetic resonance signal acquisition method according to any one of claims 1 to 8 is implemented.

10. A magnetic resonance signal acquisition system based on chemical exchange saturation transfer, characterized in that: The method comprises a sequence acquisition unit and a signal acquisition unit; the sequence acquisition unit is used to acquire a pre-configured pulse sequence, and the signal acquisition unit is used to apply the pulse sequence to the scanned object to acquire magnetic resonance signals; wherein the pulse sequence comprises: A saturation module, the saturation module is used to make the chemical exchange in the scanned object reach a steady state, the saturation module includes a plurality of saturation pulses, and there is a time gap between each pair of adjacent saturation pulses in the plurality of saturation pulses; One or more acquisition modules, each of which is used to acquire magnetic resonance signals corresponding to one or more k-space trajectories, and the application time of at least one of the acquisition modules is in the time gap between a pair of adjacent saturation pulses.

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