Spectral imaging method and magnetic resonance imaging system

Abstract

The application relates to a spectrum imaging method and a magnetic resonance imaging system. The spectrum imaging method comprises the following steps: performing signal pre-acquisition on a scanning object; determining the relative position between a specific tissue region and a region of interest according to the pre-acquisition signal, the specific tissue region containing fat; judging the chemical shift direction of the fat according to the gradient parameters of a spectrum sequence to be scanned; judging whether the gradient parameters of the spectrum sequence to be scanned need to be changed according to the chemical shift direction of the fat and the relative position between the specific tissue region and the region of interest, and then executing the spectrum sequence to be scanned or the spectrum sequence to be scanned with the gradient parameters changed. According to the chemical shift direction of the fat and the automatically determined relative position between the specific tissue region and the region of interest, it is determined whether the fat signal will affect the magnetic resonance signal of the region of interest, the excitation of the fat is reduced without moving the region of interest, the pollution is reduced, and the spectrum line quality is improved.

Description

Technical Field

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

[0002] Magnetic resonance spectroscopy (MRS) analysis can provide information about the chemistry of interest based on the chemical shift in magnetic resonance. In MRS imaging localization, slice gradients are typically used to select the region of interest (VOI). However, due to the chemical shift effect, different metabolites actually excite different VOIs. For example, the VOI of low-frequency signals will shift to areas with higher magnetic fields. If the VOI is close to the skull, improper gradient polarity selection can lead to the excitation of fat signals outside the VOI. Excited fat signals can severely contaminate the spectral lines and reduce spectral quality. Summary of the Invention

[0003] Therefore, it is necessary to provide a spectral imaging method and magnetic resonance imaging system to address the problem of poor spectral quality caused by improper gradient polarity selection in traditional schemes.

[0004] This application provides a spectral imaging method, including:

[0005] S10, Pre-acquisition of signals from the scanned object to obtain the pre-acquisition signal;

[0006] S20, based on the pre-acquisition signal, determine the relative position between the region of interest and a specific tissue region, wherein the specific tissue region contains fat;

[0007] S30, determine the chemical shift direction of the fat based on the gradient parameters of the spectral sequence to be scanned;

[0008] S40, based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, determine whether it is necessary to change the gradient parameters of the spectral sequence to be scanned, and then execute the spectral sequence to be scanned or the spectral sequence to be scanned with the gradient parameters changed.

[0009] In one embodiment, the step of pre-acquiring signals from the scanned object in S10 includes:

[0010] S110, determine the direction of the selected layer gradient and the direction of the readout gradient of the scanned object;

[0011] S120, apply a radio frequency pulse to the scanned object, and apply the layer selection gradient at the same time as the radio frequency pulse is applied;

[0012] S130, after the layer selection gradient, apply a frequency coding gradient along the direction of the readout gradient and acquire the pre-acquisition signal simultaneously with the application of the frequency coding gradient.

[0013] In one embodiment, when performing S110 to S130, the direction of the readout gradient determined in S110 is parallel to at least one of the layer selection gradient axis, the phase encoding gradient axis, and the frequency encoding gradient axis.

[0014] In one embodiment, the step of determining the relative position between the region of interest and a specific tissue region based on the pre-acquisition signal in step S20 includes:

[0015] Reconstruct the pre-acquired signal to obtain the pre-acquired image;

[0016] The pre-acquired image is projected along a set direction to obtain a projected image;

[0017] The location of the region of interest in the spectral pre-acquisition field of view is determined based on the projected image.

[0018] In one embodiment, determining the position of the region of interest in the spectral pre-acquisition field of view based on the projected image includes:

[0019] The projected image is processed using a set pixel threshold to determine the boundary of the scanned object;

[0020] The position of the region of interest in the spectral pre-acquisition field of view is determined based on the boundary of the scanned object.

[0021] In one embodiment, step S40, which involves determining whether to change the gradient parameters of the spectral sequence to be scanned based on the chemical shift direction of the fat and the relative position between the region of interest and a specific tissue region, includes:

[0022] Based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, it is determined whether the execution of the spectral sequence to be scanned will excite the fat in the specific tissue region.

[0023] In response to the execution of the spectral sequence to be scanned, fat in the specific tissue region is excited, thereby altering the gradient parameters of the spectral sequence to be scanned; or,

[0024] In response to the fact that the execution of the spectral sequence to be scanned does not excite the fat in the specific tissue region, the gradient parameters of the spectral sequence to be scanned remain unchanged.

[0025] In one embodiment, in step S40, the gradient parameter of the spectral sequence to be scanned is the gradient polarity of the spectral sequence to be scanned.

[0026] In one embodiment, the specific tissue region is located on the periphery of the region of interest.

[0027] In one embodiment, this application provides a magnetic resonance imaging system including a pre-acquisition device, a position determination device, a chemical shift determination device, a feedback device, and a sequence adjustment device. The pre-acquisition device is used to pre-acquire signals from the scanned object to obtain a pre-acquisition signal. The position determination device is connected to the pre-acquisition device and is used to determine the relative position between a region of interest (ROI) and a specific tissue region, wherein the specific tissue region includes fat, based on the pre-acquisition signal. The chemical shift determination device is connected to the position determination device and is used to determine the chemical shift direction of the fat based on the gradient polarity of the spectral sequence to be scanned. The feedback device is connected to the chemical shift determination device and is used to generate a feedback command based on the chemical shift direction of the fat and the relative position between the ROI and the specific tissue region; the feedback command is an adjustment of gradient parameters. The sequence adjustment device is connected to the feedback device and is used to adjust the gradient parameters of the spectral sequence to be scanned according to the feedback command.

[0028] In one embodiment, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in any one of the above embodiments.

[0029] This application provides a spectral imaging method and a magnetic resonance imaging system. The spectral imaging method includes: pre-acquiring a signal from a scanned object to obtain a pre-acquisition signal; determining the relative position between a region of interest (ROI) and a specific tissue region, wherein the specific tissue region contains fat, based on the pre-acquisition signal; determining the chemical shift direction of the fat based on the gradient parameters of the spectral sequence to be scanned; and determining whether the gradient parameters of the spectral sequence to be scanned need to be changed based on the chemical shift direction of the fat and the relative position between the ROI and the specific tissue region, before executing the spectral sequence to be scanned or the spectral sequence to be scanned with modified gradient parameters. The spectral imaging method adds a signal pre-acquisition step, automatically determining the relative position between the ROI and the specific tissue region using the pre-acquisition signal, and determining whether the fat signal will affect the magnetic resonance signal of the ROI based on the chemical shift direction of the fat and the automatically determined relative position between the ROI and the specific tissue region. The spectral imaging method can minimize fat excitation, reduce contamination, and improve spectral quality without moving the ROI. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating the steps of the spectral imaging method provided in one embodiment of this application;

[0032] Figure 2 This is a schematic flowchart illustrating the steps of pre-acquiring signals from the scanned object in one embodiment of this application;

[0033] Figure 3 This is a one-dimensional projection diagram of the pre-acquired signal provided in one embodiment of this application;

[0034] Figure 4 This is a schematic diagram of positive polarity gradient time-spectral excitation provided in one embodiment of this application;

[0035] Figure 5 This is a schematic diagram of spectral excitation under negative polarity gradient provided in one embodiment of this application;

[0036] Figure 6 This is a sequence diagram of a pre-acquisition signal provided in one embodiment of this application;

[0037] Figure 7 These are illustrations showing the effects of different angles in one embodiment of this application;

[0038] Figure 8 This is the gradient polarity diagram that is the default in traditional schemes;

[0039] Figure 9 This is an embodiment of the present application providing an intelligent gradient polarity map obtained using the spectral imaging method described in the present application. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0041] The serial numbers assigned to components in this document, such as "first" and "second," are used solely to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). It should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are used solely for the convenience of describing this application and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0042] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0043] Magnetic resonance spectroscopy (MR Spectroscopy, MRS) is a new examination technique developed in medical imaging in recent years. MR spectroscopy is a non-invasive method for studying the metabolism and biochemical changes of living organs and tissues, as well as for the quantitative analysis of compounds.

[0044] Spectroscopic imaging is a detection method that uses the chemical shifts of human metabolites in an MRS (Mechanical Spectroscopy) to determine molecular composition and spatial configuration. Different metabolites exhibit different chemical shifts, reflecting pathophysiological changes in human energy metabolism. Normal brain metabolites include N-acetylaspartate (NAA), creatine-phosphocreatine (Cr+Pcr), choline derivatives (Cho), inositol (mI), and glutamine-glutamate complex (Glx).

[0045] In traditional methods, to avoid chemical shift of fat during spectral imaging, the region of interest (VOI) is typically moved. However, sometimes, because the lesion is located close to the skull, moving the VOI prevents it from completely encompassing the lesion, ultimately failing to obtain the spectral signal at the lesion boundary, thus affecting clinical applications.

[0046] This application provides a spectral imaging method and a magnetic resonance imaging system. The spectral imaging method is applied to the magnetic resonance imaging system. By determining the relative position of the VOI (void of origin) and the skull through pre-acquisition signals, the offset direction of the excitation position after the scanning sequence excitation caused by fat chemical shift is predicted, thereby determining the gradient parameters in the spectral scan, thereby reducing fat excitation, reducing fat contamination, and improving spectral quality.

[0047] Please see Figure 1 , Figure 1 This is a schematic flowchart illustrating the steps of the spectral imaging method provided in this application. When performing spectral imaging of the head, this method can reduce fat contamination of the skull.

[0048] The spectral imaging method includes:

[0049] S10, perform signal pre-acquisition on the scanned object to obtain a pre-acquisition signal. The pre-acquisition signal in this step can be a pre-acquisition signal obtained from a single acquisition or the average value of signals obtained from multiple acquisitions. The scanned object can be a human body, an animal body, a water film, etc.; the scanned object can be a local tissue area such as the head, chest, or abdomen; or the scanned object can be a local organ such as the brain, heart, kidneys, or prostate. In this embodiment, the scanned object is selected as the head region of a human body.

[0050] S20, based on the pre-acquisition signal, determine the relative position between the region of interest (ROI) and a specific tissue region, where the specific tissue region contains fat. The specific tissue region is located around the RIO; for example, if the specific tissue region is located on the periphery / outer edge of the RIO, the RIO is a non-fat region. In this embodiment, the RIO and the specific tissue region may be located in the same slice of the scanned object. Execution of the spectral sequence to be scanned may cause the fat signal in the specific tissue region and the signal in the RIO to be excited; that is, the fat contained in the specific tissue region may affect the magnetic resonance signal of the RIO.

[0051] The relative position between the region of interest (ROI) and the specific tissue region can be the relative coordinates of the specific tissue region with the ROI as a reference marker within the same coordinate space / system. In one-dimensional space, the relative position between the ROI and the specific tissue region can be that the ROI is closer to the left of the specific tissue region, or the ROI is closer to the right of the specific tissue region. The specific tissue region may include boundary tissues such as the skull. The ROI is the target imaging region, such as a soft tissue region of the brain, and can also be understood as a target activation area.

[0052] S30, determine the chemical shift direction of fat based on the gradient parameters of the spectral sequence to be scanned.

[0053] Chemical shift refers to the difference in chemical composition within the main magnetic field (static magnetic field) caused by a change in resonant frequency. In this embodiment, chemical shift occurs due to the difference in resonant frequencies between protons in water and protons in fat, and this chemical shift can be oriented along the frequency coding direction and / or the layer selectable direction. As a result of the chemical shift, the precession frequency of protons in fat is typically 3.5 PPM faster than that of protons in water.

[0054] In this step, after the spectral sequence to be scanned is executed by the magnetic resonance imaging system, the magnetic resonance signal of the scanned object can be acquired. Reconstructing the aforementioned magnetic resonance signal allows for the acquisition of the spectral lines of the voxels of the scanned object. The position of the peak on the spectral line determines the metabolites, and the area under the peak represents the relative content. The spectral sequence to be scanned can be a point-resolved spectroscopy (PRESS) sequence or a stimulated-echo method (STEAM) sequence. The spectral sequence to be scanned may include gradient parameters, radio frequency pulse parameters, and acquisition windows, etc., wherein: the gradient parameters include the polarity of the gradient, the gradient ramp rate, and the gradient intensity; the radio frequency pulse parameters include the radio frequency pulse intensity and the radio frequency pulse application time, etc. The gradient parameter of the spectral sequence to be scanned can be the gradient polarity of the spectral sequence to be scanned, which can also be referred to as the direction of gradient field change. The bounding box parameters of the spectral sequence to be scanned determine the imaging field of view. The resonance frequencies (excitation and refocusing frequencies, etc.) of the spectral sequence determine the range of substances or components that can be excited within the region of interest. Based on this, the chemical shift direction of fat can be determined according to the gradient polarity of the spectral sequence to be scanned. For example, if the gradient polarity of the spectral sequence to be scanned is selected as positive, the chemical shift direction of fat is the encoding direction with a relatively higher gradient intensity; if the gradient polarity of the spectral sequence to be scanned is selected as negative, the chemical shift direction of fat is also the encoding direction with a relatively higher gradient intensity.

[0055] For example, the direction of chemical displacement of stimulated fat can be determined based on the frequency position of the excitation pulse corresponding to the VOI and / or the frequency position of the retraction pulse, and the relative position of the VOI and the skull. In this embodiment, the center frequency position of the excitation pulse is the center of the VOI, and the center of the skull is located to the right of the center of the VOI. If the chemical displacement of fat causes the stimulation of fat to be biased towards the skull, the chemical displacement of fat will cause the stimulation of fat at the skull boundary, thus reversing the gradient polarity of the layer selection; conversely, if the center of the skull is located to the left of the center of the VOI, the chemical displacement of fat will not cause the stimulation of fat at the skull boundary, thus maintaining the gradient polarity of the layer selection unchanged.

[0056] S40, based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, determine whether it is necessary to change the gradient parameters of the spectral sequence to be scanned, and then execute the spectral sequence to be scanned or the spectral sequence to be scanned with modified gradient parameters. In this step, the gradient parameters of the spectral sequence to be scanned can be the gradient polarity of the spectral sequence to be scanned, such as the polarity of the gradient selected by the slice. The gradient polarity of the spectral sequence to be scanned can be intelligently / automatically switched.

[0057] This embodiment utilizes two characteristics of clinical head scans: First, scalp fat exists only within specific tissue regions; fat is only present at the boundaries of the head, not in the center. Second, the region of interest (ROI) in clinical scans typically does not encompass the entire head; only the ROI is excited. When the spectral imaging method meets these two conditions, the location of fat is determined by judging the relative position of the brain boundary (specific tissue region) and the ROI. Once the location of fat is determined, the shift direction of fat in the ROI can be controlled by adjusting the gradient polarity, thereby reducing fat excitation. The above embodiment of this application provides a spectral imaging method that adds a signal pre-acquisition step, automatically determining the relative position between the ROI and the specific tissue region through the pre-acquisition signal. Based on the chemical shift direction of fat and the automatically determined relative position between the ROI and the specific tissue region, it is determined whether the fat signal will affect the magnetic resonance signal of the ROI. This spectral imaging method can minimize fat excitation, reduce contamination, and improve spectral quality without moving the ROI.

[0058] Please see Figure 2 , Figure 2 This is a schematic flowchart illustrating the steps of pre-acquiring signals from the scanned object in this application. In one embodiment, step S10, the step of pre-acquiring signals from the scanned object, includes:

[0059] S110, determine the direction of the selected layer gradient and the direction of the readout gradient of the scanned object, wherein the direction of the selected layer gradient is perpendicular to the direction of the readout gradient;

[0060] S120, apply a radio frequency pulse to the scanned object, and apply a layer selection gradient at the same time as the radio frequency pulse is applied;

[0061] S130, after the layer selection gradient, a frequency-encoded gradient is applied along the direction of the readout gradient, and signal acquisition is performed simultaneously as the pre-acquisition signal.

[0062] Specifically, during signal pre-acquisition of the scanned object, the pre-acquisition signal readout requires gradient encoding in the readout direction. The direction of the readout gradient is parallel to the logical coordinate axes in spectral imaging, and a layer selection gradient is applied simultaneously with excitation. The layer selection gradient is perpendicular to the direction of the readout gradient and can be any direction perpendicular to the readout gradient direction. There are three logical coordinate axes: the SS axis, the PE axis, and the RO axis. This embodiment provides the specific steps for obtaining the pre-acquisition signal. Through these steps, the following can be obtained: Figure 6 The results shown will be described in detail in the following embodiments. In this embodiment, the specific steps of the pre-acquisition signal can conveniently and quickly obtain the pre-acquisition signal, thus making sufficient preparations for further determining the relative position between the region of interest and a specific tissue region.

[0063] In one embodiment, during the execution of S110-S130, the direction of the readout gradient determined in S110 is parallel to each of the three logical coordinate axes. Alternatively, the direction of the readout gradient can be understood as being parallel to at least one of the SS axis (layer selection gradient axis), PE axis (phase encoding gradient axis), and RO axis (frequency encoding gradient axis).

[0064] In this embodiment, gradient encoding is required in the direction of the readout gradient. Specifically, gradient encoding needs to be performed on the SS axis, PE axis, and RO axis respectively. To calculate the direction of fat chemical displacement on the SS axis, the direction of the readout gradient of the pre-acquired signal needs to be consistent with the SS axis. To calculate the direction of fat chemical displacement on the PE axis, the direction of the readout gradient of the pre-acquired signal needs to be consistent with the PE axis. To calculate the direction of fat chemical displacement on the RO axis, the direction of the readout gradient of the pre-acquired signal needs to be consistent with the RO axis. Of course, if the location of the region of interest and the specific tissue region is accurately confirmed, the direction of the layer selection gradient can also be singular, that is, the direction of the layer selection gradient is parallel to only one of the logical coordinate axes to obtain the pre-acquired signal.

[0065] In one embodiment, the step of pre-acquiring signals from the scanned object in S10 includes: executing S110-S140 multiple times, reading out the relative positions of multiple sets of regions of interest and specific tissue regions on three logical coordinate axes, and averaging the results of the relative positions of each set of regions of interest and specific tissue regions on one logical coordinate axis as the pre-acquisition signal.

[0066] In this embodiment, the pre-acquisition signal is the average value after multiple measurements. Specifically, it involves repeatedly acquiring data on the relative positions of each group of regions of interest and specific tissue regions on a logical coordinate axis, and then averaging the acquisition results. Taking one axis as an example, the pre-acquisition parameters used in multiple acquisitions are exactly the same. Multiple pre-acquisition actions are performed, the signals from the multiple pre-acquisitions are averaged, and then it is calculated whether the polarity of the layer selection gradient needs to be reversed. Of course, in another embodiment, only one signal pre-acquisition can be performed on the scanning object, and the result of this single signal pre-acquisition can be used as the pre-acquisition signal.

[0067] Please see Figure 3 , Figure 3 This is a one-dimensional projection diagram of a pre-acquisition signal provided in one embodiment of this application. In one embodiment, step S20, determining the relative position between the region of interest and a specific tissue region based on the pre-acquisition signal, includes:

[0068] Reconstruct the pre-acquired signal to obtain the pre-acquired image;

[0069] The pre-acquired image is projected along a set direction to obtain a projected image;

[0070] The positions of the region of interest and the feature tissue region in the spectral pre-acquisition field of view are determined based on the projected image.

[0071] Determine the position of the pre-acquired signal within the spectral pre-acquired field of view (the field of view of the pre-acquired signal). For example... Figure 3 As shown, a reconstructed image is obtained by performing one-dimensional Fourier reconstruction on the pre-acquired signal. The image is described by the position of the projection image of the reconstructed image corresponding to the pre-acquired signal within the field of view of the pre-acquired signal. In this embodiment, the center of the field of view of the pre-acquired signal coincides with the center of the spectral acquisition field of view. The positional relationship between the center of the pre-acquired signal's field of view and the scanned object can be determined by the positional relationship between the center of the spectral acquisition field of view and the scanned object.

[0072] In one-dimensional space, there exists a first distance and a second distance between the boundary of the pre-acquisition signal and the boundary of the spectral pre-acquisition field of view. The first distance is the distance from the left boundary of the pre-acquisition signal to the left boundary of the spectral pre-acquisition field of view. The second distance is the distance from the right boundary of the pre-acquisition signal to the right boundary of the spectral pre-acquisition field of view. The center of the spectral pre-acquisition field of view coincides with the center of the spectral acquisition field of view. The range of the spectral pre-acquisition field of view may or may not coincide with the range of the spectral acquisition field of view.

[0073] If the first distance is greater than the second distance, then the center point of the spectral acquisition field of view is located near the left side of the boundary of the scanned object.

[0074] If the first distance is less than the second distance, then the center point of the spectral acquisition field of view is located near the right side of the boundary of the scanned object.

[0075] In this embodiment, specifically as follows: Figure 3 As shown, the pre-acquisition signal applies the readout gradient to the three logical coordinate axes RO, PE, and SS. The following explanation uses one direction as an example; for ease of description, the direction of the readout gradient is denoted as the x-axis (in a specific embodiment, it may be the RO axis, PE axis, or SS axis). The set direction is the direction of the readout gradient, which in a specific embodiment may be the RO axis, PE axis, or SS axis.

[0076] In one embodiment, determining the position of the region of interest in the spectral pre-acquisition field of view based on the projected image includes:

[0077] The projected image is processed using a set pixel threshold to determine the boundary of the scanned object;

[0078] The location of the region of interest in the spectral pre-acquisition field of view is determined based on the boundary of the scanned object.

[0079] The pre-acquisition field of view (FOV) is a bounded acquisition area. Reconstruction (Fourier reconstruction) of the pre-acquisition signal yields a pre-acquisition image; a one-dimensional projection of the pre-acquisition image along a predetermined direction obtains a projected image. Using the center point O of the pre-acquisition field of view as the center, and processing the projected image with a predetermined pixel threshold, the distances x1 and x2 from the boundary of the scanned object (object) to the boundary of the pre-acquisition field of view can be obtained. If x1 > x2, then point O is closer to the left side of the object, meaning the center of the pre-acquisition field of view is closer to the left side of the object. If x1 < x2, then point O is closer to the right side of the object, meaning the center of the pre-acquisition field of view is closer to the right side of the object. Therefore, the position of the region of interest within the pre-acquisition field of view is determined based on the projected image.

[0080] Please see Figure 4 and Figure 5 In one embodiment, step S30, determining the chemical shift direction of the fat based on the gradient parameters of the spectral sequence to be scanned, includes:

[0081] When the gradient polarity of the spectral sequence to be scanned is positive, the chemical shift direction of fat is the coding direction with a relatively higher gradient intensity; when the gradient polarity of the spectral sequence to be scanned is negative, the chemical shift direction of fat is also the coding direction with a relatively higher gradient intensity.

[0082] For example, taking the selection of gradient direction at different levels as an example, the resonant frequency of protons in water can be expressed as:

[0083] f1=(γ / 2π)·Gx1

[0084] The resonant frequency of protons in water can be expressed as:

[0085] f2=(γ / 2π)·Gx2-f cs

[0086] Where γ represents the magnetic separation ratio; Gx represents the gradient value along the x-direction of the layer selection gradient, Gx1 corresponds to the gradient intensity of water proton excitation, and Gx2 corresponds to the gradient intensity of adipose proton excitation; f cs It is a fixed value, specifically determined by the strength of the main magnetic field; 3T corresponds to f. cs It is 440Hz.

[0087] This embodiment uses the example where the first distance is greater than the second distance. If the first distance is greater than the second distance, the center point of the spectral acquisition field of view is located near the left side of the pre-acquired signal. It is also assumed that the region of interest in the spectrum is calculated using the water signal frequency, i.e., the interface parameter "chemical shift" is set to 4.7 ppm.

[0088] In one embodiment, determining whether to change the gradient parameters of the spectral sequence to be scanned, based on the chemical shift direction of fat and the relative position between the region of interest and the specific tissue region, may include: if the chemical shift direction of fat causes the fat in the specific tissue region to be outside the excitation range of the spectral sequence to be scanned, then there is no need to change the gradient parameters of the spectral sequence to be scanned; if the chemical shift direction of fat causes the fat in the specific tissue region to be within the excitation range of the spectral sequence to be scanned, then the gradient parameters of the spectral sequence to be scanned need to be changed.

[0089] In another embodiment, determining whether the gradient parameters of the spectral sequence to be scanned need to be changed based on the chemical shift direction of fat and the relative position between the region of interest and the specific tissue region may include: if the chemical shift direction of fat points towards the region of interest, or the chemical shift direction of fat is consistent with the direction in which the specific tissue region moves towards the region of interest, then the gradient parameters of the spectral sequence to be scanned do not need to be changed; if the chemical shift direction of fat is away from the region of interest, or the chemical shift direction of fat is opposite to the direction in which the specific tissue region moves towards the region of interest, then the gradient parameters of the spectral sequence to be scanned need to be changed.

[0090] Figure 4 This is a schematic diagram of spectral excitation under a positive polarity gradient. When an excitation pulse is applied within the VOI, Figure 4The thick solid line represents the activation region for water signals, while the dashed line represents the activation region for fat. The fat activation region is biased to the right, corresponding to... Figure 3 On the right side of the image, the fat excitation location is biased towards the center of the object. In this case, the polarity of the corresponding layer selection gradient in the spectral acquisition remains unchanged. There is an assumption here: fat only exists on the boundaries of the scanned object (or the imaging object), and the central region of the scanned object (or the imaging object) is fat-free. This assumption holds true in actual head imaging because fat is often found within the skull, which forms the boundary of the head. If the layer selection gradient is as follows... Figure 5 As shown, Figure 5 Schematic diagram of spectral excitation under negative polarity gradient. Figure 5 The thick solid line represents the activation region for water signals, while the dashed line represents the activation region for fat. The fat activation region is biased to the left, corresponding to... Figure 3 On the left side of the image, the fat excitation location is biased towards the object boundary. In this case, it's necessary to change the corresponding layer gradient polarity in the spectral acquisition. This will change the actual spectral acquisition gradient polarity to... Figure 4 This prevents the fat regions at the boundary from being excited by the excitation pulse.

[0091] In one embodiment, S40 includes:

[0092] Based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, it is determined whether the execution of the spectral sequence to be scanned will excite the fat in the specific tissue region.

[0093] In response to the execution of the spectral sequence to be scanned, fat in the specific tissue region is excited, thereby altering the gradient parameters of the spectral sequence to be scanned; or,

[0094] In response to the fact that the execution of the spectral sequence to be scanned does not excite the fat in the specific tissue region, the gradient parameters of the spectral sequence to be scanned remain unchanged.

[0095] If the chemical shift of the fat causes the excitation of the fat to be biased towards a specific tissue region, then the gradient polarity of the selected layer is reversed, and the spectral sequence to be scanned is executed again.

[0096] If the chemical shift of the fat causes the fat excitation to move away from the direction of a specific tissue region, then the gradient polarity of the selected layer remains unchanged, and the spectral sequence to be scanned is executed again.

[0097] In this embodiment, the gradient polarity of the selected layer includes: positive gradient polarity and negative gradient polarity. Reversing the gradient polarity of the selected layer means: converting positive gradient polarity to negative gradient polarity, or converting negative gradient polarity to positive gradient polarity.

[0098] In one embodiment, in step S40: the selected layers include three selected layers: Gss, Gro, and Gpe. When determining whether to change the gradient polarity of the selected layers, it is determined whether at least one of the three selected layers needs to reverse its gradient polarity. The gradient polarity includes positive polarity gradients (gradient strength gradually increases) and negative polarity gradients (gradient strength gradually decreases).

[0099] In this embodiment, to ensure accuracy, it is generally necessary to simultaneously determine whether the gradient polarity of all three selected layers needs to be reversed. In other cases, it is also possible to determine whether the gradient polarity of two of the three selected layers needs to be reversed, or to determine whether the gradient polarity of one of the three selected layers needs to be reversed.

[0100] In one specific embodiment, this application is used in magnetic resonance spectroscopy imaging. During spectral imaging localization, due to the chemical shift effect, the spatial positions of different metabolites excited may deviate. If the region of interest (ROI) is close to a specific tissue region, improper gradient polarity selection can lead to the excitation of fat signals outside the ROI. This excitation of fat signals severely contaminates the spectral lines, reducing spectral quality. In this application, by pre-acquiring data, it is determined whether the ROI is close to a specific tissue region. Then, based on the relative positions of the specific tissue region and the ROI, a reasonable gradient polarity is selected. This effectively avoids the excitation of fat signals outside the ROI, thereby reducing fat contamination and improving spectral quality.

[0101] The implementation process in this embodiment includes the following steps: (1) Before the execution of the spectral sequence to be scanned, a signal pre-acquisition of the scanned object is added to obtain a pre-acquisition signal; (2) The relative position of the region of interest and the specific tissue region is determined according to the pre-acquisition signal; (3) The layer selection gradient polarity is adjusted by the relative position of the specific tissue region and the region of interest; (4) The spectral sequence to be scanned is executed.

[0102] The specific implementation steps under the above-described specific implementation process may include:

[0103] Before spectral scanning, three signal pre-acquisitions are performed. The readout directions during the three pre-acquisitions are parallel to the SS, PE, and RO axes, respectively. The slice selection gradients during the three pre-acquisitions are perpendicular to the readout directions. A Fourier transform is performed on the obtained pre-acquisition signals to obtain the one-dimensional projections of the three slices of the scanned object onto the three logical axes. A threshold (the threshold of the spectral acquisition field of view) is set as the boundary of the one-dimensional projection of the scanned object, thereby determining the position of the scanned object (region of interest) relative to the center of the spectral acquisition field of view. The chemical shift direction of the fat in the region of interest is determined by the position of the scanned object (region of interest) relative to the center of the spectral acquisition field of view. The polarity of the slice selection gradient of the spectral sequence to be scanned is adjusted so that the fat region of interest is moved away from the boundary of the specific tissue region.

[0104] Please see Figure 6 , Figure 6 This is a sequence diagram of a pre-acquisition signal provided in one embodiment of this application. Figure 6 In this context, RF represents the applied radio frequency pulse, Gss represents the selected gradient direction, Gro represents the readout gradient direction, and ADC represents the acquisition window for the generated echo signal. Figure 7 This is a schematic diagram after spectral scanning, in which positioning frames (large boxes in the figure) are set on three positioning images (sagittal, coronal and transverse), which determine the coding region or imaging field of view; the small boxes in the figure are the imaging regions or regions of interest of the spectral sequence to be scanned. Figure 8 This is a schematic diagram of the spectral scanning results obtained using the existing fixed gradient polarity method (the left image shows the spectral lines of voxel 1, and the right image shows the spectral lines of voxel 2). Figure 9 The images show schematic diagrams of spectral scanning results obtained using the spectral imaging method described in this application (left image shows the spectral lines of voxel 1, right image shows the spectral lines of voxel 2). In both images, the horizontal axis represents the frequency position in ppm; the vertical axis represents the relative intensity of the peak value. The peak height and area under the peak value reflect the presence and content of a certain compound. (Comparison) Figure 8 and Figure 9 It can be seen that in the selection Figure 7 Given that voxel 1 and voxel 2 are two identical voxels, Figure 8 Because a fixed gradient polarity is used, the signal in the interference region is excited and collected, resulting in multiple interference peaks, making it impossible to effectively distinguish the target metabolites. Figure 9 The peak value of the target metabolite can be clearly determined without the influence of interfering metabolites.

[0105] This application also provides a magnetic resonance imaging system, including: a pre-acquisition device, a position determination device, a chemical shift determination device, a feedback device, and a sequence adjustment device.

[0106] The pre-acquisition device is used to pre-acquire signals from the scanned object to obtain pre-acquisition signals.

[0107] The location determination device is connected to the pre-acquisition device and is used to determine the relative position between the region of interest and a specific tissue region, which contains fat, based on the pre-acquisition signal.

[0108] The chemical shift determining device is connected to the position determining device and is used to determine the chemical shift direction of the fat based on the gradient polarity of the spectral sequence to be scanned.

[0109] The feedback device is connected to the chemical displacement determining device and is used to generate a feedback command based on the chemical displacement direction of the fat and the relative position between the region of interest and a specific tissue region. The feedback command is to adjust the gradient parameters.

[0110] The sequence adjustment device is connected to the feedback device and is used to adjust the gradient parameters of the spectral sequence to be scanned according to the feedback command.

[0111] In this embodiment, the magnetic resonance imaging system includes a pre-acquisition device, a position determination device, a chemical shift determination device, a feedback device, and a sequence adjustment device. The magnetic resonance imaging system uses the pre-acquisition device to pre-acquire signals from the scanned object, obtaining pre-acquisition signals. The position determination device determines the relative position between the region of interest and a specific tissue region. The chemical shift determination device determines the chemical shift direction of the fat. The feedback device generates feedback instructions to adjust gradient parameters. The sequence adjustment device adjusts the gradient parameters of the spectral sequence to be scanned according to the feedback instructions. The magnetic resonance imaging system includes the pre-acquisition device, adding a signal pre-acquisition step. The magnetic resonance imaging system uses the position determination device to determine the relative position between the region of interest and the specific tissue region, thereby predicting the chemical shift direction of the fat and ultimately deciding whether to change the gradient polarity of the spectral sequence to be scanned in the spectral imaging. The magnetic resonance imaging system can minimize fat excitation, reduce contamination, and improve spectral quality without moving the region of interest.

[0112] This application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of any of the methods described above.

[0113] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described above.

[0114] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0115] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A spectral imaging method, characterized in that, include: S10, Pre-acquisition of signals from the scanned object to obtain the pre-acquisition signal; S20, based on the pre-acquisition signal, determine the relative position between the region of interest and a specific tissue region, wherein the specific tissue region contains fat; S30, determine the chemical shift direction of the fat based on the gradient parameters of the spectral sequence to be scanned; S40, based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, determine whether it is necessary to change the gradient parameters of the spectral sequence to be scanned, and then execute the spectral sequence to be scanned or the spectral sequence to be scanned with the gradient parameters changed. In step S10, the step of pre-acquiring signals from the scanned object includes: S110, determine the direction of the selected layer gradient and the direction of the readout gradient of the scanned object; S120, apply a radio frequency pulse to the scanned object, and apply the layer selection gradient at the same time as the radio frequency pulse is applied; S130, after the layer selection gradient, a frequency coding gradient is applied along the direction of the readout gradient and the pre-acquisition signal is acquired at the same time as the frequency coding gradient is applied; In step S40, the step of determining whether to change the gradient parameters of the spectral sequence to be scanned based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region includes: Based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region, it is determined whether the execution of the spectral sequence to be scanned will excite the fat in the specific tissue region. In response to the execution of the spectral sequence to be scanned, fat in the specific tissue region is excited, thereby altering the gradient parameters of the spectral sequence to be scanned; or, In response to the fact that the execution of the spectral sequence to be scanned does not excite the fat in the specific tissue region, the gradient parameters of the spectral sequence to be scanned remain unchanged.

2. The spectral imaging method according to claim 1, characterized in that, When performing S110 to S130, the direction of the readout gradient determined in S110 is parallel to at least one of the layer selection gradient axis, the phase encoding gradient axis, and the frequency encoding gradient axis.

3. The spectral imaging method according to claim 1, characterized in that, In step S20, the step of determining the relative position between the region of interest and a specific tissue region based on the pre-acquired signal includes: Reconstruct the pre-acquired signal to obtain the pre-acquired image; The pre-acquired image is projected along a set direction to obtain a projected image; The location of the region of interest in the spectral pre-acquisition field of view is determined based on the projected image.

4. The spectral imaging method according to claim 3, characterized in that, Determining the position of the region of interest in the pre-acquisition field of view based on the projected image includes: The projected image is processed using a set pixel threshold to determine the boundary of the scanned object; The position of the region of interest in the spectral pre-acquisition field of view is determined based on the boundary of the scanned object.

5. The spectral imaging method according to any one of claims 1-4, characterized in that, In step S40, the gradient parameter of the spectral sequence to be scanned is the gradient polarity of the spectral sequence to be scanned.

6. The spectral imaging method according to any one of claims 1-4, characterized in that, The specific organizational region is located outside the region of interest.

7. A magnetic resonance imaging system, characterized in that, include: A pre-acquisition device is used to pre-acquire signals from the scanned object to obtain pre-acquisition signals; A location determination device, connected to the pre-acquisition device, is used to determine the relative position between a region of interest and a specific tissue region, wherein the specific tissue region contains fat, based on the pre-acquisition signal. A chemical shift determination device, connected to the position determination device, is used to determine the direction of chemical shift of the fat based on the gradient polarity of the spectral sequence to be scanned. A feedback device, connected to the chemical displacement determining device, is used to generate a feedback command based on the chemical displacement direction of the fat and the relative position between the region of interest and a specific tissue region. The feedback command is to adjust the gradient parameters. as well as A sequence adjustment device, connected to the feedback device, is used to adjust the gradient parameters of the spectral sequence to be scanned according to the feedback command; The pre-acquisition device is used to determine the direction of the layer selection gradient and the direction of the readout gradient of the scanned object; apply an radio frequency pulse to the scanned object, and apply the layer selection gradient at the same time as the radio frequency pulse is applied; after the layer selection gradient, apply a frequency encoding gradient along the direction of the readout gradient, and acquire the pre-acquisition signal at the same time as the frequency encoding gradient is applied; The feedback device is configured to determine whether the execution of the spectral sequence to be scanned will excite the fat in the specific tissue region based on the chemical shift direction of the fat and the relative position between the region of interest and the specific tissue region; in response to the execution of the spectral sequence to be scanned exciting the fat in the specific tissue region, the gradient parameters of the spectral sequence to be scanned are changed; or, in response to the execution of the spectral sequence to be scanned not exciting the fat in the specific tissue region, the gradient parameters of the spectral sequence to be scanned are kept unchanged.

8. The magnetic resonance imaging system according to claim 7, characterized in that, The direction of the readout gradient determined by the pre-acquisition device is parallel to at least one of the layer selection gradient axis, phase encoding gradient axis, and frequency encoding gradient axis.

9. The magnetic resonance imaging system according to claim 7, characterized in that, The position determination device is used to reconstruct the pre-acquisition signal and acquire a pre-acquisition image; project the pre-acquisition image along a set direction to acquire a projected image; and determine the position of the region of interest in the spectral pre-acquisition field of view based on the projected image.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

Images