CN113534032B - Magnetic resonance imaging method and system - Google Patents

Abstract

The embodiment of the invention discloses a magnetic resonance imaging method and system. The method includes: using a preset imaging sequence to simultaneously excite multiple layers of a scanning object, and acquiring multi-layer aliasing magnetic resonance signals of the scanning object, wherein the preset imaging sequence is set at a preset time point of a slice selection gradient There is a preset gradient peak to realize the interlayer preset field of view offset of the multilayer aliasing magnetic resonance signal in the image domain, and the preset time point is the excitation pulse in the radio frequency pulse and the first refocusing Between pulses and between any two refocusing pulses; performing interlayer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signal to generate a magnetic resonance image of each layer of the scanning object. Through the above technical solution, the de-aliasing of multi-layer aliasing signals for simultaneous multi-layer excitation imaging is realized, and the de-aliasing efficiency and image signal-to-noise ratio are improved.

Description

Magnetic resonance imaging method and system

technical field

Embodiments of the present invention relate to magnetic resonance technology, and in particular to a magnetic resonance imaging method and system.

Background technique

In order to improve the data acquisition efficiency of magnetic resonance, the current magnetic resonance imaging technology has a simultaneous multi-slice excitation imaging technology (Simultaneous Multi-Slice, SMS), which allows several slices of the scanning object to be excited at the same time. However, the acquired data obtained by this imaging technique is aliased in multiple slices, and the magnetic resonance image reconstructed directly using the acquired data is also aliased in multiple layers, and the signal-to-noise ratio of the image is low, which cannot meet the clinical needs.

Contents of the invention

Embodiments of the present invention provide a method and system for magnetic resonance imaging, so as to realize de-aliasing of multi-layer aliased signals in simultaneous multi-layer excitation imaging, and improve de-aliasing efficiency and image signal-to-noise ratio.

In a first aspect, an embodiment of the present invention provides a magnetic resonance imaging method, including:

Using a preset imaging sequence to simultaneously excite multiple layers of the scanning object, and acquire multi-layer aliasing magnetic resonance signals of the scanning object, wherein the preset imaging sequence is provided with a preset gradient at a preset time point of the slice selection gradient a sharp peak, so as to realize the interlayer preset field of view offset of the multilayer aliasing magnetic resonance signal in the image domain, and the preset time point is between the excitation pulse and the first refocusing pulse in the radio frequency pulse, and Between any two refocusing pulses;

Interlayer de-aliasing and image reconstruction are performed on the multi-layer aliased magnetic resonance signal to generate a magnetic resonance image of each layer of the scanning object.

In the second aspect, the embodiment of the present invention also provides a magnetic resonance imaging method, including:

Determining a region to be detected of the scanned object within the scanning field of view, the region to be detected includes multiple layers;

Acquiring the distance between at least two adjacent slices in the multiple slices;

A spin echo sequence is used to simultaneously excite the at least two adjacent slices, and during the execution of the spin echo sequence, a first preset gradient spike and a second preset gradient peak with different gradient moments are successively applied to the slice selection gradient. A gradient peak is set, wherein the gradient moments of the first preset gradient peak and the second preset gradient peak are determined according to the distance between the at least two adjacent slices, and the first preset gradient peak and the second application of a predetermined gradient spike causes a shift in the scanning field of view;

The receiving coils are used to acquire multi-layer aliased magnetic resonance signals of the at least two adjacent slices, and a magnetic resonance image of each slice of the scanning object is generated according to the multi-layer aliased magnetic resonance signals.

In a third aspect, an embodiment of the present invention also provides a magnetic resonance imaging system, which includes:

an MRI scanning device, and a processor communicatively connected to the MRI scanning device;

The MRI scanning device is configured to use a preset imaging sequence to simultaneously excite multiple layers of the scanning object, and acquire multi-layer aliasing magnetic resonance signals of the scanning object, wherein the preset imaging sequence selects a preset gradient in a slice A preset gradient peak is set at the time point to realize the interlayer preset field of view offset of the multilayer aliasing magnetic resonance signal in the image domain, and the preset time point is between the excitation pulse in the radio frequency pulse and the first Between a refocusing pulse and between any two refocusing pulses;

The processor is configured to perform inter-layer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signals to generate magnetic resonance images of each layer of the scanning object.

In a fourth aspect, an embodiment of the present invention also provides a magnetic resonance imaging system, which includes:

an MRI scanning device, and a processor communicatively connected to the MRI scanning device;

The MRI scanning device is used for:

Determining a region to be detected of the scanned object within the scanning field of view, the region to be detected includes multiple layers;

Acquiring the distance between at least two adjacent slices in the multiple slices;

A spin echo sequence is used to simultaneously excite the at least two adjacent slices, and during the execution of the spin echo sequence, a first preset gradient spike and a second preset gradient peak with different gradient moments are successively applied to the slice selection gradient. A gradient peak is set, wherein the gradient moments of the first preset gradient peak and the second preset gradient peak are determined according to the distance between the at least two adjacent slices, and the first preset gradient peak and the second application of a predetermined gradient spike causes a shift in the scanning field of view;

acquiring multilayer aliased magnetic resonance signals of the at least two adjacent slices by using a receiving coil;

The processor is configured to generate a magnetic resonance image of each slice of the scanning object according to the multi-layer aliased magnetic resonance signals.

In the embodiment of the present invention, the multi-layer aliasing magnetic resonance signals of the scanned object are acquired by using a preset imaging sequence to simultaneously excite the multiple layers of the scanned object, wherein the preset imaging sequence is set with a preset Gradient peaking to realize the interlayer preset field of view offset of multilayer aliasing magnetic resonance signals in the image domain, and the preset time point is between the excitation pulse and the first refocusing pulse in the radio frequency pulse and any two Between refocusing pulses; inter-layer de-aliasing and image reconstruction are performed on multi-layer aliasing magnetic resonance signals to generate magnetic resonance images of each layer of the scanning object. In the process of magnetic resonance scanning, by applying preset gradient peaks with different gradient distances to the slice selection gradient of the preset imaging sequence, the preset field of view between layers is shifted, thereby increasing the sensitivity difference between layers, and the multi-layer The aliased magnetic resonance signal is dealiased to improve the anti-aliasing efficiency and the signal-to-noise ratio of the magnetic resonance image.

Description of drawings

FIG. 1 is a flowchart of a magnetic resonance imaging method in Embodiment 1 of the present invention;

2 is a flowchart of a method for generating a preset imaging sequence in a magnetic resonance imaging method in Embodiment 2 of the present invention;

FIG. 3 is a schematic diagram of a preset imaging sequence in Embodiment 2 of the present invention;

Fig. 4 is a flowchart of a magnetic resonance imaging method in Embodiment 3 of the present invention;

FIG. 5 is a schematic structural diagram of a magnetic resonance imaging system in Embodiment 4 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention. In addition, it should be noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings but not all structures.

Embodiment one

The magnetic resonance imaging method provided in this embodiment is applicable to simultaneous multi-layer excitation magnetic resonance imaging. The method can be executed by a magnetic resonance imaging system, and the system can be realized by software and/or hardware. For example, the processes of sequence design, scanning control and signal processing can be realized by software, but the magnetic resonance scanning of the scanning object is realized by the magnetic resonance scanning device. Referring to Fig. 1, the method of the present embodiment specifically includes the following steps:

S110. Use a preset imaging sequence to simultaneously excite multiple layers of the scanning object, and acquire multi-layer aliasing magnetic resonance signals of the scanning object, wherein the preset imaging sequence is provided with a preset gradient peak at a preset time point of the slice selection gradient, In order to realize the interlayer preset field of view offset of multilayer aliasing magnetic resonance signals in the image domain, the preset time point is between the excitation pulse in the radio frequency pulse and the first refocusing pulse and any two refocusing pulses between.

Wherein, the preset imaging sequence refers to a preset pulse sequence used for magnetic resonance data acquisition, for example, it may be a fast spin echo sequence FSE. Preset gradient blips are gradient blips with a preset gradient pitch and a preset gradient waveform. The preset field of view shift between layers refers to a preset field of view shift (FOV shift) between layers, or an image shift of adjacent layers.

Specifically, in order to increase the scanning speed of the magnetic resonance, a simultaneous multi-slice excitation (Simultaneous Multi-Slice, SMS) scanning technology may be used to excite multiple layers of the scanning object to acquire magnetic resonance signals at the same time. However, the magnetic resonance signal obtained by multi-layer excitation scanning at the same time (that is, the multi-layer aliased magnetic resonance signal) is the multi-layer magnetic resonance signal mixed together, which needs to be de-aliased (separate the signals of different layers) to Magnetic resonance signals are obtained for each layer. The basis for de-aliasing between layers in magnetic resonance technology is that the coil sensitivities of the receiving coils of different layers are different, and there is a sufficient difference in coil sensitivity between layers. However, in actual scanning, due to the small distance between two adjacent layers or the few receiving coils arranged along the layer selection direction, the difference in sensitivity matrix between layers (that is, the difference in sensitivity between layers) will be small, which cannot be achieved. Nicely de-aliases.

In the embodiment of the present invention, in order to improve the anti-aliasing efficiency and the image signal-to-noise ratio of subsequent reconstructed images, the magnetic resonance scanning sequence is specially designed, that is, different gradient distances are added at different positions on the slice selection gradient of the imaging sequence Preset gradient spikes to form a preset imaging sequence. The setting of these preset gradient peaks can realize the inter-layer preset field of view offset between layers in the image domain of the magnetic resonance signal obtained by subsequent scanning, and the inter-layer preset field of view offset can ensure that the layers and There is a sufficient inter-layer sensitivity difference between the layers, so that the inter-layer sensitivity difference can be used to de-alias the obtained multi-layer aliased magnetic resonance signals well.

The adding position of the preset gradient peak corresponds to the preset time point, and the preset time point is between the excitation pulse and the first refocusing pulse or between any two refocusing pulses in the radio frequency pulse RF. Exemplarily, the preset time point is set before the signal acquisition window, and odd-numbered phase encoding positions in the phase encoding direction may be sampled. The preset time point is set after the signal acquisition window, and the even-numbered phase encoding positions in the phase encoding direction can be sampled. After the preset imaging sequence is designed, the preset imaging sequence is used to simultaneously excite multiple layers of the scanning object, and the receiving coil is used to collect magnetic resonance signals to obtain multi-layer mixed magnetic resonance signals.

S120. Perform interlayer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signal to generate a magnetic resonance image of each layer of the scanning object.

Specifically, the inter-layer sensitivity difference corresponding to the inter-layer preset field of view offset is used to perform de-aliasing processing on the multi-layer aliased magnetic resonance signal to obtain a de-aliased single-layer magnetic resonance signal. Afterwards, the image reconstruction algorithm is used to reconstruct the magnetic resonance signal of the single layer, so as to obtain the magnetic resonance image of each layer.

Exemplarily, performing interlayer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signal, and generating the de-aliased image of each layer of the scanned object includes: filling the multi-layer aliased magnetic resonance signal into K space, obtaining the aliasing K-space data; based on the inter-layer sensitivity difference corresponding to the inter-layer preset field of view offset, the inter-layer de-aliasing of the aliased K-space data is performed to generate the de-aliased K-space data of each layer of the scanning object; The K-space data is aliased for image reconstruction to obtain magnetic resonance images of each layer of the scanned object.

Specifically, the process of obtaining a magnetic resonance image may be as follows: first, the multi-layer aliased magnetic resonance signal is filled into the K space after a certain conversion (including phase encoding and frequency encoding), and the K space data of the signal aliasing (that is, the aliasing Stacked K-space data). Then, inter-layer de-aliasing is performed on the data on the aliased K-space by using the inter-layer sensitivity difference to obtain the de-aliased K-space data (ie, de-aliased K-space data) of each layer. Afterwards, according to the selected image reconstruction algorithm, corresponding reconstruction processing is performed on the de-aliased K-space data of each layer to generate a magnetic resonance image of each layer. Exemplarily, the split-slice GRAPPA algorithm, the parallel reconstruction algorithm (SENSE) and the like may be used to perform inter-layer de-aliasing on the data on the aliased K-space by using the inter-layer sensitivity difference.

In the technical solution of this embodiment, the multilayer aliasing magnetic resonance signals of the scanned object are collected by using a preset imaging sequence to simultaneously excite the multiple layers of the scanned object, wherein the preset imaging sequence is set at a preset time point of the slice selection gradient There are preset gradient peaks to realize the interlayer preset field of view offset of multilayer aliasing magnetic resonance signals in the image domain, and the preset time point is between the excitation pulse and the first refocusing pulse in the radio frequency pulse and Between any two refocusing pulses; inter-layer de-aliasing and image reconstruction are performed on the multi-layer aliased magnetic resonance signal to generate a magnetic resonance image of each layer of the scanning object. In the process of magnetic resonance scanning, by applying preset gradient peaks with different gradient distances to the slice selection gradient of the preset imaging sequence, the preset field of view between layers is shifted, thereby increasing the sensitivity difference between layers, and the multi-layer The aliased magnetic resonance signal is dealiased to improve the anti-aliasing efficiency and the signal-to-noise ratio of the magnetic resonance image.

On the basis of the above technical solution, using the preset imaging sequence to simultaneously excite the multiple layers of the scanning object, and collecting the multi-layer aliased magnetic resonance signals of the scanning object includes: based on the undersampling method, using the preset imaging sequence to simultaneously excite the multiple layers of the scanning object layer, to acquire multi-layer aliased magnetic resonance signals of the scanned object.

Specifically, in order to further increase the scanning speed of magnetic resonance, in the embodiment of the present invention, when acquiring multi-layer mixed magnetic resonance signals, it is possible to perform intra-layer scanning acceleration on the basis of multi-layer simultaneous excitation scanning combined with under-sampling scanning mode , to obtain undersampled multilayer aliased magnetic resonance signals within each layer.

Correspondingly, when each layer of the multi-layer aliased magnetic resonance signal is under-sampled, the de-aliased K-space data of each layer obtained by de-aliasing the multi-layer aliased magnetic resonance signal is the under-sampled de-aliasing K-space data.

On the basis of the above technical solution, image reconstruction is performed on the K-space data of each layer, and obtaining the magnetic resonance image of each layer of the scanning object includes: obtaining the coil sensitivity distribution map of the receiving coil; The sampled de-aliased K-space data is recovered to generate full-sampled K-space data corresponding to the under-sampled de-aliased K-space data; image reconstruction is performed based on each fully-sampled K-space data, and magnetic resonance images of each layer of the scanned object are obtained.

Specifically, for the under-sampled magnetic resonance signals in the layer, if the magnetic resonance image reconstruction is to be performed, it is necessary to fill the under-sampled K-space data first. To accurately populate k-space data, the coil sensitivity profile of the receiving coil can be utilized. This is because the receiving coil of magnetic resonance is a phased array coil, which is composed of multiple sub-coils in a certain array, and the sensitivity of each sub-coil constitutes a coil sensitivity array. The higher the degree, the stronger the signal strength in the k-space data. Therefore, the unsampled data in K space can be calculated by using the coil sensitivity distribution map and the under-sampled de-aliasing K-space data, and filled into the corresponding position in K-space to obtain the under-sampled de-aliasing of this layer The fully sampled K-space data corresponding to the K-space data. Afterwards, image reconstruction is performed on the fully sampled K-space data to obtain a magnetic resonance image of the layer.

The coil sensitivity distribution map here can be pre-existing data, or can be obtained by adding a low-resolution reference scan before the formal scan. For example, the detection area is excited, and a low-resolution, full FOV reference image of the detection area is obtained by using the body coil of the magnet itself; each receiving coil collects images of multiple receiving coils in the detection area respectively, and then the images of each receiving coil The images are divided by the reference image one by one to obtain the coil sensitivity distribution map of each receiving coil. The advantage of this setting is that it can not only further increase the scanning speed of magnetic resonance, save scanning time, but also improve the signal-to-noise ratio of the image.

Embodiment two

In this embodiment, on the basis of the first embodiment above, the "preset imaging sequence" is further optimized. The explanations of terms that are the same as or corresponding to the above-mentioned embodiments will not be repeated here. Referring to Figure 2, the method for generating a preset imaging sequence in the magnetic resonance imaging method provided in this embodiment includes:

S210. Determine a first preset gradient peak and a second preset gradient peak according to the preset field of view offset between layers.

Specifically, the inter-layer preset field of view offset is the phase offset of the scanned image in the phase encoding direction that the preset imaging sequence needs to achieve, so the value added to the imaging sequence can be calculated according to the inter-layer preset field of view offset The gradient distances of different preset gradient peaks, that is, the first preset gradient peak and the second preset gradient peak. The first preset gradient peak is set after the excitation pulse in the radio frequency pulse and before the refocusing pulse, and the first preset gradient peak is applied in the slice selection gradient direction to perform phase modulation on the K-space data line to cause the scanning object image field of view offset.

Exemplarily, S210 includes: determining the zero-order moment of the gradient according to the preset field of view offset between layers, and determining the first preset gradient peak and the second preset gradient peak according to the zero-order moment of the gradient.

Specifically, the preset field of view offset between layers and the zero-order distance of the gradient have the following relationship:

表示层间预设视场偏移对应的相位值，例如预设视场偏移为FOV/2，那么

为π；γ表示磁旋比，γ＝42.58·2·π·10⁶·T^-1；d表示层间距，即两个相邻的扫描片层之间的缝隙宽度，也可称为距离因子，例如10mm、20mm、50mm或者其他值。Among them, M represents the gradient zero step distance;

Indicates the phase value corresponding to the preset field of view offset between layers, for example, the preset field of view offset is FOV/2, then

is π; γ represents the magnetic gyro ratio, γ=42.58·2·π·10 ⁶ ·T ^-1 ; d represents the layer spacing, that is, the gap width between two adjacent scanning slices, which can also be called the distance factor , such as 10mm, 20mm, 50mm or other values.

为2π/3；预设视场偏移为FOV/4，那么

为π/2，即本申请实施例中对于预设视场偏移并无具体限制，具体可根据医师的设定确定。According to the formula (1), the zero-order moment of the gradient can be calculated according to the preset field of view offset between layers and the layer spacing. Then, 0.5M and M are respectively used as the first preset gradient spike and the second preset gradient spike. In other embodiments, when the preset field of view offset changes, the phase value corresponding to the preset field of view offset between layers will also change, for example, the preset field of view offset is FOV/3, then

is 2π/3; the preset field of view offset is FOV/4, then

is π/2, that is, there is no specific limitation on the preset field of view offset in the embodiment of the present application, which can be determined according to the setting of the physician.

S220. According to the preset phase encoding mode, determine a first preset time point between the excitation pulse of the radio frequency pulse and the first refocusing pulse, and determine a second preset time point between any two refocusing pulses of the radio frequency pulse point in time.

Wherein, the preset phase encoding mode refers to the phase encoding mode when data is filled in the K space, for example, it may be a random encoding mode, an odd (even) phase encoding mode, and the like.

Specifically, the adding position of the preset gradient spike on the slice selection gradient is related to the phase encoding mode of the scanning signal in K space, so when the preset phase encoding modes are different, the first preset gradient spike and the second preset gradient spike in the preset imaging sequence The addition positions of the two preset gradient peaks on the layer selection gradient also need to be correspondingly different. Referring to Fig. 3, the preset imaging sequence includes slice selection gradient, frequency gradient and phase encoding gradient, radio frequency pulse and signal acquisition window (ADC). One or more RF pulses with a flip angle of 180 degrees in time (referred to as refocusing pulses 304 ). On the slice selection gradient, multiple gradient spikes are applied. The first preset gradient peak 301 is at a first preset time point P0, and the first preset time point corresponds to between the excitation pulse 303 and the first refocusing pulse 304 of the radio frequency pulse. The second preset gradient peak 302 is at a second preset time point, and the second preset time point corresponds to every two refocusing pulses 304 of the radio frequency pulse. The specific position of the second preset gradient peak between the two refocusing pulses (that is, the second preset time point) depends on the preset phase encoding mode.

Exemplarily, according to the preset phase encoding mode, determining the second preset time point between any two refocusing pulses of the radio frequency pulse includes: between every two refocusing pulses, according to the preset phase encoding mode, at A second preset time point is determined between the previous focusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent focusing pulse of the radio frequency pulse.

Specifically, based on the non-overlapping sequence design requirements of phase encoding and readout encoding, between any two refocusing pulses, according to the difference in the preset phase encoding mode, the previous refocusing pulse and signal Select a time between the acquisition windows 305 (such as P11, P21 or P31), and between the signal acquisition window 305 and the last refocusing pulse of the two refocusing pulses (corresponding to P11, P21, P31 are P12, P22, P32) point as the second preset time point.

Exemplarily, according to the preset phase encoding mode, the second preset time is determined between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent refocusing pulse of the radio frequency pulse Points include: when the preset phase encoding mode is the random encoding mode, randomly between the previous focusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent focusing pulse of the radio frequency pulse, Determine the second preset time point.

Specifically, when the preset phase encoding mode is the random encoding mode, the second preset time point can be randomly determined as the position between two refocusing pulses, before or after the signal acquisition window, for example, the second preset time point in FIG. Suppose the time point can be randomly determined as P11 or P12, P21 or P22, P31 or P32.

Exemplarily, according to the preset phase encoding mode, the second preset time is determined between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent refocusing pulse of the radio frequency pulse The points include: when the preset phase encoding mode is the odd phase encoding mode, determine the second preset time point between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window; when the preset phase encoding mode is the even phase encoding mode , between the signal acquisition window and the next refocusing pulse of the radio frequency pulse, a second preset time point is determined.

Specifically, when the preset phase encoding mode is an odd encoding mode, the second preset time point is determined as the position between the previous refocusing pulse and the signal acquisition window 305, for example, the second preset time point in FIG. 3 is determined as P11, P21, P31. When the preset phase encoding mode is an even encoding mode, the second preset time point is determined as the position between the signal acquisition window 305 and the next refocusing pulse, for example, the second preset time point is determined as P12 and P22 in FIG. 3 , P32.

S230. In the slice selection gradient, add a first preset gradient peak to a first preset time point, and add a second preset gradient peak to each second preset time point.

Specifically, on the slice selection gradient of an imaging sequence (such as FSE), a first preset gradient peak of 0.5M is added to the first preset time point, and a second preset gradient peak is added to each second preset time point. Assuming a gradient peak M, a preset imaging sequence is generated.

In the technical solution of this embodiment, the first preset gradient peak and the second preset gradient peak are determined according to the preset field of view offset between layers; according to the preset phase encoding mode, between the excitation pulse of the radio frequency pulse and the first The first preset time point is determined between the focus pulses, and the second preset time point is determined between any two focus pulses of the radio frequency pulse; in the layer selection gradient, the first preset time point is added to the first preset time point. Preset gradient spikes, and add second preset gradient spikes to each second preset time point. It realizes adding the first preset gradient peak and the second preset gradient spike with different gradient distances to different positions in the gradient direction of the slice selection of the imaging sequence, generates a preset imaging sequence, and improves the subsequent multi-layer aliasing magnetic resonance The anti-aliasing efficiency of the signal.

Embodiment Three

The magnetic resonance imaging method provided in this embodiment is applicable to simultaneous multi-layer excitation magnetic resonance imaging. The method can be executed by a magnetic resonance imaging system, and the system can be realized by software and/or hardware. For example, the processes of sequence design, scanning control and signal processing can be realized by software, but the magnetic resonance scanning of the scanning object is realized by the magnetic resonance scanning device. The explanations of terms that are the same as or corresponding to the above-mentioned embodiments will not be repeated here.

Referring to Figure 4, the method of this embodiment specifically includes the following steps:

S310. Determine a to-be-detected region of the scanned object within the scanning field of view, where the to-be-detected region includes multiple slices.

Specifically, before the magnetic resonance scan is performed, the region to be detected in the scanning field of view is first determined, and the region to be detected includes two or more scanning slices, so that the magnetic resonance scan with simultaneous multi-layer excitation can be implemented subsequently. In one embodiment, the region to be detected in the scanning field of view can be selected by a positioning frame set by a doctor, or determined by an automatic recognition algorithm by a computer device. The method of obtaining the region to be detected is not specifically limited in this embodiment. Furthermore, the area to be detected usually contains multiple layers, which can be determined by setting the number of scanning layers and layer thickness by the doctor before the scanning is performed.

S320. Acquire the distance between at least two adjacent slices in the multi-slices.

Specifically, after the region to be detected is determined, the distance between every two adjacent slices (that is, the layer distance d) needs to be determined according to the set scanning parameters. Layer spacing refers to the gap width between two adjacent layers, such as 10mm, 20mm, 50mm or other values, which can also be called distance factor.

S330. Use the spin echo sequence to simultaneously excite at least two adjacent slices, and successively apply the first preset gradient peak and the second preset gradient with different gradient moments to the slice selection gradient during the execution of the spin echo sequence spikes, wherein the gradient moments of the first preset gradient spike and the second preset gradient spike are determined according to the spacing of at least two adjacent slices, and the application of the first preset gradient spike and the second preset gradient spike causes a scan Offset of field of view.

Specifically, a spin echo sequence is used to simultaneously excite scanning of at least two adjacent slices in the region to be detected. Due to the design of the scan sequence, during the execution of the spin echo sequence, the first preset gradient spike and the second preset gradient spike with different gradient distances are successively applied to the slice selection gradient of the scan sequence. The application of the two preset gradient peaks with different gradient distances will cause a relative displacement of the image in the phase encoding direction, that is, an offset of the preset field of view between layers in the image domain.

Exemplarily, determining the first preset gradient peak and the second preset gradient peak according to the distance between at least two adjacent slices includes: determining the zero-order moment of the gradient according to the distance between at least two adjacent slices, and The step moments determine a first preset gradient spike and a second preset gradient spike. Specifically, the first preset gradient peak 0.5M and the second preset gradient peak M can be obtained by calculating according to the formula (1) according to the phase value and the interlayer distance corresponding to the preset field of view offset between layers.

S340. Use the receiving coil to acquire multi-layer aliased magnetic resonance signals of at least two adjacent slices, and generate a magnetic resonance image of each slice of the scanning object according to the multi-layer aliased magnetic resonance signals.

Specifically, the receiving coil is used to collect the multi-layer aliased magnetic resonance signals, and the multi-layer aliased magnetic resonance signals are de-aliased using the inter-layer sensitivity difference corresponding to the inter-layer preset field of view offset. Afterwards, an image reconstruction algorithm is used to perform image reconstruction on the de-aliased magnetic resonance signals, to obtain a magnetic resonance image of each slice of the scanning object.

Optionally, applying the first preset gradient spike and the second preset gradient spike with different gradient moments on the slice selection gradient includes:

According to the preset phase encoding mode, the first preset time point is determined between the excitation pulse of the radio frequency pulse of the spin echo sequence and the first refocusing pulse, and the second time point is determined between any two refocusing pulses of the radio frequency pulse 2. preset time point;

In the slice selection gradient, a first preset gradient spike is added to the first preset time point, and a second preset gradient spike is added to each second preset time point.

Optionally, according to the preset phase encoding mode, determining the second preset time point between any two refocusing pulses of the radio frequency pulse includes:

Between every two refocusing pulses, according to the preset phase encoding mode, between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the next refocusing pulse of the radio frequency pulse, Determine the second preset time point.

Optionally, according to the preset phase encoding mode, a second preset time is determined between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the next refocusing pulse of the radio frequency pulse Points include:

When the preset phase encoding mode is the random encoding mode, randomly between the previous focusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent focusing pulse of the radio frequency pulse, determine the second preset time point.

Optionally, according to the preset phase encoding mode, a second preset time is determined between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the next refocusing pulse of the radio frequency pulse Points include:

When the preset phase encoding mode is an odd phase encoding mode, a second preset time point is determined between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window;

When the preset phase encoding mode is an even phase encoding mode, a second preset time point is determined between the signal acquisition window and the next refocusing pulse of the radio frequency pulse.

Optionally, generating the magnetic resonance image of each slice of the scanned object according to the multi-layer aliased magnetic resonance signal includes:

Fill the multi-layer aliased magnetic resonance signal into the K space to obtain the aliased K space data;

Based on the inter-layer sensitivity difference corresponding to the inter-layer preset field of view offset, inter-layer de-aliasing is performed on the aliased K-space data, and the de-aliased K-space data of each layer of the scanned object is generated;

Perform image reconstruction on each layer of de-aliased K-space data to obtain magnetic resonance images of each layer of the scanned object.

Optionally, simultaneously exciting at least two adjacent slices using a spin echo sequence comprises:

Based on the undersampling method, at least two adjacent slices are simultaneously excited by using the spin echo sequence;

Correspondingly, the dealiased K-space data is under-sampled dealiased K-space data.

Further, image reconstruction is performed on each layer of de-aliased K-space data, and obtaining magnetic resonance images of each layer of the scanned object includes:

Obtain the coil sensitivity distribution map of the receiving coil;

Restoring the under-sampled de-aliased K-space data of each layer according to the coil sensitivity distribution diagram, and generating the full-sampled K-space data of the corresponding under-sampled de-aliased K-space data;

Image reconstruction is performed according to the full-sampled K-space data, and magnetic resonance images of each layer of the scanning object are obtained.

In the technical solution of this embodiment, by determining the area to be detected of the scanning object in the scanning field of view, the area to be detected includes multiple slices; obtaining the distance between at least two adjacent slices in the multiple slices; using the spin echo sequence to simultaneously Exciting at least two adjacent slices, and successively applying a first preset gradient spike and a second preset gradient spike with different gradient moments on the slice selection gradient during the execution of the spin echo sequence, wherein the first preset The gradient moments of the gradient peak and the second preset gradient peak are determined according to the distance between at least two adjacent slices, and the application of the first preset gradient peak and the second preset gradient peak causes the offset of the scanning field of view; The coil collects multilayer aliased magnetic resonance signals of at least two adjacent slices, and generates a magnetic resonance image of each slice of the scanning object according to the multilayer aliased magnetic resonance signals. In the process of magnetic resonance scanning, by applying preset gradient peaks with different gradient distances to the slice selection gradient of the preset imaging sequence, the preset field of view between layers is shifted, thereby increasing the sensitivity difference between layers, and the multi-layer The aliased magnetic resonance signal is dealiased to improve the anti-aliasing efficiency and the signal-to-noise ratio of the magnetic resonance image.

Embodiment Four

This embodiment provides a magnetic resonance imaging system 500. Referring to FIG. 5, the system specifically includes: an MRI scanning device 510, and a processor 520 communicatively connected to the MRI scanning device 510;

The MRI scanning device 510 is configured to use a preset imaging sequence to simultaneously excite multiple layers of the scanning object, and acquire multi-layer aliasing magnetic resonance signals of the scanning object, wherein the preset imaging sequence is set at a preset time point of the layer selection gradient. Preset gradient peaks to realize interlayer preset field of view offset of multilayer aliasing magnetic resonance signals in the image domain, and preset time points are between the excitation pulse and the first refocusing pulse in the radio frequency pulse and any Between two refocusing pulses;

The processor 520 is configured to perform inter-layer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signal to generate a magnetic resonance image of each layer of the scanning object.

Of course, those skilled in the art can understand that the processor 520 can also implement the technical solution of the magnetic resonance imaging method provided by any embodiment of the present invention.

The magnetic resonance imaging system 500 shown in FIG. 5 is only an example, and should not limit the functions and application scope of the embodiments of the present invention. As shown in FIG. 5 , the magnetic resonance imaging system 500 further includes an output device 530 on the basis of the above technical solution.

The processor 520 can simultaneously monitor or control the MRI scanning device 510 and the output device 530 . The processor 520 may include a central processing unit (Central Processing Unit, CPU), an application-specific integrated circuit (Application-Specific Integrated Circuit, ASIC), a dedicated instruction processor (Application Specific Instruction Set Processor, ASIP), a graphics processing unit (Graphics Processing Unit , GPU), physical processor (Physics Processing Unit, PPU), digital signal processor (Digital Processing Processor, DSP), field-programmable gate array (Field-Programmable Gate Array, FPGA), ARM processor, etc. or a combination of several.

An output device 530, such as a display, may display the magnetic resonance image of the region of interest. Further, the output device 530 can also display the subject's height, weight, age, imaging site, and the working status of the MRI scanning device 510 . The type of output device 530 may be one or a combination of cathode ray tube (CRT) output device, liquid crystal output device (LCD), organic light emitting output device (OLED), plasma output device, etc.

The magnetic resonance imaging system 500 can be connected to a local area network (Local Area Network, LAN), wide area network (WideArea Network, WAN), public network, private network, proprietary network, public switched telephone network (Public Switched Telephone Network, PSTN), Internet, wireless network, virtual network, or any combination of the above.

The MRI scanning device 510 includes an MR signal acquisition module, an MR control module and an MR data storage module. Wherein, the MR signal acquisition module includes a magnet unit and a radio frequency unit. The magnet unit mainly includes a main magnet that generates a B0 main magnetic field and a gradient assembly that generates a gradient. The main magnet contained in the magnet unit can be a permanent magnet or a superconducting magnet. The gradient assembly mainly includes a gradient current amplifier (AMP) and a gradient coil. The gradient assembly can also include three independent channels Gx, Gy, and Gz. Each gradient amplifier excites A corresponding gradient coil in the gradient coil group generates a gradient field for generating a corresponding spatial encoding signal, so as to spatially locate the magnetic resonance signal. The radio frequency unit mainly includes a radio frequency transmitting coil and a radio frequency receiving coil. The radio frequency transmitting coil is used to transmit radio frequency pulse signals to the subject or the human body. The radio frequency receiving coil is used to receive the magnetic resonance signals collected from the human body. The RF coil of the unit can be divided into body coil and local coil. In one embodiment, the type of body coil or local coil may be a birdcage coil, a solenoid coil, a saddle coil, a Helmholtz coil, an array coil, a loop coil, or the like. In a specific embodiment, the local coil is configured as an array coil, and the array coil can be configured in a 4-channel mode, an 8-channel mode or a 16-channel mode. The magnet unit and the radio frequency unit can form an open low-field magnetic resonance device or a closed superconducting magnetic resonance device.

The MR control module can monitor the MR signal acquisition module and the MR data processing module including the magnet unit and the radio frequency unit. Specifically, the MR control module can receive information or pulse parameters sent by the MR signal acquisition module; in addition, the MR control module can also control the processing process of the MR data processing module. In one embodiment, the MR control module is also connected with a pulse sequence generator, a gradient waveform generator, a transmitter and a receiver, etc., and controls the magnetic field module to execute a corresponding scan sequence after receiving instructions from the console from the user.

Exemplarily, the specific process of generating MR data by the MRI scanning device 510 of the present invention includes: the main magnet generates a B0 main magnetic field, and the atomic nuclei in the subject generate a precession frequency under the action of the main magnetic field, and the precession frequency is positive to the strength of the main magnetic field The MR control module stores and sends the scan sequence (scan sequence) instructions that need to be executed, the pulse sequence generator controls the gradient waveform generator and the transmitter according to the scan sequence instructions, and the gradient waveform generator outputs a signal with a predetermined timing and waveform Gradient pulse signal, the signal passes through Gx, Gy and Gz gradient current amplifiers, and then passes through three independent channels Gx, Gy, Gz in the gradient component, and each gradient amplifier excites a corresponding gradient coil in the gradient coil group to generate Generate the gradient field of the corresponding spatially encoded signal to spatially locate the magnetic resonance signal; the pulse sequence generator also executes the scan sequence, and outputs data including timing, intensity, shape, etc. of the radio frequency pulse transmitted by the radio frequency and the timing and data acquisition of the radio frequency reception The length of the window reaches the transmitter, and at the same time, the transmitter sends the corresponding radio frequency pulse to the body transmitting coil in the radio frequency unit to generate the B1 field. Under the action of the B1 field, the signal from the excited nucleus in the patient's body is sensed by the receiving coil in the radio frequency unit , and then transmitted to the MR data processing module through the send/receive switch, after digital processing such as amplification, demodulation, filtering, and AD conversion, and then transmitted to the MR data storage module. When the MR data storage module acquires a set of original K-space data, the scanning ends. The original K-space data is rearranged into a separate K-space data group corresponding to each image to be reconstructed, and each K-space data group is input to the array processor for image reconstruction and combined with magnetic resonance signals to form a Group image data.

Through a magnetic resonance imaging system according to Embodiment 4 of the present invention, during the magnetic resonance scanning process, by applying preset gradient peaks with different gradient distances to the layer selection gradient of the preset imaging sequence, the preset field of view between layers is caused. Migration, thereby increasing the sensitivity difference between layers, de-aliasing multi-layer aliasing magnetic resonance signals, improving the efficiency of de-aliasing and the signal-to-noise ratio of magnetic resonance images.

The embodiment of the present invention also provides another magnetic resonance imaging system, which includes: an MRI scanning device, and a processor connected in communication with the MRI scanning device;

MRI scanning devices are used to:

Determining the area to be detected of the scanned object within the scanning field of view, where the area to be detected includes multiple layers;

obtaining the distance between at least two adjacent slices in the multi-slice;

Using the spin echo sequence to simultaneously excite at least two adjacent slices, and successively applying a first preset gradient spike and a second preset gradient spike with different gradient moments on the slice selection gradient during the execution of the spin echo sequence, Wherein, the gradient moment of the first preset gradient peak and the second preset gradient peak is determined according to the distance between at least two adjacent slices, and the application of the first preset gradient peak and the second preset gradient peak causes the scanning field of view offset;

acquiring multilayer aliased magnetic resonance signals of at least two adjacent slices by using a receiving coil;

The processor is configured to generate a magnetic resonance image of each slice of the scanning object according to the multi-layer aliased magnetic resonance signal.

Of course, those skilled in the art can understand that the processor can also implement the technical solution of the magnetic resonance imaging method provided by any embodiment of the present invention. For the hardware structure and functions of the magnetic resonance imaging system, please refer to the content explanation of the fourth embodiment.

Note that the above are only preferred embodiments of the present invention and applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments herein, and various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the present invention, and the present invention The scope is determined by the scope of the appended claims.

Claims (10)

1. A magnetic resonance imaging method, comprising:

simultaneously exciting multiple layers of a scanned object by using a preset imaging sequence, and acquiring multiple layers of aliasing magnetic resonance signals of the scanned object, wherein the preset imaging sequence is provided with a preset gradient peak at a preset time point of a slice selection gradient so as to realize interlayer preset field-of-view shift of the multiple layers of aliasing magnetic resonance signals on an image domain, and the preset time point is between an excitation pulse and a first refocusing pulse in a radio frequency pulse and between any two refocusing pulses;

and performing interlayer de-aliasing and image reconstruction on the multilayer aliasing magnetic resonance signals to generate magnetic resonance images of all layers of the scanning object.

2. The method according to claim 1, characterized in that the preset imaging sequence is pre-generated by:

determining a first preset gradient peak and a second preset gradient peak according to the interlayer preset field offset;

determining a first preset time point between an excitation pulse and a first refocusing pulse of the radio frequency pulse and determining a second preset time point between any two refocusing pulses of the radio frequency pulse according to a preset phase encoding mode;

in the aspect selection gradient, adding the first preset gradient peak to the first preset time point, and adding the second preset gradient peak to each of the second preset time points.

3. The method of claim 2, wherein determining a second predetermined time point between any two refocusing pulses of the rf pulse according to a predetermined phase encoding mode comprises:

and determining the second preset time point between every two refocusing pulses according to the preset phase coding mode, between the previous refocusing pulse of the radio frequency pulse and the signal acquisition window, or between the signal acquisition window and the subsequent refocusing pulse of the radio frequency pulse.

4. The method of claim 3, wherein determining the second predetermined time point between a previous echo pulse of the RF pulse and a signal acquisition window or between the signal acquisition window and a subsequent echo pulse of the RF pulse according to the predetermined phase encoding pattern comprises:

when the preset phase encoding mode is an odd phase encoding mode, determining a second preset time point between a previous refocusing pulse of the radio frequency pulse and a signal acquisition window;

and when the preset phase coding mode is an even phase coding mode, determining the second preset time point between the signal acquisition window and a backward echo pulse of the radio frequency pulse.

5. The method of claim 1, wherein performing inter-slice antialiasing and image reconstruction on the multi-slice aliased magnetic resonance signals to generate unaliased images of the scan object slices comprises:

filling the multilayer aliasing magnetic resonance signals into a K space, and acquiring aliasing K space data;

performing interlayer de-aliasing on the aliased K space data based on the interlayer sensitivity difference corresponding to the interlayer preset field offset to generate de-aliased K space data of each layer of the scanning object;

and carrying out image reconstruction on the de-aliasing K space data of each layer to obtain magnetic resonance images of each layer of the scanning object.

6. The method of claim 5, wherein simultaneously exciting multiple slices of the scan object with a preset imaging sequence, acquiring multiple slices of aliased magnetic resonance signals of the scan object comprises:

based on an undersampling mode, simultaneously exciting multiple layers of a scanning object by utilizing a preset imaging sequence, and acquiring multiple layers of aliasing magnetic resonance signals of the scanning object;

accordingly, the unaliased K-space data is undersampled unaliased K-space data.

7. The method of claim 6, wherein performing image reconstruction of each slice of the de-aliased K-space data to obtain magnetic resonance images of each slice of the scan object comprises:

acquiring a coil sensitivity distribution map of a receiving coil;

restoring the aliasing-removing K space data of each layer of undersampled data according to the coil sensitivity distribution map to generate fully sampled K space data of the corresponding undersampled aliasing-removing K space data;

and carrying out image reconstruction according to the fully sampled K space data to obtain magnetic resonance images of all layers of the scanning object.

8. A magnetic resonance imaging method, comprising:

determining a region to be detected of a scanning object in a scanning field of view, wherein the region to be detected comprises a plurality of slices;

acquiring the distance between at least two adjacent sheets in the multi-sheet;

simultaneously exciting the at least two adjacent slices by using a spin echo sequence, and successively applying a first preset gradient peak and a second preset gradient peak with different gradient moments on a slice selection gradient in the execution process of the spin echo sequence, wherein the gradient moments of the first preset gradient peak and the second preset gradient peak are determined according to the distance between the at least two adjacent slices, and the application of the first preset gradient peak and the second preset gradient peak causes the shift of the scanning visual field;

acquiring a plurality of layers of aliased magnetic resonance signals of the at least two adjacent slices by using a receiving coil, and generating a magnetic resonance image of each slice of the scanning object according to the aliased magnetic resonance signals.

9. A magnetic resonance imaging system, comprising: an MRI scanner, and a processor communicatively coupled to the MRI scanner;

the MRI scanning device is used for simultaneously exciting multiple layers of a scanned object by utilizing a preset imaging sequence and acquiring multiple layers of aliasing magnetic resonance signals of the scanned object, wherein the preset imaging sequence is provided with a preset gradient peak at a preset time point of a slice selection gradient so as to realize interlayer preset field-of-view shift of the multiple layers of aliasing magnetic resonance signals on an image domain, and the preset time point is between an excitation pulse and a first refocusing pulse in a radio frequency pulse and between any two refocusing pulses;

the processor is configured to perform inter-layer de-aliasing and image reconstruction on the multi-layer aliased magnetic resonance signals to generate magnetic resonance images of each layer of the scan object.

10. A magnetic resonance imaging system, comprising: an MRI scanner, and a processor communicatively coupled to the MRI scanner;

the MRI scanner is configured to:

determining a region to be detected of a scanning object in a scanning field of view, wherein the region to be detected comprises a plurality of layers of sheets;

acquiring the distance between at least two adjacent sheets in the multi-sheet;

simultaneously exciting the at least two adjacent slices by using a spin echo sequence, and successively applying a first preset gradient peak and a second preset gradient peak with different gradient moments on a slice selection gradient in the execution process of the spin echo sequence, wherein the gradient moments of the first preset gradient peak and the second preset gradient peak are determined according to the distance between the at least two adjacent slices, and the application of the first preset gradient peak and the second preset gradient peak causes the shift of the scanning visual field;

acquiring a plurality of layers of aliased magnetic resonance signals of the at least two adjacent slices by using a receiving coil;

the processor is configured to generate a magnetic resonance image of each slice of the scanned object from the multi-slice aliased magnetic resonance signals.

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