CN114487962A - Magnetic resonance imaging method, magnetic resonance imaging apparatus, computer device, and storage medium - Google Patents
Magnetic resonance imaging method, magnetic resonance imaging apparatus, computer device, and storage medium Download PDFInfo
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- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
- G01R33/5616—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using gradient refocusing, e.g. EPI
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- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
- G01R33/5618—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] using both RF and gradient refocusing, e.g. GRASE
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Abstract
The present application relates to a magnetic resonance imaging method, apparatus, computer device and storage medium. The method comprises the following steps: dividing the K space into a plurality of filling areas along a first direction and a second direction; exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal; filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes; and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object. By adopting the method, the data acquisition speed can be improved, and the application range of the 3D GRASE sequence and the 3D EPI sequence is expanded.
Description
Technical Field
The present application relates to the field of magnetic resonance technology, and in particular, to a magnetic resonance imaging method, apparatus, computer device, and storage medium.
Background
3D GRASE (GRAdient and Spin Echo, Spin Echo and GRAdient Echo) sequences and 3D EPI (Echo Planar Imaging) sequences are scanning sequences commonly used in magnetic resonance. In general, echo data of the 3D gps sequence and the 3D EPI sequence are padded into K space using a SORT Off-response and T2 effects (SORT) phase encoding method, as shown in fig. 1.
The SORT phase encoding method can cause phase steps in the K space along the EPI factor encoding direction, so that artifacts which are difficult to eliminate appear in the reconstructed image. Therefore, the ETS (echo time Shift) technique is also combined to eliminate the phase step-induced artifacts.
However, the ETS technology cannot use a variable density random undersampling method with a high data acquisition speed, and only can use a parallel imaging method with a relatively low data acquisition speed, so the 3D GRASE sequence and the 3D EPI sequence cannot be used in applications (such as dynamic imaging, abdominal breath-hold imaging, etc.) with a high requirement on the data acquisition speed, that is, the 3D GRASE sequence and the 3D EPI sequence are limited in clinical application range.
Disclosure of Invention
In view of the above, there is a need to provide a magnetic resonance imaging method, apparatus, computer device and storage medium capable of increasing data acquisition speed based on the use of ETS technology, thereby extending the clinical application range of 3D GRASE sequence and 3D EPI sequence.
A magnetic resonance imaging method, the method comprising:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first direction is an EPI-factor encoding direction, and the second direction is a phase encoding direction.
A magnetic resonance imaging method, the method comprising:
placing a detection object in a static magnetic field, and exciting the detection object for multiple times by using a scanning sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence include a plurality of sets of alternately distributed positive and negative readout gradients;
filling the magnetic resonance signals into a K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first partition and/or the second partition are divided into a plurality of filling regions along a second direction, and the first direction is orthogonal to the second direction.
In one embodiment, the scan sequence obtains a plurality of magnetic resonance signals per excitation, and the plurality of magnetic resonance signals are respectively filled into different filling regions of each partition.
In one embodiment, the number of filled regions in each of the plurality of sub-regions is determined based on an echo train of each excitation of a corresponding magnetic resonance signal in the scan sequence.
A magnetic resonance imaging apparatus, the apparatus comprising:
the area dividing module is used for dividing the K space into a plurality of filling areas along a first direction and a second direction;
the signal acquisition module is used for exciting the detection object for multiple times by utilizing the scanning sequence to acquire a magnetic resonance signal;
the signal filling module is used for filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; the filling areas along the first direction have the same filling mode, and the filling areas along the second direction have a random filling mode;
and the image reconstruction module is used for reconstructing an image according to the K space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first direction is an EPI-factor encoding direction, and the second direction is a phase encoding direction.
A magnetic resonance imaging apparatus, the apparatus comprising:
the signal acquisition module is used for placing a detection object in a static magnetic field and exciting the detection object for multiple times by utilizing a scanning sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence include a plurality of sets of alternately distributed positive and negative readout gradients;
the signal filling module is used for filling the magnetic resonance signals into the K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and the image reconstruction module is used for reconstructing an image according to the K space data to obtain a magnetic resonance image of the detection object.
A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detected object; alternatively, the first and second electrodes may be,
exciting a detection object for multiple times by using a scanning sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence include a plurality of sets of alternately distributed positive and negative readout gradients;
filling the magnetic resonance signals into a K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out the steps of:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
According to the magnetic resonance imaging method, the magnetic resonance imaging device, the computer equipment and the storage medium, the processor divides the K space into a plurality of filling areas along the first direction and the second direction; exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal; filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object. Because the magnetic resonance signals acquired by the positive and negative polarity readout gradients have the same filling mode in different partitions divided along the first direction, the ETS technology can be still used for eliminating artifacts caused by phase steps, and the imaging effect is ensured. And along the second direction, the fillable positions of the middle filling area are less than the fillable positions of the filling areas at the two sides, namely unfilled positions exist in the filling areas at the two sides, so that image reconstruction can be performed by using a compressed sensing algorithm, the data acquisition speed is improved, the 3D GRASE sequence and the 3D EPI sequence can be used in applications with higher requirements on the data acquisition speed, and the application range of the 3D GRASE sequence and the 3D EPI sequence is expanded.
Drawings
FIG. 1 is a schematic diagram of K space after filling in the background art;
FIG. 2 is a diagram of an embodiment of an MRI method;
figure 3 is a schematic flow chart of a magnetic resonance imaging method in one embodiment;
FIG. 4 is a schematic diagram of K-space in one embodiment;
figure 5 is a schematic flow chart of a magnetic resonance imaging method according to another embodiment;
FIG. 6a is a schematic illustration of readout gradients of a scan sequence in one embodiment;
FIG. 6b is an enlarged comparative plot of the readout gradient of the corresponding different partition of FIG. 6 a;
FIG. 7 is a flowchart illustrating a procedure of obtaining a magnetic resonance image of a subject according to a step of reconstructing an image from K-space data according to an embodiment;
FIG. 8 is a second flowchart illustrating a step of obtaining a magnetic resonance image of a subject according to the image reconstruction based on the K-space data in one embodiment;
FIG. 9 is a diagram of a data interpolation process in one embodiment;
FIG. 10 is a schematic diagram of a fully populated K space in one embodiment;
FIG. 11 is a third flowchart illustrating a step of obtaining a magnetic resonance image of a subject according to K-space data in an embodiment;
FIG. 12 is a block diagram showing the structure of a magnetic resonance imaging apparatus according to an embodiment;
fig. 13 is a block diagram showing the structure of a magnetic resonance imaging apparatus according to another embodiment;
FIG. 14 is a diagram illustrating an internal structure of a computer device according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The magnetic resonance imaging method provided by the application can be applied to the application environment as shown in fig. 2. The application environment is a magnetic resonance system, the magnetic resonance system 100 includes a bed 110, an MR scanner 120 and a processor 130, and the MR scanner 120 includes a magnet, a radio frequency transmit coil, a gradient coil and a radio frequency receive coil. The bed body 110 is used for bearing a target object 010, the radio frequency transmitting coil is used for transmitting radio frequency pulses to the target object, and the gradient coil is used for generating a gradient field which can be along a phase encoding direction, a layer selecting direction or a frequency encoding direction and the like; the radio frequency receive coil is used to receive magnetic resonance signals. In one embodiment, the magnet of the MR scanner 120 may be a permanent magnet or a superconducting magnet, and the radio frequency coils constituting the radio frequency unit may be divided into a body coil and a local coil according to functions. In one embodiment, the radio frequency transmit coil, the radio frequency receive coil may be of the kind of a birdcage coil, a solenoid coil, a saddle coil, a helmholtz coil, an array coil, a loop coil, or the like. In one embodiment, the radio frequency transmit coil is configured as a birdcage coil, 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 magnetic resonance system 100 further includes a controller 140 and an output device 150, wherein the controller 140 can simultaneously monitor or control the MR scanner 110, the processor 130 and the output device 150. The controller 140 may include one or a combination of a Central Processing Unit (CPU), an Application-Specific Integrated Circuit (ASIC), an Application-Specific Instruction Processor (ASIP), a Graphics Processing Unit (GPU), a Physical Processing Unit (PPU), a Digital Signal Processor (DSP), a Field-Programmable Gate Array (FPGA), an ARM Processor, and the like.
An output device 150, such as a display, may display a magnetic resonance image of the region of interest. Further, the output device 150 can also display the height, weight, age, imaging part, and operating state of the MR scanner 110 of the subject, and the like. The output device 150 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, and the like.
The magnetic resonance system 100 may be connected to a Local Area Network (LAN), Wide Area Network (WAN), Public Network, private Network, Public Switched Telephone Network (PSTN), the internet, wireless Network, virtual Network, or any combination thereof.
In one embodiment, the processor 130 may control the MR scanner 120 to perform equidistant or non-equidistant sampling on the detection object (part of the target object 010), and control the MR scanner 120 to acquire magnetic resonance signals of the detection object and perform fourier transform on the magnetic resonance signals to obtain a magnetic resonance image of the detection object.
In one embodiment, as shown in fig. 3, a magnetic resonance imaging method is provided, which is exemplified by the application of the method to the processor in fig. 2, and includes the following steps:
Wherein, first direction and second direction are the orthogonal relation, and K space is the partition along first direction, and can set up to middle filling area for the halving along the second direction, and both sides filling area is big, promptly: the data matrix corresponding to the middle filling area is small, and the data matrix corresponding to the edge filling areas on the two sides of the middle filling area is large. As shown in fig. 4, the K space is divided into three divisions g1, g2, and g3 in the first direction and five divisions r1 and r2 … … r5 in the second direction, and a plurality of filling regions g1r1, g2r1, and g3r1 … … are obtained. The fillable positions in the intermediate filling regions g1r3, g2r3, g3r3 are less than the fillable positions in the both-side filling regions g1r1, g2r1, g3r1, and the like. I.e. the packing density decreases in order from the middle area to its corresponding two side areas. With continued reference to fig. 4, the black dots indicate that the position is filled with data lines, and the white dots indicate that the position is not filled with data lines. The filling areas in the three divisions g1, g2 and g3 and corresponding to the same division in the second direction have the same filling pattern, i.e. the black dots form the same pattern. The different filling areas along the second direction have different filling modes, i.e. the patterns formed by the black dots are randomly distributed.
In one embodiment, the first direction is an EPI-factor encoding direction corresponding to a positive or negative polarity readout gradient encoding direction, and the second direction is a phase encoding direction.
Wherein the scan sequence may include at least one of a 3D GRASE sequence and a 3D EPI sequence, and the number of shots may be matched with the fillable positions of the middle fill area. As shown in fig. 4, the number of times of excitation is 6, the number of fillable positions in each of the intermediate fill regions g1r3, g2r3, and g3r3 is 6, the number of echoes generated by each excitation is 5, and the five echoes are filled into five fill regions, i.e., r1 to r5, divided in the second direction in a random manner.
The processor controls the MR scanner to carry out excitation on the detection object for a plurality of times according to the scanning sequence and controls the MR scanner to acquire the magnetic resonance signals generated by the detection object. The processor then acquires magnetic resonance signals from the MR scanner.
At least two filling areas along the first direction have the same filling pattern, and the filling areas along the second direction have random filling patterns. In the embodiment of the present invention, the filling pattern of each filling region may be a pattern formed by all filling positions of the filling region.
After acquiring the magnetic resonance signals, the processor fills the magnetic resonance signals into a plurality of filling areas of the K space. Wherein, along a first direction, the magnetic resonance signals are filled in respective filling positions of each filling region; in the second direction, the magnetic resonance signals are randomly filled in each of the filled regions. As shown in fig. 4, the black dots represent the filling positions in the filling region g1r1 of the magnetic resonance signals corresponding to each excitation in sequence, corresponding to the filling positions in the filling regions g2r1 and g3r 1.
It can be understood that, in the first direction, the magnetic resonance signals are filled in the respective filling positions of each filling region, and thus, an ETS (Echo-Time Shifting) method can still be used to remove artifacts caused by phase steps, ensuring an imaging effect. Along the second direction, the fillable positions of the middle filling area are less than the fillable positions of the filling areas on the two sides, that is, unfilled positions exist in the filling areas on the two sides, so that image reconstruction can be performed subsequently by using any reconstruction algorithm such as a compressed sensing algorithm, a parallel reconstruction algorithm or a neural network-based algorithm, that is, the data acquisition speed can be increased, and thus the 3D GRASE sequence and the 3D EPI sequence can be used in applications with higher requirements on the data acquisition speed.
In one embodiment, the number of filled regions of K-space in the second direction is determined from the echo train of each excitation of the corresponding magnetic resonance signal of the scan sequence. As shown in fig. 4, if the echo train length is 5, the number of the filled regions of the K space in the second direction is also 5.
And 204, carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detected object.
After the K-space data is obtained, the processor may perform image reconstruction according to the K-space data by using an algorithm such as fourier transform, and the like, so as to obtain a magnetic resonance image of the detection object.
In the magnetic resonance imaging method, the processor divides the K space into a plurality of filling areas along a first direction and a second direction; exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal; filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object. Because the magnetic resonance signals acquired by the positive and negative polarity readout gradients have the same filling mode in different partitions divided along the first direction, the ETS technology can be still used for eliminating artifacts caused by phase steps, and the imaging effect is ensured. And along the second direction, the fillable positions of the middle filling area are less than the fillable positions of the filling areas at the two sides, namely unfilled positions exist in the filling areas at the two sides, so that image reconstruction can be performed by using a compressed sensing algorithm, the data acquisition speed is improved, the 3D GRASE sequence and the 3D EPI sequence can be used in applications with higher requirements on the data acquisition speed, and the application range of the 3D GRASE sequence and the 3D EPI sequence is expanded.
In one embodiment, as shown in fig. 5, a magnetic resonance imaging method is provided, which is exemplified by the application of the method to the processor in fig. 2, and includes the following steps:
Wherein the readout gradients of the scan sequence comprise sets of alternately distributed positive polarity readout gradients and negative polarity readout gradients. FIG. 6a is a schematic diagram of a GRASE sequence according to an embodiment of the present invention, wherein RF represents RF pulses; gz represents the slice selection direction gradient field; gy denotes the phase encoding direction gradient field; gx denotes the gradient field in the readout encoding direction. In this embodiment, a plurality of 180-degree echo pulses are applied after the 90-degree excitation pulse, and a first set of positive and negative polarity-reversed frequency encoding gradients is applied during the period after the first 180-degree echo pulse and before the second 180-degree echo pulse (corresponding to the partition r1), where g1, g3 are positive gradient acquired echo signals and g2 are negative gradient acquired echo signals. A second set of positive and negative polarity-reversed frequency encoding gradients is applied after the second 180 degree refocusing pulse and before the third 180 degree refocusing pulse (corresponding to a different partition r 2). During the period after the third 180 degree echo pulse and before the fourth 180 degree echo pulse (corresponding to partition r3), a third set of positive and negative polarity reversed frequency encoding gradients is applied. It will be appreciated that there may be more 180 degree echo pulses, and the frequency encoding gradient provided between adjacent echo pulses, depending on the size of the K-space or the type of sequence. Furthermore, in the phase encoding direction, a spike/dot (blip) pulse is applied at the instant of the frequency encoding gradient inversion with reversed positive and negative polarities to move the current phase encoding line in K-space to the next position. In this embodiment, between two adjacent echo pulses, a first blip pulse is applied in the phase encode direction after the acquisition of the echo signal g1 is completed, and then the echo signal g2 is acquired; after the acquisition of the echo signal g2 is completed, a second blip pulse is applied in the phase encoding direction, and then the echo signal g3 is acquired. More specifically, the echo signals g1 and g3 are gradient echo signals, and the echo signal g2 is a spin echo signal. In this embodiment, the echo signal g2 with higher signal strength is filled in the central region of K space, and the echo signals g1 and g3 with lower signal strength are filled in the edge regions of K space, which is beneficial to obtain higher signal contrast and image contrast.
FIG. 6b is an enlarged comparison of the readout gradients of FIG. 6a for different partitions. As can be seen, the readout gradient for bin r2 has a first echo time offset from the readout gradient for bin r 1; the readout gradient of the corresponding bin r3 has a second echo time shift with respect to the readout gradient of the corresponding bin r1, and the first echo time shift is different from the second echo time shift. In this embodiment, by such an arrangement, the GRASE sequence can be implemented in combination with the ETS method, so as to change the phase of the step into a continuously and slowly increasing slope, thereby eliminating the image artifacts caused by the phase change.
The detection object is placed in a static magnetic field, and the processor controls the MR scanner to excite the detection object for a plurality of times according to a scanning sequence and controls the MR scanner to acquire magnetic resonance signals generated by the detection object. The processor then acquires magnetic resonance signals from the MR scanner.
In one embodiment, the scan sequence includes at least one of a 3D GRASE sequence and a 3D EPI sequence.
And step 302, filling the magnetic resonance signals into the K space to obtain K space data.
The magnetic resonance signal detection device comprises a K space, a positive polarity readout gradient and a negative polarity readout gradient, wherein the K space comprises a first partition and a second partition which are adjacently distributed along a first direction, part or all of the magnetic resonance signal corresponding to the positive polarity readout gradient is filled into the first partition of the K space, part or all of the magnetic resonance signal corresponding to the negative polarity readout gradient is filled into the second partition of the K space, and the first partition and the second partition have the same filling mode; for a 3D EPI sequence, the first partition and the second partition may each include one padding region. For a 3D GRASE sequence, the first partition and the second partition may include two, three, or more number of padding areas, respectively, with the middle padding area being small and the two side padding areas being large.
In this embodiment, it is assumed that each readout gradient includes N (N is an integer greater than or equal to 1) readout gradients with positive polarity and negative polarity alternately distributed, and the K space is equally divided into N partitions along the first direction. For a readout gradient comprising N positive and negative readout gradients alternately distributed, filling the magnetic resonance signal corresponding to the first positive readout gradient into the Nth of the N partitions1Partition (N)1E.n), filling the magnetic resonance signal corresponding to the first negative polarity readout gradient into the nth partition of the N partitions2Partition (N)2Is e.n and N1≠N2) Filling the magnetic resonance signal corresponding to the second positive polarity readout gradient into the Nth partition of the N partitions3Partition (N)3∈N，N3Not equal to N1 and N3≠N2). If there are more of the positive and negative polarity readout gradients, their corresponding magnetic resonance signals are filled into different ones of the N partitions. Filling the magnetic resonance signal corresponding to the first positive polarity readout gradient of each readout gradient to Nth1Filling the magnetic resonance signal corresponding to the first negative polarity read-out gradient of each read-out gradient into the Nth read-out gradient in the subarea2In the partition, and so on. At the same time, signals of different readout gradients are filled in different partitions in the second direction of the K-space, and are randomly filled in each partition in the second direction.
As shown in fig. 4, the magnetic resonance signal corresponding to g1 or g3 is filled in the first partition, and the magnetic resonance signal corresponding to g2 is filled in the second partition. And the filling position of each excited magnetic resonance signal in the first partition corresponds to the filling position in the second partition.
It can be understood that, along the first direction, the first partition and the second partition have the same filling mode with the magnetic resonance signals acquired by the corresponding positive and negative polarity readout gradients, so that the ETS technique can still be used to eliminate the artifacts caused by the phase step, and ensure the imaging effect. In each partition, the middle filling area is small, the two side filling areas are large, namely unfilled positions exist in the two side filling areas, so that image reconstruction can be performed subsequently by using a compressed sensing algorithm, and the 3D GRASE sequence and the 3D EPI sequence can be used in applications with high requirements on data acquisition speed.
And 303, carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detected object.
After the K-space data is obtained, the processor may perform image reconstruction according to the K-space data by using an algorithm such as fourier transform, and the like, so as to obtain a magnetic resonance image of the detection object. Optionally, the method for reconstructing an image from K-space data may include: the full-sampled fill area is taken as a calibration data point, and in this embodiment, the data points of the fill area contained in the section r3 are taken as calibration data points; synthesizing a filter using the calibration data points; applying a synthesis filter to the other partitions to obtain a plurality of coupled simultaneous linear equations with a plurality of unknowns; and solving a plurality of coupled simultaneous linear equations with a plurality of unknowns to obtain a complete data set of the other partitions, i.e. recovering unfilled data points of the other partitions.
In the magnetic resonance imaging method, a detection object is placed in a static magnetic field, and the detection object is excited for multiple times by using a scanning sequence to obtain a magnetic resonance signal; filling the magnetic resonance signals into a K space to obtain K space data; and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object. Because the magnetic resonance signals acquired by the positive and negative polarity readout gradients have the same filling mode in different partitions divided along the first direction, an ETS (extraction transformation set) technology can be used for eliminating artifacts caused by phase steps and ensuring the imaging effect; in each partition, the middle filling area is small, the two sides filling areas are large, namely unfilled positions exist in the two sides filling areas, therefore, a compressed sensing algorithm can be used for image reconstruction, the data acquisition speed is improved, the 3D GRASE sequence and the 3D EPI sequence can be used in applications with high requirements on the data acquisition speed, and the application range of the 3D GRASE sequence and the 3D EPI sequence is expanded.
In one embodiment, the filling of the at least three filling regions with magnetic resonance signals is a random filling pattern. As shown in fig. 4, the first partition corresponding to g1 includes 5 filling regions g1r1 to g1r5, and the second partition corresponding to g2 includes 5 filling regions g1r1 to g1r 5. For the same partition, the magnetic resonance signals may be randomly filled in each filling region, without defining the filling position.
In one embodiment, the scan sequence acquires a plurality of magnetic resonance signals per excitation, and the plurality of magnetic resonance signals are respectively filled into different filling regions in the partitions. As shown in fig. 4, a total of 6 excitations, 5 magnetic resonance signals are obtained per excitation, and 5 magnetic resonance signals are padded into r1 to r 5.
In one embodiment, the number of filling regions in each segment is determined from the echo train of each excitation of the corresponding magnetic resonance signal of the scan sequence. As shown in fig. 4, the echo train length is 5, and each partition includes 5 filling regions.
In an embodiment, the step of performing image reconstruction according to K-space data to obtain a magnetic resonance image of the detection object may adopt various manners, as shown in fig. 7, where one of the manners may include:
Since the middle filling region is small and the both-side filling regions are large in each section, unfilled positions where magnetic resonance signals are not filled exist in the both-side filling regions. And based on the filled K space data, carrying out iterative processing by using a compressed sensing algorithm to obtain undersampled data corresponding to the unfilled position in the K space.
And step 402, carrying out image reconstruction according to the K space data and the undersampled data to obtain a magnetic resonance image of the detected object.
The magnetic resonance system is provided with a plurality of coil channels, and image reconstruction is carried out according to K space data and undersampled data corresponding to each coil channel to obtain a magnetic resonance image corresponding to each coil channel; then, the magnetic resonance images of the plurality of coil channels are merged by utilizing a channel merging algorithm to obtain the magnetic resonance image of the detection object.
It can be understood that the image reconstruction is performed on each coil channel, and then the magnetic resonance images of the plurality of coil channels are combined by using the sum-of-squares algorithm, so that the problem of different signal amplitudes caused by different relative positions of each coil and the detection object can be reduced, and the imaging effect can be improved.
As shown in fig. 8, another approach may include:
and 403, based on the K space data, performing data interpolation processing by using a parallel imaging algorithm to obtain an intermediate result corresponding to the unfilled position in the K space.
And for the unfilled position in the K space, performing data interpolation processing according to the magnetic resonance signals in the filled position adjacent to the unfilled position to obtain an intermediate result corresponding to the unfilled position. The number of filled locations adjacent to unfilled locations may be determined from a preset reconstruction kernel. As shown in fig. 9, the reconstruction kernel is preset to be 3, and for each unfilled position, data interpolation processing is performed according to the magnetic resonance signals in the adjacent 3 filled positions, so as to obtain an intermediate result corresponding to the unfilled position. In this example, the intermediate result is determined by: the data line in fig. 9 that is completely filled in the vertical direction is taken as a calibration data point; synthesizing a filter using the calibration data points; applying a synthesis filter to a data set containing unfilled locations to obtain a plurality of coupled simultaneous linear equations with a plurality of unknowns; a plurality of coupled simultaneous linear equations with a plurality of unknowns are solved to obtain a complete data set. In another embodiment, the intermediate result is determined by: obtaining calibration data points for each data set, with the data lines in fig. 9 that are completely filled in the vertical direction as calibration data points; for each radio frequency receiving coil, forming a complete K-space data set according to the K-space data of the radio frequency receiving coil and the K-space data of the radio frequency receiving coils of the other channels; and repeating the steps until the K space data of the radio frequency receiving coils of all the channels form a complete K space data set.
And step 404, based on the intermediate result, performing iterative processing by using a compressed sensing algorithm to obtain undersampled data corresponding to the unfilled position.
And according to the calculated intermediate result corresponding to the unfilled position, carrying out iterative processing by using a compressed sensing algorithm to obtain the undersampled data corresponding to the unfilled position. As shown in fig. 10, the gray origin represents the undersampled data and the black origin represents the K-space data.
And 405, carrying out image reconstruction according to the K space data and the undersampled data to obtain a magnetic resonance image of the detected object.
And after the undersampled data are obtained, the undersampled data and the K space data completely fill the K space, and image reconstruction is carried out according to the K space data and the undersampled data, so that the magnetic resonance image of the detected object can be obtained.
As shown in fig. 11, yet another approach may include:
The magnetic resonance system has a plurality of coil channels, and for each coil channel, the sensitivity of each coil is calculated by using the data of the K space middle filling area as a reference line. Wherein, the sensitivity of each coil can represent the relative position relationship between the coil and the detection object.
And 407, based on the sensitivities of the coils, sequentially performing iteration processing and image reconstruction processing by using a sensitivity algorithm and a compressed sensing algorithm to obtain a magnetic resonance image of the detection object.
After the sensitivities of the plurality of coils are obtained, the sensitivity distributions of the plurality of coils can be determined. And then, carrying out iterative processing by using a sensitive algorithm and a compressed sensing algorithm to obtain undersampled data corresponding to the unfilled position in the K space, and further carrying out image reconstruction processing according to the K space data and the undersampled data corresponding to the unfilled position to obtain a magnetic resonance image of the detected object.
In the step of reconstructing the image according to the K-space data to obtain the magnetic resonance image of the detection object, because unfilled positions where the magnetic resonance signal is not filled exist in the filled areas on the two sides, the image can be reconstructed by using a compressed sensing algorithm, so that the data acquisition speed is increased, the 3D GRASE sequence and the 3D EPI sequence can be used in applications with high requirements on the data acquisition speed, and the application range of the 3D GRASE sequence and the 3D EPI sequence is expanded.
It should be understood that although the various steps in the flowcharts of fig. 2-11 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 2-11 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least some of the other steps or stages.
In one embodiment, as shown in fig. 12, there is provided a magnetic resonance imaging apparatus including:
the area dividing module 501 is configured to divide the K space into a plurality of filling areas along a first direction and a second direction;
a signal acquiring module 502, configured to acquire a magnetic resonance signal by exciting a detection object multiple times with a scanning sequence;
a signal filling module 503, configured to fill the magnetic resonance signals into multiple filling regions of the K space, so as to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
and an image reconstruction module 504, configured to perform image reconstruction according to the K-space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first direction is an EPI-factor encoding direction, and the second direction is a phase encoding direction.
In one embodiment, as shown in fig. 13, there is provided a magnetic resonance imaging apparatus including:
a signal acquisition module 601 configured to place a detection object in a static magnetic field, and excite the detection object multiple times using a scan sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence include a plurality of sets of alternately distributed positive and negative readout gradients;
a signal filling module 602, configured to fill the magnetic resonance signal into a K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and an image reconstruction module 603, configured to perform image reconstruction according to the K-space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first partition and/or the second partition are divided into a plurality of filling regions along a second direction, and the first direction is orthogonal to the second direction.
In one embodiment, the scan sequence obtains a plurality of magnetic resonance signals per excitation, and the plurality of magnetic resonance signals are respectively filled into different filling regions of each partition.
In one embodiment, the number of filling regions in each of the above-mentioned sub-regions is determined according to an echo train of each excitation of a corresponding magnetic resonance signal in the scan sequence.
In one embodiment, the image reconstruction module 603 is specifically configured to perform iterative processing by using a compressed sensing algorithm based on K space data to obtain undersampled data corresponding to an unfilled position in the K space; and carrying out image reconstruction according to the K space data and the undersampled data to obtain a magnetic resonance image of the detected object.
In one embodiment, the image reconstruction module 603 is specifically configured to perform data interpolation processing by using a parallel imaging algorithm based on K space data to obtain an intermediate result corresponding to an unfilled position in the K space; based on the intermediate result, carrying out iterative processing by using a compressed sensing algorithm to obtain under-sampled data corresponding to the unfilled position; and carrying out image reconstruction according to the K space data and the undersampled data to obtain a magnetic resonance image of the detected object.
In one embodiment, the image reconstruction module 603 is specifically configured to perform image reconstruction according to K-space data and undersampled data corresponding to each coil channel to obtain a magnetic resonance image corresponding to each coil channel; and combining the magnetic resonance images of the plurality of coil channels by using an average sum algorithm to obtain the magnetic resonance image of the detection object.
In one embodiment, the image reconstructing module 603 is specifically configured to calculate sensitivities of the coils according to data of K-space middle filling regions corresponding to the coil channels; and based on the sensitivity of each coil, sequentially performing iteration processing and image reconstruction processing by using a sensitivity algorithm and a compressed sensing algorithm to obtain a magnetic resonance image of the detected object.
For specific limitations of the magnetic resonance imaging apparatus, reference may be made to the above limitations of the magnetic resonance imaging method, which are not described in detail here. The modules in the magnetic resonance imaging apparatus can be wholly or partially implemented by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as shown in fig. 14. The computer device includes a processor, a memory, and a network interface connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The database of the computer device is used for storing magnetic resonance imaging data. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a magnetic resonance imaging method.
Those skilled in the art will appreciate that the architecture shown in fig. 14 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having a computer program stored therein, the processor implementing the following steps when executing the computer program:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first direction is an EPI-factor encoding direction, and the second direction is a phase encoding direction.
In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling mode, and the filling areas along the second direction are random filling modes;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
In one embodiment, the first direction is an EPI-factor encoding direction, and the second direction is a phase encoding direction.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above may be implemented by hardware instructions of a computer program, which may be stored in a non-volatile computer-readable storage medium, and when executed, may include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A magnetic resonance imaging method, characterized in that the method comprises:
dividing the K space into a plurality of filling areas along a first direction and a second direction;
exciting a detection object for multiple times by using a scanning sequence to acquire a magnetic resonance signal;
filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling pattern, and the filling areas along the second direction have a random filling pattern;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
2. The method of claim 1, wherein the first direction is an EPI-factor encoding direction and the second direction is a phase encoding direction.
3. A magnetic resonance imaging method, characterized in that the method comprises:
placing a detection object in a static magnetic field, and exciting the detection object for multiple times by using a scanning sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence comprise a plurality of sets of positive readout gradients and negative readout gradients distributed alternately;
filling the magnetic resonance signals into a K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and carrying out image reconstruction according to the K space data to obtain a magnetic resonance image of the detection object.
4. The method of claim 3, wherein the first partition and/or the second partition is divided into a plurality of filling regions along a second direction, and wherein the first direction is orthogonal to the second direction.
5. A method as claimed in claim 3, wherein the scan sequence acquires a plurality of magnetic resonance signals per excitation, and the plurality of magnetic resonance signals are filled into different filling regions of the respective sub-regions.
6. The method of claim 5, wherein the number of filling regions in each of the segments is determined based on an echo train of each excitation of a corresponding magnetic resonance signal of the scan sequence.
7. A magnetic resonance imaging apparatus, characterized in that the apparatus comprises:
the area dividing module is used for dividing the K space into a plurality of filling areas along a first direction and a second direction;
the signal acquisition module is used for exciting the detection object for multiple times by utilizing the scanning sequence to acquire a magnetic resonance signal;
the signal filling module is used for filling the magnetic resonance signals into a plurality of filling areas of the K space to obtain K space data; at least two filling areas along the first direction have the same filling pattern, and the filling areas along the second direction have a random filling pattern;
and the image reconstruction module is used for reconstructing an image according to the K space data to obtain a magnetic resonance image of the detection object.
8. A magnetic resonance imaging apparatus, characterized in that the apparatus comprises:
the signal acquisition module is used for placing a detection object in a static magnetic field and exciting the detection object for multiple times by utilizing a scanning sequence to obtain a magnetic resonance signal; the readout gradients of the scan sequence comprise a plurality of sets of positive readout gradients and negative readout gradients distributed alternately;
the signal filling module is used for filling the magnetic resonance signals into a K space to obtain K space data; the magnetic resonance signals corresponding to the positive polarity readout gradients are at least partially filled into the first partition of the K space, the magnetic resonance signals corresponding to the negative polarity readout gradients are at least partially filled into the second partition of the K space, and the first partition and the second partition have the same filling mode;
and the image reconstruction module is used for reconstructing an image according to the K space data to obtain a magnetic resonance image of the detection object.
9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 6.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.
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