CN110215209B - Magnetic resonance imaging method and magnetic resonance imaging system - Google Patents
Magnetic resonance imaging method and magnetic resonance imaging system Download PDFInfo
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Abstract
The invention discloses a magnetic resonance imaging method and a magnetic resonance imaging system. The method comprises the following steps: exciting a scanning part by using a preset scanning sequence to acquire an echo signal combination of each body layer of the scanning part, wherein the preset scanning sequence comprises a first scanning sequence and a second scanning sequence which appear in a preset combination form, the first scanning sequence is a spin echo sequence, the second scanning sequence is combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for body layer selection; determining first imaging data corresponding to echo signals corresponding to the first scanning sequence and second imaging data corresponding to echo signals corresponding to the second scanning sequence, and taking a preset logical operation result of the first imaging data and the second imaging data as imaging data; the magnetic resonance image of the scanning part is determined according to the imaging data, and the problems that the signal-to-noise ratio of the region of interest of the scanning part is low and the minimum TE is large in the prior art are solved.
Description
Technical Field
The embodiment of the invention relates to the technology of medical instruments, in particular to a magnetic resonance imaging method and a magnetic resonance imaging system.
Background
In a pulse Imaging sequence of Magnetic Resonance Imaging (MRI), there is a Spectrum sequence Imaging, which is Magnetic Resonance Spectroscopy (MRS) Imaging, and MRS Imaging is to acquire metabolite information by using chemical shift difference of metabolites and obtain related metabolite level change by analyzing metabolic activity. Since the Frequency difference between related metabolites increases with the increase of the B0 field, under the bandwidth of limited Radio Frequency (RF), as the B0 field strength increases, the chemical shift bias effect (error) increases, which leads to the deviation of excitation regions of different metabolites, and the SIGNAL-to-NOISE RATIO (SNR) of the boundary region is low.
For this reason, the prior art often adopts high-order broadband adiabatic excitation to solve the above problem, but this solution causes an increase in minimum echo Time (TE) due to the polarization effect and B0 field non-uniformity, and adiabatic pulses need to be used in pairs. Therefore, in a clinical scenario, because of constraints of factors such as the safety limit of the Specific Absorption Rate (SAR) and the radio frequency transmission power, the gradient performance, and the like, the minimum TE (echo time) that can be finally realized is still large, and the clinical diagnosis requirement cannot be met.
In summary, there is a need to provide a magnetic resonance imaging method that further reduces TE to meet the clinical diagnosis requirement.
Disclosure of Invention
The embodiment of the invention provides a magnetic resonance imaging method and a magnetic resonance imaging system, which aim to reduce the minimum TE and improve the analysis effect of metabolites with shorter transverse relaxation time.
In a first aspect, an embodiment of the present invention provides a magnetic resonance imaging method, including:
exciting a scanning part by using a preset scanning sequence to acquire echo signal combinations of each body layer of the scanning part, wherein the preset scanning sequence comprises a first scanning sequence and a second scanning sequence which are in a preset combination form, the first scanning sequence is a spin echo sequence, the second scanning sequence is combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for body layer selection;
determining first imaging data corresponding to echo signals corresponding to the first scanning sequence and second imaging data corresponding to echo signals corresponding to the second scanning sequence, and taking a preset logical operation result of the first imaging data and the second imaging data as imaging data;
a magnetic resonance image of the scan region is determined from the imaging data.
Further, the preset combination form is an alternate form.
Furthermore, the spin echo sequence is a 90-degree excitation pulse and a 180-degree refocusing pulse which are sequentially performed, and the 90-degree excitation pulse and the 180-degree refocusing pulse are respectively located on two layers of surfaces which are perpendicular to each other.
Further, the slice selection gradients corresponding to the 90-degree excitation pulse and the 180-degree refocusing pulse are respectively located in the x-slice direction and the y-slice direction.
Further, the spin echo sequence also includes an encoding gradient in at least one direction.
Further, a slice selection gradient direction corresponding to one of the inversion recovery pulses is the same as a slice selection gradient direction corresponding to the 180-degree echo pulse in the spin echo sequence.
Further, the scanning part is excited by using a preset scanning sequence, and the preset logical operation is a logical and operation.
Further, the exciting the scanning portion by using the preset scanning sequence to obtain the echo signal combination of each slice of the scanning portion further includes:
a saturation band is applied to a non-scanning site adjacent to a scanning site to prevent the scanning site from being superimposed with artifacts due to the motion of the non-scanning site.
In a second aspect, an embodiment of the present invention further provides a magnetic resonance imaging system, including:
a scanning device for transmitting one or more preset scanning sequences to a scanning part to acquire an echo signal combination of each slice of the scanning part in an imaging space in which a static magnetic field is formed, wherein the preset scanning sequences comprise a first scanning sequence and a second scanning sequence which are in a preset combination form, the first scanning sequence comprises a spin echo sequence, the second scanning sequence comprises a combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for slice selection;
and the image generating device is used for determining first imaging data corresponding to the echo signals corresponding to the first scanning sequence and second imaging data corresponding to the echo signals corresponding to the second scanning sequence, taking a preset logical operation result of the first imaging data and the second imaging data as imaging data, and determining a magnetic resonance image of a scanning part according to the imaging data.
Further, the scanning device comprises a radio frequency transmitting coil, a gradient coil and a controller;
the radio frequency transmitting coil is used for generating and transmitting radio frequency pulses to excite nuclear spins of the scanning part; the gradient coil is used for generating gradient pulses;
the controller is used for controlling the work of the radio frequency transmitting coil and the gradient coil so as to apply or close the inversion recovery pulse consisting of the radio frequency pulse and the gradient pulse.
The embodiment of the invention provides a magnetic resonance imaging method and a magnetic resonance imaging system, wherein a scanning part is excited by a preset scanning sequence to obtain an echo signal combination of each body layer of the scanning part, wherein the preset scanning sequence comprises a first scanning sequence and a second scanning sequence which are in a preset combination form, the first scanning sequence is a spin echo sequence, the second scanning sequence is the combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse has a layer selection function; determining first imaging data corresponding to echo signals corresponding to the first scanning sequence and second imaging data corresponding to echo signals corresponding to the second scanning sequence, taking a preset logic operation result of the first imaging data and the second imaging data as imaging data, determining a magnetic resonance image of a scanning part according to the imaging data, and realizing imaging of only the positioned part through preset logic budget.
Drawings
Fig. 1 is a flowchart of a magnetic resonance imaging method according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a first scanning sequence according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating a second scanning sequence according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a layer selection result after being excited by a first scan sequence according to an embodiment of the present invention;
FIG. 5a is a schematic diagram illustrating a layer selection result after being excited by a first inversion recovery pulse according to an embodiment of the present invention;
FIG. 5b is a schematic diagram illustrating the layer selection result after being excited by the second inversion recovery pulse according to an embodiment of the present invention;
fig. 5c is a schematic diagram illustrating a layer selection result after being excited by a 180-degree refocusing pulse according to an embodiment of the invention;
FIG. 6a is a schematic plan view of a layer selection result of imaging data according to an embodiment of the present invention;
FIG. 6b is a three-dimensional diagram illustrating a layer selection result of imaging data according to an embodiment of the present invention;
FIG. 7a is a schematic diagram of a water phantom including a portion to be analyzed (small square portion) according to an embodiment of the present invention;
figure 7b is a magnetic resonance image of a part to be analyzed (small box part) obtained on the basis of the prior art;
FIG. 7c is a magnetic resonance image of a portion to be analyzed (small box portion) according to one embodiment of the present invention;
fig. 8 is a frequency spectrum diagram of multiple voxels of a magnetic resonance image according to an embodiment of the present invention;
fig. 9 is a flowchart of a magnetic resonance imaging method according to a second embodiment of the present invention;
FIG. 10 is a diagram illustrating a second scanning sequence according to a second embodiment of the present invention;
FIG. 11 is a diagram illustrating a second scan sequence according to a second embodiment of the present invention;
FIG. 12 is a schematic diagram of slice selection results of a spin echo sequence scan including a conventional echo pulse according to a second embodiment of the present invention;
FIG. 13 is a schematic diagram of the layer selection result of the second scan sequence scan including a conventional refocusing pulse according to the second embodiment of the present invention;
fig. 14 is a block diagram of a magnetic resonance imaging system according to a third embodiment of the present invention;
fig. 15 is a schematic structural diagram of a magnetic resonance system according to a third embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1 is a flowchart of a magnetic resonance imaging method according to an embodiment of the present invention, which is suitable for obtaining magnetic resonance imaging with a smaller TE, and which can be performed by the magnetic resonance system according to the embodiment of the present invention. The method specifically comprises the following steps:
In magnetic resonance imaging, a static magnetic field is generally formed by a main magnet, then a preset scan pulse is transmitted to a scan site based on a preset scan sequence through a radio frequency transmission coil to excite nuclear spins of the scan site, and then echo signal combinations of each slice of the scan site are acquired through a receiving coil.
The preset scanning sequence comprises a first scanning sequence and a second scanning sequence which are in a preset combination form. The first scanning sequence is a spin echo sequence, the second scanning sequence is a combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse has a layer selection function.
The preset scanning pattern may be an alternating pattern, in which the nuclear spins of the scanning portion are excited by alternately using the first scanning sequence and the second scanning sequence.
The spin echo sequence is a 90-degree excitation pulse and a 180-degree echo pulse which are sequentially carried out, and the 90-degree excitation pulse and the 180-degree echo pulse are respectively positioned on two layers which are perpendicular to each other. Preferably, as shown in fig. 2, the slice selection gradient direction of the 90-degree excitation pulse is the x-slice direction, and the slice selection gradient direction of the 180-degree refocusing pulse is the y-slice direction, so that the slice selection results of the two in the x-y plane are shown in fig. 4. It will be appreciated that locating a body slice also locates individual voxels within that body slice. Of course, in other embodiments, the self-selected echo sequence may also include frequency encoding gradients along the x-, y-, or z-axis directions to enable multi-voxel signal acquisition within a selected slice plane.
And the direction of the slice selection gradient corresponding to one of the inversion recovery pulses is the same as the direction of the slice selection gradient corresponding to the 180-degree echo pulse in the spin echo sequence. Optionally, as shown in fig. 3, the inversion recovery pulse includes a first inversion recovery pulse and a second inversion recovery pulse, where the slice selection gradient direction corresponding to the first inversion recovery pulse is the z-plane direction, and the slice selection gradient direction corresponding to the second inversion recovery pulse is the y-direction, and is the same as the slice selection gradient direction corresponding to the 180-degree refocusing pulse.
Figure 3 shows a second scan sequence comprising inversion recovery pulses and spin echo sequences, when a first inversion recovery pulse perpendicular to the 90 degree excitation pulse and the 180 degree refocusing pulse is applied to the scan site, the slice selection result is shown as a solid black box in figure 5a (x-z plane), and then a second inversion recovery pulse is applied, resulting in a slice selection result as shown by a dashed black box in figure 5b (x-y plane). Since the slice direction selected by the 180-degree echo pulse of the spin echo sequence is the y slice direction, the signal in the black dashed box (x-y plane) in fig. 5b is preserved, and the slice selection result is shown as the black dashed box (x-y plane) in fig. 5 c. Since the inversion recovery pulse selects the slice direction for the refocusing process of the second scan sequence, the refocusing process does not need to reselect the slice direction, thereby reducing the minimum TE.
The spin echo sequence of this embodiment further includes an encoding gradient in at least one direction to encode each echo signal, so as to realize positioning encoding of a voxel corresponding to each echo signal. Typically, the spin echo sequence includes encoding gradients in the x, y, and z directions to spatially encode each echo signal to obtain encoded echo signals. The encoding gradient in the x-plane direction is generally used to perform frequency encoding on the echo signals, the encoding gradient in the y-plane direction is generally used to perform phase encoding on the echo signals, and the encoding gradient in the z-plane direction is generally used to perform slice selection encoding on the echo signals.
And 104, determining first imaging data corresponding to the echo signals corresponding to the first scanning sequence and second imaging data corresponding to the echo signals corresponding to the second scanning sequence, and taking a preset logical operation result of the first imaging data and the second imaging data as imaging data.
After a scanning part is excited by adopting a first scanning sequence and a second scanning sequence, a plurality of echo signals can be respectively obtained, and the echo signals corresponding to the first scanning sequence are written into a first k-space to obtain first k-space data; and writing the echo signals corresponding to the second scanning sequence into a second k-space to obtain second k-space data. The first k-space data is then converted to the image domain to obtain first imaging data, and the second k-space data is converted to the image domain to obtain second imaging data. It will be appreciated that the echo signals written in the first k-space and the second k-space are both encoded echo signals.
As can be seen from the foregoing steps, the first scanning sequence can achieve the layer selection result shown in fig. 4, and the second scanning sequence can achieve the layer selection result shown in fig. 5c, so that the slice layer corresponding to the first imaging data corresponding to the first scanning sequence is shown in fig. 4, and the slice layer corresponding to the second imaging data corresponding to the second scanning sequence is shown in fig. 5 c.
It will be appreciated that only the central "+" portion of fig. 5c is located by the second scan sequence at the same time as the first scan sequence, and for this purpose, the present embodiment logically and-operates the first imaging data corresponding to the first scan sequence with the second imaging data corresponding to the second scan sequence to obtain data located by all sequences at the same time, and takes this data as imaging data, see in particular the shaded portion of fig. 6a, and see the portion enclosed by "/" and "o" of fig. 6 b.
It should be noted that, in this embodiment, only the first imaging data and the second imaging data corresponding to the adjacent first scanning sequence and the second scanning sequence respectively need to be subjected to logical and operation, and the order of occurrence of the first imaging data and the second imaging data is not limited.
It will be appreciated that each preset scan sequence typically corresponds to a magnetic resonance image of only one slice. Therefore, one or more preset scan sequences are usually required for clinical use, and imaging data of the one or more preset scan sequences are acquired for later image reconstruction.
Preferably, in order to improve the signal-to-noise ratio of the magnetic resonance image, before scanning the scanning region, a saturation band is applied to a non-scanning region adjacent to the scanning region to prevent the scanning region from being superimposed with artifacts generated by the motion of the non-scanning region, thereby further improving the definition of the scanning region.
After the imaging data is acquired, the controller controls the image generating device to perform magnetic resonance image reconstruction on the imaging data to obtain a magnetic resonance image.
In fig. 7a, the circular portion is a water phantom, the area defined by the middle silver square is the scanning object, fig. 7b is a magnetic resonance image of the part to be analyzed (small square portion) in the scanning object obtained based on the prior art, fig. 7c is a magnetic resonance image of the part to be analyzed (small square portion) in the scanning object obtained based on the method described in this embodiment, and comparing fig. 7b and fig. 7c, it can be seen that the signal-to-noise ratio of fig. 7c (this embodiment) is higher than that of fig. 7b (prior art). Fig. 8 is a frequency spectrum diagram of multiple voxels of a magnetic resonance image, a thin line (dark gray) is the frequency spectrum diagram of the magnetic resonance image provided in this embodiment, and a thick line (light gray) is the frequency spectrum diagram of the magnetic resonance image provided in the prior art, and it can be seen from fig. 8 that the signal-to-noise ratio of the frequency spectrum diagram corresponding to the magnetic resonance image obtained by the magnetic resonance imaging method according to this embodiment is higher, and the positions of the spectral lines of each element are more accurately located, so that the magnetic resonance imaging method according to this embodiment is more stable compared with the prior art.
According to the technical scheme of the magnetic resonance imaging method provided by the embodiment, the scanning part is excited by using the preset scanning sequence to obtain the echo signal combination of each body layer of the scanning part, then the first imaging data corresponding to the echo signal corresponding to the first scanning sequence and the second imaging data corresponding to the echo signal corresponding to the second scanning sequence are determined, and the preset logic operation result of the first imaging data and the second imaging data is used as the imaging data, so that the signal to noise ratio of the magnetic resonance image of the scanning part is improved, the magnetic resonance image of the scanning part is determined according to the imaging data, and as the inversion recovery pulse selects the plane direction for the convergence of the second scanning sequence, the plane direction does not need to be selected again in the convergence process, so that the minimum TE is reduced, the problem that the minimum TE in the prior art is large is solved, the magnetic resonance imaging effect on metabolites with short transverse relaxation time in clinical diagnosis is effectively improved, and the diagnosis efficiency is improved.
Example two
Fig. 9 is a flowchart illustrating a magnetic resonance imaging method according to a second embodiment of the present invention. Referring specifically to fig. 9, the method may include the steps of:
in step 202, a scanning portion is excited by using a preset scanning sequence to obtain an echo signal combination of each slice of the scanning portion.
When the pulse of 180-degree refocusing of the first scan sequence in the preset scan sequence is specifically implemented, one or more conventional refocusing pulses may be used, and one or more pairs of adiabatic refocusing pulses may be used. FIG. 3 shows a scan sequence diagram of a spin echo sequence in which both 180 degree echo pulses are conventional echo pulses, and FIG. 10 shows a scan sequence diagram in which the spin echo sequence includes one conventional echo pulse, since only one conventional echo pulse is employed, the time required for echo is reduced, thereby reducing the minimum TE; fig. 11 is a scanning sequence diagram showing that the spin echo sequence of the second scanning sequence includes a pair of adiabatic echo pulses, and the determined layer selection result based on the second scanning sequence is shown in the foregoing embodiment, which is not described herein again. Compared with the conventional refocusing pulse, the adiabatic refocusing pulse has the characteristics of larger bandwidth, higher signal-to-noise ratio and insensitivity to B1, so that the signal-to-noise ratio of the magnetic resonance image of the scanning part is improved.
Illustratively, if the spin echo sequence includes a 90 degree excitation pulse and a conventional echo pulse. Slice selection gradient directions of the 90-degree excitation pulse and the conventional echo pulse referring to the previous embodiment, since only one conventional echo pulse is used for echo, slice selection results after the spin echo sequence scanning are shown in fig. 12.
Figure 10 shows a second scan sequence comprising inversion recovery pulses and a spin echo sequence, wherein the spin echo sequence comprises a 90 degree excitation pulse and a normal refocusing pulse, if a first inversion recovery pulse perpendicular to the 90 degree excitation pulse and the normal refocusing pulse is applied to the scan site, the first inversion recovery pulse corresponds to a slice selection result, as shown by the black solid box in figure 5a (x-z plane), and a second inversion recovery pulse parallel to the normal refocusing pulse is applied to the scan site, the corresponding slice selection result is shown by the black dashed box in figure 5b (x-y plane). Since the slice direction selected by one conventional echo pulse of the spin echo sequence is the y slice direction, the signals in the black dashed box (x-y plane) in fig. 5b are preserved, and each "-" signal is changed to a "+" signal, and each "+" signal is changed to a "-" signal, resulting in the slice selection result as the black dashed box (x-y plane) in fig. 13.
As can be seen from the foregoing steps, the first scan sequence including a conventional pulse for refocusing can achieve the layer selection result shown in fig. 12, and correspondingly, the second scan sequence can achieve the layer selection result shown in fig. 13, so that the slice layer corresponding to the first imaging data corresponding to the first scan sequence is shown in fig. 12, and the slice layer corresponding to the second imaging data corresponding to the second scan sequence is shown in fig. 13. The first imaging data is then logically anded with the second imaging data to obtain imaging data that is simultaneously localized by all sequences and taken as imaging data, see in particular the shaded portion of fig. 6a, and see the portion of fig. 6b enclosed by "/" and "o".
In step 206, a magnetic resonance image of the scanned region is determined from the imaging data.
Compared with the prior art, the spin echo sequence of the embodiment comprises a conventional echo pulse or two pairs of adiabatic echo pulses, and the conventional echo pulse is adopted to reduce the time required by echo and further reduce the minimum TE. In addition, compared with the conventional echo pulse, the adopted adiabatic echo pulse has the characteristics of larger bandwidth, higher signal-to-noise ratio and insensitivity to B1, and further improves the signal-to-noise ratio of the magnetic resonance image of the scanning part, thereby greatly improving the diagnosis effect.
EXAMPLE III
Fig. 14 is a schematic structural diagram of a magnetic resonance imaging system according to a third embodiment of the present invention. Referring to fig. 14, the system includes: a scanning device 110 and an image generating device 120. The scanning device 110 is configured to transmit one or more preset scan sequences to the scan portion in an imaging space in which a static magnetic field is formed to acquire an echo signal combination of each slice of the scan portion, wherein the preset scan sequences include a first scan sequence and a second scan sequence in a preset combination form, the first scan sequence includes a spin echo sequence, the second scan sequence is a combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for slice selection; the image generating device 120 is configured to determine first imaging data corresponding to an echo signal corresponding to the first scanning sequence and second imaging data corresponding to an echo signal corresponding to the second scanning sequence, use a preset logical operation result of the first imaging data and the second imaging data as imaging data, and determine a magnetic resonance image of a scanning portion according to the imaging data.
On the basis of the above technical solutions, the scanning device 110 includes: a radio frequency transmit coil, a gradient coil, and a controller; the radio frequency transmitting coil is used for generating and transmitting radio frequency pulses to excite nuclear spins of a scanning part; the gradient coil is used for generating gradient pulses; the controller is used for controlling the work of the radio frequency transmitting coil and the gradient coil so as to apply or close an inversion recovery pulse consisting of the radio frequency pulse and the gradient pulse.
Specifically, the controller 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.
Wherein the radio frequency transmit coils and gradient coils essentially comprise a main magnet generating a B0 main magnetic field and gradient components generating gradients. The main magnet may be a permanent magnet or a superconducting magnet; the gradient assembly mainly comprises gradient current Amplifiers (AMP) and gradient coils, and can also comprise three independent channels Gx, gy and Gz, wherein each gradient amplifier excites a corresponding gradient coil in the gradient coil set to generate gradient fields for generating corresponding spatial encoding signals so as to spatially locate the magnetic resonance signals.
It will be appreciated that the scanning apparatus 110 may also include a pulse sequencer, a gradient waveform generator, a transmitter and receiver, and a radio frequency receive coil, among others. The pulse sequence generator, the gradient waveform generator, the transmitter and the receiver are used for controlling the magnetic field module to execute a corresponding scanning sequence after receiving an instruction sent by a user from the console. And the radio frequency receiving coil is used for receiving echo signals collected from a human body, and the radio frequency transmitting coil and the radio frequency receiving coil are divided into a body coil and a local coil according to different functions. 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 one embodiment, the local coils are arranged as array coils, and the array coils can be arranged in 4-channel mode, 8-channel mode, or 16-channel mode.
As shown in fig. 15, the magnetic resonance imaging system further includes: and an output device 130.
Wherein an output device 130, such as a display, may display a magnetic resonance image of the region of interest. Further, the output device 130 can also display the height, weight, age, imaging portion, and operating state of the scanner device 110 of the subject, and the like. The output device 130 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 so on.
The magnetic resonance imaging 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.
The integrated magnetic resonance imaging system 100 illustratively explains a specific procedure for generating a magnetic resonance image by the magnetic resonance imaging system: a main magnet generates a B0 main magnetic field, and atomic nuclei in a body of a detected person generate precession frequency under the action of the main magnetic field, wherein the precession frequency is in direct proportion to the strength of the main magnetic field; the controller stores and sends a scanning instruction of a preset scanning sequence to be executed, the pulse sequence generator controls the gradient waveform generator and the transmitter according to the scanning instruction, the gradient waveform generator outputs a gradient pulse signal with a preset time sequence and waveform, the signal passes through Gx, gy and Gz gradient amplifiers and then passes through three independent channels Gx, gy and Gz in the gradient assembly, each gradient amplifier excites a corresponding gradient coil in the gradient coil group to generate a gradient field for generating a corresponding spatial coding signal so as to spatially position a magnetic resonance signal; the pulse sequence generator also executes a scanning sequence, outputs data including timing, strength, shape and the like of radio frequency transmitted radio frequency pulses and timing of radio frequency receiving and the length of a data acquisition window to the transmitter, simultaneously the transmitter sends corresponding radio frequency pulses to a body transmitting coil in the radio frequency unit to generate a B1 field, signals emitted by an excited atomic nucleus in a patient body under the action of the B1 field are sensed by a radio frequency receiving coil, then are transmitted to the controller through the transmitting/receiving switch, are subjected to digital processing such as amplification, demodulation, filtering, AD conversion and the like, and then are transmitted to the echo signal storage module. And when the echo signal storage module acquires a group of original k-space data, finishing scanning. The original k-space data is rearranged into separate k-space data sets corresponding to each image to be reconstructed, each k-space data set is input to the image generating means 120, the image generating means 120 converts each k-space data set into imaging data, and then magnetic resonance image reconstruction is performed on the imaging data to obtain a magnetic resonance image.
The technical scheme of the magnetic resonance imaging system provided by the embodiment of the invention comprises the following steps: a scanning device and an image generating device. The scanning device is used for transmitting one or more preset scanning sequences to a scanning part in an imaging space formed with a static magnetic field so as to acquire echo signal combination of each body layer of the scanning part. The image generation device is used for determining first imaging data corresponding to echo signals corresponding to a first scanning sequence and second imaging data corresponding to echo signals corresponding to a second scanning sequence, taking a preset logic operation result of the first imaging data and the second imaging data as imaging data, determining a magnetic resonance image of a scanning part according to the imaging data, and because a layer direction is selected for retrofocus of the second scanning sequence by a reversal recovery pulse, the layer direction does not need to be selected again in the retrofocus process, so that the minimum TE is reduced, the problem of larger minimum TE in the prior art is solved, the magnetic resonance imaging effect on metabolites with shorter transverse relaxation time in clinical diagnosis is effectively improved, and the diagnosis efficiency is improved.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in some detail by the above embodiments, the invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the invention, and the scope of the invention is determined by the scope of the appended claims.
Claims (7)
1. A magnetic resonance imaging method, comprising:
exciting a scanning part by using a preset scanning sequence to acquire an echo signal combination of each body layer of the scanning part, wherein the preset scanning sequence comprises a first scanning sequence and a second scanning sequence which appear in a preset combination form, the first scanning sequence is a spin echo sequence, the second scanning sequence is combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for body layer selection; the spin echo sequence is a 90-degree excitation pulse and a 180-degree echo pulse which are sequentially carried out, and the 90-degree excitation pulse and the 180-degree echo pulse are respectively positioned on two layers which are vertical to each other; the slice selection gradient direction corresponding to one inversion recovery pulse in the inversion recovery pulses is the same as the slice selection gradient direction corresponding to the 180-degree echo pulse in the spin echo sequence;
determining first imaging data corresponding to echo signals corresponding to the first scanning sequence and second imaging data corresponding to echo signals corresponding to the second scanning sequence, and taking a preset logical operation result of the first imaging data and the second imaging data as imaging data; wherein the preset logical operation is a logical and operation;
a magnetic resonance image of the scan region is determined from the imaging data.
2. The method of claim 1, wherein the predetermined combination pattern is an alternating pattern.
3. The method of claim 1, wherein the slice selection gradients corresponding to the 90 degree excitation pulse and the 180 degree refocusing pulse are located in an x-slice direction and a y-slice direction, respectively.
4. The method of claim 1, wherein the spin echo sequence further comprises an encoding gradient in at least one direction.
5. The method of claim 1, wherein the exciting the scan site with a preset scan sequence to obtain echo signal combinations for each slice of the scan site further comprises:
a saturation band is applied to a non-scanning site adjacent to a scanning site to prevent the scanning site from being superimposed with artifacts due to the motion of the non-scanning site.
6. A magnetic resonance imaging system, comprising:
a scanning device for transmitting one or more preset scanning sequences to a scanning part to acquire an echo signal combination of each slice of the scanning part in an imaging space in which a static magnetic field is formed, wherein the preset scanning sequences comprise a first scanning sequence and a second scanning sequence which are in a preset combination form, the first scanning sequence comprises a spin echo sequence, the second scanning sequence comprises a combination of an inversion recovery pulse and the spin echo sequence, and the inversion recovery pulse is used for slice selection; the gyrotron sequence is a 90-degree excitation pulse and a 180-degree gyrotron pulse which are sequentially carried out, and the 90-degree excitation pulse and the 180-degree gyrotron pulse are respectively positioned on two layers which are vertical to each other; the slice selection gradient direction corresponding to one inversion recovery pulse in the inversion recovery pulses is the same as the slice selection gradient direction corresponding to the 180-degree echo pulse in the spin echo sequence;
the image generation device is used for determining first imaging data corresponding to echo signals corresponding to the first scanning sequence and second imaging data corresponding to echo signals corresponding to the second scanning sequence, taking a preset logical operation result of the first imaging data and the second imaging data as imaging data, and determining a magnetic resonance image of a scanning part according to the imaging data; wherein the predetermined logical operation is a logical and operation.
7. The system of claim 6, wherein the scanning device comprises a radio frequency transmit coil, a gradient coil, and a controller;
the radio frequency transmitting coil is used for generating and transmitting radio frequency pulses to excite nuclear spin of the scanning part;
the gradient coil is used for generating gradient pulses;
the controller is used for controlling the work of the radio frequency transmitting coil and the gradient coil so as to apply or close the inversion recovery pulse consisting of the radio frequency pulse and the gradient pulse.
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