CN113945878A - Four-nuclide synchronous magnetic resonance imaging and image reconstruction method - Google Patents
Four-nuclide synchronous magnetic resonance imaging and image reconstruction method Download PDFInfo
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- 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]
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Abstract
The invention discloses a four-nuclide synchronous magnetic resonance imaging and image reconstruction method, which comprises the steps of setting an inspection area, a layer thickness and a sampling matrix; setting parameters of radio frequency channels corresponding to each nuclide, and setting parameters of frequency coding gradient channels; setting parameters of a layer selection gradient channel; setting parameters of a phase encoding gradient channel; starting sampling; and (5) image reconstruction. The signals of the four nuclides come from the same layer, the layer thicknesses of the nuclides are kept consistent, the fields in the frequency coding gradient direction are consistent, the layer thicknesses, the frequency coding directions and the apparent resolutions in the phase coding directions of the reconstructed images of the four nuclides are consistent, the pixel positions correspond to one another one by one, and the problems that the layer thicknesses and the FOVs of images of different nuclides have large differences in multi-core pixel synchronous imaging are solved.
Description
Technical Field
The invention relates to the technical field of magnetic resonance imaging, in particular to a four-nuclide synchronous magnetic resonance imaging and image reconstruction method.
Background
Magnetic Resonance Imaging (MRI) has been widely used in preclinical studies and medical diagnostics. The hydrogen nuclei exist widely and densely in the organism, and are the first choice nuclei for magnetic resonance imaging. However, aprotic imaging can provide information that cannot be obtained by proton imaging alone, and can be a beneficial complement to hydrogen nuclear pixel imaging.
The traditional MRI imaging method aims at multiple nuclides, and sequentially images, namely acquires signals of a series of single nuclides and reconstructs images. Multiple examinations are needed, the imaging time is very long, and it is difficult to keep a person in a static position for more than half an hour. Small movements of the examined region during multiple examinations may also introduce motion artifacts, making it difficult to register images of different nuclear species. The multi-nuclear simultaneous imaging method can provide a potential solution to the above problems.
Methods for simultaneous imaging of two nuclear species have emerged, but most are based on the magnetic rotation ratio of one of the species, calculating the radio frequency related parameters and gradient pulse parameters required by the system. The method comprises the following specific steps:
the size of the examination area in the magnetic resonance imaging is recorded as FOV, the layer thickness is recorded as Th, and the FOV, the gradient pulse intensity, the radio frequency pulse and the sampling parameter satisfy the following relations[1]：
The layer selection gradient pulse is matched with the radio frequency pulse, and the layer thickness, the layer selection gradient pulse strength Gslevel and the frequency domain width BW excited by the radio frequency pulse satisfy the following formula:
γ×Gslevel×Th＝BW
where γ is the gyromagnetic ratio of the nucleus.
The following formula is satisfied among the frequency encoding direction FOVr, the readout gradient pulse intensity Grlevel and the sampling spectrum width SW:
γ×Grlevel×FOVr＝SW
however, in the multi-nuclear synchronous magnetic resonance imaging process, the spatially encoded gradient magnetic field acts on all atomic nuclei simultaneously, the gyromagnetic ratios of different nuclear species are inherent properties of the atomic nuclei, and the difference is large, and simultaneously acquired images have different fields of view and layer thicknesses, have large resolution difference, cannot be directly registered, and are not convenient for further registration and analysis.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a four-nuclide synchronous magnetic resonance imaging and image reconstruction method, which is characterized in that the sizes of layer thickness Th and frequency coding direction inspection areas FOV corresponding to four nuclides are kept consistent in the synchronous imaging of the four nuclides, after the images are reconstructed, interpolation and scaling are carried out in the phase coding direction, and the apparent resolutions and pixel positions of the images corresponding to the four nuclides are in one-to-one correspondence.
The above object of the present invention is achieved by the following technical solutions:
a four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method, comprising the steps of:
step 1, setting an inspection area FOV, a layer thickness Th and a sampling matrix [ M N ];
wherein M is the number of sampling points, N is the number of encoding steps in the phase encoding direction, and the inspection area FOV comprises a frequency encoding direction inspection area FOVr and a phase encoding direction inspection area FOVp;
step 2, setting parameters of a first radio frequency channel f1, a second radio frequency channel f2, a third radio frequency channel f3 and a fourth radio frequency channel f4 corresponding to the first nuclear species, the second nuclear species, the third nuclear species and the fourth nuclear species,
step 3, setting parameters of a frequency coding gradient channel Gr, wherein the parameters of the frequency coding gradient channel Gr comprise: reading out the intensity of the dephasing gradient pulse, the width of the dephasing gradient pulse, the intensity Grlevel of the reading gradient pulse and the width of the reading gradient pulse;
and 4, setting parameters of the layer selection gradient channel Gs, wherein the parameters of the layer selection gradient channel Gs comprise: the gradient pulse intensity Gslevel of the selected layer, the gradient pulse width of the selected layer and the echo gradient pulse width of the selected layer;
setting parameters of a phase encoding gradient channel Gp, wherein the parameters of the phase encoding gradient channel Gp comprise phase encoding gradient pulse strength Gplevel, phase encoding gradient pulse width, phase encoding echo gradient pulse strength and phase encoding echo gradient pulse width;
step 6, starting sampling of a first radio frequency channel f1, a second radio frequency channel f2, a third radio frequency channel f3 and a fourth radio frequency channel f 4;
and 7, reconstructing an image.
Step 2 as described above comprises the steps of:
step 2.1, setting parameters of a first radio frequency channel f1, intensity Gsvel of the slice selection gradient pulse and intensity Grevel of the readout gradient pulse, wherein the parameters of the first radio frequency channel f1 comprise setting of a first excitation pulse shape and a first excitation pulse width P1First sampling spectral width SW1And a first sample time acqutime 1; calculating the frequency domain width BW of the excitation pulse corresponding to the first nuclide according to the attribute parameters of the shape of the first excitation pulse1；
Step 2.2, setting parameters of a second radio frequency channel f2, specifically including: second excitation pulse shape, second excitation pulse width P2Second sample spectral width SW2And a second sample time acqutime 2; calculating the frequency domain width BW of the second excitation pulse2；
Step 2.3, setting parameters of a third radio frequency channel f3, specifically including: third excitation pulse shape and third excitation pulse width P3The third sampling spectral width SW3And a third sample time acqutime 3; calculating the frequency domain width BW of the third excitation pulse3；
Step 2.4, setting parameters of a fourth radio frequency channel f4, specifically including: fourth excitation pulse shape and fourth excitation pulse width P4The fourth sampling spectral width SW4And a fourth sample time acqutime 4; calculating the frequency domain width BW of the fourth excitation pulse4。
In step 2.1 as described above: according to gamma1×Gslevel×Th＝BW1Calculating the gradient pulse intensity Gslevel, gamma1The magnetic spin ratio of the first nuclear species, Th the layer thickness, BW1A frequency domain width of a first excitation pulse corresponding to a first nuclear species;
according to gamma1×Grlevel×FOVr＝SW1Calculating the read gradient pulse intensity Grlevel, FOVr is the frequency coding direction checking area,
first sampling time acqutime1 ═ M/SW1M is the number of sampling points;
in the step 2.2:
frequency domain width BW of second excitation pulse2＝γ2×Gslevel×Th，γ2Is the magnetic rotation ratio of the second nuclear species; second excitation pulse width P2Attribute parameters according to the shape of the second excitation pulse and the second frequency domain width BW2Calculating to obtain;
second sample spectral width SW2＝γ2×Grlevel×FOVr；
Second sampling time acqutime2 ═ M/SW2；
In the step 2.3:
frequency domain width BW of third excitation pulse3＝γ3×Gslevel×Th，γ3Is the magnetic rotation ratio of the third nuclide; third excitation pulse width P3Attribute parameters according to the third excitation pulse shape and a third frequency domain width BW3Calculating to obtain;
third sample spectral width SW3＝γ3×Grlevel×FOVr；
Third sample time acqutime3 ═ M/SW3；
In the step 2.4:
frequency domain width BW of fourth excitation pulse4＝γ4×Gslevel×Th，γ4Is the magnetic rotation ratio of the fourth nuclear species; fourth excitation pulse width P4Attribute parameters according to the fourth excitation pulse shape and a fourth frequency domain width BW4Calculating to obtain;
fourth sample spectral width SW4＝γ4×Grlevel×FOVr；
Fourth sample time acqutime4 ═ M/SW4。
The readout gradient pulse width in step 3 as described above is set to the maximum value among the first sampling time acqutime1, the second sampling time acqutime2, the third sampling time acqutime3, and the fourth sampling time acqutime 4.
The slice selection gradient pulse width in step 4 as described above is set to the first excitation pulse width P1Second excitation pulse width P2The third excitation pulse width P3And a fourth excitation pulse width P4Maximum value of (2).
The centers of the first, second, third and fourth excitation pulses as described above are aligned, and are time-sequentially aligned with the centers of the slice selection gradient pulses,
the selective layer echo gradient pulse is applied next to the selective layer gradient pulse, and the width of the readout dispersed phase gradient pulse is kept consistent with that of the selective layer echo gradient pulse;
the area of the selective layer echo gradient pulse is equal to half of the area of the selective layer gradient pulse, the area of the readout dispersed phase gradient pulse is equal to half of the area of the readout gradient pulse,
the strength of the phase encoding echo gradient pulse is equal to-Gplevel, the width of the phase encoding echo gradient pulse is equal to that of the phase encoding gradient pulse,
the widths of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are consistent and the centers of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are aligned in time sequence,
the readout gradient pulse is applied after the readout dephasing gradient pulse,
the sampling windows of the first, second, third and fourth radio frequency channels f1, f2, f3, f4 are centered and aligned with the readout gradient pulse,
and after the sampling of the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 is finished, phase encoding echo gradient pulses are applied.
Step 7 as described above comprises the steps of:
signals acquired by the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 are respectively recorded as a first acquisition signal echo1, a second acquisition signal echo2, a third acquisition signal echo3 and a fourth acquisition signal echo4, and the first acquisition signal echo1, the second acquisition signal echo1 and the fourth acquisition signal echo4 are respectively recordedFilling the number echo2, the third acquisition signal echo3 and the fourth acquisition signal echo4 into k spaces of a first nuclide, a second nuclide, a third nuclide and a fourth nuclide respectively, and performing image reconstruction to obtain an image of each nuclide; the phase encoding direction of the reconstructed image is determined according to the respective magnetic rotation ratio and the magnetic rotation ratio gamma of the first nuclide1Interpolated up or down to the same examination area FOV.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention ensures the consistent layer thickness of the four nuclides by matching the parameters of the radio frequency channel excitation pulse and the layer selection gradient pulse width;
2. the invention ensures that FOVs of the four nuclide frequency encoding directions are consistent by matching the sampling spectrum width of the radio frequency channel;
3. the invention ensures that the apparent FOV of the two nuclides in the phase encoding direction is consistent by scaling the reconstructed image along the phase encoding direction;
4. the invention solves the problems of different nuclide layer thicknesses and large FOV difference, and is beneficial to promoting the development of the multi-core synchronous magnetic resonance imaging technology.
Drawings
FIG. 1 is a timing diagram of a pulse sequence for four-species simultaneous imaging according to an embodiment of the present invention, with the horizontal axis showing the time axis.
Detailed Description
The present invention will be described in further detail with reference to examples for the purpose of facilitating understanding and practice of the invention by those of ordinary skill in the art, and it is to be understood that the present invention has been described in the illustrative embodiments and is not to be construed as limited thereto.
A pulse sequence as shown in figure 1 is loaded on a magnetic resonance imaging system console supporting four-channel simultaneous transmit and receive.
A four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method, comprising the steps of:
step 1, setting an inspection area FOV, a layer thickness Th and a sampling matrix [ M N ];
wherein M is the number of sampling points, N is the number of encoding steps in the phase encoding direction, and the inspection area FOV comprises a frequency encoding direction inspection area FOVr and a phase encoding direction inspection area FOVp;
step 2, setting parameters of a first radio frequency channel f1, a second radio frequency channel f2, a third radio frequency channel f3 and a fourth radio frequency channel f4, wherein the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 are radio frequency channels corresponding to a first nuclear species, a second nuclear species, a third nuclear species and a fourth nuclear species respectively, and the method specifically comprises the following steps:
step 2.1, setting parameters of the first radio frequency channel f1, the intensity Ggradient of the slice selection gradient pulse and the intensity Grlevel of the readout gradient pulse, specifically as follows:
setting parameters of the first radio frequency channel f1 specifically includes: setting a first excitation pulse shape and a first excitation pulse width P1First sampling spectral width SW1And a first sample time acqutime 1; calculating the frequency domain width BW of the first excitation pulse corresponding to the first nuclide according to the attribute parameters of the first excitation pulse shape1. In this embodiment, the first excitation pulse is a Gauss pulse.
According to gamma1×Gslevel×Th＝BW1Calculating the gradient pulse intensity Gslevel, gamma1The magnetic spin ratio of the first nuclear species, Th the layer thickness, BW1The frequency domain width of the first excitation pulse corresponding to the first nuclear species.
According to gamma1×Grlevel×FOVr＝SW1Calculating the read gradient pulse intensity Grlevel, FOVr is the frequency encoding direction checking area, and the first sampling time acqutime1 is M/SW1And M is the number of sampling points.
Step 2.2, setting parameters of a second radio frequency channel f2, specifically including: second excitation pulse shape, second excitation pulse width P2Second sample spectral width SW2And a second sample time acqutime 2;
frequency domain width BW of second excitation pulse2＝γ2×Gslevel×Th，γ2Is the magnetic rotation ratio of the second nuclear species;
second excitation pulse width P2Property parameter according to the shape of the second excitation pulse andtwo frequency domain width BW2Calculating to obtain;
second sample spectral width SW2＝γ2×Grlevel×FOVr；
Second sampling time acqutime2 ═ M/SW2；
The second excitation pulse in this example is a transmit pulse.
Step 2.3, setting parameters of a third radio frequency channel f3, specifically including: third excitation pulse shape and third excitation pulse width P3The third sampling spectral width SW3And a third sample time acqutime 3;
frequency domain width BW of third excitation pulse3＝γ3×Gslevel×Th，γ3Is the magnetic rotation ratio of the third nuclide;
third excitation pulse width P3Attribute parameters according to the third excitation pulse shape and a third frequency domain width BW3Calculating to obtain;
third sample spectral width SW3＝γ3×Grlevel×FOVr；
Third sample time acqutime3 ═ M/SW3。
In this embodiment, the third excitation pulse is an exponential function modified Gauss pulse;
step 2.4, setting parameters of a fourth radio frequency channel f4, specifically including: fourth excitation pulse shape and fourth excitation pulse width P4The fourth sampling spectral width SW4And a fourth sample time acqutime 4;
frequency domain width BW of fourth excitation pulse4＝γ4×Gslevel×Th，γ4Is the magnetic rotation ratio of the fourth nuclear species;
fourth excitation pulse width P4Attribute parameters according to the fourth excitation pulse shape and a fourth frequency domain width BW4Calculating to obtain;
fourth sample spectral width SW4＝γ4×Grlevel×FOVr；
Fourth sample time acqutime4 ═ M/SW4；
In this embodiment, the fourth excitation pulse is a SINC pulse with 5 side lobes.
Step 3, setting parameters of a frequency coding gradient channel Gr, which specifically comprises the following steps: reading out the intensity of the dephasing gradient pulse, the width of the dephasing gradient pulse, the intensity Grlevel of the reading gradient pulse and the width of the reading gradient pulse; the readout gradient pulse width is set to the maximum value among the first sampling time acqutime1, the second sampling time acqutime2, the third sampling time acqutime3, and the fourth sampling time acqutime 4;
step 4, setting parameters of the layer selection gradient channel Gs, which specifically comprises the following steps: the gradient pulse intensity Gslevel of the selected layer, the gradient pulse width of the selected layer and the echo gradient pulse width of the selected layer; the gradient pulse width of the selected layer is set to be the first excitation pulse width P1Second excitation pulse width P2The third excitation pulse width P3And a fourth excitation pulse width P4Maximum value of (2).
The centers of the first, second, third and fourth excitation pulses are aligned and are time-sequentially aligned with the center of the slice selection gradient pulse.
The selective layer echo gradient pulse is applied next to the selective layer gradient pulse, and the width of the readout dispersed phase gradient pulse is kept consistent with that of the selective layer echo gradient pulse;
and calculating the intensity of the selective layer echo gradient pulse according to the fact that the area of the selective layer echo gradient pulse is equal to half of the area of the selective layer gradient pulse. The readout dephasing gradient pulse strength is calculated based on the readout dephasing gradient pulse area being equal to half the readout gradient pulse area.
Step 5, setting parameters of a phase encoding gradient channel Gp, specifically including: phase encoding gradient pulse strength Gplevel, phase encoding gradient pulse width, phase encoding echo gradient pulse strength and phase encoding echo gradient pulse width;
and calculating a phase encoding gradient pulse intensity array Gplevel (N) according to the magnetic rotation ratio of the first nuclear species, wherein N is 1,2 … N and N is the total number of the phase encoding gradient pulse intensities. The intensity of the phase encoding echo gradient pulse is equal to-Gplevel, and the width of the phase encoding echo gradient pulse is equal to that of the phase encoding gradient pulse.
The widths of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are consistent, and the centers of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are aligned in time sequence.
The readout gradient pulse is applied after the readout dephasing gradient pulse.
Step 6, during the application of the readout gradient pulse, the first rf channel f1, the second rf channel f2, the third rf channel f3 and the fourth rf channel f4 turn on sampling, wherein the sampling windows of the first rf channel f1, the second rf channel f2, the third rf channel f3 and the fourth rf channel f4 are center-aligned and are center-aligned with the readout gradient pulse.
Signals acquired by the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 are respectively denoted as a first acquisition signal echo1, a second acquisition signal echo2, a third acquisition signal echo3 and a fourth acquisition signal echo 4.
And applying phase coding echo gradient pulses after the sampling of the four radio frequency channels is finished.
And 7, reconstructing an image, which specifically comprises the following steps:
filling a first acquisition signal echo1, a second acquisition signal echo2, a third acquisition signal echo3 and a fourth acquisition signal echo4 into k spaces of a first nuclide, a second nuclide, a third nuclide and a fourth nuclide respectively, and performing image reconstruction to obtain an image of each nuclide; the phase encoding direction of the reconstructed image is determined according to the respective magnetic rotation ratio and the magnetic rotation ratio gamma of the first nuclide1Interpolated up or down to the same examination area FOV.
It should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (7)
1. A four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method is characterized by comprising the following steps:
step 1, setting an inspection area FOV, a layer thickness Th and a sampling matrix [ M N ];
wherein M is the number of sampling points, N is the number of encoding steps in the phase encoding direction, and the inspection area FOV comprises a frequency encoding direction inspection area FOVr and a phase encoding direction inspection area FOVp;
step 2, setting parameters of a first radio frequency channel f1, a second radio frequency channel f2, a third radio frequency channel f3 and a fourth radio frequency channel f4 corresponding to the first nuclear species, the second nuclear species, the third nuclear species and the fourth nuclear species,
step 3, setting parameters of a frequency coding gradient channel Gr, wherein the parameters of the frequency coding gradient channel Gr comprise: reading out the intensity of the dephasing gradient pulse, the width of the dephasing gradient pulse, the intensity Grlevel of the reading gradient pulse and the width of the reading gradient pulse;
and 4, setting parameters of the layer selection gradient channel Gs, wherein the parameters of the layer selection gradient channel Gs comprise: the gradient pulse intensity Gslevel of the selected layer, the gradient pulse width of the selected layer and the echo gradient pulse width of the selected layer;
setting parameters of a phase encoding gradient channel Gp, wherein the parameters of the phase encoding gradient channel Gp comprise phase encoding gradient pulse strength Gplevel, phase encoding gradient pulse width, phase encoding echo gradient pulse strength and phase encoding echo gradient pulse width;
step 6, starting sampling of a first radio frequency channel f1, a second radio frequency channel f2, a third radio frequency channel f3 and a fourth radio frequency channel f 4;
and 7, reconstructing an image.
2. The four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method as set forth in claim 1, wherein the step 2 comprises the steps of:
step 2.1, setting parameters of a first radio frequency channel f1, intensity Gsvel of the slice selection gradient pulse and intensity Grevel of the readout gradient pulse, wherein the parameters of the first radio frequency channel f1 comprise setting of a first excitation pulse shape and a first excitation pulse width P1First sampling spectral width SW1And a first sample time acqutime 1; calculating the excitation corresponding to the first nuclide according to the attribute parameters of the first excitation pulse shapeFrequency domain width BW of transmit pulse1；
Step 2.2, setting parameters of a second radio frequency channel f2, specifically including: second excitation pulse shape, second excitation pulse width P2Second sample spectral width SW2And a second sample time acqutime 2; calculating the frequency domain width BW of the second excitation pulse2；
Step 2.3, setting parameters of a third radio frequency channel f3, specifically including: third excitation pulse shape and third excitation pulse width P3The third sampling spectral width SW3And a third sample time acqutime 3; calculating the frequency domain width BW of the third excitation pulse3；
Step 2.4, setting parameters of a fourth radio frequency channel f4, specifically including: fourth excitation pulse shape and fourth excitation pulse width P4The fourth sampling spectral width SW4And a fourth sample time acqutime 4; calculating the frequency domain width BW of the fourth excitation pulse4。
3. The four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method as claimed in claim 2, wherein in the step 2.1: according to gamma1×Gslevel×Th＝BW1Calculating the gradient pulse intensity Gslevel, gamma1The magnetic spin ratio of the first nuclear species, Th the layer thickness, BW1A frequency domain width of a first excitation pulse corresponding to a first nuclear species;
according to gamma1×Grlevel×FOVr＝SW1Calculating the read gradient pulse intensity Grlevel, FOVr is the frequency coding direction checking area,
first sampling time acqutime1 ═ M/SW1M is the number of sampling points;
in the step 2.2:
frequency domain width BW of second excitation pulse2＝γ2×Gslevel×Th，γ2Is the magnetic rotation ratio of the second nuclear species;
second excitation pulse width P2Attribute parameters according to the shape of the second excitation pulse and the second frequency domain width BW2Calculating to obtain;
second samplingSpectral width SW2＝γ2×Grlevel×FOVr；
Second sampling time acqutime2 ═ M/SW2；
In the step 2.3:
frequency domain width BW of third excitation pulse3＝γ3×Gslevel×Th，γ3Is the magnetic rotation ratio of the third nuclide;
third excitation pulse width P3Attribute parameters according to the third excitation pulse shape and a third frequency domain width BW3Calculating to obtain;
third sample spectral width SW3＝γ3×Grlevel×FOVr；
Third sample time acqutime3 ═ M/SW3；
In the step 2.4:
frequency domain width BW of fourth excitation pulse4＝γ4×Gslevel×Th，γ4Is the magnetic rotation ratio of the fourth nuclear species; fourth excitation pulse width P4Attribute parameters according to the fourth excitation pulse shape and a fourth frequency domain width BW4Calculating to obtain;
fourth sample spectral width SW4＝γ4×Grlevel×FOVr；
Fourth sample time acqutime4 ═ M/SW4。
4. A four-nuclear synchronous magnetic resonance imaging and image reconstruction method as set forth in claim 3, wherein the readout gradient pulse width in step 3 is set to the maximum of the first sampling time acqutime1, the second sampling time acqutime2, the third sampling time acqutime3, and the fourth sampling time acqutime 4.
5. The four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method as claimed in claim 4, wherein the slice selection gradient pulse width in step 4 is set to be the first excitation pulse width P1Second excitation pulse width P2The third excitation pulse width P3And a fourth excitation pulse width P4Maximum value of (2).
6. The four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method as claimed in claim 5, wherein the centers of the first, second, third and fourth excitation pulses are aligned and are time-sequentially aligned with the center of the slice selection gradient pulse,
the selective layer echo gradient pulse is applied next to the selective layer gradient pulse, and the width of the readout dispersed phase gradient pulse is kept consistent with that of the selective layer echo gradient pulse;
the area of the selective layer echo gradient pulse is equal to half of the area of the selective layer gradient pulse, the area of the readout dispersed phase gradient pulse is equal to half of the area of the readout gradient pulse,
the strength of the phase encoding echo gradient pulse is equal to-Gplevel, the width of the phase encoding echo gradient pulse is equal to that of the phase encoding gradient pulse,
the widths of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are consistent and the centers of the phase encoding gradient pulse, the readout dephasing gradient pulse and the selective layer echo gradient pulse are aligned in time sequence,
the readout gradient pulse is applied after the readout dephasing gradient pulse,
the sampling windows of the first, second, third and fourth radio frequency channels f1, f2, f3, f4 are centered and aligned with the readout gradient pulse,
and after the sampling of the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 is finished, phase encoding echo gradient pulses are applied.
7. The four-nuclear-species synchronous magnetic resonance imaging and image reconstruction method as claimed in claim 6, wherein the step 7 comprises the steps of:
signals acquired by the first radio frequency channel f1, the second radio frequency channel f2, the third radio frequency channel f3 and the fourth radio frequency channel f4 are respectively recorded as a first acquisition signal echo1, a second acquisition signal echo2, a third acquisition signal echo3 and a fourth acquisition signal echo4, and the first acquisition signal echo1, the second acquisition signal echo2 and the third acquisition signal e are respectively recorded as a first acquisition signal echo1, a second acquisition signal echo2, a third acquisition signal echo3 and a fourth acquisition signal echo4The cho3 and the fourth acquisition signal echo4 are respectively filled in k spaces of the first nuclide, the second nuclide, the third nuclide and the fourth nuclide, and image reconstruction is carried out to obtain an image of each nuclide; the phase encoding direction of the reconstructed image is determined according to the respective magnetic rotation ratio and the magnetic rotation ratio gamma of the first nuclide1Interpolated up or down to the same examination area FOV.
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