A method for MRI image reconstruction

Abstract

The present application discloses a method for MRI image reconstruction, the method comprising: (S1) obtaining an MRI image sequence based on a T1-T2 switchable dual-mode contrast agent; wherein the MRI image sequence is an MRI image sequence obtained by continuous scanning n times, where n ≥ 2; (S2) reading the grayscale value of each single pixel in the MRI image sequence and drawing a curve of the grayscale value changing over time; (S3) calculating the time autocorrelation cumulant function and the spatial cross-correlation cumulant function of each single pixel based on the curve; and (S4) reconstructing a two-dimensional image based on the time autocorrelation cumulant function value and the spatial cross-correlation cumulant function value. The two-dimensional image reconstructed by the method has a high contrast, thereby improving the image fidelity.

Description

Technical Field

[0001] The present application relates to a method for MRI image reconstruction, and belongs to the technical field of magnetic resonance imaging. Background Art

[0002] In recent years, super-resolution optical imaging technology has developed rapidly, breaking through the limitations of the optical diffraction limit on imaging spatial resolution. Among them, super-resolution techniques based on random fluorescence fluctuations achieve a good trade-off between imaging speed and spatial resolution, offering advantages such as high resolution, low phototoxicity, low system cost, and a small number of required image frames. This technology exploits the temporal fluctuations in the intensity of the fluorescence emitted by quantum dots, known as fluorescence blinking, and improves the spatiotemporal resolution of super-resolution imaging by analyzing and processing the blinking signal through correlation functions. Fluorescence blinking follows a power law, and its generation mechanism may be the capture and loss of electrons by dangling bonds on the surface of quantum dots. When the dangling bonds are positively charged, the quantum dots emit light; when the dangling bonds are neutral or negatively charged, the quantum dots remain in a dark state.

[0003] As another non-invasive and powerful imaging technique, magnetic resonance imaging (MRI) can effectively provide information on tissue chemistry and physiological environment, and realize multi-parameter and multi-directional direct imaging. T1-weighted MRI uses longitudinal relaxation imaging, and its bright white image indicates high signal; T2-weighted MRI uses longitudinal relaxation imaging, and its gray-black image indicates high signal. T1-T2 dual-mode contrast agents are expected to achieve complementary imaging modes, further improve contrast and enhance imaging effects. At present, T1-T2 dual-mode contrast agents can realize two modes of MRI weighted imaging on the same magnetic resonance imaging machine. However, research on using the magnetic resonance scintillation effect of T1-T2 switchable dual-mode contrast agents to achieve super-resolution imaging has not been reported. Summary of the Invention

[0004] According to one aspect of the present application, a method for MRI image reconstruction is provided. The method is based on the use of a T1-T2 switchable dual-mode contrast agent to obtain an MRI image sequence in which T1-weighted images and T2-weighted images are alternately displayed (i.e., magnetic resonance scintillation). Through a fluctuation signal analysis algorithm, low-frequency components and readout noise can be eliminated, and high-frequency components can be extracted to enhance imaging resolution. The reconstructed two-dimensional image has a higher contrast, thereby improving the image fidelity.

[0005] A method for MRI image reconstruction, comprising:

[0006] (S1) Obtaining MRI image sequences based on T1-T2 switchable dual-mode contrast agents;

[0007] Wherein, the MRI image sequence is an MRI image sequence obtained by continuous scanning n times, where n≥2;

[0008] (S2) reading the grayscale value of each single pixel in the MRI image sequence and drawing a curve showing the change of the grayscale value over time;

[0009] (S3) calculating the temporal autocorrelation cumulant function and the spatial cross-correlation cumulant function of each single pixel point according to the curve;

[0010] (S4) Reconstructing a two-dimensional image based on the temporal autocorrelation cumulant function value and the spatial cross-correlation cumulant function value.

[0011] Optionally, in step (S1), the deformation of the T1-T2 switchable dual-mode contrast agent under stimulation realizes the switching between the T1-type contrast agent and the T2-type contrast agent by changing the magnetic properties;

[0012] Optionally, the stimulation is selected from external energy stimulation, selected from at least one of an alternating magnetic field, an alternating electric field, an alternating light field, an alternating temperature field, and an alternating ultrasonic field;

[0013] Optionally, the deformation is a change in particle size.

[0014] Optionally, the MRI image sequence in step (S1) is a T1-weighted image sequence;

[0015] Said n=5-500.

[0016] Optionally, n=5-200.

[0017] Optionally, n=5-100.

[0018] Optionally, the T1-T2 switchable dual-mode contrast agent has a core-shell coating structure:

[0019] wherein the shell is a hydrophilic polymer;

[0020] The core is a magnetic nanoparticle coated with polymer I, and at least one core is uniformly dispersed in the shell;

[0021] The polymer I and the hydrophilic polymer are linked via an amide bond and / or an ester bond.

[0022] Optionally, at least two cores are encapsulated in the shell; and the cores are uniformly dispersed in the shell.

[0023] Optionally, the magnetic nanoparticles are selected from at least one of the substances having the general formula shown in Formula I;

[0024] Zn x Fe 3-x O4 formula I;

[0025] The value range of x is 0.1 to 0.9;

[0026] Optionally, the surface of the polymer I contains carboxyl groups and / or anhydride groups;

[0027] The monomer of the hydrophilic polymer contains carbon-carbon unsaturated bonds, hydroxyl groups and / or amino groups.

[0028] Optionally, the value of x ranges from 0.1 to 0.5.

[0029] Optionally, the magnetic nanoparticles are selected from Zn 0.1 Fe 2.9 O4、Zn 0.2 Fe 2.8 O4、Zn 0.3 Fe 2.7 O4、Zn 0.4 Fe 2.6 At least one of O4.

[0030] Optionally, the polymer I is selected from at least one of polyisobutylene isobutylene-maleic anhydride, mercapto-polyethylene glycol-carboxyl, and amino-polyethylene glycol-carboxyl.

[0031] Optionally, the particle size of the magnetic nanoparticles is 1 nm to 20 nm.

[0032] Optionally, the upper limit of the particle size of the magnetic nanoparticles is selected from 4, 7, 10, 15, 20 nm; the lower limit is selected from 1, 4, 7, 10, 15 nm.

[0033] Optionally, the particle size of the T1-T2 switchable dual-mode contrast agent is 50 nm to 1000 nm.

[0034] Optionally, the upper limit of the particle size of the T1-T2 switchable dual-mode contrast agent is selected from 80, 100, 150, 200, 300, 400, 500, 800, 1000 nm; the lower limit is selected from 50, 80, 100, 150, 200, 400, 300, 500, 800 nm.

[0035] Optionally, the T1-T2 switchable dual-mode contrast agent is Zn 0.2 Fe 2.8 O4@polyisobutyleneisobutylene-maleic anhydride@2-hydroxyethyl methacrylate.

[0036] The preparation method of the T1-T2 switchable dual-mode contrast agent comprises:

[0037] (SI) contacting a raw material containing magnetic nanoparticles coated with polymer I and a polymerizable monomer of a hydrophilic polymer in the presence of a catalyst to perform reaction II to obtain a precursor;

[0038] (SII) A free radical initiator is added to the precursor, and a T1-T2 switchable dual-mode contrast agent is obtained through polymerization reaction III.

[0039] Optionally, in (SI), the conditions of reaction II are: temperature II is 10-40°C, and time II is not less than 1 h;

[0040] The catalyst is selected from at least one coupling agent;

[0041] The polymerizable monomer is selected from at least one of acrylate compounds;

[0042] (SII), wherein the free radical initiator is at least one selected from azo compounds;

[0043] In (SII), the conditions of the polymerization reaction III are: temperature III is 40° C. to 100° C., and time III does not exceed 4 hours.

[0044] Optionally, the coupling agent is selected from at least one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, dicyclohexylcarbodiimide, N-hydroxysuccinimide, and 4-dimethylaminopyridine.

[0045] Optionally, the acrylate compound is selected from 2-hydroxyethyl methacrylate and / or glycosyloxyethyl methacrylate.

[0046] Optionally, the temporal autocorrelation cumulant function of the single pixel point in step (S3) is expressed as:

[0047] G(r, τ)=[δF(r, t+τ)×δF(r, t)] t

[0048] =∑ i U 2 (rr i )×ε i 2 ×[δs i (t+τ)δs i (t)] t ;

[0049] Among them, the G function is a single pixel accumulation function formula with spatial r and temporal variation τ as independent variables, F is the MRI signal function, t is time, and δ is the matrix formula; U is the real part of the spatial accumulation function, that is, the pixel point expansion function in the spatial system, ε is the imaginary part of the spatial accumulation function representing the grayscale of a single pixel, and s is the temporal accumulation function part representing the change of the grayscale of a single pixel.

[0050] Optionally, the reconstruction method in step (S4) is:

[0051] The MRI light and dark signal intensity difference F of each pixel is obtained according to the temporal autocorrelation cumulant function value and the spatial cross-correlation cumulant function value, and a two-dimensional image is reconstructed according to the MRI light and dark signal intensity difference F. The MRI light and dark signal intensity difference F is expressed as:

[0052]

[0053] Where r and t are the spatial and temporal positions, respectively; N is the number of individual pixels; U is the point spread function of the system; ε is the grayscale of a single pixel; s represents the fluctuation of the grayscale of a single pixel; r i is the spatial position of the i-th single pixel.

[0054] According to another aspect of the present application, a super-resolution imaging method is provided, by adopting at least one of the MRI image reconstruction methods described above;

[0055] Optionally, the super-resolution imaging is based on magnetic resonance scintillation.

[0056] The super-resolution imaging method provided in this application is based on super-resolution imaging of magnetic resonance scintigraphy, which is used to optimize the imaging signal in time and space, and is expected to eliminate false signals, provide higher-resolution imaging effects for clinical diagnosis, and promote the development of diversified diagnostic technology platforms.

[0057] According to another aspect of the present application, there is provided an application of a method for MRI image reconstruction as described in any of the above items, or a method for super-resolution imaging as described in any of the above items in constructing a method for conventional magnetic resonance imaging, magnetic resonance diffusion-weighted imaging, magnetic resonance perfusion imaging, blood oxygen level-dependent functional imaging, or magnetic resonance spectroscopy.

[0058] According to one embodiment of the present application, a super-resolution imaging method based on magnetic resonance scintillation is provided, comprising: acquiring an MRI image sequence for a certain period of time, reading the grayscale value of a single pixel on the image to draw its time variation curve, calculating the temporal autocorrelation or spatial cross-correlation cumulant function of each pixel in the image, and reconstructing a two-dimensional image according to the values ​​of each correlation cumulant function.

[0059] In a preferred embodiment, the magnetic resonance scintillation is an alternating display of imaging signals enhanced by T1-type and T2-type contrast agents, showing a trend of light and dark changes.

[0060] In a preferred embodiment, the MRI image sequence acquired for a certain period of time is image acquisition based on a T1-T2 switchable dual-mode contrast agent;

[0061] The certain time is the time used for n consecutive rapid MRI scans;

[0062] Optionally, n is 50 to 500;

[0063] The MRI image sequence is a T1-weighted image sequence;

[0064] The T1-T2 switchable dual-mode contrast agent can deform under stimulation;

[0065] Optionally, the contrast agent is Zn 0.2 Fe 2.8 O4@polyisobutyleneisobutylene-maleic anhydride@2-hydroxyethyl methacrylate;

[0066] Optionally, the stimulation is external energy stimulation, selected from at least one of an alternating magnetic field, an alternating electric field, an alternating light field, an alternating temperature field, and an alternating ultrasonic field;

[0067] Furthermore, the stimulation is an alternating magnetic field;

[0068] The deformation realizes the switching between T1 type contrast agent and T2 type contrast agent by changing the magnetic properties;

[0069] Optionally, the deformation is a change in particle size.

[0070] In a preferred embodiment, the grayscale value of a single pixel on the read image is plotted as a time variation curve to observe the fluctuation of the grayscale value of each pixel over time.

[0071] In a preferred embodiment, the temporal autocorrelation or spatial cross-correlation cumulant function of each pixel point in the calculated image is used to obtain a correlation term of the MRI signal intensity F;

[0072] The MRI signal intensity F can be expressed as:

[0073]

[0074] Where r and t are the spatial and temporal positions, respectively; N is the number of individual pixels contained in the sample; U is the point spread function of the system; ε is the grayscale of a single pixel; s represents the fluctuation of the grayscale of a single pixel; r i is the spatial position of the i-th single pixel.

[0075] The temporal autocorrelation function can be expressed as:

[0076]

[0077] The G function is a single pixel accumulation function formula with spatial r and temporal variation τ as independent variables, F is the MRI signal function, t is time, and δ is the matrix formula; U is the real part of the spatial accumulation function, that is, the pixel expansion function in the spatial system, ε is the imaginary part of the spatial accumulation function representing the grayscale of a single pixel, and s is the temporal accumulation function part representing the change in the grayscale of a single pixel.

[0078] The spatial cross-correlation function is used to eliminate the influence of shot noise that has no correlation and comes from different pixels;

[0079] The cumulant function is used to eliminate cross terms caused by low-order correlation functions.

[0080] In a preferred embodiment, the two-dimensional image is reconstructed according to the respective correlation cumulant function values ​​to provide a contrast-enhanced scan image.

[0081] According to another embodiment of the present application, at least one application of the above detection method in conventional magnetic resonance imaging, magnetic resonance diffusion-weighted imaging, magnetic resonance perfusion imaging, blood oxygen level-dependent functional imaging, and magnetic resonance spectroscopy is provided.

[0082] The beneficial effects of this application include:

[0083] 1) The MRI image reconstruction method provided in this application is based on the use of a T1-T2 switchable dual-mode contrast agent to obtain an MRI image sequence in which T1-weighted images and T2-weighted images are alternately displayed (i.e., magnetic resonance scintigraphy). The MRI images are collected for image reconstruction. Through a fluctuation signal analysis algorithm, low-frequency components and readout noise can be eliminated, and high-frequency components can be extracted to enhance imaging resolution. The reconstructed two-dimensional image has a high contrast, thereby improving image fidelity.

[0084] 2) The MRI image reconstruction method provided in this application optimizes the imaging signal in time and space, eliminates false signals, provides higher-resolution imaging effects for clinical diagnosis, and promotes the development of diversified diagnostic technology platforms.

[0085] 3) The MRI image reconstruction method provided in the present application uses a dual-mode contrast agent that can efficiently switch between T1-type contrast agent and T2-type contrast agent, effectively providing a fluctuation signal.

[0086] 4) The MRI image reconstruction method provided in this application uses a dual-mode contrast agent that can change its particle size by applying external energy stimulation, thereby achieving efficient switching between T1-type contrast agent and T2-type contrast agent, effectively providing a fluctuation signal.

[0087] 5) The MRI image reconstruction method provided in this application uses a T1-weighted sequence for continuous rapid scanning, with a short data acquisition cycle and a high sampling frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 This is a schematic diagram of the principle of the MRI image reconstruction method of the present application.

[0089] Figure 2The T1-T2 switchable dual-mode contrast agent (Zn 0.2 Fe 2.8 Transmission electron microscope image of O4@polyisobutylene (isobutylene-maleic anhydride@2-hydroxyethyl methacrylate).

[0090] Figure 3 It is the brightest image and its average grayscale in the T1-weighted image sequence collected in Example 2.

[0091] Figure 4 It is the darkest image in the T1-weighted image sequence collected in Example 2 and its average grayscale.

[0092] Figure 5 This is the reconstructed image in Example 2. DETAILED DESCRIPTION

[0093] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0094] Unless otherwise specified, all raw materials and reagents used in this application were purchased from commercial sources and used directly without treatment. The instruments and equipment used adopted the protocols and parameters recommended by the manufacturers.

[0095] The room temperature described in this application is 25°C.

[0096] Figure 1 The flowchart of the present invention is shown, which generally reflects the concept of the present invention.

[0097] Example 1 Obtaining a T1-T2 switchable dual-mode contrast agent

[0098] Hydrophilic magnetic solid nanosphere sample (Zn 0.2 Fe 2.8 Preparation of O4@polyisobutylene (isobutylene-maleic anhydride@2-hydroxyethyl methacrylate)

[0099] (1) Zn coated with polymer I 0.2 Fe 2.8 O4(Zn 0.2 Fe 2.8 Preparation of O4-PMA

[0100] Take the oil phase Zn with an average particle size of 7 nm at a molar ratio of 1:50 0.2 Fe 2.8 O4 nanoparticles were mixed with amphiphilic polymer PMA and stirred evenly in chloroform solution by rotary evaporator at room temperature until chloroform was completely evaporated to obtain Zn 0.2 Fe 2.8 O4-PMA, the resulting Zn 0.2 Fe 2.8The average particle size of O4-PMA is 15 nm.

[0101] The oil phase Zn 0.2 Fe 2.8 The preparation method of O4 nanoparticles refers to the literature "Controlling the doping content and particle size to accurately adjust the Zn x Fe 3-x Ma, Yuanyuan, et al. "Precisely Tuning the Contrast Properties of ZnO4 Nanoparticles in Magnetic Resonance Imaging" x Fe 3-x O4Nanoparticles in Magnetic ResonanceImaging by Controlling Their Doping Content and Size." Chemistry of Materials, 2019, 31, 18, 7255-7264) were prepared; the synthesis of the amphiphilic polymer PMA and the encapsulation of Zn 0.2 Fe 2.8 The method of O4 was prepared according to the methods in the literature "Polymer-coated nanoparticles: a universal tool for biolabelling experiments" (F. Zhang, E. Lees, F. Amin, P. Rivera Gil, F. Yang, P. Mulvaney, WJ Parak, Polymer-coated nanoparticles: a universal tool for biolabelling experiments, Small, 2011, 7, 22, 3113-27) and "Design of an amphiphilic polymer for nanoparticle coating and functionalization" (CALin, RASperling, JK Li, TY Yang, PY Li, M. Zanella, WHChang, WJ Parak, Design of an amphiphilic polymer for nanoparticle coating and functionalization, Small, 2008, 4, 3, 334-41).

[0102] (2) Monomer II and Zn coated with polymer I 0.2 Fe 2.8 O4 connection

[0103] Take Zn coated with polymer I 0.2 Fe 2.8O4, monomer II and catalyst were mixed with SBB 9 (pH = 9) to form a solution to form Zn coated with polymer I. 0.2 Fe 2.8 SBB solution of O4, SBB solution of monomer II, SBB solution of catalyst.

[0104] Take Zn coated with polymer I 0.2 Fe 2.8 The SBB solution of O4 and the SBB solution of monomer II were mixed evenly in a 1.5 mL centrifuge tube, and then the SBB solution of the catalyst was added. After mixing evenly, the centrifuge tube was placed in a constant temperature shaking incubator for shaking reaction. The specific linking conditions are shown in Table 1.

[0105] Under the conditions in Table 1, after the reaction, the obtained liquid was taken out, centrifuged and washed, and the obtained SBB solution of the sample was stored in a refrigerator at about 4° C. and used as a precursor for subsequent reactions.

[0106] Table 1

[0107]

[0108]

[0109] (3) Preparation of hydrophilic magnetic solid nanosphere samples

[0110] Take the SBB solution of the above precursor in a 1.5 mL centrifuge tube and add the solution of the free radical initiator. After mixing evenly, place the centrifuge tube in a cell disruptor to react until the reaction is complete. After washing and centrifugation, the hydrophilic magnetic solid nanospheres (Zn 0.2 Fe 2.8 O4@polyisobutyleneisobutylene-maleic anhydride@2-hydroxyethyl methacrylate), the specific preparation conditions are shown in Table 2.

[0111] Table 2

[0112]

[0113] (4) Characterization of hydrophilic magnetic solid nanosphere samples

[0114] The hydrophilic magnetic solid nanosphere samples were characterized using a JEOL JEM 3010UHR transmission electron microscope from JEOL Ltd. Figure 2 As shown, the results show that the obtained hydrophilic magnetic solid nanosphere sample is a spherical sample with uniform particle size distribution, an average particle size of , and an average particle size of 400nm.

[0115] Example 2 Using Zn 0.2 Fe 2.8O4@polyisobutyleneisobutylene-maleic anhydride@2-hydroxyethyl methacrylate as a contrast agent for MRI image reconstruction

[0116] (1) Collect MRI image sequences for a certain period of time and read the grayscale values

[0117] according to Figure 1 The image reconstruction method shown utilizes the Zn 0.2 Fe 2.8 O4@polyisobutyleneisobutylene-maleic anhydride@2-hydroxyethyl methacrylate is used as a contrast agent, and the contrast agent is prepared into a uniform series of concentration gradient dilutions. The dilution is added to the sample, and the sample is scanned using the 1.5T superconducting magnetic resonance imaging system MAGNETOM Aera produced by Siemens AG. During the scanning process, an alternating magnetic field is applied to the sample to switch the contrast agent between T1-type contrast agent and T2-type contrast agent, and the T1-weighted image sequence is scanned and collected, and the number of scans is 5. The brightest and darkest states in the collected T1-weighted image sequence are as follows: Figure 3 、 Figure 4 As shown, only the average grayscale is shown in the figure.

[0118] (2) Calculate the correlation cumulant function to reconstruct the contrast-enhanced scan image

[0119] The grayscale value of each single pixel in the acquired T1-weighted image sequence is read, and multiple scans are performed in the same mode. A curve showing the change of grayscale value over time is plotted, and the temporal autocorrelation cumulative amount function and spatial cross-correlation cumulative amount function of each single pixel are calculated based on the curve. Based on the spatial and temporal accumulations, a statistical histogram is established to obtain the average variance value of the grayscale; the mean square error is substituted into the temporal autocorrelation cumulative amount function and the spatial cross-correlation cumulative amount function to calculate the MRI light and dark signal intensity difference F of each pixel, and a two-dimensional image analysis diagram of the MRI signal is reconstructed, thereby reconstructing the MRI image. The temporal autocorrelation cumulative amount function is expressed as:

[0120] G(r, τ)=[δF(r, t+τ)×δF(r, t)] t

[0121] =∑ i U 2 (rr i )×ε i 2 ×[δs i (t+τ)δs i (t)] t ;

[0122] Among them, the G function is a single pixel accumulation function formula with spatial r and temporal variation τ as independent variables, F is the MRI signal function, t is time, and δ is the matrix formula; U is the real part of the spatial accumulation function, that is, the pixel point expansion function in the spatial system, ε is the imaginary part of the spatial accumulation function representing the grayscale of a single pixel, and s is the temporal accumulation function part representing the change of the grayscale of a single pixel.

[0123] The spatial cross-correlation cumulant function is calculated using the matching algorithm of the 1.5T superconducting magnetic resonance imaging system MAGNETOM Aera;

[0124] The MRI light and dark signal intensity difference F is expressed as:

[0125]

[0126] Where r and t are the spatial and temporal positions, respectively; N is the number of individual pixels contained in the sample; U is the point spread function of the system; ε is the grayscale of a single pixel; s represents the fluctuation of the grayscale of a single pixel; r i is the spatial position of the i-th single pixel.

[0127] The reconstructed image is different from the image before reconstruction ( Figure 3 and Figure 4 ) has better resolution and can provide more intuitive scanning information. The results are as follows Figure 5 shown.

[0128] The concept of the present invention is to effectively eliminate low-frequency components and readout noise, extract high-frequency components, thereby enhancing imaging resolution and providing contrast-enhanced scanned images. Data analysis and processing using a fluctuation signal analysis algorithm optimizes image contrast and accuracy. Conventional magnetic resonance imaging, diffusion-weighted magnetic resonance imaging, magnetic resonance perfusion imaging, blood oxygenation-dependent functional imaging, and magnetic resonance spectroscopy can all be used to obtain contrast-enhanced scanned images based on the image reconstruction method of the present invention.

[0129] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for MRI image reconstruction, characterized in that: The method comprises: (S1) Obtaining MRI image sequences based on T1-T2 switchable dual-mode contrast agents; Wherein, the MRI image sequence is an MRI image sequence obtained by continuous scanning n times, where n≥2; (S2) reading the grayscale value of each single pixel in the MRI image sequence and drawing a curve showing the change of the grayscale value over time; (S3) calculating the temporal autocorrelation cumulant function and the spatial cross-correlation cumulant function of each single pixel point according to the curve; The time autocorrelation cumulant function is expressed as: The G function is a single pixel accumulation function formula with spatial r and temporal variation τ as independent variables, F is the MRI signal function, t is time, and δ is the matrix formula; U is the real part of the spatial accumulation function, i.e., the pixel spread function in the spatial system, ε is the imaginary part of the spatial accumulation function, representing the grayscale of a single pixel, and s is the temporal accumulation function, representing the change in the grayscale of a single pixel. The spatial cross-correlation cumulant function is calculated using the matching algorithm of the 1.5T superconducting magnetic resonance imaging system MAGNETOM Aera; (S4) reconstructing a two-dimensional image according to the temporal autocorrelation cumulant function value and the spatial cross-correlation cumulant function value; the reconstruction method in step (S4) is: The MRI light and dark signal intensity difference F of each pixel is obtained according to the temporal autocorrelation cumulant function value and the spatial cross-correlation cumulant function value, and a two-dimensional image is reconstructed according to the MRI light and dark signal intensity difference F. The MRI light and dark signal intensity difference F is expressed as: Where r and t are the spatial and temporal positions, respectively; N is the number of individual pixels; U is the point spread function of the system; ε is the grayscale of a single pixel; s represents the fluctuation of the grayscale of a single pixel; r i is the spatial position of the i-th single pixel.

2. The method for MRI image reconstruction according to claim 1, wherein: The deformation of the T1-T2 switchable dual-mode contrast agent under stimulation in step (S1) realizes the switching between the T1-type contrast agent and the T2-type contrast agent by changing the magnetic properties; The stimulation is selected from external energy stimulation, which is selected from at least one of an alternating magnetic field, an alternating electric field, an alternating light field, an alternating temperature field, and an alternating ultrasonic field; The deformation is a change in particle size.

3. The method for MRI image reconstruction according to claim 1, wherein: The MRI image sequence in step (S1) is a T1-weighted image sequence; Said n=5-500.

4. The method for MRI image reconstruction according to claim 1, wherein: The T1-T2 switchable dual-mode contrast agent has a core-shell coating structure: wherein the shell is a hydrophilic polymer; The core is a magnetic nanoparticle coated with polymer I, and at least one core is uniformly dispersed in the shell; The polymer I and the hydrophilic polymer are connected via an amide bond and / or an ester bond; The magnetic nanoparticles are selected from at least one substance having the general formula shown in Formula I; Zn x Fe 3-x O4 of formula I; The value range of x is 0.1 to 0.

9.

5. The method for MRI image reconstruction according to claim 4, characterized in that: The surface of the polymer I contains carboxyl groups and / or anhydride groups; The monomer of the hydrophilic polymer contains carbon-carbon unsaturated bonds, hydroxyl groups and / or amino groups.

6. The method for MRI image reconstruction according to claim 4, characterized in that: The magnetic nanoparticles are selected from Zn 0.1 Fe 2.9 O4、Zn 0.2 Fe 2.8 O4、Zn 0.3 Fe 2.7 O4、Zn 0.4 Fe 2.6 At least one of O4.

7. The method for MRI image reconstruction according to claim 4, characterized in that: The particle size of the T1-T2 switchable dual-mode contrast agent is 50 nm to 1000 nm.

8. A super-resolution imaging method, characterized in that: By adopting at least one of the MRI image reconstruction methods according to any one of claims 1 to 7.

9. The super-resolution imaging method according to claim 8, characterized in that: The super-resolution imaging is based on magnetic resonance scintillation.

10. Use of the MRI image reconstruction method according to any one of claims 1 to 7 or the super-resolution imaging method according to claim 8 or 9 in constructing conventional magnetic resonance imaging, magnetic resonance diffusion-weighted imaging, magnetic resonance perfusion imaging, blood oxygen level-dependent functional imaging, and magnetic resonance spectroscopy.

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