A method and system for magnetic resonance imaging

Abstract

The present invention relates to the field of magnetic resonance imaging, and particularly to a method and system for magnetic resonance imaging. The method includes: acquiring a spin echo sequence and a plurality of gradient echo sequences; performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map; obtaining a gradient-weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map; obtaining a relaxation decay image based on the gradient-weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation decay image; performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image. The present invention increases the types of multi-parameter maps, facilitating the rapid acquisition of multiple contrast images.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance imaging, and particularly to a method and system for magnetic resonance imaging. Background Art

[0002] In the clinical application of magnetic resonance imaging technology, magnetic resonance images of multiple parameters can provide doctors with richer diagnostic data and more reliable diagnostic bases. Therefore, how to obtain as many magnetic resonance images as possible with a limited number of scans is one of the development trends of nuclear magnetic resonance imaging technology. Currently, there are many magnetic resonance multi-parameter quantitative imaging methods. For example, Zhang Hongjie et al. designed a multi-echo FSE sequence scan, and used the multi-echo data obtained by the scan to complete the reconstruction of multiple quantitative images; Haacke et al. proposed a STAGE imaging method, which can obtain more than 8 images in one scan. The above methods are based on gradient echo sequences, but lack contrast images related to the transverse relaxation time. Summary of the Invention

[0003] In view of this, the present invention provides a method and system for magnetic resonance imaging to increase the types of multi-parameter maps obtained quickly.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A method for magnetic resonance imaging, comprising:

[0006] Obtaining a spin echo sequence and a plurality of gradient echo sequences;

[0007] Performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map;

[0008] Obtaining a gradient weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map;

[0009] Obtaining a relaxation attenuation image based on the gradient weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation attenuation image;

[0010] Performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation attenuation image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

[0011] Preferably, the obtaining a relaxation attenuation image based on the gradient weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation attenuation image includes:

[0012] Perform 3D multi-planar reconstruction on the gradient-weighted image and register it with the spin echo sequence to obtain a registered image;

[0013] Divide the registered image by the spin echo sequence to obtain a divided image;

[0014] Take the logarithm of the divided image and perform fitting to obtain the relaxation decay image;

[0015] Obtain the transverse relaxation quantitative map based on the relaxation decay image.

[0016] Preferably, the number of gradient echo sequences is P, and P = M × N; M is the number of flip angles; N is the number of echo times.

[0017] The present invention also provides a magnetic resonance imaging system, including:

[0018] A data acquisition module for acquiring a spin echo sequence and a plurality of gradient echo sequences;

[0019] A fitting module for performing fitting calculations based on a plurality of the gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map;

[0020] A gradient image module for obtaining a gradient-weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map;

[0021] A transverse quantitative map module for obtaining a relaxation decay image based on the gradient-weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation decay image;

[0022] A multi-parameter calculation module for performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

[0023] Preferably, the transverse quantitative map module includes:

[0024] A reconstruction unit for performing 3D multi-planar reconstruction on the gradient-weighted image and registering it with the spin echo sequence to obtain a registered image;

[0025] A division unit for dividing the registered image by the spin echo sequence to obtain a divided image;

[0026] An attenuation unit for taking the logarithm of the divided image and performing fitting to obtain the relaxation decay image;

[0027] A transverse quantitative map unit for obtaining the transverse relaxation quantitative map based on the relaxation decay image.

[0028] Preferably, the number of the gradient echo sequences is P, and P = M × N; M is the number of flip angles; N is the number of echo times.

[0029] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0030] The present invention relates to a method and a system for magnetic resonance imaging. The method includes: acquiring a spin echo sequence and a plurality of gradient echo sequences; performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map; obtaining a gradient weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map; obtaining a relaxation decay image based on the gradient weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation decay image; performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image. The present invention increases the types of multi-parameter maps and facilitates the rapid acquisition of multiple contrast images. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a flowchart of the method for magnetic resonance imaging of the present invention;

[0033] Figure 2 It is a structural diagram of the system for magnetic resonance imaging of the present invention;

[0034] Figure 3 It is a timing diagram of the spin echo sequence of the present invention;

[0035] Figure 4 It is a timing diagram of a plurality of gradient echo sequences of the present invention.

[0036] Symbol Explanation: 1 - Data acquisition module, 2 - Fitting module, 3 - Gradient image module, 4 - Transverse quantitative map module, 5 - Multi-parameter calculation module. Detailed Embodiments

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] The object of the present invention is to provide a method and system for magnetic resonance imaging to increase the types of multi-parameter maps obtained quickly.

[0039] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Figure 1 It is a flowchart of the method for magnetic resonance imaging of the present invention. As Figure 1 shown, the present invention provides a method for magnetic resonance imaging, including:

[0041] Step S1, obtaining a spin echo sequence and a plurality of gradient echo sequences.

[0042] Optionally, the timing diagram of the spin echo sequence is as Figure 3 shown, and a 180° pulse is used to achieve the phase rephasing of the transverse magnetization vector. Further, in order to improve the robustness to noise, the spin echo sequence is a dual-echo spin echo sequence, which is respectively defined as the first spin echo sequence and the second spin echo sequence. Figure 3 In, TR is the repetition time, and TE is the echo time.

[0043] The timing diagrams of the plurality of gradient echo sequences are as Figure 4 shown. In order to obtain the highest possible signal-to-noise ratio of the image and different contrasts, in this embodiment, 2 flip angles and 3 echo times are used to obtain 6 gradient echo sequences, where the angle of one flip angle is less than the Ernst angle of white matter tissue, and the angle of the other flip angle is greater than the Ernst angle of white matter tissue; the 3 echo times are 8, 22, and 36 respectively.

[0044] The positions of each of the gradient echo sequences are aligned with the position of the spin echo sequence.

[0045] Step S2, performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map. The fitting formula is as follows:

[0046]

[0047] In the formula: E1 and E2 are both intermediate transition quantities, ρ is the proton density value, TR is the repetition time, TE is the echo time, T1 is the fitted longitudinal relaxation time, is the fitted quasi-transverse relaxation time, θ is the flip angle, and s(θ) is the signal value of the gradient echo sequence at θ.

[0048] Step S3, obtain a gradient-weighted image based on the fitted density quantitative map, the fitted longitudinal relaxation quantitative map, and the fitted quasi-transverse relaxation quantitative map.

[0049] Since a dual-echo spin echo sequence is used in this embodiment, the obtained gradient-weighted images are also two, which are respectively defined as the first gradient-weighted image and the second gradient-weighted image. The calculation formulas are as follows:

[0050]

[0051] In the formula: S 13D is the first gradient-weighted image, S 23D is the second gradient-weighted image, TE1 is the echo time of the first spin echo sequence, TE2 is the echo time of the second spin echo sequence, and TR1 is the repetition time of the first spin echo sequence and the second spin echo sequence.

[0052] Step S4, obtain a relaxation decay image based on the gradient-weighted image and the spin echo sequence; obtain a transverse relaxation quantitative map based on the relaxation decay image. The step S4 can be implemented based on deep learning.

[0053] Specifically, the step S4 includes:

[0054] Step S41, perform 3D multi-planar reconstruction on the gradient-weighted image and register it with the spin echo sequence to obtain a registered image. The number of registered images is 2, which are respectively defined as the first registered image and the second registered image.

[0055] The calculation formulas are as follows:

[0056]

[0057] In the formula: S 01 is the first spin echo sequence, S 02 is the second spin echo sequence, T2 is the transverse relaxation time, S 11 is the first registered image, S 12 is the second registered image.

[0058] Step S42, divide the registered image by the spin echo sequence to obtain a divided image. The number of divided images is 2, which are respectively defined as the first divided image and the second divided image.

[0059] According to the principle of magnetic resonance imaging, the relevant formula for transverse relaxation: It can be obtained that:

[0060]

[0061] In the formula: is the first division image, is the second division image, T′2 is the attenuation loss term of the transverse relaxation time, usually caused by the local magnetic field change ΔB due to the inhomogeneity of the static magnetic field B0 or the magnetic susceptibility inhomogeneity, T′2 = γΔB, γ is the gyromagnetic ratio constant, for hydrogen nuclei, γ is 42.58 MHz / T.

[0062] Step S43, take the logarithm of the division image and perform fitting to obtain the relaxation attenuation image. The calculation formula is as follows:

[0063]

[0064] Step S44, obtain the transverse relaxation quantitative map based on the relaxation attenuation image.

[0065] Step S5, perform weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation attenuation image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

[0066] Figure 2 is the system structure diagram of the magnetic resonance imaging of the present invention. As Figure 2 shown, the present invention provides a magnetic resonance imaging system, including: a data acquisition module 1, a fitting module 2, a gradient image module 3, a transverse quantitative map module 4, and a multi-parameter calculation module 5.

[0067] The data acquisition module 1 is used to acquire a spin echo sequence and a plurality of gradient echo sequences.

[0068] The fitting module 2 is used to perform fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map.

[0069] The gradient image module 3 is used to obtain a gradient-weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map.

[0070] The transverse quantitative map module 4 is used to obtain a relaxation attenuation image based on the gradient-weighted image and the spin echo sequence; obtain a transverse relaxation quantitative map based on the relaxation attenuation image.

[0071] The multi-parameter calculation module 5 performs weighted summation based on the fitted density quantitative map, the fitted longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

[0072] Optionally, the transverse quantitative map module 4 includes: a reconstruction unit, a division unit, an attenuation unit, and a transverse quantitative map unit.

[0073] The reconstruction unit is configured to perform 3D multi-planar reconstruction on the gradient-weighted image and register it with the spin echo sequence to obtain a registered image.

[0074] The division unit is configured to divide the registered image by the spin echo sequence to obtain a divided image.

[0075] The attenuation unit is configured to perform logarithmic fitting on the divided image to obtain the relaxation decay image.

[0076] The transverse quantitative map unit is configured to obtain the transverse relaxation quantitative map based on the relaxation decay image.

[0077] Optionally, the number of gradient echo sequences is P, and P = M × N; M is the number of flip angles; N is the number of echo times.

[0078] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method section.

[0079] Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A method for magnetic resonance imaging, characterized in that, Including: Obtaining a spin echo sequence and a plurality of gradient echo sequences; the spin echo sequence is a double-echo spin echo sequence, which are respectively defined as a first spin echo sequence and a second spin echo sequence; Performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map; Obtaining a gradient-weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map; Obtaining a relaxation decay image based on the gradient-weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation decay image; specifically: Performing 3D multi-planar reconstruction on the gradient-weighted image and registering it with the spin echo sequence to obtain registered images; the number of registered images is 2, which are respectively defined as a first registered image and a second registered image; the calculation formula is as follows: Where: S 01 is the first spin echo sequence, S 02 is the second spin echo sequence, T2 is the transverse relaxation time, S 11 is the first registered image, is the fitted quasi-transverse relaxation time, TE1 is the echo time of the first spin echo sequence, TE2 is the echo time of the second spin echo sequence, S 12 is the second registered image; Dividing the registered images by the spin echo sequence to obtain divided images; the number of divided images is 2, which are respectively defined as a first divided image and a second divided image; According to the principle of magnetic resonance imaging, the relevant formula for transverse relaxation: It can be obtained that: Wherein: is the first division image, is the second division image, T ' 2 is the attenuation loss term of the transverse relaxation time; Performing logarithmic fitting on the divided images to obtain the relaxation decay image; The calculation formula is as follows: Obtaining the transverse relaxation quantitative map based on the relaxation decay image; Performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

2. The method for magnetic resonance imaging according to claim 1, wherein The number of the gradient echo sequences is P, and P = M × N; M is the number of flip angles; N is the number of echo times.

3. A magnetic resonance imaging system, characterized in that, Including: A data acquisition module for obtaining a spin echo sequence and a plurality of gradient echo sequences; A fitting module for performing fitting calculations based on the plurality of gradient echo sequences to obtain a fitting density quantitative map, a fitting longitudinal relaxation quantitative map, and a fitting quasi-transverse relaxation quantitative map; A gradient image module for obtaining a gradient-weighted image based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, and the fitting quasi-transverse relaxation quantitative map; A transverse quantitative map module for obtaining a relaxation decay image based on the gradient-weighted image and the spin echo sequence; obtaining a transverse relaxation quantitative map based on the relaxation decay image; specifically: Performing 3D multi-planar reconstruction on the gradient-weighted image and registering it with the spin echo sequence to obtain registered images; the number of registered images is 2, which are respectively defined as a first registered image and a second registered image; the calculation formula is as follows: Where: S 01 is the first spin echo sequence, S 02 is the second spin echo sequence, T2 is the transverse relaxation time, S 11 is the first registered image, S 12 is the second registered image; Dividing the registered images by the spin echo sequence to obtain divided images. The number of divided images is 2, which are respectively defined as a first divided image and a second divided image; According to the principle of magnetic resonance imaging, the relevant formula for transverse relaxation: It can be obtained that: In the formula: is the first divided image, is the second divided image, is the attenuation loss term of the transverse relaxation time; Performing logarithmic fitting on the divided images to obtain the relaxation decay image; The calculation formula is as follows: Obtaining the transverse relaxation quantitative map based on the relaxation decay image; A multi-parameter calculation module for performing weighted summation based on the fitting density quantitative map, the fitting longitudinal relaxation quantitative map, the relaxation decay image, and the transverse relaxation quantitative map to obtain a magnetic resonance multi-parameter image.

4. The magnetic resonance imaging system according to claim 3, characterized in that, The number of the gradient echo sequences is P, and P = M × N; M is the number of flip angles; N is the number of echo times.

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