Magnetic resonance water-fat image separation method, device, imaging system and storage medium

Abstract

In an embodiment of the present invention, a magnetic resonance water-fat image separation method, device, imaging system and storage medium are proposed. The method includes: within an echo cycle, obtaining a first echo group under a first readout gradient polarity, and obtaining a second echo group under a second readout gradient polarity; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the first echo group and the echoes in the second echo group are one-to-one symmetrical with respect to the echo center position of the echo cycle; obtaining a first echo image group based on the first echo group data obtained in each echo cycle, and obtaining a second echo image group based on the second echo group data obtained in each echo cycle; performing Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image. The technical solution in the embodiment of the present invention can improve acquisition efficiency and signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance imaging technology, and in particular to a method and device for separating water and fat images in magnetic resonance imaging, a magnetic resonance imaging system and a computer-readable storage medium. Background Art

[0002] In the MRI system, the molecular environments of hydrogen nuclei in fat and water are different, which makes their resonance frequencies different; when hydrogen protons in fat and other tissues are excited by radio frequency pulses at the same time, their relaxation times are also different. When signals are collected at different echo times, fat tissue and water show different phases and signal intensities.

[0003] The Dixon method is a method used to generate pure water proton images in magnetic resonance imaging. Its basic principle is to collect two echo signals of water and fat protons, the in-phase (In Phase) and the out-phase (Out Phase), respectively. The two signals of different phases are calculated to generate a pure water proton image and a pure fat proton image, respectively, so as to achieve the purpose of fat suppression. There are currently a variety of Dixon water-fat image separation methods, including: single-point Dixon method, two-point Dixon method and three-point Dixon method.

[0004] In the Dixon-based Turbo Spin Echo (TSE, also called Fast Spin Echo, FSE) pulse sequence, the radio frequency (RF) pulse sequence includes a 90° excitation pulse and a 180° refocusing pulse (also called a complex phase pulse). Multiple echoes can be collected between two adjacent refocusing pulses, that is, within an echo spacing (also called an echo cycle). The echoes corresponding to the corresponding positions of different refocusing pulses constitute a group of echoes, for example: the first echo after refocusing pulse 1, the first echo after refocusing pulse 2, ..., the first echo after refocusing pulse n can constitute a group of echoes, and the second echo after refocusing pulse 1, the second echo after refocusing pulse 2, ..., the second echo after refocusing pulse n can constitute another group of echoes. Each group of echoes can independently reconstruct an image. Since different echoes carry different amplitude and phase information, pure water images and pure fat images can be reconstructed separately through further calculation.

[0005] Considering that some of the current water-fat image separation methods have more dead zones and low acquisition efficiency, while others have a low signal-to-noise ratio (SNR), technicians in this field are still working on finding other solutions. Summary of the invention

[0006] In view of this, in the embodiments of the present invention, on the one hand, a method for separating water and fat images in magnetic resonance imaging is proposed, and on the other hand, a device for separating water and fat images in magnetic resonance imaging, a magnetic resonance imaging system and a computer-readable storage medium are proposed to improve acquisition efficiency and signal-to-noise ratio.

[0007] A method for separating water and fat images in magnetic resonance imaging proposed in an embodiment of the present invention comprises: within an echo cycle, obtaining a first echo group corresponding to Dixon water and fat separation calculation under a first readout gradient polarity, and obtaining a second echo group corresponding to Dixon water and fat separation calculation under a second readout gradient polarity; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group relative to the echo center position of the echo cycle; obtaining a first echo image group based on the first echo group data obtained in each echo cycle, and obtaining a second echo image group based on the second echo group data obtained in each echo cycle; performing Dixon water and fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image.

[0008] In one embodiment, the first echo group and the second echo group respectively include: a near-in-phase echo that meets the set in-phase requirement and a near-opposite-phase echo that meets the set anti-phase requirement; the Dixon water-fat separation calculation is a two-point Dixon water-fat separation calculation; or, the first echo group and the second echo group respectively include: a near-in-phase echo that meets the set in-phase requirement and two near-opposite-phase echoes that meet the set anti-phase requirement; the Dixon water-fat separation calculation is a three-point Dixon water-fat separation calculation.

[0009] In one embodiment, the use of the first echo image group and the second echo image group to perform Dixon water-fat separation calculation to obtain a water image and a fat image includes: performing phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group, performing complex averaging on each two echo images after the phase difference correction to obtain a corresponding echo average image group; and performing Dixon water-fat separation calculation on images in the obtained echo average image group to obtain a water image and a fat image.

[0010] In one embodiment, performing phase difference correction on every two echo images with symmetrical echo positions in the first echo image group and the second echo image group includes: performing a complex conjugate transform on any one of every two echo images with symmetrical echo positions in the first echo image group and the second echo image group to obtain a first processed image; subtracting the low-pass phase difference between the first processed image and the echo image that has not undergone a complex conjugate transform from the first processed image or another echo image that has not undergone a complex conjugate transform to obtain a second processed image, the second processed image and the echo image without the low-pass phase difference subtracted together constituting two echo images after phase difference correction.

[0011] In one embodiment, the use of the first echo image group and the second echo image group to perform Dixon water-fat separation calculation to obtain a water image and a fat image includes: using the first echo image group to perform Dixon water-fat separation calculation to obtain a first water image and a first fat image; using the second echo image group to perform Dixon water-fat separation calculation to obtain a second water image and a second fat image; performing modulus averaging on the first water image and the second water image to obtain a water image; and performing modulus averaging on the first fat image and the second fat image to obtain a fat image.

[0012] A magnetic resonance imaging water-fat image separation device proposed in an embodiment of the present invention includes: a data acquisition module, used to obtain a first echo group corresponding to Dixon water-fat separation calculation under a first readout gradient polarity, and obtain a second echo group corresponding to Dixon water-fat separation calculation under a second readout gradient polarity within an echo cycle; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group relative to the echo center position of the echo cycle; an image extraction module, used to obtain a first echo image group based on the first echo group data obtained in each echo cycle, and to obtain a second echo image group based on the second echo group data obtained in each echo cycle; a water-fat separation module, used to perform Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image.

[0013] In one embodiment, the first echo group and the second echo group respectively include: a near-in-phase echo that meets the set in-phase requirement and a near-inverted-phase echo that meets the set inverted-phase requirement; the Dixon water-fat separation calculation is a two-point Dixon water-fat separation calculation; or, the first echo group and the second echo group respectively include: two near-in-phase echoes that meet the set in-phase requirement and a near-inverted-phase echo that meets the set inverted-phase requirement; the Dixon water-fat separation calculation is a three-point Dixon water-fat separation calculation.

[0014] In one embodiment, the water-fat separation module includes: a first image integration module, used to perform phase difference correction on every two echo images with symmetrical echo positions in the first echo image group and the second echo image group, and perform complex averaging on every two echo images after the phase difference correction to obtain a corresponding echo average image group; a first water-fat separation calculation module, used to perform Dixon water-fat separation calculation using the images in the obtained echo average image group to obtain a water image and a fat image.

[0015] In one embodiment, the first image integration module includes: a complex conjugate transformation module, which is used to perform a complex conjugate transformation on any echo image of every two echo images with symmetrical echo positions in the first echo image group and the second echo image group to obtain a first processed image; a phase correction module, which is used to subtract the low-pass phase difference between the first processed image and the echo image that has not been subjected to complex conjugate transformation from the first processed image or another echo image that has not been subjected to complex conjugate transformation to obtain a second processed image, wherein the second processed image and the echo image without the low-pass phase difference subtracted together constitute two echo images after phase difference correction; and a complex averaging module, which is used to perform complex averaging on every two echo images after phase difference correction to obtain a corresponding echo average image group.

[0016] In one embodiment, the water-fat separation module includes: a second water-fat separation calculation module, used to perform Dixon water-fat separation calculation using the first echo image group to obtain a first water image and a first fat image; use the second echo image group to perform Dixon water-fat separation calculation to obtain a second water image and a second fat image; a second image integration module, used to perform modulus averaging on the first water image and the second water image to obtain a water image; and perform modulus averaging on the first fat image and the second fat image to obtain a fat image.

[0017] A magnetic resonance imaging water-fat image separation device proposed in an embodiment of the present invention includes: at least one memory and at least one processor, wherein: the at least one memory is used to store a computer program; the at least one processor is used to call the computer program stored in the at least one memory to execute the magnetic resonance imaging water-fat image separation method described in any of the above embodiments.

[0018] A magnetic resonance imaging system provided in an embodiment of the present invention includes the magnetic resonance imaging water-fat image separation device as described in any of the above embodiments.

[0019] A computer-readable storage medium is provided in an embodiment of the present invention, on which a computer program is stored; the computer program can be executed by a processor and implements the magnetic resonance imaging water-fat image separation method as described in any of the above embodiments.

[0020] It can be seen from the above scheme that, since two echo groups corresponding to the Dixon water-fat separation calculation are read in one echo cycle in the embodiment of the present invention, almost all the time between two refocusing pulses is used for data acquisition, which improves the data acquisition efficiency and reduces the dead zone. In addition, each echo group is read out under the same readout gradient polarity, which makes it unnecessary to perform phase correction in each echo group.

[0021] In addition, the echo images corresponding to the two echo groups can be merged to improve the signal-to-noise ratio before the water-fat separation calculation, or the water-fat separation calculation can be performed first and then the image merged to improve the signal-to-noise ratio. Compared with the traditional TSE-Dixon water-fat separation calculation method, the echoes obtained are doubled in a very similar capture time, so the signal-to-noise ratio is improved and better water-fat imaging quality is obtained. In addition, by implementing a phase correction process before averaging in the merging process, redundancy can be reduced and consistency of local and global water-fat separation results can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the above and other features and advantages of the present invention will be more apparent to those skilled in the art. In the accompanying drawings:

[0023] Figure 1 Detailed description of the invention The figure is an exemplary flow chart of the method for separating water-fat images in magnetic resonance imaging in an embodiment of the present invention.

[0024] Figure 2A Schematic diagram of the current data acquisition sequence based on the two-point Dixon method of the fast spin echo (TSE) sequence.

[0025] Figure 2B Schematic diagram of a data acquisition sequence based on a two-point Dixon method of a fast spin echo (TSE) sequence in an example of the present invention.

[0026] Figure 2C Schematic diagram of a data acquisition sequence of a three-point Dixon method based on a fast spin echo (TSE) sequence in an example of the present invention.

[0027] Figure 3 This is a schematic diagram of the process of reconstructing a water-fat separation image using collected images in an example of the present invention.

[0028] Figure 4This is a schematic diagram of a process of reconstructing a water-fat separation image using collected images in another example of the present invention.

[0029] FIG. 5A to FIG. 5C It is an exemplary structural diagram of the magnetic resonance imaging water-fat image separation device in an embodiment of the present invention.

[0030] Figure 6 This is an exemplary structural diagram of another magnetic resonance imaging water-fat image separation device in an embodiment of the present invention.

[0031] Fig. 7A and Figure 7B This is an image quality comparison diagram of an in vitro phantom water image obtained by using a traditional two-point Dixon water-fat separation algorithm and a magnetic resonance imaging water-fat image separation method in an embodiment of the present invention in an example of the present invention.

[0032] Figure 7C for Figure 7B and Fig. 7A Schematic diagram of the ratio results of the two images.

[0033] Fig. 8A and Figure 8B 2 shows an example of an image quality comparison diagram of a hip joint water image obtained by using the magnetic resonance imaging water-fat image separation method in an embodiment of the present invention and a two-point Dixon water-fat separation algorithm of a combined echo using two samplings.

[0034] The reference numerals are as follows:

[0035]

[0036] DETAILED DESCRIPTION

[0037] In the embodiment of the present invention, in order to improve the acquisition speed and reduce the motion sensitivity, a fast switching bipolar readout gradient can be used to acquire multiple echoes between every two refocusing pulses during data acquisition. In addition, considering that the recently developed Dixon reconstruction method allows sampling of near anti-phase (approximately anti-phase, such as 120° to 180°) and near in-phase (approximately in-phase, such as 0° to 30°) echoes, rather than accurately anti-phase and in-phase echoes as in the original Dixon method. Therefore, in this embodiment, it is considered to acquire two echo groups between every two refocusing pulses, and each echo group includes near anti-phase and near in-phase echoes for corresponding Dixon water-fat separation calculations, so as to improve the data acquisition speed. In addition, when using the acquired echo images to perform Dixon water-fat separation calculations, the images corresponding to different echo groups can be merged first and then water-fat separation calculations or water-fat separation calculations can be performed first and then merged, thereby improving the signal-to-noise ratio of water images and fat images.

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail with reference to the following embodiments.

[0039] Figure 1 FIG. 4 is an exemplary flow chart of a method for separating water and fat images in magnetic resonance imaging according to an embodiment of the present invention. Figure 1 As shown, the method may include the following steps:

[0040] Step 101, within one echo cycle, obtain a first echo group corresponding to the Dixon water-fat separation calculation under a first readout gradient polarity, and obtain a second echo group corresponding to the Dixon water-fat separation calculation under a second readout gradient polarity; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the first echo group and the echoes in the second echo group are one-to-one symmetrical with respect to the echo center position of the echo cycle, that is, the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group with respect to the echo center position of the echo cycle.

[0041] Figure 2A A schematic diagram of a current data acquisition sequence based on a two-point Dixon method of a turbo spin echo (TSE) sequence is shown. Figure 2B FIG. 4 shows a schematic diagram of a data acquisition sequence of a two-point Dixon method based on a fast spin echo (TSE) sequence in an example of the present invention, Figure 2C Schematic diagram of a data acquisition sequence of a three-point Dixon method based on a fast spin echo (TSE) sequence in an example of the present invention. FIG. 2A to FIG. 2C Only one spin echo period (Echo Spacing, ESP) is shown in FIG. FIG. 2A to FIG. 2C The spin echo cycle shown, i.e., two 90-degree RF pulses, includes multiple 180-degree re-phasing RF pulses, wherein RF, Gr, and Ech correspond to RF pulses, readout direction gradient, and echo data, respectively.

[0042] like Figure 2A As shown, within a spin echo cycle of the echo sequence, that is, between two 180-degree rephasing radio frequency pulses RF_1 and RF_2, the magnetic resonance imaging device applies a readout gradient in the readout gradient direction and reads an anti-phase echo Ea and an in-phase echo Eb.

[0043] like Figure 2BAs shown, within a spin echo cycle of the echo sequence, that is, between two 180-degree re-phased radio frequency pulses RF_1 and RF_2, at the first echo time (TE1) and the second echo time (TE2) symmetrical from the echo center C, the magnetic resonance imaging device applies two readout gradients in the readout gradient direction, and based on the effect of the readout gradient, reads the corresponding four echoes E1, E2, E3, and E4, and fills the read four echoes E1, E2, E3, and E4 into the k-space. Among them, echoes E1 and E3 are read out under the same readout gradient polarity, and constitute an echo pair corresponding to the two-point Dixon water-fat separation algorithm, and echoes E2 and E4 are read out under the same readout gradient polarity, and constitute another echo pair corresponding to the two-point Dixon water-fat separation algorithm. The two echo pairs have the same dephasing factor, but opposite gradient polarities. The readout is repeated in the entire echo sequence. Each echo pair, E1 and E3, E2 and E4, is obtained with the same readout gradient polarity, and water-fat separation can be performed without phase correction. Among them, echoes E2 and E3 are nearly in-phase echoes that meet the set in-phase requirements, and the two are symmetrically located relative to the echo center C of the echo cycle, and there is a complex conjugate relationship between the two; echoes E1 and E4 are nearly inverse phase echoes that meet the set anti-phase requirements, and the two are symmetrically located relative to the echo center C of the echo cycle, and there is a complex conjugate relationship between the two.

[0044] Of course, in other examples, the selection of TEs of echoes E2, E3 and echoes E1, E4 is flexible, as long as the water-fat separation is stable and the noise amplification is acceptable. For example, when a 1.5T system is used, echoes E2, E3 and echoes E1, E4 are close to in-phase and anti-phase, respectively. When a 3T system is used, they can be set in another way, that is, echoes E2, E3 are close to anti-phase, and echoes E1, E4 are close to in-phase.

[0045] It can be seen that for the two-point Dixon water-fat separation calculation method shown in FIG. 2 , the first echo group and the second echo group are echo pairs including a nearly in-phase echo that meets the set in-phase requirement and a nearly inverse-phase echo that meets the set inverse-phase requirement.

[0046] like Figure 2CAs shown, within a spin echo cycle of the echo sequence, that is, between two 180-degree re-phased radio frequency pulses RF_1 and RF_2, at the first echo time (TE1), the second echo time (TE2), and the third echo time (TE3) symmetrical from the echo center C, the magnetic resonance imaging device applies three readout gradients in the readout gradient direction, and based on the effect of the readout gradient, reads the corresponding six echoes E1, E2, E3, E4, E5, and E6, and fills the read six echoes E1, E2, E3, E4, E5, and E6 into the k-space. Among them, the echoes E1, E3, and E5 are read out under the same readout gradient polarity, and constitute an echo group corresponding to the three-point Dixon water-fat separation algorithm, and the echoes E2, E4, and E6 are read out under the same readout gradient polarity, and constitute another echo group corresponding to the three-point Dixon water-fat separation algorithm. The two echo groups have the same dephasing factor, but opposite gradient polarities. Repeat the readout in the entire echo sequence. Each echo group, E1, E3 and E5, E2, E4 and E6, is obtained with the same readout gradient polarity, and water-fat separation can be performed without phase correction. Among them, echo E3 and E4 are nearly in-phase echoes that meet the set in-phase requirements, and the two are symmetrically located relative to the echo center C of the echo cycle, and there is a complex conjugate relationship between the two; echo E1 and E6 are nearly inverted echoes that meet the set anti-phase requirements, and the two are symmetrically located relative to the echo center C of the echo cycle, and there is a complex conjugate relationship between the two. Echo E5 and E2 are also nearly inverted echoes that meet the set anti-phase requirements, and the two are symmetrically located relative to the echo center C of the echo cycle, and there is a complex conjugate relationship between the two.

[0047] It can be seen that for the three-point Dixon water-fat separation calculation method, the first echo group and the second echo group can respectively include: a nearly in-phase echo that meets the set in-phase requirement and two nearly anti-phase echoes that meet the set anti-phase requirement. And the nearly in-phase echo in the first echo group and the nearly in-phase echo in the second echo group are symmetrical with respect to the echo center position of the echo cycle, and the two nearly anti-phase echoes in the first echo group and the two nearly anti-phase echoes in the second echo group are also symmetrical with respect to the echo center position of the echo cycle.

[0048] In addition, this embodiment is also applicable to other Dixon water-fat separation calculation methods, which will not be described in detail here.

[0049] Step 102: obtaining a first echo image group based on the first echo group data acquired in each echo period, and obtaining a second echo image group based on the second echo group data acquired in each echo period.

[0050] In this step, a first echo image group is obtained based on first echo group data acquired at each echo period of the echo sequence in k-space, and a second echo image group is obtained based on second echo group data acquired at each echo period of the echo sequence in k-space.

[0051] by Figure 2B Taking the data acquisition sequence shown in FIG. 1 as an example, for the data of echo E1 acquired for each echo cycle in k-space, an inverted image corresponding to E1 can be obtained; for the data of echo E3 acquired for each echo cycle in k-space, an in-phase image corresponding to E3 can be obtained; the inverted image corresponding to E1 and the in-phase image corresponding to E3 together constitute the first echo image group. Similarly, for the data of echo E2 acquired for each echo cycle in k-space, an in-phase image corresponding to E2 can be obtained; for the data of echo E4 acquired for each echo cycle in k-space, an inverted image corresponding to E4 can be obtained; the in-phase image corresponding to E2 and the inverted image corresponding to E4 together constitute the second echo image group.

[0052] Step 103: Perform Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image.

[0053] In this step, there are two implementation methods:

[0054] The first method: image merging first and then water-fat separation calculation

[0055] Perform phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group, respectively, and perform complex averaging on each two echo images after the phase difference correction, so as to merge and obtain the corresponding echo average image group; then, perform Dixon water-fat separation calculation on the images in the obtained echo average image group to obtain a water image and a fat image. Specifically, the process of performing phase difference correction on two echo images with symmetrical echo positions may include: performing complex conjugate transformation on any one of the two echo images with symmetrical echo positions to obtain a first processed image; subtracting the low-pass phase difference between the first processed image and the echo image that has not undergone complex conjugate transformation from the first processed image or another echo image that has not undergone complex conjugate transformation to obtain a second processed image; the second processed image and the echo image without the low-pass phase difference subtracted together constitute two echo images after phase difference correction.

[0056] Still Figure 2B Take the data acquisition sequence shown as an example. Figure 3 FIG. 1 is a schematic diagram showing a process of reconstructing a water-fat separation image using a collected image in an example of the present invention. Figure 3As shown, after obtaining the first echo image group consisting of the anti-phase image corresponding to E1 and the in-phase image corresponding to E3 and the second echo image group consisting of the in-phase image corresponding to E2 and the anti-phase image corresponding to E4 mentioned in step 102, since the anti-phase image corresponding to E1 and the anti-phase image corresponding to E4 are two images with symmetrical echo positions, and the in-phase image corresponding to E3 and the in-phase image corresponding to E2 are two images with symmetrical echo positions, phase difference correction can be performed on the two images with symmetrical echo positions first. During the specific processing, the identities of the two images with symmetrical positions are equal, and the phase difference correction calculation can be performed based on either one of them. Figure 3 Only one implementation is shown, which may include the following steps:

[0057] Step 31A, performing a complex conjugate transformation on the in-phase image corresponding to E2 to obtain a first in-phase processed image; Step 31B, performing a complex conjugate transformation on the inverse phase image corresponding to E4 to obtain a first inverse phase processed image.

[0058] In other implementations, step 31A may also be to perform a complex conjugate transformation on the in-phase image corresponding to E3. Similarly, step 31B may be to perform a complex conjugate transformation on the anti-phase image corresponding to E1.

[0059] Step 32A, subtract the low-pass phase difference between the first in-phase processed image and the in-phase image corresponding to E3 from the first in-phase processed image to obtain a second in-phase processed image; Step 32B, subtract the low-pass phase difference between the first inverse-phase processed image and the inverse-phase image corresponding to E1 from the first inverse-phase processed image to obtain a second inverse-phase processed image.

[0060] In other embodiments, step 32A may also be performed by subtracting the low-pass phase difference between the first in-phase processed image and the in-phase image corresponding to E3 from the in-phase image corresponding to E3. Similarly, step 32B may be performed by subtracting the low-pass phase difference between the first inverse-phase processed image and the inverse-phase image corresponding to E1 from the inverse-phase image corresponding to E1.

[0061] Step 33A, complex average the second in-phase processed image and the in-phase image corresponding to E3, and integrate the two images into an echo averaged in-phase image; Step 33B, complex average the second inverse-phase processed image and the inverse-phase image corresponding to E1, and integrate the two images into an echo averaged inverse-phase image.

[0062] Step 34, using the echo average in-phase image and the echo average inverse-phase image to perform two-point Dixon water-fat separation calculation to obtain a water image and a fat image.

[0063] In addition, the three-point Dixon and other water-fat separation methods are similar and will not be described here one by one.

[0064] The second method: first calculate the water-fat separation and then merge the images

[0065] The first echo image group is used to perform Dixon water-fat separation calculation to obtain a first water image and a first fat image; the second echo image group is used to perform Dixon water-fat separation calculation to obtain a second water image and a second fat image; the first water image and the second water image are modulus-averaged to obtain a water image; the first fat image and the second fat image are modulus-averaged to obtain a fat image.

[0066] Still Figure 2B Take the data acquisition sequence shown as an example. Figure 4 FIG. 2 shows a schematic diagram of a process of reconstructing a water-fat separation image using a collected image in another example of the present invention. Figure 4 As shown, the process may include the following steps:

[0067] In step 41A, a two-point Dixon water-fat separation calculation is performed using the inverted image corresponding to E1 and the in-phase image corresponding to E3 to obtain a first water image W1 and a first fat image F1. In step 41B, a two-point Dixon water-fat separation calculation is performed using the in-phase image corresponding to E2 and the inverted image corresponding to E4 to obtain a second water image W2 and a second fat image F2.

[0068] Step 42A, performing a complex conjugate transform on the first water image W1 to obtain a first processed water image W1*; Step 42B, performing a complex conjugate transform on the first fat image F1 to obtain a first processed fat image F1*.

[0069] In other implementations, in step 42A, a complex conjugate transform may be performed on the second water image, and in step 42B, a complex conjugate transform may be performed on the second fat image.

[0070] Step 43A, subtracting the low-pass phase difference between the first processed water image and the second water image from the first processed water image to obtain the second processed water image; Step 43B, subtracting the low-pass phase difference between the first processed fat image and the second fat image from the first processed fat image to obtain the second processed fat image.

[0071] Step 44A, complex averaging the second processed water image and the second water image, and integrating them to obtain a water image; Step 44B, complex averaging the second processed fat image and the second fat image, and integrating them to obtain a fat image.

[0072] The above is a detailed description of the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention. The magnetic resonance imaging water-fat image separation device in the embodiment of the present invention is described in detail below. The magnetic resonance imaging water-fat image separation device in the embodiment of the present invention can be used to implement the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention. For details not disclosed in detail in the embodiment of the device of the present invention, please refer to the corresponding description in the embodiment of the method of the present invention, and will not be repeated here.

[0073] FIG. 5A to FIG. 5C FIG. 4 is an exemplary structural diagram of a magnetic resonance imaging water-fat image separation device in an embodiment of the present invention. Figure 5A As shown, the device may include: a data acquisition module 510 , an image extraction module 520 and a water-fat separation module 530 .

[0074] Among them, the data acquisition module 510 is used to obtain a first echo group corresponding to the Dixon water-fat separation calculation under a first readout gradient polarity within one echo cycle, and to obtain a second echo group corresponding to the Dixon water-fat separation calculation under a second readout gradient polarity; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the first echo group and the echoes in the second echo group are symmetrical one-to-one with respect to the echo center position of the echo cycle, that is, the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group with respect to the echo center position of the echo cycle.

[0075] The image extraction module 520 is used to obtain a first echo image group based on the first echo group data obtained in each echo period, and to obtain a second echo image group based on the second echo group data obtained in each echo period.

[0076] The water-fat separation module 530 is used to perform Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image.

[0077] Among them, the first echo group and the second echo group respectively include: a near-in-phase echo that meets the set in-phase requirement and a near-inverted-phase echo that meets the set inverted-phase requirement; the Dixon water-fat separation calculation is a two-point Dixon water-fat separation calculation; or, the first echo group and the second echo group respectively include: two near-in-phase echoes that meet the set in-phase requirement and a near-inverted-phase echo that meets the set inverted-phase requirement; the Dixon water-fat separation calculation is a three-point Dixon water-fat separation calculation.

[0078] In specific implementation, the fat separation module 530 can be implemented in a variety of ways. Figure 5B and Figure 5C One of them is shown in each.

[0079] like Figure 5B In one embodiment shown, the water-fat separation module 530 may include: a first image integration module 531 and a first water-fat separation calculation module 532. The first image integration module 531 is used to perform phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group, and perform complex averaging on each two echo images after the phase difference correction to obtain a corresponding echo average image group. The first water-fat separation calculation module 532 is used to perform Dixon water-fat separation calculation using the images in the obtained echo average image group to obtain a water image and a fat image.

[0080] The first image integration module 531 may include: a complex conjugate transformation module 5311 , a phase correction module 5312 and a complex averaging module 5313 .

[0081] The complex conjugate transformation module 5311 is used to perform a complex conjugate transformation on any echo image of every two echo images with symmetrical echo positions in the first echo image group and the second echo image group to obtain a first processed image.

[0082] The phase correction module 5312 is used to subtract the low-pass phase difference between the first processed image and the echo image that has not undergone complex conjugate transformation from the first processed image or another echo image that has not undergone complex conjugate transformation to obtain a second processed image. The second processed image and the echo image from which the low-pass phase difference has not been subtracted together constitute two echo images after phase difference correction.

[0083] The complex averaging module 5313 is used to perform complex averaging on each two echo images after phase difference correction to obtain a corresponding echo average image group.

[0084] like Figure 5B In another embodiment shown, the water-fat separation module 530 may include: a second water-fat separation calculation module 533 and a second image integration module 534 .

[0085] Among them, the second water-fat separation calculation module 533 is used to use the first echo image group to perform Dixon water-fat separation calculation to obtain a first water image and a first fat image; and use the second echo image group to perform Dixon water-fat separation calculation to obtain a second water image and a second fat image.

[0086] The second image integration module 534 is used to perform modulus averaging on the first water image and the second water image to obtain a water image; and perform modulus averaging on the first fat image and the second fat image to obtain a fat image.

[0087] Figure 6FIG. 4 is an exemplary structural diagram of another magnetic resonance imaging water-fat image separation device in an embodiment of the present invention. Figure 6 As shown, it may include: at least one memory 61 and at least one processor 62. In addition, it may also include some other components, such as communication ports, etc. These components communicate via a bus 63.

[0088] Among them, at least one memory 61 is used to store a computer program. In one embodiment, the computer program can be understood as including various modules of the magnetic resonance imaging water-fat image separation device shown in Figure 5. In addition, at least one memory 61 can also store an operating system, etc. The operating system includes but is not limited to: Android operating system, Symbian operating system, Windows operating system, Linux operating system, etc.

[0089] At least one processor 62 is used to call the computer program stored in at least one memory 61 to execute the magnetic resonance imaging water-fat image separation method described in the embodiment of the present invention. The processor 62 can be a CPU, a processing unit / module, an ASIC, a logic module or a programmable gate array, etc. It can receive and send data through the communication port.

[0090] It should be noted that not all steps and modules in the above processes and structure diagrams are necessary, and some steps or modules can be ignored according to actual needs. The execution order of each step is not fixed and can be adjusted as needed. The division of each module is only for the convenience of describing the functional division adopted. In actual implementation, a module can be implemented by multiple modules, and the functions of multiple modules can also be implemented by the same module. These modules can be located in the same device or in different devices.

[0091] It is understood that the hardware modules in the above-mentioned embodiments can be implemented mechanically or electronically. For example, a hardware module may include a specially designed permanent circuit or logic device (such as a dedicated processor, such as an FPGA or ASIC) for completing a specific operation. The hardware module may also include a programmable logic device or circuit (such as a general-purpose processor or other programmable processor) temporarily configured by software for performing a specific operation. As for whether to implement the hardware module in a mechanical manner, or using a dedicated permanent circuit, or using a temporarily configured circuit (such as configured by software), it can be determined based on cost and time considerations.

[0092] In addition, a computer-readable storage medium is provided in an embodiment of the present invention, on which a computer program is stored, and the computer program can be executed by a processor and implement the magnetic resonance imaging water-fat image separation method described in the embodiment of the present invention. Specifically, a system or device equipped with a storage medium can be provided, on which a software program code that implements the functions of any of the above embodiments is stored, and the computer (or CPU or MPU) of the system or device reads out and executes the program code stored in the storage medium. In addition, the operating system operated on the computer can also be made to complete part or all of the actual operations through instructions based on the program code. The program code read from the storage medium can also be written to a memory provided in an expansion board inserted into the computer or to a memory provided in an expansion unit connected to the computer, and then the CPU installed on the expansion board or the expansion unit is made to perform part and all of the actual operations based on the instructions of the program code, thereby realizing the functions of any of the above embodiments. The storage medium implementation for providing the program code includes a floppy disk, a hard disk, a magneto-optical disk, an optical disk (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), a magnetic tape, a non-volatile memory card, and a ROM. Alternatively, the program code may be downloaded from a server computer via a communications network.

[0093] Fig. 7A and Figure 7B , which shows an example of an image quality comparison of an in vitro phantom water image obtained by using a traditional two-point Dixon water-fat separation algorithm and a magnetic resonance imaging water-fat image separation method in an embodiment of the present invention, Figure 7C Shows Figure 7B and Fig. 7A Schematic diagram of the ratio result of two images in . In this example, the prototype system of sequential image reconstruction was realized using Siemens Integrated Development Environment for Application (IDEA), and the in vitro phantom experiment was carried out on a Siemens 0.55T magnetometer. Figure 7C As shown, the image obtained by the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention has a signal-to-noise ratio that is 30% to 40% higher than that obtained by the traditional two-point Dixon water-fat separation algorithm. It can be seen that under the same sampling efficiency, the imaging quality of the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention is higher.

[0094] Fig. 8A and Figure 8B2 shows an example of an image quality comparison of a hip joint water image obtained by using a two-point Dixon water-fat separation algorithm of a combined echo using two samplings and a magnetic resonance imaging water-fat image separation method in an embodiment of the present invention. Fig. 8A The middle one is the hip joint water image obtained by using the two-point Dixon water-fat separation algorithm of the combined echo of two samplings. Figure 8B The figure shows the hip joint water image obtained by the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention. The protocol parameters used by the two include: FOV (field of view) = 285×380×300mm2, matrix size = 180×320, sampling bandwidth = 401Hz / pixel, slice thickness = 6mm, number of slices = 25, TE / TR (echo time / repetition time) of the two = 22 / 778 and 17 / 650, Fig. 8A The corresponding sampling time TA = 2 minutes and 18 seconds, Figure 8B The corresponding sampling time TA = 1 minute 55 seconds.

[0095] visible, Figure 8B and Fig. 8A The image quality is comparable, but the sampling time corresponding to 8B is longer Fig. 8A The corresponding sampling time is short. It can be seen that under the same imaging quality condition, the sampling efficiency of the magnetic resonance imaging water-fat image separation method in the embodiment of the present invention is higher.

[0096] It can be seen from the above scheme that, since two echo groups corresponding to the Dixon water-fat separation calculation are read in one echo cycle in the embodiment of the present invention, almost all the time between two refocusing pulses is used for data acquisition, which improves the data acquisition efficiency and reduces the dead zone. In addition, each echo group is read out under the same readout gradient polarity, which makes it unnecessary to perform phase correction in each echo group.

[0097] In addition, the echo images corresponding to the two echo groups can be merged to improve the signal-to-noise ratio before the water-fat separation calculation, or the water-fat separation calculation can be performed first and then the image merged to improve the signal-to-noise ratio. Compared with the traditional TSE-Dixon water-fat separation calculation method, the echoes obtained are doubled in a very similar capture time, so the signal-to-noise ratio is improved and better water-fat imaging quality is obtained. In addition, by implementing a phase correction process before averaging in the merging process, redundancy can be reduced and consistency of local and global water-fat separation results can be ensured.

[0098] In addition, since less echo interval time is required to achieve the same dephasing factor, there is less T2 blur, so that a longer echo sequence can reduce the scanning time. Alternatively, at the same echo interval time, the technical solution in the embodiment of the present invention applies a lower readout gradient strength, resulting in less image distortion and misregistration problems between water and fat images.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for separating water and fat images in magnetic resonance imaging, characterized in that: include: In one echo cycle, a first echo group corresponding to the Dixon water-fat separation calculation is obtained under a first readout gradient polarity, and a second echo group corresponding to the Dixon water-fat separation calculation is obtained under a second readout gradient polarity (101); wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group relative to the echo center position of the echo cycle; Based on the first echo group data acquired in each echo cycle, a first echo image group is obtained; based on the second echo group data acquired in each echo cycle, a second echo image group is obtained (102); Performing Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image (103), Each of the first echo group and the second echo group includes: a nearly in-phase echo that meets the set in-phase requirement and a nearly inverted echo that meets the set inverted phase requirement; the Dixon water-fat separation calculation is a two-point Dixon water-fat separation calculation; or, Each of the first echo group and the second echo group includes: a nearly in-phase echo that meets the set in-phase requirement and two nearly inverse-phase echoes that meet the set inverse-phase requirement; the Dixon water-fat separation calculation is a three-point Dixon water-fat separation calculation.

2. The magnetic resonance imaging water-fat image separation method according to claim 1, characterized in that: The step of performing Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image (103) includes: performing phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group, and performing complex averaging on each two echo images after the phase difference correction to obtain a corresponding echo average image group; The images in the obtained echo average image group are used to perform Dixon water-fat separation calculation to obtain water images and fat images.

3. The magnetic resonance imaging water-fat image separation method according to claim 2, characterized in that: Performing phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group includes: Performing a complex conjugate transformation on any echo image of every two echo images with symmetrical echo positions in the first echo image group and the second echo image group to obtain a first processed image; The low-pass phase difference between the first processed image and the echo image that has not undergone complex conjugate transformation is subtracted from the first processed image or another echo image that has not undergone complex conjugate transformation to obtain a second processed image. The second processed image and the echo image without the low-pass phase difference subtracted together constitute two echo images after phase difference correction.

4. The magnetic resonance imaging water-fat image separation method according to claim 1, characterized in that: The step of performing Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image (103) includes: Performing Dixon water-fat separation calculation using the first echo image group to obtain a first water image and a first fat image; performing Dixon water-fat separation calculation using the second echo image group to obtain a second water image and a second fat image; Performing module averaging on the first water image and the second water image to obtain a water image; The first fat image and the second fat image are modulus-averaged to obtain a fat image.

5. A magnetic resonance imaging water-fat image separation device, characterized in that: include: A data acquisition module (510) is used to obtain, within an echo cycle, a first echo group corresponding to a Dixon water-fat separation calculation under a first readout gradient polarity, and to obtain a second echo group corresponding to a Dixon water-fat separation calculation under a second readout gradient polarity; wherein the first readout gradient polarity and the second readout gradient polarity are opposite, and the echoes in the second echo group are located at a position symmetrical to the echoes in the first echo group relative to the echo center position of the echo cycle; An image extraction module (520) is used to obtain a first echo image group based on the first echo group data obtained in each echo cycle, and to obtain a second echo image group based on the second echo group data obtained in each echo cycle; The water-fat separation module (530) is used to perform Dixon water-fat separation calculation using the first echo image group and the second echo image group to obtain a water image and a fat image. Each of the first echo group and the second echo group includes: a nearly in-phase echo that meets the set in-phase requirement and a nearly inverted echo that meets the set inverted phase requirement; the Dixon water-fat separation calculation is a two-point Dixon water-fat separation calculation; or, Each of the first echo group and the second echo group includes: two nearly in-phase echoes that meet the set in-phase requirement and one nearly inverse-phase echo that meets the set inverse-phase requirement; the Dixon water-fat separation calculation is a three-point Dixon water-fat separation calculation.

6. The magnetic resonance imaging water-fat image separation device according to claim 5, characterized in that: The water-fat separation module (530) comprises: A first image integration module (531) is used to perform phase difference correction on each two echo images with symmetrical echo positions in the first echo image group and the second echo image group, and to perform complex averaging on each two echo images after the phase difference correction to obtain a corresponding echo average image group; The first water-fat separation calculation module (532) is used to perform Dixon water-fat separation calculation using the images in the obtained echo average image group to obtain a water image and a fat image.

7. The magnetic resonance imaging water-fat image separation device according to claim 6, characterized in that: The first image integration module (531) comprises: A complex conjugate transformation module (5311) is used to perform a complex conjugate transformation on any echo image of every two echo images with symmetrical echo positions in the first echo image group and the second echo image group to obtain a first processed image; a phase correction module (5312), configured to subtract the low-pass phase difference between the first processed image and the echo image that has not been subjected to complex conjugate transformation from the first processed image or another echo image that has not been subjected to complex conjugate transformation, to obtain a second processed image, wherein the second processed image and the echo image that has not been subjected to the low-pass phase difference subtracted together constitute two echo images after phase difference correction; and The complex averaging module (5313) is used to perform complex averaging on each two echo images after phase difference correction to obtain a corresponding echo average image group.

8. The magnetic resonance imaging water-fat image separation device according to claim 5, characterized in that: The water-fat separation module (530) comprises: a second water-fat separation calculation module (533), configured to perform a Dixon water-fat separation calculation using the first echo image group to obtain a first water image and a first fat image; and perform a Dixon water-fat separation calculation using the second echo image group to obtain a second water image and a second fat image; The second image integration module (534) is used to perform modulus averaging on the first water image and the second water image to obtain a water image; and perform modulus averaging on the first fat image and the second fat image to obtain a fat image.

9. A magnetic resonance imaging water-fat image separation device, characterized in that: include: At least one memory (61) and at least one processor (62), wherein: The at least one memory (61) is used to store a computer program; The at least one processor (62) is used to call the computer program stored in the at least one memory (61) to execute the magnetic resonance imaging water-fat image separation method according to any one of claims 1 to 4.

10. A magnetic resonance imaging system, comprising the magnetic resonance imaging water-fat image separation device as claimed in claims 5 to 9.

11. A computer-readable storage medium having a computer program stored thereon; characterized in that: The computer program can be executed by a processor and implements the magnetic resonance imaging water-fat image separation method according to any one of claims 1 to 4.

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