WO2018082028A1

WO2018082028A1 - Cartesian k-space collection method and system for three-dimensional dynamic magnetic resonance imaging

Info

Publication number: WO2018082028A1
Application number: PCT/CN2016/104667
Authority: WO
Inventors: 朱艳春; 李硕; 杨洁; 谢耀钦
Original assignee: 深圳先进技术研究院
Priority date: 2016-11-04
Filing date: 2016-11-04
Publication date: 2018-05-11

Abstract

Proposed are a Cartesian k-space collection method and system for three-dimensional dynamic magnetic resonance imaging. The method comprises: establishing a k-space model in a three-dimensional Cartesian coordinate system and determining a collection track of an echo signal in the model, wherein the collection track of the echo signal is: collecting all the echo signals along one coordinate direction in parallel, and the coordinates of each of the echo signals in a plane formed by the other two coordinate directions being obtained by the two-dimensional golden section ratio; determining, according to the collection track, a scanning time sequence and an encoding gradient required to apply a magnetic field by a magnetic resonance imaging system; setting the magnetic resonance imaging system according to the time sequence and the encoding gradient, and collecting k-space data conforming to the collection track. The method can achieve the continuous collection of three-dimensional k-space data and make the collected k-space data be approximately and uniformly distributed within any time window, thereby preventing streak artifacts from being generated in image reconstruction and achieving high-temporal-resolution three-dimensional dynamic magnetic resonance imaging.

Description

Cartesian k-space acquisition method and system for three-dimensional dynamic magnetic resonance imaging

Technical field

The present application relates to the field of three-dimensional dynamic magnetic resonance imaging technology, and in particular, to a Cartesian k-space acquisition method and system for three-dimensional dynamic magnetic resonance imaging.

Background technique

Magnetic Resonance Imaging (MRI) uses nuclear magnetic resonance to excite the spin nuclei in the human body and then receives the electromagnetic signals released by the spin nuclei to reconstruct human tissue image information. It has no radiation, multi-contrast imaging and soft tissue. The advantages of high contrast have become an important tool for clinical medical examination. The data acquired during the magnetic resonance imaging process is called k-space data. All the data are composed of k-space. The acquired trajectory is called k-space trajectory. Reconstruction of k-space data can obtain magnetic resonance images. Three-dimensional dynamic magnetic resonance imaging is a technique for tracking and imaging the dynamic physiological processes of human tissues and organs (such as heart beat, drug metabolism, etc.) by magnetic resonance imaging. This technique performs continuous and repeated scanning on a specific imaging space. A series of time-dependent k-space data is obtained. By filtering and reconstructing these data, a set of dynamic images can be obtained with time. By performing data analysis on the dynamic images, a series of biological processes that reflect the occurrence and development of lesions can be obtained. Quantitative or semi-quantitative parameters of pathophysiological information are of great value for both research and diagnosis. Dynamic magnetic resonance imaging has been widely used in fields such as Cardiac Cine MRI, Dynamic Contrast Enhanced MRI (DCE-MRI).

In this type of dynamic magnetic resonance imaging technology, the temporal resolution is low due to the limitation of the acquisition time of the three-dimensional k-space data. In organ imaging with approximate periodic motion, such as three-dimensional imaging of cardiac films, although multiple motion cycle repeat acquisition and retrospective reconstruction methods can be used to improve temporal resolution, it is difficult to guarantee acquisition in any time window due to the limitation of the acquisition scheme. To the k space The data is approximately evenly distributed.

Current 3D dynamic magnetic resonance imaging acquisition methods are obtained by repeatedly acquiring some or all of the k-space data, such as three-dimensional Cartesian acquisition and three-dimensional radial acquisition. The three-dimensional Cartesian acquisition method realizes the coding in two dimensions by layer selection gradient coding and phase coding, and then realizes the data acquisition in the third dimension by frequency coding, thereby realizing the filling of the three-dimensional k-space. The three-dimensional radial acquisition method achieves the filling of the three-dimensional k-space by simultaneously encoding and collecting the three layers of the selected layer, the phase and the frequency. For these two methods, reconstructing a set of 3D motion images requires repeated acquisition of all or a large amount of 3D k-space data, so the time resolution is low, and the image reconstruction requires the selection of k-space data within a specific time window, and a time is collected. The window is then collected for the next time window to ensure uniform distribution of k-space data, so the freedom of image reconstruction is limited. In addition, there is a Cartesian and radial hybrid acquisition method, which uses radial acquisition in the plane and Cartesian acquisition in the direction of the selected gradient. Although the acquisition time can be reduced to some extent by undersampling, the k-space data is uniform. Sexuality is still limited by a certain dimension coding scheme. The temporal resolution of dynamic imaging is difficult to improve. In addition, due to the radial acquisition method, it is easy to be affected by streak artifacts in reconstructed images, especially in under-sampling reconstruction. . In addition, most of the existing dynamic magnetic resonance imaging techniques achieve dynamic imaging by reconstructing data from post-screening and recombination, so it is generally difficult to obtain continuous dynamic images.

Summary of the invention

In order to solve the above problems in the prior art, an object of the present application is to provide a Cartesian k-space acquisition method and system suitable for three-dimensional dynamic magnetic resonance imaging, which can realize continuous acquisition of three-dimensional k-space data, so that the collected The k-space data is approximately evenly distributed in any time window, improving the temporal resolution of 3D dynamic magnetic resonance imaging and avoiding the influence of streak artifacts in the reconstructed image.

In order to achieve the above object, a Cartesian k-space acquisition method suitable for three-dimensional dynamic magnetic resonance imaging proposed by the embodiments of the present application includes: establishing a k-space model in a three-dimensional Cartesian coordinate system, and determining The acquisition trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction, and the coordinates of each echo signal in a plane formed by the other two coordinate directions are Calculating a two-dimensional golden section ratio; determining a time series of the magnetic resonance scan according to the collected trajectory, and calculating a coding gradient of the applied magnetic field required by the magnetic resonance imaging system; setting the magnetic resonance imaging system according to the time series and the coding gradient, and Acquiring k-space data that conforms to the acquisition trajectory.

To achieve the above objective, a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging proposed by the embodiment of the present application includes: a modeling module for establishing a k-space model in a three-dimensional Cartesian coordinate system, and determining a model back The acquisition trajectory of the wave signal, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction, and the coordinates of each echo signal in the plane formed by the other two coordinate directions are determined by two-dimensional gold. a calculation module for determining a time series of the magnetic resonance scan according to the collected trajectory, and calculating a coding gradient of the applied magnetic field required by the magnetic resonance imaging system; and an acquisition module for calculating the time series and the coding gradient according to the time series A magnetic resonance imaging system is provided and k-space data conforming to the acquisition trajectory is acquired.

The technical solution provided by the embodiment of the present application can collect uniform k-space data, thereby improving the time resolution of dynamic imaging, and the specific advantages are as follows:

1. Uniformity: It can realize the data collected in any length time window, in any position time window, and in any combination time window, which is approximately evenly distributed in the Cartesian k space. Therefore, the selection of data has a high degree of freedom in image reconstruction, and a dynamic image with higher temporal resolution can be obtained by an appropriate image reconstruction method, and the influence of streak artifacts in the reconstructed image is avoided.

2, reconstruction speed: can be applied to common reconstruction methods, simple reconstruction, and can make the calculated acquisition coordinates can correspond to Cartesian grid points, the reconstruction speed is faster.

3. Application: It is beneficial to perform three-dimensional magnetic resonance imaging (such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) on dynamic physiological processes, and also facilitates three-dimensional magnetic resonance imaging of organs with approximate periodic motion (such as heart, stomach). , lungs, etc.).

The aspects and advantages of the present invention will be set forth in part in the description which follows.

DRAWINGS

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings to be used in the embodiments or the prior art description will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present application, and other drawings can be obtained according to the drawings without any creative work for those skilled in the art.

1 is a schematic flow chart of a Cartesian k-space acquisition method suitable for three-dimensional dynamic magnetic resonance imaging according to an embodiment of the present application;

2 is a schematic flow chart of determining coordinates of a Cartesian k-space acquisition echo according to an embodiment of the present application;

3 is a schematic flow chart of determining coordinates of a Cartesian k-space data acquisition echo according to another embodiment of the present application;

4 is a schematic diagram of data distribution of a Cartesian k-space collected in an embodiment of the present application;

5 is a schematic diagram of three selection modes of a k-space time window in dynamic magnetic resonance image reconstruction according to an embodiment of the present application;

6 is a schematic diagram of k-space data uniformity comparison in different time window selection modes according to an embodiment of the present application;

7 is a schematic structural diagram of a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging according to an embodiment of the present application;

8 is a schematic structural diagram of a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging according to another embodiment of the present application;

FIG. 9 is an apparatus according to an embodiment of the present invention.

detailed description

Embodiments of the present application provide a Cartesian k-space acquisition method and apparatus for three-dimensional dynamic magnetic resonance imaging.

The technical solutions in the embodiments of the present application are clearly and completely described in the following, in which the technical solutions in the embodiments of the present application are clearly and completely described. The embodiments are only a part of the embodiments of the present application, and not all of them. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present application without departing from the inventive scope shall fall within the scope of the application.

FIG. 1 is a schematic flow chart of a Cartesian k-space acquisition method suitable for three-dimensional dynamic magnetic resonance imaging according to an embodiment of the present application. As shown in Figure 1, the method includes:

Step 101: Establish a k-space model in a three-dimensional Cartesian coordinate system, and determine an acquisition trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction, each The coordinates of the echo signal in the plane formed by the other two coordinate directions are calculated from the two-dimensional golden ratio.

Step 102: Determine a time series of the magnetic resonance scan according to the collected trajectory, and calculate a coding gradient of the applied magnetic field required by the magnetic resonance imaging system.

Step 103: Set a magnetic resonance imaging system according to the time series and the encoding gradient, and collect k-space data that conforms to the collected trajectory.

Specifically, the three-dimensional k-space collected in this embodiment is a cube as a whole. In the three-dimensional Cartesian k-space, the acquisition trajectory of the echo signal is: all echo signals are collected in parallel along one coordinate direction, and the coordinates of each echo signal in the plane formed by the other two coordinate directions are divided by two-dimensional golden ratio. It is calculated that the filling of the three-dimensional Cartesian k-space is finally realized by collecting the echo signals conforming to the above trajectory.

Since the three-dimensional Cartesian k-space does not adopt the radial acquisition mode, the embodiment of the present application can adapt to the existing image reconstruction technology, avoid the influence of the stripe artifact, and the reconstruction is simple. Since the echo signals are collected in the same direction, the position of the echo signal can be determined by collecting the coordinates in the vertical plane of the direction. The acquisition position is calculated according to the two-dimensional golden ratio, which can make the collected k-space data more uniform and reconstruct a continuous three-dimensional dynamic image with high time resolution.

Hereinafter, an embodiment of the present application will be described by taking the frequency encoding direction along the x-axis direction, the phase encoding direction along the y-axis direction, and the layer-coding direction along the z-axis direction as an example. In practical applications, the correspondence between the three coding directions and the coordinate axes can be adjusted as needed, but all belong to the protection scope of this patent.

According to an embodiment of the present application, the corresponding phase encoding and layer selection encoding may be calculated according to the two-dimensional golden section scaling coefficient. Specifically, the two-dimensional golden section scale coefficients are GR ₁ and GR ₂ , which are obtained from the eigenvectors of the generalized Fibonacci sequence. After taking the four digits after the decimal point, GR1 ≈ 0.4656, GR2 ≈ 0.6823. The basic steps for calculating the 2D golden section scale factor are as follows:

1. Solving the eigenvalues of the two-dimensional Fibonacci transformation matrix;

2. Solving and corresponding feature vector d;

3. Take two values of non-1 in the feature vector d as the two-dimensional golden section scale coefficients GR1 and GR2, GR1≈0.4656, and GR2≈0.6823.

The detailed calculation method is in the literature [Gao S, Zhu YC, Li S, Bao SL (2014) An optimal direction strategy of diffusion sensitive gradient mangnetic fields in magnetic resonance diffusion tensor imaging based on generalized Fibonacci sequence. Acta Physica Sinica 63] Detailed description will not be repeated here.

Based on the above, embodiments of the present invention are capable of providing an approximately uniform k-space distribution over any time window. This is beneficial to improve the temporal resolution of dynamic imaging and the freedom of k-space data selection during image reconstruction. In dynamic contrast-enhanced magnetic resonance imaging, high temporal resolution can provide more accurate physiological processes of tissue and organ, which will help to further study and diagnose the disease.

It is assumed that the resolution of k-space is: Res _x × Res _y × Res _z , where Res _x , Res _y , Res _z represent the number of codes in the x, y, and z directions, respectively. Since the echo signals are collected in the same direction, the position of the echo signal can be determined by collecting the coordinates in the vertical plane. Therefore, the position of each echo can be determined by the two parameters y and z in the plane coordinates. Therefore, if you want to achieve high time resolution of 3D k-space acquisition, you only need to optimize the two parameters y and z. The calculation method of the corresponding positions of the two phase codes and the layer selection codes in the k-space yOz plane in the embodiment of the present application is described below.

According to an embodiment of the present application, as shown in FIG. 2, the acquisition trajectory of the echo signal is calculated by the following steps:

1) Let the plane coordinate of the echo signal acquired in the i-th time in the plane perpendicular to it be (y _i , z _i ), and the initial echo number is i=i ₀ .

2) Calculate the plane coordinates (y _i , z _i ) according to the two-dimensional golden section scale factor.

Specifically, y _i and z _i respectively correspond to GR1, GR2, and in one embodiment of the present application, plane coordinates (y _i , z _i ) can be calculated according to the following formula:

y _i = mod(i × GR ₁ , 1) × Res _y , z _i = mod(i × GR ₂ , 1) × Res _z

or,

y _i = mod(i × GR ₂ , 1) × Res _y , z _i = mod(i × GR ₁ , 1) × Res _z

Among them, mod(a,b) is the remainder of a/b.

The obtained yi and zi are used to set the position of the echo acquired in the i-th time in the k-space yOz plane.

3) According to the preset cutoff condition, it is judged whether the acquisition is finished, that is, whether the echo signal acquired by the i th is the last echo signal collected.

The preset cutoff condition is manually set, for example, the acquisition time is 20 minutes, or 100,000 echo signals are collected.

4) If yes, the acquisition ends, otherwise let i=i+1, repeat 1) to 3) until the end of the acquisition.

According to an embodiment of the present application, the number i ₀ of the initial echo acquired by the echo may be an arbitrary natural number, and the echo signal may be collected from an acquisition track at an arbitrary position to fill the k space.

In another embodiment of the present application, the plane coordinate (y _i , z _i ) may also be calculated according to the two-dimensional golden section scale coefficient by another method: assigning the calculated value of (y _i , z _i ) to The nearest integer grid point in the plane; the coordinates of the integer grid point are checked in a preset range; when the same coordinates are not present, the coordinates of the integer grid point are collected as the back The plane coordinate of the wave signal; if the same coordinates already exist, the plane coordinates (y _i+1 , z _i+1 ) are calculated according to the two-dimensional golden section scale factor. It is also possible to pre-store the plane coordinates of the echo signals calculated each time into an array; the array is called to determine the acquisition trajectory of the echo signals when the k-space data is acquired. As shown in Figure 3, the process of confirming the acquisition trajectory is as follows:

201) Set an empty array M=[] that can store two-dimensional coordinates.

202) Let the coordinates of the echo acquired in the ith time in the k-space yOz plane be: (y _i , z _i ). Let j=i. (Initial value i=i ₀ )

203) Determine whether i is greater than Res _y × Res _z .

If yes, execute 204), if no, execute 205).

204) Let M(i)=M(i-Res _y ×Res _z ), (y _i , z _i )=M(i). Go to 209).

205) Calculate r _y =round(mod(j×GR ₁ ,1)×Res _y ), r _z =round(mod(j×GR ₂ ,1)×Res _z ).

Where mod(a,b) is the remainder of the a/b, and round(c) is the rounding of c.

206) Find whether there is a point coordinate value (r _y , r _z ) in M.

If not, execute 207), if present, execute 208).

207) Let M(i)=(r _y , r _z ), and (y _i , z _i )=M(i), and obtain y _i and z _i for setting the echo of the ith acquisition at k The position within the space yOz plane.

208) Let j=j+1. Repeat 205) to 206).

209) Determine whether the acquisition ends according to the preset cutoff condition.

If yes, the acquisition is ended, otherwise i=i+1, repeat 202) to 209) until the end of the acquisition.

Specifically, the calculated y _i and z _{i are} assigned to integer grid points in the corresponding nearest k-space plane. If the coordinates of the grid point exist within the set continuous time window, the next two-dimensional coordinate value is continuously calculated according to the two-dimensional golden ratio until the coordinate value of the obtained integer grid point is in the set continuous time window. Does not exist inside, and then sets the coordinate value to the plane coordinate of the acquired echo. Preferably, the set continuous time window corresponds to the k-space resolution, and the array M can be pre-calculated according to the set k-space resolution. Each time the echo is acquired in the actual scan, the coordinate values in M can be called in order to determine the position of the phase encoding and the layer selection code corresponding to the echo acquired each time. It is worth noting that M only needs to store the former (Res _y × Res _z ) values, and the subsequent acquisition loop calls M. The calculation method of M is similar to the above method, and can be implemented by programming means, and will not be described herein.

According to an embodiment of the present application, in order to acquire k-space data conforming to the collected trajectory, the magnetic resonance imaging system uses a corresponding physical gradient magnetic field in all three coordinate directions of x, y, and z. Calculating the coding gradient of the applied magnetic field required by the magnetic resonance imaging system, and calculating the coding gradient of the three directional magnetic fields to be applied in the ith acquisition according to the coordinates x _i , y _i , z _i of the respective acquisition points on the i-th acquisition trajectory . The relationship between the coding gradients G _{x, y, z} applied to the i-th acquisition and x _i , y _i , z _i can be described by the following equation, regardless of the actual hardware conditions and the like:

Where k _{x, y, z} are the coordinates of the i-th acquisition trajectory in k-space, corresponding to x _i , y _i and z _i ; γ is the gyromagnetic ratio, and t is the time applied by the gradient.

After the corresponding k-space data is acquired according to the code, a continuous three-dimensional dynamic image can be reconstructed by processing the k-space data.

The embodiments of the present application can realize that the data collected in any time window is approximately evenly distributed in the three-dimensional Cartesian k-space, and the under-sampling reconstruction technology can realize dynamic magnetic resonance image reconstruction with high time resolution, and can realize continuous motion. Or dynamic imaging. The uniformity of the k-space data collected by the method of the embodiment of the present application is evaluated by a specific simulation experiment.

Taking the echo direction in the x direction, k spatial resolution as 100×100×100, and continuously acquiring 1000 times and 10000 echoes as an example, FIG. 4 is two kinds of k spaces acquired by using the method of the embodiment of the present invention in the yOz plane. The distribution of coordinate points within. The steps 1) to 4) are referred to as method 1, and the steps 201)-207) are referred to as method 2, and the two columns (a) and (b) in FIG. 4 are successively collected using method 1 and method 2, respectively. The results of 1000 and 10,000 echoes.

In order to evaluate the uniformity of k-space data in the yOz plane, the average distance of each point from all points in its neighborhood can be calculated, and then the standard deviation of all these distance values is counted. The standard deviation is closer to 0, indicating each point. The closer the distance between all points in the neighborhood, the more uniform the distribution. The neighborhood of each point is a circle with a radius of R centered on that point, and R is determined by:

Where T is the total number of acquisitions, and Res _y and Res _z are the resolutions in the y and z directions, that is, the number of codes. Fig. 5 is a three selection mode of k-space data in dynamic magnetic resonance image reconstruction, wherein (a) is a different continuous acquisition times, that is, time windows of different lengths, (b) is a time window of different positions, and (c) is A combination of different time windows. Figure 6 shows the k-space data distribution uniformity comparison in different time window selection modes, including different acquisition times (a), different time window positions (b), and different time window combinations (c). Under the condition, the average distance value standard deviation of the Cartesian k-space data collected by the two methods is compared, and the number of acquisitions of (b) and (c) is 5000.

It can be seen from the evaluation results of FIG. 4-6 that the k-space data collected by the acquisition method proposed by the embodiment of the present invention has good uniformity in the Cartesian k-space, and the two methods proposed by the present invention are in three different k-spaces. The statistical standard deviation in the data selection mode is very small, close to 0, which proves that the k-space data obtained by the method of the present invention has better spatial uniformity.

In summary, the Cartesian k-space acquisition method of the embodiment of the present invention has the following advantages:

Based on the same inventive concept, the embodiment of the present application further provides a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging, which can be used to implement the method described in the above embodiments, as described in the following embodiments. The Cartesian k-space acquisition system for 3D dynamic magnetic resonance imaging solves the problem similarly to the Cartesian k-space acquisition method for 3D dynamic magnetic resonance imaging, so it is suitable for Cartesian k-space acquisition of 3D dynamic magnetic resonance imaging. The implementation of the system can be seen in the implementation of the Cartesian k-space acquisition method applicable to three-dimensional dynamic magnetic resonance imaging, and the repetition will not be repeated. As used hereinafter, the term "unit" or "module" may implement a combination of software and/or hardware of a predetermined function. Although the apparatus described in the following embodiments is preferably implemented in software, hardware, or a combination of software and hardware, is also possible and contemplated.

FIG. 7 is a schematic structural diagram of a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging according to an embodiment of the present application. The system of this embodiment may be configured as a logical component that implements a corresponding function, or may be an electronic device that runs a corresponding functional software. As shown in FIG. 7, the Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging includes a modeling module 10, a calculation module 20, and an acquisition module 30.

Specifically, the modeling module 10 is configured to establish a k-space model in a three-dimensional Cartesian coordinate system, and determine a collection trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals along a coordinate The directions are collected in parallel, and the coordinates of each echo signal in the plane formed by the other two coordinate directions are calculated by the two-dimensional golden ratio.

The calculation module 20 is configured to determine a time series of the magnetic resonance scan according to the collected trajectory, and calculate a coding gradient of the applied magnetic field required by the magnetic resonance imaging system.

The acquisition module 30 is configured to set the magnetic resonance imaging system according to the time series and the coding gradient, and acquire k-space data that conforms to the collected trajectory.

FIG. 8 is a schematic structural diagram of a Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging according to another embodiment of the present application. As shown in FIG. 8, on the basis of FIG. 7, the modeling module 10 further includes a computing unit 11, a meshing unit 12, a de-weighting unit 13, and a storage unit 14.

Specifically, the modeling module 10 is further configured to determine a collection trajectory of the echo signal by the following steps:

1) Set the echo signal to be collected along the x-axis direction. The plane coordinate of the echo signal acquired in the i-th time is (y _i , z _i ) in the plane perpendicular to it, and the initial echo number is i=i ₀ ;

2) Calculate the plane coordinates (y _i , z _i ) according to the two-dimensional golden section scale coefficient;

3) judging whether the acquisition is finished according to the preset cutoff condition, that is, whether the echo signal collected by the i th is the last echo signal collected;

The two-dimensional golden section ratio coefficient is GR1, GR2, GR1≈0.4656, and GR2≈0.6823; the coordinates of the echo signal in two directions in the vertical plane correspond to GR1 and GR2, respectively.

The number i0 of the initial echo may be any natural number.

The modeling module 10 further includes a computing unit 11 that calculates the echo signal in a vertical plane yOz by the following equation when the resolution of the three-dimensional k-space is Res _x ×Res _y ×Res _z and the echo signal is acquired along the x-axis direction The plane coordinates (y _i , z _i ) inside:

y _i = mod(i × GR ₁ , 1) × Res _y , z _i = mod(i × GR ₂ , 1) × Res _z

or,

y _i = mod(i × GR ₂ , 1) × Res _y , z _i = mod(i × GR ₁ , 1) × Res _z

Among them, mod(a,b) is the remainder of a/b.

The meshing unit 12 is configured to assign the calculated value of (y _i , z _i ) to the nearest integer grid point in the plane.

The de-weighting unit 13 is configured to check the coordinates of the integer grid points within a preset range. If the same coordinates are not present, the coordinates of the integer grid points are used as plane coordinates for acquiring the echo signals; If the same coordinates already exist, the plane coordinates (y _i+1 , z _i+1 ) are calculated according to the two-dimensional golden section scale factor.

The storage unit 14 is configured to store in advance the plane coordinates of the echo signal calculated each time.

The acquisition module 30 is further configured to call coordinates in the storage unit when acquiring k-space data to determine a collection trajectory of the echo signal.

The device of the embodiment can realize continuous acquisition of three-dimensional k-space data and improve the time resolution of three-dimensional dynamic magnetic resonance imaging, and the specific advantages are as follows:

Embodiments of the present invention also provide a computer readable storage medium including computer readable instructions that, when executed, cause a processor to perform at least the following operations: establishing a k-space model in a three-dimensional Cartesian coordinate system, Determining an acquisition trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction, and coordinates of each echo signal in a plane formed by the other two coordinate directions Calculated by a two-dimensional golden section ratio; determining a time series of the magnetic resonance scan according to the collected trajectory, and calculating a coding gradient of the applied magnetic field required by the magnetic resonance imaging system; and setting the magnetic resonance imaging system according to the time series and the coding gradient, And acquiring k-space data that conforms to the collected trajectory.

The embodiment of the present invention further provides an apparatus. As shown in FIG. 9, the apparatus includes: a processor 901 and a memory 902 including computer readable instructions that, when executed, cause the processor to perform the following operations: The k-space model in the three-dimensional Cartesian coordinate system determines the acquisition trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction, and each echo signal is The coordinates in the plane formed by the other two coordinate directions are calculated by the two-dimensional golden ratio; the time series of the magnetic resonance scan is determined according to the collected trajectory, and the coding gradient of the applied magnetic field required by the magnetic resonance imaging system is calculated; The time series and the coding gradient set up the magnetic resonance imaging system and acquire k-space data that conforms to the acquired trajectory.

The embodiments of the present application can realize that the data collected in any time window is approximately evenly distributed in the three-dimensional Cartesian k-space, and the under-sampling reconstruction technology can realize dynamic magnetic resonance image reconstruction with high time resolution, and can realize continuous motion. Or dynamic imaging.

It should be noted that in the description of the present application, the terms "first", "second" and the like are used for descriptive purposes only, and are not to be construed as indicating or implying relative importance. Further, in the description of the present application, the meaning of "a plurality" is two or more unless otherwise stated.

Any process or method description in the flowcharts or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a particular logical function or process. And the scope of the preferred embodiments of the present application includes additional implementations, in which the functions may be performed in a substantially simultaneous manner or in the reverse order depending on the functions involved, in accordance with the illustrated or discussed order. It will be understood by those skilled in the art to which the embodiments of the present application pertain.

It should be understood that portions of the application can be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented by any one or combination of the following techniques well known in the art: having logic gates for implementing logic functions on data signals. Discrete logic circuit ASICs with suitable combinational logic gates, Programmable Gate Arrays (PGAs), Field Programmable Gate Arrays (FPGAs), etc.

One of ordinary skill in the art can understand that all or part of the steps carried by the method of implementing the above embodiments can be completed by a program to instruct related hardware, and the program can be stored in a computer readable storage medium. When executed, one or a combination of the steps of the method embodiments is included.

In the description of the present specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means a specific feature described in connection with the embodiment or example. A structure, material or feature is included in at least one embodiment or example of the application. In the present specification, the schematic representation of the above terms does not necessarily mean the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

While the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are illustrative and are not to be construed as limiting the scope of the present application. The embodiments are subject to variations, modifications, substitutions and variations.

Claims

A Cartesian k-space acquisition method for three-dimensional dynamic magnetic resonance imaging, comprising:

The k-space model in the three-dimensional Cartesian coordinate system is established to determine the acquisition trajectory of the echo signals in the model. The trajectory of the echo signals is: all echo signals are collected in parallel along a coordinate direction, and each echo signal The coordinates in the plane formed by the other two coordinate directions are calculated from the two-dimensional golden ratio;

Determining a time series of the magnetic resonance scan according to the collected trajectory, and calculating a coding gradient of the applied magnetic field required by the magnetic resonance imaging system;

A magnetic resonance imaging system is provided according to the time series and the coding gradient, and k-space data conforming to the acquisition trajectory is acquired.
The method according to claim 1, wherein the three coordinate directions in the three-dimensional Cartesian coordinate system are in one-to-one correspondence with the frequency encoding direction, the phase encoding direction, and the layer selection encoding direction, respectively.
The method according to claim 1, wherein the method for calculating the acquisition trajectory of the echo signal comprises the following steps:

1) Set the echo signal to be acquired along the x-axis frequency encoding direction. The plane coordinate of the echo signal acquired in the i-th plane is (y i , z i ) in the plane perpendicular to it, and the initial echo number is i=i 0 ;

2) calculating the plane coordinates (y i , z i ) according to the two-dimensional golden section scale coefficient;

3) judging whether the acquisition is finished according to the preset cutoff condition, that is, whether the echo signal collected by the i th is the last echo signal collected;

4) If yes, the acquisition ends, otherwise let i=i+1, repeat 1) to 3) until the end of the acquisition.
The method according to claim 3, wherein the two-dimensional golden section scale coefficient is GR1, GR2, GR1 ≈ 0.4656, and GR2 ≈ 0.6823; coordinates of the echo signals in two directions in a vertical plane are respectively GR1 and GR2 correspond to each other.
The method according to claim 4, wherein the resolution of the three-dimensional k-space is Res x ×Res y ×Res z , and the echo signal is acquired along the x-axis direction, and the echo signal is calculated by the following formula Plane coordinates (y i , z i ) in the vertical plane yOz:

y i = mod(i × GR 1 , 1) × Res y , z i = mod(i × GR 2 , 1) × Res z

or,

y i = mod(i × GR 2 , 1) × Res y , z i = mod(i × GR 1 , 1) × Res z

Among them, mod(a,b) is the remainder of a/b.
The method according to any one of claims 3-5, wherein the calculating the plane coordinates (y i , z i ) according to the two-dimensional golden section scale coefficient further comprises:

Assigning the calculated value of (y i , z i ) to the nearest integer grid point in the plane;

Checking the coordinates of the integer grid points within a preset range;

When the same coordinates do not exist, the coordinates of the integer grid points are taken as plane coordinates for acquiring the echo signals;

If the same coordinates already exist, the plane coordinates (y i+1 , z i+1 ) are calculated according to the two-dimensional golden section scale factor.
The method according to claim 6, wherein the determining the trajectory of the echo signal in the model further comprises:

The plane coordinates of the echo signal calculated each time are pre-stored in the array;

The array is called when the k-space data is acquired to determine the acquisition trajectory of the echo signal.
The method according to claim 3, characterized in that the number i 0 of the initial echo acquired by the echo is an arbitrary natural number.
A Cartesian k-space acquisition system suitable for three-dimensional dynamic magnetic resonance imaging, comprising:

The modeling module is configured to establish a k-space model in a three-dimensional Cartesian coordinate system, and determine an acquisition trajectory of the echo signal in the model, wherein the trajectory of the echo signal is: all echo signals are collected in parallel along a coordinate direction The coordinates of each echo signal in the plane formed by the other two coordinate directions are calculated by the two-dimensional golden ratio;

a calculation module, configured to determine a time series of the magnetic resonance scan according to the collected trajectory, and calculate a coding gradient of an applied magnetic field required by the magnetic resonance imaging system;

And an acquisition module, configured to set a magnetic resonance imaging system according to the time series and the coding gradient, and acquire k-space data that conforms to the collected trajectory.
The system according to claim 9, wherein the modeling module is specifically configured to determine an acquisition trajectory of the echo signal by the following steps:

1) Set the echo signal to be acquired along the x-axis frequency encoding direction. The plane coordinate of the echo signal acquired in the i-th plane is (y i , z i ) in the plane perpendicular to it, and the initial echo number is i=i 0 ;

2) Calculate the plane coordinates (y i , z i ) according to the two-dimensional golden section scale coefficient;

3) judging whether the acquisition is finished according to the preset cutoff condition, that is, whether the echo signal collected by the i th is the last echo signal collected;

4) If yes, the acquisition ends, otherwise let i=i+1, repeat 1) to 3) until the end of the acquisition.
The system according to claim 10, wherein said two-dimensional golden division ratio coefficients are GR1, GR2, GR1 ≈ 0.4656, and GR2 ≈ 0.6823; coordinates of the echo signals in two directions in a vertical plane are respectively GR1 and GR2 correspond to each other.
The system of claim 10 wherein said modeling module comprises:

a calculation unit for calculating a plane coordinate of the echo signal in a vertical plane yOz by the following formula when the resolution of the three-dimensional k-space is Res x ×Res y ×Res z and the echo signal is acquired along the x-axis direction ( y i ,z i ):

y i = mod(i × GR 1 , 1) × Res y , z i = mod(i × GR 2 , 1) × Res z

or,

y i = mod(i × GR 2 , 1) × Res y , z i = mod(i × GR 1 , 1) × Res z

Among them, mod(a,b) is the remainder of a/b.
The system of any of claims 10-12, wherein the modeling module further comprises:

a meshing unit for assigning a calculated value of (y i , z i ) to a nearest integer grid point in the plane;

The de-weighting unit is configured to check the coordinates of the integer grid point within a preset range. If the same coordinates are not present, the coordinates of the integer grid point are used as plane coordinates for acquiring the echo signal; If the same coordinates already exist, the plane coordinates (y i+1 , z i+1 ) are calculated according to the two-dimensional golden section scale factor.
The system of claim 10, wherein the modeling module further comprises:

a storage unit, configured to pre-store a plane coordinate of the echo signal calculated each time;

The collection module is further configured to call coordinates in the storage unit to determine a collection trajectory of the echo signal when acquiring k-space data.
The system of claim 10 wherein said initial echo number i 0 is any natural number.