阅读说明：本技术 骨骼组织定量成像方法、系统、介质及终端 (Bone tissue quantitative imaging method, system, medium and terminal ) 是由 魏红江 张明 于 2020-12-23 设计创作，主要内容包括：本发明提供一种骨骼组织定量成像方法、系统、介质及终端,包括以下步骤：基于超短回波时间序列采集骨骼组织的磁共振图像；对所述磁共振图像进行水脂分离,得到水图、脂肪图和场图；对所述场图进行去背景场处理,得到局部场图像；对所述局部场图像进行偶极子反演,得到所述骨骼组织的定量磁化率图像。本发明的骨骼组织定量成像方法、系统、介质及终端基于超短回波时间成像和定量磁化率成像,实现骨骼组织的定量成像,具有很好的临床实用性。(The invention provides a bone tissue quantitative imaging method, a bone tissue quantitative imaging system, a bone tissue quantitative imaging medium and a bone tissue quantitative imaging terminal, which comprise the following steps: acquiring a magnetic resonance image of bone tissue based on the ultrashort echo time sequence; performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map; performing background field removing processing on the field image to obtain a local field image; and carrying out dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue. The bone tissue quantitative imaging method, the bone tissue quantitative imaging system, the bone tissue quantitative imaging medium and the bone tissue quantitative imaging terminal are based on ultra-short echo time imaging and quantitative magnetic susceptibility imaging, and have good clinical practicability.)

1. A method for quantitative imaging of bone tissue, characterized by: the method comprises the following steps:

acquiring a magnetic resonance image of bone tissue based on the ultrashort echo time sequence;

performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map;

performing background field removing processing on the field image to obtain a local field image;

and carrying out dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue.

2. The method of quantitative bone tissue imaging according to claim 1, wherein: and the ultrashort echo time sequence adopts a hard pulse without applying a layer selection gradient to carry out signal excitation.

3. The method of quantitative bone tissue imaging according to claim 1, wherein: acquiring a magnetic resonance image of bone tissue based on an ultra-short echo time sequence comprises the following steps:

acquiring multichannel magnetic resonance original k-space data of bone tissues based on an ultrashort echo time sequence;

calculating a density compensation function of the magnetic resonance original k-space data according to the sampling trajectory;

performing density compensation on the magnetic resonance original k space data of the non-Cartesian space according to the density compensation function;

performing gridding processing on the magnetic resonance original k space data of the non-Cartesian space after density compensation by using a convolution kernel function, so that the magnetic resonance original k space data of the non-Cartesian space is resampled to a Cartesian coordinate system;

acquiring a magnetic resonance original image of each channel by utilizing Fourier transform based on magnetic resonance original k-space data under a Cartesian coordinate system;

and (3) channel merging is carried out on the magnetic resonance original images of all the channels by using a self-adaptive algorithm to obtain a multi-echo magnetic resonance image of the bone tissue.

4. The method of quantitative bone tissue imaging according to claim 1, wherein: and performing water-fat separation on the magnetic resonance image based on a graph cut algorithm.

5. The method of quantitative bone tissue imaging according to claim 1, wherein: the background field removing treatment of the field pattern comprises the following steps:

carrying out threshold processing on the amplitude image of the field map to obtain a mask of a bone region;

and removing the background field outside the bone region based on a PDF algorithm to obtain the local field image.

6. The method of quantitative bone tissue imaging according to claim 1, wherein: performing dipole inversion on the local field image based on a STAR-QSM algorithm.

7. The method of quantitative bone tissue imaging according to claim 1, wherein: the skeletal tissue includes one or a combination of knee joint cartilage and cortical bone.

8. A quantitative bone tissue imaging system, characterized by: the device comprises an acquisition module, a separation module, a removal module and an imaging module;

the acquisition module is used for acquiring a magnetic resonance image of bone tissue based on an ultrashort echo time sequence;

the separation module is used for performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map;

the removing module is used for carrying out background field removing processing on the field pattern to obtain a local field image;

the imaging module is used for carrying out dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue.

9. A storage medium having stored thereon a computer program, characterized in that the program, when being executed by a processor, is adapted to carry out the method for quantitative imaging of bone tissue according to any one of claims 1 to 7.

10. A terminal, comprising: a processor and a memory;

the memory is used for storing a computer program;

the processor is configured to execute the computer program stored in the memory to cause the terminal to perform the quantitative bone tissue imaging method according to any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of quantitative imaging, in particular to a method, a system, a medium and a terminal for quantitative imaging of bone tissues.

Background

The magnetic resonance image can reflect the anatomical structure, metabolism and function information of human tissues, and has wide application in clinic. Human tissues are generally classified into the following three categories according to the transverse relaxation time (T2 time):

(1) long T2 time (> 10ms) tissues such as gray matter, muscle;

(2) short T2 time (1ms to 10ms) tissue, such as cartilage;

(3) ultrashort T2 time (< 1ms) tissues, such as cortical bone, etc.

Tissue with a short time T2 decays very quickly after excitation by the radio frequency pulse. Due to the limitations of imaging parameters and hardware, conventional magnetic resonance sequences cannot image these tissues, and appear as dark signals or even no signals on the image.

Ultrashort Echo Time Echo (UTE) imaging sequences are often used to image these tissues with short transverse relaxation times. By means of special radio frequency excitation and k-space acquisition modes, the limitation of the conventional sequence Echo Time (TE) is overcome, the TE is shortened to dozens of microseconds, and magnetic resonance signals can be captured before signals generated by tissues with short T2 Time are attenuated.

Magnetic susceptibility is an inherent property of matter. After an object placed in a magnetic field is magnetized, the field generated by the object itself causes a change in the local magnetic field, which in turn affects the phase image of the magnetic resonance. Quantitative Susceptibility imaging (QSM) is an imaging method for quantitatively extracting a tissue Susceptibility value. In general, QSM includes three major steps of phase unwrapping, background field removal, and dipole inversion. QSM is now commonly used for research in the field of brain science, due to its sensitivity to iron deposition and demyelination. At present, QSM is also used for researches on non-brain tissue structures such as heart, liver, cartilage and the like.

The knee joint cartilage (articular cartilage) can maintain the normal movement of the knee joint on one hand, and can provide buffer on the other hand to prevent uneven stress on the joint surface. The internal structure of articular cartilage is a network structure composed of collagen fibers. Cartilage has a layered structure, with collagen fibers in different arrangements in the superficial, intermediate and deep layers. In the superficial layer, the direction of collagen fibers is almost parallel to the cartilage surface; the collagen fibers in the middle layer are irregularly arranged; the deep collagen fibers are approximately perpendicular to the cartilage surface. Cortical bone (cortical bone) has a compact texture and good pressure resistance, and is distributed on the surface of bone. The research on the structure and the characteristics of articular cartilage and cortical bone has important significance for researching the pathogenesis of arthritis, osteoporosis and other bone diseases.

T2 times for cartilage and cortical bone are short, making it difficult to image using conventional magnetic resonance sequences. Both tissues with fast signal decay can be imaged by the UTE sequence. In the prior art, researches based on QSM images of conventional gradient echo (GRE) sequences show that each layer of cartilage has different magnetic susceptibility characteristics because the trend of collagen fibers in each layer of the cartilage and a main magnetic field form different included angles. But because of the short time of cartilage T2, susceptibility images obtained using conventional echo times may lose some detail.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method, a system, a medium and a terminal for quantitative imaging of bone tissue, which are based on ultra-short echo time imaging and quantitative susceptibility imaging, and which achieve quantitative imaging of bone tissue with high definition and strong practicability.

To achieve the above and other related objects, the present invention provides a method for quantitative imaging of bone tissue, comprising the steps of: acquiring a magnetic resonance image of bone tissue based on the ultrashort echo time sequence; performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map; performing background field removing processing on the field image to obtain a local field image; and carrying out dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue.

In an embodiment of the present invention, the ultrashort echo time sequence is signal-excited by a hard pulse without applying a slice selection gradient.

In an embodiment of the invention, acquiring the magnetic resonance image of the bone tissue based on the ultra-short echo time sequence comprises the following steps

The method comprises the following steps: acquiring a magnetic resonance image of bone tissue based on an ultra-short echo time sequence comprises the following steps:

acquiring multichannel magnetic resonance original k-space data of bone tissues based on an ultrashort echo time sequence;

calculating a density compensation function of the magnetic resonance original k-space data according to the sampling trajectory;

performing density compensation on the magnetic resonance original k space data of the non-Cartesian space according to the density compensation function;

performing gridding processing on the magnetic resonance original k space data of the non-Cartesian space after density compensation by using a convolution kernel function, so that the magnetic resonance original k space data of the non-Cartesian space is resampled to a Cartesian coordinate system;

acquiring a magnetic resonance original image of each channel by utilizing Fourier transform based on magnetic resonance original k-space data under a Cartesian coordinate system;

and (3) channel merging is carried out on the magnetic resonance original images of all the channels by using a self-adaptive algorithm to obtain a multi-echo magnetic resonance image of the bone tissue.

In an embodiment of the invention, the magnetic resonance image is subjected to water-fat separation based on a graph cut algorithm.

In an embodiment of the present invention, the background field removing process for the field pattern includes the following steps:

carrying out threshold processing on the amplitude image of the field map to obtain a mask of a bone region;

and removing the background field outside the bone region based on a PDF algorithm to obtain the local field image.

In one embodiment of the present invention, the dipole inversion is performed on the local field image based on the STAR-QSM algorithm.

In an embodiment of the invention, the bone tissue includes one or a combination of knee joint cartilage and cortical bone.

Correspondingly, the invention provides a quantitative bone tissue imaging system, which comprises an acquisition module, a separation module, a removal module and an imaging module;

the acquisition module is used for acquiring a magnetic resonance image of bone tissue based on an ultrashort echo time sequence;

the separation module is used for performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map;

the removing module is used for carrying out background field removing processing on the field pattern to obtain a local field image;

the imaging module is used for carrying out dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue.

The present invention provides a storage medium having stored thereon a computer program which, when executed by a processor, implements the above-described method of quantitative imaging of bone tissue.

The present invention provides a terminal, including: a processor and a memory;

the memory is used for storing a computer program;

the processor is used for executing the computer program stored in the memory so as to enable the terminal to execute the bone tissue quantitative imaging method.

As described above, the bone tissue quantitative imaging method, system, medium and terminal of the present invention have the following advantages:

(1) the ultra-short echo time imaging and the quantitative magnetic resonance imaging are combined, so that the quantitative imaging of the bone tissue is realized, and the anatomical structures of the bone tissue and the bone tissue can be well displayed;

(2) by comparing the difference of the magnetic susceptibility values of articular cartilage and cortical bone between arthritis patients or patients with other skeletal diseases and normal subjects, an effective tool is provided for the subsequent clinical study of cartilage and skeleton.

Drawings

FIG. 1 is a flow chart illustrating a method for quantitative bone tissue imaging according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a framework of a quantitative bone tissue imaging method according to an embodiment of the invention;

FIG. 3 is a schematic illustration of quantitative imaging of bone tissue in one embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a quantitative imaging system for bone tissue according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of a terminal according to an embodiment of the invention.

Description of the element reference numerals

41 acquisition module

42 separation module

43 removal module

44 imaging module

51 processor

52 memory

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.

It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

The bone tissue quantitative imaging method, the bone tissue quantitative imaging system, the bone tissue quantitative imaging medium and the bone tissue quantitative imaging terminal combine ultra-short echo time imaging and quantitative magnetic susceptibility imaging to achieve quantitative imaging of bone tissue, are clear in details, meet application requirements of bone tissue imaging, and have high practicability. In particular, the skeletal tissue includes one or a combination of knee joint cartilage and cortical bone. The knee joint cartilage will be described in detail below as an example.

As shown in fig. 1 and 2, in one embodiment, the method for quantitative imaging of bone tissue of the present invention comprises the following steps:

step S1, acquiring a magnetic resonance image of the bone tissue based on the ultra-short echo time sequence.

In particular, a magnetic resonance image of bone tissue is acquired using an ultra-short echo time sequence. And the ultrashort echo time sequence adopts a hard pulse without applying a selective layer gradient to carry out signal excitation. The hard pulse has a larger bandwidth and can excite the effective volume covered by the whole knee joint coil. Frequency encoding is applied in three gradient directions of x, y and z, and radial k-space acquisition from the center to the outside is realized by controlling the gradient magnitude direction, namely, radial trajectories are used for filling the whole spherical k-space. When a three-dimensional (3D) ultrashort echo time sequence is selected to acquire a magnetic resonance image, a 12-channel knee joint coil is adopted to acquire signals. The specific parameters include: the echo time includes one ultra-short echo TE1 ═ 0.05ms (50 μ s), two conventional echoes TE2 ═ 2.24ms, and TE3 ═ 3.53 ms; the repetition time TR is 6000 ms; the FOV is 160 × 200 mm; the in plane resolution is 0.9 multiplied by 0.9 mm; the layer thickness was 0.9mm and there were 254 layers.

In an embodiment of the present invention, acquiring a magnetic resonance image of bone tissue based on an ultrashort echo time sequence includes the following steps:

11) multichannel magnetic resonance raw k-space data of bone tissue are acquired based on an ultrashort echo time sequence.

12) Calculating a density compensation function of the magnetic resonance raw k-space data according to the actual radial sampling trajectory.

13) And performing density compensation on the magnetic resonance original k-space data of the non-Cartesian space according to the density compensation function.

14) And performing gridding processing on the density-compensated magnetic resonance original k-space data of the non-Cartesian space by using a convolution kernel function, so that the magnetic resonance original k-space data of the non-Cartesian space is resampled to a Cartesian coordinate system.

15) And acquiring a magnetic resonance original image of each channel based on the magnetic resonance original k-space data under a Cartesian coordinate system by utilizing Fourier transform.

16) And (3) channel merging is carried out on the magnetic resonance original images of all the channels by using a self-adaptive algorithm to obtain a multi-echo magnetic resonance image of the bone tissue.

And step S2, performing water-fat separation on the magnetic resonance image to obtain a water map, a fat map and a field map.

Specifically, due to the presence of fat in the knee joint and the difference in resonance frequency of hydrogen protons in fat and water, magnetic susceptibility values obtained directly using conventional quantitative magnetic susceptibility image reconstruction procedures are inaccurate. Water-fat separation of the magnetic resonance images is therefore required. In an embodiment of the invention, the magnetic resonance image is subjected to water-fat separation based on a graph cut algorithm.

And step S3, performing background field removing processing on the field pattern to obtain a local field image.

In an embodiment of the present invention, the background field removing process for the field pattern includes the following steps:

31) and carrying out threshold processing on the amplitude image of the field map to obtain a mask of a bone region.

32) Removing the background field outside the bone region based on a PDF (project onto Dipole field) algorithm to obtain the local field image.

And step S4, performing dipole inversion on the local field image to obtain a quantitative magnetic susceptibility image of the bone tissue.

Specifically, the local field image is dipole inverted based on a STAR-QSM (streamingreduction in QSM) algorithm.

In the quantitative magnetic susceptibility image obtained by the bone tissue quantitative imaging method of the present invention, the femoral knee cartilage shown on the right side of fig. 3 has a clear structure on the image, and the deep layer of the femoral knee cartilage shows diamagnetism. The magnetic susceptibility value gradually shows a change trend from diamagnetism to paramagnetism towards the shallow layer. This change law is related to the anisotropy of magnetic susceptibility of collagen fibers in cartilage. The collagen fibrils in the deep layer run approximately parallel to the main magnetic field, while the collagen fibrils in the shallow layer run approximately perpendicular to the main magnetic field. This difference results in a difference in the measured susceptibility values of the various layers of cartilage. At the same time, quantitative magnetic susceptibility imaging of cortical bone on the left side of fig. 3 is also clear. Because the image acquired by the method is iso-voxel, the cortical bone structure can be well observed in the section by the quantitative bone tissue imaging method compared with other acquisition modes adopting thicker layer thickness on the axial surface, and the total body of the cortical bone structure is diamagnetic.

As shown in fig. 4, in one embodiment, the quantitative bone tissue imaging system of the present invention includes an acquisition module 41, a separation module 42, a removal module 43, and an imaging module 44.

The acquisition module 41 is configured to acquire a magnetic resonance image of bone tissue based on an ultra-short echo time sequence.

The separation module 42 is connected to the acquisition module 41, and is configured to perform water-fat separation on the magnetic resonance image to obtain a water map, a fat map, and a field map.

The removing module 43 is connected to the separating module 42, and is configured to perform background field removing processing on the field pattern to obtain a local field image.

The imaging module 44 is connected to the removing module 43, and is configured to perform dipole inversion on the local field image to obtain a quantitative susceptibility image of the bone tissue.

The structures and principles of the acquisition module 41, the separation module 42, the removal module 43, and the imaging module 44 correspond to the steps of the bone tissue quantitative imaging method, and therefore, the description thereof is omitted here.

It should be noted that the division of the modules of the above apparatus is only a logical division, and the actual implementation may be wholly or partially integrated into one physical entity, or may be physically separated. And the modules can be realized in a form that all software is called by the processing element, or in a form that all the modules are realized in a form that all the modules are called by the processing element, or in a form that part of the modules are called by the hardware. For example: the x module can be a separately established processing element, and can also be integrated in a certain chip of the device. In addition, the x-module may be stored in the memory of the apparatus in the form of program codes, and may be called by a certain processing element of the apparatus to execute the functions of the x-module. Other modules are implemented similarly. All or part of the modules can be integrated together or can be independently realized. The processing element described herein may be an integrated circuit having signal processing capabilities. In implementation, each step of the above method or each module above may be implemented by an integrated logic circuit of hardware in a processor element or an instruction in the form of software. These above modules may be one or more integrated circuits configured to implement the above methods, such as: one or more Application Specific Integrated Circuits (ASICs), one or more microprocessors (DSPs), one or more Field Programmable Gate Arrays (FPGAs), and the like. When a module is implemented in the form of a Processing element scheduler code, the Processing element may be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor capable of calling program code. These modules may be integrated together and implemented in the form of a System-on-a-chip (SOC).

The storage medium of the present invention has stored thereon a computer program which, when executed by a processor, implements the above-described method for quantitative imaging of bone tissue. Preferably, the storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic disk, U-disk, memory card, or optical disk.

As shown in fig. 5, in an embodiment, the terminal of the present invention includes: a processor 51 and a memory 52.

The memory 52 is used for storing computer programs.

The memory 52 includes: various media that can store program codes, such as ROM, RAM, magnetic disk, U-disk, memory card, or optical disk.

The processor 51 is connected to the memory 52 and is configured to execute the computer program stored in the memory 52, so as to enable the terminal to execute the above-mentioned quantitative bone tissue imaging method.

Preferably, the Processor 51 may be a general-purpose Processor, including a Central Processing Unit (CPU), a Network Processor (NP), and the like; the Integrated Circuit may also be a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic device, or discrete hardware components.

In conclusion, the bone tissue quantitative imaging method, the bone tissue quantitative imaging system, the bone tissue quantitative imaging medium and the bone tissue quantitative imaging terminal combine ultra-short echo time imaging and quantitative magnetic resonance imaging, so that the bone tissue quantitative imaging is realized, and the anatomical structures of the bone tissue and the bone tissue can be well displayed; by comparing the difference of the magnetic susceptibility values of articular cartilage and cortical bone between arthritis patients or patients with other skeletal diseases and normal subjects, an effective tool is provided for the subsequent clinical study of cartilage and skeleton. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.