Patent Publication Number: US-2020292651-A1

Title: Magnetic resonance temperature imaging method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/CN2017/119483, filed on Dec. 28, 2017 which claims priority to Chinese Patent Application No. 201711387804.1, filed on Dec. 20, 2017. The disclosures of the aforementioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the field of magnetic resonance, and specifically, to a magnetic resonance temperature imaging method and apparatus. 
     BACKGROUND 
     Magnetic resonance temperature imaging can be used to monitor temperature distribution and changes of a tested object in a non-invasive, real time, and in vivo manner. Magnetic resonance can be used to monitor temperatures based on different temperature sensitive parameters, and common parameters include proton density (PD), a relaxation time, a diffusion coefficient, and a proton resonance frequency shift (PRFS). In water, there is a linear relationship between a proton resonance frequency and a temperature, and the linear relationship is tissue-independent, and therefore a PRFS-based magnetic resonance temperature imaging technology is most widely applied. However, this technology cannot be applied to fat-containing tissue because hydrogen protons in fat are temperature-insensitive. In this case, there is a non-linear relationship between the fat-containing tissue and a temperature change, and the non-linear relationship is related to a ratio of water to the fat in the tissue. To implement temperature imaging for the fat-containing tissue, impact of the fat needs to be eliminated or corrected. 
     SUMMARY 
     In view of this, embodiments of the present invention are intended to provide a magnetic resonance temperature imaging method and apparatus, to alleviate the foregoing problem. 
     According to a first aspect, an embodiment of the present invention provides a magnetic resonance temperature imaging method, where the magnetic resonance temperature imaging method includes: 
     Obtaining a first strength amplitude value of a water signal, a first phase value of the water signal, a first strength amplitude value of a fat signal, a first phase value of the fat signal, a first transverse relaxation time of water, a first transverse relaxation time of fat, and a first field drift caused by a non-uniform main magnetic field, based on a preset magnetic resonance signal model, a pre-assigned initial water-fat tissue temperature image, and a water-fat separation algorithm; obtaining a second strength amplitude value of the water signal, a second phase value of the water signal, a second strength amplitude value of the fat signal, a second phase value of the fat signal, a second transverse relaxation time of the water, a second transverse relaxation time of the fat, a second field drift caused by the non-uniform main magnetic field, and a second water-fat tissue temperature image that minimize a difference between signal strength after the first time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the first time based on the initial water-fat tissue temperature image, the first strength amplitude value of the water signal, the first phase value of the water signal, the first strength amplitude value of the fat signal, the first phase value of the fat signal, the first transverse relaxation time of the water, the first transverse relaxation time of the fat, and the first field drift caused by the non-uniform main magnetic field; 
     Obtaining a third strength amplitude value of the water signal, a third phase value of the water signal, a third strength amplitude value of the fat signal, a third phase value of the fat signal, a third transverse relaxation time of the water, a third transverse relaxation time of the fat, and a third field drift caused by the non-uniform main magnetic field that minimize a difference between signal strength after the second time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the second time by keeping the second water-fat tissue temperature image unchanged and based on the second water-fat tissue temperature image, the second strength amplitude value of the water signal, the second phase value of the water signal, the second strength amplitude value of the fat signal, the second phase value of the fat signal, the second transverse relaxation time of the water, the second transverse relaxation time of the fat, and the second field drift caused by the non-uniform main magnetic field; and 
     Obtaining a fourth strength amplitude value of the water signal, a fourth strength amplitude value of the fat signal, a fourth field drift caused by the non-uniform main magnetic field, and a water-fat tissue temperature image at a current moment that minimize a difference between signal strength after the third time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the third time by keeping the third phase value of the water signal, the third phase value of the fat signal, the third transverse relaxation time of the water, and the third transverse relaxation time of the fat unchanged and based on the second water-fat tissue temperature image, the third strength amplitude value of the water signal, the third phase value of the water signal, the third strength amplitude value of the fat signal, the third phase value of the fat signal, the third transverse relaxation time of the water, the third transverse relaxation time of the fat, and the third field drift caused by the non-uniform main magnetic field. 
     According to a second aspect, an embodiment of the present invention further provides a magnetic resonance temperature imaging apparatus, where the magnetic resonance temperature imaging apparatus includes: 
     A first calculation unit, configured to obtain a first strength amplitude value of a water signal, a first phase value of the water signal, a first strength amplitude value of a fat signal, a first phase value of the fat signal, a first transverse relaxation time of water, a first transverse relaxation time of fat, and a first field drift caused by a non-uniform main magnetic field, based on a preset magnetic resonance signal model, a pre-assigned initial water-fat tissue temperature image, and a water-fat separation algorithm; 
     A second calculation unit, configured to obtain a second strength amplitude value of the water signal, a second phase value of the water signal, a second strength amplitude value of the fat signal, a second phase value of the fat signal, a second transverse relaxation time of the water, a second transverse relaxation time of the fat, a second field drift caused by the non-uniform main magnetic field, and a second water-fat tissue temperature image that minimize a difference between signal strength after the first time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the first time based on the initial water-fat tissue temperature image, the first strength amplitude value of the water signal, the first phase value of the water signal, the first strength amplitude value of the fat signal, the first phase value of the fat signal, the first transverse relaxation time of the water, the first transverse relaxation time of the fat, and the first field drift caused by the non-uniform main magnetic field; 
     A third calculation unit, configured to obtain a third strength amplitude value of the water signal, a third phase value of the water signal, a third strength amplitude value of the fat signal, a third phase value of the fat signal, a third transverse relaxation time of the water, a third transverse relaxation time of the fat, and a third field drift caused by the non-uniform main magnetic field that minimize a difference between signal strength after the second time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the second time by keeping the second water-fat tissue temperature image unchanged and based on the second water-fat tissue temperature image, the second strength amplitude value of the water signal, the second phase value of the water signal, the second strength amplitude value of the fat signal, the second phase value of the fat signal, the second transverse relaxation time of the water, the second transverse relaxation time of the fat, and the second field drift caused by the non-uniform main magnetic field; and 
     A fourth calculation unit, configured to obtain a fourth strength amplitude value of the water signal, a fourth strength amplitude value of the fat signal, a fourth field drift caused by the non-uniform main magnetic field, and a water-fat tissue temperature image at a current moment that minimize a difference between signal strength after the third time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the third time by keeping the third phase value of the water signal, the third phase value of the fat signal, the third transverse relaxation time of the water, and the third transverse relaxation tune of the fat unchanged and based on the second water-fat tissue temperature image, the third strength amplitude value of the water signal, the third phase value of the water signal, the third strength amplitude value of the fat signal, the third phase value of the fat signal, the third transverse relaxation time of the water, the third transverse relaxation time of the fat, and the third field drift caused by the non-uniform main magnetic field. 
     According to the magnetic resonance temperature imaging method and apparatus provided in the present invention, accuracy and precision of the water-fat tissue temperature image at the current moment are improved by using a two-step iterative temperature estimation algorithm in comparison with the prior art, the magnetic resonance signal model includes multiple fat peaks, and the fourth strength amplitude value of the water signal, the fourth strength amplitude value of the fat signal, the fourth field drift caused by the non-uniform main magnetic field, and the water-fat tissue temperature image at the current moment that minimize the difference between the signal strength and the signal strength before the fitting are estimated. In this way, it is ensured that a temperature result is unbiased. 
     To make the foregoing objectives, features, and advantages of the present invention clearer and easier to understand, preferred embodiments are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a structural block diagram of a server according to the present invention; 
         FIG. 2  is a flowchart of a magnetic resonance temperature imaging method according to the present invention; and 
         FIG. 3  is a functional and structural block diagram of a magnetic resonance temperature imaging apparatus according to the present invention. 
     
    
    
     Reference numerals:  100 —Magnetic resonance temperature imaging apparatus;  200 —Server;  101 —Memory;  102 —Storage controller;  103 —Processor;  104 —Peripheral interface;  301 —First calculation unit;  302 —Second calculation unit;  303 —Third calculation unit;  304 —Filtering unit;  305 —Fourth calculation unit. 
     DESCRIPTION OF EMBODIMENTS 
     The following clearly and comprehensively describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Clearly, the described embodiments are merely some but not all of the embodiments of the present invention. Components in the embodiments of the present invention described and shown in the accompanying drawings usually can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the protection scope of the present invention, but is merely intended to represent the selected embodiments of the present invention. All other embodiments obtained by a person skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     A magnetic resonance temperature imaging method and apparatus provided in the preferred embodiments of the present invention can be applied to a server  200 .  FIG. 1  is a structural block diagram of a server  200  according to an embodiment of the present invention. As shown in  FIG. 1 , the server  200  includes a magnetic resonance temperature imaging apparatus  100 , a memory  101 , a storage controller  102 , one or more processors (only one processor is shown in the figure)  103 , a peripheral interface  104 , and the like. These components communicate with each other by using one or more communications buses/signal lines. The magnetic resonance temperature imaging apparatus  100  includes at least one software function module that may be stored in the memory  101  in the form of software or firmware or that may be built into an operating system (OS) of the server  200 . 
     The memory  101  may be configured to store a software program and a module, for example, a program instruction/module corresponding to the magnetic resonance temperature image apparatus and method in the embodiments of the present invention. The processor  103  executes various functional applications and data processing, for example, the magnetic resonance temperature imaging method provided in the embodiments of the present invention, by running the software program and the module stored in the memory  101 . The memory  101  may include a high speed random access memory, and may further include a nonvolatile memory, for example, one or more magnetic storage apparatuses or flash memories, or other nonvolatile solid state memories. Access to the memory  101  by the processor  103  and other possible components may be under the control of the storage controller  102 . 
     The peripheral interface  104  couples various input/output apparatuses to the processor  103  and the memory  101 . In some embodiments, the peripheral interface  104 , the processor  103 , and the storage controller  102  may be implemented in a single chip. In other examples, the peripheral interface  104 , the processor  103 , and the storage controller  102  each may be implemented by a separate chip. 
     It can be understood that the structure shown in  FIG. 1  is merely an example, and the server  200  may alternatively include more or fewer components than those shown in  FIG. 1 , or have a configuration different from that shown in  FIG. 1 . The components shown in  FIG. 1  may be implemented by hardware, software, or a combination thereof. 
     Referring to  FIG. 2 , an embodiment of the present invention provides a magnetic resonance temperature imaging method. The magnetic resonance temperature imaging method includes the following steps. 
     Step S 201 : Obtain a first strength amplitude value of a water signal, a first phase value of the water signal, a first strength amplitude value of a fat signal, a first phase value of the fat signal, a first transverse relaxation time of water, a first transverse relaxation time of fat, and a first field drift caused by a non-uniform main magnetic field, based on a preset magnetic resonance signal model, a pre-assigned initial water-fat tissue temperature image, and a water-fat separation algorithm. 
     Specifically, the preset magnetic resonance signal model is 
     
       
         
           
             
               
                 
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     where S n  represents signal strength at an echo time TE n , W represents a strength value of the water signal, F represents a strength value of the fat signal, Y represents a gyromagnetic ratio, B 0  represents strength of the main magnetic field, a represents a temperature coefficient of a hydrogen proton in the water, P represents the number of fat peaks, a corresponding relative amplitude value and chemical shift are respectively β p  and f F,p , Σ p=1   p β P 32 1, T 2,w   *  represents a transverse relaxation time of the water, T 2,P   *  represents a transverse relaxation time of the fat, f b  represents a field drift caused by the non-uniform main magnetic field, N represents the total number of collected echoes, and ΔT represents a water-fat tissue temperature image. 
     Step S 202 : Obtain a second strength amplitude value of the water signal, a second phase value of the water signal, a second strength amplitude value of the fat signal, a second phase value of the fat signal, a second transverse relaxation time of the water, a second transverse relaxation time of the fat, a second field drift caused by the non-uniform main magnetic field, and a second water-fat tissue temperature image that minimize a difference between signal strength after the first time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the first time based on the initial water-fat tissue temperature image, the first strength amplitude value of the water signal, the first phase value of the water signal, the first strength amplitude value of the fat signal, the first phase value of the fat signal, the first transverse relaxation time of the water, the first transverse relaxation time of the fat, and the first field drift caused by the non-uniform main magnetic field. 
     Specifically, the preset magnetic resonance signal model is fitted for the first time based on an equation 
     
       
         
           
             
               
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     Step S 203 : Smooth the second water-fat tissue temperature image by using a low-pass filter, to obtain a smoothed second water-fat tissue temperature image. 
     Specifically, the second water-fat tissue temperature image is smoothed by using the low-pass filter based on an equation Δ{tilde over (T)} i =(1−μ)ΔT i +μΔ T , to obtain the smoothed second water-fat tissue temperature image, where ΔT i  represents a current temperature estimation value of the i th  pixel, Δ T  represents an average value of temperature values of all pixels, and Δ{tilde over (T)} i  represents a temperature value obtained after the i th  pixel is smoothed. 
     Step S 204 : Obtain a third strength amplitude value of the water signal, a third phase value of the water signal, a third strength amplitude value of the fat signal, a third phase value of the fat signal, a third transverse relaxation time of the water, a third transverse relaxation time of the fat, and a third field drift caused by the non-uniform main magnetic field that minimize a difference between signal strength after the second time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the second time by keeping the smoothed second water-fat tissue temperature image unchanged and based on the second water-fat tissue temperature image, the second strength amplitude value of the water signal, the second phase value of the water signal, the second strength amplitude value of the fat signal, the second phase value of the fat signal, the second transverse relaxation time of the water, the second transverse relaxation time of the fat, and the second field drift caused by the non-uniform main magnetic field. 
     Specifically, the preset magnetic resonance signal model is fitted for the second time based on an equation 
     
       
         
           
             
               
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     Step S 205 : Obtain a fourth strength amplitude value of the water signal, a fourth strength amplitude value of the fat signal, a fourth field drift caused by the non-uniform main magnetic field, and a water-fat tissue temperature image at a current moment that minimize a difference between signal strength after the third time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the third time by keeping the third phase value of the water signal, the third phase value of the fat signal, the third transverse relaxation time of the water, and the third transverse relaxation time of the fat unchanged and based on the second water-fat tissue temperature image, the third strength amplitude value of the water signal, the third phase value of the water signal, the third strength amplitude value of the fat signal, the third phase value of the fat signal, the third transverse relaxation time of the water, the third transverse relaxation time of the fat, and the third field drift caused by the non-uniform main magnetic field. 
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     According to the magnetic resonance temperature imaging method, first, the preset magnetic resonance signal model is fitted to obtain the second strength amplitude value of the water signal, the second phase value of the water signal, the second strength amplitude value of the fat signal, the second phase value of the fat signal, the second transverse relaxation time of the water, the second transverse relaxation time of the fat, the second field drift caused by the non-uniform main magnetic field, and the second water-fat tissue temperature image that minimize the difference between the signal strength and the signal strength before the fitting, to ensure that temperature estimation is unbiased, in other words, ensure accuracy of the second water-fat tissue temperature image; then, the second water-fat tissue temperature image is smoothed, and the third strength amplitude value of the water signal, the third phase value of the water signal, the third strength amplitude value of the fat signal, the third phase value of the fat signal, the third transverse relaxation time of the water, the third transverse relaxation time of the fat, and the third field drift caused by the non-uniform main magnetic field that minimize the difference between the signal strength after the second time of fitting and the signal strength before the fitting are estimated, where in this case, the obtained third phase value of the water signal, third phase value of the fat signal, third transverse relaxation time of the water, and third transverse relaxation time of the fat are accurate; and finally, the fourth strength amplitude value of the water signal, the fourth strength amplitude value of the fat signal, the fourth field thin caused by the non-uniform main magnetic field, and the water-fat tissue temperature image at the current moment are obtained by fitting the signal model again by keeping the third phase value of the water signal, the third phase value of the fat signal, the third transverse relaxation time of the water, and the third transverse relaxation time of the fat unchanged, where in this case, precision of the obtained preset magnetic resonance signal model is improved because of a decreased number of free variables in the preset magnetic resonance signal model. 
     In addition, the water-fat tissue temperature image at the current moment may be used as an initial value of the next cycle, and steps S 201  to S 205  are repeated to obtain a water-fat tissue temperature image at the next moment. 
     Referring to  FIG. 3 , an embodiment of the present invention further provides a magnetic resonance temperature imaging apparatus  100 . It should be noted that basic principles and technical effects of the magnetic resonance temperature imaging apparatus  100  provided in this embodiment of the present invention are the same as those in the foregoing embodiment. For brevity, refer to the corresponding content in the foregoing embodiment for content not mentioned in this embodiment of the present invention. The magnetic resonance temperature imaging apparatus  100  includes a first calculation unit  301 , a second calculation unit  302 , a third calculation unit  303 , a filtering unit  304 , and a fourth calculation unit  305 . 
     The first calculation unit  301  is configured to obtain a first strength amplitude value of a water signal, a first phase value of the water signal, a first strength amplitude value of a fat signal, a first phase value of the fat signal, a first transverse relaxation time of water, a first transverse relaxation time of fat, and a first field drift caused by a non-uniform main magnetic field, based on a preset magnetic resonance signal model, a pre-assigned initial water-fat tissue temperature image, and a water-fat separation algorithm. 
     The preset magnetic resonance signal model is 
     
       
         
           
             
               
                 
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     where S n  represents signal strength at an echo time TE n , W represents a strength value of the water signal, F represents a strength value of the fat signal, Y represents a gyromagnetic ratio, B 0  represents strength of the main magnetic field, α represents a temperature coefficient of a hydrogen proton in the water, P represents the number of fat peaks, a corresponding relative amplitude value and chemical shift are respectively β p  and f F,p , Σ p=1   p β p =1, T 2,w   *  represents a transverse relaxation time of the water, T 2,F   *  represents a transverse relaxation time of the fat, f b  represents a field drift caused by the non-uniform main magnetic field, N represents the total number of collected echoes, and ΔT represents a water-fat tissue temperature image. 
     It can be understood that the first calculation unit  301  can perform step S 201 . 
     The second calculation unit  302  is configured to obtain a second strength amplitude value of the water signal, a second phase value of the water signal, a second strength amplitude value of the fat signal, a second phase value of the fat signal, a second transverse relaxation time of the water, a second transverse relaxation time of the fat, a second field drift caused by the non-uniform main magnetic field, and a second water-fat tissue temperature image that minimize a difference between signal strength after the first time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the first time based on the initial water-fat tissue temperature image, the first strength amplitude value of the water signal, the first phase value of the water signal, the first strength amplitude value of the fat signal, the first phase value of the fat signal, the first transverse relaxation time of the water, the first transverse relaxation time of the fat, and the first field drift caused by the non-uniform main magnetic field. 
     The second calculation unit  302  is configured to fit the preset magnetic resonance signal model for the first time based on an equation 
     
       
         
           
             
               
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     It can be understood that the second calculation unit  302  can perform step S 202 . 
     The filtering unit  304  is configured to smooth the second water-fat tissue temperature image by using a low-pass filter, to obtain a smoothed second water-fat tissue temperature image. 
     It can be understood that the filtering unit  304  can perform step S 203 . 
     The filtering unit  304  is configured to smooth the second water-fat tissue temperature image by using the low-pass filter based on an equation Δ{tilde over (T)} i =(1−μ)ΔT i +μΔ T , to obtain the smoothed second water-fat tissue temperature image, where ΔT i  represents a current temperature estimation value of the i th  pixel, Δ T  represents an average value of temperature values of all pixels, and Δ{tilde over (T)} i  represents a temperature value obtained after the i th  pixel is smoothed. 
     The third calculation unit  303  is configured to obtain a third strength amplitude value of the water signal, a third phase value of the water signal, a third strength amplitude value of the fat signal, a third phase value of the fat signal, a third transverse relaxation time of the water, a third transverse relaxation time of the fat, and a third field drift caused by the non-uniform main magnetic field that minimize a difference between signal strength after the second time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the second time by keeping the second water-fat tissue temperature image unchanged and based on the second water-fat tissue temperature image, the second strength amplitude value of the water signal, the second phase value of the water signal, the second strength amplitude value of the fat signal, the second phase value of the fat signal, the second transverse relaxation time of the water, the second transverse relaxation time of the fat, and the second field drift caused by the non-uniform main magnetic field. 
     The third calculation unit  303  is configured to fit the preset magnetic resonance signal model for the second time based on an equation 
     
       
         
           
             
               
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     It can be understood that the third calculation unit  303  can perform step S 204 . 
     The fourth calculation unit  305  is configured to obtain a fourth strength amplitude value of the water signal, a fourth strength amplitude value of the fat signal, a fourth field drift caused by the non-uniform main magnetic field, and a water-fat tissue temperature image at a current moment that minimize a difference between signal strength after the third time of fitting and signal strength before the fitting, by fitting the preset magnetic resonance signal model for the third time by keeping the third phase value of the water signal, the third phase value of the fat signal, the third transverse relaxation time of the water, and the third transverse relaxation time of the fat unchanged and based on the second water-fat tissue temperature image, the third strength amplitude value of the water signal, the third phase value of the water signal, the third strength amplitude value of the fat signal, the third phase value of the fat signal, the third transverse relaxation time of the water, the third transverse relaxation time of the fat, and the third field drift caused by the non-uniform main magnetic field. 
     Specifically, the fourth calculation unit  305  is configured to fit the preset magnetic resonance signal model for the third time based on an equation 
     
       
         
           
             
               
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     It can be understood that the fourth calculation unit  305  can perform step S 205 . 
     In conclusion, according to the magnetic resonance temperature imaging method and apparatus, accuracy and precision of the water-fat tissue temperature image at the current moment are improved by using a two-step iterative temperature estimation algorithm, the magnetic resonance signal model includes multiple fat peaks, and the fourth strength amplitude value of the water signal, the fourth strength amplitude value of the fat signal, the fourth field drift caused by the non-uniform main magnetic field, and the water-fat tissue temperature image at the current moment that minimize the difference between the signal strength and the signal strength before the fitting are estimated. In this way, it is ensured that a temperature result is unbiased. 
     In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other manners. The apparatus embodiment described above is merely an example. For example, flowcharts and block diagrams in the accompanying drawings show possible implementation architectures, functions, and operations of the apparatus, the method, and the computer program product according to the multiple embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a part of one module, program segment, or code. The part of the module, program segment, or code includes one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may be executed in an order different from that noted in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or two consecutive blocks may sometimes be executed in a reverse order, and this depends on functions involved. It should also be noted that each block in the block diagrams and/or flowcharts and a combination of blocks in the block diagrams and/or flowcharts may be implemented by using a dedicated hardware-based system for executing a specified function or action, or may be implemented by using a combination of dedicated hardware and a computer instruction. 
     In addition, the functional modules in the various embodiments of the present invention may be integrated together to form a separate part, or each module may exist alone, or two or more modules may be integrated to form a separate part. 
     If the functions are implemented in the form of software functional modules and sold or used as separate products, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present invention, essentially or the part contributing to the prior art, may be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for enabling a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or some of the steps of the method described in the embodiments of the present invention. The storage medium includes various media that can store program code, for example, a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, and an optical disk. It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between such entities or operations. In addition, the term “include”, “comprise”, or their any other variant is intended to cover a non-exclusive inclusion, so that a process, a method, an article, or a device that includes a series of elements not only includes these elements, but also includes other elements that are not expressly listed, or further includes elements inherent to such process, method, article, or device. An element preceded by “includes a . . . ” further includes, without more constraints, additional identical elements in the process, method, article, or device that includes the element. 
     The foregoing descriptions are merely preferred embodiments of the present invention, and are not intended to limit the present invention. A person skilled in the art can make various modifications and changes to the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and the principle of the present invention shall fall within the protection scope of the present invention. It should be noted that similar reference numerals and letters represent similar terms in the following accompanying drawings. Therefore, once an item is defined in one accompanying drawing, the item does not need to be further defined and explained in subsequent accompanying drawings. 
     The foregoing descriptions are merely specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Variations or replacements that can be readily figured out by any person skilled in the art within the technical scope of the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. 
     It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between such entities or operations. In addition, the term “include”, “comprise”, or their any other variant is intended to cover a non-exclusive inclusion, so that a process, a method, an article, or a device that includes a series of elements not only includes these elements, but also includes other elements that are not expressly listed, or further includes elements inherent to such process, method, article, or device. An element preceded by “includes a . . . ” further includes, without more constraints, additional identical elements in the process, method, article, or device that includes the element.