CN111090069A

CN111090069A - Quantitative magnetic resonance imaging parameter determination method, device, equipment and storage medium

Info

Publication number: CN111090069A
Application number: CN201911148335.7A
Authority: CN
Inventors: 王海峰; 邹莉娴; 刘新; 梁栋; 郑海荣
Original assignee: Shenzhen Institute of Advanced Technology of CAS
Current assignee: Shenzhen Institute of Advanced Technology of CAS
Priority date: 2019-11-21
Filing date: 2019-11-21
Publication date: 2020-05-01
Anticipated expiration: 2039-11-21
Also published as: CN111090069B; WO2021098690A1

Abstract

The application belongs to the technical field of magnetic resonance imaging, and provides a quantitative magnetic resonance imaging parameter determination method, a device, equipment and a storage medium. The method comprises the steps of obtaining a plurality of magnetic resonance images of a tested object based on a preset MRF pulse sequence, and extracting an evolution signal of each voxel from the plurality of magnetic resonance images; determining the transverse relaxation time of each voxel according to a simulation signal matched with the evolution signal of each voxel in a preset dictionary; the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting transverse magnetization vectors of the tested object; the evolution signal is used to characterize the change in signal intensity for each voxel in the plurality of magnetic resonance images. The method for determining the quantitative magnetic resonance imaging parameters increases the sensitivity of transverse relaxation time detection and improves the accuracy of detecting the transverse relaxation time of the tissue based on MRF.

Description

Quantitative magnetic resonance imaging parameter determination method, device, equipment and storage medium

Technical Field

The present application relates to the field of magnetic resonance imaging technologies, and in particular, to a method, an apparatus, a device, and a storage medium for determining quantitative magnetic resonance imaging parameters.

Background

Quantitative magnetic resonance imaging has tissue specificity for detecting human pathological tissues, can help doctors to better distinguish healthy tissues from pathological tissues, and has very important clinical diagnosis and research values.

Magnetic Resonance Fingerprinting (MRF) is a new type of rapid quantitative Magnetic Resonance imaging parameter determination technique. The MRF scans the subject with a set of pseudo-randomly varying pulse sequences such that different tissue types (with voxels as carriers) from the subject exhibit a characteristic signal evolution (i.e. fingerprint). And then matching the obtained fingerprint with a plurality of dictionary entries in a dictionary which is obtained in advance to obtain quantitative values of a plurality of organization attribute parameters of each organization type. The tissue property parameters include a longitudinal relaxation time (hereinafter referred to as T1) and a transverse relaxation time (hereinafter referred to as T2).

At present, the pulse sequence of MRF is mainly a steady-state free precession sequence based on inversion recovery, the inversion recovery sequence is particularly sensitive to T1, and the steady-state free precession sequence has a relatively high signal-to-noise ratio, so that the pulse sequence based on MRF has certain advantages for acquiring tissue property parameters of different subjects. However, due to the inhomogeneity of the magnetic field and the short duration of T2, the magnetic resonance image obtained based on the current MRF pulse sequence is insensitive to the difference of T2 for each tissue type, resulting in a low accuracy of the obtained T2.

Disclosure of Invention

In view of this, embodiments of the present application provide a method, an apparatus, a device, and a storage medium for determining quantitative magnetic resonance imaging parameters, so as to solve the technical problem in the prior art that a transverse relaxation time in quantitative magnetic resonance imaging is inaccurate.

In a first aspect, an embodiment of the present application provides a quantitative magnetic resonance imaging parameter determination method, including:

acquiring a plurality of magnetic resonance images of a tested object based on a preset MRF pulse sequence; the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting the magnetization vector of the tested object;

extracting an evolution signal of each voxel from a plurality of magnetic resonance images; wherein the evolution signal is used to characterize the variation of signal intensity of each voxel in the plurality of magnetic resonance images;

determining the transverse relaxation time of the tissue represented by each voxel according to a simulation signal which is most matched with the evolution signal of each voxel in a preset dictionary; the dictionary comprises a plurality of analog signals generated by performing signal analog evolution on the MRF pulse sequence and transverse relaxation time corresponding to each analog signal in a one-to-one mode.

In one possible implementation form of the first aspect, the radio frequency pulse train comprises sequentially excited 90 ° excitation pulses, at least one 180 ° excitation pulse and-90 ° excitation pulses.

In one possible implementation form of the first aspect, the interval time between two adjacent excitation pulses in the radio frequency pulse train is the same.

In a possible implementation manner of the first aspect, the duration of each radio frequency pulse train is a dwell time after the magnetization vector is flipped to the transverse plane, and the durations of a plurality of radio frequency pulse trains are sequentially increased.

In a possible implementation manner of the first aspect, each radio frequency pulse train is followed by a radio frequency pulse for sampling, and the flip angle of each radio frequency pulse is less than or equal to 10 °.

In a possible implementation manner of the first aspect, determining a transverse relaxation time of a tissue represented by each voxel according to a simulated signal in a preset dictionary that best matches an evolution signal of each voxel includes:

comparing the time signal of each voxel with all analog signals in a preset dictionary to obtain the analog signal with the highest matching degree with the magnetic resonance signal of each voxel in the dictionary;

for each voxel, the transverse relaxation time corresponding to the analog signal with the highest degree of matching with the evolution signal of the voxel is taken as the transverse relaxation time of the voxel.

In one possible implementation form of the first aspect, the MRF pulse sequence further comprises an inversion recovery based gradient echo sequence.

In a second aspect, the present application provides a quantitative magnetic resonance imaging parameter determining apparatus, including:

the pre-imaging module is used for acquiring a plurality of magnetic resonance images of the tested object based on a preset MRF pulse sequence; the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting the magnetization vector of the tested object;

a signal acquisition module for extracting an evolution signal of each voxel from a plurality of magnetic resonance images; wherein the evolution signal is used to characterize the variation of signal intensity of each voxel in the plurality of magnetic resonance images;

the parameter determination module is used for determining the transverse relaxation time of the tissue represented by each voxel according to the analog signal which is most matched with the evolution signal of each voxel in the preset dictionary; the dictionary comprises a plurality of analog signals generated by performing signal analog evolution on the MRF pulse sequence and transverse relaxation time corresponding to each analog signal in a one-to-one mode.

In a third aspect, an embodiment of the present application provides a quantitative magnetic resonance imaging parameter determination apparatus, including a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor implements the steps of any one of the methods of the first aspect when executing the computer program.

In a fourth aspect, the present application provides a computer-readable storage medium, where a computer program is stored, and when executed by a processor, the computer program implements the steps of any one of the methods in the first aspect.

In a fifth aspect, the present application provides a computer program product, which when run on a terminal device, causes the terminal device to execute the method of any one of the above first aspects.

The method for determining the quantitative magnetic resonance imaging parameters, provided by the embodiment of the application, comprises the steps of obtaining a plurality of magnetic resonance images of a tested object based on a preset MRF pulse sequence; and extracting the evolution signal of each voxel from a plurality of magnetic resonance images, and determining the transverse relaxation time of the tissue represented by each voxel according to the analog signal matched with the evolution signal of each voxel in a preset dictionary, thereby realizing the quantification of the transverse relaxation time in the magnetic resonance imaging. Compared with the MRF pulse sequence in the prior art, the MRF sequence in the embodiment of the present application includes a plurality of sequentially excited radio frequency pulse trains, and during the MRF sequence is executed to perform magnetic resonance imaging, the radio frequency pulses in each radio frequency pulse train flip hydrogen nuclei of the in-vivo tissue of the subject to be tested to generate transverse magnetization vectors, and re-excite the transverse magnetization vectors within the duration of the radio frequency pulse train, so that weighting of T2 relaxation is achieved, and therefore, the quantitative magnetic resonance imaging parameter determination method provided by the embodiment of the present application improves the sensitivity of transverse relaxation time detection, and can obtain accurate transverse relaxation time.

It is understood that the beneficial effects of the second aspect to the fifth aspect can be referred to the related description of the first aspect, and are not described herein again.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1 is a schematic diagram of an architecture of a quantitative magnetic resonance imaging system according to an embodiment of the present application;

fig. 2 is a schematic flow chart of a quantitative magnetic resonance imaging parameter determination method according to an embodiment of the present application;

FIG. 3 is a schematic diagram of an RF burst provided in accordance with an embodiment of the present application;

FIG. 4 is an evolution signal of a single voxel provided by an embodiment of the present application;

FIG. 5 is a schematic flow chart for determining transverse voxel relaxation times according to an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of a pulse sequence provided by another embodiment of the present application;

FIG. 7 is a diagram of pseudo-randomly varying flip angles and repetition times provided by an embodiment of the present application;

FIG. 8 is a dictionary schematic provided by an embodiment of the present application;

FIG. 9 is a schematic diagram of a quantitative magnetic resonance imaging parameter determining apparatus according to an embodiment of the present application;

fig. 10 is a schematic structural diagram of a quantitative magnetic resonance imaging parameter determining apparatus according to an embodiment of the present application.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Furthermore, in the description of the present application and the appended claims, the terms "first," "second," and the like are used for distinguishing between descriptions and not necessarily for describing or implying relative importance.

First, the concepts involved in the present application are explained as follows:

the basic principle of Magnetic Resonance Imaging (MRI) is as follows: the hydrogen atoms of the tissue spin motion creating a magnetic moment. Under the action of a strong and uniform main magnetic field, the spin magnetic moments of hydrogen atoms originally irregularly arranged can be arranged along the direction of the main magnetic field to form macroscopic magnetization vectors (including longitudinal magnetization vectors and transverse magnetization vectors). Under the excitation of radio frequency pulses, macroscopic magnetization vectors are turned to the direction vertical to a main magnetic field, the magnetization vectors cut a radio frequency coil in the precession rotation of hydrogen atoms to generate electromagnetic induction signals, and a magnetic resonance image is formed through data reconstruction.

Magnetic Resonance Fingerprinting (MRF): the quantitative magnetic resonance imaging method is quick and can simultaneously obtain a plurality of tissue attribute parameters.

Pulse Sequence refers to the combination of radio frequency Pulse, spatial coding, and echo sampling at a certain time Sequence.

The Repetition Time (TR) refers to the Time interval between two adjacent fire pulses in a pulse sequence.

Echo Time (TE) refers to the Time between excitation of the excitation pulse and acquisition of the echo signal.

Relaxation: under the excitation of the excitation pulse, the proton absorption energy in the tested object is in an excitation state; the process by which the protons in the excited state return to their original state after the excitation pulse has terminated is called relaxation.

T1: longitudinal relaxation time, the time required for the longitudinal magnetization vector to recover from zero to two-thirds of the total signal intensity.

T2: transverse relaxation time, the time required for the transverse magnetization vector to decay from one hundred percent to one third.

Flip Angle (FA): the angle at which the excitation pulse causes the magnetization vector to deviate in the direction of the main magnetic field. At 90 ° FA, the magnetization vector is perpendicular to the main magnetic field direction, flipping to the transverse plane.

Quantitative magnetic resonance imaging parameter determination refers to determining values of tissue property parameters of a subject, wherein the tissue property parameters of the subject include T1, T2, proton density, and the like. The quantitative tissue attribute parameters can help doctors to better distinguish healthy tissues from pathological tissues in an absolute sense, and the doctors can more objectively compare different examinations in subsequent researches. The most widely used tissue attribute parameters at present include T1 and T2.

Magnetic resonance fingerprint imaging (hereinafter abbreviated as MRF) is a method for determining parameters of fast quantitative magnetic resonance imaging. Compared with traditional T1 and T2 quantitative methods, the MRF can simultaneously obtain parameter values of a plurality of tissue attribute parameters. The MRF mainly comprises the following steps: adopting different TR and FA to acquire data of the interested region of the tested object in each excitation of the pulse sequence; then generating a dictionary based on a classical ladder Bloch model according to parameters of the pulse sequence, wherein the dictionary comprises a plurality of analog time signals and organization attribute parameter values corresponding to the analog time signals; finally, after the acquired data are reconstructed, an evolution signal (namely, a fingerprint) of a single voxel changing along with time is acquired; comparing the evolution signal of each voxel with the simulated time signals contained in the dictionary one by one, searching and obtaining the best matching simulated time signal of each voxel from the dictionary, and taking the tissue attribute parameter value corresponding to the best matching simulated time signal as the tissue attribute parameter value of the voxel. Due to the fact that tissue attribute parameters of different tissue types of the tested object are different, based on different evolution signals of different tissue types, which can be obtained by the same pulse sequence, the tissue attribute parameter values of different tissue types (all voxels) of the tested object can be obtained by repeating the process.

Fig. 1 is a schematic architecture diagram of a quantitative magnetic resonance imaging system according to an embodiment of the present application, and as shown in fig. 1, the quantitative magnetic resonance imaging system includes a magnetic resonance apparatus 10 and an image reconstruction apparatus 20.

Wherein the magnetic resonance apparatus 10 is configured to execute user-entered scan instructions and acquire magnetic resonance data, the magnetic resonance apparatus 10 includes a display, one or more input devices, and a processor. The display provides a user input interface for receiving user input of a scan command for generating a pulse sequence.

The magnetic resonance apparatus 10 may be connected to the image reconstruction apparatus 20 via a communication system including a wired or wireless network connection for transmitting the processing instructions and magnetic resonance data input by the user to the image reconstruction apparatus 20.

The image reconstruction device 20 is a server that receives the magnetic resonance data and the processing instructions sent by the magnetic resonance device 10, processes the magnetic resonance data according to the processing instructions to generate a reconstructed magnetic resonance image, and determines quantitative values of the tissue property parameters from the magnetic resonance image. The processing instructions include fourier transformation of the magnetic resonance data, image reconstruction, pattern matching, dictionary generation, and the like.

The image reconstruction device 20 may also include a display, one or more input devices for receiving user input of scanning instructions or processing instructions.

The quantitative magnetic resonance imaging parameter determination system may further comprise one or more networked user terminals, e.g. mobile handsets, smart computers, etc. A networked user terminal may be connected to the magnetic resonance apparatus 10 via a communication system to enable remote access and control of the magnetic resonance apparatus 10.

In practice, the magnetic resonance apparatus 10 receives user-entered scan commands and generates corresponding pulse signals, including in particular, radio frequency pulses for generating gradient waveforms for performing a prescribed scan and for controlling a radio frequency generator to generate desired frequency, phase and pulse amplitude waveforms.

After the excitation pulse is terminated, the magnetic resonance apparatus 10 acquires and transmits magnetic resonance data to the image reconstruction apparatus 20, and the image reconstruction apparatus 20 performs image reconstruction and pattern matching in magnetic resonance fingerprint imaging (MRF) to determine quantitative values of tissue property parameters.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be exemplarily described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments listed below, are within the scope of protection of the present invention.

Fig. 2 is a schematic flowchart of a quantitative magnetic resonance imaging parameter determination method according to an embodiment of the present application, and mainly relates to a process of how to accurately quantify T2 in MRF. As shown in fig. 1, the quantitative magnetic resonance imaging parameter determination method includes:

s201, acquiring a plurality of magnetic resonance images of a tested object based on a preset MRF pulse sequence; wherein the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting the magnetization vector of the tested object.

The object to be tested comprises a plurality of different tissue types, and different tissue types can obtain different evolution signals based on the same pulse sequence to scan the object to be tested. Illustratively, the subject may include a phantom, a living body (animal or human), an ex vivo organ or tissue, and the like.

Wherein the resonance characteristics differ for different tissue types. Illustratively, the tissue types may include water, fat, bone, muscle, blood, and the like.

The MRF pulse sequence is a pulse sequence generated based on the MRF framework. Unlike conventional magnetic resonance imaging, the MRF framework generates a target pulse sequence using a series of varying sequence blocks that produce sequential excitation of radio frequency pulses and are applied to different tissue types to produce different signal evolutions.

In the present embodiment, the MRF pulse sequence includes a plurality of radio frequency pulse trains sequentially excited, and the plurality of radio frequency pulse trains are used to excite the magnetization vector of the subject to perform T2 magnetization preparation.

Wherein, T2 magnetization preparation refers to transverse magnetization preparation of hydrogen nuclei of a tested object so as to improve the sensitivity of T2 detection. Since T2 is used to characterize the decay characteristic of the transverse magnetization vector, the magnetization preparation can be a multiple focusing of the transverse magnetization vector to encode the transverse relaxation specificity of the subject multiple times.

Wherein, the transverse magnetization vector is the macroscopic expression of the magnetic moments of a plurality of hydrogen nuclei of the tested object in a transverse plane. When a subject enters the main magnetic field, magnetic moments of a plurality of hydrogen nuclei of the subject nutate about the direction of the main magnetic field. Each magnetic moment is a vector, and the sum of the vectors of all magnetic moments is the magnetization vector. The magnetization vectors include longitudinal magnetization vectors and transverse magnetization vectors. In the absence of an excitation pulse, the direction of the magnetization vector is parallel to the main magnetic field, the magnetization vector parallel to the main magnetic field is the longitudinal magnetization vector, and the magnetization vector perpendicular to the magnetic field is the transverse magnetization vector.

In the present embodiment, each rf pulse train comprises an excitation pulse, a 180 ° flipping pulse and a 90 ° flipping pulse, which are sequentially excited, wherein the excitation pulse is used to flip the magnetization vector to the transverse plane, obtaining a larger transverse magnetization vector; the 180 DEG flip pulse is used for flipping the directions of all magnetic moments constituting the transverse magnetization vector by 180 DEG; the flipping pulse is used to flip the relaxed transverse magnetization vector back to the longitudinal plane. Between the excitation pulse of the radio frequency pulse and the 90-degree turning pulse, the 180-degree turning pulse is excited once, namely, the vector direction of the current transverse magnetization vector is turned by 180 degrees, so that multiple encoding of transverse relaxation specificity can be realized, and the sensitivity of T2 detection is improved. Wherein, the 180 DEG turning pulse can be one or more.

In one embodiment, the radio frequency pulse train comprises sequentially excited 90 ° excitation pulses, at least one 180 ° excitation pulse, and-90 ° excitation pulses; wherein the 90 ° excitation pulse is the above-mentioned excitation pulse, the 180 ° excitation pulse is the above-mentioned 180 ° inversion pulse, and the-90 ° excitation pulse is the above-mentioned 90 ° inversion pulse. The interval time between two adjacent excitation pulses in the radio frequency pulse train is the same. The number of the 180-degree excitation pulses can be multiple, each 180-degree excitation pulse is used for overturning a transverse magnetization vector in a transverse plane once, and transverse relaxation specificity can be coded for multiple times by arranging the multiple 180-degree excitation pulses. .

Referring to fig. 3, fig. 3 is a schematic diagram of an rf pulse train according to the present embodiment, as shown in fig. 3, the pulse train includes two rf pulse trains, each of which includes a sequentially excited 90 ° excitation pulse, a 180 ° excitation pulse, and a-90 ° excitation pulse. The interval between the 90 ° excitation pulse and the 180 ° excitation pulse is the same as the interval between the 180 ° excitation pulse and the-90 ° excitation pulse. When the tested object is scanned based on the pulse sequence, the 90-degree excitation pulse directly and completely overturns the magnetization vector to the transverse plane to obtain the maximum transverse magnetization vector, after the 90-degree excitation pulse is excited, the transverse magnetization vector enters a relaxation state and starts to attenuate until the 180-degree excitation pulse overturns the vector directions of all magnetic moments in the current transverse magnetization vector by 180 degrees to obtain the overturned transverse magnetization vector, the overturned transverse magnetization vector is continuously attenuated until the-90-degree excitation pulse overturns the attenuated transverse magnetization vector to the longitudinal plane, and the T2 magnetization preparation of the tested object is completed.

The duration of each radio frequency pulse train is the dwell time after the magnetization vector is overturned to the transverse plane, and is specifically embodied as the interval time between an excitation pulse and an overturning pulse of the radio frequency pulse train; illustratively, as shown in FIG. 3, each RF burst has a duration of 90 excitation pulses and a spacing between-90 excitation pulses.

The duration of each radio frequency burst may be different, as the T2 of the tissue represented by different voxels is different, as is the sensitivity of the T2 to different voxels. The duration of each radio frequency burst is set to a preparation time sensitive to T2 of the tissue represented by the different voxels, the durations of the plurality of radio frequency bursts being sequentially increasing. Illustratively, the radio frequency excitation pulse trains comprise 3, 3 radio frequency excitation pulse trains having durations of 5 milliseconds, 25 milliseconds, and 35 milliseconds, respectively. The duration of the rf excitation pulse train typically does not exceed 100 milliseconds.

In this embodiment, the video pulse train is used for T2 preparation of the subject, so that after each radio frequency pulse train, one radio frequency pulse for sampling may be set, where the flip angle of each radio frequency pulse is 10 ° or less. In practical application, after each radio frequency excitation pulse train is finished, a radio frequency pulse is applied, each voxel generates an echo at the moment, and the acquisition of echo signals is carried out through a sampling window (analog-to-digital conversion device A/D).

In this embodiment, based on the MRF pulse sequence, scanning of the subject is performed to acquire a magnetic resonance image of the subject, and the method specifically includes S2011 to S2013:

s2011, acquiring pulse sequence parameters of the MRF pulse sequence;

the pulse sequence parameters are used to characterize the radio frequency pulse train of the MRF pulse sequence, the combination of the radio frequency pulses used for sampling in time sequence. Meanwhile, the pulse sequence parameters also include the flip angle FA of each pulse, the repetition time TR, the echo time TE and the phase change of the rf pulse in each shot.

And S2012, sending the pulse sequence parameters to the magnetic resonance device so that the magnetic resonance device generates a pulse signal based on the pulse sequence parameters and acquires a plurality of sampling data of the tested object.

The way in which the magnetic resonance apparatus acquires the sampled data based on the pulse sequence parameters may be implemented based on the prior art, and will not be described herein again.

S2013, receiving the plurality of sampling data, performing Fourier transform on each sampling data, and generating a magnetic resonance image of the tested object corresponding to each sampling data.

The magnetic resonance equipment stores the sampled data obtained by sampling according to a certain arrangement mode to form a sampled data space. And generating a magnetic resonance image according to the signal intensity of each sampling point in the sampling data space and the position of the sampling point. Specifically, for data obtained by linear sampling, the data are uniformly distributed on grid points, and a magnetic resonance image is obtained by converting the signal intensity of each voxel into a corresponding gray value in a two-dimensional plane through inverse fourier transform.

S202, extracting an evolution signal of each voxel from a plurality of magnetic resonance images; wherein the evolution signal is used to characterize the change in signal intensity of each voxel in the plurality of magnetic resonance images.

The signal intensity of each voxel is different at different sampling time, and the signal intensity is reflected on the magnetic resonance image as different gray values. The signal intensity of each voxel point is acquired from a plurality of magnetic resonance images, and the signals are sequentially combined according to the sampling time of the magnetic resonance images, namely the evolution signal of each voxel is obtained.

Referring to fig. 4, fig. 4 is a diagram illustrating an evolution signal of a single voxel according to an embodiment of the present application. In practical application, the sampling time point is set to 1000 in advance, and the MRF pulse sequence is executed at each sampling time point, so that 1000 undersampled magnetic resonance images are obtained. And combining the signal intensity of each pixel point in 1000 magnetic resonance images according to time to obtain an evolution signal curve of each pixel point, namely the evolution signal of each voxel. It should be understood that pixel points in the magnetic resonance image correspond one-to-one to voxels of the subject.

S203, determining the transverse relaxation time of the tissue represented by each voxel according to the analog signal which is most matched with the evolution signal of each voxel in the preset dictionary; the dictionary comprises a plurality of analog signals generated by performing signal analog evolution on the MRF pulse sequence and transverse relaxation time corresponding to each analog signal in a one-to-one mode.

A dictionary may be obtained in advance, and the dictionary includes a plurality of analog signals generated by performing analog evolution of signals based on the MRF pulse sequence, and transverse relaxation times corresponding to each analog signal one to one.

The signal simulated evolution can be obtained by a bloch model simulation calculation. Each analog signal is a dictionary entry in the dictionary, and each dictionary entry corresponds to a T2.

Illustratively, T2 is first unevenly divided according to the physiological characteristics of the subject. For example, to cover the subject, the range of T2 is set to 0-500 milliseconds. The T2 for less than 100 milliseconds was increased at a gradient of 2 milliseconds, the portion for more than 100 milliseconds and less than 200 milliseconds was increased at a gradient of 5 milliseconds, and the portion for more than 200 milliseconds was increased at a gradient of 50 milliseconds, creating multiple sets of T2. Then, based on the parameter set of the MRF pulse sequence in step S201, a simulation time signal is obtained by a bloch model simulation calculation, and a dictionary entry is obtained for each group of T2 transformed until all groups of T2 are subjected to the simulation calculation, generating a dictionary containing a plurality of dictionary entries. Wherein, the Bloch model represents the change of the magnetization vector of the proton under the action of the magnetic field along with the relaxation time.

Referring to fig. 5, fig. 5 mainly relates to how to determine T2 of each voxel, and as shown in fig. 5, the transverse relaxation time of each voxel is determined according to the analog signal matched with the evolution signal of each voxel in the preset dictionary, which specifically includes S501 and S502:

s501, comparing the time signal of each voxel with all analog signals in a preset dictionary to obtain the analog signal with the highest matching degree with the magnetic resonance signal of each voxel in the dictionary.

And S502, regarding each voxel, taking the transverse relaxation time corresponding to the analog signal with the highest degree of matching with the evolution signal of the voxel as the transverse relaxation time of the voxel.

First, each dictionary entry in the dictionary is normalized. The comparison is then made based on the dot product operation. Specifically, after a dictionary and an evolution signal of each voxel are obtained, comparing the evolution signal of the voxel with each dictionary entry in a preset dictionary one by one for each voxel, and obtaining a dictionary condition with the highest matching degree with the evolution signal of the voxel in the dictionary; the T2 corresponding to the dictionary entry is taken as the T2 of the voxel. The introduction of the dictionary enables the MRF to be integrated with system parameters of a magnetic resonance device, such as main magnetic field nonuniformity and radio frequency pulse nonuniformity, improves the robustness of the MRF, and enables the MRF to be suitable for quantitative magnetic resonance imaging parameter determination of different tissue positions and different time periods.

The MRF pulse sequence is a pulse sequence generated based on the MRF framework. Unlike conventional magnetic resonance imaging, the MRF framework generates a target pulse sequence using a series of varying sequence blocks that produce sequential excitation of radio frequency pulses and are applied to different tissue types to produce different signal evolutions. And parameter values of a plurality of tissue attribute parameters can be obtained simultaneously according to the signal evolution. The tissue property parameters may include, among others, the longitudinal relaxation time T1, the main magnetic field strength B0, etc.

Specifically, the dictionary may include a plurality of analog signals generated by performing signal analog evolution based on the MRF pulse sequence, and characteristic physical parameters corresponding to each analog signal in a one-to-one manner. Wherein the characteristic physical parameters may include, in addition to the transverse relaxation time, the longitudinal relaxation time T1, the main magnetic field strength B0, etc. And then determining the characteristic physical parameters of the tissue represented by each voxel according to the analog signal which is most matched with the evolution signal of each voxel in the preset dictionary.

Referring to fig. 6, fig. 6 is a schematic diagram of a pulse sequence according to another embodiment of the present application, as shown in fig. 6, the MRF pulse sequence includes two sequentially excited rf pulse trains, an inversion recovery pulse, and a balanced steady-state auto-precession sequence.

In this embodiment, the MRF may include a T2 preparation sequence block, a T2 preparation sequence block for generating a plurality of radio frequency pulse trains sequentially excited, and an inversion recovery pulse sequence block for generating inversion recovery pulses. The MRF realizes the rapid addition of a plurality of pulse sequence blocks through the frame design of the sequence blocks.

In this embodiment, the MRF pulse sequence may further include a gradient echo sequence based on inversion recovery. The repetition time and flip angle of the gradient echo sequence based on inversion recovery are different in each excitation of the MRF pulse sequence. The gradient echo sequence based on inversion recovery comprises inversion recovery pulses and gradient echo sequence pulses which are sequentially excited, and can be realized by adding an inversion recovery sequence block and a gradient echo acquisition sequence block in an MRF framework. The inversion recovery sequence is sensitive to T1, and the sensitivity of the magnetic resonance signal to T1 can be improved by setting the inversion recovery sequence, so that the accuracy T1 value is obtained.

The inversion recovery pulse (IR) includes sequential firing of a 180 ° rf pulse and a 90 ° rf pulse. The interval between two rf pulses is the inversion latency. When the device is used, a magnetization vector is excited based on 180-degree radio frequency pulses, then the device is excited by using 90-degree radio frequency pulses after waiting for a period of time (inversion time TI), and two radio frequency pulses form echoes.

Illustratively, the magnetization vector is first excited by a 180 ° pulse of inversion recovery, causing it to invert 180 °, then waiting for the first time T1, at which time the longitudinal magnetization vector will partially recover, and then applying a plurality of small-angle radio frequency pulses (having 90 ° pulse components) to invert the longitudinal magnetization vector of the current magnitude to the transverse coordinates for data acquisition. After the longitudinal magnetization vector completely recovers the steady state, the operation is repeated by changing the value of the inversion time TI, and different inversion times are selected, so that the chemical shift artifact can be reduced, and a more accurate T1 value can be obtained.

The gradient echo sequence is used for echo sampling, and the gradient echo sequence can be a balanced steady free precession sequence. A feature of the balanced steady state free precession sequence is that both transverse and longitudinal magnetization vectors reach steady state after multiple radio frequency excitations. Since the radio frequency angle of excitation can be very small, TR can be set very short, so the scanning time of the equilibrium steady state free precession sequence is greatly reduced relative to the scanning time of the ordinary gradient echo sequence.

In practice, MRF can be obtained by varying the pulse sequence parameters at each acquisition time point to evolve the signal either spatially incoherent or temporally incoherent. The pulse sequence parameters that can be varied include the flip angle FA, pulse phase, repetition time TR, echo time TE, and sampling pattern of each pulse. Illustratively, in the present embodiment, in each firing of the MRF pulse sequence, the repetition time TR and the flip angle FA of the equilibrium steady-state automatic precession sequence are varied randomly in position to obtain evolution signals that are spatially incoherent, i.e., the evolution signals of each voxel. The random variation curve of the position of the repetition time TR and the flip angle FA of the equilibrium steady-state automatic precession sequence can be seen in fig. 7.

The procedure of scanning a subject based on the MRF pulse sequence of this embodiment to acquire a magnetic resonance image of the subject is the same as in S2011 to S2013, and only the pulse sequence parameters are different. In particular, the pulse sequence parameters are used to characterize the timing combination of the radio frequency pulse train of the MRF pulse sequence, the radio frequency pulses used for sampling, the inversion recovery pulses, and the balanced steady state autopulsion pulses. Meanwhile, the pulse sequence parameters also include the flip angle FA of each pulse, the repetition time TR, the echo time TE and the phase change of the rf pulse in each shot. Illustratively, the flip angle FA and the repetition time TR of the equilibrium steady-state automatic precession pulse vary pseudo-randomly with time.

After acquiring a plurality of magnetic resonance images of a tested object, extracting an evolution signal of each voxel of the tested object from the plurality of magnetic resonance images; wherein the evolution signal is used to characterize the change in signal intensity of each voxel in the plurality of magnetic resonance images. Then, determining a tissue attribute parameter value of each voxel according to a simulation signal matched with the evolution signal of each voxel in a preset dictionary; the dictionary comprises a plurality of analog signals generated by performing signal simulation evolution on the MRF pulse sequence shown in FIG. 6, and tissue attribute parameter values corresponding to the analog signals one by one. The organization attribute parameter values include T1 and T2.

Wherein, the dictionary can be obtained by calculation in advance through a Bloch model simulation.

Illustratively, the range of T1 is set to 0-5000 milliseconds and the range of T2 is set to 0-500 milliseconds. Firstly, arranging and combining tissue parameter values to generate a plurality of groups of tissue parameter values, wherein each group of tissue parameters comprises T1 and T2, and T2 and T1 of each group of tissue parameters are not identical; then, according to the parameter set of the MRF pulse sequence in step S201, a simulation time signal is obtained by a bloch model simulation calculation, and each group of the organization parameter values is transformed, a dictionary entry is obtained until all the groups of the organization parameter values are subjected to the simulation calculation, and a dictionary including a plurality of dictionary entries is generated. Wherein, the Bloch model represents the change of the magnetization vector of the proton under the action of the magnetic field along with the relaxation time.

Referring to fig. 8, fig. 8 is a dictionary diagram provided in the present embodiment, as shown in fig. 8, each group of tissue property parameter values corresponds to an analog signal. The organization attribute parameters include T1 and T2, and the number of dictionary entries of the dictionary is determined by the number of permutation combinations of T2 and T1. It should be understood that the tissue property parameter may also include other tissue property parameters such as proton density.

In the quantitative magnetic resonance imaging method provided in this embodiment, the MRF pulse sequence includes not only the radio frequency pulse train for exciting the magnetization vector, but also a gradient echo sequence based on inversion recovery, and FA and TR of the gradient echo sequence change pseudo-randomly in each excitation of the MRF pulse sequence, so that signals of each voxel of the object to be tested can be spatially encoded. On one hand, the MRF pulse sequence can simultaneously obtain accurate T1 and T2 through the arrangement of the radio frequency pulse train and the inversion recovery pulse. On the other hand, in the MRF scheme, system parameters of some magnetic resonance equipment, such as main magnetic field nonuniformity, radio frequency pulse nonuniformity and the like, can be integrated through dictionary design, so that the robustness of the MRF is improved, and the MRF is suitable for quantitative magnetic resonance imaging of different tissue types and different time periods.

It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

Based on the quantitative magnetic resonance imaging parameter determination provided by the above embodiment, the embodiment of the present invention further provides an embodiment of an apparatus for implementing the above method embodiment.

Fig. 9 is a schematic diagram illustrating a configuration of a quantitative magnetic resonance imaging parameter determining apparatus according to an embodiment of the present application. As shown in fig. 9, the quantitative magnetic resonance imaging parameter determination apparatus 90 includes: a pre-imaging module 901, a signal acquisition module 902, and a parameter determination module 903.

A pre-imaging module 901, configured to acquire a plurality of magnetic resonance images of a subject based on a preset MRF pulse sequence; the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting the magnetization vector of the tested object;

a signal acquisition module 902 for extracting an evolution signal of each voxel from a plurality of magnetic resonance images; wherein the evolution signal is used to characterize the variation of signal intensity of each voxel in the plurality of magnetic resonance images;

a parameter determining module 903, configured to determine, according to a simulation signal that is most matched with the evolution signal of each voxel in a preset dictionary, a transverse relaxation time of a tissue represented by each voxel; the dictionary comprises a plurality of analog signals generated by performing signal analog evolution on the MRF pulse sequence and transverse relaxation time corresponding to each analog signal in a one-to-one mode.

Optionally, in pre-imaging module 901, the radio frequency pulse train comprises sequentially excited 90 ° excitation pulses, at least one 180 ° excitation pulse, and-90 ° excitation pulses.

The interval time between two adjacent excitation pulses in the radio frequency pulse train is the same.

The duration of each radio frequency pulse train is the staying time after the magnetization vector is overturned to the transverse plane, and the durations of the plurality of radio frequency pulse trains are sequentially increased.

Each radio frequency pulse train is followed by a radio frequency pulse for sampling, and the flip angle of each radio frequency pulse is less than or equal to 10 degrees.

The MRF pulse sequence also includes a gradient echo sequence based on inversion recovery.

Optionally, the parameter determining module 903 is specifically configured to:

comparing the time signal of each voxel with all analog signals in a preset dictionary to obtain the analog signal with the highest matching degree with the magnetic resonance signal of each voxel in the dictionary; the dictionary comprises a plurality of analog signals generated by performing signal analog evolution on the MRF pulse sequence and a corresponding relation between each analog signal and transverse relaxation time.

The quantitative magnetic resonance imaging parameter determining apparatus provided in this embodiment acquires a plurality of magnetic resonance images of a subject based on a preset MRF pulse sequence; and extracting the evolution signal of each voxel from a plurality of magnetic resonance images, and determining the transverse relaxation time of the tissue represented by each voxel according to the analog signal matched with the evolution signal of each voxel in a preset dictionary, thereby realizing the quantification of the transverse relaxation time in the magnetic resonance imaging. Compared with the MRF pulse sequence in the prior art, the MRF sequence in the embodiment of the present application includes a plurality of sequentially excited radio frequency pulse trains, and during the MRF sequence is executed to perform magnetic resonance imaging, the radio frequency pulses in each radio frequency pulse train flip hydrogen nuclei of the in-vivo tissue of the subject to be tested to generate transverse magnetization vectors, and re-excite the transverse magnetization vectors within the duration of the radio frequency pulse train, so that weighting of T2 relaxation is achieved, and therefore, the quantitative magnetic resonance imaging parameter determination method provided by the embodiment of the present application improves the sensitivity of transverse relaxation time detection, and can obtain accurate transverse relaxation time.

The quantitative magnetic resonance imaging parameter determining apparatus provided in the embodiment shown in fig. 9 can be used to implement the technical solutions in the above method embodiments, and the implementation principle and technical effects are similar, which is not described herein again.

It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-mentioned division of the functional units and modules is illustrated, and in practical applications, the above-mentioned function distribution may be performed by different functional units and modules according to needs, that is, the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-mentioned functions. Each functional unit and module in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units are integrated in one unit, and the integrated unit may be implemented in a form of hardware, or in a form of software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working processes of the units and modules in the system may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

Fig. 10 is a schematic diagram of a quantitative magnetic resonance imaging parameter determination apparatus provided in an embodiment of the present application. As shown in fig. 10, the quantitative magnetic resonance imaging parameter determination terminal device 10 of the embodiment includes: at least one processor 1001, a memory 1002, and computer programs stored in the memory 1002 and executable on the processor 1001. The quantitative magnetic resonance imaging parameter determination apparatus further comprises a communication component 1003, wherein the processor 1001, the memory 1002 and the communication component 1003 are connected by a bus 1004.

The processor 1001, when executing the computer program, implements the steps in each of the above-described embodiments of the quantitative magnetic resonance imaging parameter determination method, such as steps S201 to S203 in the embodiment shown in fig. 2. Alternatively, the processor 1001, when executing the computer program, implements the functions of each module/unit in each device embodiment described above, for example, the functions of the modules 901 to 903 shown in fig. 9.

Illustratively, a computer program may be partitioned into one or more modules/units, which are stored in the memory 1002 and executed by the processor 1001 to accomplish the present application. The one or more modules/units may be a series of computer program instruction segments capable of performing certain functions for describing the execution of a computer program in the quantitative magnetic resonance imaging image reconstruction device 100.

In this embodiment, the quantitative magnetic resonance imaging parameter determining device may be a cloud server or a user terminal. The user terminal may be, but is not limited to, various personal computers, notebook computers, smart phones, etc. capable of running applications. The cloud server may be a server for realizing a single function, or may be a server for realizing multiple functions, specifically, an independent physical server, or a physical server cluster.

It will be appreciated by those skilled in the art that figure 10 is merely an example of a quantitative magnetic resonance imaging parameter determination device and does not constitute a limitation of quantitative magnetic resonance imaging parameter determination devices and may include more or less components than those shown, or combine certain components, or different components such as input output devices, network access devices, buses, etc.

The Processor 1001 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory 1002 may be an internal memory unit of the quantitative mri parameter determining device, or may be an external memory device for quantitative mri parameter determination, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash Card (Flash Card), and so on. The memory 1002 is used for storing the computer programs and other programs and data required by the quantitative magnetic resonance imaging image reconstruction device. The memory 1002 may also be used to temporarily store data that has been output or is to be output.

The bus may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended ISA (EISA) bus, or the like. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, the buses in the figures of the present application are not limited to only one bus or one type of bus.

The embodiments of the present application further provide a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the computer program implements the steps that can be implemented in the above method embodiments.

Embodiments of the present application provide a computer program product, which when run on a quantitative magnetic resonance imaging parameter determination apparatus, causes the quantitative magnetic resonance imaging parameter determination apparatus to implement the steps in the above method embodiments when executed.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium and can implement the steps of the embodiments of the methods described above when the computer program is executed by a processor. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer readable medium may include at least: any entity or apparatus capable of carrying computer program code to a quantitative magnetic resonance imaging parameter determination device, a recording medium, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), an electrical carrier signal, a telecommunications signal, and a software distribution medium. Such as a usb-disk, a removable hard disk, a magnetic or optical disk, etc. In certain jurisdictions, computer-readable media may not be an electrical carrier signal or a telecommunications signal in accordance with legislative and patent practice.

In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

In the embodiments provided in the present application, it should be understood that the disclosed apparatus/network device and method may be implemented in other ways. For example, the above-described apparatus/network device embodiments are merely illustrative, and for example, the division of the modules or units is only one logical division, and there may be other divisions when actually implementing, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not implemented. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.

Claims

1. A quantitative magnetic resonance imaging parameter determination method, comprising:

acquiring a plurality of magnetic resonance images of a tested object based on a preset MRF pulse sequence; wherein the MRF pulse sequence comprises a plurality of radio frequency pulse trains which are sequentially excited, and the radio frequency pulse trains are used for exciting the magnetization vector of the tested object;

extracting an evolution signal of each voxel from the plurality of magnetic resonance images; wherein the evolution signal is used to characterize the change in signal intensity of each voxel in the plurality of magnetic resonance images;

2. The quantitative magnetic resonance imaging parameter determination method as set forth in claim 1, wherein the radio frequency pulse train includes a sequentially excited 90 ° excitation pulse, at least one 180 ° excitation pulse, and a-90 ° excitation pulse.

3. A quantitative magnetic resonance imaging parameter determination method as claimed in claim 2, characterized in that the interval time between two adjacent excitation pulses in the radio frequency pulse train is the same.

4. The quantitative magnetic resonance imaging parameter determination method as claimed in claim 1, wherein the duration of each of the radio frequency pulse trains is a dwell time after the magnetization vector is flipped to a transverse plane, and the durations of a plurality of the radio frequency pulse trains are sequentially increased.

5. A method for quantitative magnetic resonance imaging parameter determination as claimed in claim 1, characterized in that each radio frequency pulse train is followed by a radio frequency pulse for sampling, each of said radio frequency pulses having a flip angle of 10 ° or less.

6. A quantitative magnetic resonance imaging parameter determination method as claimed in any one of claims 1-5, characterized in that said determining the transverse relaxation time of the tissue represented by each voxel from the simulated signal in the predetermined dictionary that best matches the evolution signal of each voxel comprises:

and regarding each voxel, taking the transverse relaxation time corresponding to the analog signal with the highest degree of matching with the evolution signal of the voxel as the transverse relaxation time of the voxel.

7. The quantitative magnetic resonance imaging parameter determination method of claim 1, wherein the MRF pulse sequence further comprises an inversion recovery based gradient echo sequence.

8. A quantitative magnetic resonance imaging parameter determination apparatus, comprising:

9. A quantitative magnetic resonance imaging parameter determination apparatus comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the method according to any of claims 1 to 7 when executing the computer program.

10. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 7.