阅读说明：本技术 磁共振成像方法、设备及存储介质 (Magnetic resonance imaging method, apparatus and storage medium ) 是由 丁海艳 司东岳 于 2020-05-27 设计创作，主要内容包括：本发明提供磁共振成像方法、设备和存储介质。该方法包括：获得心电门控触发时间Ttrigger；针对第一心动周期,确定反转恢复脉冲和T2准备脉冲之间的时间间隔TD<Sub>1</Sub>、T2准备脉冲的持续时间TE<Sub>1</Sub>、以及T2准备脉冲和第一数据采集射频脉冲之间的时间间隔TD<Sub>2</Sub>；在第一心动周期内,按照TD<Sub>1</Sub>、TE<Sub>1</Sub>、TD<Sub>2</Sub>和Ttrigger,激发前述脉冲,并且在激发第一数据采集射频脉冲时采集反转恢复T2准备图像信号,其中激发第一数据采集射频脉冲还基于呼吸导航信号的控制；在第二心动周期内,按照Ttrigger,基于呼吸导航信号的控制激发第二数据采集射频脉冲并且采集参考图像信号,两个周期内呼吸导航信号的控制是独立的；以及根据两个图像信号生成磁共振图像。该方案能够显著提高图像的对比度和空间分辨率。(The invention provides a magnetic resonance imaging method, a magnetic resonance imaging apparatus and a storage medium. The method comprises the following steps: obtaining an electrocardio-gating triggering time Ttrigger; determining a time interval TD between an inversion recovery pulse and a T2 preparation pulse for a first cardiac cycle 1 T2 duration TE of the preparation pulse 1 And a time interval TD between the T2 preparation pulse and the first data acquisition RF pulse 2 (ii) a In the first cardiac cycle, according to TD 1 、TE 1 、TD 2 And Ttrigger to fire the aforementioned pulses and to fire a first data acquisition radio frequency pulse that is also based on control of the respiratory navigation signal, and to acquire an inversion recovery T2 ready image signal when the first data acquisition radio frequency pulse is fired; in a second cardiac cycle, according to Ttrigger, a second data acquisition radio frequency pulse is excited based on the control of the respiratory navigation signal and a reference image signal is acquired, and the control of the respiratory navigation signal in the two cycles is independent; and generating a magnetic resonance image from the two image signals. The scheme can remarkably improve the contrast and the spatial resolution of the image。)

1. A magnetic resonance imaging method, comprising:

obtaining the cardiac electric gating trigger time Ttrigger of the subject;

determining inversion recovery for a first cardiac cycleFirst time interval TD between a complex pulse and a T2 preparation pulse₁T2 duration TE of the preparation pulse₁And a second time interval TD between the T2 preparation pulse and the first data acquisition RF pulse₂；

In the first cardiac cycle, according to the first time interval TD₁The duration TE₁The second time interval TD₂And the electrocardio-gating trigger time Ttrigger, sequentially exciting an inversion recovery pulse, a T2 preparation pulse and a first data acquisition radio frequency pulse, and acquiring an inversion recovery T2 preparation image signal when the first data acquisition radio frequency pulse is excited, wherein the excitation of the first data acquisition radio frequency pulse is also based on the control of a first respiratory navigation signal;

in a second cardiac cycle, according to the cardiac gating trigger time Ttrigger, a second data acquisition radio frequency pulse is excited based on the control of a second respiratory navigation signal and a reference image signal is acquired, wherein the control of the first respiratory navigation signal is independent of the control of the second respiratory navigation signal; and

a magnetic resonance image is generated from the inversion recovery T2 preparation image signal and the reference image signal.

2. The method of claim 1, wherein a T2 preparation pulse is also excited during the second cardiac cycle prior to said exciting the second data acquisition radio frequency pulse and acquiring the reference image signal.

3. The method of claim 1 or 2, wherein the first cardiac cycle is a first cardiac cycle in a repeating unit in a phase sensitive sequence and the second cardiac cycle is a second cardiac cycle in the repeating unit.

4. A method according to claim 1 or 2, wherein said determining a first time interval TD between an inversion recovery pulse and a T2 preparation pulse₁T2 duration TE of the preparation pulse₁And T2 preparation pulse and first data acquisition RF pulseSecond time interval TD between bursts₂The method comprises the following steps:

obtaining basic physical parameters of magnetic resonance for normal myocardial tissue and blood, respectively, of the subject;

presetting the duration TE₁；

According to said basic physical parameter and said duration TE₁Calculating said first time interval TD₁And said second time interval TD₂。

5. The method of claim 4, wherein said basic physical parameters comprise a longitudinal relaxation time T1 and a transverse relaxation time T2, said calculating said first time interval TD₁And said second time interval TD₂The method comprises the following steps:

respectively taking the normal myocardial tissue and the blood as target tissues to establish a steady-state magnetization vector M of the target tissues_ssWith the longitudinal relaxation time T1, the transverse relaxation time T2, the first time interval TD₁The duration TE₁And said second time interval TD₂A first mathematical relationship therebetween;

respectively taking the normal myocardial tissue and the blood as target tissues, and establishing the image signal intensity of the target tissues according to the following formula

determining the first time period according to the first mathematical relationship and the second mathematical relationship based on the image signal intensity of the normal myocardial tissue being 0 and the image signal intensity of the blood being minimumSeparate TD₁And said second time interval TD₂。

6. The method of claim 5, wherein the first mathematical relationship is represented as:

wherein the content of the first and second substances,

RX＝RR-(TD₁+TE₁+TD₂)-n×TR；

R1＝RR-n×TR；

TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse;

RR represents the cardiac cycle of the subject;

α₁a flip angle representative of the first data acquisition radio frequency pulse;

α₂a flip angle representative of the second data acquisition radio frequency pulse;

n represents the number of echoes of the data acquisition radio frequency pulse.

7. The method of claim 5, wherein the method further comprises: presetting a duration TE of a T2 preparation pulse for the second cardiac cycle₂；

The first mathematical relationship is represented as:

wherein the content of the first and second substances,

RX＝RR-(TD₁+TE₁+TD₂)-n×TR；

R1＝RR-n×TR-TE₂；

TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse;

RR represents the cardiac cycle of the subject;

α₁representing a flip angle of a first data acquisition radio frequency pulse;

α₂a flip angle representing a second data acquisition radio frequency pulse;

n represents the number of echoes of the data acquisition radio frequency pulse.

8. The method of claim 1, wherein a flip angle of the first data acquisition radio frequency pulse is greater than a flip angle of the second data acquisition radio frequency pulse.

9. The method of claim 1, wherein the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse are both a spoiled gradient echo sequence, a balanced steady state free precession sequence, a spin echo sequence, or a planar echo sequence.

10. The method of claim 1, wherein a separate liposuction procedure is performed during each cardiac cycle prior to the excitation of the first data acquisition radio frequency pulse and the excitation of the second data acquisition radio frequency pulse.

11. A magnetic resonance imaging apparatus comprising a processor and a memory, wherein the memory has stored therein computer program instructions for performing the magnetic resonance imaging method as claimed in any one of claims 1 to 10 when executed by the processor.

12. A storage medium on which program instructions are stored, which program instructions are operable when executed to perform a magnetic resonance imaging method as claimed in any one of claims 1 to 10.

Technical Field

The present invention relates to the field of medical imaging, and more particularly, to a magnetic resonance imaging method, apparatus, and storage medium.

Background

Magnetic resonance imaging technology utilizes the nuclear magnetic resonance phenomenon to image a human body, is a common medical image examination mode, and can be applied to various medical application scenes. For example, atrial fibrillation is one of the most common clinical arrhythmias, and radiofrequency ablation of the left atrium and pulmonary vein isolation are the primary treatments for controlling atrial fibrillation. The fibrosis degree of the atrium and scar tissue after radiofrequency ablation are related to recurrence of atrial fibrillation, so that the fibrosis degree of the atrium and anatomical structure information of surrounding tissues can help decision before ablation, and scar injury generated by ablation can reflect healing. Magnetic resonance imaging of the atria can advantageously help physicians learn anatomical information about a subject to facilitate their making reasonable medical decisions.

The first problem faced in magnetic resonance imaging is the effect on imaging quality of the subject's heart's own motion and respiratory motion compensation.

For the self-movement of the heart, an electrocardio-gating method can be adopted, electrocardio signals are detected through a body surface electrode, the movement period of the heart is reflected, and then data acquisition is carried out in the period of relative rest of the movement of the heart. Typically the acquisition time of one cardiac cycle is 100-.

For respiratory motion compensation, common methods include breath holding and respiratory navigation. Breath holding sequences require the subject to coordinate breath holding, scanning during breath holding, and eliminating the effects of respiratory motion. One breath holding time is usually about 10 seconds, is limited by scanning time, can only be used for two-dimensional imaging or multilayer two-dimensional imaging, and is limited in imaging resolution. This method is also affected by the physiological condition of the subject, and failure to complete breath holding can affect image quality. The respiratory navigation method enables a subject to breathe freely, excites a columnar area at the diaphragm and performs one-dimensional imaging for monitoring respiratory movement. In the data acquisition of each cardiac cycle, only the data when the respiratory motion reaches a specific position is retained, and the actual scanning time of the method depends on the respiratory navigation efficiency. The method can be used for three-dimensional high-resolution imaging due to the fact that the acquisition time is prolonged.

In some application scenarios, such as the imaging of atrial scars described above, since the thickness of the atrial wall is very thin, typically 2-4mm, and is susceptible to partial volume effects, it is desirable to improve the contrast between the scar and the adjacent blood signals, while also requiring higher resolution than for ventricular imaging. Because the heart can be influenced by self-motion and respiratory motion, the breath-holding mode is generally adopted in the existing imaging sequence, so that the scanning time and the resolution ratio are limited, and the imaging scanning time based on the existing respiratory navigation mode can also be influenced by the respiratory navigation efficiency. Thus, an ideal magnetic resonance image cannot be obtained.

In summary, a new magnetic resonance imaging method is needed to improve image contrast and spatial resolution.

Disclosure of Invention

The present invention has been made in view of the above problems. According to an aspect of the present invention, there is provided a magnetic resonance imaging method including:

obtaining the cardiac electric gating trigger time Ttrigger of the subject;

determining a first time interval TD between an inversion recovery pulse and a T2 preparation pulse for a first cardiac cycle₁T2 duration TE of the preparation pulse₁And a second time interval TD between the T2 preparation pulse and the first data acquisition RF pulse₂；

In the first cardiac cycle, according to the first time interval TD₁The duration TE₁The second time interval TD₂And the electrocardio-gating trigger time Ttrigger, sequentially exciting an inversion recovery pulse, a T2 preparation pulse and a first data acquisition radio frequency pulse, and acquiring an inversion recovery T2 preparation image signal when the first data acquisition radio frequency pulse is excited, wherein the excitation of the first data acquisition radio frequency pulse is also based on the control of a first respiratory navigation signal;

in a second cardiac cycle, according to the cardiac gating trigger time Ttrigger, a second data acquisition radio frequency pulse is excited based on the control of a second respiratory navigation signal and a reference image signal is acquired, wherein the control of the first respiratory navigation signal is independent of the control of the second respiratory navigation signal; and

a magnetic resonance image is generated from the inversion recovery T2 preparation image signal and the reference image signal.

Illustratively, the T2 preparation pulse is also excited during the second cardiac cycle before said exciting the second data acquisition radio frequency pulse and acquiring the reference image signal.

Illustratively, the first cardiac cycle is a first cardiac cycle in a repeating unit in a phase sensitive sequence and the second cardiac cycle is a second cardiac cycle in the repeating unit.

Illustratively, the first time interval TD between the determined inversion recovery pulse and the T2 preparation pulse₁T2 duration TE of the preparation pulse₁And a second time interval TD between the T2 preparation pulse and the first data acquisition RF pulse₂The method comprises the following steps:

obtaining basic physical parameters of magnetic resonance for normal myocardial tissue and blood, respectively, of the subject;

presetting the duration TE₁；

According to said basic physical parameter and said duration TE₁Calculating said first time interval TD₁And said second time interval TD₂。

Exemplarily, the basic physical parameters include a longitudinal relaxation time T1 and a transverse relaxation time T2, and the calculating the first time interval TD₁And said second time interval TD₂The method comprises the following steps:

respectively taking the normal myocardial tissue and the blood as target tissues to establish a steady-state magnetization vector M of the target tissues_SSWith the longitudinal relaxation time T1, the transverse relaxation time T2, the first time interval TD₁The duration TE₁And said second time interval TD₂A first mathematical relationship therebetween;

respectively taking the normal myocardial tissue and the blood as target tissues, and establishing the image signal intensity of the target tissues according to the following formula

With said steady-state magnetization vector M_SSThe longitudinal relaxation time T1, the transverse relaxation time T2, the first time interval TD₁The duration TE₁And said second time interval TD₂The second mathematical relationship between:

determining the first time interval TD from the first mathematical relationship and the second mathematical relationship based on the image signal intensity of the normal myocardial tissue being 0 and the image signal intensity of the blood being minimal₁And said second time interval TD₂

Illustratively, the first mathematical relationship is represented as:

wherein the content of the first and second substances,

RX＝RR-(TD₁+TE₁+TD₂)-n×TR；

R1＝RR-n×TR；

TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse;

RR represents the cardiac cycle of the subject;

α₁a flip angle representative of the first data acquisition radio frequency pulse;

α₂a flip angle representative of the second data acquisition radio frequency pulse;

n represents the number of echoes of the data acquisition radio frequency pulse.

Illustratively, the method further comprises: presetting a duration TE of a T2 preparation pulse for the second cardiac cycle₂；

The first mathematical relationship is represented as:

wherein the content of the first and second substances,

RX＝RR-(TD₁+TE₁+TD₂)-n×TR；

R1＝RR-n×TR-TE₂；

TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse;

RR represents the cardiac cycle of the subject;

α₁representing a flip angle of a first data acquisition radio frequency pulse;

α₂a flip angle representing a second data acquisition radio frequency pulse;

n represents the number of echoes of the data acquisition radio frequency pulse.

Illustratively, the flip angle of the first data acquisition radio frequency pulse is greater than the flip angle of the second data acquisition radio frequency pulse.

Illustratively, the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse are both a spoiled gradient echo sequence, a balanced steady state free precession sequence, a spin echo sequence, or a planar echo sequence.

Illustratively, a liposuction procedure is performed separately during each cardiac cycle prior to energizing the first data acquisition radio frequency pulse and energizing the second data acquisition radio frequency pulse.

According to another aspect of the present invention, there is also provided a magnetic resonance imaging apparatus comprising a processor and a memory, wherein the memory has stored therein computer program instructions for executing the magnetic resonance imaging method described above when the computer program instructions are executed by the processor.

According to yet another aspect of the present invention, there is also provided a storage medium having stored thereon program instructions for performing the magnetic resonance imaging method described above when executed.

According to the magnetic resonance imaging method, the magnetic resonance imaging device and the storage medium, a three-dimensional image signal is acquired in two cardiac cycles respectively. The image signals acquired in the first cardiac cycle are obtained using inversion recovery and a T2 preparation pulse, which enables the generation of phase sensitive images of dark blood contrast, and the image signals acquired in the second cardiac cycle can be used as a reference for phase sensitive image reconstruction. The acquisition of the two image signals adopts an independent respiration navigation method, so that the acquisition of the image signals can obtain higher navigation efficiency. Thereby, the generated magnetic resonance image can be made higher in contrast and spatial resolution.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail embodiments of the present invention with reference to the attached drawings. The accompanying drawings are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings, the same reference numerals generally denote the same signals or pulses, etc.

Figure 1 shows a schematic flow diagram of a magnetic resonance imaging method according to an embodiment of the invention;

FIG. 2 shows a schematic diagram of an imaging sequence according to one embodiment of the invention;

FIGS. 3a and 3b show atrial magnetic resonance images from the same subject after atrial radio frequency ablation surgery according to the prior art and one embodiment of the present invention, respectively;

FIGS. 3c and 3d show enlarged images of corresponding parts of FIGS. 3a and 3b, respectively;

figure 4 shows a schematic diagram of the contrast to noise ratio (CNR) between different tissues in a magnetic resonance image according to the prior art and one embodiment of the invention; and

figure 5 shows a schematic flow diagram of a magnetic resonance imaging method according to another embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. It is to be understood that the described embodiments are merely a subset of embodiments of the invention and not all embodiments of the invention, with the understanding that the invention is not limited to the example embodiments described herein. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention described herein without inventive step, shall fall within the scope of protection of the invention.

In order to obtain images of higher contrast and spatial resolution, embodiments of the present invention provide a magnetic resonance imaging method. The magnetic resonance imaging method can be applied to various target tissues such as atria, ventricles and even blood vessels of a subject. The magnetic resonance imaging method adopts a delayed intensified imaging technology. The subject was injected with gadolinium contrast agent and then imaged approximately 10 minutes later. For example, in the case of magnetic resonance imaging of the atrium, where more contrast agent remains in the myocardial fibrosis and scar tissue than in the normal myocardium, the signal in the T1-weighted image is enhanced because the contrast agent decreases the longitudinal relaxation time T1 of the biological tissue. The magnetic resonance imaging method is particularly suitable for scar detection of target tissues.

Figure 1 shows a schematic flow diagram of a magnetic resonance imaging method 100 according to an embodiment of the invention. As shown in fig. 1, the magnetic resonance imaging method 100 includes the following steps.

And step S110, obtaining the cardiac gating trigger time Ttrigger of the subject. The motion of the heart affects the imaging effect. The heart rate is different for each subject. An Electrocardiogram (ECG) may be acquired by attaching electrodes to the skin surface of the chest of a subject and by an electrocardiographic monitoring device. In an electrocardiogram, the time interval between two R-waves is called the cardiac cycle (RR). The cardiac cycle may be determined by detecting the R-wave. Each image signal in the imaging sequence is acquired during a respective cardiac cycle. It is understood that the image signals are used to generate corresponding magnetic resonance images.

And in each cardiac cycle, determining the moment of acquiring the image signal according to the electrocardio gating signal. Since image signal acquisition needs to be performed at a time when the heart is relatively stationary, e.g., at the end of diastole, to obtain optimal cardiac motion compensation, only a small fraction of the time is available for data acquisition in each cardiac cycle. And after the electrocardio-gating trigger time Ttrigger from the R peak, the image signal is collected. The acquired image signals can be less disturbed by the motion of the heart by means of the cardiac gating technique. It is understood that the triggering time Ttrigger for the cardiac gating can be preset by the scanning personnel according to experience, and may be, for example, 500 and 700 ms.

Step S120, determining a first time interval TD between an inversion recovery pulse and a T2 preparation pulse for a first cardiac cycle₁T2 duration TE of the preparation pulse₁And a second time interval TD 2 between the preparation pulse and the first data acquisition radio frequency pulse IMG₂。

FIG. 2 shows a schematic of an imaging sequence according to one embodiment of the present inventionFigure (a). Two cardiac cycles of the imaging sequence are shown in figure 2. It will be appreciated that more imaging cycles are included in the imaging sequence, not shown in fig. 2. In the first cardiac cycle, the inversion recovery pulse IR, T2 is used to prepare the pulse T₂PREP₁And a first data acquisition radio frequency pulse IMG.

With the inversion recovery pulse IR, the magnetization vector can be inverted and the image signal will gradually recover from "-1" to "+ 1". If data is acquired at the time of the zero crossing of the normal myocardial signal, an image of maximum contrast can be obtained.

Adding a T2 preparation pulse T after the inversion recovery pulse IR₂PREP₁The contrast of the image is adjusted according to the transverse relaxation time T2 of different tissues. T2 preparation pulse T₂PREP₁The tissue magnetization vector is attenuated according to the weighting of T2, and the magnetization vector is recovered slowly due to the larger T2 value of blood, thereby achieving the effect of black blood. Wherein the inversion recovery pulses IR and T2 prepare the pulse T₂PREP₁The time interval therebetween being a first time interval TD₁T2 preparation pulse T₂PREP₁Is TE₁。

At T2 a pulse T is prepared₂PREP₁Thereafter, a first data acquisition radio frequency pulse IMG is excited. T2 preparation pulse T₂PREP₁And the time interval between the first data acquisition radio frequency pulses IMG is a second time interval TD₂。

In this step S120, a first time interval TD of the imaging parameters is determined₁Duration TE₁And a second time interval TD₂. In one example, this may be determined manually by taking measurements or settings for the subject based on the experience of a physician. For example, prepare pulse T for T2₂PREP₁Duration TE of₁Since T2 prepares the pulse T₂PREP₁The intensity of the image signal is reduced and thus can be set to a small value; but if the duration TE₁Too small may result in insufficient compression of the blood signal in the image signal, resulting in a reduced contrast of the image. Thus, in view of the above, one can continue to considerTime TE₁Set to a value between 20-30ms, for example 25 ms. First time interval TD₁And a second time interval TD₂May be set according to the T1 and T2 values of the target tissue to be imaged.

Step S130, in the first cardiac cycle, according to the first time interval TD₁Duration TE₁A second time interval TD₂And an electrocardio gate control trigger time Ttrigger to sequentially excite an inversion recovery pulse IR and a T2 preparation pulse T₂PREP₁And a first data acquisition radio frequency pulse IMG.

As described above and shown in fig. 2, the first data acquisition rf pulse IMG is activated after Ttrigger time from the occurrence of the R peak. A time interval (TE) prior to and spaced from a time of excitation of the first data acquisition radio frequency pulses IMG₁+TD₂) At the moment of time TE of excitation duration₁T2 preparation pulse T₂PREP₁. Preparing for a pulse T at excitation T2₂PREP₁Before the time of (a) and with the excitation T2 preparation pulse T₂PREP₁Time interval TD₁The inversion recovery pulse IR is excited.

Upon excitation of the first data acquisition radio frequency pulse IMG, an acquisition inversion recovery T2 prepares an image signal. The inversion recovery T2 prepares that the image signal is a signal that actually generates a magnetic resonance image directly.

Optionally, the first data acquisition radio frequency pulse IMG for acquiring data is any radio frequency pulse that can be used for magnetic resonance imaging, such as a Spoiled Gradient Echo (SPGR), a Balanced Steady State free precession sequence (BSSFP), a Spin Echo (SE), or a plane Echo (EPI). And a proper data reading mode is preferably adopted according to needs, so that the requirement of the imaging process on the uniformity of the magnetic field intensity can be remarkably reduced, and the scheme can be applied to a high-field (such as 3T) magnetic resonance system. Preferably, SPGR is used. The SPGR is insensitive to the inhomogeneity of a magnetic field, has no memory effect, basically has no preparation process approaching a steady state, and is more suitable for the condition that data acquisition needs to be completed in a segmented mode, namely more suitable for three-dimensional data scanning.

Data acquisition radio frequency pulses cause the net magnetization vector to deviate from the main magnetic field direction. The angle of the net magnetization vector deviating from the main magnetic field direction under the action of the data acquisition radio frequency pulse can be called as the flip angle of the data acquisition radio frequency pulse. In the data acquisition operation, the flip angle of the data acquisition radio frequency pulse determines the magnitude of the acquirable signal, i.e. the projection of the magnetization vector onto a plane (x-y plane) perpendicular to the direction of the main magnetic field. If the magnetization vectors before flipping are the same, the larger the flip angle, the larger the projection onto the x-y plane, and the larger the signal acquired. Thus, the first data acquisition radio frequency pulses IMG excited in the first cardiac cycle may employ a larger flip angle, for example: 15 to 20 degrees.

In addition, the excitation of the first data acquisition radiofrequency pulse IMG is also based on the first respiratory navigation signal iNAV₁And (4) controlling. By monitoring the change of the position of the diaphragm muscle along with the respiratory motion, the position change of the heart along with the respiratory motion can be indirectly estimated. It is desirable that the acquired image signals are acquired while the diaphragm muscle is in a desired position.

Collecting a first respiratory navigation signal iNAV in a short time before a time period Ttrigger from the R peak of the cardiac gating signal₁. According to the first respiratory navigation signal iNAV₁And judging whether the current moment meets a preset condition, namely whether the thoracic diaphragm is in an expected position at the current moment. In one example, the first respiratory navigation signal iNAV is acquired₁Thereafter, the acquisition inversion recovery T2 prepares an image signal. According to the collected respiratory navigation signal iNAV₁It is determined whether the acquired inversion recovery T2 preparation image signal meets the requirements of respiratory motion compensation, i.e., it is determined whether the inversion recovery T2 preparation image signal acquired during the present cardiac cycle is valid. Thereby deciding whether to re-perform the acquisition operation or to jump to the next signal acquisition operation. In the subsequent imaging process, the image signal is prepared only with the effective inversion recovery T2, and the image signal is prepared ignoring the ineffective inversion recovery T2. In another example, respiration is being acquiredNavigation signal iNAV₁Then, according to the respiratory navigation signal iNAV₁And judging whether the current time meets a preset condition. In accordance with the respiratory navigation signal iNAV₁In the case where it is determined that the current time meets the predetermined condition, the image signal acquisition operation is performed until the inversion recovery T2 of this step is completed to prepare for the signal acquisition operation. The respiratory navigation technology is utilized, so that the subject can freely breathe in the magnetic resonance imaging process. But also enlarges the imaging visual field and improves the spatial resolution of the image.

Step S140, in the second cardiac cycle, according to the triggering time Ttrigger of the cardiac gating, based on the second respiratory navigation signal iNAV₂Activates the second data acquisition radio frequency pulses REF and acquires the reference image signals.

Similar to the first cardiac cycle, in the second cardiac cycle, a second data-acquisition radio-frequency pulse REF is excited after a time of Ttrigger from the occurrence of the R-peak. Upon excitation of the second data acquisition radio frequency pulses REF, reference image signals are acquired. The reference image signal is used to correct the phase of the inversion recovery T2 ready image signal. The positive and negative values of the intensity of the inversion recovery T2 preparation image signal can thereby be retained, thereby ensuring the contrast of the magnetic resonance image. The imaging sequence of an embodiment of the present invention may be referred to as a phase sensitive sequence, which includes the first cardiac cycle and the second cardiac cycle described above.

The smaller the projection of the magnetization vector in the direction of the original parallel main magnetic field, the longer the time it takes to recover to the steady state magnetization vector. Therefore, when the flip angle of the data acquisition radio frequency pulse is small, although the acquirable signal is small, the speed of the magnetization vector returning to the steady state is fast. Thus, the second data acquisition radio frequency pulse REF excited in the second cardiac cycle may employ a smaller flip angle, e.g., 5 to 10 degrees, than the first data acquisition radio frequency pulse IMG excited in the first cardiac cycle. Therefore, the inversion recovery T2 preparation image signals acquired in the first cardiac cycle can be ensured to be strong enough to be used for generating the magnetic resonance image; and the magnetization vector can be quickly restored to a stable state after the reference image signal is acquired in the second cardiac cycle, so that the quality of the magnetic resonance image is further ensured.

The second data acquisition radio frequency pulse REF may employ a data acquisition radio frequency pulse similar to the first data acquisition radio frequency pulse IMG, such as SPGR.

Similar to the first data acquisition radio frequency pulse IMG, the second data acquisition radio frequency pulse REF is based on a second respiratory navigation signal iNAV₂And (4) controlling. And will not be described in detail herein for the sake of brevity.

First respiratory navigation signal iNAV in first cardiac cycle₁And a second respiratory navigation signal iNAV in a second cardiac cycle₂Is independent of the control of (a). The method is used for respectively carrying out respiratory navigation on the acquisition of the inversion recovery T2 preparation image signal and the reference image signal in the phase sensitive sequence, and the image signal which meets the respiratory receiving condition can be acquired without simultaneously meeting the respiratory receiving condition of the two image signals. In other words, for any one of the inversion recovery T2 preparation image signal and the reference image signal, it is only necessary that it individually satisfies the breath reception condition to retain the acquired data until the required data acquisition is completed.

In one example, the phase sensitive sequence includes a plurality of repeating units. Each repeating unit comprises two cardiac cycles, the first cardiac cycle being the first cardiac cycle in the repeating unit and the second cardiac cycle being the second cardiac cycle in the repeating unit. In other words, the first cardiac cycle and the second cardiac cycle are two consecutive cardiac cycles that alternate with each other in a phase sensitive sequence. If the inversion recovery T2 acquired for the first cardiac cycle prepares the image signal sig1 to satisfy the respiratory reception condition and the reference image signal sig2 acquired for the second cardiac cycle does not satisfy, the signal sig1 is received but the signal sig2 is rejected and the next repeating unit is continued. Since two image signals sig1 and sig2 are correlated, a repeating unit acquisition pattern is also needed when one of the signals is acquired completely until the other signal is also acquired completely. At this point, the complete signal has been acquired without receiving new data.

It is understood that k-space is the data space in which the acquisition operation is performed. k-space can be divided into segments. The image signal used to fill each segment can be acquired within one cardiac cycle. The image signals acquired for several cardiac cycles together can fill the complete k-space (i.e., the acquisition is complete) for reconstruction of the image. Here, the first cardiac cycle includes one or more cardiac cycles, and the number of cardiac cycles in the second cardiac cycle is the same as the first cardiac cycle due to the correlation between the two image signals sig1 and sig 2. All the signals sig1 acquired in the first cardiac cycle fill the k-space corresponding to the inversion recovery T2 preparation image. All signals sig2 acquired for the second cardiac cycle together fill k-space corresponding to the reference image. Thus, a magnetic resonance image can be reconstructed using the image signal prepared by the inversion recovery T2 with the reference image signal as a phase reference.

In the foregoing example, the first cardiac cycle and the second cardiac cycle alternate. That is, the inversion recovery T2 prepares for the image signal and the reference image signal to be alternately acquired. Thus, the reference image signal is more closely matched to the true valid inversion recovery T2 preparation image signal, and the ideal magnetic resonance image can be generated without complex calculations to register the reference image signal with the latter.

Alternatively, the first cardiac cycle and the second cardiac cycle may be other distributions in the phase sensitive sequence. For example, all first cardiac cycles precede the second cardiac cycle. Thus, first, the acquisition inversion recovery T2 prepares the image signal until it fills its k-space; the reference image signal is then acquired until it fills its k-space. For another example, q second cardiac cycles are set for every p first cardiac cycles set. Even further, the first cardiac cycle and the second cardiac cycle may be completely randomly distributed in the phase sensitive sequence.

In these alternative examples, registration calculations have to be performed to ensure the quality of the generated magnetic resonance images, since the first cardiac cycle may be temporally spaced from the corresponding second cardiac cycle by a large interval.

In step S150, a magnetic resonance image is generated from the inversion recovery T2 preparation image signal and the reference image signal. In this step, the phase of the inversion recovery T2 preparatory image signal is corrected based on the reference image signal, that is, the positive and negative values of the intensity of the inversion recovery T2 preparatory image signal are determined, whereby a magnetic resonance image in which the image contrast is maintained is generated based on the inversion recovery T2 preparatory image signal.

In the magnetic resonance imaging method, a three-dimensional image signal is acquired in each of two cardiac cycles. The image signals acquired in the first cardiac cycle are obtained using inversion recovery and a T2 preparation pulse, which enables the generation of phase sensitive images of dark blood contrast, and the image signals acquired in the second cardiac cycle can be used as a reference for phase sensitive image reconstruction. The acquisition of the two image signals adopts an independent respiration navigation method, so that the acquisition of the two image signals can obtain higher navigation efficiency. Thereby, the generated magnetic resonance image can be made higher in contrast and spatial resolution.

Fig. 3a and 3b show atrial magnetic resonance images from the same subject after atrial radio frequency ablation surgery according to prior art and one embodiment of the present invention, respectively. Fig. 3c and 3d show enlarged views of corresponding parts in fig. 3a and 3b, respectively. As shown in fig. 3a, 3b, 3c and 3d, in the magnetic resonance image obtained by the magnetic resonance imaging method according to the embodiment of the present invention, blood is significantly darkened, and thus scar tissue is more significant.

Figure 4 shows a schematic representation of the contrast to noise ratio between different types of tissue in a magnetic resonance image according to the prior art and one embodiment of the invention. In the histogram in fig. 4, the left rectangle in each pair of rectangles from left to right represents the contrast to noise ratio according to the prior art, and the right rectangle represents the contrast to noise ratio according to an embodiment of the present invention. As shown in fig. 4, although the comparative signal-to-noise ratios of scar tissue and normal tissue obtained according to the embodiment of the present invention were slightly lower than those according to the prior art, the comparative signal-to-noise ratios of scar tissue and blood obtained according to the embodiment of the present invention were significantly higher than those obtained according to the prior art; but also the significant reduction obtained according to the embodiments of the present invention compared to the comparative signal-to-noise ratio of blood and normal tissue obtained according to the prior art.

Thus, magnetic resonance images generated in accordance with embodiments of the present invention desirably reflect the myocardial tissue status of a subject, particularly scar tissue therein. Thus, the magnetic resonance imaging method is particularly suitable for scar detection.

Fig. 5 shows a schematic view of an imaging sequence according to another embodiment of the invention. Only two cardiac cycles of the imaging sequence are also shown in fig. 5. The respective pulses in the first cardiac cycle in fig. 5 are the same as the respective pulses in the first cardiac cycle in fig. 2, and are not described again here for brevity. Each pulse in the second cardiac cycle in fig. 2 is also the same as the corresponding pulse in the second cardiac cycle in fig. 5, and this part of the pulses is not repeated. The imaging sequence shown in figure 5 differs from the imaging sequence shown in figure 2 in that in the second cardiac cycle of figure 5 a preparation pulse T2 is excited T2 prior to the excitation of the first data acquisition radio frequency pulse IMG in the first cardiac cycle₂PREP₁Similarly, prior to the excitation of the second data acquisition radio frequency pulse REF and the acquisition of the reference image signals, a preparation pulse T is also excited T2₂PREP₂. T2 preparation pulse T in the second cardiac cycle₂PREP₂Duration TE of₂With the preparation pulse T of T2 in the first cardiac cycle₂PREP₁Duration TE of₁May be the same or different.

In the second cardiac cycle, T2 preparation pulse T is also fired₂PREP₁Does not affect the acquisition of the reference image signal, and does not affect the acquisition of the inversion recovery T2 preparation image signal. However, the pulse T is prepared by adding T2 in the second cardiac cycle₂PREP₁Angiographic imaging can be simultaneously obtained providing anatomical information of the target tissue. For example, for atrial imaging, while magnetic resonance images are acquired, angiographic images of the vicinity of the atrium can be acquired, providing anatomical information of the atrium and surrounding pulmonary veins.

By the aid of the scheme, a subject is prevented from physical examination for multiple times, time efficiency of an operator is remarkably improved, and user experience is better.

As shown in fig. 2 and 5, a grease pressing operation (FS) may be performed prior to energizing the first data acquisition radio frequency pulse IMG and the second data acquisition radio frequency pulse REF, respectively. The fat pressing operation is beneficial to reducing breathing artifacts and obviously improving the imaging quality.

It is understood that the image signal acquisition in step S130 and step S140 can adopt a parallel sampling technique and any other k-space down-sampling technique.

Illustratively, the above step S120 determines, for a first cardiac cycle, a first time interval TD between an inversion recovery pulse and a T2 preparation pulse in the cardiac cycle₁T2 duration TE of the preparation pulse₁And a second time interval TD between the T2 preparation pulse and the first data acquisition RF pulse₂Comprises the following steps. First, basic physical parameters of magnetic resonance are obtained for normal myocardial tissue and blood of a subject, respectively. Then, the duration TE of the preparation pulse is preset T2₁. For example, the duration may be set to any value between 20-30 ms. Finally, according to the basic physical parameters and the duration TE₁Calculating a first time interval TD₁And a second time interval TD₂。

At a determined magnetic field strength, different tissues have different values of the physical parameter. When the biological tissue changes, the value of the physical parameter changes accordingly. T2 duration TE of preparation pulse₁Directly influencing the aforesaid first time interval TD₁And a second time interval TD₂. In this solution, the duration TE of the preparation pulse is preset based on the basic physical parameters of the magnetic resonance of the normal myocardial tissue and blood of the subject and the T2₁To determine the first time interval TD₁And a second time interval TD₂. Thus, the first time interval TD determined₁And a second time interval TD₂Can darken normal myocardial tissues and blood and improve the contrast of a magnetic resonance image.

Illustratively, the basic physical parameters include a longitudinal relaxation time T1 and a transverse relaxation time T2. The longitudinal relaxation time T1 can be obtained from the pre-scan T1 parametric map. Alternatively, the longitudinal relaxation time T1 may be set empirically, for example, the longitudinal relaxation time T1 of normal myocardium is set to 550ms, the longitudinal relaxation time T1 of blood is set to 350ms, and the longitudinal relaxation time T1 of scar tissue is set to 200 ms. The transverse relaxation time T2 may be set according to an empirical value. For example, the transverse relaxation time T2 of normal myocardial tissue is set to 40ms, the transverse relaxation time T2 of blood is set to 120ms, and the transverse relaxation time T2 of scar tissue is set to 70 ms.

The above steps are based on basic physical parameters and duration TE₁Calculating the first time interval TD₁And said second time interval TD₂Comprises the following steps.

1) Respectively taking normal myocardial tissue and blood as target tissues to establish a steady-state magnetization vector M of the target tissues_SSWith a longitudinal relaxation time T1, a transverse relaxation time T2, a first time interval TD₁Duration TE₁And a second time interval TD₂A first mathematical relationship therebetween.

Steady state magnetization vector M_SSIs the longitudinal magnetization vector intensity at the time before the excitation of the inversion recovery pulse IR

Is considered to be the longitudinal magnetization vector in the first cardiac cycle at the beginning of the imaging sequenceIn the aforementioned example of including a plurality of repeating units consisting of the first cardiac cycle and the second cardiac cycle in the phase sensitive sequence for imaging, after one repeating unit, i.e., one cycle, through inversion recovery, T2 attenuation by the T2 preparation pulse, disturbance of two image acquisitions, and T1 recovery process of an intermediate time, at the first cardiac cycle of the next repeating unit, the longitudinal magnetization vectorStill return to the steady state and still,

in this step, the steady state magnetization vector M of the target tissue can be adjusted_SSDenoted longitudinal relaxation time T1, transverse relaxation time T2, first time interval TD₁Duration TE₁A second time interval TD₂And other mathematical functions that affect the parameters. Illustratively, the mathematical function may be obtained using bloch's equation.

2) Respectively using normal myocardial tissue and blood as target tissue, and establishing image signal intensity of target tissue according to the following formulaAnd the steady state magnetization vector M_SSLongitudinal relaxation time T1, transverse relaxation time T2, first time interval TD₁Duration TE₁And a second time interval TD₂The second mathematical relationship between:

in the above mathematical relationship, the image signal intensity of the target tissue is determinedExpressed as the steady state magnetization vector M_SSFirst time interval TD₁Duration TE₁And a second time interval TD₂Is used as a mathematical function of (2).

3) Based on the fact that the image signal intensity of normal myocardial tissue is 0 and the image signal intensity of blood is minimum, determining a first time interval TD according to a first mathematical relationship and a second mathematical relationship₁And a second time interval TD₂。

Can make simultaneous equations to let the image signal intensity of normal myocardial tissue

And the image signal intensity of bloodAre all 0, i.e.:

then, based on the first mathematical relation and the second mathematical relation, the equation is solved, and the first time interval TD is obtained through calculation₁And a second time interval TD₂。

In some cases, the simultaneous equations may not have a solution, i.e., the image signal intensity of normal myocardial tissue cannot be madeAnd the image signal intensity of blood

And is also 0. In this case, the intensity of the image signal of the normal myocardial tissue is selected0, intensity of image signal of bloodFirst time interval TD when taking the minimum value₁And a second time interval TD₂。

In the above-described embodiment, the first time interval TD is calculated in which the image signal intensity of the normal myocardial tissue is 0 and the image signal intensity of the blood is minimized₁And a second time interval TD₂. According to the first time interval TD₁And a second time interval TD₂The implemented imaging sequence further ensures that the contrast between the scar and the adjacent blood signals in the magnetic resonance image and normal myocardial tissue is large.

Steady state magnetization vector M_SSThe influencing parameters comprise a T1 value, a T2 value, an electrocardio gating triggering time Ttrigger, a heart rate, a flip angle of a data acquisition radio frequency pulse, repetition time, echo number and the like of target tissues. Therefore, the temperature of the molten metal is controlled,the first mathematical relationship may be established based on these influencing parameters.

In the example of the imaging sequence shown in fig. 2, the magnetization vector reaches a steady state before the inversion pulse IR is excited in the first cardiac cycle, as described earlier.

Preparing pulse T at excitation inversion recovery pulse IR and T2₂PREP₁Thereafter and at a time prior to the excitation of the first data acquisition radio frequency pulse IMG, image signal intensity

Can be expressed as follows:

image signal intensity at a time after the first data acquisition radio frequency pulse IMG is excited

Can be expressed as follows:

wherein TR denotes the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse, which are identical, the repetition time being determined to a minimum value according to the magnetic resonance imaging system, e.g. 5.4ms α₁Representing a flip angle, e.g. 18 degrees, of the first data acquisition radio frequency pulse. n represents the number of echoes of the data acquisition radio frequency pulse. The number of echoes n may be given according to an acquisition time (e.g. 100 to 200ms) limit, e.g. the number of echoes is 30.

In the second cardiac cycle, the image signal strength at a time before the second data acquisition radio frequency pulse REF is excited

Can be expressed as follows:

where R1 is RR-nxtr, and RR denotes the cardiac cycle of the subject.

In the second cardiac cycle, the image signal strength at a time after the excitation of the second data acquisition radio frequency pulse REFCan be expressed as follows:

wherein, α₂Representing a flip angle of the second data acquisition radio frequency pulse, e.g., 10 degrees.

Image signal intensity before inversion recovery pulse IR in the next first cardiac cycle

Can be expressed as:

wherein RX is RR- (TD)₁+TE₁+TD₂)-n×TR。

The image signal intensityI.e. equal to the steady state magnetization vector M_SSI.e. by

The steady state magnetization vector M can be obtained according to the formula_SSThe mathematical relational expression of (a):

wherein the content of the first and second substances,

in the example of the imaging sequence shown in fig. 5, the preparation pulse T may be preset T2 for the second cardiac cycle₂PREP₂Duration TE of₂. As previously described, it may prepare for pulse T with T2 in the first cardiac cycle₂PREP₁Duration TE of₁The same or different. Similarly, the magnetization vector reaches a steady state before the inversion pulse IR is excited in the first cardiac cycle.

Preparing pulse T at excitation inversion recovery pulse IR and T2₂PREP₁Thereafter and at a time prior to the excitation of the first data acquisition radio frequency pulse IMG, image signal intensityCan be expressed as follows:

image signal intensity at a time after the first data acquisition radio frequency pulse IMG is excitedCan be expressed as follows:

wherein TR represents the repetition time of the first data acquisition RF pulse and the second data acquisition RF pulse, which are identical, α₁A flip angle representative of the first data acquisition radio frequency pulse; n represents the data acquisition radio frequencyThe number of echoes of the pulse. These parameters are introduced in the above examples and will not be described herein for brevity.

In the second cardiac cycle, T2 preparation pulse T is excited₂PREP₂Previous time, image signal intensityCan be expressed as follows:

wherein R1 is RR-n × TR-TE₂And RR denotes the cardiac cycle of the subject.

Preparing for a pulse T at excitation T2₂PREP₂Image signal strength at a time after and before the activation of the second data acquisition radio frequency pulse REF

Can be expressed as follows:

in the second cardiac cycle, the image signal strength at a time after the excitation of the second data acquisition radio frequency pulse REFCan be expressed as follows:

wherein, α₂Representing a flip angle of the second data acquisition radio frequency pulse, e.g., 10 degrees.

Image signal intensity before inversion recovery pulse IR in the next first cardiac cycle

Can be expressed as:

wherein RX is RR- (TD)₁+TE₁+TD₂)-n×TR。

The image signal intensity

I.e. equal to the steady state magnetization vector M_SSI.e. by

The steady state magnetization vector M can be obtained according to the formula_SSThe mathematical relational expression of (a):

wherein the content of the first and second substances,

RX＝RR-(TD₁+TE₁+TD₂)-n×TR。

the mathematical expression modes of the respective steady-state magnetization vectors in different examples are given above, and the steady-state magnetization vector expressions obtained by the two modes ideally simulate the real steady-state magnetization vector in the imaging sequence, so that the imaging effect is further ensured.

According to yet another aspect of the invention, a magnetic resonance imaging apparatus is also provided. The system includes a processor and a memory. The memory stores computer program instructions for implementing the steps in the method of magnetic resonance imaging according to an embodiment of the invention. The processor is adapted to execute the computer program instructions stored in the memory to perform the respective steps of the magnetic resonance imaging method according to an embodiment of the invention.

According to yet another aspect of the present invention, there is also provided a storage medium having stored thereon program instructions, which, when executed by a computer or processor, cause the computer or processor to perform the respective steps of the magnetic resonance imaging method of an embodiment of the present invention and to implement the respective modules in the magnetic resonance imaging apparatus according to an embodiment of the present invention. The storage medium may include, for example, a storage component of a tablet computer, a hard disk of a personal computer, Read Only Memory (ROM), Erasable Programmable Read Only Memory (EPROM), portable compact disc read only memory (CD-ROM), USB memory, or any combination of the above storage media. The computer-readable storage medium may be any combination of one or more computer-readable storage media.

In the description provided herein, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the invention and aiding in the understanding of one or more of the various inventive aspects. However, the method of the present invention should not be construed to reflect the intent: that the invention as claimed requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

It will be understood by those skilled in the art that all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where such features are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.

It should be noted that the word 'comprising' does not exclude the presence of elements or steps not listed in a claim. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names. The letters one, two, three, etc. are respectively equivalent to the numbers 1, 2, 3, etc. corresponding to the letters. Thus, the first, second, and third etc. are equivalent to the 1 st, 2 nd, and 3 rd etc. corresponding thereto, respectively.

The above description is only for the specific embodiment of the present invention or the description thereof, and the protection scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and the changes or substitutions should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.