CN111631713B - Magnetic resonance imaging method, equipment and storage medium - Google Patents

Abstract

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 of the preparation pulse TE ₁ And T2 time interval TD between the preparation pulse and the first data acquisition radio frequency 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 collect inversion recovery T2 preparatory image signals when the first data acquisition radio frequency pulse is fired, wherein firing the first data acquisition radio frequency pulse is further based on control of the respiratory navigation signal; 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.

Description

Magnetic resonance imaging method, equipment and storage medium

technical field

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

Background technique

Magnetic resonance imaging technology uses nuclear magnetic resonance phenomenon to image the human body, which has become a common medical imaging examination method and can be applied to various medical application scenarios. For example, atrial fibrillation is one of the most common arrhythmias in clinical practice, and radiofrequency ablation of the left atrium and pulmonary vein isolation are the main treatments to control atrial fibrillation. The degree of atrial fibrosis and the scar tissue after radiofrequency ablation are related to the recurrence of atrial fibrillation. Therefore, the information of atrial fibrosis and the anatomical structure of the surrounding tissue can help decision-making before ablation, and the scar injury produced by ablation can also reflect the prognosis. Magnetic resonance imaging of the atrium can advantageously help physicians understand the subject's anatomical information so that they can make rational medical decisions.

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

For the movement of the heart itself, the method of ECG gating can be used to detect the ECG signal through the body surface electrodes to reflect the heart movement cycle, and then perform data collection during the period when the heart movement is relatively static. Usually the acquisition time of one cardiac cycle is 100-200ms, so the data of one image needs to be acquired in multiple cardiac cycles.

For respiratory motion compensation, commonly used methods include breath-hold and breath navigation. The breath-hold sequence requires the subjects to cooperate with holding their breath, and scan during the breath-hold to exclude the influence of breathing motion. A breath-holding time is usually about 10 seconds, limited by the scanning time, it can only be used for two-dimensional imaging or multi-layer two-dimensional imaging, and the imaging resolution is also limited. This method is also affected by the subject's own physiological condition, and the inability to complete the breath-hold will affect the image quality. The method of breathing navigation allows the subject to breathe freely, excites a columnar region located at the diaphragm and performs one-dimensional imaging for monitoring breathing movements. In the data acquisition of each cardiac cycle, only the data when the respiratory motion reaches a specific position will be retained, and the actual scan time of this method depends on the respiratory navigation efficiency. Due to the extended acquisition time, it can be used for 3D high-resolution imaging.

In some application scenarios, such as the above-mentioned imaging of atrial scars, the thickness of the atrial wall is very thin, usually 2-4mm, which is easily affected by the partial volume effect. Therefore, it is necessary to improve the contrast between the scar and the adjacent blood signals. Higher resolution than ventricular imaging is required. Since the heart is affected by its own motion and breathing motion, the breath-holding method is generally used in the existing imaging sequence, so the scanning time and resolution will be limited, and the imaging scanning time based on the existing breathing navigation method will also be limited. Effects of respiratory navigation efficiency. As a result, an ideal magnetic resonance image cannot be obtained.

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

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problems. According to one aspect of the present invention, a magnetic resonance imaging method is provided, comprising:

Obtain the ECG gating trigger time Ttrigger of the subject;

For the first cardiac cycle, determine a first time interval TD ₁ between the inversion recovery pulse and the T2 prep pulse, the duration of the T2 prep pulse TE ₁ , and the second time interval between the T2 prep pulse and the first data acquisition radio frequency pulse time interval TD ₂ ;

In the first cardiac cycle, inversion recovery is sequentially excited according to the first time interval TD ₁ , the duration TE ₁ , the second time interval TD ₂ and the ECG gating trigger time Ttrigger the pulse, the T2 preparation pulse and the first data acquisition radio frequency pulse, and the inversion recovery T2 preparation image signal is collected 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 the first respiratory navigation signal;

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

Exemplarily, in the second cardiac cycle, before the excitation of the second data acquisition radio frequency pulse and the acquisition of the reference image signal, the T2 preparation pulse is also excited.

Exemplarily, the first cardiac cycle is the first cardiac cycle in the repeating unit in the phase-sensitive sequence, and the second cardiac cycle is the second cardiac cycle in the repeating unit.

Exemplarily, the determining a first time interval TD ₁ between the inversion recovery pulse and the T2 prepare pulse, the duration of the T2 prepare pulse TE ₁ , and the second time interval between the T2 prepare pulse and the first data acquisition radio frequency pulse. Time interval TD ₂ includes:

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

preset the duration TE ₁ ;

The first time interval TD ₁ and the second time interval TD ₂ are calculated according to the basic physical parameters and the duration TE ₁ .

Exemplarily, the basic physical parameters include a longitudinal relaxation time T1 and a transverse relaxation time T2, and the calculating the _first time interval TD1 and the _second time interval TD2 includes:

Taking the normal myocardial tissue and the blood as the target tissue respectively, establish the steady-state magnetization vector M _SS of the target tissue, the longitudinal relaxation time T1, the transverse relaxation time T2, and the _first time interval TD1 , the first mathematical relationship between the duration TE ₁ and the second time interval TD ₂ ;

与所述稳态磁化向量M_SS、所述纵向弛豫时间T1、所述横向弛豫时间T2、所述第一时间间隔TD₁、所述持续时间TE₁和所述第二时间间隔TD₂之间的第二数学关系：Taking the normal myocardial tissue and the blood as the target tissue respectively, the image signal intensity of the target tissue is established according to the following formula

with the steady state magnetization vector M _SS , the longitudinal relaxation time T1 , the transverse relaxation time T2 , the first time interval TD ₁ , the duration TE ₁ and the second time interval TD ₂ The second mathematical relationship between:

Based on the image signal intensity of the normal myocardial tissue being 0 and the image signal intensity of the blood being the minimum, the first time interval TD1 and the second time interval TD1 are determined according to the _first mathematical relationship and the second mathematical relationship time interval TD ₂

Exemplarily, the first mathematical relationship is expressed as:

in,

RX=RR-(TD ₁ +TE ₁ +TD ₂ )-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;

α ₁ represents the flip angle of the first data acquisition radio frequency pulse;

α ₂ represents the flip angle of the second data acquisition radio frequency pulse;

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

Exemplarily, the method further includes: for the second cardiac cycle, presetting the duration TE ₂ of the T2 preparation pulse;

The first mathematical relationship is expressed as:

in,

RX=RR-(TD ₁ +TE ₁ +TD ₂ )-n×TR;

R1=RR-n×TR-TE ₂ ;

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;

α ₁ represents the flip angle of the first data acquisition radio frequency pulse;

α ₂ represents the flip angle of the second data acquisition radio frequency pulse;

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

Exemplarily, 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.

Exemplarily, the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse are both a destructed gradient echo sequence, a balanced steady state free precession sequence, a spin echo sequence or an echo plane sequence.

Exemplarily, in each cardiac cycle, before the excitation of the first data acquisition radio frequency pulse and the excitation of the second data acquisition radio frequency pulse, the fat reduction operation is performed respectively.

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 stores computer program instructions, and the computer program instructions are used for execution when the processor is run. The above magnetic resonance imaging method.

According to another aspect of the present invention, a storage medium is also provided, and program instructions are stored on the storage medium, and the program instructions are used to execute the above magnetic resonance imaging method when running.

According to the magnetic resonance imaging method, device, and storage medium of the embodiments of the present invention, a three-dimensional image signal is collected in two cardiac cycles respectively. Image signals acquired in the first cardiac cycle are obtained using inversion recovery and T2 prep pulses, which can generate a phase-sensitive image with dark blood contrast, and 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 the method of independent breathing navigation, which enables the acquisition of the image signals to achieve higher navigation efficiency. Thereby, the contrast and spatial resolution of the generated magnetic resonance image can be made higher.

The above description is only an overview of the technical solutions of the present invention, in order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand , the following specific embodiments of the present invention are given.

Description of drawings

The above and other objects, features and advantages of the present invention will become more apparent from the detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. The accompanying drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification, and together with the embodiments of the present invention, they are used to explain the present invention, and do not limit the present invention. In the drawings, the same reference numerals generally represent the same signal or pulse or the like.

Fig. 1 shows a schematic flowchart of a magnetic resonance imaging method according to an embodiment of the present invention;

Figure 2 shows a schematic diagram of an imaging sequence according to an embodiment of the present invention;

Fig. 3a and Fig. 3b show atrial magnetic resonance images from the same subject undergoing atrial radiofrequency ablation according to the prior art and an embodiment of the present invention, respectively;

Figures 3c and 3d show enlarged images of corresponding parts in Figures 3a and 3b, respectively;

FIG. 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 present invention; and

FIG. 5 shows a schematic flowchart of a magnetic resonance imaging method according to another embodiment of the present invention.

Detailed ways

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. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of the embodiments of the present invention, and it should be understood that the present invention is not limited by the example embodiments described herein. Based on the embodiments of the present invention described in the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

In order to obtain images with 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 the atrium, ventricle, and even blood vessels of the subject. The magnetic resonance imaging method uses delayed enhancement imaging technology. Subjects were injected with gadolinium contrast and then imaged approximately 10 minutes later. Taking magnetic resonance imaging of the atrium as an example, at this time, the retention of contrast agent in myocardial fibrosis and scar tissue will be more than that in normal myocardium. Because the contrast agent will reduce the longitudinal relaxation time T1 of biological tissue, the signal in the T1-weighted image will be reduced. will be enhanced. The magnetic resonance imaging method is especially suitable for scar detection of target tissue.

FIG. 1 shows a schematic flowchart of a magnetic resonance imaging method 100 according to an embodiment of the present invention. As shown in FIG. 1 , the magnetic resonance imaging method 100 includes the following steps.

Step S110, obtaining the ECG gating trigger time Ttrigger of the subject. The movement of the heart can affect the imaging results. The heart rate of each subject was different. An electrocardiogram (ECG) can be obtained by attaching electrodes to the skin surface of the subject's chest and by means of an electrocardiogram monitoring device. In an electrocardiogram, the time interval between two R waves is called the cardiac cycle (RR). The cardiac cycle can be determined by detecting R waves. Each image signal in the imaging sequence is acquired separately during one cardiac cycle. It will be appreciated that the image signals are used to generate corresponding magnetic resonance images.

In each cardiac cycle, according to the ECG gating signal, the time to acquire the image signal is determined. Since image signal acquisition needs to be performed when the heart is relatively still, such as a moment at the end of diastole, in order to obtain optimal cardiac motion compensation, there is only a small period of time suitable for data acquisition in each cardiac cycle. After the ECG gate trigger time Ttrigger starts from the R peak, the image signal starts to be collected. Through the ECG gating technology, the acquired image signal can be less disturbed by the heart movement. It can be understood that the triggering time Ttrigger of the ECG gating can be preset by the scanning personnel according to experience, for example, it can be 500-700 ms.

Step S120, for the first cardiac cycle, determine the _first time interval TD1 between the inversion recovery pulse and the T2 preparation pulse, the duration of the T2 preparation pulse _TE1 , and the difference between the T2 preparation pulse and the first data acquisition radio frequency pulse IMG. the _second time interval TD2 between.

Figure 2 shows a schematic diagram of an imaging sequence according to one embodiment of the invention. Two cardiac cycles in this imaging sequence are shown in FIG. 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, the T2 preparation pulse T2 PREP ₁ and the _first data acquisition radio frequency pulse IMG are used.

Using the inversion recovery pulse IR, the magnetization vector can be reversed, and the image signal will gradually recover from "-1" to "+1". Maximum contrast images can be obtained if data are acquired at the zero-crossing point of the normal myocardial signal.

The T2 preparation pulse T ₂ PREP ₁ is added after the inversion recovery pulse IR, and the contrast of the image is adjusted according to the transverse relaxation time T2 of different tissues. The T2 preparation pulse T ₂ PREP ₁ makes the tissue magnetization vector attenuate according to the weight of T2. Since the T2 value of blood is large, the recovery of the magnetization vector is slow, so as to achieve the effect of black blood. The time interval between the inversion recovery pulse IR and the T2 preparation pulse T ₂ PREP ₁ is the first time interval TD ₁ , and the duration of the T2 preparation pulse T ₂ PREP ₁ is TE ₁ .

After the T2 preparation pulse T ₂ PREP ₁ , the first data acquisition radio frequency pulse IMG is excited. The time interval between the T2 preparation pulse T ₂ PREP ₁ and the first data acquisition radio frequency pulse IMG is the second time interval TD ₂ .

In this step S120, imaging parameters are determined for a first time interval TD ₁ , a duration TE ₁ and a second time interval TD ₂ . In one example, it may be determined manually by taking measurements or settings for the subject based on physician experience. For example, for the duration TE ₁ of the T2 preparation pulse T ₂ PREP ₁ , since the T2 preparation pulse T ₂ PREP ₁ will reduce the intensity of the image signal, it can be set to a smaller value; but if the duration TE ₁ is too small, it may be As a result, the blood signal in the image signal cannot be sufficiently suppressed, resulting in a reduction in the contrast of the image. Therefore, considering the above factors, the duration TE ₁ can be set to a value between 20-30ms, for example 25ms. The _first time interval TD1 and the _second time interval TD2 may 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 TD ₁ , the duration TE ₁ , the second time interval TD ₂ and the ECG gating trigger time Ttrigger, sequentially excite the inversion recovery pulse IR and the T2 preparation pulse T ₂ PREP ₁ and the first data acquisition radio frequency pulse IMG.

As described above and as shown in FIG. 2 , the timing starts from the time when the R peak occurs, and after the time of Ttrigger, the first data acquisition radio frequency pulse IMG is excited. At the moment before the moment when the first data acquisition radio frequency pulse IMG is excited, and at the time interval (TE ₁ +TD ₂ ) from the moment when the first data acquisition radio frequency pulse IMG is excited, a T2 preparation pulse T ₂ PREP with a duration of TE ₁ is excited ₁ . The inversion recovery pulse IR is fired at a time interval TD1 from the time at which the T2 preparation pulse T ₂ PREP ₁ is excited, and at a time interval TD ₁ from the time at which the T2 preparation pulse T ₂ PREP ₁ is excited.

When the first data acquisition radio frequency pulse IMG is excited, the inversion recovery T2 preparation image signal is acquired. This inversion recovery T2 preparation image signal is a signal that actually directly generates a magnetic resonance image.

Optionally, the first data acquisition radio frequency pulse IMG used to acquire data is a Spoiled Gradient Echo (SPGR), a Balanced Steady State Free Precession (BSSFP), and a Spin Echo Sequence. (Spin Echo, SE) or echo plane sequence (Echo-Planar Imaging, EPI) and any other radio frequency pulse that can be used for magnetic resonance imaging. A suitable data reading method is preferably used as required, which can significantly reduce the requirement on the uniformity of the magnetic field intensity in the imaging process, so that the solution can be applied to a high-field (eg 3T) magnetic resonance system. Preferably, SPGR is employed. SPGR is insensitive to the inhomogeneity of the magnetic field, has no memory effect, and basically does not have a preparation process approaching a steady state.

Data acquisition RF pulses deviate the net magnetization vector from the direction of the main magnetic field. The angle at which the net magnetization vector deviates from the direction of the main magnetic field under the action of the data acquisition radio frequency pulse can be called 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 size of the collectable signal, that is, the projection size of the magnetization vector on the plane (x-y plane) perpendicular to the direction of the main magnetic field. If the magnetization vector before flipping is the same, the larger the flip angle, the larger the projection on the x-y plane, and the larger the collected signal. Therefore, the first data acquisition radio frequency pulse IMG excited in the first cardiac cycle may adopt a larger flip angle, for example, 15 to 20 degrees.

In addition, the excitation of the first data acquisition radio frequency pulse IMG is also based on the control of the first respiratory navigation signal iNAV ₁ . By monitoring the change in the position of the pectoral diaphragm with respiratory motion, it is possible to indirectly estimate the positional change of the heart with respiratory motion. It is desirable that the acquired image signals are acquired when the pectoral diaphragm is in the desired position.

The first respiratory navigation signal iNAV ₁ is collected in a short period of time before the time period Ttrigger has elapsed since the R peak of the ECG gating signal. According to the first breathing navigation signal iNAV ₁ , it is determined whether the current moment meets the predetermined condition, that is, whether the pectoral diaphragm is at the desired position at the current moment. In one example, after acquiring the first respiratory navigation signal iNAV ₁ , an inversion recovery T2 preparation image signal is acquired. According to the collected respiratory navigation signal iNAV ₁ , it is determined whether the collected inversion recovery T2 preparation image signal meets the requirements of respiratory motion compensation, that is, whether the inversion recovery T2 preparation image signal collected in the current cardiac cycle is valid. Therefore, it is decided whether to re-execute the acquisition operation or jump to the next signal acquisition operation. In the subsequent imaging process, only the valid inversion recovery T2 preparation image signal is used, and the invalid inversion recovery T2 preparation image signal is ignored. In another example, after the breathing navigation signal iNAV ₁ is collected, it is determined whether the current moment meets the predetermined condition according to the breathing navigation signal iNAV ₁ . When it is determined according to the breathing navigation signal iNAV ₁ that the current moment meets the predetermined condition, the image signal acquisition operation is performed until the inversion recovery T2 of this step is completed to prepare the signal acquisition operation. Using breathing navigation techniques, subjects were able to breathe freely during the magnetic resonance imaging procedure. It also expands the imaging field of view and improves the spatial resolution of the image.

Step S140 , in the second cardiac cycle, according to the ECG gating trigger time Ttrigger, based on the control of the second breathing navigation signal iNAV ₂ , the second data acquisition radio frequency pulse REF is excited and the reference image signal is acquired.

Similar to the first cardiac cycle, in the second cardiac cycle, the timing starts from the moment when the R peak occurs, and after the time of Ttrigger, the second data acquisition radio frequency pulse REF is excited. When the second data acquisition radio frequency pulse REF is excited, the reference image signal is acquired. The reference image signal is used to correct the phase of the inversion recovery T2-ready image signal. Therefore, the positive and negative values of the intensity of the inversion recovery T2 preparation image signal can be retained, thereby ensuring the contrast of the magnetic resonance image. The imaging sequence of the embodiment of the present invention may be called a phase-sensitive sequence, and the imaging sequence includes the above-mentioned first cardiac cycle and second cardiac cycle.

The smaller the projection of the magnetization vector in the direction of the original parallel main magnetic field, the longer it takes to restore the steady state magnetization vector. Therefore, when the flip angle of the data acquisition radio frequency pulse is small, although the acquired signal is small, the speed of the magnetization vector returning to the steady state is faster. Thus, the second data acquisition radio frequency pulse REF excited in the second cardiac cycle may adopt a smaller flip angle, eg, 5 to 10 degrees, than the first data acquisition radio frequency pulse IMG excited in the first cardiac cycle. In this way, it can be ensured that the inversion recovery T2 preparation image signal acquired in the first cardiac cycle is strong enough to be used to generate a magnetic resonance image; and the magnetization vector can be recovered quickly after the reference image signal is acquired in the second cardiac cycle. steady state, further ensuring the quality of magnetic resonance images.

The second data acquisition radio frequency pulse REF may use 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 the control of the second respiratory navigation signal iNAV ₂ . For brevity, details are not repeated here.

The control of the first respiratory navigation signal iNAV ₁ in the first cardiac cycle is independent of the control of the second respiratory navigation signal iNAV ₂ in the second cardiac cycle. The acquisition of the inversion recovery T2 preparation image signal and the reference image signal in the phase sensitive sequence is performed separately for breathing navigation, and the image signal that meets the breathing receiving condition can be collected without the need for the two image signals to meet the breathing receiving condition at the same time. In other words, for any one of the inversion recovery T2 preparation image signal and the reference image signal, the acquired data can be retained until the required data acquisition is completed as long as it satisfies the respiration receiving condition alone.

In one example, the phase sensitive sequence includes a plurality of repeating units. Each repeating unit includes two cardiac cycles, the aforementioned first cardiac cycle is the first cardiac cycle in the repeating unit, and the aforementioned second cardiac cycle is 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 ready image signal sig1 acquired in the first cardiac cycle satisfies the respiration reception condition, but the reference image signal sig2 acquired in the second cardiac cycle does not, the signal sig1 is received, but the signal sig2 is rejected, and the next repetition is continued unit. Since the two image signals sig1 and sig2 are related, when one of the signals is collected completely, the repeating unit collection mode needs to be performed until the other signal is also collected completely. At this point, the complete signal has been acquired and no new data needs to be received.

It can be understood that k-space is the data space in which acquisition operations are 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 over several cardiac cycles can be combined to fill a complete k-space (ie, complete acquisition) for reconstructing an 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 sig2. All the signals sig1 collected in the first cardiac cycle together fill the k-space corresponding to the inversion recovery T2 preparation image. All the signals sig2 collected in the second cardiac cycle together fill the k-space corresponding to the reference image. Therefore, the magnetic resonance image can be reconstructed by using the inversion recovery T2 preparation image signal with the reference image signal as the phase reference.

In the preceding example, the first cardiac cycle and the second cardiac cycle alternate. That is, the inversion recovery T2 prepares the image signal and the reference image signal to acquire alternately. As a result, the reference image signal is more closely matched to the truly effective inversion-recovery T2-ready image signal, and an ideal magnetic resonance image can be generated without the need for complex calculations to register the reference image signal with the latter.

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

In these alternative examples, since the first cardiac cycle and the corresponding second cardiac cycle may be separated in time by a large interval, registration calculations must be performed to ensure the quality of the magnetic resonance images generated.

Step S150, generating a magnetic resonance image according to the inversion recovery T2 preparation image signal and the reference image signal. In this step, the phase of the inversion recovery T2 preparation image signal is corrected according to the reference image signal, that is, the positive and negative values of the intensity of the inversion recovery T2 preparation picture signal are determined, thereby generating a preserved image according to the inversion recovery T2 preparation picture signal. Contrast magnetic resonance images.

In the above magnetic resonance imaging method, a three-dimensional image signal is acquired in two cardiac cycles respectively. Image signals acquired in the first cardiac cycle are obtained using inversion recovery and T2 prep pulses, which can generate a phase-sensitive image with dark blood contrast, and 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 the method of independent breathing navigation, which enables the acquisition of the two image signals to achieve higher navigation efficiency. Thereby, the contrast and spatial resolution of the generated magnetic resonance image can be made higher.

Figures 3a and 3b show atrial magnetic resonance images from the same subject undergoing atrial radiofrequency ablation according to the prior art and one embodiment of the present invention, respectively. Figures 3c and 3d show enlarged views of corresponding parts in Figures 3a and 3b, respectively. As shown in Fig. 3a, Fig. 3b, Fig. 3c and Fig. 3d, in the magnetic resonance image obtained by the magnetic resonance imaging method according to the embodiment of the present invention, the blood is obviously darkened, so that the scar tissue is more obvious.

FIG. 4 shows a schematic diagram of the contrast-to-noise ratio between different types of tissues in a magnetic resonance image according to the prior art and an embodiment of the present invention. In the bar graph in FIG. 4 , the left rectangle in each pair of rectangles from left to right represents the comparative noise ratio according to the prior art, and the right rectangle represents the comparative signal to noise ratio according to the embodiment of the present invention. As shown in FIG. 4 , although the contrast signal-to-noise ratio of scar tissue and normal tissue obtained according to the embodiment of the present invention is slightly lower than that of the prior art, the contrast signal-to-noise ratio of scar tissue and blood obtained according to the prior art is slightly lower than that of the scar tissue and blood obtained according to the prior art. In comparison, the obtained according to the embodiment of the present invention is significantly higher; and compared with the contrast signal-to-noise ratio of blood and normal tissue obtained according to the prior art, the obtained according to the embodiment of the present invention is significantly lower.

Therefore, the magnetic resonance images generated according to the embodiments of the present invention ideally reflect the state of the myocardial tissue of the subject, especially the scar tissue therein. Thus, the magnetic resonance imaging method is particularly suitable for scar detection.

Figure 5 shows a schematic diagram of an imaging sequence according to another embodiment of the invention. Also only two cardiac cycles in this imaging sequence are 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 , which will not be repeated here for brevity. The pulses in the second cardiac cycle in FIG. 2 are also the same as the corresponding pulses in the second cardiac cycle in FIG. 5 , and the description of these pulses is omitted. The imaging sequence shown in FIG. 5 differs from the imaging sequence shown in FIG. 2 in that, in the second cardiac cycle of FIG. 5 , the excitation of the T2 preparation pulse T ₂ PREP ₁ is similar to the excitation of the first data acquisition radio frequency pulse IMG before the excitation of the first data acquisition radio frequency pulse IMG in the first cardiac cycle. Ground, the T2 preparation pulse T ₂ PREP ₂ is also fired before the second data acquisition radio frequency pulse REF is fired and the reference image signal is acquired. The duration TE ₂ of the T2 preparation pulse T ₂ PREP ₂ in the second cardiac cycle may be the same as or different from the duration TE ₁ of the T2 preparation pulse T ₂ PREP ₁ in the first cardiac cycle.

In the second cardiac cycle, the T2 preparation pulse T ₂ PREP ₁ is also excited, which does not affect the acquisition of the reference image signal, nor does it affect the acquisition of the inversion recovery T2 preparation image signal. However, by adding the T2 prep pulse T ₂ PREP ₁ in the second cardiac cycle, angiographic images can be obtained simultaneously, providing information on the anatomy of the target tissue. For example, for atrial imaging, angiographic images near the atria can be obtained at the same time as the magnetic resonance images, providing information on the anatomy of the atria and surrounding pulmonary veins.

The above solution not only avoids multiple physical examinations of the subjects, but also significantly improves the operator's time efficiency and provides a better user experience.

As shown in FIG. 2 and FIG. 5 , before exciting the first data acquisition radio frequency pulse IMG and the second data acquisition radio frequency pulse REF, a fat pressing operation (FS) may be performed, respectively. Liposuction can help reduce breathing artifacts and significantly improve image quality.

It can be understood that the image signal acquisition in the above steps S130 and S140 may adopt the parallel sampling technology and any other k-space downsampling technology.

Exemplarily, in the above step S120, for the first cardiac cycle, determine the _first time interval TD1 between the inversion recovery pulse and the T2 preparation pulse in the cardiac cycle, the duration of the T2 preparation pulse _TE1 , and the T2 preparation pulse The _second time interval TD2 between the first data acquisition radio frequency pulse includes the following steps. First, the basic physical parameters of magnetic resonance were obtained for the normal myocardial tissue and blood of the subject, respectively. Then, the duration TE ₁ of the T2 preparation pulse is preset. For example, the duration can be set to any value between 20-30ms. Finally, according to the basic physical parameters and the duration TE ₁ , the first time interval TD ₁ and the second time interval TD ₂ are calculated.

Under a certain magnetic field strength, different tissues have different physical parameter values. When the biological tissue changes, the physical parameter values will also change. The duration TE ₁ of the T2 preparation pulse directly affects the aforementioned first time interval TD ₁ and second time interval TD ₂ . In this technical solution, the first time interval TD ₁ and the second time interval TD are determined based on the basic physical parameters of the magnetic resonance of the normal myocardial tissue and blood of the subject and the preset duration TE ₁ of the T2 preparation pulse ₂ . Therefore, the determined _first time interval TD1 and the _second time interval TD2 can darken the normal myocardial tissue and blood more, and improve the contrast of the magnetic resonance image.

Illustratively, the basic physical parameters include longitudinal relaxation time T1 and transverse relaxation time T2. The longitudinal relaxation time T1 can be obtained from the T1 parameter map before scanning. Alternatively, the longitudinal relaxation time T1 can also be set according to experience, 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 200ms. . The transverse relaxation time T2 can 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 70ms.

The above steps to calculate the _first time interval _TD1 and the _second time interval TD2 according to basic physical parameters and duration TE1 include the following steps.

1) Taking normal myocardial tissue and blood as the target tissue, respectively, establish the steady-state magnetization vector M _SS of the target tissue, the longitudinal relaxation time T1, the transverse relaxation time T2, the first time interval TD ₁ , the duration TE ₁ and the second _The first mathematical relationship between time intervals TD2.

的稳态值，即认为在成像序列开始的第一个心动周期内，纵向磁化向量

在前述用于成像的相位敏感序列中包括多个由第一心动周期和第二心动周期构成的重复单元的示例中，经历一个重复单元，即一次循环，经过反转恢复，T2准备脉冲导致的T2衰减，两次图像采集的扰动，以及中间时间的T1恢复过程，在下一个重复单元的第一心动周期，纵向磁化向量

依然恢复到稳态，

The steady-state magnetization vector M _SS is the longitudinal magnetization vector strength at the moment before the excitation inversion recovery pulse IR

The steady-state value of , that is, the longitudinal magnetization vector is considered to be in the first cardiac cycle at the beginning of the imaging sequence.

In the aforementioned example in which the phase-sensitive sequence for imaging includes a plurality of repeating units consisting of a first cardiac cycle and a second cardiac cycle, one repeating unit, ie, one cycle, undergoes inversion recovery, resulting in a T2 prep pulse. T2 decay, perturbation of two image acquisitions, and T1 recovery process at intermediate times, in the first cardiac cycle of the next repeat unit, the longitudinal magnetization vector

still returns to steady state,

In this step, the steady-state magnetization vector M _SS of the target tissue can be expressed as longitudinal relaxation time T1 , transverse relaxation time T2 , first time interval TD ₁ , duration TE ₁ , second time interval TD ₂ and others Mathematical functions that affect parameters. Illustratively, the mathematical function can be obtained using the Bloch equation.

与稳态磁化向量M_SS、纵向弛豫时间T1、横向弛豫时间T2、第一时间间隔TD₁、持续时间TE₁和第二时间间隔TD₂之间的第二数学关系：2) Take normal myocardial tissue and blood as the target tissue respectively, and establish the image signal intensity of the target tissue according to the following formula

A second mathematical relationship with steady state magnetization vector M _SS , longitudinal relaxation time T1 , transverse relaxation time T2 , first time interval TD ₁ , duration TE ₁ and second time interval TD ₂ :

表示为稳态磁化向量M_SS、第一时间间隔TD₁、持续时间TE₁和第二时间间隔TD₂的数学函数。In the above mathematical relationship, the image signal intensity of the target tissue is

Denoted as a mathematical function of the steady state magnetization vector M _SS , the first time interval TD ₁ , the duration TE ₁ and the second time interval TD ₂ .

3) Based on the image signal intensity of normal myocardial tissue being 0 and the image signal intensity of blood being the smallest, the first time interval TD ₁ and the second time interval TD ₂ are determined according to the first mathematical relationship and the second mathematical relationship.

和血液的图像信号强度

均为0，即：Simultaneous equations can be used to get the image signal intensity of normal myocardial tissue

and blood image signal strength

Both are 0, that is:

Then, based on the above-mentioned first mathematical relationship and the second mathematical relationship, the above-mentioned equation is solved to obtain the first time interval TD ₁ and the second time interval TD ₂ by calculation.

和血液的图像信号强度

同时为0。在这种情况下，选择让正常心肌组织的图像信号强度

为0，血液的图像信号强度

取最小值时的第一时间间隔TD₁和第二时间间隔TD₂。In some cases, the above simultaneous equations may have no solution, that is, the image signal intensity of normal myocardial tissue cannot be obtained.

and blood image signal strength

Also 0. In this case, choose to let the image signal intensity of normal myocardial tissue

is 0, the image signal strength of blood

The first time interval TD ₁ and the second time interval TD ₂ when taking the minimum value.

In the above solution, the first time interval TD ₁ and the second time interval TD ₂ are calculated so that the image signal intensity of normal myocardial tissue is 0 and the image signal intensity of blood is the smallest. The imaging sequence realized according to the _first time interval TD1 and the _second time interval TD2 further ensures that the contrast between scars and adjacent blood signals and normal myocardial tissue in the magnetic resonance image is relatively large.

The influence parameters of steady-state magnetization vector M _SS include T1 value, T2 value of target tissue, ECG gate trigger time Ttrigger, heart rate, flip angle of data acquisition RF pulse, repetition time and number of echoes. Therefore, the above-mentioned first mathematical relationship can be established based on these influencing parameters.

In the example of the imaging sequence shown in Figure 2, as previously described, the magnetization vector reaches steady state before the inversion pulse IR is fired in the first cardiac cycle.

可以表示如下：Immediately after the excitation of the inversion recovery pulse IR and the T2 preparation pulse T ₂ PREP ₁ and before the excitation of the first data acquisition radio frequency pulse IMG, the image signal intensity

It can be expressed as follows:

可以表示如下：Immediately after the excitation of the first data acquisition radio frequency pulse IMG, the image signal intensity

It can be expressed as follows:

Wherein, TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse, which are the same. This repetition time is a minimum value determined by the magnetic resonance imaging system, eg 5.4 ms. α ₁ represents the flip angle of the first data acquisition radio frequency pulse, for example, 18 degrees. n represents the number of echoes of the data acquisition radio frequency pulse. The number of echoes n can be given according to the acquisition time (eg 100 to 200ms) limit, eg the number of echoes is 30.

可以表示如下：In the second cardiac cycle, at the moment before the excitation of the second data acquisition radio frequency pulse REF, the image signal intensity

It can be expressed as follows:

Among them, R1=RR-n×TR, RR represents the cardiac cycle of the subject.

可以表示如下：In the second cardiac cycle, at the moment after the excitation of the second data acquisition radio frequency pulse REF, the image signal intensity

It can be expressed as follows:

Wherein, α ₂ represents the flip angle of the second data acquisition radio frequency pulse, for example, 10 degrees.

可以表示为：Image signal intensity before the inversion recovery pulse IR in the next first cardiac cycle

It can be expressed as:

Wherein, RX=RR-(TD ₁ +TE ₁ +TD ₂ )-n×TR.

即等于稳态磁化向量M_SS，即

The image signal strength

That is, it is equal to the steady-state magnetization vector M _SS , that is,

According to the above formula, the mathematical relationship expression of the steady-state magnetization vector M _SS can be obtained:

in,

In the example of the imaging sequence shown in FIG. 5 , the duration TE ₂ of the T2 preparation pulse T ₂ PREP ₂ may be preset for the second cardiac cycle. As before, it may be the same as or different from the duration TE ₁ of the T2 prep pulse T ₂ PREP ₁ in the first cardiac cycle. Similarly, the magnetization vector reaches steady state before firing the inversion pulse IR in the first cardiac cycle.

可以表示如下：Immediately after the excitation of the inversion recovery pulse IR and the T2 preparation pulse T ₂ PREP ₁ and before the excitation of the first data acquisition radio frequency pulse IMG, the image signal intensity

It can be expressed as follows:

可以表示如下：Immediately after the excitation of the first data acquisition radio frequency pulse IMG, the image signal intensity

It can be expressed as follows:

Wherein, TR represents the repetition time of the first data acquisition radio frequency pulse and the second data acquisition radio frequency pulse, which are the same; α ₁ represents the flip angle of the first data acquisition radio frequency pulse; n represents the return time of the data acquisition radio frequency pulse number of waves. These parameters are introduced in the above examples, and are not repeated here for brevity.

可以表示如下：In the second cardiac cycle, immediately before the excitation T2 prep pulse T ₂ PREP ₂ , the image signal intensity

It can be expressed as follows:

Wherein, R1=RR-n×TR-TE ₂ , and RR represents the cardiac cycle of the subject.

可以表示如下：Immediately after the excitation of the T2 preparation pulse T ₂ PREP ₂ and before the excitation of the second data acquisition radio frequency pulse REF, the image signal intensity

It can be expressed as follows:

可以表示如下：In the second cardiac cycle, at the moment after the excitation of the second data acquisition radio frequency pulse REF, the image signal intensity

It can be expressed as follows:

Wherein, α ₂ represents the flip angle of the second data acquisition radio frequency pulse, for example, 10 degrees.

可以表示为：Image signal intensity before the inversion recovery pulse IR in the next first cardiac cycle

It can be expressed as:

Wherein, RX=RR-(TD ₁ +TE ₁ +TD ₂ )-n×TR.

即等于稳态磁化向量M_SS，即

The image signal strength

That is, it is equal to the steady-state magnetization vector M _SS , that is,

According to the above formula, the mathematical relationship expression of the steady-state magnetization vector M _SS can be obtained:

in,

RX=RR-(TD ₁ +TE ₁ +TD ₂ )-n×TR.

The mathematical expressions of the respective steady-state magnetization vectors in different examples are given above. The expressions of the steady-state magnetization vectors obtained by these two methods ideally simulate the real steady-state magnetization vectors in the imaging sequence, thus further ensuring that Imaging effect.

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

According to yet another aspect of the present invention, a storage medium is also provided, on which program instructions are stored, and when the program instructions are executed by a computer or a processor, the computer or the processor is made to execute the embodiments of the present invention The corresponding steps of the magnetic resonance imaging method are used to implement the corresponding modules in the magnetic resonance imaging apparatus according to the 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 disk read only memory (CD-ROM), USB memory, or any combination of the above storage media. The computer-readable storage medium can be any combination of one or more computer-readable storage media.

In the description provided herein, numerous specific details are set forth. It will be 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 is to be understood that in the description of the exemplary embodiments of the invention, various features of the invention are sometimes grouped together , or in its description. However, this method of the invention should not be interpreted as reflecting the intention that the invention as claimed requires more features than are expressly recited in each claim. Rather, as the corresponding claims reflect, the invention lies in the fact that the corresponding technical problem may be solved with 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 features disclosed in this specification (including the accompanying claims, abstract and drawings) and any method or apparatus so disclosed may be used in any combination, except that the features are mutually exclusive. Processes or units are combined. Each feature disclosed in this specification (including 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 although some of the embodiments described herein include certain features, but not others, included in other embodiments, that combinations of features of different embodiments are intended to be within the scope of the invention within 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 use of the words first, second, third, etc. does not denote any order. These words can be interpreted as names. The characters one, two, three, etc. here are equivalent to the corresponding numbers 1, 2, 3, etc., respectively. Thus, the first, second, and third, etc., are equivalent to the corresponding 1st, 2nd, and 3rd, etc., respectively.

The above is only the specific embodiment of the present invention or the description of the specific embodiment, and the protection scope of the present invention is not limited thereto. Any changes or substitutions should be included 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.

Claims (11)

1. A magnetic resonance imaging method, comprising:

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 cycle ₁ T2 duration of the preparation pulse TE ₁ And a second time interval TD between the T2 preparation pulse and the first data acquisition RF pulse ₂ Wherein the first cardiac cycle is a first cardiac cycle in a repeating unit in a phase-sensitive sequence;

in the first cardiac cycle, according to the first time interval TD ₁ The duration TE ₁ The second time interval TD ₂ And the electrocardio-gating trigger time Ttrigger sequentially excites an inversion recovery pulse, a T2 preparation pulse and a first data acquisition radio frequency pulse, and acquires 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, the second cardiac cycle is a second cardiac cycle in the repeating unit, the inversion recovery T2 preparation image signal and the reference image signal are associated, for any one of the inversion recovery T2 preparation image signal and the reference image signal, the image signal is acquired as long as the respiratory navigation signal corresponding to the image signal alone meets a respiratory receiving condition, and when the acquisition of any one of the inversion recovery T2 preparation image signal and the reference image signal is complete, the acquisition mode of the repeating unit is continued, wherein the acquisition of the complete image signal does not need to receive new data until another image signal is also complete; and

and generating a magnetic resonance image according to the inversion recovery T2 preparation image signal and the reference image signal.

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

3. Method according to claim 1 or 2, wherein said determining a first time interval TD between an inversion recovery pulse and a T2 preparation pulse ₁ T2 duration of the preparation pulse TE ₁ And a second time interval between the T2 preparation pulse and the first data acquisition RF pulseTD ₂ The 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 TE ₁ ；

According to said basic physical parameter and said duration TE ₁ Calculating said first time interval TD ₁ And said second time interval TD ₂ 。

4. The method according to claim 3, wherein said basic physical parameters comprise a longitudinal relaxation time T1 and a transverse relaxation time T2, said calculating said first time interval TD ₁ And said second time interval TD ₂ The 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 _SS With said longitudinal relaxation time T1, said transverse relaxation time T2, said first time interval TD ₁ The duration TE ₁ And said second time interval TD ₂ A 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

And the steady state magnetization vector M _SS The longitudinal relaxation time T1, the transverse relaxation time T2, the first time interval TD ₁ The duration TE ₁ And said second time interval TD ₂ The second mathematical relationship between:

determining 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 minimumTime interval TD ₁ And said second time interval TD ₂ 。

5. The method of claim 4, wherein the first mathematical relationship is represented as:

wherein,

RX＝RR-(TD ₁ +TE ₁ +TD ₂ )-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;

α ₁ a flip angle representative of the first data acquisition radio frequency pulse;

α ₂ a flip angle representative of the second data acquisition radio frequency pulse;

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

6. The method of claim 4, wherein the method further comprises: presetting a duration TE of a T2 preparation pulse for the second cardiac cycle ₂ ；

The first mathematical relationship is represented as:

wherein,

RX＝RR-(TD ₁ +TE ₁ +TD ₂ )-n×TR；

R1＝RR-n×TR-TE ₂ ；

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;

α ₁ representing a flip angle of a first data acquisition radio frequency pulse;

α ₂ a flip angle representing a second data acquisition radio frequency pulse;

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

7. 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.

8. 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.

9. 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.

10. 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 9 when executed by the processor.

11. A storage medium on which program instructions are stored which, when executed, are for performing a magnetic resonance imaging method as claimed in any one of claims 1 to 9.

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