技术领域technical field
本发明涉及磁共振成像技术领域，具体地，涉及一种利用稳态自由进动序列的磁共振成像方法。The invention relates to the technical field of magnetic resonance imaging, in particular to a magnetic resonance imaging method using a steady-state free precession sequence.
背景技术Background technique
时间反转稳态进动(Time-reversed Fast Imaging with Steady-state Precession,timereversed FISP,or PSIF,or Contrast Enhanced Fourier Acquired Steady state，CE-FAST)信号是一种重T2加权的梯度回波信号。相比于传统基于快速自旋回波T2加权信号，它具有采集速度快，选择性吸收率低等优点。Time-reversed Fast Imaging with Steady-state Precession, timereversed FISP, or PSIF, or Contrast Enhanced Fourier Acquired Steady state (CE-FAST) signal is a heavily T2-weighted gradient echo signal. Compared with the traditional T2-weighted signal based on fast spin echo, it has the advantages of fast acquisition speed and low selective absorption rate.
回波平移(Echo Shift，ES)信号是一种重T2*加权的梯度回波信号，它具有长回波时间(Echo Time，TE)的特点，对于相位变化也十分敏感，通常用于磁共振温度成像等实时监控领域。Echo shift (Echo Shift, ES) signal is a heavy T2* weighted gradient echo signal, which has the characteristics of long echo time (Echo Time, TE) and is also very sensitive to phase changes, usually used in magnetic resonance Real-time monitoring fields such as temperature imaging.
目前业界对这两种信号通常是利用对应的序列分别进行采集，而在某些实时监控领域，需要同时采集回波平移信号和时间反转稳态进动信号，以获取温度信息和组织T2变化信息。At present, the industry usually uses corresponding sequences to collect these two signals separately, but in some real-time monitoring fields, it is necessary to collect echo translation signals and time-reversal steady-state precession signals at the same time to obtain temperature information and tissue T2 changes information.
发明内容Contents of the invention
本发明实施例的主要目的在于提供一种利用稳态自由进动序列的磁共振成像方法，以解决现有技术中不能同时采集回波平移信号和时间反转稳态进动信号的问题。The main purpose of the embodiments of the present invention is to provide a magnetic resonance imaging method using a steady-state free precession sequence, so as to solve the problem in the prior art that echo translation signals and time-reversed steady-state precession signals cannot be collected simultaneously.
为了实现上述目的，本发明实施例提供一种利用稳态自由进动序列的磁共振成像方法，包括：In order to achieve the above purpose, an embodiment of the present invention provides a magnetic resonance imaging method using a steady-state free precession sequence, including:
循环执行一稳态自由进动序列；其中，执行该稳态自由进动序列的过程包括：Cyclic execution of a steady-state free precession sequence; wherein, the process of executing the steady-state free precession sequence includes:
步骤1，施加激发脉冲，同时施加第一层面选择梯度A；Step 1, applying an excitation pulse, and simultaneously applying a first layer selection gradient A;
步骤2，在施加所述第一层面选择梯度A之后，施加第二层面选择梯度B、第一相位编码梯度U、以及读出预散相梯度J；Step 2, after applying the first slice selection gradient A, applying the second slice selection gradient B, the first phase encoding gradient U, and reading out the pre-dispersion gradient J;
步骤3，在施加所述第二层面选择梯度B、第一相位编码梯度U、以及读出预散相梯度J之后，施加第一读出梯度G；Step 3, after applying the second layer selection gradient B, the first phase encoding gradient U, and the readout pre-dispersion gradient J, apply the first readout gradient G;
步骤4，在施加所述第一读出梯度G的同时采集磁共振信号，得到回波平移信号；Step 4, acquiring magnetic resonance signals while applying the first readout gradient G to obtain echo translation signals;
步骤5，采集得到回波平移信号之后，施加第三层面选择梯度D；Step 5, after acquiring the echo translation signal, applying the third layer selection gradient D;
步骤6，在施加所述第三层面选择梯度D之后，施加第二读出梯度H；Step 6, after applying the third layer selection gradient D, applying a second readout gradient H;
步骤7，在施加所述第二读出梯度H的同时采集磁共振信号，得到时间反转稳态进动信号；Step 7, acquiring magnetic resonance signals while applying the second readout gradient H, to obtain time-reversed steady-state precession signals;
步骤8，采集得到时间反转稳态进动信号之后，施加读出回聚梯度F、第二相位编码梯度V、第四层面选择梯度C；Step 8: After acquiring the time-reversed steady-state precession signal, apply the readout refocusing gradient F, the second phase encoding gradient V, and the fourth layer selection gradient C;
其中，所述第一层面选择梯度A、第二层面选择梯度B、第四层面选择梯度C、第三层面选择梯度D满足如下关系：Wherein, the selection gradient A of the first level, the selection gradient B of the second level, the selection gradient C of the fourth level, and the selection gradient D of the third level satisfy the following relationship:
MC＝-MA/2，MC =-MA /2,
2MB–MD＝MA，2MB -MD =MA ,
MA是第一层面选择梯度A的矩，MA is the moment of the selection gradient A of the first layer,
MB是第二层面选择梯度B的矩，MB is the moment of the selection gradient B of the second layer,
MC是第四层面选择梯度C的矩，MC is the moment of the selection gradient C of the fourth layer,
MD是第三层面选择梯度D的矩；MD is the moment of the selection gradient D of the third level;
其中，所述第一相位编码梯度U、第二相位编码梯度V满足如下关系：Wherein, the first phase encoding gradient U and the second phase encoding gradient V satisfy the following relationship:
MU＝-MV，MU =-MV ,
MU是第一相位编码梯度U的矩，MU is the moment of the first phase encoding gradient U,
MV是第二相位编码梯度V的矩；MV is the moment of the second phase encoding gradient V;
利用循环执行所述稳态自由进动序列得到的回波平移信号和时间反转稳态进动信号填充k空间；Filling k-space with echo translation signals and time-reversed steady-state precession signals obtained by cyclically executing the steady-state free-precession sequence;
对所述k空间的数据进行傅里叶变换，得到磁共振图像。performing Fourier transform on the k-space data to obtain a magnetic resonance image.
借助于上述技术方案，本发明设计了一种新的稳态自由进动序列，执行该序列可同时采集回波平移信号和时间反转稳态进动信号，相比于现有技术，本发明能够满足同时采集回波平移信号和时间反转稳态进动信号的需要，获取温度信息和组织T2变化信息，明显缩短磁共振成像时间。With the help of the above technical solution, the present invention designs a new steady-state free precession sequence, which can simultaneously collect echo translation signals and time-reversed steady-state precession signals. Compared with the prior art, the present invention It can meet the needs of simultaneously collecting echo translation signals and time-reversed steady-state precession signals, obtain temperature information and tissue T2 change information, and significantly shorten the time of magnetic resonance imaging.
附图说明Description of drawings
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only of the present invention. For some embodiments, those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.
图1是本发明提供的利用稳态自由进动序列的磁共振成像方法流程示意图；Fig. 1 is a schematic flow chart of a magnetic resonance imaging method utilizing a steady-state free precession sequence provided by the present invention;
图2是本发明提供的一种用于磁共振二维成像的稳态自由进动序列实例示意图；Fig. 2 is a schematic diagram of an example of a steady-state free precession sequence for magnetic resonance two-dimensional imaging provided by the present invention;
图3是本发明提供的另一种用于磁共振二维成像的稳态自由进动序列实例示意图；Fig. 3 is another schematic diagram of an example of a steady-state free precession sequence for magnetic resonance two-dimensional imaging provided by the present invention;
图4是本发明提供的一种用于磁共振三维成像的稳态自由进动序列实例示意图；Fig. 4 is a schematic diagram of an example of a steady-state free precession sequence for magnetic resonance three-dimensional imaging provided by the present invention;
图5中(a)是本发明采集到的回波平移图像；(b)是本发明采集到的时间反转稳态进动图像；(c)是单独利用回波平移序列采集到的回波平移图像；(d)是单独利用时间反转稳态进动序列扫描的时间反转稳态进动图像。Among Fig. 5 (a) is the echo translation image that the present invention gathers; (b) is the time reversal steady-state precession image that the present invention gathers; (c) is the echo that utilizes the echo translation sequence to gather alone Translational image; (d) is the time-reversed steady-state precession image scanned by the time-reversed steady-state precession sequence alone.
具体实施方式Detailed ways
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.
本发明提供一种利用稳态自由进动序列的磁共振成像方法，如图1所示，该方法包括：The present invention provides a kind of magnetic resonance imaging method utilizing steady-state free precession sequence, as shown in Figure 1, the method comprises:
步骤S1，循环执行一稳态自由进动序列。Step S1, cyclically execute a steady-state free precession sequence.
稳态自由进动序列包括激发脉冲、层面选择方向(Z方向)的梯度、相位编码方向(Y方向)的梯度、读出方向(X方向)的梯度。The steady-state free precession sequence includes the excitation pulse, the gradient in the slice selection direction (Z direction), the gradient in the phase encoding direction (Y direction), and the gradient in the readout direction (X direction).
具体的，步骤S1中执行稳态自由进动序列的循环次数与相位编码的编码数相对应，取决于磁共振图像的分辨率(扫描参数)。Specifically, the number of cycles for performing the steady-state free precession sequence in step S1 corresponds to the number of phase encodings, and depends on the resolution (scanning parameters) of the magnetic resonance image.
步骤S1中，单次执行稳态自由进动序列具体包括如下分步骤：In step S1, the single execution of the steady-state free precession sequence specifically includes the following sub-steps:
步骤S11，施加激发脉冲，同时施加第一层面选择梯度A。Step S11 , applying an excitation pulse and simultaneously applying a first layer selection gradient A.
具体的，激发脉冲是一组等间距、相同翻转角度的脉冲信号。第一层面选择梯度A施加于层面选择方向。Specifically, the excitation pulse is a group of pulse signals with equal intervals and the same flip angle. The first slice selection gradient A is applied in the slice selection direction.
步骤S12，在施加第一层面选择梯度A之后，施加第二层面选择梯度B、第一相位编码梯度U、以及读出预散相梯度J。Step S12 , after applying the first slice selection gradient A, applying the second slice selection gradient B, the first phase encoding gradient U, and the readout pre-dispersion gradient J.
具体的，第二层面选择梯度B施加于层面选择方向；第一相位编码梯度U施加于相位编码方向；读出预散相梯度J施加于读出方向。Specifically, the second slice selection gradient B is applied to the slice selection direction; the first phase encoding gradient U is applied to the phase encoding direction; and the readout pre-dispersion gradient J is applied to the readout direction.
步骤S13，在施加第二层面选择梯度B、第一相位编码梯度U、以及读出预散相梯度J之后，施加第一读出梯度G。Step S13 , after applying the second slice selection gradient B, the first phase encoding gradient U, and the readout pre-dispersion gradient J, the first readout gradient G is applied.
具体的，第一读出梯度G施加于读出方向。Specifically, the first readout gradient G is applied in the readout direction.
步骤S14，在施加第一读出梯度G的同时采集磁共振信号，得到回波平移信号。Step S14, collecting magnetic resonance signals while applying the first readout gradient G to obtain echo translation signals.
步骤S15，采集得到回波平移信号之后，施加第三层面选择梯度D。Step S15 , after acquiring the echo translation signal, applying the third layer selection gradient D.
具体的，第三层面选择梯度D施加于层面选择方向。Specifically, the third layer selection gradient D is applied in the layer selection direction.
步骤S16，在施加第三层面选择梯度D之后，施加第二读出梯度H。Step S16, after applying the third layer selection gradient D, applying a second readout gradient H.
具体的，第二读出梯度H施加于读出方向。Specifically, the second readout gradient H is applied in the readout direction.
步骤S17，在施加第二读出梯度H的同时采集磁共振信号，得到时间反转稳态进动信号。Step S17 , collecting magnetic resonance signals while applying the second readout gradient H to obtain time-reversed steady-state precession signals.
步骤S18，采集得到时间反转稳态进动信号之后，施加读出回聚梯度F、第二相位编码梯度V、第四层面选择梯度C。Step S18 , after acquiring the time-reversed steady-state precession signal, apply the readout refocusing gradient F, the second phase encoding gradient V, and the fourth layer selection gradient C.
具体的，读出回聚梯度F施加于读出方向；第二相位编码梯度V施加于相位编码方向；第四层面选择梯度C施加于层面选择方向。Specifically, the readout refocusing gradient F is applied to the readout direction; the second phase encoding gradient V is applied to the phase encoding direction; and the fourth slice selection gradient C is applied to the slice selection direction.
为了达到同时采集回波平移信号和时间反转稳态进动信号的目的，本发明中，第一层面选择梯度A、第二层面选择梯度B、第四层面选择梯度C、第三层面选择梯度D应满足如下关系：In order to achieve the purpose of simultaneously collecting the echo translation signal and the time-reversed steady-state precession signal, in the present invention, the first layer selects the gradient A, the second layer selects the gradient B, the fourth layer selects the gradient C, and the third layer selects the gradient D should satisfy the following relationship:
MC＝-MA/2，MC =-MA /2,
2MB–MD＝MA，2MB -MD =MA ,
MA是第一层面选择梯度A的矩，MA is the moment of the selection gradient A of the first layer,
MB是第二层面选择梯度B的矩，MB is the moment of the selection gradient B of the second layer,
MC是第四层面选择梯度C的矩，MC is the moment of the selection gradient C of the fourth layer,
MD是第三层面选择梯度D的矩。MD is the moment of the selection gradient D of the third level.
具体的，第一层面选择梯度A是配合激发脉冲用于激发采集对象的某一层所需要的梯度，它由激发层厚和激发脉冲的带宽等参数决定。Specifically, the gradient A selected for the first layer is the gradient required to excite a certain layer of the object to be collected with the excitation pulse, and is determined by parameters such as the thickness of the excitation layer and the bandwidth of the excitation pulse.
本发明适用于磁共振二维成像和磁共振三维成像。The invention is suitable for two-dimensional magnetic resonance imaging and three-dimensional magnetic resonance imaging.
在磁共振二维成像中，每一个重复周期内，仅在相位编码方向(Y方向)施加第一相位编码梯度U和第二相位编码梯度V。其中，施加第一相位编码梯度U的目的是使自旋子具备不同的初始相位，以区分相应体素的位置，用于磁共振二维成像，但在下一个重复周期来临前，需使所有自旋子的相位回聚，为此就要施加与第一相位编码梯度U强度相同、极性相反的第二相位编码梯度V(即回聚梯度)。也就是说，第一相位编码梯度U、第二相位编码梯度V应满足关系：MU＝-MV，MU是第一相位编码梯度U的矩，MV是第二相位编码梯度V的矩。In two-dimensional magnetic resonance imaging, the first phase encoding gradient U and the second phase encoding gradient V are only applied in the phase encoding direction (Y direction) in each repetition period. Among them, the purpose of applying the first phase encoding gradient U is to make the spinons have different initial phases, so as to distinguish the positions of corresponding voxels for two-dimensional magnetic resonance imaging, but before the next repetition period comes, all spinons need to be For the phase refocusing of the rotor, it is necessary to apply a second phase encoding gradient V with the same strength as the first phase encoding gradient U but opposite in polarity (ie refocusing gradient). That is to say, the first phase encoding gradient U and the second phase encoding gradient V should satisfy the relationship: MU =-MV , MU is the moment of the first phase encoding gradient U, and MV is the moment of the second phase encoding gradient V moment.
在磁共振三维成像中，每一个重复周期内，除了在相位编码方向施加第一相位编码梯度U和第二相位编码梯度V之外，还需要在层面选择方向(Z方向)施加第三相位编码梯度S和第四相位编码梯度T。其中，施加第三相位编码梯度S是在施加第一层面选择梯度A之后，施加第一读出梯度G之前；施加第四相位编码梯度T是在采集得到时间反转稳态进动信号之后；并且，第三相位编码梯度S、第四相位编码梯度T应满足关系：MS＝-MT，MS是第三相位编码梯度S的矩，MT是第四相位编码梯度T的矩。In three-dimensional magnetic resonance imaging, in each repetition period, in addition to applying the first phase encoding gradient U and the second phase encoding gradient V in the phase encoding direction, it is also necessary to apply the third phase encoding in the slice selection direction (Z direction). Gradient S and fourth phase encoding gradient T. Wherein, applying the third phase encoding gradient S is after applying the first slice selection gradient A and before applying the first readout gradient G; applying the fourth phase encoding gradient T is after acquiring the time-reversed steady-state precession signal; Moreover, the third phase encoding gradient S and the fourth phase encoding gradient T should satisfy the relationship: MS =-MT , MS is the moment of the third phase encoding gradient S, and MT is the moment of the fourth phase encoding gradient T.
步骤S2，利用循环执行稳态自由进动序列得到的回波平移信号和时间反转稳态进动信号填充k空间。Step S2, using the echo translation signal and the time-reversed steady-state precession signal obtained by cyclically executing the steady-state free precession sequence to fill the k-space.
步骤S3，对k空间的数据进行傅里叶变换，得到磁共振图像。Step S3, performing Fourier transform on the k-space data to obtain a magnetic resonance image.
执行该稳态自由进动序列，每个重复周期内施加不同的相位编码梯度以覆盖整个k空间，将k空间的信号做傅里叶变换即可得到对应的图像信息。The steady-state free precession sequence is executed, and different phase encoding gradients are applied in each repetition period to cover the entire k-space, and the corresponding image information can be obtained by Fourier transforming the signal in the k-space.
若激发脉冲的自由感应衰减(Free Induction Decay，FID)信号没有衰减完全，而进入到了回波平移信号的采集窗口内，就会对采集回波平移信号造成干扰。考虑到这一点，本发明中，为了使得激发脉冲的FID信号不影响采集回波平移信号，层面选择梯度A、B、C、D还应满足关系：∣MA/2+MB∣≧MA/2，以使激发脉冲的FID信号很快衰减完全。If the free induction decay (Free Induction Decay, FID) signal of the excitation pulse is not attenuated completely, but enters the acquisition window of the echo translation signal, it will cause interference to the acquisition of the echo translation signal. Considering this point, in the present invention, in order to make the FID signal of the excitation pulse not affect the acquired echo translation signal, the slice selection gradients A, B, C, and D should also satisfy the relationship: ∣MA /2+MB ∣≧MA /2, so that the FID signal of the excitation pulse decays completely quickly.
在一种较佳的实施例中，令MB＝–MA，MD＝MA，即可满足上述关系∣MA/2+MB∣≧MA/2。In a preferred embodiment, if MB =–MA and MD =MA , the above relationship |MA /2+MB |≧MA /2 can be satisfied.
本发明提供一种如图2所示的可应用于图1所示方法进行磁共振二维成像的稳态自由进动序列实例，该序列包括激发脉冲、层面选择方向的梯度、相位编码方向的梯度、读出方向的梯度。The present invention provides an example of a steady-state free precession sequence that can be applied to the method shown in FIG. 1 for two-dimensional magnetic resonance imaging as shown in FIG. Gradient, the gradient in the readout direction.
图2中，激发脉冲是一组等间距、相同翻转角度α的脉冲信号。ADC#1表示在施加第一读出梯度G的同时采集回波平移信号。ADC#2表示在施加第二读出梯度H的同时采集时间反转稳态进动信号。In Fig. 2, the excitation pulse is a group of pulse signals with equal intervals and the same flip angle α. ADC#1 represents the acquisition of the echo translation signal while applying the first readout gradient G. ADC#2 represents the acquisition of a time-reversed steady-state precession signal while a second readout gradient H is applied.
基于图2，每一个重复周期内，在施加第一读出梯度G之后，以及施加第二读出梯度H之前，还包括：施加读出回聚-预散相梯度E，并且，图2中的读出预散相梯度J、第一读出梯度G、读出回聚-预散相梯度E、第二读出梯度H、读出回聚梯度F满足如下关系：Based on FIG. 2, in each repetition cycle, after applying the first readout gradient G and before applying the second readout gradient H, it also includes: applying the readout refocusing-pre-dispersion gradient E, and, in FIG. 2 The readout pre-dispersion gradient J, the first readout gradient G, the readout refocusing-pre-dispersion gradient E, the second readout gradient H, and the readout refocusing gradient F satisfy the following relationship:
MJ＝-MG/2，MJ =-MG /2,
ME＝-(MG+MH)/2，ME = -(MG +MH )/2,
MF＝-MH/2，MF =-MH /2,
MJ是读出预散相梯度J的矩，MJ is the moment of the readout pre-dephasing gradient J,
MG是第一读出梯度G的矩，MG is the moment of the first readout gradient G,
ME是读出回聚-预散相梯度E的矩，ME is the moment of readout refocusing-predispersing gradient E,
MH是第二读出梯度H的矩，MH is the moment of the second readout gradient H,
MF是读出回聚梯度F的矩。MF is the moment of readout refocusing gradient F.
具体的，第一读出梯度G、第二读出梯度H需配合模数转换器执行采集磁共振信号的工作，它们的大小由采样点数、采集带宽和读出方向的视野大小等参数决定。Specifically, the first readout gradient G and the second readout gradient H need to cooperate with the analog-to-digital converter to perform the work of acquiring magnetic resonance signals, and their sizes are determined by parameters such as the number of sampling points, acquisition bandwidth, and field of view in the readout direction.
以下为执行图2所示稳态自由进动序列的工作过程及原理：The following is the working process and principle of implementing the steady-state free precession sequence shown in Figure 2:
每个重复周期内：During each recurrence:
(1)激发脉冲通过射频线圈施加到采集对象上，同时配合第一层面选择梯度A，使得空间中某个平面上所有的自旋子被激发；(1) The excitation pulse is applied to the acquisition object through the radio frequency coil, and at the same time, the gradient A is selected in conjunction with the first layer, so that all the spinons on a certain plane in the space are excited;
(2)施加第一相位编码梯度U，使得自旋子具备一定的不同的初始相位，用于磁共振二维成像；(2) Applying the first phase encoding gradient U so that the spinons have certain different initial phases for magnetic resonance two-dimensional imaging;
(3)施加读出预散相J；(3) apply the readout pre-dispersion phase J;
(4)施加第一读出梯度G，同时开启模数转换器，采集磁共振信号，此时采集到的磁共振信号为回波平移信号；(4) Applying the first readout gradient G, and simultaneously turning on the analog-to-digital converter to collect magnetic resonance signals, the magnetic resonance signals collected at this time are echo translation signals;
(5)施加读出回聚-预散相梯度E；(5) Apply readout refocusing-pre-dispersion gradient E;
(6)施加第二读出梯度H，同时开启模数转换器，采集磁共振信号，此时采集到的信号为时间反转稳态进动信号。(6) The second readout gradient H is applied, and the analog-to-digital converter is turned on at the same time to collect magnetic resonance signals. The signals collected at this time are time-reversed steady-state precession signals.
基于图2所示的序列，本发明还可以结合部分回波(不对称)技术减小重复周期，缩短磁共振成像的时间。由于部分回波技术使得回波中心不在读出梯度G\H和采集的磁共振信号(回波信号\时间反转稳态进动信号)的中心，减少了读出梯度G和H的持续时间，从而能够缩短重复周期。这种情况下，读出方向的梯度仅需满足：MJ+ME+MF+MG+MH＝0；其中梯度J、E、F的极性相同；梯度G、H与梯度J、E、F的极性相反。Based on the sequence shown in FIG. 2 , the present invention can also combine partial echo (asymmetric) technology to reduce the repetition period and shorten the time of magnetic resonance imaging. Due to the partial echo technology, the echo center is not at the center of the readout gradient G\H and the acquired magnetic resonance signal (echo signal\time-reversed steady-state precession signal), reducing the duration of the readout gradient G and H , so that the repetition period can be shortened. In this case, the gradient in the readout direction only needs to satisfy: MJ + ME + MF + MG + MH = 0; where gradients J, E, and F have the same polarity; gradients G, H and gradient J , E, F are opposite in polarity.
本发明提供另一种如图3所示的可应用于图1所示方法进行磁共振二维成像的稳态自由进动序列实例，该序列包括激发脉冲、层面选择方向的梯度、相位编码方向的梯度、读出方向的梯度。其中，梯度J、G、H、F满足关系：MJ+MF+MG+MH＝0；并且，第一读出梯度G和第二读出梯度H的极性相反。The present invention provides another example of a steady-state free precession sequence as shown in FIG. 3 that can be applied to the method shown in FIG. 1 for two-dimensional magnetic resonance imaging. The sequence includes excitation pulses, gradients in slice selection directions, and phase encoding directions The gradient of the readout direction and the gradient of the readout direction. Wherein, the gradients J, G, H, and F satisfy the relationship: MJ +MF +MG +MH =0; and, the polarities of the first readout gradient G and the second readout gradient H are opposite.
与图2所示的稳态自由进动序列相比，图3所示的序列中，施加第一读出梯度G之后，以及施加第二读出梯度H之前，不施加读出回聚-预散相梯度E。这是因为图3所示的序列是使用双极型读出的方式去掉读出回聚-预散相梯度E，以达到减小重复周期的效果，缩短磁共振成像的时间。Compared with the steady-state free precession sequence shown in Fig. 2, in the sequence shown in Fig. 3, after applying the first readout gradient G and before applying the second readout gradient H, no readout refocusing-pre- Dephase gradient E. This is because the sequence shown in FIG. 3 uses a bipolar readout method to remove the readout refocusing-pre-dispersion gradient E, so as to achieve the effect of reducing the repetition period and shorten the time of magnetic resonance imaging.
本发明提供一种如图4所示的可应用于图1所示方法进行磁共振三维成像的稳态自由进动序列实例，该序列包括激发脉冲、层面选择方向的梯度、相位编码方向的梯度、读出方向的梯度。The present invention provides an example of a steady-state free precession sequence as shown in FIG. 4 that can be applied to the method shown in FIG. 1 for three-dimensional magnetic resonance imaging. The sequence includes excitation pulses, gradients in slice selection directions, and gradients in phase encoding directions , the gradient in the readout direction.
图4中，激发脉冲是一组等间距、相同翻转角度α的脉冲信号。ADC#1表示在施加第一读出梯度G的同时采集回波平移信号。ADC#2表示在施加第二读出梯度H的同时采集时间反转稳态进动信号。In Fig. 4, the excitation pulse is a group of pulse signals with equal intervals and the same flip angle α. ADC#1 represents the acquisition of the echo translation signal while applying the first readout gradient G. ADC#2 represents the acquisition of a time-reversed steady-state precession signal while a second readout gradient H is applied.
基于图4，每一个重复周期内，在施加所述第一层面选择梯度A之后，施加第一读出梯度G之前，还包括：在层面选择方向施加第三相位编码梯度S；以及，在采集得到时间反转稳态进动信号之后，还包括：在层面选择方向施加第四相位编码梯度T。Based on FIG. 4 , in each repetition period, after applying the first slice selection gradient A and before applying the first readout gradient G, it further includes: applying a third phase encoding gradient S in the slice selection direction; and, during the acquisition After obtaining the time-reversed steady-state precession signal, the method further includes: applying a fourth phase encoding gradient T in the slice selection direction.
在一种较佳的实施例中，图4的第三相位编码梯度S可以与第二层面选择梯度B合并，第四相位编码梯度T可以与第四层面选择梯度C合并。In a preferred embodiment, the third phase encoding gradient S in FIG. 4 can be combined with the second layer selection gradient B, and the fourth phase encoding gradient T can be combined with the fourth layer selection gradient C.
图5中，(a)是本发明采集到的二维回波平移图像；(b)本发明采集到的二维时间反转稳态进动图像；(c)是单独利用回波平移序列采集到的回波平移图像；(d)是单独利用时间反转稳态进动序列扫描的时间反转稳态进动图像。Among Fig. 5, (a) is the two-dimensional echo translation image that the present invention collects; (b) the two-dimensional time-reversal steady-state precession image that the present invention collects; (c) is to utilize echo translation sequence acquisition alone The obtained echo translation image; (d) is the time-reversal steady-state precession image scanned by the time-reversal steady-state precession sequence alone.
基本共同采集参数为：The basic common acquisition parameters are:
视野范围：384mm*384mmField of view: 384mm*384mm
层厚：5mmLayer thickness: 5mm
分辨率：384*384Resolution: 384*384
脉冲翻转角：20degreePulse flip angle: 20degree
本发明提出的序列：The sequence proposed by the present invention:
重复时间/回波时间：8ms/2.4ms，采集带宽：610Hz/pixelRepetition time/echo time: 8ms/2.4ms, acquisition bandwidth: 610Hz/pixel
回波平移序列：Echo panning sequence:
重复时间/回波时间：5ms/2.5ms，采集带宽：592Hz/pixelRepetition time/echo time: 5ms/2.5ms, acquisition bandwidth: 592Hz/pixel
时间反转稳态进动序列：Time-reversed steady-state precession sequence:
重复时间/回波时间：5ms/2.5ms，采集带宽：592Hz/pixelRepetition time/echo time: 5ms/2.5ms, acquisition bandwidth: 592Hz/pixel
对比图5(a)～(d)可知，本发明采集的图像与单独利用回波平移序列和时间反转稳态进动序列分别采集到的图像具有相似的对比度。但本发明能够满足同时采集回波平移信号和时间反转稳态进动信号的需要，获取温度信息和组织T2变化信息，明显缩短磁共振成像时间。Comparing Figures 5(a) to (d), it can be seen that the images collected by the present invention have similar contrast to the images collected by using the echo translation sequence and the time-reversal steady-state precession sequence alone. However, the present invention can meet the requirement of simultaneously collecting echo translation signals and time-reversal steady-state precession signals, obtain temperature information and tissue T2 change information, and significantly shorten the magnetic resonance imaging time.
以上所述的具体实施例，对本发明的目的、技术方案和有益效果进行了进一步详细说明，所应理解的是，以上所述仅为本发明的具体实施例而已，并不用于限定本发明的保护范围，凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.
本领域技术人员还可以了解到本发明实施例列出的各种说明性逻辑块(illustrativelogical block)，单元，和步骤可以通过电子硬件、电脑软件，或两者的结合进行实现。为清楚展示硬件和软件的可替换性(interchangeability)，上述的各种说明性部件(illustrativecomponents)，单元和步骤已经通用地描述了它们的功能。这样的功能是通过硬件还是软件来实现取决于特定的应用和整个系统的设计要求。本领域技术人员可以对于每种特定的应用，可以使用各种方法实现所述的功能，但这种实现不应被理解为超出本发明实施例保护的范围。Those skilled in the art can also understand that various illustrative logical blocks (illustrativelogical blocks), units, and steps listed in the embodiments of the present invention can be implemented by electronic hardware, computer software, or a combination of both. To clearly demonstrate the interchangeability of hardware and software, the various illustrative components, units and steps above have generally described their functions. Whether such functions are implemented by hardware or software depends on the specific application and overall system design requirements. Those skilled in the art may use various methods to implement the described functions for each specific application, but such implementation should not be understood as exceeding the protection scope of the embodiments of the present invention.
本发明实施例中所描述的各种说明性的逻辑块，或单元，或装置都可以通过通用处理器，数字信号处理器，专用集成电路(ASIC)，现场可编程门阵列或其它可编程逻辑装置，离散门或晶体管逻辑，离散硬件部件，或上述任何组合的设计来实现或操作所描述的功能。通用处理器可以为微处理器，可选地，该通用处理器也可以为任何传统的处理器、控制器、微控制器或状态机。处理器也可以通过计算装置的组合来实现，例如数字信号处理器和微处理器，多个微处理器，一个或多个微处理器联合一个数字信号处理器核，或任何其它类似的配置来实现。Various illustrative logic blocks, or units, or devices described in the embodiments of the present invention can be implemented by a general-purpose processor, a digital signal processor, an application-specific integrated circuit (ASIC), a field programmable gate array or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to implement or operate the described functions. The general-purpose processor may be a microprocessor, and optionally, the general-purpose processor may also be any conventional processor, controller, microcontroller or state machine. A processor may also be implemented by a combination of computing devices, such as a digital signal processor and a microprocessor, multiple microprocessors, one or more microprocessors combined with a digital signal processor core, or any other similar configuration to accomplish.
本发明实施例中所描述的方法或算法的步骤可以直接嵌入硬件、处理器执行的软件模块、或者这两者的结合。软件模块可以存储于RAM存储器、闪存、ROM存储器、EPROM存储器、EEPROM存储器、寄存器、硬盘、可移动磁盘、CD-ROM或本领域中其它任意形式的存储媒介中。示例性地，存储媒介可以与处理器连接，以使得处理器可以从存储媒介中读取信息，并可以向存储媒介存写信息。可选地，存储媒介还可以集成到处理器中。处理器和存储媒介可以设置于ASIC中，ASIC可以设置于用户终端中。可选地，处理器和存储媒介也可以设置于用户终端中的不同的部件中。The steps of the method or algorithm described in the embodiments of the present invention may be directly embedded in hardware, a software module executed by a processor, or a combination of both. The software modules may be stored in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM or any other storage medium in the art. Exemplarily, the storage medium can be connected to the processor, so that the processor can read information from the storage medium, and can write information to the storage medium. Optionally, the storage medium can also be integrated into the processor. The processor and the storage medium can be set in the ASIC, and the ASIC can be set in the user terminal. Optionally, the processor and the storage medium may also be set in different components in the user terminal.
在一个或多个示例性的设计中，本发明实施例所描述的上述功能可以在硬件、软件、固件或这三者的任意组合来实现。如果在软件中实现，这些功能可以存储与电脑可读的媒介上，或以一个或多个指令或代码形式传输于电脑可读的媒介上。电脑可读媒介包括电脑存储媒介和便于使得让电脑程序从一个地方转移到其它地方的通信媒介。存储媒介可以是任何通用或特殊电脑可以接入访问的可用媒体。例如，这样的电脑可读媒体可以包括但不限于RAM、ROM、EEPROM、CD-ROM或其它光盘存储、磁盘存储或其它磁性存储装置，或其它任何可以用于承载或存储以指令或数据结构和其它可被通用或特殊电脑、或通用或特殊处理器读取形式的程序代码的媒介。此外，任何连接都可以被适当地定义为电脑可读媒介，例如，如果软件是从一个网站站点、服务器或其它远程资源通过一个同轴电缆、光纤电缆、双绞线、数字用户线(DSL)或以例如红外、无线和微波等无线方式传输的也被包含在所定义的电脑可读媒介中。所述的碟片(disk)和磁盘(disc)包括压缩磁盘、镭射盘、光盘、DVD、软盘和蓝光光盘，磁盘通常以磁性复制数据，而碟片通常以激光进行光学复制数据。上述的组合也可以包含在电脑可读媒介中。In one or more exemplary designs, the above functions described in the embodiments of the present invention may be implemented in hardware, software, firmware or any combination of the three. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media and communication media that facilitate transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a general purpose or special computer. For example, such computer-readable media may include, but are not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other device that can be used to carry or store instructions or data structures and Other medium of program code in a form readable by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. In addition, any connection is properly defined as a computer-readable medium, for example, if the software is transmitted from a website site, server, or other remote source via a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) Or transmitted by wireless means such as infrared, wireless and microwave are also included in the definition of computer readable media. Disks and discs include compact discs, laser discs, optical discs, DVDs, floppy discs, and Blu-ray discs. Disks usually reproduce data magnetically, while discs usually reproduce data optically using lasers. Combinations of the above can also be contained on a computer readable medium.
| Application Number | Priority Date | Filing Date | Title |
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| CN201410826073.6ACN104523274B (en) | 2014-12-25 | 2014-12-25 | A Magnetic Resonance Imaging Method Using Steady-State Free Precession Sequence |
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| CN201410826073.6ACN104523274B (en) | 2014-12-25 | 2014-12-25 | A Magnetic Resonance Imaging Method Using Steady-State Free Precession Sequence |
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| CN104523274Atrue CN104523274A (en) | 2015-04-22 |
| CN104523274B CN104523274B (en) | 2016-11-09 |
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| CN201410826073.6AActiveCN104523274B (en) | 2014-12-25 | 2014-12-25 | A Magnetic Resonance Imaging Method Using Steady-State Free Precession Sequence |
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