System and method for synchronous multi-slice magnetic resonance imaging
阅读说明：本技术 同步多层磁共振成像的系统、方法 (System and method for synchronous multi-slice magnetic resonance imaging ) 是由 郑远 赵乐乐 徐健 张卫国 于 2020-07-10 设计创作，主要内容包括：本发明涉及一种同步多层磁共振成像的系统。在多个帧的每一帧中,该系统可以指示MRI扫描仪对受试目标的多个切片位置中的每个切片位置进行多个PE步骤以获取回波信号。可以在帧的至少一些PE步骤的每一个PE步骤中施加相位调制磁场梯度。对于每一帧,该系统可以基于相应的回波信号来重建代表该帧中的切片位置的混叠图像。该系统还可以基于混叠图像来生成多个参考切片图像。该系统可以进一步基于混叠图像和参考切片图像来重建至少一个切片图像。每个切片图像可以代表每一帧中的多个切片位置中的一个切片位置。(The invention relates to a system for synchronous multi-slice magnetic resonance imaging. In each of the plurality of frames, the system may instruct the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject to acquire echo signals. A phase-modulated magnetic field gradient may be applied in each of at least some of the PE steps of the frame. For each frame, the system may reconstruct an aliased image representing the slice position in the frame based on the corresponding echo signal. The system may also generate a plurality of reference slice images based on the aliased images. The system may further reconstruct at least one slice image based on the aliased image and the reference slice image. Each slice image may represent one of a plurality of slice positions in each frame.)
1. A system for synchronized multi-slice magnetic resonance imaging, comprising:
at least one storage device storing a set of instructions; and
at least one processor in communication with the at least one storage device, wherein the set of instructions, when executed, are configured to direct the system to perform operations comprising:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals, wherein a phase-modulated magnetic field gradient is applied in each of at least a portion of the PE steps in the frame;
for each frame of the plurality of frames, reconstructing an aliased image representing a plurality of slice locations in the frame based on the corresponding set of echo signals;
Generating a plurality of reference slice images based on the resulting plurality of aliased images, wherein each of the plurality of reference slice images represents each of the plurality of slice positions in more than one of the plurality of frames; and
reconstructing at least one slice image based on the plurality of aliased images and the plurality of reference slice images, wherein each slice image of the at least one slice image represents one slice position of the plurality of slice positions in each frame of the plurality of frames.
2. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein:
the plurality of slice positions comprises a first slice position and at least one second slice position; and
for the PE steps corresponding to PE lines at the same position in K-space and applied in a pair of frames of the plurality of frames, a phase difference between the at least one second slice position and the first slice position is different in one of the PE steps.
3. The synchronized multi-slice magnetic resonance imaging system of claim 2, wherein:
the at least one second slice position comprises a second slice position; and
For the PE step corresponding to a PE line at the same position in K-space and applied in a pair of frames of the plurality of frames, a phase difference between the second slice position and the first slice position varies by 180 degrees in one of the PE steps.
4. The synchronized multi-slice magnetic resonance imaging system of claim 2, wherein:
the at least one second slice position comprises two second slice positions;
for the PE step corresponding to a PE line at the same position in K-space and applied in a pair of frames of the plurality of frames,
in one of the PE steps, a phase difference between the first slicing position and one of the two second slicing positions varies by 120 degrees; and
in one of the PE steps, a phase difference between the first slice position and the other of the two second slice positions varies by 240 degrees.
5. The synchronized multi-slice magnetic resonance imaging system of claim 2, wherein the at least one second slice position in each pair of successive PE steps in the plurality of PE steps is out of phase in at least one frame in the plurality of frames.
6. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein the reconstructing the at least one slice image based on the plurality of aliased images and the plurality of reference slice images is according to a parallel imaging reconstruction algorithm.
7. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein:
applying a compensating magnetic field gradient in a slice encoding direction after readout of the corresponding echo signal in at least one PE step in at least one of the plurality of frames, wherein the compensating magnetic field gradient has a same magnitude and an opposite gradient direction as the phase-modulated magnetic field gradient applied in the at least one PE step.
8. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein:
in at least one PE step in at least one of the plurality of frames, a phase modulated RF excitation pulse is applied to excite the plurality of slice positions, and phase modulation in the at least one PE step is achieved by combining the phase modulated RF excitation pulse and the phase modulated magnetic field gradient applied in the at least one PE step.
9. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein the plurality of PE steps are implemented using at least one of a bSSFP pulse sequence, a FSE pulse sequence, an EPI pulse sequence, an spGRE pulse sequence.
10. The synchronized multi-slice magnetic resonance imaging system of claim 1, wherein in at least one PE step in at least one of the plurality of frames, the phase-modulated magnetic field gradients are applied along a slice encoding direction after the plurality of slice locations are excited and before the corresponding echo signals are read out.
11. A synchronized multi-slice magnetic resonance imaging system, comprising:
at least one storage device storing a set of instructions; and
at least one processor in communication with the at least one storage device, wherein the set of instructions, when executed, are configured to direct the system to perform operations comprising:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals; wherein each echo signal of the set of echo signals corresponds to a PE line in K-space, the plurality of slice locations comprising a first slice location and at least one second slice location;
Reconstructing at least one slice image based on the plurality of sets of echo signals acquired in the plurality of frames, wherein each slice image of the at least one slice image represents one slice position of the plurality of slice positions in each frame of the plurality of frames;
wherein a phase-modulated magnetic field gradient is applied in at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied in a pair of the plurality of frames.
12. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein in at least one PE step in at least one of the plurality of frames, the phase-modulated magnetic field gradients are applied along a slice encoding direction after the plurality of slice locations are excited and before the corresponding echo signals are read out.
13. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein to reconstruct the at least one slice image the at least one processor is further configured to instruct the system to perform operations comprising:
For each frame of the plurality of frames, reconstructing an aliased image representative of the plurality of slice locations in the frame based on the corresponding set of echo signals;
generating a plurality of reference slice images based on the resulting plurality of aliased images, wherein each of the plurality of reference slice images represents each of the plurality of slice positions in more than one of the plurality of frames; and
reconstructing the at least one slice image based on the plurality of aliased images and the plurality of reference slice images.
14. The synchronized multi-slice magnetic resonance imaging system of claim 13, wherein the reconstructing the at least one slice image based on the plurality of aliased images and the plurality of reference slice images is according to a parallel imaging reconstruction algorithm.
15. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein:
applying a compensating magnetic field gradient along a slice encoding direction after readout of the corresponding echo signal in at least one PE step in at least one of the plurality of frames, wherein the compensating magnetic field gradient has a same magnitude and an opposite gradient direction as the phase-modulated magnetic field gradient applied in the at least one PE step.
16. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein:
in at least one PE step in at least one of the plurality of frames, a phase modulated RF excitation pulse is applied to excite the plurality of slice positions, and phase modulation in the at least one PE step is achieved by combining the phase modulated RF excitation pulse and the phase modulated magnetic field gradient applied in the at least one PE step.
17. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein the at least one second slice position in each pair of successive PE steps in the plurality of PE steps is out of phase in at least one frame in the plurality of frames.
18. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein:
the at least one second slice position comprises a second slice position; and
for the PE step in a pair of frames corresponding to PE lines at the same position in K-space and applied to the plurality of frames, a phase difference between the second slice position and the first slice position varies by 180 degrees in one of the PE steps.
19. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein:
the at least one second slice position comprises two second slice positions;
for the PE step in a pair of frames corresponding to PE lines at the same position in K-space and applied to the plurality of frames,
in one of the PE steps, a phase difference between the first slicing position and one of the two second slicing positions varies by 120 degrees; and
in one of the PE steps, a phase difference between the first slice position and the other of the two second slice positions varies by 240 degrees.
20. The synchronized multi-slice magnetic resonance imaging system of claim 11, wherein the plurality of PE steps are implemented using at least one of a bSSFP pulse sequence, a FSE pulse sequence, an EPI pulse sequence, an spGRE pulse sequence.
21. A method of synchronized multi-slice magnetic resonance imaging, implemented on a computing device having at least one processor and at least one memory device, the method comprising the steps of:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals, wherein a phase-modulated magnetic field gradient is applied in each of at least a portion of the PE steps in the frame;
For each frame of the plurality of frames, reconstructing an aliased image representing a plurality of slice locations in the frame based on the corresponding set of echo signals;
generating a plurality of reference slice images based on the resulting plurality of aliased images, wherein each of the plurality of reference slice images represents each of the plurality of slice positions in more than one of the plurality of frames; and
reconstructing at least one slice image based on the plurality of aliased images and the plurality of reference slice images, wherein each slice image of the at least one slice image represents one slice position of the plurality of slice positions in each frame of the plurality of frames.
22. A method of synchronized multi-slice magnetic resonance imaging, implemented on a computing device having at least one processor and at least one memory device, the method comprising the steps of:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals; wherein each echo signal of the set of echo signals corresponds to a PE line in K-space, the plurality of slice locations comprising a first slice location and at least one second slice location;
Reconstructing at least one slice image based on the plurality of sets of echo signals acquired in the plurality of frames, wherein each slice image of the at least one slice image represents one slice position of the plurality of slice positions in each frame of the plurality of frames;
wherein a phase-modulated magnetic field gradient is applied in at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied in a pair of the plurality of frames.
23. A non-transitory computer-readable storage medium storing instructions for synchronized multi-slice magnetic resonance imaging, the instructions, when accessed by at least one processor of a system, instruct the system to perform a method comprising:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals, wherein a phase-modulated magnetic field gradient is applied in each of at least a portion of the PE steps in the frame;
For each frame of the plurality of frames, reconstructing an aliased image representing a plurality of slice locations in the frame based on the corresponding set of echo signals;
generating a plurality of reference slice images based on the resulting plurality of aliased images, wherein each of the plurality of reference slice images represents each of the plurality of slice positions in more than one of the plurality of frames; and
reconstructing at least one slice image based on the plurality of aliased images and the plurality of reference slice images, wherein each slice image of the at least one slice image represents one slice position of the plurality of slice positions in each frame of the plurality of frames.
24. A non-transitory computer-readable storage medium storing instructions for synchronized multi-slice magnetic resonance imaging, the instructions, when accessed by at least one processor of a system, instruct the system to perform a method comprising:
instructing the MRI scanner to perform a plurality of PE steps for each of a plurality of slice positions of the subject target in each of a plurality of frames to acquire a set of echo signals; wherein each echo signal of the set of echo signals corresponds to a PE line in K-space, the plurality of slice locations comprising a first slice location and at least one second slice location;
Reconstructing at least one slice image based on the sets of echo signals acquired in the plurality of frames, each slice image of the at least one slice image representing one slice position of the plurality of slice positions in each frame of the plurality of frames;
wherein a phase-modulated magnetic field gradient is applied in at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied in a pair of the plurality of frames.
Technical Field
The present invention relates to the field of Magnetic Resonance Imaging (MRI), and in particular, to a system and method for synchronous Multi-Slice (SMS) MRI.
Background
SMS imaging has been applied to MRI to simultaneously excite multiple slice positions of a subject (e.g., a scanned object) to speed up the scanning process. In general, additional reference scans may need to be performed to acquire reference data for each slice position for slice separation. For example, reference slice images of slice positions may be reconstructed and coil sensitivity profiles of different receiver coils may be determined. The slice images for each individual slice position may be separated from the aliased images acquired in the SMS based on the coil sensitivity profiles. However, additional reference scans may result in additional scan times and impair the advantages of SMS. Accordingly, there is a need to develop a system and method for synchronized multi-slice magnetic resonance imaging (i.e., SMS-MRI) to eliminate the need for additional reference scans and improve imaging efficiency.
Disclosure of Invention
According to one aspect of the invention, a system for simultaneous multi-slice magnetic resonance imaging is provided. The system may include: at least one storage device storing a set of instructions; and at least one processor in communication with the at least one storage device. The at least one processor, when executing the set of instructions, may be configured to direct the system to: in each of the plurality of frames, the at least one processor may be configured to direct the system to instruct the MRI scanner to perform a plurality of Phase-Encoding (PE) steps for each of a plurality of slice positions of the object under test to obtain a set of echo signals. A phase-modulated magnetic field gradient may be applied in each of at least a portion of the PE steps of the plurality of PE steps in the frame. For each of the plurality of frames, the at least one processor may be configured to instruct the system to reconstruct an aliased image representing a plurality of slice locations in the frame based on the corresponding set of echo signals. The at least one processor may be further configured to instruct the system to generate a plurality of reference slice images based on the resulting plurality of aliased images. Each of the plurality of reference slice images may represent each of the plurality of slice positions in more than one of the plurality of frames. The at least one processor may be further configured to instruct the system to reconstruct at least one slice image based on the plurality of aliased images and the plurality of reference slice images. Wherein each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames.
In some embodiments, the plurality of slice positions may include a first slice position and at least one second slice position. For the PE step corresponding to a PE line at the same position in K-space and applied in a pair of frames of the plurality of frames, a phase difference between the at least one second slice position and the first slice position may be different in one of the PE steps.
In some embodiments, the at least one second slice position may comprise one second slice position. For the PE step corresponding to a PE line at the same position in K-space and applied in a pair of frames of the plurality of frames, a phase difference between the second slice position and the first slice position may vary by 180 degrees in one of the PE steps.
In some embodiments, the at least one second slice position may include two second slice positions. For the PE step corresponding to a PE line at the same position in K-space and applied to a pair of frames of the plurality of frames, a phase difference between the first slice position and one of the two second slice positions may be changed by 120 degrees in one of the PE steps. In one of the PE steps, a phase difference between the first slicing position and the other of the two second slicing positions may be varied by 240 degrees.
In some embodiments, the phase of the at least one second slice position in each pair of consecutive PE steps in the plurality of PE steps may be different in at least one of the plurality of frames.
In some embodiments, the reconstructing the at least one slice image based on the plurality of aliased images and the plurality of reference slice images may be performed according to a parallel imaging reconstruction algorithm.
In some embodiments, in at least one PE step in at least one of the plurality of frames, after readout of the corresponding echo signals, a compensating magnetic field gradient may be applied along a slice encoding direction. Wherein the compensation magnetic field gradient and the phase modulated magnetic field gradient applied in the at least one PE step may have the same magnitude and opposite gradient directions.
In some embodiments, in at least one PE step in at least one of the plurality of frames, a phase modulating RF excitation pulse may be applied to excite the plurality of slice positions, and phase modulation in the at least one PE step may be achieved by combining the phase modulating RF excitation pulse and the phase modulating magnetic field gradient applied in the at least one PE step.
In some embodiments, the multiple PE steps may be implemented using at least one of a bSSFP (all: balanced Steady-State Free Precession, Chinese), FSE (all: Fast SpinEcho, Chinese: Fast spin Echo) pulse sequence, EPI (all: Echo Planar Imaging, Chinese: Echo Planar Imaging) pulse sequence, and spGRE (all: diffused Gradient Echo, Chinese: attenuated Gradient Echo) pulse sequence.
In some embodiments, the phase-modulated magnetic field gradient may be applied along a slice encoding direction after the plurality of slice positions are excited and before the corresponding echo signals are read out in at least one PE step in at least one of the plurality of frames.
According to one aspect of the invention, a system for simultaneous multi-slice magnetic resonance imaging is provided. The system may include: at least one storage device storing a set of instructions; and at least one processor in communication with the at least one storage device. The at least one processor, when executing the set of instructions, may be configured to direct the system to: in each of the plurality of frames, the at least one processor is configured to instruct the system to instruct the MRI scanner to perform a plurality of PE steps on each of a plurality of slice positions of the subject target to acquire a set of echo signals. Wherein each echo signal of the set of echo signals may correspond to a PE line in K-space, the plurality of slice positions may include a first slice position and at least one second slice position. The at least one processor may be further configured to instruct the system to reconstruct at least one slice image based on the sets of echo signals acquired in the plurality of frames. Wherein each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames. In at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames, a phase-modulated magnetic field gradient may be applied such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied in a pair of the plurality of frames.
In some embodiments, for each of the plurality of frames, the at least one processor may be configured to reconstruct an aliased image representing the plurality of slice locations in the frame based on the corresponding set of echo signals. The at least one processor may be further configured to instruct the system to generate a plurality of reference slice images based on the resulting plurality of aliased images. Each of the plurality of reference slice images may represent each of the plurality of slice positions in more than one of the plurality of frames. The at least one processor may be further configured to instruct the system to reconstruct the at least one slice image based on the plurality of aliased images and the plurality of reference slice images.
According to another aspect of the invention, a method for synchronized multi-slice magnetic resonance imaging is provided. In each of the plurality of frames, the method may include: the MRI scanner is instructed to perform a plurality of PE steps for each of a plurality of slice positions of the subject object to acquire a set of echo signals. A phase-modulated magnetic field gradient may be applied in each of at least a portion of the PE steps of the plurality of PE steps in the frame. For each frame of the plurality of frames, the method may comprise: reconstructing aliased images representative of a plurality of slice locations in the frame based on the corresponding set of echo signals. The method may further include generating a plurality of reference slice images based on the obtained plurality of aliased images. Wherein each of the plurality of reference slice images may represent each of the plurality of slice positions in more than one of the plurality of frames; the method may further include reconstructing at least one slice image based on the plurality of aliased images and the plurality of reference slice images. Wherein each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames.
In some embodiments, the plurality of slice positions comprises a first slice position and at least one second slice position; and for the PE step corresponding to a PE line at the same position in K space and applied to a pair of frames of the plurality of frames, a phase difference between the at least one second slice position and the first slice position is different in one of the PE steps.
In some embodiments, the at least one second slice position comprises one second slice position; and for the PE step in a pair of frames corresponding to a PE line at the same position in K-space and applied to the plurality of frames, a phase difference between the second slice position and the first slice position varies by 180 degrees in one of the PE steps.
In some embodiments, the at least one second slice position comprises two second slice positions; for the PE steps corresponding to PE lines at the same location in K-space and applied in a pair of frames of the plurality of frames: in one of the PE steps, a phase difference between the first slice position and one of the two second slice positions varies by 120 degrees; and in one of the PE steps, a phase difference between the first slicing position and the other of the two second slicing positions varies by 240 degrees.
In some embodiments, the at least one second slice position in each pair of consecutive PE steps in the plurality of PE steps is out of phase in at least one of the plurality of frames.
In some embodiments, said reconstructing said at least one slice image based on said plurality of aliased images and said plurality of reference slice images is according to a parallel imaging reconstruction algorithm.
In some embodiments, in at least one PE step in at least one of the plurality of frames, after readout of the corresponding echo signal, a compensation magnetic field gradient is applied along a slice encoding direction, wherein the compensation magnetic field gradient has the same magnitude and an opposite gradient direction as the phase-modulated magnetic field gradient applied in the at least one PE step.
In some embodiments, in at least one PE step in at least one of the plurality of frames, a phase modulated RF excitation pulse is applied to excite the plurality of slice positions, and phase modulation in the at least one PE step is achieved by combining the phase modulated RF excitation pulse and the phase modulated magnetic field gradient applied in the at least one PE step.
In some embodiments, the plurality of PE steps are implemented using at least one of a bSSFP pulse sequence, a FSE pulse sequence, an EPI pulse sequence, and an spGRE pulse sequence.
In some embodiments, the phase-modulated magnetic field gradients are applied along a slice encoding direction after the plurality of slice positions are excited and before the corresponding echo signals are read out in at least one PE step in at least one of the plurality of frames.
According to another aspect of the invention, a method for synchronized multi-slice magnetic resonance imaging is provided. In each of the plurality of frames, the method may include: the MRI scanner is instructed to perform a plurality of PE steps for each of a plurality of slice positions of the subject object to acquire a set of echo signals. Wherein each echo signal of the set of echo signals may correspond to one PE line in K-space. The plurality of slice positions may include a first slice position and at least one second slice position. The method further includes reconstructing at least one slice image based on the sets of echo signals acquired in the plurality of frames. Wherein each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames. In at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames, a phase-modulated magnetic field gradient may be applied such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied in a pair of the plurality of frames.
In some embodiments, the phase-modulated magnetic field gradients are applied along a slice encoding direction after the plurality of slice positions are excited and before the corresponding echo signals are read out in at least one PE step in at least one of the plurality of frames.
In some embodiments, said reconstructing said at least one slice image comprises: for each frame of the plurality of frames, reconstructing an aliased image representing the plurality of slice locations in the frame based on the corresponding set of echo signals; generating a plurality of reference slice images based on the resulting plurality of aliased images, wherein each of the plurality of reference slice images represents each of the plurality of slice positions in more than one of the plurality of frames; and reconstructing the at least one slice image based on the plurality of aliased images and the plurality of reference slice images.
In some embodiments, said reconstructing said at least one slice image based on said plurality of aliased images and said plurality of reference slice images is according to a parallel imaging reconstruction algorithm.
In some embodiments, in at least one PE step in at least one of the plurality of frames, after readout of the corresponding echo signal, a compensation magnetic field gradient is applied along a slice encoding direction, wherein the compensation magnetic field gradient has the same magnitude and an opposite gradient direction as the phase-modulated magnetic field gradient applied in the at least one PE step.
In some embodiments, in at least one PE step in at least one of the plurality of frames, a phase modulated RF excitation pulse is applied to excite the plurality of slice positions, and phase modulation in the at least one PE step is achieved by combining the phase modulated RF excitation pulse and the phase modulated magnetic field gradient applied in the at least one PE step.
In some embodiments, the at least one second slice position in each pair of consecutive PE steps in the plurality of PE steps is out of phase in at least one of the plurality of frames.
In some embodiments, the at least one second slice position comprises one second slice position; and for the PE step in a pair of frames corresponding to a PE line at the same position in K-space and applied to the plurality of frames, a phase difference between the second slice position and the first slice position varies by 180 degrees in one of the PE steps.
In some embodiments, the at least one second slice position comprises two second slice positions; for the PE steps corresponding to PE lines at the same location in K-space and applied in a pair of frames of the plurality of frames: in one of the PE steps, a phase difference between the first slice position and one of the two second slice positions varies by 120 degrees; and in one of the PE steps, a phase difference between the first slicing position and the other of the two second slicing positions varies by 240 degrees.
In some embodiments, the plurality of PE steps are implemented using at least one of a bSSFP pulse sequence, a FSE pulse sequence, an EPI pulse sequence, an spGRE pulse sequence.
According to another aspect of the invention, a non-transitory computer-readable storage medium is provided that stores instructions for synchronized multi-slice magnetic resonance imaging that, when accessed by at least one processor of a system, instruct the system to perform a method. In each of the plurality of frames, the method may include: the MRI scanner is instructed to perform a plurality of PE steps for each of a plurality of slice positions of the subject object to acquire a set of echo signals. A phase-modulated magnetic field gradient may be applied in each of at least a portion of the PE steps of the plurality of PE steps in the frame. For each frame of the plurality of frames, the method may comprise: reconstructing aliased images representative of a plurality of slice locations in the frame based on the corresponding set of echo signals. The method may further include generating a plurality of reference slice images based on the obtained plurality of aliased images. Wherein each of the plurality of reference slice images may represent each of the plurality of slice positions in more than one of the plurality of frames; the method may further include reconstructing at least one slice image based on the plurality of aliased images and the plurality of reference slice images. Wherein each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames.
According to another aspect of the invention, a non-transitory computer-readable storage medium is provided that stores instructions for synchronized multi-slice magnetic resonance imaging that, when accessed by at least one processor of a system, instruct the system to perform a method. In each of the plurality of frames, the method may include: the MRI scanner is instructed to perform a plurality of PE steps for each of a plurality of slice positions of the subject object to acquire a set of echo signals. Wherein each echo signal of the set of echo signals may correspond to one PE line in K-space. The plurality of slice positions may include a first slice position and at least one second slice position. The method further includes reconstructing at least one slice image based on the sets of echo signals acquired in the plurality of frames. Each of the at least one slice image may represent one of the plurality of slice positions in each of the plurality of frames. Wherein in at least a portion of the PE steps of the plurality of PE steps in each of the plurality of frames, a phase-modulated magnetic field gradient may be applied such that a phase difference between the at least one second slice position and the first slice position in one of the PE steps is different for the PE steps corresponding to the PE line at a same location in K-space and applied to a pair of frames of the plurality of frames.
Additional features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following and the accompanying drawings or may be learned from practice or verification of the invention by way of example. The features of the present invention can be implemented by the practice or use of the methods, instrumentalities and combinations set forth in the detailed examples discussed below.
Drawings
The invention is further described by means of a number of exemplary embodiments, which are described in detail with reference to the drawings. These embodiments are non-limiting exemplary embodiments, which are not drawn to scale with reference to the accompanying drawings in which like reference numerals represent like structures in the several views of the drawings, and in which:
FIG. 1 is a schematic view of an MRI system in some embodiments of the present invention;
FIG. 2 is a schematic view of an MRI scanner in some embodiments of the present invention;
FIG. 3 is a schematic diagram of exemplary hardware and/or software components of a computing device in some embodiments of the invention;
FIG. 4 is a schematic diagram of exemplary hardware and/or software components of a mobile device in some embodiments of the present invention;
FIG. 5 is a schematic diagram of a framework of an exemplary processing device in some embodiments of the invention;
FIG. 6 is a flow diagram of an exemplary process for synchronizing multi-slice MRI in some embodiments of the present invention;
FIG. 7 is a schematic diagram of an exemplary bSSFP pulse sequence in some embodiments of the invention;
FIGS. 8A and 8B are exemplary aliased images of two slice locations in the heart in some embodiments of the invention;
FIGS. 9A and 9B are exemplary reference slice images of two slice locations in a heart in some embodiments of the invention;
FIG. 10 is an exemplary cardiac slice image in some embodiments of the invention;
FIG. 11 is a schematic diagram of an exemplary bSSFP pulse sequence in some embodiments of the invention;
FIG. 12 is a schematic diagram of an exemplary FSE pulse sequence in some embodiments of the invention;
fig. 13 is a schematic diagram of an exemplary EPI pulse sequence in some embodiments of the invention.
Detailed Description
In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In general, well-known methods, procedures, systems, components, and/or circuits have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present invention. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but covers the broadest scope consistent with the claims.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, "a" or "an" may refer to the singular and may include the plural unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should be understood that the terms "system," "unit," "module" and/or "block" as used herein are a way of distinguishing different components, elements, components, parts or assemblies at different levels in ascending order. However, if other terms of another expression can achieve the same purpose, these terms may be substituted therefor.
Generally, the terms "module," "unit," or "block" as used herein refer to a logical component contained in hardware or firmware, or to a collection of software instructions. The modules, units or blocks described herein may be implemented in software and/or hardware and may be stored in any type of non-transitory computer readable medium or another storage device. In some embodiments, software modules/units/blocks may be compiled and linked into an executable program. It should be appreciated that software modules may be invoked from other modules/units/blocks or themselves, and/or may be invoked in response to a detected event or interrupt. The software modules/units/blocks for running on a computing device (e.g.,
It will be understood that when an element, engine, module, or block is referred to as being "on," "connected to," or "coupled to" another element, engine, module, or block, it can be directly on, connected, coupled, or communicated to the other element, engine, module, or block, or intervening elements, engines, modules, or blocks may be present, unless the context clearly dictates otherwise. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed features. The terms "pixel" and "voxel" are used interchangeably herein to refer to an element in an image. The term "image" is used herein to refer to various forms of images including two-dimensional images, three-dimensional images, four-dimensional images, and the like.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention.
These and other features of the present invention, and the manner of operation and function of the related elements of structure, as well as the combination of parts and manufacturing costs, will become more apparent upon consideration of the following description of the invention taken in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. It will be understood that the figures are not drawn to scale.
The present invention provides systems and methods for non-invasive biomedical imaging, for example for disease diagnosis or research purposes. The system and method provided by the present invention are primarily concerned with SMS in MRI systems. It should be understood that this is for illustrative purposes only. The system and method provided by the present invention can be applied to any other kind of imaging system. In some embodiments, the imaging system may include a single modality imaging system and/or a multi-modality imaging system. The single modality imaging system may comprise, for example, an MRI system. The multi-modality imaging system may include, for example, an X-ray imaging-magnetic resonance imaging (X-ray MRI) system, a single photon emission computed tomography magnetic resonance imaging (SPECT-MRI) system, a digital subtraction angiography magnetic resonance imaging (DSA-MRI) system, a computed tomography-magnetic resonance imaging (MRI-CT) system, a positron emission tomography-magnetic resonance imaging (PET-MRI) system, and the like.
One aspect of the invention relates to a system and method for simultaneous imaging of multiple slice positions of a subject using an MRI scanner. The plurality of slice positions may include a first slice position and at least one second slice position. In each of the plurality of frames, the system and method may cause the MRI scanner to apply a plurality of PE steps to each of the plurality of slice locations to acquire a set of echo signals. In each of at least some of the PE steps in each frame, a phase-modulated magnetic field gradient (also referred to as a phase-modulated gradient for simplicity) may be applied such that the PE steps correspond to PE lines at the same location in K-space and are applied in a pair of frames of the plurality of frames, a phase difference between the at least one second slice location and the first slice location being different in one of the PE steps.
By applying phase modulation gradients, the systems and methods may reconstruct one or more slice images, each of which may represent a single slice location in a frame, based on multiple sets of echo signals acquired in the frame without performing additional reference scans. For example, the systems and methods may reconstruct aliased images of slice locations in each frame based on the corresponding set of echo signals, and generate reference slice images of slice locations based on the aliased images (e.g., linearly combine the aliased images). The system and method may further reconstruct slice images based on the aliased image and the reference slice images. In this manner, the system and method may avoid the need for additional reference scans, reduce scan time, and/or improve imaging efficiency, and/or improve the experience of scanning the object.
Furthermore, in some embodiments, the phase modulation of the present invention may be achieved by one or more phase modulation gradients applied by the Z-coil of the MRI scanner alone, or in combination with phase modulated Radio Frequency (RF) excitation pulses. Conventional methods for phase modulation when automatically calibrating SMS in multiple frames, such as controlled aliasing in parallel imaging, result in higher acceleration (CAIPIRINHA) techniques that may be limited by the pulse sequence using only phase-modulated RF excitation pulses, so that without an echo sequence, only one PE data line is acquired per RF excitation pulse. The system and the method provided by the invention can be suitable for not only an attenuated Gradient Echo (spGRE) sequence, but also a balanced Steady-State free precession (bSSFP) pulse sequence. The technique of the present invention can also be applied to sequences having an Echo train, such as Echo Planar Imaging (EPI) pulse sequences and Fast Spin Echo (FSE) pulse sequences.
FIG. 1 is a schematic diagram of an exemplary MRI system 100 in accordance with some embodiments of the present invention. Referring to fig. 1, an MRI system 100 may include an MRI scanner 110 (or MR scanner), a
The
The subject scanned by the
For ease of illustration, a coordinate system 160 including an X-axis, a Y-axis, and a Z-axis is provided in FIG. 1. The X and Z axes shown in fig. 1 may be horizontal and the Y axis may be vertical. As shown in fig. 1, the positive X-direction along the X-axis may be from the right side to the left side of the
In some embodiments, the
The
The storage device 130 may store data, instructions, and/or any other information. In some embodiments, the storage device 130 may store data acquired from the
In some embodiments, the storage device 130 may be connected to a network 150 to communicate with one or more other components in the MRI system 100 (e.g., the
The terminal 140 may be used to enable user interaction between a user and the MRI system 100. For example, one or more of the terminals 140 may accept user-entered instructions for the
The network 150 may include any suitable network that may facilitate the exchange of information and/or data for the MRI system 100. In some embodiments, one or more components of the MRI system 100 (e.g., the
The above description is intended to be illustrative of the invention and not to limit the scope of the invention. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. In some embodiments, the MRI system 100 may include one or more additional components and/or may omit one or more of the components described above. Additionally or alternatively, two or more components of the MRI system 100 may be integrated into a single component. For example, the
Fig. 2 is a schematic diagram of an
The gradient coils 202 may be located inside the
In some embodiments, the
When the
When used as a receiver, the
In some embodiments, the gradient coils 202 and the RF coils 203 may be positioned circumferentially with respect to the subject. It will be appreciated by those skilled in the art that the
In some embodiments, the
In some embodiments, the
An MRI system (e.g., MRI system 100 disclosed in the present invention) may be generally used to obtain internal images of a particular region of interest (ROI) from a scanned object for diagnostic, therapeutic, and like purposes. An MRI system includes a main magnet (e.g., main magnet 201) assembly for providing a strong, uniform main magnetic field to align the individual magnetic moments of H atoms within a subject's body. In this process, the H atoms oscillate around their poles at their natural lamor frequency. If the tissue is conditioned by an additional magnetic field, which is tuned to the larmor frequency, the H atoms absorb additional energy, rotating the net aligning moment of the H atoms. The additional magnetic field may be provided by an RF excitation signal (e.g., an RF signal generated by the RF coil 203). When the additional magnetic field is removed, the magnetic moments of the H atoms rotate back into alignment with the main magnetic field, thereby sending echo signals that are received and processed to form an MR image. T1 relaxation can be the process by which the net magnetization grows/recovers parallel to the main magnetic field to its original maximum. T1 may be the time constant for regrowth of the longitudinal magnetization (e.g., along the main magnetic field). The T2 relaxation may be the process of the transverse component of magnetization decaying or dephasing. T2 may be the time constant for the decay/dephasing of the transverse magnetization.
If the main magnetic field is uniform over the entire body of the scan target, the RF excitation signal can non-selectively excite all H atoms in the sample. Thus, for imaging a particular region of the scanned target body, the magnetic field gradients Gx, Gy, and Gz (e.g., produced by the gradient coils 202) having particular times, frequencies, and phases in the X, Y and Z directions may be superimposed on the uniform magnetic field such that the RF excitation signal excites H atoms in a desired slice of the scanned target body and unique phase and frequency information is encoded in the echo signal according to the position of the H atoms in the "image slice".
Typically, the portion of the scan target body to be imaged is scanned through a series of measurement cycles in which the RF excitation signals and the magnetic field gradients Gx, Gy and Gz vary according to the MRI imaging protocol being used. A protocol may be designed for one or more tissues, diseases, and/or clinical conditions to be imaged. A protocol may include a number of pulse sequences oriented in different planes and/or having different parameters. The pulse sequence may include a spin echo sequence, a gradient echo sequence, a diffusion sequence, an inversion recovery sequence, and the like, or any combination thereof. For example, the spin echo sequence may include a Fast Spin Echo (FSE) pulse sequence, a Turbo Spin Echo (TSE) pulse sequence, a fast acquisition with relaxation enhancement (RARE) pulse sequence, a half fourier acquisition single turbine spin echo (HASTE) pulse sequence, a Turbine Gradient Spin Echo (TGSE) pulse sequence, or the like, or any combination thereof. As another example, the gradient echo sequence may include a bSSFP pulse sequence, an spGRE pulse sequence, an EPI pulse sequence, a Steady State Free Precession (SSFP) pulse sequence, or similar sequences, or any combination thereof. The protocol may also include information about image contrast and/or ratio, ROI, slice thickness, imaging type (e.g., T1 weighted imaging, T2 weighted imaging, proton density weighted imaging, etc.), T1, T2, echo type (spin echo, Fast Spin Echo (FSE), fast recovery FSE, single FSE, gradient echo, fast imaging with steady state processes, etc.), flip angle value, acquisition Time (TA), echo Time (TE), repetition Time (TR), Echo Train Length (ETL), number of phases, Number of Excitations (NEX), inversion time, bandwidth (e.g., RF receiver bandwidth, RF transmitter bandwidth, etc.), or the like, or any combination thereof. For each MRI scan, the resulting echo signals may be digitally processed to reconstruct an image according to the MRI imaging protocol used.
Fig. 3 is a schematic diagram of exemplary hardware and/or software components of a
The
For purposes of illustration only, only one processor is depicted in
The
I/O330 may input and/or output signals, data, information, and the like. In some embodiments, I/O330 may enable a user to interact with
The
Fig. 4 is a schematic diagram of exemplary hardware and/or software components of a
As shown in FIG. 4, the
To implement the various modules, units and their functions described in this disclosure, a computer hardware platform may be used as the hardware platform for one or more of the elements described herein. A computer with user interface elements may be used to implement a Personal Computer (PC) or other type of workstation or terminal device, and, when suitably programmed, the computer may also act as a server.
Fig. 5 is a block diagram of an
The
The aliased
The reference
The slice
It should be noted that the foregoing description is for illustrative purposes only, and is not intended to limit the scope of the present invention. Many variations and modifications may be made in light of the above teachings of the invention by those of ordinary skill in the art. However, those variations and modifications do not depart from the scope of the present invention. As an implementable embodiment, the
FIG. 6 is a flow chart of an exemplary process for synchronized multi-slice MRI according to some embodiments of the present invention. In some embodiments, the
In some embodiments, the
In
A frame as used in this disclosure may refer to a time period of any duration. The plurality of frames may be continuous or discontinuous frames. Different frames may have the same duration or different durations. The PE step may refer to a single acquisition step for spatial encoding along the phase encoding direction. Each PE step in a frame may acquire echo signals from an excited slice location, where the acquired echo signals may be stored as a single row of PE lines of the k-space matrix corresponding to the frame. The K-space matrix corresponding to the frame may be a two-dimensional matrix of a Kx axis along the frequency encoding direction and a Ky axis along the phase encoding direction. The K-space matrix corresponding to the frame may be used to reconstruct an aliased image corresponding to the frame, as described in detail in
In some embodiments, the matrix size of the K-space matrix corresponding to a certain frame may be associated with the resolution of the aliased image of the frame to be reconstructed. For example, to reconstruct an aliased image with a resolution of 256 × 128, it may be necessary to generate a K-space matrix of 256 × 128. That is, 256 PE steps may need to be applied in a particular frame to fill 256 PE lines of the K-space matrix. The duration of a particular frame may be determined based on the count (or number) of PE steps and the unit duration of each PE step. In some embodiments, the K-space matrices corresponding to the plurality of frames may have the same matrix size. In the K-space matrix of different frames, PE lines located in the same row can be considered to be located at the same position in K-space. PE steps corresponding to PE lines located at the same position in K space and applied in different frames may be considered to correspond to each other.
In some embodiments, multiple PE steps may be performed by applying a particular sequence of pulses during a frame. For example, a first pulse sequence without an echo sequence may be applied. The first pulse sequence may comprise a plurality of RF excitation pulses and only one echo signal (i.e. data corresponding to a single PE line) may be acquired after each RF excitation pulse. Exemplary first pulse sequences without an echo sequence may include a bSSFP pulse sequence, an spGRE pulse sequence, and so forth. In some embodiments, each RF excitation pulse in the first pulse sequence may be a multiband RF pulse, which may simultaneously apply a radio frequency pulse of a slice selection gradient to simultaneously excite multiple slice locations to be imaged.
As another example, a second pulse sequence with an echo train may be applied in the frame to perform the corresponding PE step. After each single RF excitation pulse, the second pulse sequence may acquire multiple echo signals (i.e., data corresponding to multiple PE lines). Exemplary second pulse sequences with echo sequences may include EPI pulse sequences, FSE pulse sequences, and the like. In some embodiments, different pulse sequences may be suitable for scanning different objects. For example, EPI pulse sequences may be applied to scan the brain of a scan target.
In
In some embodiments, for each frame, the
To achieve a preset FOV shift in the aliased image of the frame, a phase modulation gradient may be applied by the gradient coils (e.g., Z-coils) of the MRI scanner along the slice encoding direction (i.e., the Z-direction of coordinate system 160). For example, in each PE step (or portion thereof) in a frame, the Z-coil of the MRI scanner may apply a phase modulation gradient in the slice encoding direction after the excitation slice position is applied and before the corresponding echo signal is read out. Since phase modulation gradients are applied in the PE step, each slice position may have a specific phase when acquiring the corresponding echo signal.
In some embodiments, the phase modulation gradient may be designed for use in the frame, thereby avoiding the need for additional reference scans for the slice position. For example, the phase difference between the second slice position and the first slice position is different for a corresponding PE step applied in a pair of frames of the plurality of frames, where the pair of frames may be two consecutive frames or discontinuous frames thereof. For example, as shown in fig. 7, in each first PE step in
In some embodiments, in at least one PE step of at least one frame, after readout of the respective echo signals, a compensating magnetic field gradient may be applied along the slice encoding direction. The compensation magnetic field gradient may have the same amplitude and in the opposite gradient direction as the phase modulation gradient applied in the at least one PE step. This may eliminate or reduce the influence of the phase modulation gradient applied in at least one PE step on the echo signal acquisition in the next PE step. In some embodiments, in each PE step in which a phase modulation gradient is applied, a compensation magnetic field gradient may be applied after the readout of the corresponding echo signal. For example, during a frame in which the bSSFP pulse sequence is applied, a compensating magnetic field gradient may be applied in each PE step in the frame. Alternatively, the PE step in the frame may be performed without compensating magnetic field gradients, e.g. in which an spGRE pulse sequence is applied.
In some embodiments, a phase modulated RF excitation pulse may be applied in at least one PE step of at least one frame to excite a plurality of slice positions, and the phase modulation in the at least one PE step may be achieved by combining the phase modulated RF excitation pulse and a phase modulation gradient applied in the at least one PE step. For example, in order to obtain a phase difference of 180 degrees between the second slice position and the first slice position in the PE step, a phase difference of 90 degrees may be obtained by a phase modulated RF excitation pulse, and another phase difference of 90 degrees may be achieved by a phase modulation gradient. More description of the configuration of the pulse sequence applied in a frame can be found elsewhere in the present invention. See, for example, fig. 7-13 and their associated description.
In
A reference slice image in the present invention refers to an image representing each of a plurality of slice positions in more than one of a plurality of frames. The temporal resolution of the reference slice image is lower than the temporal resolution of the aliased image reconstructed in
In some embodiments, the reference slice image may be generated by combining (e.g., linearly combining) at least two aliased images reconstructed in
In
The reconstruction of the at least one slice image may be performed by a parallel imaging reconstruction algorithm based on the aliased image and the reference slice image. For example, a slice-wide auto-calibration partially parallel acquisition (GRAPPA) algorithm, a simultaneous acquisition spatial harmonics (SMASH) algorithm, a sensitivity encoding (SENSE) algorithm, etc. In some embodiments, for each slice position in each frame, a corresponding slice image may be reconstructed in
In some embodiments, the subject target may experience physiological motion during multiple frames. For example, the subject object may include a heart of a scanned object undergoing cardiac motion. A plurality of slice locations in a scanned target heart may be imaged to generate a series of slice images at each of the slice locations in a plurality of cardiac phases. For scanning slice positions in the target heart, the respective slice images may dynamically show the cardiac motion of the slice positions along the time dimension in different cardiac phases. In some embodiments, the scan target may have little or no physiological motion during multiple frames. For example, the subject target may include a brain of a scanning target. A plurality of slice locations in the brain of a scan target may be imaged to generate a series of slice images for each slice location. For scanning slice locations in the target brain, the corresponding slice images may dynamically show changes in the active regions of the brain (e.g., changes in blood flow).
It should be noted that the above description of
FIG. 7 is a schematic diagram of an exemplary
For purposes of illustration, the application of the
In some embodiments, during each PE step in
Ideally, in the PE step of
The application of the
In some embodiments, the
A1＝S1+S1， (1)
A2＝S1-S2。 (2)
The aliased image a1 and the aliased image a2 may be linearly combined according to equations (3) and (4), respectively, to determine a reference slice image F1 representing slice position S1 in
the reference slice image F1 and the reference slice image F2 may have a lower temporal resolution than the aliased image a1 and the aliased image a 2. The
In some embodiments, the
FIG. 11 illustrates a schematic diagram of an exemplary
The application of the
The application of the
In some embodiments, the
A3＝S3+S4+S5， (5)
The reference slice image F3 representing the slice position S3 in the
the reference slice image F3, the reference slice image F4, and the reference slice image F5 may have a lower temporal resolution than the aliased image A3, the aliased image a4, and the aliased image a 5. The
Fig. 12 is a schematic diagram of an exemplary
Similar to the
Fig. 13 is a schematic diagram of an exemplary EPI pulse sequence 1300 according to some embodiments of the present invention. The EPI pulse sequence 1300 may be applied by an MRI scanner (e.g., MRI scanner 110) to simultaneously image slice position S8 and slice position S9 of the subject target. As shown in fig. 13, EPI pulse sequence 1300 may be applied in frame 8 and frame 9 with different modulation strategies. During each of frame 8 and frame 9, multiple echoes for different PE steps may be acquired using the re-gradient after a single RF excitation pulse.
Similar to the
It should be noted that fig. 7, 11, 12, and 13 and the above-described exemplary pulse sequences depicted therein may be arbitrary and are provided herein for illustrative purposes only and are not intended to limit the scope of the present invention. Many variations and modifications may be made to the teachings of the present invention by those of ordinary skill in the art. However, those variations and modifications do not depart from the scope of the present invention. In some embodiments, the phase of a particular slice position in a particular PE step may be modulated to a value other than any other value as shown. In addition, the phase modulation in a certain PE step can be achieved by a separate phase modulation gradient or RF excitation pulse in combination with phase modulation as described above. Further, the formulas provided above are illustrative examples and may be modified in various ways. For example, a plurality of aliased images of the plurality of frames may be reconstructed, and a reference slice image for a certain slice position may be generated based on any two or more of the plurality of aliased images.
Having thus described the basic concepts, it will become apparent to those skilled in the art from this detailed disclosure, which is presented by way of example only, and not by way of limitation. Various alterations, modifications and improvements will occur to those skilled in the art, though not expressly stated herein. Such alterations, modifications, and variations are intended to be suggested by this disclosure and are intended to be within the spirit and scope of the exemplary embodiments of this invention.
Furthermore, certain terminology is used to describe embodiments of the invention. For example, the terms "one embodiment," "an embodiment," and "some embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, it is emphasized and should be appreciated that two or more references to "one embodiment" or "an alternative embodiment" in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined as suitable in one or more embodiments of the invention.
Moreover, those skilled in the art will appreciate that various aspects of the invention may be illustrated and described in any of a number of patentable contexts, including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, various aspects of the present invention may be embodied entirely in hardware, entirely in software (including firmware, resident software, micro-code, etc.), or in a combination of software and hardware, and these implementations may be referred to herein generally as "modules," units, "" components, "" devices "or" systems. Furthermore, various aspects of the present invention may take the form of a computer program product comprising one or more computer-readable media having computer-readable program code embodied therein.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electromagnetic, optical, etc., or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, radio frequency, or the like, or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of more than one programming language, including object oriented programming languages such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C + +, C #, VB.net, Python, and the like, conventional programming languages such as C, Visual Basic, Fortran 2103, Perl, COBOL 2102, PHP, ABAP, dynamic programming languages such as Python, Ruby, and Groovy, or other programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer, partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider), or in a cloud computing environment, or as a service, such as a software as a service (SaaS).
Furthermore, the order of enumeration of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes and methods to any order unless otherwise specified in the claims. While the foregoing disclosure discusses, by way of various examples, what are presently considered to be various useful embodiments of the present invention, it is to be understood that such details are solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although implementations of the various components described above may be embodied in a hardware device, they may also be implemented as a software-only solution, such as an installation on an existing server or mobile device.
Similarly, it should be appreciated that in the foregoing description of embodiments of the invention, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Inventive embodiments may lie in less than all features of a single foregoing disclosed embodiment.
In some embodiments, numbers used to describe and claim quantities or characteristics of certain embodiments of an application should be understood as modified in certain instances by the term "about", "approximately", or "substantially". For example, "about," "approximately," or "substantially" may mean some variation of the stated value (e.g., ± 1%, ± 5%, ± 10%, or ± 20%) unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some of the embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible.
Each patent, patent application, publication of a patent application, and other material (e.g., articles, books, specifications, publications, documents, articles, and/or the like) cited herein is hereby incorporated by reference in its entirety for all purposes, to the extent any filing record does not inconsistent or conflict with this document, or to the extent any filing record does not necessarily conflict with any filing record, the broadest scope of the claims that are associated with this document may have a limiting effect. For example, the description, definition, and/or use of terms in this document shall control if there is any inconsistency or conflict between the description, definition, and/or use of terms associated with any of the combined materials and the terms associated with this document.
Finally, it is to be understood that the embodiments of the application disclosed herein illustrate the principles of the embodiments of the application. Other modifications that may be employed are within the scope of the invention. Thus, by way of example, and not limitation, alternative configurations of embodiments of the application may be utilized in accordance with the teachings herein. Accordingly, embodiments of the present invention are not limited to the precise embodiments shown and described.
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