Magnetic Resonance Imaging System and Method, and Computer-Readable Storage Medium

Abstract

The present invention provides a magnetic resonance imaging system and method, and a computer-readable storage medium. The magnetic resonance imaging method includes: acquiring a plurality of k-space data sets using a plurality of sets of imaging sequences, each set of imaging sequences including a pre-dephasing gradient pulse and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the plurality of sets of imaging sequences have a standard area difference in sequence when sorted according to the area value; respectively reconstructing magnetic resonance images from each of the plurality of k-space data sets; taking an average value of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging, and particularly to a magnetic resonance imaging (MRI) system and method, and a computer-readable storage medium. Background Art

[0002] Traditional magnetic resonance echo planar imaging (EPI) is a fast acquisition imaging technique. In this technique, an entire image can be formed by multiple echo signals generated after a single radio frequency (RF) excitation. Therefore, fast imaging can be achieved. However, this imaging technique is prone to Nyquist artifacts, which may be caused by reasons such as eddy currents, gradient coil heating, and gradient delay. Additionally, in EPI, multi-channel reception and parallel acquisition techniques are used simultaneously, resulting in aliasing artifacts in the image edge region.

[0003] Some methods for suppressing Nyquist artifacts or aliasing artifacts have been proposed in the prior art. However, it is difficult to suppress these two different types of artifacts simultaneously, and the suppression effect of the artifacts needs to be further improved. Summary of the Invention

[0004] One aspect of the present invention provides a magnetic resonance imaging method, including:

[0005] Acquiring a plurality of k-space data sets using multiple sets of imaging sequences, each set of imaging sequences including a prephasing gradient pulse and a plurality of phase encoding gradients applied after the prephasing gradient pulse, wherein the prephasing gradient pulses in the multiple sets of imaging sequences have a standard area difference in sequence when sorted by area value;

[0006] Reconstructing a magnetic resonance image from each of the plurality of k-space data sets respectively; and

[0007] Taking an average value of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

[0008] On the other hand, the standard area difference is 2 / N of the area of any phase encoding gradient, where N is the number of sets of imaging sequences.

[0009] On the other hand, the number of sets of imaging sequences is greater than 2.

[0010] On the other hand, each set of imaging sequences further includes a radio frequency excitation pulse, a radio frequency refocusing pulse, and a diffusion gradient pulse. The diffusion gradient pulse includes a dephasing gradient pulse and a rephasing gradient pulse, and the dephasing gradient pulse and the rephasing gradient pulse are symmetrically applied before and after the radio frequency refocusing pulse respectively, and the prephasing gradient pulse is applied after the rephasing gradient pulse.

[0011] On the other hand, each set of imaging sequences further includes a plurality of frequency-encoding gradients, the directions of the plurality of frequency-encoding gradients are alternately reversed, and the plurality of phase-encoding gradients are respectively applied when the directions of the plurality of frequency-encoding gradients are reversed.

[0012] Another aspect of the present invention further provides a magnetic resonance imaging method, including:

[0013] Acquiring a plurality of k-space data sets using multiple sets of imaging sequences, each set of imaging sequences including an echo planar imaging sequence part and a preparation part applied before the echo planar imaging sequence part, and the echoes of the plurality of k-space data sets having standard phase offsets in sequence when sorted according to phase values;

[0014] Respectively reconstructing magnetic resonance images from each of the plurality of k-space data sets; and

[0015] Taking the average value of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

[0016] On the other hand, the standard phase offset is 2π / N, where N is the number of k-space data sets.

[0017] On the other hand, the number of k-space data sets is greater than 2.

[0018] On the other hand, the preparation sequence includes a spin echo sequence, a gradient echo sequence, a diffusion-weighted sequence, or a spin echo-diffusion weighted sequence.

[0019] Another aspect of the present invention further provides a computer-readable storage medium, the computer-readable storage medium including a stored computer program, wherein when the computer program is run, it executes the magnetic resonance imaging method in any of the above aspects.

[0020] Another aspect of the present invention further provides a magnetic resonance imaging (MRI) system, including:

[0021] Gradient coils configured to generate encoding gradients;

[0022] Radio frequency (RF) coils configured to generate RF pulses; and

[0023] A processor connected to the gradient coils and the RF coils, the processor being configured to:

[0024] Instruct the gradient coils and the RF coils to generate multiple sets of imaging pulse sequences to acquire a plurality of k-space data sets, each set of imaging sequences including pre-dephasing gradient pulses and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulses, wherein the pre-dephasing gradient pulses in the multiple sets of imaging sequences have standard area differences in sequence when sorted according to area values;

[0025] Reconstruct magnetic resonance images separately from each of the plurality of k-space data sets; and

[0026] Take an average of the magnitudes of the magnetic resonance images to generate a magnetic resonance image of the average magnitude.

[0027] It should be understood that the above brief description is provided to introduce some concepts further described in the detailed description in a simplified form. This does not mean identifying the key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Moreover, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any section of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] With reference to the accompanying drawings, the present invention will be better understood by reading the following description of non-limiting embodiments, wherein:

[0029] Figure 1 is a schematic diagram of a magnetic resonance imaging (MRI) system according to an exemplary embodiment;

[0030] Figure 2 is a flowchart of a magnetic resonance imaging method according to an exemplary embodiment of the present invention;

[0031] Figure 3 is Figure 2 a schematic diagram of an exemplary imaging sequence used in the method shown;

[0032] Figure 4 is a schematic diagram of a k-space data acquisition trajectory obtained according to an exemplary embodiment of the present invention;

[0033] Figure 5 is a flowchart of a magnetic resonance imaging method according to another exemplary embodiment of the present invention;

[0034] Figure 6 is a comparison of an image obtained by the method according to an exemplary embodiment of the present invention with an image obtained by a conventional method.

[0035] The drawings illustrate the described components, systems, and methods of the magnetic resonance imaging method and system. Together with the following description, the drawings illustrate and explain the structural principles, methods, and principles described herein. In the drawings, for clarity, the thickness and dimensions of the components may be enlarged or otherwise modified. Well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the described components, systems, and methods. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention will be described below. It should be noted that in the specific description of these embodiments, for the sake of concise description, it is impossible for this specification to describe all features of the actual embodiments in detail. It should be understood that in the actual implementation process of any one of the embodiments, just as in the process of any engineering project or design project, in order to achieve the specific goals of the developer and to meet system-related or business-related restrictions, various specific decisions are often made, and these will also change from one embodiment to another. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present invention, some design, manufacturing or production changes based on the technical content disclosed in this disclosure are only conventional technical means and should not be understood as the content of this disclosure being insufficient.

[0037] Unless otherwise defined, the technical terms or scientific terms used in the claims and the specification should have the ordinary meanings understood by those of ordinary skill in the art to which they belong. The terms "first", "second" and similar terms used in this specification and the claims do not denote any order, quantity or importance, but are only used to distinguish different components. The terms "a" or "an" and the like do not denote a quantity limitation, but rather denote the presence of at least one. The terms "comprising" or "including" and the like are intended to mean that the elements or items appearing before "comprising" or "including" cover the elements or items listed after "comprising" or "including" and their equivalent elements, and do not exclude other elements or items. The terms "connected" or "coupled" and the like are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections. In addition, it should be understood that the reference to "one embodiment" or "an embodiment" of the present disclosure is not intended to be construed as excluding the existence of additional embodiments that also include the recited features.

[0038] Referring to the accompanying drawings, the present disclosure describes a magnetic resonance system and a magnetic resonance imaging method capable of suppressing Nyquist artifacts and acceleration artifacts. By using multiple sets of imaging sequences to acquire multiple sets of k-space data, magnetic resonance images are reconstructed from each of the multiple k-space data sets respectively, and the amplitudes of the multiple magnetic resonance images are averaged to generate a magnetic resonance image with an average amplitude. Each of the above-mentioned sets of imaging sequences includes a pre-dephasing gradient pulse and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the multiple sets of imaging sequences have a standard area difference in sequence when sorted by area value. In this way, the artifacts in the echoes of the multiple imaging pulse sequences are attenuated, so that both Nyquist artifacts and acceleration artifacts are suppressed in the average MR image. And since the amplitude average value is used, the signal intensity is not reduced, so that a good signal-to-noise ratio (SNR) can be achieved.

[0039] Referring Figure 1 , a schematic diagram of an exemplary MRI (Magnetic Resonance Imaging) system 100 according to some embodiments is shown. The operation of the MRI system 100 is controlled by an operator workstation 110, which includes an input device 114, a control panel 116, and a display 118. The input device 114 can be a joystick, keyboard, mouse, trackball, touch-activated screen, voice control, or any similar or equivalent input device. The control panel 116 can include a keyboard, touch-activated screen, voice control, buttons, sliders, or any similar or equivalent control device. The operator workstation 110 is coupled to and communicates with a computer system 120, which enables the operator to control the generation and viewing of images on the display 118. The computer system 120 includes a plurality of components that communicate with each other via an electrical and / or data connection module 122. The connection module 122 can be a direct wired connection, a fiber optic connection, a wireless communication link, etc. The computer system 120 can include a central processing unit (CPU) 124, a memory 126, and an image processor 128. In some embodiments, the image processor 128 can be replaced by image processing functions implemented in the CPU 124. The computer system 120 can be connected to an archival media device, permanent or backup memory, or a network. The computer system 120 can be coupled to and communicate with a separate MRI system controller 130.

[0040] The MRI system controller 130 includes a set of components that communicate with each other via an electrical and / or data connection module 132. The connection module 132 can be a direct wired connection, an optical fiber connection, a wireless communication link, etc. The MRI system controller 130 can include a CPU 131, a sequence pulse generator 133 that communicates with the operator workstation 110, a transceiver (or RF transceiver) 135, a memory 137, and an array processor 139. In some embodiments, the sequence pulse generator 133 can be integrated into the resonance assembly 140 of the MRI system 100. The MRI system controller 130 can receive commands from the operator workstation 110 to indicate the MRI scan sequence to be performed during an MRI scan. The MRI system controller 130 is also coupled to and communicates with a gradient driver system 150, which is coupled to a gradient coil assembly 142 to generate magnetic field gradients during an MRI scan.

[0041] The sequence pulse generator 133 may also receive data from a physiological acquisition controller 155, which receives signals from a plurality of different sensors (such as an electrocardiogram (ECG) signal from electrodes attached to a patient), and these sensors are connected to an object or patient 170 undergoing an MRI scan. The sequence pulse generator 133 is coupled to and communicates with a scan room interface system 145, which receives signals from various sensors associated with the state of the resonance assembly 140. The scan room interface system 145 is also coupled to and communicates with a patient positioning system 147, which sends and receives signals to control the movement of the patient table to a desired position for an MRI scan.

[0042] The MRI system controller 130 provides gradient waveforms to the gradient driver system 150, which includes G x 、G y and G z amplifiers, etc. Each G x 、G y and G zGradient amplifiers each drive a corresponding gradient coil in gradient coil assembly 142 to generate magnetic field gradients for spatially encoding MR signals during an MRI scan. Gradient coil assembly 142 is disposed within resonance assembly 140, which also includes a superconducting magnet having a superconducting coil 144 that, in operation, provides a static, homogeneous longitudinal magnetic field B0 through a cylindrical imaging volume 146. Resonance assembly 140 also includes an RF body coil 148 that, in operation, provides a transverse magnetic field B1 that is substantially perpendicular to B0 throughout the cylindrical imaging volume 146. Resonance assembly 140 may also include an RF surface coil 149 for imaging different anatomical structures of a patient undergoing an MRI scan. RF body coil 148 and RF surface coil 149 may be configured to operate in a transmit and receive mode, a transmit mode, or a receive mode.

[0043] An object or patient 170 undergoing an MRI scan may be positioned within the cylindrical imaging volume 146 of resonance assembly 140. A transceiver 135 in MRI system controller 130 generates RF excitation pulses that are amplified by RF amplifier 162 and provided to RF body coil 148 via a transmit / receive switch (T / R switch) 164.

[0044] As described above, RF body coil 148 and RF surface coil 149 may be used to transmit RF excitation pulses and / or receive resulting MR signals from a patient undergoing an MRI scan. MR signals emitted by nuclei excited within the patient being scanned by MRI may be sensed and received by RF body coil 148 or RF surface coil 149 and sent back through T / R switch 164 to preamplifier 166. T / R switch 164 may be controlled by a signal from sequence pulse generator 133 to electrically connect RF amplifier 162 to RF body coil 148 during the transmit mode and to connect preamplifier 166 to RF body coil 148 during the receive mode. T / R switch 164 may also enable RF surface coil 149 to be used in the transmit mode or the receive mode.

[0045] In some embodiments, MR signals sensed and received by RF body coil 148 or RF surface coil 149 and amplified by preamplifier 166 are stored in memory 137 as a raw k-space data array for post-processing. A reconstructed magnetic resonance image may be obtained by transforming / processing the stored raw k-space data.

[0046] In some embodiments, the MR signals sensed and received by the RF body coil 148 or the RF surface coil 149 and amplified by the preamplifier 166 are demodulated, filtered, and digitized in the receiving portion of the transceiver 135 and transmitted to the memory 137 in the MRI system controller 130. For each image to be reconstructed, this data is rearranged into separate k-space data arrays, and each of these separate k-space data arrays is input to the array processor 139, which is operated to Fourier transform the data into an array of image data.

[0047] The array processor 139 uses a transform method, most commonly the Fourier transform, to create images from the received MR signals. These images are transferred to the computer system 120 and stored in the memory 126. In response to commands received from the operator workstation 110, the image data can be stored in long-term memory or can be further processed by the image processor 128 and transferred to the operator workstation 110 for presentation on the display 118.

[0048] In various embodiments, the components of the computer system 120 and the MRI system controller 130 can be implemented on the same computer system or on multiple computer systems. It should be understood that Figure 1 the MRI system 100 shown is for illustration. Suitable MRI systems can include more, fewer, and / or different components.

[0049] The MRI system controller 130 and the image processor 128 can each or jointly include a computer processor and a storage medium on which a program of predetermined data processing to be executed by the computer processor is recorded. For example, programs for implementing scan processing (such as scan procedures, imaging sequences), image reconstruction, image processing, etc. can be stored on the storage medium. For example, a program for implementing the magnetic resonance imaging method of the embodiments of the present invention can be stored. The above storage medium can include, for example, ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or non-volatile memory card.

[0050] The above "imaging sequence" refers to a combination of pulses with specific amplitudes, widths, directions, and timings applied during the execution of a magnetic resonance imaging scan. These pulses can generally include, for example, radio frequency pulses and gradient pulses. The radio frequency pulses can include, for example, radio frequency excitation pulses, radio frequency refocusing pulses, inversion recovery pulses, etc. The gradient pulses can include, for example, the above-mentioned gradient pulses for slice selection, gradient pulses for phase encoding, gradient pulses for frequency encoding, gradient pulses for phase shift, gradient pulses for dephasing, etc.

[0051] Generally, multiple scan sequences can be preset in a magnetic resonance system so as to enable selection of a sequence adapted to clinical detection requirements, which may include, for example, imaging site, imaging function, imaging effect, etc.

[0052] For example, a magnetic resonance imaging sequence capable of simultaneously suppressing Nyquist artifacts and acceleration artifacts in the embodiments of the present invention can be preset. The imaging sequence may include a preparation sequence and an echo planar imaging (EPI) sequence, where the preparation sequence is applied before the EPI sequence. Traditional EPI is an accelerated imaging technique, in which an entire image can be formed by multiple echo signals generated after a single radio frequency (RF) excitation. In k-space, an echo is generated along each phase line of k-space. In k-space acquisition, two adjacent echoes are acquired in opposite directions, such as a forward echo and a reverse echo. Eddy currents caused by rapid gradient changes, poor magnetic field uniformity, gradient coil heating, gradient system delay, etc. may all cause the forward echo and the reverse echo not to be perfectly mirrored to each other, and thus introduce artifacts into the image during reconstruction. For example, the delay starting from the first echo will propagate to all subsequent echoes, resulting in a timing difference between the peaks of odd and even echoes. When performing Fourier transform, this phase error will cause a shift in the signal intensity in the phase encoding direction of half of the image, which is called Nyquist ghosting. Additionally, in EPI, since multiple echoes are acquired rapidly, parallel acceleration artifacts due to aliasing appear in the image edge region.

[0053] Reference Figure 2 , a flowchart of a magnetic resonance imaging method 200 according to an exemplary embodiment is shown.

[0054] In step 210, multiple k-space data sets are acquired using multiple sets of imaging pulse sequences.

[0055] In step 220, magnetic resonance images are reconstructed from each of the multiple k-space data sets respectively.

[0056] In step 230, the amplitudes of the reconstructed magnetic resonance images are averaged to generate a magnetic resonance image with an average amplitude.

[0057] Reference Figure 3 , a schematic diagram of an exemplary imaging sequence 300 to which the method 200 is applied is shown. Each set of imaging sequences includes an EPI sequence 204 and a preparation sequence 202 applied before the EPI sequence. As an example, the preparation sequence 202 may include an SE-DWI (spin echo - diffusion weighted) sequence. For example, it may include a radio frequency (RF) excitation pulse 212 and a radio frequency refocusing pulse 214 applied in sequence, and slice selection gradients (G SS)Pulses 222 and 224.

[0058] Further, the preparation sequence 202 may further include diffusion gradients (G DG ) pulses for proton diffusion weighting. Diffusion weighting techniques can be applied to the diagnosis of tissue function in various organs (e.g., brain, cartilage, and liver) and various applications (e.g., pathology, oncology). Diffusion refers to the random movement of molecules in a system. In biological tissues, the diffusion of water molecules forms a pattern based on the tissue structure and properties. In some disease states, the diffusion pattern may be disrupted, and in the regions affected by the disease, the amount of diffusion may change. Therefore, tissue abnormalities can be detected by studying the changes in diffusion. Diffusion-weighted magnetic resonance imaging techniques utilize the diffusion of water molecules to visualize internal physiology. The contrast of diffusion-weighted images reflects the differences in diffusion rates between tissues. Diffusion weighting techniques are particularly useful when conventional MRI sequences (e.g., T2-weighted imaging) do not show significant changes in the images. For example, in a pathological condition such as a stroke caused by local ischemia, the signal intensity on T2 does not change until at least 8 hours after the onset of the stroke. On the other hand, DWI can show changes in the brain as early as 30 minutes after the onset of the stroke and show significant signal differences within one hour of the onset.

[0059] The diffusion gradient pulse includes a phase-shifting gradient pulse 232 and a rephasing gradient pulse 234, and the phase-shifting gradient pulse 232 and the rephasing gradient pulse 234 are symmetrically applied on both sides (before and after) of the radiofrequency refocusing pulse 214, respectively.

[0060] The above-mentioned radiofrequency excitation pulse 212 may be, for example, a 90-degree radiofrequency pulse, and the radiofrequency refocusing pulse 214 may be a 180-degree radiofrequency pulse, both of which can be generated by a transmit coil (e.g., Figure 1 the RF body coil 148 therein). In some embodiments, the radiofrequency excitation pulse 212 itself can be selectively tuned to only excite water protons. The slice selection gradient pulses 222 and 224 and the diffusion gradient pulses 232 and 234 can be generated by a gradient coil assembly (e.g., Figure 1 the gradient coil assembly 142 therein).

[0061] The phase-shifting gradient pulse 232 is used to introduce a phase shift to the protons according to their positions, and the rephasing gradient pulse 234 reverses the changes made by the phase-shifting gradient pulse 232. For fixed spins, their phases are not affected by the diffusion gradient pulse because any phase accumulation from the phase-shifting gradient pulse 232 will be reversed by the rephasing gradient pulse 234. However, diffusing spins move to different positions between the phase-shifting gradient pulse 232 and the rephasing gradient pulse 234, lose their phases, and the signal is lost. That is, if the protons move, the rephasing gradient pulse 234 will not be able to completely cancel the phase shift caused by the phase-shifting gradient pulse 232. Therefore, there will be signal attenuation. This signal attenuation from the net movement of protons is given by the Stejskal-Tanner formula:

[0062] S(b) = S0e -bD (1).

[0063] where S(b) is the signal received when applying a specific pair of diffusion gradient pulses, S0 is the signal intensity without any diffusion gradient, e is a constant, D is the diffusion or apparent diffusion coefficient (ADC), and b is the diffusion weighting degree for a specific pair of diffusion gradient pulses. The value of b can be controlled by manipulating the intensity, duration, and spacing of the pair of diffusion gradient pulses 232 and 234. Specifically, the value of b is given by:

[0064]

[0065] where γ is the gyromagnetic ratio of the hydrogen proton, a constant, G is the amplitude of the diffusion gradient pulse, δ is the duration of the diffusion gradient pulse, and Δ is the time between applying two diffusion gradient pulses. In clinical applications, usually the sequence is set to provide multiple images with a range of diffusion directions and b-values, and sometimes an ADC map can be calculated. For example, several DW (diffusion-weighted) images with different b-values can be obtained by changing the configuration of the pair of diffusion gradient pulses. At higher b-values, the effect of diffusion is more obvious in the images and in tissues with high diffusion, as shown by the low-signal regions in the images, while tissues with restricted diffusion are shown as high-signal regions.

[0066] Using the SE-DWI sequence as the preparation sequence is just an application example. In other examples, the preparation sequence 202 can be other types of sequences, such as the GRE (gradient echo) sequence, the SE sequence, the DWI sequence, etc.

[0067] After the preparation sequence 202 ends, the EPI sequence 204 can be immediately executed to perform rapid acquisition of k-space data. Rapid image acquisition can minimize the impact of overall motion on the images. The EPI sequence 204 includes a pre-dephasing gradient pulse 240 and multiple phase-encoding gradients (G applied after the pre-dephasing gradient pulse 240PE )Pulses (241, 242, 243 …) and multiple frequency-encoding gradients (G FE )Pulses (251, 252, 253 …). The prephasing gradient pulse 240, multiple phase-encoding gradient pulses, and multiple frequency-encoding gradient pulses can be generated by a gradient coil (e.g., Figure 1 the gradient coil assembly 142 in

[0068] As Figure 3 shown, after the prephasing gradient pulse 240 ends, there are multiple small “spikes” at each position where the frequency-encoding gradient pulse is inverted, i.e., the above-mentioned multiple phase-encoding gradient pulses. The multiple phase-encoding gradient pulses oscillate rapidly to generate multiple gradient echoes. The directions of the multiple frequency-encoding gradient pulses are alternately inverted, and the multiple phase-encoding gradient pulses are respectively applied when the directions of the multiple frequency-encoding gradient pulses are inverted. For example, spike 241 is applied at the start of the negative frequency-encoding (or readout) gradient pulse 251; spike 242 is placed at the inversion from the negative readout gradient 251 to the positive readout gradient 252, and spike 243 is placed at the inversion from the positive readout gradient 252 to the negative readout gradient 253, and so on. The spikes have a constant size, and each adds further phase encoding to the previous spike.

[0069] In each set of imaging sequences, the phase of the corresponding multiple gradient echoes can be controlled by setting the area of the prephasing gradient 240. The areas of the prephasing gradient pulses 240 of the multiple sets of imaging sequences used in the magnetic resonance imaging method of the embodiments of the present invention are different. Specifically, when the prephasing gradient pulses 240 of the multiple sets of imaging sequences are sorted according to the area values, they successively have a standard area difference. And, in the embodiments of the present invention, the execution order of the above-mentioned multiple sets of imaging sequences can be the same as or different from the sorting according to the area values, that is, the multiple sets of imaging sequences can be executed in sequence, where the area of the prephasing gradient pulse 240 gradually increases or decreases by a fixed value according to the execution order of the sequences; or the multiple sets of imaging sequences can be executed in sequence, where the area values of the prephasing gradient pulses 240 do not increase or decrease successively according to the execution order of the sequences. In this way, by changing the area value of the prephasing gradient pulse 40 in this manner, when a relatively large number of k-space data sets are acquired, both the Nyquist artifacts and the aliasing artifacts in the average magnitude image obtained from the magnetic resonance image based on the multiple k-space data can be better suppressed.

[0070] For example, if 5 sets of imaging sequences are used, and the first set of imaging sequences is as Figure 3 shown ( Figure 3If the initial area of the pre-spoiler gradient pulse 240 is A1 and the standard area difference A2 is schematically shown by a dashed line therein), then in the second to fifth imaging sequences, the areas of the pre-spoiler gradient pulses can be A1 + A2, A1 + 2A2, A1 + 3A2, A1 + 4A2 respectively, or can also be A1 - A2, A1 - 2A2, A1 - 3A2, A1 - 4A2 respectively. In the above examples, for the first imaging sequence, there is a second imaging sequence, and the area difference between its pre-spoiler gradient pulse is A2 or -A2. For the second imaging sequence, there is a third imaging sequence, and the area difference between its pre-spoiler gradient pulse is also A2 or -A2, and so on. The above first to fifth imaging sequences are not necessarily executed in sequence. For example, the execution order of the imaging sequences can be the second, fifth, first, fourth, and third imaging sequences, or any other combination order.

[0071] In one embodiment, the above standard area difference is 2 / N of the area of any phase-encoding gradient pulse, where N is the number of groups of the multi-group imaging sequence. Suppose the area of the phase-encoding gradient pulse is A3. Taking a 5-group imaging sequence as an example, the standard area difference If the area of the pre-spoiler gradient pulse of the first imaging sequence is A1, then the areas of the pre-spoiler gradient pulses of the second to fifth imaging sequences are respectively

[0072] Since the area of the pre-spoiler gradient pulse 240 affects the phases of multiple gradient echoes in the corresponding sequence, the k-space phase-encoding lines are also offset as a whole.

[0073] Reference Figure 4 , according to Figure 2 's pulse sequence shows a schematic diagram of the k-space data acquisition trajectory. First, a k-space data set 411 is acquired along the lowest line in the presence of the frequency-encoding gradient pulse 251. When the spike 242 is applied, a k-space data set 412 is acquired along the second lowest line in the presence of the frequency-encoding gradient pulse gradient 252, and so on. When the spike 242 is applied, more k-space data sets are obtained respectively in the presence of the frequency-encoding gradient pulse gradient 252. Each spike adds a constant phase encoding to the previous spike, forming a regular path through the k-space. The amplitude of the frequency-encoding gradient pulse is usually large, so that appropriate values can be sampled quickly, and the entire data set can be collected within a single free induction decay (FID).

[0074] Refer back to Figure 2, as described above, multiple k-space data sets are acquired by using multiple (e.g., 5 sets) slightly different imaging sequences. In the first set of imaging sequences, the pre-dephasing gradient pulse 240 has an initial area A1, and k-space data is acquired through the first set of imaging sequences, where an exemplary schematic diagram of the k-space data acquisition trajectory line is as shown in Figure 4 411 in. In the second set of imaging sequences, a standard area difference A2 (e.g., A3 is the area of the spike 241) is subtracted from (or can also be added to) the initial area A1 of the pre-dephasing gradient pulse 240. Therefore, the k-space data acquisition trajectory line corresponding to this second imaging sequence becomes Figure 4 412 in, where the trajectory line as a whole moves downward by the The k-space data acquisition trajectory line corresponding to this third imaging sequence becomes Figure 4 413 in, where, compared with Figure 4 412 in, the trajectory line as a whole moves downward again by the And so on, the k-space data acquisition trajectory lines 414 and 415 shown in Figure 4 are obtained through the third to fifth imaging sequences. Image reconstruction is performed respectively based on these k-space data, and an average amplitude image of 5 images is generated, which can effectively suppress Nyquist artifacts and aliasing artifacts. An appropriate number of k-space data sets and corresponding imaging sequence groups can be selected based on the effect of artifact suppression.

[0075] In some embodiments, the reconstruction includes a Fourier transform from k-space to image space, as is known in the art. Then (e.g., based on the following formula (3)), the amplitudes of multiple MR images are averaged to generate an average MR image:

[0076]

[0077] where N is the number of groups of the multiple sets of imaging sequences, the number of acquired k-space data sets, or the number of times the imaging sequence is repeatedly executed, and N is an integer.

[0078] Generally speaking, the amplitude of the MR signal is greater than the amplitude of the ghost signal. Similarly, when the amplitudes of images acquired multiple times are averaged, the ghost artifacts are attenuated in the signal region while the amplitude of the MR signal remains unchanged.

[0079] Referring to Figure 5 , a flowchart 500 of a magnetic resonance imaging method according to another exemplary embodiment of the present invention is shown. This method can be implemented by an MRI system (e.g., Figure 1performed by the MRI system 100 in []. In step 510, multiple k-space data sets are acquired using multiple sets of magnetic resonance imaging sequences. Each set of imaging sequences includes an echo planar imaging (EPI) sequence and a preparation sequence applied before the EPI sequence. When the echoes of the multiple k-space data sets are sorted according to the phase values, they sequentially have a standard phase shift. For example, the multiple k-space data sets can be similar to the data sets shown in Figure 3 as shown.

[0080] Among them, the preparation sequence can be similar to the preparation sequence shown in Figure 2 For example, it can include a pair of diffusion gradient pulses symmetric to the radiofrequency refocusing pulse. The diffusion gradient pulse includes a dephasing gradient pulse and a rephasing gradient pulse. The dephasing gradient pulse introduces a phase shift to the protons according to the position of the protons, and the rephasing gradient pulse reverses the change made by the dephasing gradient pulse. The phase of the fixed spins is not affected by the diffusion gradient pulse because any phase accumulation from the dephasing gradient pulse will be reversed by the rephasing gradient pulse. If the protons move, the rephasing gradient pulse will not be able to completely cancel the phase shift caused by the dephasing gradient pulse, and there will be signal attenuation. The diffusion weighting degree can be controlled by adjusting the configuration of the diffusion gradient (such as intensity, duration, and spacing). The preparation sequence can also have other deformations. For example, sequences such as individual GRE, SE, DWI, or any combination thereof can also be used as the preparation sequence.

[0081] The readout sequence after the preparation sequence can include an EPI sequence. In the EPI sequence, after the pre-dephasing gradient, there are small phase-encoding gradient pulses at each position where the frequency-encoding gradient pulse is inverted, such as the above-mentioned "spikes". The spikes have a constant size, and each adds further phase encoding to the previous spike, forming a regular path in the k-space. According to the k-space data acquisition, the even echoes and the odd echoes are in opposite directions. For example, if the odd echoes (or lines) are forward, the even echoes (or lines) are backward, and vice versa.

[0082] Between multiple acquisitions, the odd and even echoes in a group have a standard phase shift relative to another group. In one embodiment, the standard phase shift is 2π / N, where N is the number of k-space data sets, and N can be greater than 2. Taking the above five groups of k-space data acquisitions as an example, in the first k-space data set, the k-space data acquisition trajectory line has an initial phase, while in the second k-space data set, the trajectory line as a whole moves by the spacing between the odd and even trajectory lines That is, the phase is shifted by In the third k-space data set, the trajectory line as a whole moves by the spacing between the odd and even trajectory lines again The phase is shifted by And so on, in the fourth k-space data set, the phase is shifted relative to the initial phase by In the fifth k-space data set, the phase is shifted relative to the initial phase by

[0083] In step 520, after acquiring multiple sets of k-space data according to multiple imaging sequences, MR images are reconstructed from each k-space data set respectively. In some embodiments, the reconstruction includes a Fourier transform from k-space to image space, as is known in the art.

[0084] In step 530, the magnitudes of the multiple MR images are averaged to generate an average magnitude MR image. Ghost artifacts in the signal region are attenuated and suppressed by averaging the magnitudes of multiple acquisitions.

[0085] Reference Figure 6 , according to an exemplary embodiment, the images obtained by the methods disclosed herein are compared with the images obtained by conventional methods. Image 610 is acquired using a conventional method, where Nyquist ghosting 612 and acceleration artifacts 614 are clearly visible in the image. For comparison, images 633, 634, 635, and 636 are acquired using the method of an embodiment of the present invention, where 3, 4, 5, and 6 imaging sequences are used respectively and 3, 4, 5, and 6 k-space data sets are obtained respectively. It can be seen that both Nyquist ghosting and acceleration artifacts are effectively suppressed. Image 640 is an axial brain image of a volunteer acquired using a conventional method, where Nyquist ghosting and acceleration artifacts are clearly visible in the image. For comparison, images 653, 654, 655, and 656 are axial brain images of the same volunteer acquired using the method of an embodiment of the present invention, where 3, 4, 5, and 6 imaging sequences are used respectively and 3, 4, 5, and 6 k-space data sets are obtained respectively. It can be seen that Nyquist artifacts and acceleration artifacts are substantially suppressed.

[0086] An exemplary embodiment of the present invention can also provide a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is run, it executes the magnetic resonance imaging method of any of the above embodiments.

[0087] Based on the above description, an exemplary embodiment of the present invention can also provide a magnetic resonance imaging (MRI) system, including:

[0088] Gradient coils, configured to generate encoding gradients;

[0089] Radio frequency (RF) coils, configured to generate RF pulses; and

[0090] A processor, connected to a gradient coil and an RF coil, is configured to execute the magnetic resonance imaging method of any of the above embodiments. For example, the processor is configured to instruct the gradient coil and the RF coil to generate multiple sets of imaging sequences to acquire multiple k-space data sets, reconstruct magnetic resonance images respectively from each of the multiple k-space data sets; and take an average of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude. Each of the multiple sets of imaging sequences includes a pre-dephasing gradient pulse and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the multiple sets of imaging sequences have a standard area difference in sequence when sorted by area value.

[0091] Except for any previously indicated modifications, those skilled in the art can design many other variations and alternative arrangements without departing from the spirit and scope of this description, and the appended claims are intended to cover such modifications and arrangements. Thus, although the information has been specifically and detailedly described above in connection with the currently considered most practical and preferred aspects, it will be apparent to those of ordinary skill in the art that many modifications can be made without departing from the principles and concepts set forth herein, including but not limited to form, function, mode of operation, and use. Similarly, as used herein in all aspects, the examples and embodiments are only intended to be illustrative and should not be construed in any way as restrictive.

[0092] The purpose of providing the above specific embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive, but the present invention is not limited to these specific embodiments. Those skilled in the art should understand that various modifications, equivalent replacements, and changes etc. can be made to the present invention, as long as these transformations do not violate the spirit of the present invention, they should be within the protection scope of the present invention.

Claims

1. A magnetic resonance imaging method, the magnetic resonance imaging method comprising: Acquiring a plurality of k-space data sets using a plurality of sets of imaging sequences, each set of imaging sequences including a pre-dephasing gradient pulse and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the plurality of sets of imaging sequences have a standard area difference in sequence when sorted by area value; Reconstructing magnetic resonance images respectively from each of the plurality of k-space data sets; And Taking an average of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

2. The magnetic resonance imaging method according to claim 1, wherein, The standard area difference is 2 / N of the area of any one of the phase-encoding gradients, where N is the number of sets of the plurality of sets of imaging sequences.

3. The magnetic resonance imaging method according to claim 1, wherein, The number of sets of the plurality of sets of imaging sequences is greater than 2.

4. The magnetic resonance imaging method according to claim 1, wherein Each set of imaging sequences further includes a radio frequency excitation pulse, a radio frequency refocusing pulse, and a diffusion gradient pulse, the diffusion gradient pulse including a phase-shifting gradient pulse and a rephasing gradient pulse, the phase-shifting gradient pulse and the rephasing gradient pulse being symmetrically applied before and after the radio frequency refocusing pulse respectively, and the pre-dephasing gradient pulse being applied after the rephasing gradient pulse.

5. The magnetic resonance imaging method according to claim 1, wherein, Each set of imaging sequences further includes a plurality of frequency-encoding gradients, the directions of the plurality of frequency-encoding gradients being alternately reversed, and the plurality of phase-encoding gradients being respectively applied when the directions of the plurality of frequency-encoding gradients are reversed.

6. A magnetic resonance imaging method, the magnetic resonance imaging method comprising: Acquiring a plurality of k-space data sets using a plurality of sets of imaging sequences, each set of imaging sequences including an echo planar imaging sequence and a preparation sequence applied before a part of the echo planar imaging sequence, the echoes of the plurality of k-space data sets having a standard phase shift in sequence when sorted by phase value; Reconstructing magnetic resonance images respectively from each of the plurality of k-space data sets; And Taking an average of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

7. The magnetic resonance imaging method according to claim 6, wherein, The standard phase shift is 2π / N, where N is the number of the k-space data sets.

8. The magnetic resonance imaging method according to claim 6, wherein, The number of the k-space data sets is greater than 2.

9. The magnetic resonance imaging method according to claim 6, wherein, The preparation sequence includes a spin echo sequence, a gradient echo sequence, a diffusion weighted sequence, or a spin echo-diffusion weighted sequence.

10. A computer-readable storage medium, the computer-readable storage medium comprising a stored computer program, wherein, When the computer program is run, the magnetic resonance imaging method according to any one of claims 1 to 9 is executed.

11. A magnetic resonance imaging system, comprising: Gradient coils configured to generate encoding gradients; Radio frequency coils configured to generate radio frequency pulses; And A processor connected to the gradient coils and the radio frequency coils, the processor being configured to: Instruct the gradient coils and the radio frequency coils to generate a plurality of sets of imaging sequences to acquire a plurality of k-space data sets, each set of imaging sequences including a pre-dephasing gradient pulse and a plurality of phase-encoding gradients applied after the pre-dephasing gradient pulse, wherein the pre-dephasing gradient pulses in the plurality of sets of imaging sequences have a standard area difference in sequence when sorted by area value; Reconstruct magnetic resonance images respectively from each of the plurality of k-space data sets; And Taking an average of the amplitudes of the magnetic resonance images to generate a magnetic resonance image with an average amplitude.

12. The magnetic resonance imaging system according to claim 11, wherein, The standard area difference is 2 / N of the area of any phase encoding gradient, where N is the number of groups of the multi-component imaging sequence.

13. The magnetic resonance imaging system according to claim 11, wherein, When the echoes of the multiple k-space data sets are sorted according to the phase values, they successively have a standard phase shift.

14. The magnetic resonance imaging system according to claim 13, wherein, The standard phase shift is 2π / N, where N is the number of the k-space data sets.

Images