Method for collecting and processing MR data, MRI system and method, and storage medium

Abstract

The embodiment of the present invention provides a method for collecting and processing magnetic resonance data, a magnetic resonance imaging system and method, and a computer-readable storage medium. The method for collecting and processing magnetic resonance data includes: filling multiple groups of echo data collected after multiple excitations of imaging tissue into K space, wherein the K space filling order of at least two groups of the multiple groups of echo data is opposite; and reconstructing an image based on the echo data filled in the K space.

Description

Technical Field

[0001] The embodiments disclosed in the present invention relate to medical imaging technology, and more specifically to a method for acquiring and processing magnetic resonance data, a magnetic resonance imaging system and a method. Background Art

[0002] Magnetic resonance imaging (MRI) is a medical imaging modality that can obtain images of the human body without using X-rays or other ionizing radiation. MRI uses a magnet with a strong magnetic field to generate a main magnetic field B0. When the part of the human body to be imaged is positioned in the main magnetic field B0, the nuclear spins associated with the hydrogen nuclei in the human tissue are polarized, so that the tissue of the part to be imaged generates a longitudinal magnetization vector on a macroscopic level. When a radio frequency field B1 that intersects with the direction of the main magnetic field B0 is applied, the direction of proton rotation changes, so that the tissue of the part to be imaged generates a transverse magnetization vector on a macroscopic level. After the radio frequency field B1 is removed, the transverse magnetization vector decays in a spiral shape until it returns to zero, and a free induction decay signal is generated during the decay process. The free induction decay signal can be collected as a magnetic resonance signal, and the tissue image of the part to be imaged can be reconstructed based on the collected signal. The gradient system is used to transmit a layer selection gradient pulse, a phase encoding gradient pulse, and a frequency encoding gradient pulse (also called a readout gradient pulse) to provide three-dimensional position information for the above-mentioned magnetic resonance signal to achieve image reconstruction.

[0003] Based on different clinical applications, the magnetic resonance imaging system can be configured to perform imaging scans on human tissue according to different scanning sequences. Generally, different scanning sequences have their own characteristics in clinical applications, such as advantages and disadvantages. For example, some scanning sequences that can achieve rapid data acquisition can achieve rapid imaging and are widely used in clinical practice, but there are also image quality issues, such as blurred images that are not conducive to medical observation. Summary of the invention

[0004] An embodiment of the present invention provides a method for acquiring and processing magnetic resonance data, comprising:

[0005] Filling multiple groups of echo data acquired after multiple excitations of imaging tissue into K space, wherein the K space filling order of at least two groups of the multiple groups of echo data is opposite; and

[0006] An image is reconstructed based on the echo data filled in the K-space.

[0007] Optionally, the K-space filling order of every two adjacent groups of the multiple groups of echo data is opposite.

[0008] Optionally, each echo is filled into a phase encoding line of the K space, and the reverse K space filling order comprises:

[0009] gradually filling from the first phase encoding line of the K space to the second phase encoding line of the K space; and

[0010] The second phase encoding line of the K space is gradually filled toward the first phase encoding line of the K space.

[0011] Optionally, the first phase encoding line is located at a first edge of the K space or between the first edge and the center of the K space; the second phase encoding line is located at a second edge of the K space or between the second edge and the center of the K space, and the first edge and the second edge are opposite.

[0012] Optionally, the first phase encoding line is located at the center of the K space, and the second phase encoding line is located at a first edge or a second edge of the K space, and the first edge is opposite to the second edge.

[0013] Optionally, the method further comprises:

[0014] Calculating an average value of each corresponding echo in a plurality of groups of echo data filled into the K space;

[0015] Determine a center position echo based on an average value of the corresponding echoes, wherein the center position echo is an echo corresponding to a valid echo time;

[0016] The echo position in each group of echo data filled in the K space is translated to move the center position echo to the center of the K space.

[0017] Optionally, determining the center position echo based on the average value of the corresponding echoes includes:

[0018] Determine the currently set echo time;

[0019] determining an echo interval time based on a pre-stored reference echo chain;

[0020] Calculating a reference echo sequence number based on the currently set echo time and the echo interval time;

[0021] Determine the echo in the reference echo chain that is located at the reference echo sequence number;

[0022] Determine, from the average values ​​of the corresponding echoes, an average value closest to the echo at the reference echo number; and,

[0023] The echo associated with the closest mean value is determined as the center position echo.

[0024] Optionally, reconstructing an image based on the echo data filled in the K space includes: reconstructing an image based on an average value of each corresponding echo in each group of echo data after translation in the K space.

[0025] Optionally, a set of echo data acquired after each excitation of the imaging tissue includes a plurality of echoes acquired based on a plurality of consecutive radio frequency refocusing pulses.

[0026] Another embodiment of the present invention provides a magnetic resonance imaging method, comprising:

[0027] executing a first cycle of the scanning sequence to obtain a first echo chain including a plurality of first echoes;

[0028] Filling the plurality of first echoes onto a plurality of phase encoding lines in the K space respectively according to a first order;

[0029] executing a second cycle of the scanning sequence to obtain a second echo chain including a plurality of second echoes;

[0030] Filling the plurality of second echoes onto the plurality of phase encoding lines respectively according to a second order;

[0031] The first order and the second order are opposite.

[0032] Optionally, the plurality of first echoes are generated in response to a plurality of radio frequency refocusing pulses within the first period, and the plurality of second echoes are generated in response to a plurality of radio frequency refocusing pulses within the second period.

[0033] Optionally, the scanning sequence is a single-shot fast spin echo sequence.

[0034] Optionally, the first period and the second period are adjacent.

[0035] Optionally, the first order is: multiple first echoes in the first echo chain are sequentially filled from the first phase encoding line of the K space to the second phase encoding line of the K space; the second order is: multiple second echoes in the second echo chain are sequentially filled from the second phase encoding line of the K space to the first phase encoding line of the K space.

[0036] Optionally, the center of the K space is located on the first phase encoding line, the second phase encoding line, or between the first phase encoding line and the second phase encoding line.

[0037] Another embodiment of the present invention provides a computer-readable storage medium for storing a computer program, wherein the computer program is used in a magnetic resonance imaging system to enable the magnetic resonance imaging system to execute the method of any one of the above embodiments.

[0038] Another embodiment of the present invention provides a magnetic resonance imaging system, comprising:

[0039] Scanner;

[0040] a data acquisition unit; and

[0041] A controller for:

[0042] Controlling the scanner to execute a first cycle and a second cycle of a scanning sequence to respectively obtain a first echo chain including a plurality of first echoes and a second echo chain including a plurality of second echoes; and,

[0043] Control the data acquisition unit to acquire the multiple first echoes and the multiple second echoes, and fill the multiple first echoes onto the multiple phase encoding lines of the K space in sequence according to a first order, and fill the multiple second echoes onto the multiple phase encoding lines in sequence according to a second order; the first order and the second order are opposite.

[0044] It should be understood that the brief description above is provided to introduce some concepts further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, 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

[0045] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0046] Figure 1 A schematic structural diagram of a magnetic resonance imaging system is shown;

[0047] Figure 2 A flow chart showing a method for acquiring and processing magnetic resonance data according to an embodiment of the present invention;

[0048] Figure 3 On one hand, a group of echo data acquired after each excitation of the imaging tissue is shown, and on the other hand, a scanning sequence for scanning the imaging tissue and generating a plurality of echoes is shown;

[0049] Figure 4 A method for acquiring and processing magnetic resonance data provided by another embodiment of the present invention is shown;

[0050] Figure 5 A flow chart for determining a center position echo based on an average value of each corresponding echo is shown;

[0051] Figure 6 Shows the Figure 3The filling result after translation of the two sets of echo data obtained in Nex1 and Nex2;

[0052] Figure 7 A flow chart of a magnetic resonance imaging method provided by another embodiment of the present invention is shown;

[0053] Figure 8 A diagram showing the amplitude variation of a signal distributed in the K space obtained by collecting magnetic resonance data using an existing method is shown;

[0054] Fig. 9 Shows the Figure 8 The point spread function diagram obtained by inverse Fourier transforming the signal in;

[0055] Fig.10 A diagram showing the amplitude variation of a signal distributed in the K space obtained by using an embodiment of the present invention;

[0056] Fig.11 Shows the Fig.10 The point spread function diagram obtained by inverse Fourier transforming the signal in;

[0057] Fig.12 An image obtained by using an existing data acquisition method is shown;

[0058] Fig.13 The image obtained by using the data acquisition method of the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0059] Figure 1 A schematic diagram of the structure of a magnetic resonance imaging (MRI) system is shown, and the magnetic resonance imaging system 100 includes a scanner 110. The scanner 110 is used to perform magnetic resonance scanning on an object (e.g., a human body) 16 to generate image data of a region of interest of the object 16, and the region of interest may be a predetermined imaging site or imaging tissue. In one embodiment, the image data may include two-dimensional image data of multiple slices (or tomography) of the region of interest.

[0060] The magnetic resonance imaging system may include a controller 120, which is coupled to the scanner 110, for controlling the scanner 110 to perform the above-mentioned magnetic resonance scanning process. Specifically, the controller 120 can send sequence control signals to relevant components of the scanner 110 (such as a radio frequency generator and a gradient coil driver to be described below) through a sequence generator (not shown in the figure), so that the scanner 110 performs a preset scanning sequence.

[0061] Those skilled in the art will understand that the above-mentioned "scan sequence" refers to a combination of pulses with specific amplitude, width, direction and timing applied when performing magnetic resonance imaging scans, and these pulses can generally include, for example, radio frequency pulses and gradient pulses. The radio frequency pulses can include, for example, radio frequency transmission pulses and radio frequency refocusing pulses used to excite protons in the human body to resonate. The gradient pulses can include, for example, layer selection gradient pulses, phase encoding gradient pulses, frequency encoding gradient pulses, etc. Generally, multiple scan sequences can be pre-set in the magnetic resonance system so that a sequence that is compatible with clinical detection requirements can be selected, and the clinical detection requirements can include, for example, imaging sites, imaging functions, imaging effects, etc.

[0062] In practice, it may be necessary to select different scanning sequence types based on different clinical applications, such as echo planar imaging (EPI) sequence, gradient echo (GRE) sequence, spin echo (SE) sequence, fast spin echo (FSE) sequence, single-shot fast spin echo (SSFSE), diffusion-weighted imaging (DWI) sequence, inversion recovery (IR) sequence, etc., and each scanning sequence may have different scanning sequence parameters in different clinical applications, such as the number of excitations (Nex), echo time, echo chain length, repetition time, inversion recovery time, etc.

[0063] The number of excitations mentioned above refers to the number of times the same tissue is excited, for example, it may be the number of times the radio frequency emission pulses are applied.

[0064] In one example, the scanner 110 may include a main magnet assembly 111 , a bed 112 , a radio frequency generator 113 , a radio frequency transmission coil 114 , a gradient coil driver 115 , a gradient coil assembly 116 , and a data acquisition unit 117 .

[0065] The main magnet assembly 111 generally includes an annular superconducting magnet defined in a housing, and the annular superconducting magnet is installed in an annular vacuum container. The annular superconducting magnet and its housing define a cylindrical space surrounding the object 16, such as Figure 1 The scanning cavity 118 is shown. The main magnet assembly 111 generates a constant magnetic field, namely, the B0 field, along the Z direction of the scanning cavity 118. Generally, a relatively uniform portion of the B0 field is formed in the central region of the main magnet.

[0066] The bed 112 is used to carry the object 16 and respond to the control of the controller 120 to move along the Z direction to enter and exit the above-mentioned scanning cavity 118. For example, in one embodiment, the imaging volume of the object 16 can be positioned in the central area of ​​the scanning cavity where the magnetic field strength is relatively uniform, so as to facilitate scanning and imaging of the imaging volume of the object 16.

[0067] The Z direction is usually a direction extending from the head to the feet (or from the feet to the head) when the subject 16 is positioned on the bed 112. For example, the selected layer may be a slice at any position in the Z direction.

[0068] The magnetic resonance system transmits a static magnetic pulse signal to the subject 16 located in the scanning cavity by using the formed B0 field, so that the precession of protons in the resonance volume in the subject 16 is ordered, and a longitudinal magnetization vector Mz is generated.

[0069] The RF generator 113 is used to respond to the control signal of the controller 120 to generate RF pulses, such as RF excitation pulses. The RF excitation pulses are amplified (for example, by an RF power amplifier (not shown)) and then applied to the RF transmitting coil 114, so that the RF transmitting coil 114 transmits a RF field B1 orthogonal to the B0 field to the object 16 to excite the atomic nuclei in the above-mentioned resonance volume, thereby generating a transverse magnetization vector Mxy.

[0070] The radio frequency transmitting coil 114 may include, for example, a body coil arranged along the periphery of the main magnet, or a head coil dedicated to head imaging. The body coil may be connected to a transmit / receive (T / R) switch (not shown), and the body coil may be switched between a transmit mode and a receive mode by controlling the transmit / receive switch. In the receive mode, the body coil may be used to receive magnetic resonance signals from the subject 16.

[0071] After the radio frequency excitation pulse ends, the proton group loses phase, the macroscopic transverse magnetization vector in the tissue gradually decays, and the transverse magnetization vector of the object 16 gradually returns to zero, generating a free induction decay signal, that is, a magnetic resonance signal that can be collected. The above magnetic resonance signal can be collected in the form of "echo", such as spin echo or gradient echo, and the echo collection method used may affect the scanning time, imaging quality and other indicators.

[0072] Spin echo usually uses radio frequency refocusing pulses to refocus the phase of the proton group, gradually increasing the transverse magnetization vector so that the echo can be collected after the radio frequency refocusing pulse ends. The scanning sequences using the spin echo method include but are not limited to SE, FSE and SSFSE. In the SE sequence, a radio frequency refocusing pulse is applied once after the radio frequency transmission pulse and an echo is collected. Each collected echo is filled into a phase encoding line of the K space in turn. In the FSE sequence, multiple radio frequency refocusing pulses are applied after the radio frequency transmission pulse within a repetition time, and multiple echoes are collected. The multiple echoes are filled into multiple phase encoding lines of the K space. Compared with the SE sequence, the number of repetitions required for the FSE sequence, that is, the repetition time, is significantly reduced, thereby speeding up the scanning time. In the SSFSE sequence, after the radio frequency transmission pulse, a continuously applied radio frequency refocusing pulse is used to collect all the echoes required for the K space, and they are filled into all the phase encoding lines of the K space within a repetition time. Compared with the FSE sequence, SSFSE only needs one radio frequency excitation to collect all echoes, so it has a shorter scanning time. But at the same time, for FSE and SSFSE sequences, due to the continuous attenuation of the macroscopic transverse magnetization vector and the long echo chain, the signal amplitude of each echo is different, which will cause contrast blurring of the reconstructed image, and this problem is particularly obvious for the SSFSE sequence.

[0073] The gradient coil driver 115 is configured to respond to a gradient pulse control signal or a shim control signal sent by the controller 120 to provide appropriate current / power to the gradient coil assembly 116 .

[0074] The gradient coil assembly 116 forms a changing magnetic field in the imaging space to provide three-dimensional position information for the magnetic resonance signal, and is used to generate a compensation magnetic field for the B0 field to shim the B0 field.

[0075] The gradient coil assembly 116 may include three gradient coils, and the three gradient coils are used to generate magnetic field gradients tilted to three spatial axes (e.g., X-axis, Y-axis, and Z-axis) that are perpendicular to each other. More specifically, the gradient coil assembly 116 applies a magnetic field gradient in a slice selection direction (Z-direction) to select a layer in the imaging volume. Those skilled in the art understand that the layer is any one of a plurality of two-dimensional slices distributed along the Z-direction in the three-dimensional imaging volume. When the imaging is scanned, the radio frequency transmitting coil 114 transmits a radio frequency excitation pulse to the layer of the imaging volume and excites the layer. The gradient coil assembly 116 applies a magnetic field gradient in a phase encoding direction (Y-direction) to phase encode the magnetic resonance signal of the excited layer. The gradient coil assembly 116 applies a gradient field in a frequency encoding direction of the object 16 to frequency encode the magnetic resonance signal of the excited layer.

[0076] The data acquisition unit 117 is used to respond to the data acquisition control signal of the controller 120 to acquire the above-mentioned magnetic resonance signal (for example, received by the body coil or the surface coil). In one embodiment, the data acquisition unit 117 may include, for example, a radio frequency preamplifier, a phase detector and an analog / digital converter, wherein the radio frequency preamplifier is used to amplify the magnetic resonance signal, the phase detector is used to perform phase detection on the amplified magnetic resonance signal, and the analog / digital converter is used to convert the phase-detected magnetic resonance signal from an analog signal to a digital signal.

[0077] The data acquisition unit 117 is further used to respond to the data storage control signal of the controller 120 to store the digitized magnetic resonance signal (or echo) in the K space. The K space is a filling space of the original data of the magnetic resonance signal with spatial positioning encoding information. Specifically, the data acquisition unit 117 responds to the data storage control signal of the controller 120 to fill the digitized magnetic resonance signal into the K space in a specific manner.

[0078] The magnetic resonance imaging system 100 may include an image reconstruction unit 130 for performing inverse Fourier transformation on the data stored in the K space to reconstruct a three-dimensional image or a series of two-dimensional slice images of the imaging volume of the object 16. Specifically, the image reconstruction unit 130 may perform the above image reconstruction based on communication with the controller 120.

[0079] The magnetic resonance imaging system 100 may include a processing unit 140, which may perform any required image processing on the above three-dimensional image or any image in the image sequence, such as image correction, determining display parameters of the image, etc. The above image processing may be an improvement or adaptive adjustment made to the image in any aspect of contrast, uniformity, clarity, brightness, etc. Specifically, the processing unit 140 may perform the above image processing based on communication with the controller 120.

[0080] In one embodiment, the controller 120, the image reconstruction unit 130 and the processing unit 140 may respectively or jointly include a computer and a storage medium, on which a predetermined control program and a data processing program to be executed by the computer are recorded, for example, the storage medium may store programs for implementing imaging scanning, image reconstruction, image processing, etc., for example, the storage medium may store programs for implementing the magnetic resonance data storage method and the magnetic resonance imaging method of the embodiment of the present invention. The above-mentioned storage medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card.

[0081] The magnetic resonance imaging system 100 may include a display unit 150, which may be used to display an operation interface and various data, images or parameters generated during data acquisition and processing.

[0082] The magnetic resonance imaging system 100 includes a console 160, which may include user input devices such as a keyboard and a mouse, and the controller 120 can respond to control commands generated by the user based on operating the console 160 or an operating panel / button set on the main magnet housing to communicate with the scanner 110, the image reconstruction unit, the processing unit 140, the display unit 150, etc.

[0083] Figure 2 A flow chart of a method for acquiring and processing magnetic resonance (MR) data according to an embodiment of the present invention is shown. As shown in FIG2 , the method includes step S21 and step S23.

[0084] In step S21, multiple groups of echo data acquired after multiple excitations of imaging tissues are filled into the K space, wherein the K space filling order of at least two groups of the multiple groups of echo data is opposite.

[0085] In step S23 , an image is reconstructed based on the echo data filled in the K-space.

[0086] Specifically, "multiple excitations of imaging tissue" refers to repeated acquisition of magnetic resonance data of the same imaging tissue (e.g., a layer of the imaging volume), and may also refer to repeated application of radio frequency emission pulses to the same imaging tissue, the number of times the imaging tissue is excited is the number of excitations (NEX).

[0087] In each set of echo data, the echo generated or collected earlier has a larger signal amplitude than the echo generated or collected later, that is, the signal amplitude of the echo gradually decreases according to the order in which the echoes are generated or collected.

[0088] Optionally, the K-space filling order of each two adjacent groups of the multiple groups of echo data is opposite, that is, the echoes collected after two adjacent excitations are filled into the K-space in opposite order.

[0089] In one example, the reverse K-space filling order includes: gradually filling from the first phase encoding line of the K-space to the second phase encoding line of the K-space; and gradually filling from the second phase encoding line to the first phase encoding line.

[0090] In one embodiment, the first phase encoding line may be located at the first edge of the K space, and the second phase encoding line may be located at the second edge of the K space. The first edge and the second edge may be respectively arranged on both sides of the center of the K space, and the number of phase encodings between the first edge and the second edge may be determined based on the image size. For example, corresponding to a 128*128 image, the K space has at least 128 phase encoding lines. In some applications, 128 echoes need to be collected to fill the at least 128 phase encoding lines. At this time, the first phase encoding line and the second phase encoding line are respectively located at the two edges of the filling space, namely the first edge and the second edge. Then, for one set of echo data, it is filled from the first edge to the second edge, and for another set of echo data, it is filled from the second edge to the first edge.

[0091] In other applications, only half the number of echoes need to be collected to fill half of the K space, and the data of the other half of the K space is obtained by mirroring based on the filled half of the K space data, so as to obtain the entire K space filling data in this way. For example, for the 128*128 image, only an echo chain with 64 echoes can be collected, and the 64 echoes in one group of echo chains are sequentially filled from the center of the K space to an edge, such as the second edge, and the 64 echoes in another group of echo chains are sequentially filled from the second edge to the center of the K space in the reverse direction. In an embodiment using such an application, the first phase encoding line is located at the center of the K space, and the second phase encoding line is located at the second edge of the K space.

[0092] In applications where only half of the K space needs to be filled, in order to facilitate subsequent image reconstruction, a small number of more echoes are usually collected to fill part of the phase encoding lines of the other half of the K space. For example, for the 128*128 image, an echo chain with 72 echoes can be collected. At this time, the first phase encoding line can be located between the first edge and the center of the K space, and the 72 echoes in a group of echo chains are filled from the first phase encoding line located between the first edge and the center of the K space to the second edge in sequence (through the center of the K space), and the 74 echoes in another group of echo chains are filled from the second edge in sequence (through the center of the K space) to the first phase encoding line in the reverse direction. In an embodiment using this filling method, the first phase encoding line is located between the first edge and the center of the K space, and the second phase encoding line is located at the second edge.

[0093] Figure 3 On the one hand, a set of echo data collected after each excitation of the imaging tissue is shown. 0 , e 1 ,e 2 …e n+m Schematic diagram of being filled into the K space. The above K space may include multiple phase encoding lines y -m ,y-m+1 …y -1 y 0 ,y 1 ,y 2 …y n ,y 0 Located at the center of K space, y n Located at the edge of the K space, such as the second edge, the K space may also have a first edge corresponding to the second edge. The above-mentioned edge, first edge, and second edge refer to the position of the first or last echo filling, rather than being used to limit the storage capacity of the K space itself. Where n and m are both natural numbers. For example, n can be equal to 63 (corresponding to the first edge from y 0 to y 63 64 phase encoding lines), m can be equal to 8 (for multiple acquisitions of 8 phase encoding lines y -8 to y -1 Those skilled in the art will appreciate that these phase encoding lines have a stepped phase gradient in sequence.

[0094] As an example, in one excitation Nex1, multiple echoes e 0 , E 1 ,E 2 …E n+m From the first phase encoding line in K space (e.g. y -m ) gradually moves to the second phase encoding line in K space (e.g., y n ) is filled, at this time, the filling signal of the first phase encoding line has a larger signal amplitude, and the signal amplitude gradually decreases from the first phase encoding line to the second phase encoding line.

[0095] As an example, in another excitation Nex2, multiple echoes e 0 , E 1 ,E 2 …E n+m The second phase encoding line from K space (e.g. y n ) gradually moves toward the first phase encoding line in K space (e.g., y -m ) is filled, at this time, the filling signal of the second phase encoding line has a larger signal amplitude, and the signal amplitude from the second phase encoding line to the first phase encoding line gradually increases.

[0096] Furthermore, when the imaging tissue is further repeatedly excited and the corresponding multiple groups of echo data are collected, the filling can be performed in the opposite direction relative to the previous filling. For example, in another excitation Nex3, the multiple groups of echoes are gradually filled from the first phase encoding line of the K space to the second phase encoding line. At this time, the filling signal of the first phase encoding line has a larger signal amplitude, and the signal amplitude gradually decreases from the first phase encoding line to the second phase encoding line.

[0097] Figure 3 On the other hand, it is also shown that the imaging tissue is scanned and the plurality of echoes are generated. 0 , e 1 ,e 2 …e n+m A scanning sequence, wherein each excitation of the imaging tissue is achieved by applying a single radio frequency transmission pulse, and a plurality of radio frequency refocusing pulses are continuously applied after the single radio frequency transmission pulse to generate the corresponding echo e 0 , e 1 ,e 2 …e n+m When K-space filling is performed, each echo fills a phase encoding line of the K-space. In one example, the radio frequency transmission pulse is a radio frequency pulse with an angle of 90 degrees or approximate angle, and the radio frequency refocusing pulse is a radio frequency pulse with an angle of 180 degrees or approximate angle.

[0098] The above-mentioned scanning sequence is preferably an SSFSE sequence, wherein a plurality of RF refocusing pulses are continuously applied after a single RF transmission pulse, and the echoes collected based on the plurality of RF refocusing pulses can fill the entire K space. Through the embodiments of the present invention, when the SSFSE sequence is used for imaging, it is possible to ensure a sufficiently short imaging time and to have improved image sharpness, especially the sharpness of the edge of the image.

[0099] In step S23, reconstructing an image based on the echo data filled in the K space may include: reconstructing an image based on an average value of multiple groups of echo data filled in the K space. Multiple echoes of the same tissue are obtained by repeatedly acquiring the same imaging tissue multiple times, and the average signal amplitude of the multiple echoes is obtained, thereby avoiding data errors caused by image reconstruction based only on a group of echoes obtained after one excitation.

[0100] Furthermore, when the K-space is filled in the reverse order, the amplitudes of multiple echoes at the same encoding line are different. For example, in Nex1, the phase encoding line y -m -y n The signal amplitude on the phase encoding line y changes from maximum to minimum gradually, while in Nex2, the phase encoding line y -m -y n The signal amplitude on the phase encoding line gradually changes from the minimum to the maximum, and so on, so that the average value of the signal amplitude of each phase encoding line is closer to the average value of the signal amplitude of other phase encoding lines (the difference is smaller).

[0101] Figure 4 A method for collecting and processing magnetic resonance data provided by another embodiment of the present invention is shown. Figure 4 As shown, this method is Figure 1The method of the illustrated embodiment is similar, except that the method further comprises steps S41, S43 and S45.

[0102] In step S41, the average value of each corresponding echo in the multiple groups of echo data filled in the K space is calculated. In step S42, the center position echo is determined based on the average value of each corresponding echo, and the center position echo is the echo corresponding to the effective echo time. In step S45, the echo position in each group of echo data filled in the K space is translated to move the center position echo to the center of the K space.

[0103] Those skilled in the art understand that when performing magnetic resonance imaging scanning, the echo time (TE) may be set automatically or manually, which refers to the time between the center of the radio frequency transmission pulse and the center of an echo in the same cycle (or the same repetition time) of the scanning sequence. Therefore, based on the set echo time and echo spacing (ESP) time, the sequence number of the echo corresponding to the echo time can be determined. In the prior art, the echo with the sequence number is usually filled to the center of the K space. For example, when the echo time is 4 milliseconds and the echo spacing is 1 millisecond, when filling the K space, the 4th echo in the echo chain can be filled in the center of the K space, and then the other echoes can be filled in according to the order.

[0104] However, when the K space is filled in the reverse order of the embodiments of the present invention, the sequence number determined by the prior art will no longer be suitable for filling into the center of the K space. In order to improve the image clarity without changing the contrast, the effective echo time (effective TE) needs to be recalculated. In this embodiment, a reference echo chain can be pre-stored in the magnetic resonance imaging system. The reference echo chain is an echo chain for scanning, data acquisition and filling of a specific substance according to the prior art. The specific substance has the same or similar property characteristics as the imaging tissue of the human body (for example, having the same or similar T2 (transverse relaxation time) value). Each echo of the reference echo chain has a fixed echo interval (for example, 1 millisecond).

[0105] Figure 5 FIG. 4 shows a flow chart for determining the center position echo based on the average value of each corresponding echo. Figure 5 As shown, in step S43, the center position echo is determined based on the average value of each corresponding echo, which may specifically include the following steps:

[0106] Step S51: Determine the currently set echo time (e.g., 4 milliseconds);

[0107] Step S52: Determine the echo interval time (e.g., 1 millisecond) based on the pre-stored reference echo chain;

[0108] Step S53: Calculate the reference echo serial number based on the currently set echo time and the echo interval time, and the reference echo serial number is the serial number of a certain echo in the reference echo chain. For example, the reference echo serial number is determined by dividing the set echo time by the echo interval, that is, the fourth of all echoes in the reference echo chain is the reference echo serial number;

[0109] Step S54: determining an echo located at a reference echo sequence number in the reference echo chain, such as the fourth echo, which has a specific signal amplitude, such as 0.25;

[0110] Step S55: determining the average value closest to the echo at the reference echo number among the average values ​​of the corresponding echoes, for example, determining the one closest to 0.25 (for example, 0.251) from the average values ​​of the first echo value to the last echo value in the multiple groups of echo data determined in step S41 as the closest average value (or effective average value); and,

[0111] Step S56: Determine the echo associated with the closest average value as the above-mentioned center position echo.

[0112] For example, Figure 3 As shown in the current filling result, the 9th echo (e 8 ) is located at the center of the K space, and if the result obtained in step S43 is that the average value of the sixth echo is 0.251, which is closest to 0.25, then in step S45, by translating the position of each group of echo data in the K space, the sixth echo in each group of echo data is located at the phase encoding line y at the center of the K space. 0 The above-mentioned “translation” means that the order of the echoes themselves is not changed.

[0113] Figure 6 Shows the Figure 3 The filling result after translation of the two sets of echo data obtained in Nex1 and Nex2.

[0114] Therefore, when image reconstruction is performed in step S23, image reconstruction may be performed based on each group of echo data after translation in the K space, and specifically, image reconstruction may be performed based on the average value of each corresponding echo after translation.

[0115] Figure 7 FIG. 2 shows a flow chart of a magnetic resonance imaging (MRI) method provided by another embodiment of the present invention. Figure 7 As shown, the method includes steps S71, S72, S73 and S74.

[0116] In step S71, a first cycle of a scanning sequence is executed to obtain a first echo chain including a plurality of first echoes. Figure 3 The scanning sequence shown is similar to that shown in the figure. Those skilled in the art will understand that one cycle of the scanning sequence may be the time from the start of a radio frequency excitation to the end of a corresponding echo chain, or the time between the centers of two adjacent radio frequency transmission pulses (i.e., the repetition time). When it is necessary to repeatedly collect magnetic resonance data of the same imaging tissue N times, N (N is greater than 1) cycles of the same scanning sequence may be executed, wherein a radio frequency transmission pulse and a plurality of radio frequency refocusing pulses located after the radio frequency transmission pulse may be applied in each cycle. Each first echo is generated based on a plurality of radio frequency refocusing pulses in the first cycle. For example, a first echo that can fill a phase encoding line may be collected after each radio frequency refocusing pulse.

[0117] In step S72, the multiple first echoes are filled into the multiple phase encoding lines of the K space respectively according to a first order. For example, the first order may be: the multiple first echoes in the first echo chain are filled from the first phase encoding line of the K space to the second phase encoding line of the K space in sequence.

[0118] In step S73, the second cycle of the scanning sequence is executed to obtain a second echo chain including a plurality of second echoes. In this step, in the second cycle, a radio frequency transmission pulse and a plurality of radio frequency refocusing pulses located after the radio frequency transmission pulse are applied, and each second echo is generated based on the plurality of radio frequency refocusing pulses in the second cycle.

[0119] In step S74, the plurality of second echoes are respectively filled onto the plurality of phase encoding lines in a second order, wherein the first order is opposite to the second order. For example, the second order may be: the plurality of second echoes in the second echo chain are sequentially filled from the second phase encoding line to the first phase encoding line.

[0120] As described above, the center of the K space may be located on the first phase encoding line, the second phase encoding line, or between the first phase encoding line and the second phase encoding line. Specific application examples may be similar to the corresponding descriptions above and will not be repeated here.

[0121] The scanning sequence is preferably an SSFSE sequence, and optionally, it can also be an FSE sequence. Even if the K space cannot be completely filled after one excitation in the FSE sequence, as long as the echoes on multiple phase encoding lines are repeatedly acquired multiple times, the image clarity can be improved by reversing the filling order of the echoes acquired twice adjacently.

[0122] In one embodiment, the first cycle and the second cycle are adjacent. When multiple cycles of a scanning sequence are performed for the same imaging tissue, the K-space filling order of the echoes collected in every two adjacent cycles can be reversed.

[0123] In other embodiments, the first cycle and the second cycle may not be adjacent. For example, in one embodiment, when there are 4 cycles, the K-space filling order of the echoes collected in the first two cycles may be the same, while the K-space filling order of the echoes collected in the last two cycles may be opposite to the first two filling orders.

[0124] For another example, when there are five cycles, the K-space filling order of the echoes collected in only one cycle may be opposite to the filling order in other cycles, as long as it helps to improve the image clarity.

[0125] Based on the above description, an embodiment of the present invention can also provide a magnetic resonance imaging system, which can include a scanner, a data acquisition unit and a controller. The structure and working principle of the magnetic resonance imaging system of this embodiment can be similar to Figure 1 The system shown in the figure is different in that the controller is used to control the scanner and the data acquisition unit to perform the above-mentioned magnetic resonance imaging method embodiment, for example:

[0126] Controlling the scanner to execute a first cycle and a second cycle of a scanning sequence to respectively obtain a first echo chain including a plurality of first echoes and a second echo chain including a plurality of second echoes; and,

[0127] The data acquisition unit is controlled to acquire the multiple first echoes and the multiple second echoes, and the multiple first echoes are sequentially filled onto the multiple phase encoding lines of the K space in a first order, and the multiple second echoes are sequentially filled onto the multiple phase encoding lines in a second order, wherein the first order is opposite to the second order.

[0128] Based on the above description, an embodiment of the present invention may also provide a computer-readable storage medium for storing a computer program, wherein the computer program is used in a magnetic resonance imaging system to control the magnetic resonance imaging system to execute the above-mentioned method for acquiring and processing magnetic resonance data and any embodiment of the magnetic resonance imaging method.

[0129] Figure 8 The figure shows the amplitude variation diagram of the signal distributed in the K space obtained by collecting magnetic resonance data using the existing method. Fig. 9 Shows the Figure 7 The point spread function diagram obtained by inverse Fourier transforming the signal in; Fig.10 FIG. 4 shows a graph showing the amplitude variation of a signal distributed in the K space obtained by using an embodiment of the present invention. Fig.11 Shows the Fig.10 The point spread function diagram obtained by inverse Fourier transform of the signal in. Among them, Figure 8 There is a big difference in the signal amplitude between the center area of ​​K space and the edge area. Fig.10There is a smaller signal amplitude difference in the image, which is conducive to reconstructing a clearer image and reducing the blur problem that easily occurs at the edge of the image. Fig. 9 The signal distribution in is wider, while Fig.11 The signal distribution in is relatively concentrated, which reflects that the reconstructed image has better spatial resolution when the embodiment of the present invention is adopted.

[0130] Fig.12 shows an image obtained by using the existing data acquisition method, Fig.13 shows an image obtained by using the data acquisition method of an embodiment of the present invention, Fig.13 The image shown has better clarity.

[0131] As used herein, an element or step described in the singular and preceded by the word "one" or "an" should be understood as not excluding the plural number of the element or step, unless such exclusion is explicitly stated. In addition, reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that simultaneously incorporate the described features. Moreover, unless explicitly stated to the contrary, an embodiment "comprising", "including", "having" an element or multiple elements with a specific property may include additional such elements that do not have the property. The terms "including" and "in which" are used as the concise language equivalents of the corresponding terms "comprising" and "wherein". In addition, in the appended claims, the terms "first", "second" and "third" etc. are used only as markers and are not intended to impose numerical requirements or specific positional order on their objects.

[0132] This written description uses examples to disclose the invention, including the best mode, and also enables a person of ordinary skill in any relevant art to implement the invention, including making and using any device or system and performing any covered method. The scope of patent protection for the invention is defined by the claims and may include other examples known to those skilled in the art. If they have structural elements that are indistinguishable from the literal language of the claims, or if they include equivalent structural elements that are insubstantially different from the literal language of the claims, it is intended that such other examples fall within the scope of the claims.

Claims

1. A method for collecting and processing magnetic resonance data, comprising: Filling multiple groups of echo data acquired after multiple excitations of imaging tissue into K space, wherein the K space filling order of at least two groups of the multiple groups of echo data is opposite; Calculating an average value of each corresponding echo in a plurality of groups of echo data filled into the K space; Determine a center position echo based on an average value of the corresponding echoes, wherein the center position echo is an echo corresponding to a valid echo time; translating the echo position in each set of echo data filled in the K space to move the center position echo to the center of the K space; and, An image is reconstructed based on an average value of each corresponding echo in each group of echo data after translation in the K space.

2. The method of claim 1, wherein: The K-space filling order of each two adjacent groups of the multiple groups of echo data is opposite.

3. The method of claim 1, wherein: Each echo is filled into one phase encoding line of the K-space, and the reverse K-space filling order includes: gradually filling from the first phase encoding line of the K space to the second phase encoding line of the K space; and The second phase encoding line of the K space is gradually filled toward the first phase encoding line of the K space.

4. The method of claim 3, wherein: The first phase encoding line is located at a first edge of the K space or between the first edge and the center of the K space; The second phase encoding line is located at a second edge of the K space or between the second edge and the center of the K space, and the first edge and the second edge are opposite to each other.

5. The method of claim 3, wherein: The first phase encoding line is located at the center of the K space, and the second phase encoding line is located at a first edge or a second edge of the K space, and the first edge is opposite to the second edge.

6. The method of claim 1, wherein: Determining the center position echo based on the average value of the corresponding echoes includes: Determine the currently set echo time; determining an echo interval time based on a pre-stored reference echo chain; Calculating a reference echo sequence number based on the currently set echo time and the echo interval time; Determine the echo in the reference echo chain that is located at the reference echo sequence number; Determine, from the average values ​​of the corresponding echoes, an average value closest to the echo at the reference echo number; and, The echo associated with the closest mean value is determined as the center position echo.

7. The method of claim 1, wherein: A set of echo data acquired after each excitation of imaging tissue includes multiple echoes acquired based on multiple consecutive radio frequency refocusing pulses.

8. A magnetic resonance imaging method, comprising: executing a first cycle of the scanning sequence to obtain a first echo chain including a plurality of first echoes; Filling the plurality of first echoes onto a plurality of phase encoding lines in the K space respectively according to a first order; executing a second cycle of the scanning sequence to obtain a second echo chain including a plurality of second echoes; Filling the plurality of second echoes onto the plurality of phase encoding lines respectively in a second order, wherein the first order is opposite to the second order; Calculating an average value of the first echo and the second echo on each phase encoding line; Determine a center position echo based on an average value of a first echo and a second echo on each phase encoding line, wherein the center position echo is an echo corresponding to a valid echo time; translating the echo positions of the first echo and the second echo to move the center position echo to the center of the K space; and, An image is reconstructed based on an average value of each of the first echoes and the corresponding second echoes after translation in the K space.

9. The method of claim 8, wherein: The plurality of first echoes are generated in response to a plurality of radio frequency refocusing pulses in the first period, and the plurality of second echoes are generated in response to a plurality of radio frequency refocusing pulses in the second period.

10. The method of claim 8, wherein: The scanning sequence is a single-shot fast spin echo sequence.

11. The method of claim 8, wherein: The first period and the second period are adjacent.

12. The method of claim 8, wherein: The first sequence is: the multiple first echoes in the first echo chain are sequentially filled from the first phase encoding line of the K space to the second phase encoding line of the K space; The second order is: the multiple second echoes in the second echo chain are sequentially filled from the second phase encoding line of the K space to the first phase encoding line of the K space.

13. The method of claim 12, wherein: The center of the K space is located on the first phase encoding line, on the second phase encoding line, or between the first phase encoding line and the second phase encoding line.

14. A computer-readable storage medium for storing a computer program, wherein the computer program is used in a magnetic resonance imaging system to cause the magnetic resonance imaging system to execute the method according to any one of claims 1 to 13.

15. A magnetic resonance imaging system, comprising: Scanner; Data acquisition unit; as well as, A controller for: Controlling the scanner to execute a first cycle and a second cycle of a scanning sequence to respectively obtain a first echo chain including a plurality of first echoes and a second echo chain including a plurality of second echoes; and, Controlling the data acquisition unit to acquire the plurality of first echoes and the plurality of second echoes, and sequentially filling the plurality of first echoes onto the plurality of phase encoding lines of the K space in a first order, and sequentially filling the plurality of second echoes onto the plurality of phase encoding lines in a second order; the first order and the second order are opposite; Calculating an average value of the first echo and the second echo on each phase encoding line; Determine a center position echo based on an average value of a first echo and a second echo on each phase encoding line, wherein the center position echo is an echo corresponding to a valid echo time; translating the echo positions of the plurality of first echoes and the plurality of second echoes to move the center position echo to the center of the K space; and, An image is reconstructed based on an average value of each of the first echoes and the corresponding second echoes after translation in the K space.

16. The system of claim 15, wherein: The first sequence is: the multiple first echoes are sequentially filled from the first phase encoding line of the K space to the second phase encoding line of the K space; The second order is: the multiple second echoes are sequentially filled from the second phase encoding line to the first phase encoding line.

17. The system of claim 16, wherein: The center of the K space is located on the first phase encoding line, on the second phase encoding line, or between the first phase encoding line and the second phase encoding line.

Images