CN107582057B - Magnetic resonance imaging method and device - Google Patents
Magnetic resonance imaging method and device Download PDFInfo
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- CN107582057B CN107582057B CN201710915393.2A CN201710915393A CN107582057B CN 107582057 B CN107582057 B CN 107582057B CN 201710915393 A CN201710915393 A CN 201710915393A CN 107582057 B CN107582057 B CN 107582057B
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Abstract
The invention provides a magnetic resonance imaging method and a magnetic resonance imaging device. The magnetic resonance imaging method comprises the following steps: performing a first transformation on the single-layer calibration data and the multi-layer simultaneous imaging data in the K-space to obtain a first single-layer calibration data and a first multi-layer simultaneous imaging data in an intermediate domain, the intermediate domain being located between the K-space and the image domain; calculating a coil combination coefficient according to the first single-layer calibration data; performing data layering according to the coil merging coefficient and the first multi-layer simultaneous imaging data to obtain a plurality of single-layer data in an intermediate domain; and performing a second transformation on the plurality of slice data in the intermediate domain to obtain a magnetic resonance image. The magnetic resonance imaging method and the magnetic resonance imaging device have the characteristics of small reconstruction calculation amount, high reconstruction speed and the like.
Description
Technical Field
The invention mainly relates to the field of magnetic resonance imaging, in particular to an image reconstruction method and device for magnetic resonance multilayer simultaneous imaging.
Background
Magnetic Resonance Imaging (MRI) technology is increasingly used in clinical diagnosis and scientific research, and has the advantages of safety, multiple contrast ratios, good resolution capability on soft tissues and the like. However, the longer imaging time required for magnetic resonance imaging techniques compared to other medical imaging techniques (e.g., ultrasound imaging, CT imaging) not only reduces patient comfort, increases the sensitivity of image quality to motion, but also presents certain challenges for its application in dynamic process imaging.
The multi-layer Simultaneous imaging (SMS) technique as described in document 1 can effectively shorten the magnetic resonance imaging scan time, and has been greatly developed in recent years. The basic process of the multilayer simultaneous imaging technology is that a plurality of slices at different positions in space are excited simultaneously, a gradient field is used for space coding, and then signals are received by a coil array. If the number of slices to be acquired is N and the time required for each slice to be acquired is t, then the total time required for scanning by the conventional magnetic resonance imaging method is N × t. In contrast, if the number of slices acquired and simultaneously excited for simultaneous imaging of multiple slices is m, the total time required for scanning is shortened to N/m × t. Figure 1 shows a slice schematic of two slices simultaneously excited and acquired. In the scheme shown in FIG. 1, slice 1 and slice N/2+1 are excited simultaneously and acquired simultaneously, slice 2 and slice N/2+2 are excited simultaneously and acquired simultaneously, slice 3 and slice N/2+3 are excited simultaneously and acquired simultaneously, and so on.
Different from the traditional imaging method, the data directly acquired by the multi-layer simultaneous imaging technology contains information of a plurality of slice layers, and simple reconstruction brings aliasing artifacts among the plurality of slice layers. Document 2 describes a more common multi-slice simultaneous imaging reconstruction method, slice-GRAPPA (GeneRalized automatic Parallel acquisition). The method utilizes the difference of the sensitivity of each coil in the receiving array, calculates the coil (channel) combination coefficient for layering aliasing data in K space by using calibration data collected by single-layer excitation in advance (as shown in figure 2 a), and then applies the combination coefficient to multi-layer simultaneous imaging K space data to realize layering (as shown in figure 2 b). The layered data can then be imaged by conventional reconstruction methods (e.g., fourier transform).
The conventional multilayer simultaneous imaging technology described above is to calculate coil combination coefficients in a K space and to layer multilayer aliasing images in the K space, and this image reconstruction method has a large calculation amount and low memory read-write efficiency, which leads to a slow image reconstruction speed.
Document 1: barth M, Breuer F, Koopmans PJ, Norris DG, Poser ba, simultaneousultisiltislice (SMS) imaging techniques, magn Reson med.2016; 75(1):63-81.
Document 2: setcommpop K, GagoskiBA, polinieni JR, Witzel T, Wedeen VJ, waldll. blippod-controlled influencing in parallel imaging for simultaneouslly planar imaging with reduced g-factor polarity. 67(5):1210-24.
Disclosure of Invention
The invention aims to provide an image reconstruction method and device for magnetic resonance multilayer simultaneous imaging, which have the characteristics of small reconstruction calculation amount, high reconstruction speed and the like.
In order to solve the above technical problem, the present invention provides a magnetic resonance imaging method, including: performing a first transformation on the single-layer calibration data and the multi-layer simultaneous imaging data in the K-space to obtain a first single-layer calibration data and a first multi-layer simultaneous imaging data in an intermediate domain, the intermediate domain being located between the K-space and the image domain; calculating a coil combination coefficient according to the first single-layer calibration data; carrying out data layering according to the coil merging coefficient and the first multilayer simultaneous imaging data to obtain single-layer data in a middle domain; and performing a second transformation on the plurality of slice data in the intermediate domain to obtain a magnetic resonance image.
In an embodiment of the invention, the calculating the coil combining coefficient according to the first single-layer calibration data includes: applying a first phase modulation to the first single layer calibration data to construct a first coefficient matrix; constructing a first target vector from the first single layer calibration data without applied phase modulation; and calculating the coil combination coefficient according to the first coefficient matrix and the first target vector.
In an embodiment of the present invention, the data layering according to the coil combination coefficient and the first multi-slice simultaneous imaging data includes: applying a second phase modulation to the first multi-slice simultaneous imaging data to construct a second coefficient matrix; and calculating the single-slice data in the middle domain according to the coil merging coefficient and the second coefficient matrix.
In an embodiment of the invention, the first transform is a fourier transform along a frequency encoding direction.
In an embodiment of the present invention, the multi-slice simultaneous imaging data is obtained by exciting a target region multiple times, the target region includes a plurality of scanning slices, and the number of the scanning slices is greater than the number of exciting times.
In one embodiment of the invention, at least a first excitation and a second excitation are performed on the target region, the first excitation corresponding to a first set of scan layers and the second excitation corresponding to a second set of scan layers.
In an embodiment of the invention, the first group of scanning layers or the second group of scanning layers includes a plurality of scanning layers arranged at intervals, and during the period when the second group of scanning layers is activated, the first transformation is performed on the imaging data corresponding to the first group of scanning layers.
In an embodiment of the invention, the second transform is a fourier transform along the phase encoding direction.
In another aspect of the invention there is provided a magnetic resonance imaging apparatus comprising: the device comprises a first transformation module, a second transformation module and a third transformation module, wherein the first transformation module is used for carrying out first transformation on single-layer calibration data and multi-layer simultaneous imaging data in a K space to obtain first single-layer calibration data and first multi-layer simultaneous imaging data in an intermediate domain, and the intermediate domain is positioned between the K space and an image domain; the coil merging coefficient calculation module is used for calculating a coil merging coefficient according to the first single-layer calibration data; the data layering module is used for carrying out data layering according to the coil merging coefficient and the first multilayer simultaneous imaging data to obtain single-layer data in a middle domain; and
a second transformation module for performing a second transformation on the plurality of slice data in the intermediate domain to obtain a magnetic resonance image.
In an embodiment of the present invention, the coil combination coefficient calculation module is configured to perform the following steps: applying a first phase modulation to the first single layer calibration data to construct a first coefficient matrix; constructing a first target vector from the first single layer calibration data without applied phase modulation; and calculating the coil combination coefficient according to the first coefficient matrix and the first target vector.
In an embodiment of the invention, the data layering module is configured to perform the following steps: applying a second phase modulation to the first multi-slice simultaneous imaging data to construct a second coefficient matrix; and calculating the single-slice data in the middle domain according to the coil merging coefficient and the second coefficient matrix.
In an embodiment of the invention, the first transform is a fourier transform along a frequency encoding direction.
In an embodiment of the present invention, the multi-slice simultaneous imaging data is obtained by exciting a target region multiple times, the target region includes a plurality of scanning slices, and the number of the scanning slices is greater than the number of exciting times.
In one embodiment of the invention, at least a first excitation and a second excitation are performed on the target region, the first excitation corresponding to a first set of scan layers and the second excitation corresponding to a second set of scan layers.
In an embodiment of the invention, the first group of scanning layers or the second group of scanning layers includes a plurality of scanning layers arranged at intervals, and during the period when the second group of scanning layers is activated, the first transformation is performed on the imaging data corresponding to the first group of scanning layers.
In an embodiment of the invention, the second transform is a fourier transform along the phase encoding direction.
In another aspect of the invention, a magnetic resonance imaging apparatus is provided, comprising a memory, a processor and computer instructions stored on the memory and executable on the processor, wherein the processor when executing the computer instructions implements the method as described above.
In another aspect of the invention, a computer readable medium is provided having computer instructions stored thereon, wherein the computer instructions, when executed by a processor, perform the method as described above.
In a further aspect of the invention a magnetic resonance imaging system is provided comprising a magnetic resonance imaging apparatus as described above.
Compared with the prior art, the invention has the following advantages:
compared with the traditional way of calculating the coil combination coefficients in the K space and layering the multi-layer aliasing image in the K space, the method has the advantages that the coil combination coefficients are calculated in the middle domain, and the multi-layer aliasing image is layered in the middle domain. And data can be read and written in the middle domain by taking the whole frequency coding line as a unit, so that the read-write efficiency of the memory is improved. In addition, the invention can also carry out one or more of the first transformation, the calculation of coil merging coefficients and the data layering when acquiring multi-layer simultaneous imaging data, and shortens the time required from the acquisition of data to the output of a final image.
Drawings
FIG. 1 is a slice schematic of two-slice simultaneous excitation, simultaneous acquisition of a multi-slice simultaneous imaging technique.
Fig. 2a and 2b are schematic diagrams of basic steps of a slice-GRAPPA multi-layer simultaneous imaging reconstruction method.
Figure 3 is a schematic diagram of the structure of a magnetic resonance imaging system.
Figure 4 is a schematic diagram of the basic process of magnetic resonance imaging.
Fig. 5 is a schematic diagram of the substeps of converting from K-space to the image domain.
Fig. 6 is a basic flowchart of an image reconstruction method for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention.
FIG. 7 is a basic flow chart for calculating coil combining coefficients according to an embodiment of the present invention.
FIG. 8 is a basic flow diagram for layering multiple layers of aliased images according to an embodiment of the invention.
Fig. 9 is a basic block diagram of an image reconstruction apparatus for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention.
FIG. 10 is a diagram illustrating the results of layering multiple layers of aliased images according to an embodiment of the invention.
Fig. 11 is a schematic structural diagram of an image reconstruction apparatus for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention.
FIG. 12 is a schematic diagram of a computer-readable medium of an embodiment of the invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.
As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
A magnetic resonance imaging system typically comprises a magnet having an aperture, a transmit coil for transmitting radio frequency signals and a receive coil for receiving magnetic resonance signals, gradient coils for spatially localizing the magnetic resonance signals, a pulse generator for generating a scan sequence, and a control system. The magnetic resonance imaging system is operated by an operator (clinician) controlling a console connected to the control system, which may include a keyboard or other input device, a control panel and a display to input commands and display the generated images.
Fig. 3 is a schematic structural diagram of a magnetic resonance imaging system in which a clinician first places a subject 3 on a bed 1 and places a local coil (not shown in the figure) for receiving magnetic resonance signals on the body surface of the subject 3 when performing a magnetic resonance examination; then the clinician controls the scanning bed to move towards the aperture formed by the magnet 2 by operating the console connected with the control system 5, after the magnetic resonance imaging system monitors that the clinician sends an instruction of the movement of the scanning bed 1, the control system 5 monitors the movement range of the scanning bed immediately, and when the scanning bed 1 enters the edge of the scanning imaging area 4, the control system 5 controls the pulse sequence generator to generate a corresponding sequence for scanning. During the movement of the bed 1, the receiving coils placed on the surface of the subject's body can move with the bed 1 in the inner space of the magnet space, and the receiving coils at different positions are opened or closed by the control system 5 so as to receive the corresponding magnetic resonance signals.
Each signal of the magnetic resonance contains information of the full slice, so that spatial localization encoding, i.e. frequency encoding and phase encoding, of the magnetic resonance signals is required. The MR signals acquired by the MR receiving coil are actually radio waves with spatially encoded information, and belong to analog signals rather than digital information, and need to be converted into digital information through analog-to-digital conversion (ADC), and the digital information is filled into K space to become a digital data lattice. The K-space is a filling space of the MR signal raw digital data with spatial localization coding information, and each MR image has its corresponding K-space data lattice. The basic procedure of magnetic resonance imaging mainly comprises the steps as shown in figure 4: firstly, a pulse signal generated by radio frequency excitation can excite a body region of a detected person to generate precession nuclear spin; secondly, through spatial encoding, the receiving coil can simultaneously acquire a response signal with spatial positioning encoding information, and the response signal represents an MR signal generated by precession nuclear spin of a body region of a detected person; then, the MR signals are filled into a K space through analog-to-digital conversion; finally, the data of the K space is subjected to Fourier transform, so that the spatial positioning coding information in the original data can be decoded, MR signals with different frequencies, phases and amplitudes are resolved, the different frequencies and the phases represent different spatial positions, the amplitudes represent MR signal intensity, and the MR digital information with different frequencies, phases and signal intensities is distributed to corresponding pixels to obtain MR image data, namely, an MR image is reconstructed.
It should be appreciated that the Fourier transform of the K-space data lattice, the assignment to individual pixels, and the like, may be performed in a laptop computer, desktop computer, server, tablet, or the like, von Neumann architecture computer. Those skilled in the art will also appreciate that the processes may also be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof.
Fig. 5 shows a schematic view of the substeps of converting from K-space to the image domain. The conversion from K-space to the image domain can generally be divided into two sub-steps: (a) carrying out first transformation on the data of the K space so as to obtain corresponding data of an intermediate domain; (b) the data of the intermediate domain is subjected to a second transformation, resulting in an image in the image domain. In practice, the first transformation and the second transformation will generally be combined into a single transformation operation. Taking the example of performing a two-dimensional fourier transform on the K-space data, the two-dimensional fourier transform may be decomposed into data obtained by performing a one-dimensional fourier transform (corresponding to a first transform) on the K-space data to obtain an intermediate domain, and the one-dimensional fourier transform may include along a phase encoding direction or along a frequency encoding direction; the data in the intermediate domain is then subjected to a one-dimensional fourier transform (corresponding to the second transform) which may include along the frequency encoding direction or along the phase encoding direction, to obtain an image in the image domain.
As described in the background art, a commonly used multilayer simultaneous imaging technique is to calculate a coil combination coefficient in a K space and to layer a multilayer aliasing image in the K space, and this image reconstruction method needs to start data processing after the data collection of an original K space is completed, and has a low read-write efficiency for a memory, which results in a slow image reconstruction speed. In order to overcome the above disadvantages in the prior art, the inventor of the present invention proposes to perform a first transformation on K-space data acquired simultaneously in multiple layers, transform the K-space data into an intermediate domain, then perform calculation of coil merging coefficients in the intermediate domain, and layer multiple layers of aliasing images in the intermediate domain to obtain single-layer data, and finally perform a second transformation on the single-layer data to obtain a final image. The single-layer data obtained by the processing mode is in the middle domain, the calculation amount of subsequent reconstruction can be reduced, the reading and writing of the memory in the calculation process can be carried out by taking the whole frequency coding line as a unit, and the efficiency of the reading and writing of the memory is improved by processing the block data. Therefore, the invention can accelerate the image reconstruction speed of multilayer simultaneous imaging.
The slice-GRAPPA method is taken as an example to demonstrate the feasibility of the invention.
The slice-GRAPPA method for coil combination coefficient calculation and slice separation in K-space is briefly described as follows. Before the magnetic resonance scanning, scanning parameters are set for the control system 5, wherein the scanning parameters may include scanning parameters corresponding to a single layer and scanning parameters corresponding to simultaneous excitation of multiple layers, and further, the scanning parameters corresponding to a single layer or scanning parameters corresponding to simultaneous excitation of multiple layers may include gradient parameters, radio frequency parameters, and the like; the control system 5 sends the scanning parameters to the spectrometer system to generate a corresponding gradient scanning sequence or a radio frequency pulse sequence; the gradient scanning sequence drives the gradient coil to generate a corresponding gradient field, and the radio frequency pulse sequence drives the radio frequency coil to generate a corresponding radio frequency field; each layer of a region to be detected of a detected person generates precession nuclear spin under the excitation of a radio frequency field, and the corresponding precession nuclear spin of each layer is subjected to gradient encoding under the action of a gradient field to generate a magnetic resonance signal corresponding to each layer, and the magnetic resonance signal is filled into a K space to obtain single-layer acquisition K space data. In one embodiment, the single-layer acquisition K-space data may be a K-space center region for each layer. Similarly, multiple layers (such as two layers, three layers and the like) of the region to be detected of the detected object generate precession nuclear spins under the simultaneous excitation of a radio frequency field, and gradient encoding is carried out on the precession nuclear spins corresponding to the multiple layers simultaneously under the action of a gradient field to generate multiple layers of corresponding magnetic resonance signals, and the magnetic resonance signals are filled into a K space, so that multiple layers of K space data can be acquired simultaneously.
In one embodiment, multi-channel K-space data of a single layer excitation is used as calibration data. After the size of the K-space convolution kernel is determined, a coefficient matrix B required to solve the coil combination coefficients may be generated from calibration data in K-space and contain multi-channel data. If the number of slices per simultaneous excitation is p, the coefficient matrix B can be represented as (A)1+A2+…Ap) Wherein A isiAnd acquiring data for the single slice of the calibration data, wherein i is the number of each slice, and i is more than or equal to 1 and less than or equal to p.
The coil merging coefficient X to be solved satisfies the following relation:
BX＝Atar(1)
where X is a multiple coil (channel) combining coefficient, AtarIs a fitting target vector extracted from the K-space single slice calibration data. Here B, AtarAs is known, the coil combining coefficient X can be calculated by:
X＝(BTB)-1BTAtar(2)
in the formula, the T at the upper right corner represents the transposition operation of the matrix; the-1 in the upper left corner represents the inverse of the matrix.
Multi-slice simultaneous imaging with slice aliasing data can be used to construct the coefficient matrix C. Recording the monolithic layer data separated from the K space as D, and separating the monolithic layer data D by using the coil merging coefficient X calculated in the previous step:
D＝CX (3)
the following demonstrates the invention to be true. The matrices that are (segmented) fourier transformed in the frequency coding direction are left-multiplied at both ends of equation (1) to obtain:
FroBX＝FroAtar(4)
is provided with
AF_tar＝FroAtarThe coil combination coefficient X can be calculated as follows:
it can be seen that the coil combining coefficients X calculated by equations (5) and (3) are equal, where ro represents the frequency encoding direction or the readout direction; froRepresenting a fourier transform along a frequency encoding direction; a. theF_tarRepresenting the fitted target vector after fourier transformation along the frequency encoding direction.
When layering the layer aliasing data, it is necessary to construct a coefficient matrix after fourier transform in the frequency coding direction
Data D after single-slice Fourier transform along frequency directionF_tar(i.e., the slice data in the middle domain) can be calculated by:
DF_tar＝CFX (6)
for the coefficient matrix B, C, the column direction data can be segmented and constructed as that the original K-space data is shifted by a certain amount along the frequency coding direction, and the maximum shift amount is determined by the size of the convolution kernel. A. thetarThe original K-space data, which is free of translation, is arranged along the frequency encoding direction. Depending on the nature of the fourier transform, a shift in K-space before the transform will result in a linear phase modulation on the transformed result. The strength of linear phase modulation is related to the translation size of K space, and the translation of each unit in the K space brings 2 pi/N phase change of adjacent pixels to the result of Fourier transform, wherein N is the total number of pixels in the direction of Fourier transform, N is a positive integer, and N is more than or equal to 1 and less than or equal to 128.
As can be seen from the above demonstration, the coil merging coefficients calculated by the present invention are the same as those calculated by the conventional method, and the single slice data D in the middle domain calculated by the present inventionF_tarThe method is the same as the single-slice data obtained by transforming the single-slice data D in the K space calculated in the traditional mode into the intermediate domain, so that the result obtained by the processing mode provided by the invention is correct and does not influence the correctness of the finally reconstructed image.
Furthermore, it should be understood by those skilled in the art that the above-mentioned processing method for K-space data lattices proposed in the present invention can be applied to, for example, CAIPIRINHA (Breuer FA, Blaimer M, Heidemann RM, Mueller MF, Grisswhite MA, Jakob PM.controlled amplification in Parallel amplification resources in high amplification, Magn Reson Med.2005; 53(3):684-91.), SP-SG (Stephen F.Cauley, Jonathan R.Polimeni, Himanshu Bhat, DingxinWang, Laurence L.Wald, and Kawin Interslon-luminescence Slash, tissue filtration resource, Technique filtration resource, 201493. mu.93. mu.M. 102. and 93. mu.3. M. For example, the feasibility of applying the above-mentioned processing method of K-space data lattice to CAIPIRINHA, SP-SG and other methods proposed by the present invention is not demonstrated herein.
Fig. 6 is a basic flowchart of an image reconstruction method for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention. The image reconstruction method 100 for magnetic resonance multi-slice simultaneous imaging may comprise the steps of:
step 110: a first transformation is performed on the single-layer calibration data and the multi-layer simultaneous imaging data in K-space to obtain first single-layer calibration data and first multi-layer simultaneous imaging data in an intermediate domain. Wherein the intermediate domain is located between the K-space and the image domain.
Step 120: and calculating a coil combination coefficient according to the first single-layer calibration data.
Step 130: data layering is performed according to the coil merging coefficients and the first multi-slice simultaneous imaging data to obtain single-slice data in the middle domain.
In an embodiment, the image reconstruction method 100 for magnetic resonance multi-slice simultaneous imaging may further include the step 140: a second transformation is performed on the slice data in the mid-domain to obtain a magnetic resonance image.
In step 110, the first transform may be a fourier transform along the frequency encoding direction.
In step 120, the sub-steps as shown in fig. 7 may be included:
substep 121: applying a first phase modulation to the first single layer calibration data to construct a first coefficient matrix;
substep 122: constructing a first target vector from the first single layer calibration data without applied phase modulation;
substep 123: and calculating a coil combination coefficient according to the first coefficient matrix and the first target vector.
It is understood that substeps 121 and 122 may be performed in any order, i.e., substep 121 may be performed first and substep 122 may be performed later; a restrictive sub-step 122 may also be performed, followed by sub-step 121; substeps 121 and 122 may also be performed simultaneously.
In step 130, the sub-steps as shown in fig. 8 may be included:
substep 131: applying a second phase modulation to the first multi-slice simultaneous imaging data to construct a second coefficient matrix;
substep 132: and calculating according to the coil merging coefficient and the second coefficient matrix to obtain the single-slice data in the middle domain.
It should be appreciated that substep 131 may be performed at any time after substep 110 and before substep 132. For example, in an embodiment, substep 131 may be performed concurrently with any one or more of substeps 121, 122, and 123; in another embodiment, sub-step 131 may be performed between sub-steps 121 and 122.
In step 140, the second transform may be a fourier transform along the phase encoding direction.
In an embodiment, the image reconstruction method 100 for magnetic resonance multi-slice simultaneous imaging is performed wherein intermediate data may be stored in a memory, e.g., one or more of the first single-slice calibration data, the first multi-slice simultaneous imaging data, the coil merging coefficients, and the single-slice data may be stored in the memory. Since the data are all data in the middle domain, when the data are read and written, the data can be read and written by taking the whole frequency coding line as a unit, so that the data can be processed in blocks, and the reading and writing efficiency of the memory is improved. It should be appreciated that the memory may be RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
In a non-limiting embodiment, part of the calculations of the image reconstruction method 100 for magnetic resonance multi-slice simultaneous imaging may be performed while acquiring multi-slice simultaneous imaging data. That is, the data processing of the present invention can be performed while acquiring multiple layers of simultaneous imaging data. Compared with the traditional method which needs to acquire all data and then starts processing, the method can shorten the time from the acquisition of the data to the output of the final image.
In addition, it should be understood that methods of preprocessing data in K-space or in the intermediate domain may also be applied to the present invention, such as Bruder H, Fischer H, Reinfelder HE, Schmitt f. imagerecovery for echo planar imaging with non-acquired imaging. magn reset med.1992; 23(2) 311-23, published Echo-Planar Imaging data calibration, etc. This section is not the focus of the present invention and will not be described.
Fig. 9 is a basic block diagram of an image reconstruction apparatus for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention. The image reconstruction apparatus 200 for magnetic resonance multi-slice simultaneous imaging may include:
the first transformation module 210 is configured to perform a first transformation on the single-layer calibration data and the multi-layer simultaneous imaging data in the K-space to obtain a first single-layer calibration data and a first multi-layer simultaneous imaging data in the intermediate domain. Where the intermediate domain is located between the K-space and the image domain, the first transformation may be a fourier transformation along the frequency encoding direction.
And a coil combination coefficient calculating module 220, configured to calculate a coil combination coefficient according to the first single-layer calibration data.
And a data layering module 230, configured to perform data layering according to the coil merging coefficient and the first multi-slice simultaneous imaging data to obtain single-slice data in the middle domain.
In an embodiment, the magnetic resonance multi-slice simultaneous imaging image reconstruction apparatus 200 may further comprise a second transformation module 240 for performing a second transformation on the slice data to obtain the magnetic resonance image.
In one embodiment, the coil combination coefficient calculation module 220 may calculate the coil combination coefficient by performing the following steps: applying a first phase modulation to the first single layer calibration data to construct a first coefficient matrix; constructing a first target vector from the first single layer calibration data without applied phase modulation; and calculating a coil combination coefficient according to the first coefficient matrix and the first target vector.
In an embodiment, data layering module 230 may layer the level-aliased data by performing the following steps: applying a second phase modulation to the first multi-slice simultaneous imaging data to construct a second coefficient matrix; and calculating to obtain the single-slice data in the middle domain according to the coil merging coefficient and the second coefficient matrix.
In an embodiment, the image reconstruction apparatus 200 for magnetic resonance multi-slice simultaneous imaging may further comprise a memory 250 for storing intermediate data. The intermediate data may be one or more of first single layer calibration data, first multi-layer simultaneous imaging data, coil merging coefficients, and single layer data. Since the data are all data in the middle domain, when the data are read and written, the data can be read and written by taking the whole frequency coding line as a unit, so that the data can be processed in blocks, and the reading and writing efficiency of the memory is improved. It should be appreciated that the memory 250 may be RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
In a non-limiting embodiment, the image reconstruction apparatus 200 for magnetic resonance multi-slice simultaneous imaging may perform one or more of the first transformation, the calculation of coil merging coefficients, and the data slicing while acquiring multi-slice simultaneous imaging data. That is, the data processing of the present invention can be performed while acquiring multiple layers of simultaneous imaging data. Compared with the traditional device which needs to acquire all data and can start processing, the invention can shorten the time from the acquisition of data to the output of the final image.
FIG. 10 is a diagram illustrating the results of layering multiple layers of aliased images according to an embodiment of the invention. As can be seen from fig. 10, the original aliased image is processed by the method and apparatus of the present invention to obtain completely separated layer 1 and layer 2.
Fig. 11 is a schematic structural diagram of an image reconstruction apparatus for magnetic resonance multi-slice simultaneous imaging according to an embodiment of the present invention. Referring to fig. 11, the image reconstruction apparatus 300 for magnetic resonance multi-slice simultaneous imaging includes a memory 310 and a processor 320. The memory 310 has stored thereon computer code which, when run on the processor 320, is configured to cause the apparatus 300 to perform at least the image reconstruction method of magnetic resonance multi-slice simultaneous imaging as described above.
FIG. 12 is a schematic diagram of a computer-readable medium of an embodiment of the invention. The computer readable medium 400 has stored thereon computer code which, when run on a processor, is configured to perform the image reconstruction method of magnetic resonance multi-slice simultaneous imaging as described above.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The various illustrative logical modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.
In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software as a computer program product, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a web site, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk (disk) and disc (disc), as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks (disks) usually reproduce data magnetically, while discs (discs) reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
Although the present invention has been described with reference to the present specific embodiments, it will be appreciated by those skilled in the art that the above embodiments are merely illustrative of the present invention, and various equivalent changes and substitutions may be made without departing from the spirit of the invention, and therefore, it is intended that all changes and modifications to the above embodiments within the spirit and scope of the present invention be covered by the appended claims.
Claims (10)
1. A magnetic resonance imaging method, comprising:
performing a first transformation on the single-layer calibration data and the multi-layer simultaneous imaging data in the K-space to obtain a first single-layer calibration data and a first multi-layer simultaneous imaging data in an intermediate domain, the intermediate domain being located between the K-space and the image domain;
calculating a coil combination coefficient according to the first single-layer calibration data;
carrying out data layering on the first multilayer simultaneous imaging data of the middle domain according to the coil merging coefficient to obtain a plurality of single-layer data of the middle domain; and
a second transformation is performed on the plurality of slice data in the mid-domain to obtain a magnetic resonance image.
2. The method of claim 1, wherein calculating coil combining coefficients from the first single layer calibration data comprises:
applying a first phase modulation to the first single layer calibration data to construct a first coefficient matrix;
constructing a first target vector from the first single layer calibration data without applied phase modulation; and
and calculating the coil merging coefficient according to the first coefficient matrix and the first target vector.
3. The method of claim 1, wherein the data-layering first multi-slice simultaneous imaging data of an intermediate domain according to the coil merging coefficients comprises:
applying a second phase modulation to the first multi-slice simultaneous imaging data of the intermediate domain to construct a second coefficient matrix; and
and calculating the single-layer data in the middle domain according to the coil merging coefficient and the second coefficient matrix.
4. The method of claim 1, wherein the first transform is a fourier transform along a frequency coding direction.
5. The method of claim 1, wherein the multi-slice simultaneous imaging data prior to performing the first transformation is obtained by exciting a target region a plurality of times, the target region comprising a plurality of scan slices, and wherein the number of scan slices is greater than the number of excitations.
6. The method of claim 5, wherein at least a first shot and a second shot are performed on the target region, the first shot corresponding to a first set of scan layers and the second shot corresponding to a second set of scan layers.
7. The method of claim 6, wherein the first set of scan layers or the second set of scan layers comprises a plurality of scan layers arranged at intervals, and wherein a first transformation is performed on imaging data corresponding to the first set of scan layers during the second set of scan layers is activated.
8. The method of claim 1, wherein the second transform is a fourier transform along a phase encoding direction.
9. A magnetic resonance imaging apparatus comprising:
the device comprises a first transformation module, a second transformation module and a third transformation module, wherein the first transformation module is used for carrying out first transformation on single-layer calibration data and multi-layer simultaneous imaging data in a K space to obtain first single-layer calibration data and first multi-layer simultaneous imaging data in an intermediate domain, and the intermediate domain is positioned between the K space and an image domain;
the coil merging coefficient calculation module is used for calculating a coil merging coefficient according to the first single-layer calibration data;
the data layering module is used for carrying out data layering on the first multilayer simultaneous imaging data of the middle domain according to the coil merging coefficient so as to obtain single-layer data in the middle domain; and
a second transformation module for performing a second transformation on the plurality of slice data in the intermediate domain to obtain a magnetic resonance image.
10. A magnetic resonance imaging apparatus comprising a memory, a processor and computer instructions stored on the memory and executable on the processor, characterized in that the processor implements the method of any one of claims 1 to 8 when executing the computer instructions.
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