CN113945877B - Magnetic resonance black blood imaging method and system - Google Patents
Magnetic resonance black blood imaging method and system Download PDFInfo
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Abstract
The embodiment of the invention discloses a magnetic resonance black blood imaging method and a magnetic resonance black blood imaging system. The method comprises the following steps: exciting a scanning object simultaneously by using a preparation pulse module in a preset imaging sequence, wherein the scanning object comprises a first number of layers with blood flow signals suppressed; when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers; repeatedly executing black blood excitation and signal acquisition according to the third quantity within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of a fourth quantity of layers; and performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers to generate magnetic resonance black blood images of each layer. By the technical scheme, the acquisition of the magnetic resonance signals with the simultaneous complete suppression of the blood flow signals is realized, and the magnetic resonance black blood imaging speed is improved.
Description
Technical Field
The embodiment of the invention relates to a magnetic resonance technology, in particular to a magnetic resonance black blood imaging method and a magnetic resonance black blood imaging system.
Background
The magnetic resonance black blood imaging technique refers to a technique of suppressing a blood flow signal in a magnetic resonance imaging process, so that blood in an obtained image presents a black low signal, and surrounding tissues present a bright high signal.
Currently, the common magnetic resonance black blood imaging techniques mainly include: spatial pre-saturation, double Inversion Recovery (DIR), triple Inversion Recovery (TIR), quad Inversion Recovery (QIR), DENTY preparation pulse, etc. The DIR pulse module typically consists of one non-selective pulse (reversing the magnetization of the whole volume) and one selective pulse (reversing the magnetization of the imaging slice), the TIR pulse module adds a third selective pulse IR (reversing the fat of the imaging slice) after DIR, and the QIR pulse module adds a DIR module after DIR, thus alleviating sensitivity to T1. The relevant principle feature of these methods is to suppress the fluid signal in the scan slice or space before radio frequency excitation by using some magnetization preparation pulses (also called preparation pulses) while preserving the magnetization vector of the stationary tissue, and then acquire several lines in k-space of a single slice so that the final image is displayed as a black blood vessel image.
However, in the above-mentioned black blood imaging methods, only one layer of magnetic resonance signals with blood flow signals completely suppressed can be acquired, and in the case that the scanning part includes multiple layers, the acquisition time of the multiple layers of black blood imaging is too long.
Disclosure of Invention
The embodiment of the invention provides a magnetic resonance black blood imaging method and a magnetic resonance black blood imaging system, which are used for realizing acquisition and imaging of magnetic resonance signals with completely suppressed multilayer blood flow signals, improving the magnetic resonance black blood imaging speed and reducing the imaging time length of multilayer black blood.
In a first aspect, an embodiment of the present invention provides a magnetic resonance black blood imaging method, including:
exciting a scan object simultaneously with a preliminary pulse module in a preset imaging sequence, the scan object comprising a first number of slices, and blood flow signals of the first number of slices being suppressed;
when reaching a preset inversion time, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in the preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanning object;
repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to a third number within one repetition time of the preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of a fourth number of layers of the scanning object;
performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers to generate magnetic resonance black blood images of each layer of the scanning object;
Wherein the first number is less than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between two layers and the first number.
In a second aspect, embodiments of the present invention also provide a magnetic resonance black blood imaging system, the system comprising:
an MRI scanning device, a processor in communication with the MRI scanning device;
the MRI scanner is used for:
simultaneously exciting a first number of blood flow suppression levels of a scanned object with a preliminary pulse module in a preset imaging sequence;
when reaching a preset inversion time, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in the preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanning object;
repeatedly performing black blood excitation of the first number of slices and signal acquisition of the second number of slices within one repetition time of the preset imaging sequence according to a third number, and generating interlayer aliasing magnetic resonance signals of a fourth number of slices of the scanning object, wherein the first number is smaller than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between two slices and the first number;
The processor is used for performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers and generating magnetic resonance black blood images of each layer of the scanning object.
The embodiment of the invention simultaneously excites a scanning object by utilizing a preparation pulse module in a preset imaging sequence, wherein the scanning object comprises a first number of layers, and blood flow signals of the first number of layers are restrained; when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object; repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to the third number within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of the fourth number of layers of the scanned object; performing interlayer aliasing and image reconstruction on interlayer aliasing magnetic resonance signals of a fourth number of layers to generate magnetic resonance black blood images of each layer of a scanning object; wherein the first number is less than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between the two layers and the first number. The method and the device realize that the black blood excitation module (namely the preparation pulse module) and the simultaneous multi-layer acquisition imaging module are repeatedly executed within one repetition time of a preset imaging sequence, so that the preparation pulse module is utilized to simultaneously inhibit multi-layer blood flow signals, and when the preset inversion time of all zero crossing points of the multi-layer blood flow signals is reached, the acquisition imaging module is utilized to simultaneously excite the multi-layer to be imaged, so that the aliasing magnetic resonance signals of the multi-layer simultaneous imaging are obtained, the problem that only one layer of blood flow signals cross the zero crossing points when the multi-layer black blood imaging is carried out is solved, the magnetic resonance black blood imaging speed is improved, and the multi-layer black blood imaging duration is reduced.
Drawings
FIG. 1 is a flow chart of a method of magnetic resonance black blood imaging in accordance with a first embodiment of the present invention;
FIG. 2 is a flow chart of a method of magnetic resonance black blood imaging in accordance with a second embodiment of the present invention;
FIG. 3 is a schematic sequence diagram of a multi-layer simultaneous acquisition fast spin echo sequence in a second embodiment of the invention;
FIG. 4 is a schematic sequence diagram of a double-inversion recovery sequence in a second embodiment of the present invention;
FIG. 5 is a schematic diagram of a sequence design within a repetition time of a predetermined imaging sequence according to a second embodiment of the present invention;
FIG. 6 is a schematic diagram of another sequence design within a repetition time of a predetermined imaging sequence in a second embodiment of the present invention;
FIG. 7 is a schematic diagram of yet another sequence design within a repetition time of a predetermined imaging sequence in a second embodiment of the present invention;
FIG. 8 is a schematic diagram of yet another sequence design within a repetition time of a predetermined imaging sequence in a second embodiment of the present invention;
FIG. 9 is a schematic representation of a sequence design over a repetition time of an imaging sequence used in acquiring reference images in accordance with one of the second embodiments of the present invention;
fig. 10 is a schematic structural diagram of a magnetic resonance black blood imaging system according to a fourth embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
Example 1
The magnetic resonance black blood imaging method provided by the embodiment can be suitable for the condition that black blood imaging is simultaneously carried out on a plurality of layers in magnetic resonance. The method may be performed by a magnetic resonance black blood imaging system, which may be implemented in software and/or hardware. For example, the sequence design, the scan control, the signal processing and other processes can be implemented in a software mode, but the magnetic resonance scanning of the scanning object is implemented by a magnetic resonance scanning device. Referring to fig. 1, the method of this embodiment specifically includes the following steps:
s110, simultaneously exciting a scanning object by using a preparation pulse module in a preset imaging sequence, wherein the scanning object comprises a first number of layers, and blood flow signals of the first number of layers are restrained.
The preset imaging sequence is a preset pulse sequence for magnetic resonance data acquisition. A preparatory pulse module refers to a pulse sequence implemented prior to acquisition imaging that may contain at least one non-selective pulse (reversing the magnetization of the entire volume) and at least one selective pulse (reversing the magnetization of the imaging slice) for suppressing fluid signals (e.g., blood) within the scan slice while preserving the magnetization vector of the stationary tissue. Illustratively, the preliminary pulse module is a spatial pre-saturation sequence, a double inversion recovery sequence, a triple inversion recovery sequence, a quad inversion recovery sequence, or a DENTY preliminary pulse sequence. I.e. the preliminary pulse module may employ any pulse module implementing the black blood technique in the related art.
The first number M1 refers to a preset number of slices, which corresponds to the number of slices of the selective pulse excitation of the preset pulse module, which may be given at the time of sequence design. Illustratively, the first number may be equal to or less than the fourth number M. The fourth number M corresponds to the total number of slices to be imaged within a single repetition Time (TR) of the preset imaging sequence, determined by the imaging requirements. In the embodiment of the invention, the black blood imaging layer acceleration is realized by simultaneous multi-layer excitation imaging technology (Simultaneous Multi-Slice, SMS), so that the imaging layer number is at least 2 each time, and the layer with the blood flow signal suppressed at least needs to cover the imaging layer number, so that the first number is not less than two layers. In order to increase the imaging speed, unnecessary pulse excitation operations are reduced, and the first number does not exceed the fourth number.
In order to achieve the consistent simultaneous zero crossing (no longitudinal magnetization vector) of the blood flow signals of multiple layers and achieve complete suppression of the blood flow signals of multiple layers, the simultaneous multi-layer excitation imaging technique is applied to the preparation pulse module in the embodiment of the invention. During scanning imaging, a scan subject (also referred to as black blood excitation) is first excited simultaneously with a preparation pulse module during a repetition Time (TR) of a preset imaging sequence. The scan object contains at least a first number of slices. Each of the first number of layers is simultaneously pulsed after having been magnetized by the non-selective pulse, so that the blood flow inhibition in each layer is uniform. In this first number of layers, gaps (inter-layer distances) exist between any adjacent layers.
And S120, when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with the blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object.
The preset inversion time refers to a preset inversion time TI. The preset reversal time is illustratively determined from the longitudinal relaxation time T1 of the blood flow, the repetition time TR and the third number. The third number N refers to a further number set in advance, which corresponds to the number of repeated executions of the combined module of the preliminary pulse module and the acquisition imaging module within one repetition time TR, which is given at the time of sequence design. As an example, the preset inversion time is determined by calculating the formula ti=t1 x (In (2) -In (1+exp (-TR/T1/N)), where In represents the base-e logarithm and In2 represents the base-e logarithm.
The second number M2 refers to a further number set in advance, which corresponds to the number of layers to be excited at one signal acquisition. The second number is illustratively determined from the fourth number and the third number, and the second number is intermediate the two layers and the first number. When the imaging sequence design is preset, the total imaging layer number (the fourth number M) and the number of repeated execution times (the third number N) of the combination modules within one repetition time TR are set, and then the number of imaging layer numbers (the second number M2) excited by the acquisition imaging module in one combination module, that is, m2=m/N, can be calculated. Likewise, since simultaneous multi-layer excitation imaging and blood flow suppression levels need to cover at least the imaging levels, the second number needs to be not less than 2 layers and needs not to exceed the first number.
After the selective pulse application in the preparation pulse module, the longitudinal magnetization vectors of the blood flow in the selection planes will be consistently tapered, waiting for a preset reversal time, with the longitudinal magnetization vectors of the blood flow in the selection planes all being exactly zero crossing, at which time the blood flow signal is completely suppressed. Therefore, when the preset inversion time after the application of the preparation pulse module is reached in the repetition time, an acquisition imaging module is applied to the scanning object, the acquisition imaging module can excite the second number of layers simultaneously in the layers with the first number of blood flow signals restrained, and the magnetic resonance receiving coil can acquire the magnetic resonance signals of the second number of layers of the scanning object. The magnetic resonance signals of the second number of slices are multi-slice aliased magnetic resonance signals, called inter-slice aliased magnetic resonance signals, due to the simultaneous acquisition of the multiple slices. It will be appreciated that the blood flow signal in the acquired inter-layer aliased magnetic resonance signal is zero.
Illustratively, any two of the second number of planes of simultaneous excitation of blood flow inhibition planes are non-adjacent. For example, the second number of layers are layers 1 and 3, respectively, or layers 2 and 4, respectively, etc. The advantage of this arrangement is that by increasing the interlayer spacing of the signal acquisition layer, the interlayer sensitivity difference can be enlarged, thereby improving the interlayer aliasing efficiency of the interlayer aliasing magnetic resonance signals and also improving the image signal-to-noise ratio of the magnetic resonance black blood image.
S130, repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to the third number within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of the fourth number of layers of the scanning object.
If the second number is smaller than the fourth number (the third number is not 1), then executing one combination module in one TR cannot realize the magnetic resonance black blood imaging of the fourth number of layers, so the third number of combination modules needs to be repeatedly designed in one TR of the preset imaging sequence. In this way, when the scan object is scanned by using the preset imaging sequence, S110 and S120 are repeatedly performed in sequence for a third number of times, and each time the second number of slices of the inter-layer aliasing magnetic resonance signals can be obtained, a total of fourth number of slices of the inter-layer aliasing magnetic resonance signals can be obtained in one TR.
And S140, performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers to generate a magnetic resonance black blood image of each layer of the scanning object.
And performing interlayer aliasing (separating signals of different layers) on the interlayer aliasing magnetic resonance signals of the fourth number of layers by using the interlayer visual field offset and/or the reference image to obtain an aliasing single-layer magnetic resonance signal. Then, image reconstruction is carried out on the single-layer magnetic resonance signals by using an image reconstruction algorithm, so that the magnetic resonance black blood image of each layer can be obtained.
Based on the above description, the preset imaging sequence of the embodiment of the present invention combines the black blood imaging technology (embodied as the preparation pulse module) and the simultaneous multi-layer imaging technology (embodied as the acquisition imaging module), and as long as the simultaneous imaging of the fourth number of layers can be realized, the sequence types and numbers of the preparation pulse module and the acquisition imaging module can be changed within one repetition time.
According to the technical scheme, a scanning object is excited simultaneously by using a preparation pulse module in a preset imaging sequence, the scanning object comprises a first number of layers, and blood flow signals of the first number of layers are restrained; when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object; repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to the third number within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of the fourth number of layers of the scanned object; performing interlayer aliasing and image reconstruction on interlayer aliasing magnetic resonance signals of a fourth number of layers to generate magnetic resonance black blood images of each layer of a scanning object; wherein the first number is less than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between the two layers and the first number. The method and the device realize that the black blood excitation module (namely the preparation pulse module) and the simultaneous multi-layer acquisition imaging module are repeatedly executed within one repetition time of a preset imaging sequence, so that the preparation pulse module is utilized to simultaneously inhibit multi-layer blood flow signals, and when the preset inversion time of all zero crossing points of the multi-layer blood flow signals is reached, the acquisition imaging module is utilized to simultaneously excite the multi-layer to be imaged, so that the aliasing magnetic resonance signals of the multi-layer simultaneous imaging are obtained, the problem that only one layer of blood flow signals cross the zero crossing points when the multi-layer black blood imaging is carried out is solved, the magnetic resonance black blood imaging speed is improved, and the multi-layer black blood imaging duration is reduced.
Example two
The present embodiment exemplifies the sequence design of the "preset imaging sequence" based on the first embodiment described above. On the basis, the method is further optimized for carrying out interlayer aliasing and image reconstruction on interlayer aliasing magnetic resonance signals of a fourth number of layers and generating magnetic resonance black blood images of each layer of the scanning object. Wherein, the explanation of the same or corresponding terms as the above embodiments is not repeated herein. Referring to fig. 2, the magnetic resonance black blood imaging method provided in the present embodiment includes:
s210, simultaneously exciting a scanning object by using a preparation pulse module in a preset imaging sequence, wherein the scanning object comprises a first number of layers, and blood flow signals of the first number of layers are restrained.
And S220, when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with the blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object.
The first preset gradient peak and the second preset gradient peak with different gradient moments are applied in sequence in the layer-selecting gradient direction in the acquisition imaging module, so that interlayer preset field of view offset of interlayer aliasing magnetic resonance signals on an image domain is realized.
The first preset gradient peak and the second preset gradient peak refer to gradient peaks (gradient peaks) having different preset gradient distances and preset gradient waveforms, respectively, for example, the first preset gradient peak is set to be half of the zero order moment of the gradient, and the second preset gradient peak is set to be the zero order moment of the gradient. The inter-layer preset field of view offset refers to a preset field of view offset (FOV shift) from layer to layer, or an adjacent layer image shift.
The basis for interlayer aliasing in the magnetic resonance technology is that the coil sensitivities of the receiving coils at different layers are different, and enough coil sensitivity difference exists between the layers. However, in actual scanning, due to the reason that the layer spacing between two adjacent layers is small or the number of receiving coils arranged along the layer selecting direction is small, the sensitivity matrix difference (i.e. the interlayer sensitivity difference) between the layers is small, and thus the aliasing cannot be well removed. To solve this problem, a preset imaging sequence is specially designed in this embodiment. Referring to fig. 3, a first preset gradient spike is added at P0 between the excitation pulse 303 and the first refocusing pulse 304 of the radio frequency pulse on the slice selection gradient of the preset imaging sequence; meanwhile, depending on the phase encoding mode, a position may be selected between the previous one of the two refocusing pulses and the signal acquisition window (ADC) 305 (e.g., P11, P21, or P31), and between the signal acquisition window 305 and the next one of the two refocusing pulses (P12, P22, P32 for P11, P21, P31) to increase the second preset gradient spike. The arrangement of the preset gradient peaks can realize the interlayer preset field of view offset of the magnetic resonance signals between layers on the image domain, and the interlayer preset field of view offset can ensure that the layers have enough interlayer sensitivity difference, so that the aliasing magnetic resonance signals between the layers can be well unmixed.
And S230, repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to the third number of layers within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of the fourth number of layers of the scanning object.
Illustratively, the first number is 4, the second number is 2, the third number is 2, and the fourth number is 4 during one repetition time.
Referring to fig. 4 and 5, in one example, the design of the preset imaging sequence is illustrated with the preliminary pulse module being a double inversion recovery sequence DIR and the acquisition imaging module being a multi-slice acquisition mode fast spin echo sequence (multi-band fast spin echo). As shown in fig. 4, a DIR schematic diagram used in an embodiment of the present application, when a QRS wave is detected, a first inversion pulse (the first RF pulse of the RF axis in the figure) is first applied, and the inversion pulse may be a 180-degree inversion pulse that is not a slice selection, i.e., all tissues in the scanned subject are inverted. Then, a second inversion pulse is applied Ma Shijia, which is a multi-band rf pulse that cooperates with the linearly varying magnetic field strength to achieve simultaneous excitation of multiple layers. The multiband rf Pulse may be designed by modulating a sine Pulse (Sinc Pulse) or an SLR Pulse by a frequency shift characteristic, or may be obtained by a PINS algorithm or the like.
In one embodiment, the multi-band radio frequency pulse is obtained by: firstly, calculating actual scanning setting parameters according to scanning parameters set by a user and the number of layers of a first number of scanning objects to be excited simultaneously; the multiband radio frequency pulse is calculated from parameters such as layer thickness and layer spacing for each of the first number of layers.
Referring to fig. 4, the multiband rf pulse may include a plurality of sub-SINC waveforms, and a corresponding slice selection Gradient (GS) is applied along the direction of the slice selection gradient, that is: the second inversion pulse cooperates with the gradient in the slice selection direction as a slice selection inversion pulse in such a way that the real trajectory requirements for the gradient waveform are reduced, so that the desired excitation profile is more easily obtained. In this embodiment, the SINC waveform may be obtained as follows:
wherein N represents a first number of floors; t represents time; i represents the label of the current layer; dω is related to the layer thickness and layer spacing of the first number of layers and can be expressed by the following formula:
wherein BW represents a set bandwidth of the multi-band radio frequency pulse; Δz represents the layer thickness of the first number of layers; dz represents the interlayer spacing.
Referring to fig. 5, a total of 4 layers need to be imaged within a repetition time TR in the preset imaging sequence, i.e. the fourth number M is 4; the number of repeated executions (third number N) of the combined module (dir+mb_fse) is 2, that is, the pulse modules contained in one TR are DIR, mb_ FSE, DIR, MB _fse in sequence; the selective pulsing of the DIR module in each combination module simultaneously excites 4 planes, i.e. the first number N is 4, the blood flow signals of the 4 planes being suppressed; the number of layers at which the selective pulses of the mb_fse module in each combining module are simultaneously excited can be calculated to be 4/2=2, i.e. the second number is 2. The scanning implementation process of the preset imaging sequence comprises the following steps: in one TR, a DIR module is firstly applied, and simultaneously, the layers of 4 blood flow signals of a scanned object are excited to be restrained, and the magnetization of the 4 imaging layers is reversed; after the preset inversion time TI corresponding to the longitudinal magnetization vector zero crossing point of the blood flow reaches, applying an MB_FSE module, simultaneously exciting the 1 st layer and the 3 rd layer in the layers with the 4 blood flow signals suppressed, and collecting interlayer aliasing magnetic resonance signals of the two layers; then, continuing to apply the DIR module, and simultaneously exciting the layers with the 4 blood flow signals being suppressed, and reversing the magnetization of the 4 imaging layers; and after the preset inversion time TI is reached, applying an MB_FSE module, simultaneously exciting the 2 nd layer and the 4 th layer in the 4 blood flow inhibition layers, and collecting interlayer aliasing magnetic resonance signals of the two layers.
Illustratively, the first number is 4, the second number is 4, the third number is 1, and the fourth number is 4 during one repetition time.
Referring to FIG. 6, in one example, the design of the preset imaging sequence is illustrated with the DIR module and the MB_FSE module as examples. In total, 4 layers need to be imaged within one repetition time TR in the preset imaging sequence, i.e. the fourth number M is 4; the number of repeated execution times (third number N) of the combination modules (dir+mb_fse) is 1, that is, pulse modules contained in one TR are a DIR module and an mb_fse module in sequence; the selective pulsing of the DIR modules in each combination module simultaneously excites 4 planes, i.e. the first number N is 4; the number of layers at which the selective pulses of the mb_fse module in each combining module are simultaneously excited can be calculated to be 4/1=4, i.e. the second number is 4. In this example, the level at which the blood flow signal is suppressed and the acquisition imaging level overlap entirely. The scanning implementation process of the preset imaging sequence comprises the following steps: in one TR, a DIR module is firstly applied, and simultaneously, the layers of 4 blood flow signals of a scanned object are excited to be restrained, and the magnetization of the 4 imaging layers is reversed; and after the preset inversion time TI is reached, applying an MB_FSE module, simultaneously exciting the layers with the 4 blood flow signals being suppressed, and collecting 4-layer aliasing interlayer aliasing magnetic resonance signals.
In one embodiment, a fat suppression pulse may also be applied between the DIR module and the mb_fse module. Referring to fig. 7, in one example, the design of the preset imaging sequence is illustrated with a three-reflection recovery sequence TIR module and an mb_fse module. The first number, the second number, the third number, and the fourth number are designed the same as the example of fig. 6. The pulse modules included in one TR are, in turn, a TIR module and an mb_fse module, and the TIR module includes a DIR module and an IR module. The scanning implementation process of the preset imaging sequence comprises the following steps: in one TR, a DIR module is firstly applied, and simultaneously, the layers of 4 blood flow signals of a scanned object are excited to be restrained, and the magnetization of the 4 imaging layers is reversed; after the preset inversion time TI is reached, an IR module is applied, and simultaneously the layers with the 4 blood flow signals being restrained are excited, and the magnetization of fat of the 4 imaging layers is inverted; inversion time TI corresponding to zero crossing point of longitudinal magnetization vector of fat Fat After the acquisition, the MB_FSE module is continuously applied, the layers with the 4 blood flow signals being restrained are excited at the same time, and the acquisition of 4-layer aliasing interlayer aliasing magnetic resonance signals is carried out.
Referring to fig. 8, in one example, the design of the preset imaging sequence is illustrated with a four reverse recovery sequence QIR module and an mb_fse module. The first number, the second number, the third number, and the fourth number are designed the same as the example of fig. 6. The pulse modules contained in one TR are QIR and mb_fse modules in sequence, while the QIR module contains 2 DIR modules. The scanning implementation process of the preset imaging sequence comprises the following steps: within one TR, a first DIR module is applied first, while exciting the layers of the scanned object where the 4 blood flow signals are suppressed, reversing the magnetization of the 4 imaging layers; after the first preset inversion time TI1 is reached, a second DIR module is applied, and the layers with the 4 blood flow signals restrained are excited again and simultaneously, the magnetization of the 4 imaging layers is inverted, so that the sensitivity to the inversion time is reduced; and after the second preset inversion time TI2 is reached, continuing to apply the MB_FSE module, simultaneously exciting the layers on which the 4 blood flow signals are restrained, and collecting 4-layer aliasing interlayer aliasing magnetic resonance signals. Note that TI1 and TI2 are empirically set inversion times such that the combination of TI1 and TI2 suppresses the blood flow signal as much as possible.
S240, filling interlayer aliasing magnetic resonance signals of the fourth number of layers into the K space to obtain aliasing K space data.
When the interlayer aliasing magnetic resonance signals of the fourth number of layers are processed, the interlayer aliasing magnetic resonance signals are firstly subjected to certain conversion (including phase coding and frequency coding) and then are filled into a K space, and K space data (namely aliasing K space data) of signal aliasing are obtained.
S250, performing interlayer aliasing on the aliasing K space data based on interlayer sensitivity differences corresponding to interlayer preset field of view offset, and generating aliasing K space data of each layer of the scanning object.
And then, performing layer-to-layer aliasing on the aliasing K space data by using the interlayer sensitivity difference generated by the interlayer preset field of view offset to obtain the aliasing K space data (namely, the aliasing K space data) of each layer. In some embodiments, the reference image may also be utilized to obtain the inter-layer sensitivity difference. Illustratively, the inter-layer de-aliasing of the aliased K-space data using inter-layer sensitivity differences may employ a sub-calibrated parallel acquisition (Split-slice GRAPPA) algorithm, a parallel reconstruction algorithm (SENSE), or the like.
S260, performing image reconstruction on the aliasing K space data of each layer to obtain a magnetic resonance black blood image of each layer of the scanning object.
And finally, carrying out corresponding reconstruction processing on the antialiased K space data of each layer according to the selected image reconstruction algorithm, and generating a magnetic resonance black blood image of each layer.
According to the technical scheme of the embodiment, when the imaging sequence is designed in a preset mode, the first number is set to be 4, the second number is set to be 2, the third number is set to be 2, and the fourth number is set to be 4 in one repetition time; or setting the first number to 4, the second number to 4, the third number to 1, and the fourth number to 4 in one repetition time; and designing the preliminary pulse module as one of a DIR module, a TIR module, and a QIR module. On the premise of meeting the imaging requirements of black blood imaging while meeting the fourth number of layers, various deformation designs of preset imaging sequences are provided, so that the black blood imaging speed is improved, and the flexibility and diversity of the sequence design of the black blood imaging with accelerated layers are improved. Filling interlayer aliasing magnetic resonance signals of a fourth number of layers into a K space to obtain aliasing K space data; performing interlayer dealiasing on the aliased K space data based on interlayer sensitivity differences corresponding to interlayer preset view field offsets to generate the dealiased K space data of each layer of the scanning object; and carrying out image reconstruction on the aliasing K space data of each layer to obtain the magnetic resonance black blood image of each layer of the scanning object. The anti-aliasing efficiency of the interlayer aliasing magnetic resonance signals is further improved, and the image quality of the magnetic resonance black blood image is further improved.
On the basis of the above technical solution, in S220, using the acquisition imaging module in the preset imaging sequence to simultaneously excite the second number of slices of the slices in which the blood flow signal is suppressed, acquiring the interlayer aliasing magnetic resonance signals of the second number of slices of the scan object includes: based on an undersampling mode, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of a scanning object; accordingly, the antialiased K-space data is undersampled antialiased K-space data.
In order to further improve the magnetic resonance scanning speed, in the embodiment of the invention, when the interlayer aliasing magnetic resonance signals are acquired, the interlayer scanning acceleration can be carried out by combining an undersampled scanning mode on the basis of simultaneous excitation scanning of multiple layers, so as to obtain the interlayer aliasing magnetic resonance signals undersampled in each layer. Then the post-aliasing, antialiased K-space data is undersampled, antialiased K-space data.
Accordingly, S260 includes: acquiring a coil sensitivity distribution diagram, recovering the undersampled aliasing K space data of each layer according to the coil sensitivity distribution diagram, and generating full-sampling K space data of the corresponding undersampled aliasing K space data; and carrying out image reconstruction according to the all-sampling K space data to obtain the magnetic resonance black blood image of each layer of the scanning object.
For in-layer undersampled magnetic resonance signals, if a magnetic resonance image reconstruction is to be performed, the undersampled K-space data needs to be filled first. To accurately populate K-space data, a coil sensitivity profile of the receive coil may be utilized. This is because the receiving coil of the magnetic resonance is a phased array coil, which is formed by combining a plurality of sub-coils according to a certain array, and the sensitivity of each sub-coil forms a coil sensitivity array, and the higher the coil sensitivity in the coil sensitivity array is, the stronger the signal intensity in the K space data is. Therefore, the coil sensitivity distribution diagram and the undersampled and antialiased K space data can be utilized to calculate the data which is not sampled in the K space, and the data is filled into the corresponding position in the K space, so that the full-sampling K space data corresponding to the undersampled and antialiased K space data of the layer is obtained. And then, carrying out image reconstruction on the fully sampled K space data to obtain a magnetic resonance image of the layer.
The coil sensitivity profile may be pre-existing data or may be obtained by adding a low resolution reference scan prior to the main scan. For example, in the fourth number 4 example, the detection region may be excited using the imaging sequence shown in fig. 9 (the preparation pulse module DIR excites 4 layers, the acquisition imaging module FSE images 1 layer, the combination module dir+fse is repeatedly performed 4 times), the existing single-layer black blood imaging sequence, the existing non-black blood imaging sequence, or the like, and a low resolution, full FOV reference image of the detection region is obtained using the magnet's own body coil; and respectively acquiring images of a plurality of receiving coils of the detection area by each receiving coil, and then dividing the images of each receiving coil by a reference image one by one to obtain a coil sensitivity distribution map of each receiving coil. The advantage of this arrangement is that it can further increase the magnetic resonance scanning speed, save scanning time and increase the image signal-to-noise ratio.
Example III
The present embodiment provides a magnetic resonance imaging method based on the first and second embodiments. The method comprises the following steps:
firstly, a preparation pulse module in a preset imaging sequence is utilized to excite a scanning object at the same time, and blood flow signals of a plurality of layers of scanning are restrained, wherein the preparation pulse module comprises a first reverse pulse and a second reverse pulse, the first reverse pulse is a non-layer selection reverse pulse, and the second reverse pulse is a multiband layer selection reverse pulse.
Secondly, magnetic resonance signals of at least two layers are acquired simultaneously within one repetition time of a preset imaging sequence, and interlayer aliasing exists in the magnetic resonance signals of the at least two layers. Alternatively, two or more acquisitions may be performed during a single repetition time, with two slices of magnetic resonance signals acquired simultaneously during each acquisition. For example, the scan object comprises four slices, a first acquisition simultaneously acquires magnetic resonance signals of a first slice and a third slice within a repetition time, and a second acquisition simultaneously acquires magnetic resonance signals of a second slice and a fourth slice.
Then, the reference signals of each layer of the scanned object are acquired respectively. For example, a preliminary pulse module may be applied to the scan subject such that blood flow signals of multiple layers are suppressed; and, respectively acquiring a blood flow suppressed reference signal for each layer within one repetition time;
Finally, in the image reconstruction process, the interlayer aliased magnetic resonance signals are subjected to aliasing according to the reference signals so as to acquire a magnetic resonance image of each layer.
Example IV
The present embodiment provides a magnetic resonance imaging system, see fig. 10, which specifically includes: an MRI scanner 1010, and a processor 1020 communicatively coupled to the MRI scanner 1010;
MRI scanning device 1010 for:
exciting a scanning object simultaneously by using a preparation pulse module in a preset imaging sequence, wherein the scanning object comprises a first number of layers, and blood flow signals of the first number of layers are restrained;
when the preset inversion time is reached, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object;
repeatedly executing black blood excitation of a first number of layers and signal acquisition of a second number of layers according to a third number within one repetition time of a preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of a fourth number of layers of a scanning object, wherein the first number is smaller than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between two layers and the first number;
A processor 1020 for:
and performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers to generate magnetic resonance black blood images of each layer of the scanning object.
Optionally, the preset reversal time is determined in dependence of the longitudinal relaxation time, the repetition time and the third number of blood flows.
Optionally, the preparation pulse module is a spatial pre-saturation sequence, a double inversion recovery sequence, a triple inversion recovery sequence, a four inversion recovery sequence, or a DENTY preparation pulse sequence.
Optionally, the acquisition imaging module is a spin echo sequence or a fast spin echo sequence.
Optionally, during one repetition time, the first number is 4, the second number is 2, the third number is 2, and the fourth number is 4.
Optionally, during one repetition time, the first number is 4, the second number is 4, the third number is 1, and the fourth number is 4.
Optionally, a first preset gradient peak and a second preset gradient peak with different gradient moments are sequentially applied in a layer-selecting gradient direction in the acquisition imaging module, so that interlayer preset field of view offset of interlayer aliasing magnetic resonance signals on an image domain is realized.
Optionally, the processor 1020 includes:
the aliasing K space data acquisition module is used for filling interlayer aliasing magnetic resonance signals of a fourth number of layers into the K space to acquire aliasing K space data;
The aliasing module is used for performing interlayer aliasing on the aliasing K space data based on interlayer sensitivity differences corresponding to interlayer preset field of view offset to generate aliasing K space data of each layer of the scanning object;
and the black blood image reconstruction module is used for carrying out image reconstruction on the antialiased K space data of each layer to obtain a magnetic resonance black blood image of each layer of the scanning object.
Further, the MRI scanner 1010 is specifically configured to:
based on an undersampling mode, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in a preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of a scanning object;
accordingly, the antialiased K-space data is undersampled antialiased K-space data;
accordingly, the black blood image reconstruction module is specifically configured to:
acquiring a coil sensitivity distribution diagram, recovering the undersampled aliasing K space data of each layer according to the coil sensitivity distribution diagram, and generating full-sampling K space data of the corresponding undersampled aliasing K space data;
and carrying out image reconstruction according to the all-sampling K space data to obtain the magnetic resonance black blood image of each layer of the scanning object.
The magnetic resonance imaging system 1000 shown in fig. 10 is merely an example and should not be construed as limiting the functionality and scope of use of embodiments of the present invention. As shown in fig. 10, the magnetic resonance imaging system 1000 further includes an output device 1030 based on the above technical solution.
The processor 1020 may monitor or control both the MRI scanner 1010 and the output device 1030. The processor 1020 may include one or a combination of several of a central processing unit (Central Processing Unit, CPU), application-specific integrated circuit (ASIC), application-specific instruction processor (Application Specific Instruction Set Processor, ASIP), graphics processing unit (Graphics Processing Unit, GPU), physical processor (Physics Processing Unit, PPU), digital signal processor (Digital Processing Processor, DSP), field-programmable gate array (Field-Programmable Gate Array, FPGA), ARM processor, etc.
An output device 1030, such as a display, may display a magnetic resonance image of the region of interest. Further, the output device 1030 may also display the subject's height, weight, age, imaging location, operating status of the MRI scanner 1010, and the like. The type of the output device 1030 may be one or a combination of several of a Cathode Ray Tube (CRT) output device, a liquid crystal output device (LCD), an organic light emitting output device (OLED), a plasma output device, etc.
The magnetic resonance imaging system 1000 may be connected to a local area network (Local Area Network, LAN), wide area network (Wide Area Network, WAN), public network, private network, proprietary network, public switched telephone network (Public Switched Telephone Network, PSTN), the internet, wireless network, virtual network, or any combination thereof.
The MRI scanning device 1010 includes an MR signal acquisition module, an MR control module, and an MR data storage module. The MR signal acquisition module comprises a magnet unit and a radio frequency unit. The magnet unit mainly includes a main magnet generating a B0 main magnetic field and a gradient assembly generating a gradient. The main magnet contained in the magnet unit may be a permanent magnet or a superconducting magnet, the gradient assembly mainly comprises gradient current Amplifiers (AMPs), gradient coils, and the gradient assembly may further comprise three independent channels Gx, gy, gz, each gradient amplifier exciting a corresponding one of the gradient coils in the gradient coil set to generate gradient fields for generating corresponding spatially encoded signals for spatially localization of the magnetic resonance signals. The radio frequency unit mainly comprises a radio frequency transmitting coil and a radio frequency receiving coil, wherein the radio frequency transmitting coil is used for transmitting radio frequency pulse signals to a person to be detected or a human body, the radio frequency receiving coil is used for receiving magnetic resonance signals acquired from the human body, and the radio frequency coils forming the radio frequency unit can be divided into a body coil and a local coil according to different functions. In one embodiment, the type of body coil or local coil may be a birdcage coil, a solenoid coil, a saddle coil, a helmholtz coil, an array coil, a loop coil, or the like. In one particular embodiment, the local coils are provided as array coils, and the array coils may be provided in a 4-channel mode, an 8-channel mode, or a 16-channel mode. The magnet unit and the radio frequency unit may constitute an open low field magnetic resonance device or a closed superconducting magnetic resonance device.
The MR control module may monitor an MR signal acquisition module, an MR data processing module, comprising a magnet unit and a radio frequency unit. Specifically, the MR control module may receive the information or pulse parameters sent by the MR signal acquisition module; in addition, the MR control module can also control the processing procedure of the MR data processing module. In one embodiment, the MR control module is further connected to a pulse sequence generator, a gradient waveform generator, a transmitter, a receiver, etc., and controls the magnetic field module to execute a corresponding scanning sequence after receiving instructions from the console.
Illustratively, the specific process of generating MR data by the MRI scanner 1010 of the present invention includes: the main magnet generates a B0 main magnetic field, and atomic nuclei in the subject generate precession frequency under the action of the main magnetic field, wherein the precession frequency is in direct proportion to the intensity of the main magnetic field; the MR control module stores and transmits an instruction of a scan sequence to be executed, the pulse sequence generator controls the gradient waveform generator and the transmitter according to the scan sequence instruction, the gradient waveform generator outputs gradient pulse signals with preset time sequences and waveforms, the signals pass through Gx, gy and Gz gradient current amplifiers, and then pass through three independent channels Gx, gy and Gz in the gradient assembly, and each gradient amplifier excites a corresponding gradient coil in the gradient coil group to generate a gradient field for generating corresponding spatial coding signals so as to spatially locate magnetic resonance signals; the pulse sequence generator also executes a scanning sequence, outputs data including timing, intensity, shape and the like of radio frequency pulses transmitted by radio frequency, timing of radio frequency reception and length of a data acquisition window to the transmitter, simultaneously the transmitter transmits corresponding radio frequency pulses to a body transmitting coil in the radio frequency unit to generate a B1 field, signals emitted by excited atomic nuclei in a patient body under the action of the B1 field are perceived by a receiving coil in the radio frequency unit, and then transmitted to an MR data processing module through a transmitting/receiving switch, and is subjected to digital processing such as amplification, demodulation, filtering, AD conversion and the like, and then transmitted to an MR data storage module. After the MR data storage module acquires a set of raw K-space data, the scan ends. The original K-space data is rearranged into separate K-space data sets corresponding to each image to be reconstructed, each K-space data set is input to an array processor, and after image reconstruction, a set of image data is formed by combining magnetic resonance signals.
According to the magnetic resonance imaging system provided by the embodiment of the invention, the black blood excitation module (namely the preparation pulse module) and the simultaneous multi-layer acquisition imaging module which correspond to the first step and the second step are repeatedly executed within one repetition time of a preset imaging sequence, so that the preparation pulse module is utilized to simultaneously inhibit multi-layer blood flow signals, and when the preset inversion time of all zero crossing points of the multi-layer blood flow signals is reached, the acquisition imaging module is utilized to simultaneously excite the multi-layer to be imaged, so that the aliasing magnetic resonance signals of the multi-layer simultaneous imaging are obtained, the problem that only one layer of blood flow signals cross the zero crossing points during the multi-layer black blood imaging is solved, the magnetic resonance black blood imaging speed is improved, and the multi-layer black blood imaging duration is reduced.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (10)
1. A method of magnetic resonance black blood imaging comprising:
exciting a scan object simultaneously with a preliminary pulse module in a preset imaging sequence, the scan object comprising a first number of slices, and blood flow signals of the first number of slices being suppressed;
when reaching a preset inversion time, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in the preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanning object;
repeatedly executing black blood excitation of the first number of layers and signal acquisition of the second number of layers according to a third number within one repetition time of the preset imaging sequence, and generating interlayer aliasing magnetic resonance signals of a fourth number of layers of the scanning object;
performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers to generate magnetic resonance black blood images of each layer of the scanning object;
wherein the first number is less than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between 2 and the first number.
2. The method of claim 1, wherein the preset reversal time is determined from a longitudinal relaxation time of blood flow, the repetition time, and the third number.
3. The method of claim 1, wherein the preliminary pulse module is a spatial pre-saturation sequence, a double inversion recovery sequence, a triple inversion recovery sequence, a quad inversion recovery sequence, or a DENTY preliminary pulse sequence.
4. The method of claim 1, wherein the acquisition imaging module is a fast spin echo sequence.
5. The method of claim 1, wherein the first number is 4, the second number is 2, the third number is 2, and the fourth number is 4 during a repetition time.
6. The method of claim 1, wherein the first number is 4, the second number is 4, the third number is 1, and the fourth number is 4 during one repetition time.
7. The method according to claim 1 or 4, wherein a first preset gradient peak and a second preset gradient peak with different gradient moments are sequentially applied in a slice-selecting gradient direction in the acquisition imaging module so as to realize an inter-slice preset field of view offset of the inter-slice aliased magnetic resonance signal on an image domain.
8. The method of claim 7, wherein performing interlayer aliasing and image reconstruction on the interlayer aliased magnetic resonance signals of the fourth number of slices, generating a magnetic resonance black blood image of each slice of the scan subject comprises:
filling the interlayer aliasing magnetic resonance signals of the fourth number of layers into a K space to obtain aliasing K space data;
performing interlayer aliasing on the aliasing K space data based on interlayer sensitivity differences corresponding to the interlayer preset view field offset to generate aliasing K space data of each layer of the scanning object;
and carrying out image reconstruction on the antialiased K space data of each layer to obtain the magnetic resonance black blood image of each layer of the scanning object.
9. The method of claim 8, wherein simultaneously exciting a second number of slices of the slice in which blood flow signals are suppressed with an acquisition imaging module in the preset imaging sequence, acquiring the inter-layer aliased magnetic resonance signals of the second number of slices of the scan subject comprises:
based on an undersampling mode, simultaneously exciting a second number of layers in each layer in which blood flow signals are suppressed by using an acquisition imaging module in the preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanned object;
Correspondingly, the antialiased K-space data is undersampled antialiased K-space data;
correspondingly, performing image reconstruction on the aliasing K space data of each layer, and obtaining the magnetic resonance black blood image of each layer of the scanning object comprises the following steps:
acquiring a coil sensitivity distribution diagram, and recovering the undersampled K-space data of each layer according to the coil sensitivity distribution diagram to generate full-sampling K-space data of the corresponding undersampled K-space data;
and carrying out image reconstruction according to the all-sampling K space data to obtain the magnetic resonance black blood image of each layer of the scanning object.
10. A magnetic resonance black blood imaging system, the system comprising: an MRI scanning device, a processor in communication with the MRI scanning device;
the MRI scanner is used for:
exciting a scan object simultaneously with a preliminary pulse module in a preset imaging sequence, the scan object comprising a first number of slices, and blood flow signals of the first number of slices being suppressed;
when reaching a preset inversion time, simultaneously exciting a second number of layers in each layer with blood flow signals restrained by using an acquisition imaging module in the preset imaging sequence, and acquiring interlayer aliasing magnetic resonance signals of the second number of layers of the scanning object;
Repeatedly performing black blood excitation of the first number of slices and signal acquisition of the second number of slices within one repetition time of the preset imaging sequence according to a third number, and generating interlayer aliasing magnetic resonance signals of a fourth number of slices of the scanning object, wherein the first number is smaller than or equal to the fourth number, the second number is determined according to the fourth number and the third number, and the second number is between 2 and the first number;
the processor is used for performing interlayer aliasing and image reconstruction on the interlayer aliasing magnetic resonance signals of the fourth number of layers and generating magnetic resonance black blood images of each layer of the scanning object.
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