CN112806982A - Magnetic resonance imaging method, device, equipment, storage medium and system - Google Patents
Magnetic resonance imaging method, device, equipment, storage medium and system Download PDFInfo
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Abstract
The embodiment of the invention discloses a magnetic resonance imaging method, a magnetic resonance imaging device, magnetic resonance imaging equipment, a magnetic resonance imaging storage medium and a magnetic resonance imaging system, wherein the magnetic resonance imaging method comprises the following steps: controlling a main magnet to generate a main magnetic field; controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances; the radio frequency receive coil is controlled to receive the magnetic resonance signals and the magnetic resonance signals are reconstructed to generate a magnetic resonance image of the target region. The magnetic resonance imaging method provided by the embodiment of the invention enables excitation layers of different substances to be completely staggered when the radio frequency pulse is excited, realizes simultaneous multi-layer acquisition of at least two layers of simultaneous excitation based on common radio frequency pulse, further enables substances in a magnetic resonance image reconstructed based on a magnetic resonance signal not to be staggered, and improves the magnetic resonance imaging effect.
Description
Technical Field
The embodiment of the invention relates to the technical field of imaging, in particular to a magnetic resonance imaging method, a magnetic resonance imaging device, magnetic resonance imaging equipment, a magnetic resonance imaging storage medium and a magnetic resonance imaging system.
Background
Magnetic Resonance Imaging (MRI) is an imaging technique in which a substance containing nuclei with non-zero spins placed in a magnetic field is excited by Radio Frequency (RF) electromagnetic waves to generate Nuclear Magnetic Resonance (NMR), magnetic resonance signals are acquired by an induction coil, and the magnetic resonance signals are reconstructed in an image according to a certain mathematical method. MRI imaging has excellent resolution for soft tissue imaging and great obvious superiority for disease diagnosis. However, in the magnetic resonance imaging process, the precession frequencies of the imaging protons in different substances are greatly different under the same magnetic field, which may cause substance stratification in imaging and poor imaging effect.
Disclosure of Invention
The embodiment of the invention provides a magnetic resonance imaging method, a magnetic resonance imaging device, magnetic resonance imaging equipment and a storage medium, and aims to improve the imaging effect of magnetic resonance imaging.
In a first aspect, an embodiment of the present invention provides a magnetic resonance imaging method, including:
controlling a main magnet to generate a main magnetic field;
controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances;
the radio frequency receive coil is controlled to receive the magnetic resonance signals and the magnetic resonance signals are reconstructed to generate a magnetic resonance image of the target region.
Optionally, the method for determining the bandwidth of the rf pulse further includes:
acquiring the chemical displacement of an imaging proton in a first substance relative to an imaging proton in a second substance, wherein the first substance and the second substance are different substances;
acquiring the excitation layer distance of the first substance and the second substance;
and determining the radio frequency pulse bandwidth according to the main magnetic field strength, the chemical displacement, the excitation layer thickness and the excitation layer face distance.
Optionally, further, acquiring a chemical displacement amount of the imaging proton in the first substance relative to the imaging proton in the second substance, includes:
acquiring a first precession frequency of an imaging proton in a first substance and a second precession frequency of the imaging proton in a second substance;
and determining the chemical displacement according to the difference between the first precession frequency and the second precession frequency.
Optionally, further, determining a radio frequency pulse bandwidth according to the main magnetic field strength, the chemical displacement, the excitation layer thickness, and the excitation layer distance includes:
and determining the radio frequency pulse bandwidth according to the BW-B0-k-T/delta x, wherein BW is the radio frequency pulse bandwidth, B0 is the main magnetic field strength, k is the chemical displacement, T is the excitation layer thickness, and delta x is the excitation layer distance.
Optionally, further, the controlling the radio frequency transmission coil to transmit radio frequency pulses to excite a target region of the subject to generate magnetic resonance signals of the target region includes:
determining a plurality of excitation layer combinations according to a preset excitation layer, wherein the excitation layer group comprises a first excitation layer of a first substance and a second excitation layer of a second substance;
for each excitation layer combination, determining the central frequency of a radio-frequency pulse corresponding to the excitation layer combination according to a first excitation layer in the excitation layer combinations;
transmitting radio frequency pulses based on the center frequency and the radio frequency pulse bandwidth to obtain magnetic resonance signals of the first substance at the first excitation level and magnetic resonance signals of the second substance at the second excitation level;
the center frequency of the radio frequency pulses is sequentially changed until the excitation of all excitation plane combinations is completed.
Optionally, further, reconstructing the magnetic resonance signals to generate a magnetic resonance image of the target region includes:
acquiring first signal data and first reference data corresponding to a first substance of the excitation layer and second signal data and second reference data corresponding to a second substance of the excitation layer aiming at each excitation layer;
reconstructing a first material image of the first material from the first signal data and the first reference data, and reconstructing a second material image of the second material from the second signal data and the second reference data;
and combining the first substance image and the second substance image to obtain a target image of the excitation layer.
In a second aspect, an embodiment of the present invention further provides a magnetic resonance imaging apparatus, including:
the main magnetic field control module is used for controlling a main magnet to generate a main magnetic field;
the radio frequency pulse control module is used for controlling the radio frequency transmitting coil to transmit radio frequency pulses to excite a target region of a detected person so as to generate magnetic resonance signals of the target region, wherein the radio frequency pulse bandwidth of the radio frequency pulses is determined according to the difference of the precession frequencies of imaging protons in different substances;
and the signal processing module is used for controlling the radio frequency receiving coil to receive the echo signal and generating a magnetic resonance image of the target area based on the echo signal.
In a third aspect, an embodiment of the present invention further provides a computer device, where the computer device includes:
one or more processors;
storage means for storing one or more programs;
when the one or more programs are executed by the one or more processors, the one or more processors implement the magnetic resonance imaging method as provided by any of the embodiments of the present invention.
In a fourth aspect, embodiments of the present invention further provide a computer-readable storage medium, on which a computer program is stored, which when executed by a processor, implements a magnetic resonance imaging method as provided in any of the embodiments of the present invention.
In a fifth aspect, an embodiment of the present invention further provides a magnetic resonance imaging system, including a main magnet, a radio frequency coil, and a processor;
a main magnet for generating a main magnetic field;
a radio frequency coil for transmitting radio frequency pulses and receiving magnetic resonance signals;
a processor for performing a magnetic resonance imaging method as provided by any of the embodiments of the invention.
The embodiment of the invention generates a main magnetic field by controlling a main magnet; controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances; the radio frequency receiving coil is controlled to receive the magnetic resonance signals, the magnetic resonance signals are reconstructed to generate a magnetic resonance image of a target area, the radio frequency pulse bandwidth is determined according to the precession frequency difference of imaging protons in different substances, the target area is excited based on the determined radio frequency pulse bandwidth to generate the magnetic resonance signals, so that the excitation layers of the different substances are completely staggered when the radio frequency pulses are excited, simultaneous multi-layer acquisition of simultaneous excitation of at least two layers based on common radio frequency pulses is realized, further, the substances in the magnetic resonance image reconstructed based on the magnetic resonance signals are not staggered, and the magnetic resonance imaging effect is improved.
Drawings
Fig. 1a is a flowchart of a magnetic resonance imaging method according to an embodiment of the present invention;
FIG. 1b is a schematic diagram of a slice circulation method according to an embodiment of the present invention;
FIG. 1c is a schematic diagram of another slice cycling method provided in accordance with an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a magnetic resonance imaging apparatus according to a second embodiment of the present invention;
fig. 3 is a schematic structural diagram of a computer device according to a third embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1a is a flowchart of a magnetic resonance imaging method according to an embodiment of the present invention. The present embodiment is applicable to the situation when performing magnetic resonance scanning imaging. The method may be performed by a magnetic resonance imaging apparatus, which may be implemented in software and/or hardware, for example, which may be configured in a computer device. As shown in fig. 1a, the method comprises:
and S110, controlling a main magnet to generate a main magnetic field.
In this embodiment, the main magnet may surround a bore having a receiving space. In the acquisition of magnetic resonance signals, a subject can be sent into the bore, and the computer device controls the main magnet to generate a main magnetic field, wherein the subject is positioned in a visual field area formed by the main magnetic field.
The main magnet generates a static magnetic field with uniform and stable height, so that protons in the tissues of a detected body form a magnetic moment in the main magnetic field, and the protons are controlled to spin along the direction of the magnetic field at the lamor frequency; at the moment, nuclear magnetism generated by proton spin in the body of the detected object and a main magnetic field interact to generate precession. Wherein, the magnetic field intensity of the main magnetic field can be set according to actual requirements. Within a certain range, the higher the main magnetic field strength, the higher the signal-to-noise ratio of the image.
And S120, controlling the radio frequency transmitting coil to transmit radio frequency pulses to excite a target region of the examinee so as to generate magnetic resonance signals of the target region, wherein the radio frequency pulse bandwidth of the radio frequency pulses is determined according to the difference of the precession frequencies of the imaging protons in different substances.
In order to solve the technical problem of serious material dislocation in an image obtained by magnetic resonance imaging in the prior art, in this embodiment, by setting a proper radio frequency pulse bandwidth, excitation layers of different materials are completely staggered during radio frequency pulse excitation, and simultaneous multi-layer acquisition (SMS) in which one layer is excited simultaneously by using a common radio frequency pulse is realized. After the proper radio frequency pulse bandwidth is set, when the magnetic resonance signals are acquired, the radio frequency transmitting coil is controlled to transmit radio frequency pulses based on the set radio frequency pulse bandwidth, and the radio frequency receiving coil receives echo signals to obtain the magnetic resonance signals.
When acquiring magnetic resonance signals, protons in different substances in the body of the subject precess. The same kind of magnetic nucleus, in the same magnetic field environment, should have the same precession frequency if not interfered by other factors. But a general substance is usually in the form of molecules, and other atomic nuclei or electrons in the molecules will affect a certain magnetic atomic nucleus. That is, if the same magnetic nucleus is in different molecules, the precession frequency will be different even if the same uniform main magnetic field is present, and the above phenomenon is called chemical shift phenomenon in the magnetic resonance field. The degree of chemical shift is directly proportional to the strength of the main magnetic field, with higher field strengths giving more pronounced chemical shifts. In conventional magnetic resonance imaging, the object of imaging is protons, and the precession frequencies of protons in different molecules will also differ, i.e. chemical shifts will occur. In human tissue, the most typical proton chemical shift phenomenon exists between water molecules and fat. The proton precession frequencies in water molecules and fat differed by about 3.5ppm, 440Hz at 3T field strength and about 220Hz at 1.5T field strength. The difference in precession frequency of protons in water molecules and fat can lead to misforming of the material when imaged. Based on this, the rf pulse bandwidth can be determined based on the difference in precession frequencies of different substances, such that only one substance is excited at a time. In this embodiment, the different substances may include a first substance water and a second substance fat.
Optionally, the method for determining the bandwidth of the radio frequency pulse includes: acquiring the chemical displacement of the imaging proton in the first substance relative to the imaging proton in the second substance; acquiring the excitation layer distance of the first substance and the second substance; and determining the radio frequency pulse bandwidth according to the main magnetic field strength, the chemical displacement, the excitation layer thickness and the excitation layer face distance. Specifically, the chemical displacement of the imaging proton in the second substance relative to the imaging proton in the first substance and the preset excitation plane distance between the first substance and the second substance are obtained, and the radio frequency pulse bandwidth can be determined according to the main magnetic field strength, the chemical displacement, the excitation layer thickness and the excitation plane distance. The excitation layer distance can be set according to actual requirements, but the excitation layer distance needs to be larger than the excitation layer thickness, so that the first substance and the second substance are prevented from being overlapped during excitation. The chemical displacement of the imaging proton in the first substance relative to the imaging proton in the second substance can be calculated in advance, directly obtained when the radio frequency pulse bandwidth is determined, and also can be directly calculated when the radio frequency pulse bandwidth is determined.
Wherein obtaining a chemical displacement amount of the imaging proton in the first substance relative to the imaging proton in the second substance comprises: acquiring a first precession frequency of an imaging proton in a first substance and a second precession frequency of the imaging proton in a second substance; and determining the chemical displacement according to the difference between the first precession frequency and the second precession frequency. Alternatively, the amount of chemical displacement is determined from the difference between a first precession frequency of the imaging protons in the first substance and a second precession frequency of the imaging protons in the second substance.
In one embodiment, determining the rf pulse bandwidth based on the main magnetic field strength, the amount of chemical shift, the excitation layer thickness, and the excitation slice distance comprises: and determining the radio frequency pulse bandwidth according to the BW-B0-k-T/delta x, wherein BW is the radio frequency pulse bandwidth, B0 is the main magnetic field strength, k is the chemical displacement, T is the excitation layer thickness, and delta x is the excitation layer distance. Specifically, the rf pulse bandwidth can be calculated from BW, B0 · k · T/Δ x. The larger the distance between the first and second excitation level (i.e., the excitation level distance) the smaller the required rf pulse bandwidth, while the excitation layer thickness is constant. In the limit case, i.e. when the excitation layer thickness is equal to the rf pulse bandwidth, BW is B0.
In one embodiment of the invention, controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region includes: determining a plurality of excitation layer combinations according to a preset excitation layer, wherein the excitation layer group comprises a first excitation layer of a first substance and a second excitation layer of a second substance; for each excitation layer combination, determining the central frequency of a radio-frequency pulse corresponding to the excitation layer combination according to a first excitation layer in the excitation layer combinations; transmitting radio frequency pulses based on the center frequency and the radio frequency pulse bandwidth to obtain magnetic resonance signals of the first substance at the first excitation level and magnetic resonance signals of the second substance at the second excitation level; the center frequency of the radio frequency pulses is sequentially changed until the excitation of all excitation plane combinations is completed. It should be noted that, in the present embodiment, the magnetic resonance signal of the first substance and the magnetic resonance signal of the second substance at the same excitation slice are obtained by two excitations. For example, the excitation levels may be determined according to requirements, and in order to acquire the magnetic resonance signal of the first substance and the magnetic resonance signal of the second substance on the same excitation level, a pairwise combination of excitation level combinations is constructed based on all excitation levels, so that the first substance and the second substance are respectively excited at different excitation levels in the excitation level combinations during one excitation. After the excitation plane combinations are determined, for each excitation plane combination, the center frequency of the radio frequency pulse required for excitation of the excitation plane combination is determined based on the excitation plane of the first material in the excitation plane combination. And sequentially adjusting the central frequency of the radio frequency pulse until the combined excitation of all the excitation layers is completed to obtain the magnetic resonance signals of all the excitation layers.
Alternatively, the excitation of each species per excitation level may be achieved based on a slice-through method. Any two excitation layers are included in each excitation layer combination for excitation until the excitation of all the substances in all the excitation layers is completed.
In one embodiment, the excitation level combinations are constructed based on all excitation levels, which may be excitation level combinations that divide all excitation levels into two-by-two combinations. And exciting for each excitation layer combination twice to obtain the magnetic resonance signals of the substances of each excitation layer in the excitation layer combination until the excitation of all the excitation layer combinations is completed to obtain the magnetic resonance signals of the substances in each excitation layer. Fig. 1b is a schematic diagram of a slice-cycling method according to an embodiment of the present invention, as shown in fig. 1b, each excitation slice combination is excited twice, and magnetic resonance signals of substances of each excitation slice in the excitation slice combination are obtained. Taking the first substance as water and the second substance as fat as an example, the excitation level combination filled with dots in fig. 1b is the ith excitation level combination. And at the time of the second excitation, changing the polarity of the layer selection gradient to excite the water of the n layers and the fat of the m layers to obtain the magnetic resonance signals of the water of the n layers and the magnetic resonance signals of the fat of the m layers until the excitation of all excitation layer surface combinations is completed.
In one embodiment, the excitation slice combination is constructed based on all excitation slices, and each excitation slice combination can be sequentially excited to obtain the magnetic resonance signal of each substance in each excitation slice by using the adjacent excitation slices as the excitation slice combination. Fig. 1c is a schematic diagram of another slice-through method provided in an embodiment of the invention, as shown in fig. 1c, each excitation slice combination is excited once to obtain a magnetic resonance signal of a first substance at a first excitation slice and a magnetic resonance signal of a second substance at a second excitation slice in the excitation slice combination. Taking the first substance as water and the second substance as fat as examples, the excitation level combination filled with dots in fig. 1c is the ith excitation level combination, and the excitation level combination filled with lines is the (i + 1) th excitation level combination. Exciting water in m layers and fat in m +1 layers when the ith excitation layer combination is excited, and obtaining magnetic resonance signals of the water in m layers and the fat in m +1 layers; when the (i + 1) th excitation layer combination is excited, water and fat of the (m + 1) th layer are excited, and magnetic resonance signals of the water of the (m + 1) th layer and the fat of the (m + 2) th layer are obtained until excitation of all the excitation layer combinations is completed.
And S130, controlling the radio frequency receiving coil to receive the magnetic resonance signal, and reconstructing the magnetic resonance signal to generate a magnetic resonance image of the target area.
Optionally, after acquiring the magnetic resonance signal, a magnetic resonance image is reconstructed based on the magnetic resonance signal. In this embodiment, because different substances are excited in different layers during a single excitation, the single excitation cannot obtain data of different substances in the same layer, that is, the single excitation cannot reconstruct a magnetic resonance image of a certain layer. Data of different substances in the same slice can be obtained through multiple excitations, substance maps in the slice are obtained based on the substance data, and the substance maps are combined to obtain a magnetic resonance image of the slice.
Optionally, controlling the radio frequency receiving coil to receive the magnetic resonance signal, and reconstructing the magnetic resonance signal to generate a magnetic resonance image of the target region includes: for each excitation of the received magnetic resonance signal, separating the magnetic resonance signal by using reference data to obtain a first substance signal of a first excitation layer and a second substance signal of a second excitation layer in the excitation layer combination, and reconstructing a first substance image of the first excitation layer and a second substance image of the second excitation layer; and combining the first substance image and the second substance image of the same excitation layer obtained by different times of excitation to obtain a target image of the excitation layer. It will be appreciated that two excitation slices are excited at each excitation and therefore the acquired magnetic resonance signals are superimposed with the signal data of the first and second substances. For the magnetic resonance signals obtained by each excitation, including the first substance signal of the first excitation layer and the second substance signal of the second excitation layer, the superposed magnetic resonance signals can be separated by using the acquired reference data based on the PTx signal separation method, so that the first substance signal and the second substance signal are separated, the separated first substance image of the first excitation layer and the separated second substance image of the second excitation layer are reconstructed, the substance images of different excitation layers are obtained in the same manner during the excitation again until the excitation of all the excitation layers is completed, the first substance image and the second substance image of each excitation layer can be obtained, and the first substance image and the second substance image of the same excitation layer excited at different times are combined, so that the target image of the excitation layer can be obtained. Taking the first substance as water and the second substance as fat as an example, after each excitation, the obtained magnetic resonance signals are separated by using the reference data to obtain signal data of a water layer and a fat layer, and then a water map of the water layer and a fat map of the fat layer are obtained. Through the slice circulation, a water map and a fat map of each slice can be obtained according to the method, and the water map and the fat map of each slice are combined to obtain a magnetic resonance image of the water-fat faultless slice.
For example, a first excitation may yield data for a first substance at level 1 and data for a second substance at level 2, and a second excitation may yield data for the first substance at level 2 and data for the second substance at level 1. Reconstructing an image 1 of the first substance at the slice 1 according to the data of the first substance at the slice 1 obtained by the first excitation, reconstructing an image 2 of the second substance at the slice 1 according to the data of the second substance at the slice 1 obtained by the second excitation, and merging the image 1 and the image 2 to obtain a magnetic resonance image of the slice 1; an image 3 of the second material at the slice plane 2 is reconstructed from the data of the second material at the slice plane 2 obtained by the first excitation, an image 4 of the first material at the slice plane 1 is reconstructed from the data of the first material at the slice plane 2 obtained by the second excitation, and the image 3 and the image 4 are combined to obtain a magnetic resonance image of the slice plane 2.
In the above process, when acquiring the reference signal, the target layer (i.e. the water layer) needs to be excited separately to generate the magnetic resonance signal, the layers other than the target layer cannot be excited, and the information that needs to be extracted from the reference signal is only related to the relative position of the target layer and the coil. In one embodiment, the reference data may be obtained by exciting the sample using small-angle, large-bandwidth pulses, and the excitation pulse bandwidth may be selected such that Δ x is much smaller than the excitation layer thickness, which may be selected to approximate that the target layer is excited alone, and the excitation pulse angle is selected according to SAR requirements. In another embodiment, the layers except the target layer may be saturated, and the target layer may be excited by the excitation pulse, or only one layer of the sample may be excited to obtain the reference data.
The embodiment of the invention generates a main magnetic field by controlling a main magnet; controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances; the radio frequency receiving coil is controlled to receive the magnetic resonance signals, the magnetic resonance signals are reconstructed to generate a magnetic resonance image of a target area, the radio frequency pulse bandwidth is determined according to the precession frequency difference of imaging protons in different substances, the target area is excited based on the determined radio frequency pulse bandwidth to generate the magnetic resonance signals, so that the excitation layers of the different substances are completely staggered when the radio frequency pulses are excited, simultaneous multi-layer acquisition of simultaneous excitation of at least two layers based on common radio frequency pulses is realized, further, the substances in the magnetic resonance image reconstructed based on the magnetic resonance signals are not staggered, and the magnetic resonance imaging effect is improved.
Example two
Fig. 2 is a schematic structural diagram of a magnetic resonance imaging apparatus according to a second embodiment of the present invention. The magnetic resonance imaging apparatus may be implemented in software and/or hardware, for example, the magnetic resonance imaging apparatus may be configured in a computer device. As shown in fig. 2, the apparatus comprises a main magnetic field control module 210, a radio frequency pulse control module 220 and a signal processing module 230, wherein:
a main magnetic field control module 210 for controlling a main magnet to generate a main magnetic field;
a radio frequency pulse control module 220 for controlling the radio frequency transmission coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein the radio frequency pulse bandwidth of the radio frequency pulses is determined according to the difference of precession frequencies of imaging protons in different substances;
a signal processing module 230 for controlling the radio frequency receiving coil to receive the magnetic resonance signal and reconstruct the magnetic resonance signal to generate a magnetic resonance image of the target region.
According to the embodiment of the invention, the main magnet is controlled to generate the main magnetic field through the main magnetic field control module; the radio frequency pulse control module controls the radio frequency transmitting coil to transmit radio frequency pulses to excite a target region of a detected person so as to generate magnetic resonance signals of the target region, wherein the radio frequency pulse bandwidth of the radio frequency pulses is determined according to the difference of precession frequencies of imaging protons in different substances; the signal processing module controls the radio frequency receiving coil to receive the magnetic resonance signal, the magnetic resonance signal is reconstructed to generate a magnetic resonance image of a target area, the radio frequency pulse bandwidth is determined according to the precession frequency difference of imaging protons in different substances, the target area is excited based on the determined radio frequency pulse bandwidth to generate the magnetic resonance signal, so that the excitation layers of the different substances are completely staggered when the radio frequency pulse is excited, simultaneous multi-layer acquisition of simultaneous excitation of at least two layers based on common radio frequency pulses is realized, further, the substances in the magnetic resonance image reconstructed based on the magnetic resonance signal are not staggered, and the magnetic resonance imaging effect is improved.
Optionally, on the basis of the foregoing scheme, the apparatus further includes a radio frequency bandwidth determining module, including:
a chemical displacement unit for acquiring a chemical displacement of an imaging proton in a first substance relative to an imaging proton in a second substance, wherein the first substance and the second substance are different substances;
the excitation layer distance unit is used for acquiring the excitation layer distance of the first substance and the second substance;
and the radio frequency pulse bandwidth unit is used for determining the radio frequency pulse bandwidth according to the main magnetic field strength, the chemical displacement, the excitation layer thickness and the excitation layer face distance.
Optionally, on the basis of the above scheme, the chemical displacement unit is specifically configured to:
acquiring a first precession frequency of an imaging proton in a first substance and a second precession frequency of the imaging proton in a second substance;
and determining the chemical displacement according to the difference between the first precession frequency and the second precession frequency.
Optionally, on the basis of the above scheme, the radio frequency pulse bandwidth unit is specifically configured to:
and determining the radio frequency pulse bandwidth according to the BW-B0-k-T/delta x, wherein BW is the radio frequency pulse bandwidth, B0 is the main magnetic field strength, k is the chemical displacement, T is the excitation layer thickness, and delta x is the excitation layer distance.
Optionally, on the basis of the foregoing scheme, the rf pulse control module 220 is specifically configured to:
determining a plurality of excitation layer combinations according to a preset excitation layer, wherein the excitation layer group comprises a first excitation layer of a first substance and a second excitation layer of a second substance;
for each excitation layer combination, determining the central frequency of a radio-frequency pulse corresponding to the excitation layer combination according to a first excitation layer in the excitation layer combinations;
transmitting radio frequency pulses based on the center frequency and the radio frequency pulse bandwidth to obtain magnetic resonance signals of the first substance at the first excitation level and magnetic resonance signals of the second substance at the second excitation level;
the center frequency of the radio frequency pulses is sequentially changed until the excitation of all excitation plane combinations is completed.
Optionally, on the basis of the foregoing scheme, the signal processing module 230 is specifically configured to:
for each excitation of the received magnetic resonance signal, separating the magnetic resonance signal by using reference data to obtain a first substance signal of a first excitation layer and a second substance signal of a second excitation layer in the excitation layer combination, and reconstructing a first substance image of the first excitation layer and a second substance image of the second excitation layer;
and combining the first substance image and the second substance image of the same excitation layer obtained by different times of excitation to obtain a target image of the excitation layer.
Optionally, on the basis of the above scheme, the first substance is water, and the second substance is fat.
The magnetic resonance imaging device provided by the embodiment of the invention can execute the magnetic resonance imaging method provided by any embodiment of the invention, and has corresponding functional modules and beneficial effects of the execution method.
EXAMPLE III
Fig. 3 is a schematic structural diagram of a computer device according to a third embodiment of the present invention. FIG. 3 illustrates a block diagram of an exemplary computer device 312 suitable for use in implementing embodiments of the present invention. The computer device 312 shown in FIG. 3 is only an example and should not bring any limitations to the functionality or scope of use of embodiments of the present invention.
As shown in FIG. 3, computer device 312 is in the form of a general purpose computing device. The components of computer device 312 may include, but are not limited to: one or more processors 316, a system memory 328, and a bus 318 that couples the various system components including the system memory 328 and the processors 316.
The system memory 328 may include computer system readable media in the form of volatile memory, such as Random Access Memory (RAM)330 and/or cache memory 332. The computer device 312 may further include other removable/non-removable, volatile/nonvolatile computer system storage media. By way of example only, the storage device 334 may be used to read from and write to non-removable, nonvolatile magnetic media (not shown in FIG. 3, and commonly referred to as a "hard drive"). Although not shown in FIG. 3, a magnetic disk drive for reading from and writing to a removable, nonvolatile magnetic disk (e.g., a "floppy disk") and an optical disk drive for reading from or writing to a removable, nonvolatile optical disk (e.g., a CD-ROM, DVD-ROM, or other optical media) may be provided. In these cases, each drive may be connected to bus 318 by one or more data media interfaces. Memory 328 may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the invention.
A program/utility 340 having a set (at least one) of program modules 342 may be stored, for example, in memory 328, such program modules 342 including, but not limited to, an operating system, one or more application programs, other program modules, and program data, each of which examples or some combination thereof may comprise an implementation of a network environment. Program modules 342 generally perform the functions and/or methodologies of the described embodiments of the invention.
The computer device 312 may also communicate with one or more external devices 314 (e.g., keyboard, pointing device, display 324, etc.), with one or more devices that enable a user to interact with the computer device 312, and/or with any devices (e.g., network card, modem, etc.) that enable the computer device 312 to communicate with one or more other computing devices. Such communication may occur via input/output (I/O) interfaces 322. Also, computer device 312 may communicate with one or more networks (e.g., a Local Area Network (LAN), a Wide Area Network (WAN), and/or a public network, such as the Internet) through network adapter 320. As shown, network adapter 320 communicates with the other modules of computer device 312 via bus 318. It should be appreciated that although not shown in the figures, other hardware and/or software modules may be used in conjunction with the computer device 312, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems, among others.
The processor 316 executes programs stored in the system memory 328 to perform various functional applications and data processing, such as implementing a magnetic resonance imaging method provided by an embodiment of the present invention, the method including:
controlling a main magnet to generate a main magnetic field;
controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances;
the radio frequency receive coil is controlled to receive the magnetic resonance signals and the magnetic resonance signals are reconstructed to generate a magnetic resonance image of the target region.
Of course, it will be understood by those skilled in the art that the processor may also implement the technical solution of the magnetic resonance imaging method provided by any embodiment of the present invention.
Example four
The fourth embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the magnetic resonance imaging method provided by the fourth embodiment of the present invention, and the method includes:
controlling a main magnet to generate a main magnetic field;
controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances;
the radio frequency receive coil is controlled to receive the magnetic resonance signals and the magnetic resonance signals are reconstructed to generate a magnetic resonance image of the target region.
Of course, the computer-readable storage medium stored thereon may be used for storing a computer program, which is not limited to the above method operations and may also be used for executing the operations related to the magnetic resonance imaging method provided by any embodiment of the present invention.
Computer storage media for embodiments of the invention may employ any combination of one or more computer-readable media. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated data signal may take many forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may also be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C + +, or the like, as well as conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).
EXAMPLE five
The embodiment provides a magnetic resonance imaging system, which comprises a main magnet, a radio frequency coil and a processor; a main magnet for generating a main magnetic field; a radio frequency coil for transmitting radio frequency pulses and receiving magnetic resonance signals; a processor for performing a magnetic resonance imaging method as provided by any of the embodiments of the invention.
The magnetic resonance imaging system provided by the embodiment of the invention determines the radio frequency pulse bandwidth according to the precession frequency difference of different substances of a detected body through the processor, and the processor controls the main magnet to generate a main magnetic field during imaging; controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region; the radio frequency receiving coil is controlled to receive the magnetic resonance signals, the magnetic resonance signals are reconstructed to generate a magnetic resonance image of a target area, excitation layers of different substances are completely staggered when the radio frequency pulses are excited, simultaneous multi-layer acquisition of at least two layers of simultaneous excitation based on common radio frequency pulses is realized, substances in the magnetic resonance image reconstructed based on the magnetic resonance signals are not staggered, and the magnetic resonance imaging effect is improved.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments illustrated 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, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A magnetic resonance imaging method, comprising:
controlling a main magnet to generate a main magnetic field;
controlling a radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein a radio frequency pulse bandwidth of the radio frequency pulses is determined according to difference of precession frequencies of imaging protons in different substances;
and controlling a radio frequency receiving coil to receive the magnetic resonance signals, and reconstructing the magnetic resonance signals to generate a magnetic resonance image of the target area.
2. The method of claim 1, wherein the determining the bandwidth of the rf pulse comprises:
acquiring the chemical displacement of an imaging proton in a first substance relative to an imaging proton in a second substance, wherein the first substance and the second substance are different substances;
acquiring the excitation layer distance of the first substance and the second substance;
and determining the radio frequency pulse bandwidth according to the main magnetic field strength, the chemical displacement, the excitation layer thickness and the excitation layer face distance.
3. The method of claim 2, wherein said obtaining a chemical displacement of imaging protons in a first material relative to imaging protons in a second material comprises:
acquiring a first precession frequency of an imaging proton in a first substance and a second precession frequency of the imaging proton in a second substance;
determining the amount of chemical displacement from the difference between the first precession frequency and the second precession frequency.
4. The method of claim 2, wherein determining the radio frequency pulse bandwidth from the main magnetic field strength, the amount of chemical shift, an excitation layer thickness, and the excitation slice distance comprises:
determining the radio frequency pulse bandwidth according to BW-B0-k-T/delta x, wherein BW is the radio frequency pulse bandwidth, B0 is the main magnetic field strength, k is the chemical displacement, T is the excitation layer thickness, and delta x is the excitation slice distance.
5. The method of claim 1, wherein controlling the radio frequency transmit coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region comprises:
determining a plurality of excitation layer combinations according to a preset excitation layer, wherein the excitation layer group comprises a first excitation layer of a first substance and a second excitation layer of a second substance;
for each excitation plane combination, determining the center frequency of a radio-frequency pulse corresponding to the excitation plane combination according to a first excitation plane in the excitation plane combinations;
transmitting radio frequency pulses based on the center frequency and the radio frequency pulse bandwidth to obtain magnetic resonance signals of a first substance at a first excitation level and magnetic resonance signals of a second substance at a second excitation level;
and sequentially changing the central frequency of the radio frequency pulse until the excitation of all the excitation layer combination is completed.
6. The method of claim 5, wherein controlling the radio frequency receive coil to receive the magnetic resonance signals, reconstructing the magnetic resonance signals to generate a magnetic resonance image of the target region comprises:
for each excitation of the received magnetic resonance signal, separating the magnetic resonance signal by using reference data to obtain a first substance signal of a first excitation layer and a second substance signal of a second excitation layer in the excitation layer combination, and reconstructing a first substance image of the first excitation layer and a second substance image of the second excitation layer;
and combining the first substance image and the second substance image of the same excitation layer obtained by different times of excitation to obtain a target image of the excitation layer.
7. A magnetic resonance imaging apparatus, characterized by comprising:
the main magnetic field control module is used for controlling a main magnet to generate a main magnetic field;
a radio frequency pulse control module for controlling a radio frequency transmitting coil to transmit radio frequency pulses to excite a target region of a subject to generate magnetic resonance signals of the target region, wherein the radio frequency pulse bandwidth of the radio frequency pulses is determined according to the difference of precession frequencies of imaging protons in different substances;
and the signal processing module is used for controlling the radio frequency receiving coil to receive the magnetic resonance signal and reconstructing the magnetic resonance signal to generate a magnetic resonance image of the target area.
8. A computer device, the device comprising:
one or more processors;
storage means for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to implement the magnetic resonance imaging method as recited in any one of claims 1-6.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the magnetic resonance imaging method as set forth in any one of claims 1-6.
10. A magnetic resonance imaging system comprising a main magnet, a radio frequency coil and a processor;
the main magnet is used for generating a main magnetic field;
the radio frequency coil is used for transmitting radio frequency pulses and receiving magnetic resonance signals;
the processor for performing the magnetic resonance imaging method as claimed in any one of claims 1-6.
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