CN110794352B - Method for inhibiting magnetic resonance image artifact - Google Patents
Method for inhibiting magnetic resonance image artifact Download PDFInfo
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- CN110794352B CN110794352B CN201810868872.8A CN201810868872A CN110794352B CN 110794352 B CN110794352 B CN 110794352B CN 201810868872 A CN201810868872 A CN 201810868872A CN 110794352 B CN110794352 B CN 110794352B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
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Abstract
The invention discloses a method for inhibiting magnetic resonance image artifacts, and belongs to the technical field of magnetic resonance imaging. It comprises the following steps: (1) acquiring TV, TR and Ny parameters; (2) calculating MaxT; (3) calculating SegMent; (4) calculating LoopCount; (5) calculate phaseindex_i; (6) collecting original data; (7) rearranging the original data; (8) a routine reconstruction procedure of magnetic resonance; an artifact free image is obtained. The system can effectively inhibit the image artifact caused by periodic instability of the system.
Description
Technical Field
The invention relates to a method for inhibiting magnetic resonance image artifacts, and belongs to the technical field of magnetic resonance imaging.
Background
Magnetic Resonance Imaging (MRI) technology has become an important tool in medical diagnostics. However, due to defects in the magnetic resonance technology itself or the magnetic resonance system itself, various artifacts often exist in the image, which affect clinical medical diagnosis. For example, in order to maintain a low temperature superconducting state of a magnet bore, a coldhead is required to cool the interior of the magnet bore, and the coldhead of the magnet periodically operates to cause periodic fluctuations in the main magnetic field strength, which can cause dithering of the magnetic resonance frequency, thereby causing image artifacts. In order to eliminate image artifacts caused by the periodic operation of the cold head, the cold head needs to be closed when the image is acquired, so that the cold head is in a stop working state, and then the cold head is started to refrigerate the magnet cavity after the image acquisition is completed, but because the image acquisition time and the acquisition parameters of the magnetic resonance are closely related, the acquisition time is different, if the closing time is too long, the temperature inside the magnet is possibly increased, so that the superconducting magnet is possibly quenched.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: a method for suppressing magnetic resonance image artifacts is provided, which solves the problem of magnetic resonance image artifacts caused by periodic instability of the system at present.
The technical problems to be solved by the invention are realized by adopting the following technical scheme:
a method of suppressing magnetic resonance image artifacts comprising the steps of:
(1) Acquiring the period time TV (unit: ms) of the shake of the magnetic resonance system, the repetition time TR (unit: ms) of the imaging pulse sequence and the phase coding times Ny of the imaging pulse sequence;
(2) Calculating the least common multiple MaxT of the periodic time TV of the system jitter and the repetition time TR of the imaging pulse sequence;
(3) The number of TRs that can be accommodated in one MaxT time is calculated: segmend=maxt/TR;
(4) The SegMent number required to scan all phase encodings Ny is calculated: loopcount=ceil (Ny/segmend), where "Ceil" represents the smallest integer calculated to be greater than or equal to the specified expression;
(5) Calculating the position sequence of the phase code of the ith scan in K space:
phaseindex_i= (i% segmentt) × loopcount+i/segmente, where i is an integer from 0 to Ny-1, "%" in the formula represents the remainder of dividing i by segmente and "/" represents the integer of dividing i by segmente, resulting in a recalculated scan phase encoding order phaseindex_i;
(6) When the imaging pulse sequence is scanned, the original data are acquired according to the phase coding sequence obtained by recalculation;
(7) After the original data acquisition is completed, the reconstruction module firstly arranges acquired data in K space according to the phase coding sequence during reconstruction to obtain conventional K space data;
(8) The normal artifact-free magnetic resonance image can be obtained by performing fourier transform on the conventional K-space data.
Wherein, the step (8) is a conventional calculation method of the magnetic resonance imaging technology, and belongs to the prior art. The innovation point proposed by the present invention is how to recalculate the scan phase coding order phaseindex_i.
The beneficial effects of the invention are as follows: the invention does not need extra hardware equipment or extra image acquisition time, but performs data acquisition according to the recalculated phase encoding step sequence by recalculating the phase encoding step sequence in the pulse sequence module, and after the acquired data are arranged in K space, conventional K space data are obtained, and normal magnetic resonance images with artifact eliminated can be obtained by performing Fourier transform on the conventional K space data, so that the problem of image artifact caused by periodic instability of the system can be effectively restrained.
Drawings
FIG. 1 is a schematic flow chart of the steps of the present invention;
FIG. 2 is a diagram of a conventional phase encode sequential scan to obtain an image with ghost;
fig. 3 shows a phase encoding sequence scanned by the recalculation of the present invention to obtain an image without ghost.
Detailed Description
The invention will be further described with reference to the following detailed drawings, in order to make the technical means, the creation characteristics, the achievement of the purpose and the effect of the invention easy to understand.
Examples
In this embodiment, it will be demonstrated how the invention can be applied to gradient echo sequences to suppress magnetic resonance image artifacts produced by the operation of a magnet coldhead. In this embodiment, the period tv=2000 ms of the system jitter caused by the magnet coldhead, and this parameter is saved in the scanning host through the configuration file; the repetition time TR of the pulse sequence is set to 200ms, and the parameter is set by a user through scanning software running in a scanning host; the number of phase encodings Ny of the pulse sequence is set to 256, which is set by the user via the scanning software running in the scanning host.
As shown in fig. 1, a method of suppressing magnetic resonance image artifacts includes the steps of:
(1) Acquiring the period time TV=2000 ms of the shake of the magnetic resonance system, the repetition time TR=200 ms of the imaging pulse sequence and the phase coding frequency Ny=256 of the imaging pulse sequence;
(2) Calculating the least common multiple maxt=2000 ms of the cycle time TV of the system jitter and the repetition time TR of the imaging pulse sequence;
(3) The number of TRs that can be accommodated in one MaxT time is calculated: segmend=maxt/tr=2000 ms/200 ms=10;
(4) The SegMent number required to scan all phase encodings Ny is calculated: loopcount=ceil (Ny/segmentt) =ceil (256/10) =26, where "Ceil" represents the smallest integer that is calculated to be greater than or equal to the specified expression;
(5) Calculating the position sequence of the phase code of the ith scan in K space: phaseIndex_i= (i% SegMent) ×LoopCount+i/SegMent= (i% 10) ×26+i/10, where i is an integer from 0 to Ny-1, "%" in the formula represents the remainder of dividing i by SegMent, and "/" represents the integer of dividing i by SegMent, resulting in a recalculated scan phase encoding order:
{0,26,52,78,104,130,156,182,208,234,1,27,53,79,105,131,157,183,209,235,2,28,54,80,106,132,158,184,210,236,……}；
(6) When the imaging pulse sequence is scanned, the original data is acquired according to the phase coding sequence obtained by recalculation, namely, the sequence of scanning PhaseIndex_i phase data is carried out for the ith time;
(7) After the original data acquisition is completed, the reconstruction module firstly arranges acquired data in K space according to the phase coding sequence during reconstruction to obtain conventional K space data; in this embodiment, during reconstruction, the reconstruction module firstly arranges acquired data in K space according to the phase encoding sequence of phaseindex_i to obtain conventional K space data;
(8) The normal artifact-free magnetic resonance image can be obtained by performing fourier transform on the conventional K-space data.
As shown in fig. 2, a conventional phase encoding sequence is used to scan an image with a ghost.
As shown in fig. 3, the phase encoding sequence obtained by recalculation of the present invention is used to scan an image without ghost.
As can be seen by comparing fig. 2 and fig. 3, fig. 3 is an image artifact cancellation due to the application of the inventive solution.
The invention does not need extra hardware equipment or extra image acquisition time, but performs data acquisition according to the recalculated phase encoding step sequence by recalculating the phase encoding step sequence in the pulse sequence module, and arranges acquired data in K space according to the conventional phase encoding sequence to obtain conventional K space data, and performs Fourier transformation on the conventional K space data to obtain a normal magnetic resonance image with artifact removed.
The foregoing has shown and described the basic principles and main features of the present invention and the advantages of the present invention. It will be appreciated by persons skilled in the art that the present invention is not limited to the embodiments described above, but is capable of numerous variations and modifications without departing from the spirit and scope of the invention, which is defined in the claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (1)
1. A method of suppressing magnetic resonance image artifacts, comprising the steps of:
(1) Acquiring the period time TV of the shake of a magnetic resonance system, the repetition time TR of an imaging pulse sequence and the phase coding times Ny of the imaging pulse sequence;
(2) Calculating the least common multiple MaxT of the periodic time TV of the system jitter and the repetition time TR of the imaging pulse sequence;
(3) The number of TRs that can be accommodated in one MaxT time is calculated: segmend=maxt/TR;
(4) The SegMent number required to scan all phase encodings Ny is calculated: loopcount=ceil (Ny/segmend), where "Ceil" represents the smallest integer calculated to be greater than or equal to the specified expression;
(5) Calculating the position sequence of the phase code of the ith scan in K space: phaseindex_i= (i% segmentt) × loopcount+i/segmente, where i is an integer from 0 to Ny-1, "%" in the formula represents the remainder of dividing i by segmente and "/" represents the integer of dividing i by segmente, resulting in a recalculated scan phase encoding order phaseindex_i;
(6) When the imaging pulse sequence is scanned, the original data are acquired according to the phase coding sequence obtained by recalculation;
(7) After the original data acquisition is completed, the reconstruction module firstly arranges acquired data in K space according to the phase coding sequence during reconstruction to obtain conventional K space data;
(8) The normal artifact-free magnetic resonance image can be obtained by performing fourier transform on the conventional K-space data.
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| CN117054944B (en) * | 2023-10-13 | 2024-01-23 | 安徽福晴医疗装备有限公司 | Method for eliminating balanced steady-state free precession sequence artifact based on phase rearrangement |
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