CN1548007A - Magnetic resonance imaging method - Google Patents
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- CN1548007A CN1548007A CNA031235077A CN03123507A CN1548007A CN 1548007 A CN1548007 A CN 1548007A CN A031235077 A CNA031235077 A CN A031235077A CN 03123507 A CN03123507 A CN 03123507A CN 1548007 A CN1548007 A CN 1548007A
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- 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
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5615—Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
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Abstract
The magnetic resonance imaging method includes the following steps: sending one chip-selecting RF exciting pulse to apply one transverse magnetic field to one sheet of the 3D structure; generating one first phase encoding gradient pulse and one second phase encoding gradient pulse to sample K space; collecting echo signal and one read gradient repeatedly to form one echo chain; phase modulating the echo signals in K space and arranging the echo signals in phase difference linearly; and re-constructing image via Fourier transformation. The present invention can inhibit pseuto image in magnetic resonance image and raise image quality.
Description
(1) technical field
A kind of MR imaging method of the present invention particularly relates to a kind of method that suppresses pseudo-shadow in the magnetic resonance image (MRI), is used to improve picture quality.
(2) background technology
US6.037,771 have disclosed a kind of MR imaging method, and when an interested three-D volumes, for example tissue is among the static magnetic field B0 of a magnetic resonance system, and the spin magnetic moment in this tissue can be arranged along this magnetic field B 0.If any externally-applied magnetic field B1, then they can be with Rameau (Larmor) frequency by precession.When this interested three-D volumes was further applied a radio-frequency (RF) excited magnetic field B 1, the magnetic moment Mz that prolonged the B0 arrangement originally can be rotated X-Y plane, becomes horizontal magnetic moment Mt.After excitation field B1 removed, a signal was sent in the spin of excited target, and this signal is received and handles.Before above-mentioned excitation field removed the back acquired signal, (Gx, Gy Gz), promptly read gradient G x for one, one the second phase encoding gradient Gy and the first phase encoding gradient Gz also above-mentioned three-D volumes to be applied magnetic field gradient.Treat imaging area and carry out a series of scan cycle, in these circulations, above-mentioned gradient changes according to a special localization method, to determine the locus of signal.The signal that above-mentioned scanning result sends with the above-mentioned spin of being excited constitutes echo-signal, and this signal is gathered with digitized and by computer carries out K space Fourier transformation, so that reconstructed image.The K space claims the frequency space again, and the axle of raw data matrix is called Kx and Ky, and above-mentioned matrix is divided into four quadrants, and the plane that above-mentioned two axles form is called the K space.
In prior art, two kinds of methods of gathering echo-signal are arranged.A kind of is that an echo-signal is once gathered in the every excitation of three-D volumes that is among the magnetostatic field B0, excitation once again, gather an echo-signal again, time between two excitation pulses is called the repetition time (TR), so repeat, until collecting enough echo-signals, then these signals are carried out Fourier transformation in the K space, so that reconstructed image.The defective of this method is, is the quality that guarantees image, needs after each excitation just encourage, thereby image taking speed to be slow to one section magnetic moment of above-mentioned interested three-D volumes recovery time next time.
Another kind is quick echo acquirement method, as shown in Figure 1, to be among the magnetostatic field B0 the every excitation of three-D volumes once, the some echo-signals of continuous acquisition are carried out quick echo acquirement, among the figure only example show 4 such echo-signals (1,2,3 and 4), its signal intensity is to weaken gradually.Though the phase place of these echoes is consistent in theory, in fact,, there is phase contrast between these echoes because magnetic resonance system can not be flawless, as shown in Figure 2, the phase difference value of each echo-signal increases gradually.In addition, moved in signal acquisition process by imaging object and also can produce above-mentioned differing.Fig. 3 and 4 expressions are existing carries out width of cloth modulation and phase place a kind of typical symmetric configuration when modulating to above-mentioned echo-signal in the K space, in width of cloth modulation, first echo signal is placed on the spatial central authorities of K, three follow-up echoes are placed on the both sides of above-mentioned first echo, echo-signal 1,2 respectively symmetrically, 3 and 4 amplitude uses 11 respectively, 21,31,41.In the phase place modulation, first echo signal is placed on the spatial central authorities of K, and three follow-up echoes are placed on the both sides of above-mentioned first echo respectively symmetrically, echo-signal 1,2, and 3 and 4 phase contrast uses 12,22,32,42 respectively.Then these signals are comprised the processing of K space Fourier transformation, so that reconstructed image.Though this method has the advantage of fast imaging,, it is flawless that magnetic resonance imaging system can not be built, because the eddy current in pole plate and the gradient coil exists, or other imperfection part, there is pseudo-shadow (artifact) in the magnetic resonance image (MRI), make the downgrade of image.So-called pseudo-shadow is a kind of image quality index, is meant in the magnetic resonance image (MRI) the inconsistent that part of signal intensity of spatial distribution with tissue.
People attempt to improve picture quality by the hardware that improves magnetic resonance imaging system, and the gradient coil that for example adopts shielding is to reduce the generation of eddy current, and this improvement is effectively, increases but its shortcoming is a manufacturing cost.The method that another kind improves picture quality is the performance of reduction system, for example, the maximum performance of restriction gradient coil, its shortcoming is to give full play to the performance of equipment.
(3) summary of the invention
The purpose of this invention is to provide a kind of MR imaging method, it can reduce the appearance of pseudo-shadow, improves the definition of image.
Another object of the present invention provides a kind of method that reduces pseudo-shadow in the magnetic resonance image (MRI), under quick echo acquirement pattern, does not need to change the hardware of magnetic resonance imaging system, does not also need to reduce the performance of this system, just can reduce the pseudo-shadow in the image.
Above-mentioned purpose of the present invention is to be realized by the technical scheme of claim 1, promptly, a kind of MR imaging method, obtain MR data from an interested three-D volumes and generate image, comprise the steps: that (1) send sheet choosing layer RF excitation pulses, apply a horizontal magnetic field on the thin slice in above-mentioned three-D volumes; (2) produce one first phase encoding gradient pulses, its along first of passing above-mentioned thin slice to the K space samples; (3) produce one second phase encoding gradient pulses, it is on the above-mentioned thin slice plane second to the K space samples along one; (4) gather echo-signal, gather one then and read gradient, this read gradient along one be on the above-mentioned thin slice plane and perpendicular to above-mentioned second the 3rd to the K space samples; (5) repeat above-mentioned steps (2), (3), (4) gather some above-mentioned echo-signals, form an echo train; The invention is characterized in: modulate the phase place of above-mentioned each echo-signal in the K space (6), makes above-mentioned each echo-signal be arrangement linearly substantially by the size of phase difference value; (7) through the synthetic echo-signal of above-mentioned steps (6) Fourier transformation reconstructed image.
According to an aspect of the present invention, above-mentioned each echo-signal is according to the ascending sequence arrangement of phase difference value in above-mentioned modulation step (6), and this layout is the ladder form, near linear arrangement, and does not adopt aforesaid symmetric configuration.In addition, in the K space width of cloth of above-mentioned each echo-signal is modulated, wherein above-mentioned each echo-signal puts in order with above-mentioned identical by putting in order of phase difference value.
According to a further aspect in the invention, above-mentioned each echo-signal also can be according to the descending sequence arrangement of phase difference value in above-mentioned modulation step (6), and this layout also is the ladder form, near linear arrangement.Equally, in the K space width of cloth of above-mentioned each echo-signal is modulated, wherein above-mentioned each echo-signal puts in order with above-mentioned identical by putting in order of phase difference value.
(4) description of drawings
For ease of understanding the present invention, specify embodiments of the invention below with reference to accompanying drawings.Wherein:
Fig. 1 represents once encouraging the back to gather the situation of some echoes fast in the prior art, and each echo-signal intensity is decay successively basically;
Fig. 2 represents the phase difference value of each echo-signal that collects shown in Figure 1, and the phase contrast of subsequent echoes signal is increasing;
Fig. 3 represents a kind of existing K space echo-signal modulator approach, forms a typical symmetric configuration in width of cloth modulation back;
Fig. 4 represents the described method by Fig. 3, after echo-signal is correspondingly carried out the phase place modulation, and a kind of symmetric configuration of formation;
Fig. 5 represents to rearrange sequences of echo signals in the K space among the embodiment of the inventive method, and each echo-signal is linear arrangement substantially by the ascending order of its phase difference value;
Fig. 6 represents that each echo-signal has also correspondingly been carried out width of cloth modulation among the embodiment shown in Figure 5;
Fig. 7 represents the image B that obtains after the image A that obtains under the existing echo symmetric arrays pattern and echo of the present invention are by the phase contrast linear arrangement, and pseudo-shadow obviously reduces in the image B, image quality improvement.
(5) specific embodiment
MR imaging method according to the embodiment of the inventive method, an interested three-D volumes is put among the static magnetic field B0 of magnetic resonance imaging system, apply a radio-frequency (RF) excited magnetic field again, after radio-frequency (RF) excited magnetic field is removed, magnetic resonance signal is sent in the spin of being excited, on three mutually orthogonal directions, produce phase encoding gradient respectively, magnetic resonance signal is encoded, receive these echo-signals then, in the K space above-mentioned echo-signal is carried out Fourier transformation, thereby obtain image.Concrete steps are that (1) sends a sheet choosing layer RF excitation pulses, applies a horizontal magnetic field on the thin slice in above-mentioned three-D volumes; (2) produce one first phase encoding gradient pulses, its along first of passing above-mentioned thin slice to the K space samples; (3) produce one second phase encoding gradient pulses, it is on the above-mentioned thin slice plane second to the K space samples along one; (4) gather echo-signal, gather one then and read gradient, this read gradient along one be on the above-mentioned thin slice plane and perpendicular to above-mentioned second the 3rd to the K space samples; (5) repeat above-mentioned steps (2), some above-mentioned echo-signals are repeatedly gathered in (3), (4), form an echo train.Above-mentioned technology belongs to known multiecho acquisition technique, does not give unnecessary details at this.
As illustrated in Figures 5 and 6, the improvements of method of the present invention are, rearrange sequences of echo signals in the K space.Specific practice is, above-mentioned each echo-signal to be linearly substantially by the ascending order of phase difference value to arrange above-mentioned each echo-signal modulation in the K space.For ease of understanding, look back Fig. 2 earlier, in an echo train, because each echo-signal is to be gathered down with different condition (for example residual magnetic field influence) in the different time by many echo acquirements technology, each echo all has certain phase difference, phase contrast 12 minimums of first echo-signal 1, the phase contrast 22 of second echo-signal 2 is big slightly, the phase contrast 32 of the 3rd echo-signal 3 is bigger, phase contrast 42 maximums of the 4th echo-signal 4, its rule are that the phase contrast of echo-signal of late more collection is big more.Many echo acquirements technology can be gathered more echoes and is not limited to above-mentioned four after a radio-frequency (RF) excited.By changing software, can change putting in order of each echo-signal in the K space.In the embodiment shown in fig. 5, each echo-signal is arranged again according to the ascending order of its phase difference value, make the approaching arrangement linearly of order of the phase contrast of each echo.From left to right, phase contrast 12 minimums of echo-signal 1 are arranged in the most left, the phase contrast 22 of second echo-signal 2 ranks a left side slightly greatly and plays second, the phase contrast 32 bigger left sides of ranking of the 3rd echo-signal 3 play the 3rd, phase contrast 42 maximums of the 4th echo-signal 4 are positioned at right-hand member, according to this arrangement, the phase shift of each echo-signal is ladder and increases progressively the form arrangement, as shown in phantom in FIG. near linear relationship.
Fig. 6 expresses a synthetic situation of each echo-signal, can see that putting in order of each echo is identical with the order of Fig. 5.From left to right, the amplitude 11 of echo-signal 1 is arranged in the most left, and the amplitude 21 of second echo-signal 2 ranks a left side to be played the amplitude 31 of the second, the three echo-signal 3 and rank a left side and play the amplitude 42 of the three, the four echo-signal 4 and be positioned at right-hand member.These echo-signals Fourier transformation reconstructed image then.
In echo train, phase contrast between each echo-signal is excessive to be a major reason that causes the pseudo-shadow that occurs in the magnetic resonance image (MRI), known these phase contrasts are owing to system's imperfection and eddy current etc. cause, so improvement project in the past is also at the problems referred to above.The inventor finds, if the phase shift between above-mentioned each echo-signal is approaching linear, so above-mentioned phase contrast will only can cause that image moves some pixels, and can not produce pseudo-shadow or hangover, reduce picture quality.The present invention is based on that this discovery makes.
Among another embodiment according to the inventive method (not shown go out), opposite with last embodiment, each echo-signal is arranged again according to the descending order of its phase difference value, the phase shift of each echo-signal is the stairway degression form arranges, and each echo-signal is arranged linearly by phase contrast is approaching.In the width of cloth of each echo-signal modulation simultaneously, putting in order of each echo also correspondingly changes.In this embodiment, other technical characterictic and last embodiment are identical, repeat no more.
Fig. 7 represents the image B that obtains after the image A that obtains under the existing echo symmetric arrays pattern and echo of the present invention are by the phase contrast linear arrangement.This relatively demonstration, the remarkable result of the present invention aspect raising magnetic resonance image (MRI) quality.Image A is obtained by prior art, can see among the figure having serious pseudo-shadow.And pseudo-shadow obviously reduces in the image B, particularly near the edge of image sharpness of border many, picture quality is greatly improved.
According to the present invention, do not need to change the hardware designs of magnetic resonance system, as long as the part software of system is made amendment, just can reduce pseudo-shadow, improve picture quality, thereby adopt the cost of technical solution of the present invention lower, and can at short notice improved magnetic resonance system be put goods on the market.
Claims (5)
1, a kind of MR imaging method obtains MR data from an interested three-D volumes and generates image, comprises the steps:
(1) sends a sheet choosing layer RF excitation pulses, apply a horizontal magnetic field on the thin slice in above-mentioned three-D volumes;
(2) produce one first phase encoding gradient pulses, its along first of passing above-mentioned thin slice to the K space samples;
(3) produce one second phase encoding gradient pulses, it is on the above-mentioned thin slice plane second to the K space samples along one;
(4) gather echo-signal, gather one then and read gradient, this read gradient along one be on the above-mentioned thin slice plane and perpendicular to above-mentioned second the 3rd to the K space samples;
(5) repeat above-mentioned steps (2), (3), (4) gather some above-mentioned echo-signals, form an echo train;
It is characterized in that:
(6) in the K space phase place of above-mentioned each echo-signal is modulated, make above-mentioned each echo be arrangement linearly substantially by the size of phase difference value;
(7) through the synthetic echo-signal of above-mentioned steps (6) Fourier transformation reconstructed image.
2, method according to claim 1, wherein, above-mentioned each echo-signal is according to the ascending sequence arrangement of phase difference value in above-mentioned steps (6).
3, method according to claim 2 wherein, further comprises in above-mentioned steps (6), in the K space width of cloth of above-mentioned each echo-signal is modulated, and wherein above-mentioned each echo-signal puts in order with above-mentioned identical by putting in order of phase difference value.
4, method according to claim 1, wherein, above-mentioned each echo-signal is according to the descending sequence arrangement of phase difference value in above-mentioned steps (6).
5, method according to claim 4 wherein, further comprises in above-mentioned steps (6), in the K space width of cloth of above-mentioned each echo-signal is modulated, and wherein above-mentioned each echo-signal puts in order with above-mentioned identical by putting in order of phase difference value.
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| Application Number | Priority Date | Filing Date | Title |
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| CNB031235077A CN100366218C (en) | 2003-05-09 | 2003-05-09 | Magnetic resonance imaging method |
| PCT/EP2004/004989 WO2004099809A1 (en) | 2003-05-09 | 2004-05-10 | Method of magnetic resonance imaging |
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| CNB031235077A CN100366218C (en) | 2003-05-09 | 2003-05-09 | Magnetic resonance imaging method |
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| CN1548007A true CN1548007A (en) | 2004-11-24 |
| CN100366218C CN100366218C (en) | 2008-02-06 |
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| WO (1) | WO2004099809A1 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101937064A (en) * | 2008-12-04 | 2011-01-05 | 奥萝瑞磁振造影公司 | Extending the resolution of mri data by combining subsets from plural image acquisitions |
| CN104833931A (en) * | 2014-02-10 | 2015-08-12 | 西门子公司 | Method and device for controlling magnetic resonance imaging system |
| CN104903740A (en) * | 2012-12-18 | 2015-09-09 | 皇家飞利浦有限公司 | Phantom based MR field mapping of polarizing magnetic field |
| CN104939828A (en) * | 2014-03-28 | 2015-09-30 | 阿尔贝特-路德维希斯弗赖堡大学 | Method for magnetic resonance imaging |
| WO2017173617A1 (en) * | 2016-04-07 | 2017-10-12 | Shanghai United Imaging Healthcare Co., Ltd. | System and method for fast imaging in magnetic resonance imaging |
| CN112716476A (en) * | 2019-10-28 | 2021-04-30 | 通用电气精准医疗有限责任公司 | Magnetic resonance imaging method and system, computer readable storage medium |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5151656A (en) * | 1990-12-11 | 1992-09-29 | General Electric Company | Correction of nmr data acquired by an echo-planar technique |
| EP0572074B1 (en) * | 1992-05-27 | 1998-10-21 | Koninklijke Philips Electronics N.V. | Method and apparatus for magnetic resonance imaging |
| CA2187964C (en) * | 1996-10-16 | 2005-02-01 | Kecheng Liu | Sliding interleaved motsa for magnetic resonance imaging |
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2003
- 2003-05-09 CN CNB031235077A patent/CN100366218C/en not_active Expired - Fee Related
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- 2004-05-10 WO PCT/EP2004/004989 patent/WO2004099809A1/en active Application Filing
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101937064A (en) * | 2008-12-04 | 2011-01-05 | 奥萝瑞磁振造影公司 | Extending the resolution of mri data by combining subsets from plural image acquisitions |
| CN104903740A (en) * | 2012-12-18 | 2015-09-09 | 皇家飞利浦有限公司 | Phantom based MR field mapping of polarizing magnetic field |
| CN104833931A (en) * | 2014-02-10 | 2015-08-12 | 西门子公司 | Method and device for controlling magnetic resonance imaging system |
| CN104833931B (en) * | 2014-02-10 | 2018-02-16 | 西门子公司 | Method and apparatus for controlling magnetic resonance imaging system |
| CN104939828A (en) * | 2014-03-28 | 2015-09-30 | 阿尔贝特-路德维希斯弗赖堡大学 | Method for magnetic resonance imaging |
| WO2017173617A1 (en) * | 2016-04-07 | 2017-10-12 | Shanghai United Imaging Healthcare Co., Ltd. | System and method for fast imaging in magnetic resonance imaging |
| CN112716476A (en) * | 2019-10-28 | 2021-04-30 | 通用电气精准医疗有限责任公司 | Magnetic resonance imaging method and system, computer readable storage medium |
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| Publication number | Publication date |
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| CN100366218C (en) | 2008-02-06 |
| WO2004099809A1 (en) | 2004-11-18 |
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