CN1063625C - Technology of reforming magnetic resonance presentation - Google Patents
Technology of reforming magnetic resonance presentation Download PDFInfo
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- CN1063625C CN1063625C CN 94108779 CN94108779A CN1063625C CN 1063625 C CN1063625 C CN 1063625C CN 94108779 CN94108779 CN 94108779 CN 94108779 A CN94108779 A CN 94108779A CN 1063625 C CN1063625 C CN 1063625C
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Abstract
The present invention relates to a magnetic resonance imaging image reconstruction technique for correcting low order phase shift and high order phase shift by first order phase shift correction and subimage processing. The present invention adopts the square of original magnetic resonance images to correct the first order phase shift by self-correlation processing, the images are divided into a plurality of subimages by grids, and the subimages are processed by initial phase adjustment and quick splicing. The method can correct the low order phase shift and the high order phase shift which are relevant to the spatial position, discontinuous boundary points in the images does not need to be determined and picked out in the self-correlation process, and therefore, the present invention reduces the calculation processing time and quickly reconstructs the images. The present invention can be used for magnetic resonance imaging reconstruction techniques, such as inversion recovery contrast grade determination or a Dixon chemical shift imaging method.
Description
The present invention relates to the phase error correction treatment technology in the magnetic resonance imaging image reconstruction method, this processing method can be applicable to the phase error correction in the magnetic resonance imaging image reconstruction method of determining of inversion recovery contrast for example or Dixon chemical shift imaging method.
Some atomic nucleus as hydrogen nuclei, has a kind of characteristic that is referred to as to spin, and the electric charge of motion has a magnetic field around nuclear, be a very little very little dipole moment thereby regard it as so long, is called nuclear magnetic moment.Big water gaging is arranged in the human body, thereby contain a large amount of hydrogen atoms, if one group of hydrogen atom is placed in the stationary magnetic field that adds, then the polarity of its nuclear magnetic moment can be slightly more than the hydrogen nuclei number of arranging against outer magnetic field direction along the number of the hydrogen nuclei of outer magnetic field direction arrangement, this difference has formed a clean magnetic field, with magnetization vector is sign, its existing amplitude has direction again, and with certain frequency around externally-applied magnetic field (as gyro) precession, this motion frequency is called Larmor frequency, and it is directly proportional with the intensity of external magnetic field.In the present getable high-intensity magnetic field scope of people, Larmor frequency is all in radio-frequency range.
If the electromagnetic wave that equals Larmor frequency with a frequency that adds acts on the human body that places external magnetic field, thereby hydrogen nuclei then wherein will absorb the direction (departing from its poised state) that this electromagnetic energy changes magnetization vector, suppose in very short interval, the direction of above-mentioned magnetization vector that enough makes the electromagnetic energy that adds departs from its original direction α angle, claim that then this electromagnetic pulse is the α pulse, the electromagnetic pulse that adds is called radio-frequency pulse again in magnetic resonance imaging.
After radio-frequency pulse finishes, within a period of time, magnetization vector will return to its poised state gradually, and hydrogen nuclei discharges the energy of electromagnetic field that adds of absorption simultaneously, radiated electromagnetic wave, Here it is so-called magnetic resonance signal.The recovery of magnetization vector from nonequilibrium condition towards its poised state is a progressive formation, is referred to as relaxation, and it is determined by material internal structure and residing state thereof.Relaxation can be divided into relaxation parallel and perpendicular to outer magnetic field boundary both direction, and uses T
1And T
2Two feature relaxation times characterize respectively.
Magnetic resonance imaging (MRI) needs with a radio-frequency coil receiving magnetic resonance signals, by adding radio-frequency pulse, magnetization vector is deflected, magnetization vector with the vertical transverse plane in magnetic field in precession, the magnetic flux that passes coil is changed, the variation of magnetic flux induces electric current in coil, the size of the interior mobile electric current of coil is signal intensity in other words, be proportional to the size of magnetization vector cross stream component, relevant with hydrogen atom density, simultaneously also with T
1And T
2Two relaxation times are relevant.
The spatial information of magnetic resonance image (MRI) forms with gradient magnetic, magnetic field intensity is formed clocklike in the space distribute.The resonant frequency of hydrogen nuclei that is in the magnetic field intensity lower position is lower than the resonant frequency that is in the high position hydrogen nuclei of magnetic field intensity, utilize this difference on the frequency to carry out space encoding, to determine the one-dimensional space position of hydrogen nuclei, the gradient magnetic of this one dimension correspondence is called the frequency coding gradient.Another dimension space coding is set up by the phase place difference, and gradient direction and frequency coding gradient that it uses are perpendicular, are referred to as phase encoding gradient.The 3rd gradient and frequency coding gradient and phase place compile that the plane that gradient constitutes is perpendicular, and its effect is chip select, and the sectional position of wanting imaging on the promptly selected human body is called the chip select gradient.As long as on different directions, in the different interval, add above-mentioned three kinds of gradient magnetics respectively, just can obtain representing the magnetic resonance signal in transverse section, sagittal plane, coronalplane and even any direction cross section.Time, amplitude relation between radio-frequency pulse and three gradient waveforms are referred to as pulse train.
The magnetic resonance imaging system collection is decoded to the signal that collects through the magnetic resonance signal of above-mentioned coding, i.e. image reconstruction just obtains the magnetic resonance image (MRI) in any direction cross section.Because magnetic resonance signal is a complex signal, the magnetic resonance image (MRI) that obtains also is plural number, and its amplitude, phase place are by hydrogen atom density, relaxation time T
1, T
2And sweep parameter is determined.
Inversion recovery (Inversion Recovery writes a Chinese character in simplified form IR) scanning technique, see G.M.Bydder and I.R.Young for details, JCAT 9 in 1985,659-675 " MR Imaging:Clinical use of the Inversion RecoverySequence ", be a kind of technology commonly used in the magnetic resonance imaging, be used for strengthening the T of magnetic resonance image (MRI)
1Contrast.This technology is divided into " just " spin and " bearing " spin with the spin in the biological tissue.Inversion recovery time T I by suitable selection resonance as shown in Figure 2, strengthens the T of some tissue of magnetic resonance image (MRI)
1Contrast promptly has different T
1Biological tissue on magnetic resonance image (MRI), the plus or minus grey scale signal can be arranged, therefore, the relative magnetic resonance conventional sweep of this image technology obtains the T of image
1Contrast can be strengthened greatly., the T on the inversion recovery image
1Contrast depends on the phase value of correctly determining each picture dot of image.For various reasons, in the scanning of image process, can introduce the additional phase shift (phase error) relevant, not only comprise the single order phase shift (linear phase error) linear, also comprise other high-order phase shift with the locus with the locus.
(X Y) can be expressed as φ to additional phase shift φ 0
0(X, Y)=φ
0+ α
1X+ β
1Y+ α
2X
2+ β
2Y
2+ γ
11XY+ ... φ wherein
0Be the zeroth order phase shift, X, Y are two directions of orthogonal space, α
1X, β
1Y is the single order phase shift, α
2X
2, β
2Y
2, γ
11XY is the second order phase shift, and the above phase shift of second order and second order is called the high-order phase shift.These phase shift meetings seriously influence T
1Contrast.
Dixon chemical shift imaging method, see W.T.Dixon for details, Radiology in 1984,153,189-194 " simple proton spectroscopicImaging " is the fine difference that utilizes hydrogen nuclei resonant frequency in the different chemical composition (as water and fat), by adjusting the time of data acquisition, form water and fatty homophase image and anti-phase image, the two is separated the spatial distribution map that obtains separately through plus and minus calculation.Effective application of this method depends on the phase shift correction of the anti-phase image of success.
Ahn and Cho were at IEEE Trans.MI-6 in 1987, proposed in P32-36 " the ANew Phase Correction Method in NMR Imaging Basedon Autocorrec ation and Histogram Analysis " literary composition to extract the single order additional phase shift with the auto-correlation computation of plural number image, promptly be adjacent the long-pending single order additional phase shift that on average extracts of the complex conjugate of picture dot, and proofread and correct the method for each picture dot point phase value with them with plural image.This method need be judged the SPA sudden phase anomalies between different biological tissues in the image, the phasetophase breakpoint that produces as phase jump " π " between " just ", " bearing " spin, and need reject, therefore increased the time of the complexity and the calculation process of calculation process.And the method for Ahn and Cho only can proofread and correct zeroth order and single order phase shift, and is powerless to the high-order phase shift.
The objective of the invention is to propose a kind ofly can simply proofread and correct the low order relevant in the magnetic resonance plural number image and the method for high-order phase shift with the locus.
For achieving the above object, the present invention proposes a kind of method with low order and high-order phase error in single order phase shift correction, the adjustment of image subsection initial phase and the quick image connection correction magnetic resonance image (MRI).Main technical scheme is that the auto-correlation computation with original complex image square extracts the single order additional phase shift relevant with the locus, and is used for the single order phase shift correction of view picture image; The reuse grid is partitioned into the experimental process image to the view picture image, and each image subsection is carried out the initial phase adjustment; The initial phase adjustment that each image subsection is carried out is by choosing a reference vector in the image subsection scope, with all picture dots in the image subsection scope after the reference vector projection symbol and the mould of corresponding picture dot as output; Utilize the adjacent mesh complex operator image border condition of continuity then, the quadratic sum that is the difference of adjacent mesh complex operator image border picture dot is got minimum, determine the sign symbol of each image subsection, can avoid the phase inversion that image subsection may occur in the initial phase adjustment like this; With the grouping iterative manner, 42 * 2 the image subsection that each is adjacent up and down is divided into one group earlier, determines the sign symbol of each image subsection in every group with the image subsection border condition of continuity; After by this view picture image being done the successive processing in image subsection border, again each 42 * 2 adjacent up and down image subsections splicing is become a bigger image subsection, step by step all grid image subsections are spliced successively, till forming the view picture image.Can realize quick image connection like this, obtain an image complete, that correct contrast is arranged quickly.
The invention has the advantages that: compared with prior art, the present invention proposes the relevant computing of square asking with plural number image, extract the single order phase shift factor, avoided plural image commonly used in the past to ask relevant, the problem of determining and rejecting of the phasetophase breakpoint that exists in the method as Ahn and Cho proposition; The present invention proposes the phasing of the image subsection splicing of carrying out with the adjustment of image subsection initial phase with the image subsection border condition of continuity; The invention allows for the quick splicing that realizes image with the mode of grouping iteration.Space low order and high-order phase shift that the present invention utilizes the initial phase adjustment of the space single order phase shift correction of view picture image and image subsection and the quick splicing of image subsection to exist on the corrected image effectively, but fast processing reduces operation time.
Below in conjunction with accompanying drawing embodiments of the invention are described in detail.
Fig. 1. expression can be used MRI system block diagram of the present invention
Fig. 2. expression inversion recovery pulse train sketch map
Fig. 3. the flow chart of presentation image processing procedure
Fig. 4. the presentation image grid is cut apart and quick splicing sketch map
Error phase on the present embodiment image that to be the MRI system carry out when the image reconstruction the magnetic resonance signal that obtained by inversion-recovery sequence scanning is proofreaied and correct.Can implement MRI system block diagram of the present invention as shown in Figure 1, main magnet 120 provides a uniform stationary magnetic field among the figure, the person of being scanned 123, be in and send into main magnet 120 intracavity on the sick bed 121, the operation of whole M RI system is to be undertaken by operating board 100 control master computers 101, when beginning to scan, master computer 101 sequence controller 102 of corresponding instruction and parameter can being packed into, sequence controller 102 is just controlled its inner gradient waveform generator, radio frequency generation unit and rf receiver unit work.102 inner gradient waveform generators drive X, Y, and Z three road gradient amplifiers 103 are X, Y, Z three road gradient coils 104 provide enough big pulse current to form the gradient magnetic of three directions.102 internal radio frequency generation units excitation radio-frequency (RF) power amplification 105 provides enough big pulse power for the radio-frequency sending coil in the magnetic field 106, produces the electromagnetic field of the rf frequency of moment, and the hydrogen nuclei in the exciting human departs from thermal equilbrium state.After radio-frequency pulse finished, these hydrogen nucleis of being excited just recovered to thermal equilbrium state, produced magnetic resonance signal.RF receiving coil 107 detects this faint magnetic resonance signal, and delivers to the internal radio frequency receptor of sequence controller 102 after lawnmower amplifier 108 amplifies.
The inside receptor of sequence controller 102 finish to after the detection of magnetic resonance signal and the A/D conversion with transfer of data in the internal memory of master computer 101, be stored on the hard disk of master computer, thereby finish data acquisition.
In scanning process, three tunnel gradients play a part to select lamella, frequency coding and phase code respectively, and they and radio-frequency transmissions, radio frequency reception all concern successively by the regular hour or work simultaneously, be decided by designed pulse train.
In embodiment of the present invention, the design of inversion recovery pulse train as shown in Figure 2.First 180 ° of radio-frequency pulses make the magnetization vector of spin by forwarding to along the main field direction and the main field opposite direction, through after the relaxation of TI, because of different tissues has different T
1So some spin is " just " spin along the main field direction, some spin and main field are " bearing " spin in the other direction.The impulse waveform of its rear section constitutes spin-echo sequence commonly used in the magnetic resonance imaging.90 ° of radio-frequency pulses excite these " just ", " bearing " spin once more, form spin echo at the TE place by second 180 ° of radio-frequency pulse.TE is called the echo time, is numerically equal to 2 times of the interval of 180 ° of pulse centers extremely thereafter of 90 ° of pulse centers.Sheet selects gradient G Z1 and 90 °, 180 ° of radio-frequency pulses to be used for the thick lamella of candidate body space one stator, and GZ2 is used for compensating because of sheet selects the phase place of the spin phase place that gradient causes and disperses.Frequency coding gradient G X1, GX2 finish the phase place dispersion and phase place is returned poly-effect.Phase encoding gradient GY change amplitude behind each TR is once finished spatial phase code.The echo-signal that forms around echo time TE is gathered, shown in Fig. 2 data sampling window.TR is called sequence period, is numerically equal to the repetition time of radio-frequency pulse.
The initial data that master computer 101 obtains gatherer process is delivered to and is carried out the image reconstruction computing in the array processor 109 and comprise the phase error correction that carries out two-dimentional fourier-transform and following process, obtains correct, T
1The inversion recovery magnetic resonance image (MRI) that contrast is big.Image after the reconstruct is delivered on the hard disk of master computer 101 and is stored, and deliver on the screen of image subsystem 110 for show, analyze, diagnosis uses.
If the original complex image that obtains through two-dimentional fourier-transform is that (X, Y), the phase error correction process is shown in Fig. 3 handling process for I.Step 1:
Square image of definition plural number image be S (X, Y)
S (X, Y)=I (X, Y) I (X, Y)＜1〉or S (X, Y)=I (X, Y) I (X, Y)/| I (X, Y) |＜2〉wherein || be modulo operation, | I (X, Y) | be the mould of original complex pattern,＜2 definition in S (X, Y) (X, mould value Y) is identical for mould value and I.Step 2:
Extract the single order additional phase shift with square auto-correlation computation of plural number image.Half of the auto-correlation computation averaging of income phase place of squared plural number image is as estimation of each picture dot image single order additional phase shift, for example for directions X: △ Px (y)=1/2 Arg (∑ (S (x, y) S (x-1, y) '))＜3 〉
Arg[wherein] be to get the phase angle computing.
On the inversion recovery image, " just ", " bear " and be spun on plural visual I (X certainly, Y) can form the phasetophase breakpoint on, and square after plural visual S (X, Y) upward just become automatically continuously, (as the method for Ahn and Cho proposition) directly asks related operation need determine and reject the problem of phasetophase breakpoint with the plural number image in the single order phase shift correction method of having avoided using always, simplified calculating process widely, accelerated arithmetic speed.By＜3〉the phase place △ Px (y) that asks is original complex image I (X is Y) along the single order additional phase shift of space X direction.Plural visual I through the single order phase shift correction
c(x y) is:
I
c(x，y)=I(x，y)·exp(-i·x·△P
x(y)) <4>
For the Y direction, can realize the single order phase shift correction of two dimensional surface image X and Y both direction with carrying out the single order phase shift correction with quadrat method.Step 3:
In order to proofread and correct the phase shift relevant better image is divided into the experimental process image with grid, with 2 with the locus
n* 2
nGrid divide needed view picture image for good, the grid as 8 * 8 carries out the initial phase adjustment to each image subsection.Specific practice desirable one characterizes the distribute reference vector n of orientation of this image subsection plural number picture dot, for example: n=exp{i (1/2) Arg[∑ Ic (x, y) Ic (x, y)] }＜5
With all multiple picture dots in the image subsection behind the n direction projection (asking inner product) symbol and the mould of this picture dot as output, finish the initial phase adjustment of image subsection.The contrast that may produce image subsection after this initial phase adjustment is inverted, and can utilize image to carry out the quick splicing of image subsection in the due seriality of image subsection boundary.Step 4:
The quick splicing of image subsection comprises the iteration to the processing of adjacent image subsection border discontinuity and image subsection splicing.Fig. 4 .1 is 8 * 8 image subsections that grid is cut apart, and Fig. 4 .2 is through 1 spliced image subsection grid, this moment image subsection enlarged areas 4 times, Fig. 4 .3 is through 2 spliced image subsection grids, Fig. 4 .4 is the view picture image that forms.Promptly each adjacent up and down 4 width of cloth (2 * 2) image subsection is divided into one group, in every group, get the minimum border condition of continuity with the quadratic sum of the difference of adjacent mesh image subsection border picture dot as the splicing of adjacent mesh image subsection, determine the sign symbol of each image subsection, can proofread and correct the contrast that after the adjustment of image subsection initial phase, may occur like this and be inverted.This is organized four width of cloth image subsections be spliced into a bigger image subsection, successively remaining image subsection is done same the processing and splicing, become 4 * 4 image subsection grids after all image subsections are dealt with, show as Fig. 4 .2; Repeat this processing procedure more step by step, become 2 * 2 image subsection grids, show as Fig. 4 .3; Remake single treatment at last and be spliced into the view picture image, show as Fig. 4 .4.This processing method can realize image connection fast, obtain quickly one complete, recoverable low order and high-order phase shift, the image of correct contrast is arranged.
Claims (4)
1. a kind of phase error correction processing method in the magnetic resonance imaging image reconstruction method, it is characterized in that: the original magnetic resonance plural number image that obtains with two-dimentional fourier-transform square carry out auto-correlation computation, the single order phase shift relevant on the corrected image with the locus; Again image is divided into the experimental process image with grid, each image subsection is carried out the initial phase adjustment in the image subsection scope, and carry out the image subsection splicing, realize the low order of view picture image and the correction of high-order phase shift with the condition of continuity on image subsection border.
2. processing method as claimed in claim 1, it is characterized in that: the initial phase adjustment that each image subsection is carried out is by choosing a reference vector in the image subsection scope, with all picture dots in the image subsection scope after the reference vector projection symbol and the mould of corresponding picture dot as output.
3. processing method as claimed in claim 1 is characterized in that: the quadratic sum of the difference of adjacent mesh image subsection border picture dot is got the minimum border condition of continuity as the image subsection splicing.
4. as claim 1,2 or 3 described processing methods, it is characterized in that, 42 * 2 image subsections that each is adjacent up and down are divided into one group earlier, in every group, determine the sign symbol of each image subsection by the adjacent mesh image subsection border condition of continuity, after by this view picture image being done the successive processing in image subsection border, again above-mentioned each adjacent up and down bigger image subsection of 42 * 2 image subsection splicings becoming, step by step all grid image subsections are spliced successively, up to forming the view picture image.
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|---|---|---|---|
| CN 94108779 CN1063625C (en) | 1994-08-04 | 1994-08-04 | Technology of reforming magnetic resonance presentation |
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|---|---|---|---|
| CN 94108779 CN1063625C (en) | 1994-08-04 | 1994-08-04 | Technology of reforming magnetic resonance presentation |
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|---|---|
| CN1116078A CN1116078A (en) | 1996-02-07 |
| CN1063625C true CN1063625C (en) | 2001-03-28 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1993629B (en) * | 2004-07-29 | 2010-09-15 | 大塚制药株式会社 | Solid sample nuclear magnetic resonance measuring method |
Families Citing this family (11)
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|---|---|---|---|---|
| JP3454760B2 (en) * | 1999-10-22 | 2003-10-06 | ジーイー・メディカル・システムズ・グローバル・テクノロジー・カンパニー・エルエルシー | Phase distribution measuring method and apparatus, phase correcting method and apparatus, and magnetic resonance imaging apparatus |
| CN100423028C (en) * | 2003-09-04 | 2008-10-01 | 皇家飞利浦电子股份有限公司 | Adaptive image homogeneity correction for high field magnetic resonance imaging |
| JP5179182B2 (en) * | 2005-07-27 | 2013-04-10 | 株式会社日立メディコ | Magnetic resonance imaging system |
| CN101422364B (en) * | 2007-11-02 | 2010-05-19 | 上海卡勒幅磁共振技术有限公司 | Magnetic resonance image seamless splicing method |
| CN101427924B (en) * | 2008-07-16 | 2010-07-28 | 山东省肿瘤医院 | Method for acquiring complete anatomy image with segmenting pencil-beam CT image by split joint |
| JP5977158B2 (en) * | 2012-11-30 | 2016-08-24 | ジーイー・メディカル・システムズ・グローバル・テクノロジー・カンパニー・エルエルシー | Detection apparatus, magnetic resonance apparatus, detection method, and program |
| DE102013209295B4 (en) * | 2013-05-21 | 2016-11-17 | Siemens Healthcare Gmbh | Correction of MR image datasets using a similarity of temporally successive datasets |
| CN104459587B (en) * | 2013-09-17 | 2018-02-09 | 北京万东医疗科技股份有限公司 | A kind of flowing compensation method for MRI system |
| CN105640554B (en) | 2014-11-12 | 2017-11-28 | 上海联影医疗科技有限公司 | MR imaging method |
| US10295633B2 (en) * | 2014-12-04 | 2019-05-21 | Koninklijke Philips N.V. | Dixon magnetic resonance imaging using prior knowledge |
| CN111521963B (en) * | 2020-05-06 | 2021-02-19 | 电子科技大学 | Method for automatically adapting and outputting gradient waveform rate and magnetic resonance system |
-
1994
- 1994-08-04 CN CN 94108779 patent/CN1063625C/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1993629B (en) * | 2004-07-29 | 2010-09-15 | 大塚制药株式会社 | Solid sample nuclear magnetic resonance measuring method |
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