CN105902270B - A kind of four point Dixon method for separate imaging of water and fat of supper-fast single-shot - Google Patents
A kind of four point Dixon method for separate imaging of water and fat of supper-fast single-shot Download PDFInfo
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Abstract
The invention discloses a kind of four point Dixon method for separate imaging of water and fat of supper-fast single-shot.The present invention uses the single-shot water fat separation sequence and data processing method of miscellaneous editions, is mainly used for enhancing signal-to-noise ratio and accelerates sweep speed simultaneously to obtain and eliminate same phasor, reverse phase figure, water picture and the fat picture of an inhomogeneous broadening effect and obtain field pattern Δ B0With it is accurateDistribution map.While ensure that quick scanning, meet the clinical diagnosis needs of the sufferer for infant and restlessness.
Description
Technical field
The present invention relates to four point Dixon water fat of mr imaging technique field more particularly to a kind of supper-fast single-shot
Method for separate imaging.
Background technology
Dixon separate imaging of water and fat technologies are that water and fat are utilized on the basis of magnetic resonance gradient echo or spin echo technique
The chemical shift difference of fat carries out phase code and obtains in human anatomic structure water and fat constituent respectively by Data Post
Enhance a kind of advanced magnetic resonance imaging technique of development.Traditional Dixon separate imaging of water and fat technologies include two point Dixon and three
Point Dixon technologies are widely used to clinical diagnosis, to lesion under the conditions of fat suppression it is clear development and fats disease
Make a definite diagnosis with unique value.Compared to two point Dixon technologies, three point Dixon technologies be conducive to overcome ambient noise interfere and
The pixel of accurate ownership water fat boundary, can eliminate ditch side effect, and be conducive to accurately calculate the initial phase φ of echo0With
Phase error phi is to exclude the interference of hardware physical effect and field inhomogeneous broadening effect.For three point Dixon imaging techniques, phase
Position coding includes three phases, and clinically there are commonly (0, π, 2 π), (- π, 0, π), even (θ0+θ,θ0+2θ,θ0+3θ)；Although
Here three phases theoretically can be selected arbitrarily in magnetic resonance imaging, but is clinically needed and passed through conducive to water fat signal
Certain phase difference realizations efficiently separate, while needing to keep compared with high s/n ratio, it is also necessary to ensure the algorithm effect of analysis of image data
Rate is sufficiently high to reach clinically real-time application requirement.The realization of three point Dixon imaging techniques is broadly divided into two ways：It is a kind of
It is to scan the image (including two with phasor and a reverse phase figure) for obtaining three phase codes respectively three times, another kind is to pass through
Three echo systems of single-shot realize that single pass obtains the image of three phase codes, and the latter is than the former in scan efficiency
Improve three times.It can be divided into again based on gtadient echo and based on certainly using three point Dixon imaging techniques of single-shot mode
Two kinds of cycle wave, the former is clinically more efficient, is equivalent to the efficiency of the T1 weighted imagings based on SPGR, but this abdomen at
It still cannot fully meet clinical diagnosis needs especially for the sufferer of infant and restlessness as in the case of.
Invention content
The sufferer of infant and restlessness still cannot be filled in the case of in order to overcome prior art efficiency to improve
Divide and meet the technical issues of clinical diagnosis needs, the present invention provides a kind of separation of four point Dixon water fat of supper-fast single-shot
Imaging method.
Four point Dixon method for separate imaging of water and fat of a kind of supper-fast single-shot provided by the invention, includes the following steps：
Step S100：Single-shot water fat separation sequence uses soft pulse single gtadient echo or spin echo mode, by N group sequence lists
Member is constituted, and every group of sequence units acquire the Dixon echoes of one group of four phase code；Step S200：In first group of echo filling
Heart district domain, second group of echo fill immediate area, and so on, until k-space fill, four k-space plural number squares of acquisition altogether
Battle array corresponds to two that T1 is weighted with phasor and two reverse phase figures respectively；Or N group echoes fill central area, second group of echo
Immediate area is filled, and so on, until k-space has been filled, four k-space complex matrixs of acquisition, correspond to T respectively altogether2 *Weighting
Two with phasor and two reverse phase figures；Step S300：Four k-space complex matrixs are first carried out along frequency coding direction respectively
One-dimensional inverse Fourier transform obtains four blending space two-dimensional complex number arraysWithAnd it is rightWithTake plural number altogether
It is chosen in four arrays after yoke and corresponds to ky=0 row vector, is denoted as WithIt calculatesWithBetween phase difference φ1AndWithBetween phase difference and Δ φ2；WithIt is multiplied by respectivelyWith
Then, rightWithIt carries out one-dimensional inverse Fourier transform respectively along phase-encoding direction and obtains two same phasorsWith two reverse phase figuresStep S400：With phasor and reverse phase figure according to
WithThe water fat separate picture of signal-to-noise ratio enhancing is generated respectively and shortens N times of sweep time.
Wherein, the choosing layer pulse of step S100 use small angle soft pulse or spin echo soft pulse, frequency encoding gradient by
One prepared gradient and a series of equally spaced trapezoidal gradients are constituted, and adjacent trapezoidal gradient integral area is equal but polarity phase
Instead；Phase encoding gradient encodes gradient G by preliminary phasesp0Gradient G is encoded with a series of opposite polarity triangular phasesΔpStructure
At each triangular phase encodes gradient GΔpIt is placed in the middle position of two adjacent frequency encoding gradients；Each sequence repeats
Unit acquires one group of Dixon echo under the effect of bipolarity frequency encoding gradient.
Wherein, single-shot water fat separation sequence carries out fractional scanning using supper-fast scan mode, and single-shot generates
N group Dixon echoes carry out phase code respectively, four echoes share a step phase code in group.
Wherein, single-shot water fat separation sequence uses 3-D scanning mode, increases an additional phase selecting layer direction
Position coding gradient simultaneously acquires signal by the same manner, and mating data processing module increases an edge in image reconstruction and selects layer side
To one-dimensional discrete Fourier transform, then carry out phasing and obtaining pellicular water fat separate picture by the same manner.
Wherein, single-shot water fat separation sequence enhances scan mode using signal noise ratio (snr) of image, carries out phase in the usual way
Position coding, each level that scans obtain the same phasor of N groupsWith reverse phase figureAnd obtain N group water pictures and fat
Picture, i.e.,WithIt is logical
Cumulative realization signal-to-noise ratio is crossed to be remarkably reinforced.
Advantageous effect：The present invention uses the single-shot water fat separation sequence and data processing method of miscellaneous editions, mainly
For enhancing signal-to-noise ratio and accelerating sweep speed simultaneously to obtain and eliminate the same phasor, reverse phase figure, water of an inhomogeneous broadening effect
Picture and fat picture and acquisition field pattern Δ B0With accurate T2 *Distribution map.While ensure that quick scanning, meet for
The clinical diagnosis of the sufferer of infant and restlessness needs.
Description of the drawings
Fig. 1 two dimension single-shot water fat separation sequence I.
In figure, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on gtadient echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, TE are the echo times, and Δ τ is the time interval between echo vertex, Gp0It is preliminary phases coding gradient, GΔp
It is triangular phase coding gradient, GspoilerIt is damage phase gradient, radio frequency excitation pulse can select low-angle.
Fig. 2 two dimension single-shot water fat separation sequence II.
Wherein, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on spin echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, TE are the echo times, and Δ τ is the time interval between echo vertex, Gp0It is preliminary phases coding gradient, GΔp
It is triangular phase coding gradient, GspoilerIt is damage phase gradient.
Fig. 3 work flow diagrams.
Wherein, SS indicates that slice selective gradient direction, RO indicate that frequency encoding gradient direction, PE indicate phase encoding gradient side
To A indicates echo amplitude attenuation ratio, and N is sequence repetition unit number or Dixon echo group numbers.
Fig. 4 three-dimensional single-shot water fat separation sequence I.
Wherein, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on gtadient echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, TE are the echo times, and Δ τ is the time interval between echo vertex, Gp0It is preliminary phases coding gradient, GΔp
It is triangular phase coding gradient, GspoilerIt is damage phase gradient, it includes that phase reunion gradient exists to select layer direction phase encoding gradient
Interior, radio frequency excitation pulse can select low-angle.
Fig. 5 three-dimensional single-shot water fat separation sequence II.
Wherein, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on spin echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, TE are the echo times, and Δ τ is the time interval between echo vertex, Gp0It is preliminary phases coding gradient, GΔp
It is triangular phase coding gradient, GspoilerIt is the damage phase gradient of variable-magnitude, it includes phase to select layer direction phase encoding gradient
Including the reunion gradient of position.
Fig. 6 signal-to-noise ratio enhanced edition two dimension water fat separation sequence I.
Wherein, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on gtadient echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, the time interval Δ Δs of τ=1/ f/2, TE between echo vertex are echo time, GspoilerIt is variable-magnitude
Damage phase gradient.
Fig. 7 signal-to-noise ratio enhanced edition two dimension water fat separation sequence II.
Wherein, the start-up portion of sequence is by the four point Dxion Sequence compositions of single-shot based on spin echo, including N
A sequence repetition unit, each sequence repetition unit acquire two with phase echo and two under the effect of bipolarity frequency encoding gradient
A reverse phase echo, TE are the echo times, and Δ τ is the time interval between echo vertex, GspoilerIt is damage phase gradient.
Specific implementation mode
For make present invention solves the technical problem that, the technical solution that uses and the technique effect that reaches it is clearer, below
The present invention is described in further detail in conjunction with the accompanying drawings and embodiments.It is understood that specific implementation described herein
Example is used only for explaining the present invention rather than limitation of the invention.It also should be noted that for ease of description, attached drawing
In only the parts related to the present invention are shown rather than full content.
One, the principle of the invention
The present invention constitutes independent function module installation and operation by water fat separation sequence and corresponding data processing module
In on high-performance magnetism resonance imaging system.Wherein, water fat separation sequence (see Fig. 1 and Fig. 2) using single-shot spin echo or
Gtadient echo mode is made of N group sequence units, and every group of sequence units acquire the Dixon echoes of one group of four phase code, and
With there are three sweeping scheme and data processing module, workflow is as shown in Figure 3.It is strong that sequence shown in FIG. 1 is suitable for gradient
Larger and smaller width situation is spent, the field inhomogeneous broadening effect in TE periods is negligible here；And sequence shown in Fig. 2 is suitable for ladder
The situation that intensity is smaller and width is larger is spent, the field inhomogeneous broadening effect in TE periods be can not ignore here.Wherein, slice selective gradient and choosing
Layer pulse is for scanning chunk or level selection, and design method is as regular gradient echo sequence；Frequency encoding gradient by
One prepared gradient and a series of equally spaced trapezoidal gradients are constituted, and adjacent trapezoidal gradient integral area is equal but polarity phase
Instead；Phase encoding gradient encodes gradient by preliminary phases and a series of opposite polarity triangular phase coding gradients are constituted, phase
Position coding gradient is applied to the centre position of positive-negative polarity frequency encoding gradient.The sequence of the two versions is all made of fractional scanning
Mode executes, and each sequence repetition unit acquires two with phase echo and two reverse phases under the effect of bipolarity frequency encoding gradient
Echo, the time interval between echo vertex are typically set to the Δ f/2 of Δ τ=1/, and PE system and k-space filling mode are such as
It is lower described：
By the N number of region of the division of k-space, NPEFor the half of all phase code step numbers (Dim2), each area filling has
NPEThe data points of/N k-space line, every k-space line are Dim1.Phase code cycle-index is NPE/ N, preliminary phases are compiled
Code gradient Gp0Amplitude from zero gradually increasing or decreasing until phase encoding gradient maximum value (GP) 1/N, stepping be ± Gp/
NPE, and phase encoding gradient G is setΔp=± GP/ N, here positive sign correspond to the k-space first half, negative sign corresponds to k-space lower half,
GP0Determine the initial position of k-space line, GP0+i·GΔp(i=0 to N-1) determines the position of current k-space line.Every group 4 points
Dixon sequence units acquire four Dixon echoes, and first group of echo fills central area, and second group of echo fills immediate area,
And so on, until k-space has been filled.
Then, data processing module extracts first together from k-space file by single echo data points (i.e. Dim1)
Phase echo data, first reverse phase echo data, second with phase echo data, second reverse phase echo data, build respectively
Four k-space data matrixes, first carrying out one-dimensional inverse Fourier transform respectively along frequency coding direction obtains four blending spaces two
The plural array of dimensionWithAnd it is rightWithPhase is carried out in the following manner after taking complex conjugate and time reversal
Bit correction：
A. it chooses in four arrays and corresponds to ky=0 row vector, is denoted asWith
B. it calculatesWithBetween phase difference φ1AndWithBetween phase difference and Δ φ2；
C.WithIt is multiplied by respectivelyWith
Then, rightWithIt carries out one-dimensional inverse Fourier transform respectively along phase-encoding direction and obtains four figures
Image field two-dimensional complex number arrayWithEach array size is Dim12NPE。
As N=1, the data analysis with phasor and reverse phase figure is based on following formula：
Here, subscript 0 represents same phase, and 1 represents reverse phase,WhereinIt is apparent lateral relaxation time constant.
In the case of N=1, A can be measured based on front two with each image pixel intensities of phasor, that is,Meanwhile according toAcquisition can be calculatedDistribution map.
It is available according to formula (1) and (2)It is calculated by four-quadrant arctan functionPhase solution is carried out by common fitting of a polynomial or region growth method
It twines.Again willWithIt is multiplied by respectivelyInitial phase is eliminated, and is multiplied by e respectivelyi·φ、ei·2φAnd ei·3φTo eliminate
Field inhomogeneous broadening effect.After eliminating phase errorIt calculatesFor determining that water or fatty pixel exist
The ownership of intersection.
Then, according to the following formula by water picture and fat as carrying out separation and respectively cumulative mean：
Work as N>When 1, as long as first group of echo filling k-space center line (i.e. T1Weight situation), still with phasor and reverse phase figure
It can be based on formula (1) to formula (4) and carry out data analysis, and water picture and fatty picture are obtained based on formula (5) and formula (6)：
Work as N>When 1, if N group echoes filling k-space center line (i.e. T2 *Weight situation), then
Above formula reflects that amplitude and phase property with phasor and reverse phase figure are mainly determined by k-space center line.By formula (7) and
Formula (9) can obtainAccording toIt can be calculatedParameter distribution figure.In addition, anyway by four-quadrant
Cut function calculatingAnd increased by common fitting of a polynomial or region
Method carries out phase unwrapping, and according to Δ B0=φ/(2 π γ Δ τ) obtains field pattern.It willWithMultiply respectively
With ei·(2N-2)φ、ei·(2N-1)φ、ei·(2N)φAnd ei·(2N+1)φ, field is uneven and local magnetic susceptibility effect to eliminating, then passes throughInitial phase φ 0 is calculated, thenWithIt is multiplied by respectivelyTo disappear
Except initial phase.After eliminating phase errorIt calculatesFor determining that water or fatty pixel are having a common boundary
The ownership at place.In fact, Δ B during each Δ τ in sequence0Additional phase error phi and additional amplitude fading will be generated
A, if (2N-2) φ in formula (7) to (10) is incorporated to φ0, A2N-2It is merged intoThen formula (7) to (10) is in shape
Formula (1) can be still equal in formula to (4), therefore also can carry out data processing with foregoing manner.It finally, will according to formula (5) and formula (6)
Water picture and fat are as carrying out separation and respectively cumulative mean.
4N times of scan efficiency can be improved in the water fat isolation technics, while obtaining the water picture of signal-to-noise ratio enhancing and fatty picture, also
It can obtainParameter distribution figure is suitable for various clinical application environment, including infant and hyperactivity patient profiles.
Sequence shown in Fig. 4 and Fig. 5 is the three-dimensional version of the water fat isolation technics, in addition to needing that layer direction is being selected to carry out Fourier
Transformation is outer, can obtain pellicular water fat separate picture with similar data processing method.In addition, sequence shown in Fig. 6 and Fig. 7 is noise
Than enhanced water fat separation sequence, routinely spin echo or gradient echo imaging mode carry out phase code and k-space is filled out
It fills, the same phasor of gained each groupWithAnd reverse phase figureWithIt can equally be carried out at data by formula (1) to (4)
Reason, and it is as follows to finally obtain water fat separate picture：
Two, embodiment
Embodiment 1
The sequence shown in Stowage Plane one on 1.5T magnetic resonance imaging systems, and arrange parameter table, wherein Dim1=256,
Dim2=192, N=4, Δ τ=2.3ms, TR=160ms.It executes sequence and acquires 4 groups of echoes of T1 weightings, every group by four
Dixon echoes are constituted.K-space divides 4 regions by echo group number, and for zone number j from 1 to 4, each area filling has NPE/ N=
24 k-space lines.
The k-space first half is filled, preliminary phases gradient G is setP0For phase encoding gradient maximum value Gp1/4, phase
Position coding is divided into NPE/ N=24 is walked, and cycle-index i is from 1 to 24, and first group of echo fills central area, and phase encoding gradient is
i·(GP/N)/(NPE/ N)=iGP/96；Jth group echo fills j-th of periphery region, phase encoding gradient iGP/96+
(j-1)·GΔp, wherein GΔp=Gp/4.K-space lower half is filled, G is setP0Bear maximum value for phase encoding gradient 1/4
.
It is acquired in part Fourier, N is setPE=Dim2X%=192 (wherein X%=100%), here X%
It is the practical execution step number of phase code.
Then, data processing module is executed, first is extracted by single echo data points (256) from k-space file
With phase echo data, first reverse phase echo data, second with phase echo data and second reverse phase echo data, difference structure
Four two-dimensional complex number arrays are made, size is 256 × 192, and one-dimensional discrete inverse Fourier transform is carried out simultaneously along frequency coding direction
Phasing is carried out in the manner aforesaid to oppisite phase data, then carrying out one-dimensional discrete inverse Fourier transform along phase-encoding direction obtains
It arrivesWithA and κ, most back-pushed-type (5) and formula (6) are calculated in the manner aforesaid) obtain water picture and fatty picture.Sequence
Row execute primary sweep time as 0.16 × 192/4 × 100%=7.7 (s).
Embodiment 2：
The sequence shown in Stowage Plane one on 3.0T magnetic resonance imaging systems, and arrange parameter table, wherein Dim1=256,
Dim2=192, N=8, Δ τ=1.1ms, TR=160ms.It executes sequence and acquires 4 groups of echoes of T1 weightings, every group by four
Dixon echoes are constituted.K-space divides 8 regions by echo group number, and for zone number j from 1 to 8, each area filling has NPE/ N=
12 k-space lines.
The k-space first half is filled, preliminary phases gradient G is setP0For phase encoding gradient maximum value GP1/8, phase
Position coding is divided into NPE/ N=12 is walked, and cycle-index i is from 1 to 12, and first group of echo fills central area, and phase encoding gradient is
i·(GP/N)/(NPE/ N)=iGP/96；Jth group echo fills j-th of periphery region, phase encoding gradient iGP/96+
(j-1)·GΔp, wherein GΔp=Gp/8.K-space lower half is filled, G is setP0Bear maximum value for phase encoding gradient 1/8
.
It is acquired in part Fourier, N is setPE=Dim2X%=192 (wherein X%=100%), here X%
It is the practical execution step number of phase code.
Then, data processing module is executed, first is extracted by single echo data points (256) from k-space file
With phase echo data, first reverse phase echo data, second with phase echo data and second reverse phase echo data, difference structure
Four two-dimensional complex number arrays are made, size is 256 × 192, and one-dimensional discrete inverse Fourier transform is carried out simultaneously along frequency coding direction
Phasing is carried out in the manner aforesaid to oppisite phase data, then one-dimensional discrete Fourier transform is carried out to space along frequency coding direction
Frequency domain obtains then by PCSS modes part Fourier reconstructionWithIn the manner aforesaid calculate A and
κ, most back-pushed-type (5) and formula (6)) obtain water picture and fatty picture.Sequence execute primary sweep time be 0.16 × 192/8 ×
60%=2.3 (s).
Three, innovative point of the present invention
Water fat isolation technics includes the single-shot water fat separation sequence and data processing method of miscellaneous editions in the present invention,
It is mainly used for enhancing signal-to-noise ratio and accelerates sweep speed simultaneously to obtain and eliminate same phasor, the reverse phase of an inhomogeneous broadening effect
Figure, water picture and fat picture and acquisition field pattern Δ B0With accurate T2 *Distribution map.
Entire single-shot water fat separation sequence uses soft pulse single gtadient echo or spin echo mode, by N group sequences
Column unit is constituted, and every group of sequence units acquire the Dixon echoes of one group of four phase code (such as 0, π, 2 π, 3 π).
Layer pulse is selected to use small angle soft pulse or spin echo soft pulse, frequency encoding gradient is by a prepared gradient and one
The equally spaced trapezoidal gradient of series is constituted, and adjacent trapezoidal gradient integral area is equal but polarity is opposite；Phase encoding gradient
Gradient G is encoded by preliminary phasesp0Gradient G is encoded with a series of opposite polarity triangular phasesΔpIt constitutes, each phase code
Gradient GΔpIt is placed in the middle position of two adjacent frequency encoding gradients；Each sequence repetition unit is in bipolarity frequency coding
One group of Dixon echo is acquired under gradient effect.
The single-shot water fat separation sequence can be used supper-fast scan mode and carry out fractional scanning, what single-shot generated
N group Dixon echoes carry out phase code respectively, and four echoes share a step phase code in group.
First group of echo fills central area, and second group of echo fills immediate area, and so on, until k-space is filled
It is complete, four k-space complex matrixs are obtained altogether, correspond to two that T1 is weighted respectively with phasor and two reverse phase figures.
N group echoes fill central area, and second group of echo fills immediate area, and so on, until k-space is filled
It is complete, four k-space complex matrixs are obtained altogether, correspond to T respectively2 *Two of weighting are the same as phasor and two reverse phase figures.
Four k-space complex matrixs, first carried out respectively along frequency coding direction one-dimensional inverse Fourier transform obtain four it is mixed
Close space two-dimensional plural number arrayWithAnd it is rightWithCorrespondence in four arrays is chosen after taking complex conjugate
ky=0 row vector, is denoted asWithIt calculatesWithBetween phase difference φ1AndWithBetween phase difference and Δ φ2；WithIt is multiplied by respectivelyWithThen, rightWithEdge
Phase-encoding direction carries out one-dimensional inverse Fourier transform and obtains two same phasors respectivelyWithWith two reverse phase figuresWith
With phasor and reverse phase figure according toWith
The water fat separate picture of signal-to-noise ratio enhancing is generated respectively and shortens N times of sweep time.
3-D scanning mode can also be used in single-shot water fat separation sequence, increases an additional phase selecting layer direction
It encodes gradient and acquires signal by the same manner, mating data processing module increases an edge in image reconstruction and selects layer direction
One-dimensional discrete Fourier transform, then carry out phasing and obtaining pellicular water fat separate picture by the same manner.
Signal noise ratio (snr) of image enhancing scan mode can also be used in single-shot water fat separation sequence, carries out phase in the usual way
Coding, each level that scans obtain the same phasor of N groupsWithWith reverse phase figureWithAnd obtain N group water pictures and fat
Picture, i.e.,WithIt is logical
Cumulative realization signal-to-noise ratio is crossed to be remarkably reinforced.
Finally it should be noted that：The above embodiments are only used to illustrate the technical solution of the present invention., rather than its limitations；To the greatest extent
Present invention has been described in detail with reference to the aforementioned embodiments for pipe, it will be understood by those of ordinary skill in the art that：Its is right
Technical solution recorded in foregoing embodiments is modified, and is either equally replaced to which part or all technical features
It changes, the range for various embodiments of the present invention technical solution that it does not separate the essence of the corresponding technical solution.
Claims (5)
1. a kind of four point Dixon method for separate imaging of water and fat of supper-fast single-shot, which is characterized in that the supper-fast single swashs
Four point Dixon method for separate imaging of water and fat of hair include the following steps：
Step S100：Single-shot water fat separation sequence uses soft pulse single gtadient echo or spin echo mode, by N group sequences
Column unit is constituted, and every group of sequence units acquire the Dixon echoes of one group of four phase code；
Step S200：First group of echo fills central area, and second group of echo fills immediate area, and so on, until k-space
It has been filled that, obtain four k-space complex matrixs altogether, corresponded to two that T1 is weighted respectively with phasor and two reverse phase figures；Or
N group echoes fill central area, and second group of echo fills immediate area, and so on, until k-space fill, it is total to
Four k-space complex matrixs are obtained, correspond to T respectively2 *Two of weighting are the same as phasor and two reverse phase figures；Wherein, T2 *It is apparent cross
To relaxation time；
Step S300：Four k-space complex matrixs, first carrying out one-dimensional inverse Fourier transform respectively along frequency coding direction obtains four
A blending space two-dimensional complex number arrayWithAnd it is rightWithCorrespondence in four arrays is chosen after taking complex conjugate
ky=0 row vector, is denoted asWithIt calculatesWithBetween phase difference φ1AndWithBetween phase difference and Δ φ2；WithIt is multiplied by respectivelyWithThen, rightWithEdge
Phase-encoding direction carries out one-dimensional inverse Fourier transform and obtains two same phasors respectivelyWith two reverse phase figures
Step S400：With phasor and reverse phase figure according toWithWhereinA0=1, The water fat separate picture of signal-to-noise ratio enhancing is generated respectively and shortens sweep time N
Times.
2. the four point Dixon method for separate imaging of water and fat of supper-fast single-shot according to right 1, which is characterized in that step
The choosing layer pulse of S100 uses small angle soft pulse or spin echo soft pulse, and frequency encoding gradient is by a prepared gradient and a system
It arranges equally spaced trapezoidal gradient to constitute, and adjacent trapezoidal gradient integral area is equal but polarity is opposite；Phase encoding gradient by
Preliminary phases encode gradient Gp0Gradient G is encoded with a series of opposite polarity triangular phasesΔpIt constitutes, each triangular phase
Encode gradient GΔpIt is placed in the middle position of two adjacent frequency encoding gradients；Each sequence repetition unit is in bipolar resistant frequency
One group of Dixon echo is acquired under coding gradient effect.
3. the four point Dixon method for separate imaging of water and fat of supper-fast single-shot according to right 1, which is characterized in that single
Water fat separation sequence is excited to carry out fractional scanning using supper-fast scan mode, the N group Dixon echoes difference that single-shot generates
Phase code is carried out, four echoes share a step phase code in group.
4. the four point Dixon method for separate imaging of water and fat of supper-fast single-shot according to right 1, which is characterized in that single
It excites water fat separation sequence to use 3-D scanning mode, increases an additional phase encoding gradient and by same selecting layer direction
Mode acquires signal, and mating data processing module increases the one-dimensional discrete Fourier for selecting layer direction in an edge in image reconstruction
Then transformation carries out phasing by the same manner and obtains pellicular water fat separate picture.
5. the four point Dixon method for separate imaging of water and fat of supper-fast single-shot according to right 1, which is characterized in that single
It excites water fat separation sequence to enhance scan mode using signal noise ratio (snr) of image, carries out phase code, each scanning slice in the usual way
Face obtains the same phasor of N groupsWith reverse phase figureAnd obtain N group water pictures and fatty picture, i.e.,With
Wherein,M indicates integer, and value range is from 1
To N；Realize that signal-to-noise ratio is remarkably reinforced by cumulative.
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| CN102369454A (en) * | 2009-03-30 | 2012-03-07 | 皇家飞利浦电子股份有限公司 | Two-point dixon technique with flexible choice of echo times |
| CN104597420A (en) * | 2015-02-02 | 2015-05-06 | 清华大学 | Magnetic resonance diffusion imaging method based on multiple excitation |
| CN103513202B (en) * | 2012-06-16 | 2016-04-27 | 上海联影医疗科技有限公司 | DIXON water fat separation method in a kind of nuclear magnetic resonance |
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| CN102369454A (en) * | 2009-03-30 | 2012-03-07 | 皇家飞利浦电子股份有限公司 | Two-point dixon technique with flexible choice of echo times |
| CN103513202B (en) * | 2012-06-16 | 2016-04-27 | 上海联影医疗科技有限公司 | DIXON water fat separation method in a kind of nuclear magnetic resonance |
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