CN105902270A - Ultra-fast single-excitation four-point Dixon water-fat separation imaging method - Google Patents

Abstract

The invention discloses an ultra-fast single-excitation four-point Dixon water-fat separation imaging method. Single-excitation water-fat separation sequences and data processing modes of multiple versions are adopted, and the method is mainly used for enhancing the signal to noise ratio and increasing the scanning speed to obtain a same-phase diagram, a reverse-phase diagram, a water image and a fat image in which the field asymmetry effect is eliminated and obtain a field distribution diagram delta B0 and a precise distribution diagram (please see the formula in the description). Fast scanning is guaranteed, and meanwhile the clinical diagnosis needs of infants and restless patients are met.

Description

A kind of 4 Dixon method for separate imaging of water and fat of supper-fast single-shot

Technical field

The present invention relates to mr imaging technique field, particularly relate to 4 Dixon water fat of a kind of supper-fast single-shot Method for separate imaging.

Background technology

Dixon separate imaging of water and fat technology is to utilize water and fat 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 each through Data Post Strengthen a kind of advanced magnetic resonance imaging technique of development.Traditional Dixon separate imaging of water and fat technology includes 2 Dixon and three Point Dixon technology is widely used to clinical diagnosis, to the focus clearly development and fats disease under the conditions of fat suppression Make a definite diagnosis have uniqueness value.Compare 2 Dixon technology, 3 Dixon technology be conducive to overcoming ambient noise interference and Accurately belong to the pixel of water fat boundary, ditch side effect can be eliminated, and be conducive to accurately calculating the initial phase φ of echo₀With Phase error phi is to get rid of hardware physical effect and the interference of field inhomogeneous broadening effect.For 3 Dixon imaging techniques, phase Position coding includes three phase places, and that commonly uses clinically has (0, π, 2 π), (-π, 0, π), even (θ₀+θ,θ₀+2θ,θ₀+3θ)；Although Here three phase places can arbitrarily select in theory in magnetic resonance imaging, but need beneficially water fat signal clinically and pass through Some phase difference realizes efficiently separating, simultaneously need to keep relatively high s/n ratio, in addition it is also necessary to ensure the algorithm effect of analysis of image data Rate is sufficiently high to reach to apply the most in real time requirement.The realization of 3 Dixon imaging techniques is broadly divided into two ways: a kind of Being the image (including two with phasor and an anti-phase figure) of three scanning, three phase codes of acquisition respectively, another kind is to pass through Three echo system of single-shot realize single pass obtain three phase codes image, the latter than the former in scan efficiency Improve three times.3 the Dixon imaging techniques using single-shot mode can be divided into again based on gtadient echo with based on certainly Two kinds of cycle ripple, the former is the most in hgher efficiency, is equivalent to the efficiency of T1 weighted imaging based on SPGR, but this becomes at belly In the case of Xiang, the sufferer especially for infant and restlessness still can not fully meet clinical diagnosis needs.

Summary of the invention

In order to overcome prior art efficiency still can not fill for the sufferer of infant and restlessness in the case of improving Divide the technical problem meeting clinical diagnosis needs, the invention provides 4 Dixon water fat of a kind of supper-fast single-shot and separate Formation method.

4 Dixon method for separate imaging of water and fat of the supper-fast single-shot of one that the present invention provides, comprise 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 list Unit is constituted, and often group sequence units gathers the Dixon echo of one group of four phase code；Step S200: during first group of echo is filled Heart region, second group of echo fills immediate area, by that analogy, until k-space has been filled, obtains four k-space plural number squares altogether Battle array, two of the most corresponding T1 weighting with phasor and two anti-phase figures；Or N group echo filling central area, second group of echo Fill immediate area, by that analogy, until k-space has been filled, obtain four k-space complex matrixs, the most corresponding T altogether₂ ^*Weighting Two with phasor and two anti-phase figures；Step S300: four k-space complex matrixs, is first carried out respectively along frequency coding direction One-dimensional inverse Fourier transform obtains four blending space two-dimensional complex number arraysWithAnd it is rightWithTake plural number altogether Corresponding k in four arrays is chosen after yoke_yThe row vector of=0, is designated as WithCalculateWithBetween phase difference φ₁AndWithBetween phase difference and Δ φ₂；WithIt is multiplied by respectivelyWith Then, rightWithCarry out one-dimensional inverse Fourier transform along phase-encoding direction respectively and obtain two same phasorsWith two anti-phase figuresStep S400: with phasor and anti-phase figure according to WithProduce the water fat separate picture of signal to noise ratio enhancing respectively and shorten sweep time N times.

Wherein, the choosing layer pulse of step S100 uses little angle soft pulse or spin echo soft pulse, frequency encoding gradient by One preparation gradient and a series of equally spaced trapezoidal gradient are constituted, and adjacent trapezoidal gradient integral area is equal but polarity phase Instead；Phase encoding gradient is encoded gradient G by preliminary phases_p0Gradient G is encoded with a series of opposite polarity triangular phase_ΔpStructure Become, each phase encoding gradient G_ΔpIt is placed in the middle position of adjacent two frequency encoding gradient；Each sequence repetition unit exists One group of Dixon echo is gathered under bipolarity frequency encoding gradient effect.

Wherein, single-shot water fat separation sequence uses supper-fast scan mode to carry out fractional scanning, and single-shot produces N group Dixon echo carry out phase code respectively, organize interior four echoes and share a step phase code.

Wherein, single-shot water fat separation sequence uses 3-D scanning mode, increases an extra phase selecting layer direction Position coding gradient also presses the same manner collection signal, and supporting data processing module increases an edge and selects layer side when image reconstruction To one-dimensional discrete Fourier transform, then carry out phasing by the same manner and obtain pellicular water fat separate picture.

Wherein, single-shot water fat separation sequence uses signal noise ratio (snr) of image to strengthen scan mode, carries out phase in the usual way Position coding, each scanning aspect obtains the same phasor of N groupWith anti-phase figureAnd obtain N group water picture and fat Picture, i.e.WithLogical Crossing and cumulative realizing signal to noise ratio and be remarkably reinforced.

Beneficial effect: the present invention uses single-shot water fat separation sequence and the data processing method of miscellaneous editions, mainly For strengthening signal to noise ratio and adding fast scan speed to obtain and to eliminate the same phasor of an inhomogeneous broadening effect, anti-phase figure, water simultaneously Picture and fat picture and acquisition field pattern Δ B₀AccuratelyDistribution map.While ensure that quickly scanning, meet for The clinical diagnosis of the sufferer of infant and restlessness needs.

Accompanying drawing explanation

Fig. 1 two dimension single-shot water fat separation sequence I.

In figure, the start-up portion of sequence is by 4 Dxion Sequence composition of single-shot based on gtadient echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, TE is the echo time, and Δ τ is the time interval between echo summit, G_p0It is that preliminary phases encodes gradient, G_Δp It is that triangular phase encodes gradient, G_spoilerBeing to 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 4 Dxion Sequence composition of single-shot based on spin echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, TE is the echo time, and Δ τ is the time interval between echo summit, G_p0It is that preliminary phases encodes gradient, G_Δp It is that triangular phase encodes gradient, G_spoilerIt is to damage phase gradient.

Fig. 3 workflow diagram.

Wherein, SS represents slice selective gradient direction, and RO represents frequency encoding gradient direction, and PE represents phase encoding gradient side To, A represents echo amplitude attenuation ratio, and N is sequence repetition unit number or Dixon echo group number.

Fig. 4 three-dimensional single-shot water fat separation sequence I.

Wherein, the start-up portion of sequence is by 4 Dxion Sequence composition of single-shot based on gtadient echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, TE is the echo time, and Δ τ is the time interval between echo summit, G_p0It is that preliminary phases encodes gradient, G_Δp It is that triangular phase encodes gradient, G_spoilerBeing to damage phase gradient, phase place reunion gradient exists to select layer direction phase encoding gradient to include In, 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 4 Dxion Sequence composition of single-shot based on spin echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, TE is the echo time, and Δ τ is the time interval between echo summit, G_p0It is that preliminary phases encodes gradient, G_Δp It is that triangular phase encodes gradient, G_spoilerIt is the damage phase gradient of variable-magnitude, selects layer direction phase encoding gradient to include phase 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 4 Dxion Sequence composition of single-shot based on gtadient echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, time interval Δ τ=1/ Δ f/2, TE between echo summit are the echo times, G_spoilerIt it 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 4 Dxion Sequence composition of single-shot based on spin echo, including N Individual sequence repetition unit, each sequence repetition unit gathers two homophase echoes and two under bipolarity frequency encoding gradient effect Individual anti-phase echo, TE is the echo time, and Δ τ is the time interval between echo summit, G_spoilerIt is to damage phase gradient.

Detailed description of the invention

Technical scheme and the technique effect reached for making to present invention solves the technical problem that, using are clearer, below The present invention is described in further detail in conjunction with the accompanying drawings and embodiments.It is embodied as it is understood that described herein Example is used only for explaining the present invention, rather than limitation of the invention.It also should be noted that, for the ease of describing, accompanying drawing In illustrate only part related to the present invention rather than full content.

One, the principle of the invention

The present invention is constituted independent functional module installation and operation by water fat separation sequence and corresponding data processing module On high-performance magnetism resonance imaging system.Wherein, water fat separation sequence (see Fig. 1 and Fig. 2) use single-shot spin echo or Gtadient echo mode, is made up of N group sequence units, and often group sequence units gathers the Dixon echo of one group of four phase code, and Being furnished with three sweeping schemes and data processing module, its workflow is as shown in Figure 3.It is strong that sequence shown in Fig. 1 is applicable to gradient The situation that degree is relatively big and width is less, the field inhomogeneous broadening effect in TE period is negligible here；And the sequence shown in Fig. 2 is applicable to ladder Degree intensity is less and width is bigger situation, the field inhomogeneous broadening effect in TE period be can not ignore here.Wherein, slice selective gradient and choosing Layer pulse is used for scanning chunk or level selection, and its design is as regular gradient echo sequence；Frequency encoding gradient by One preparation gradient and a series of equally spaced trapezoidal gradient are constituted, and adjacent trapezoidal gradient integral area is equal but polarity phase Instead；Phase encoding gradient is made up of preliminary phases coding gradient and a series of opposite polarity triangular phase coding gradient, phase Position coding gradient is applied to the centre position of positive-negative polarity frequency encoding gradient.The sequence of the two version all uses fractional scanning Mode performs, each sequence repetition unit under bipolarity frequency encoding gradient effect, gather two homophase echoes and two anti-phase Echo, the time interval between echo summit is typically set to Δ τ=1/ Δ f/2, PE system and k-space filling mode such as Lower described:

By N number of for the division of k-space region, N_PEFor the half of all phase code step numbers (Dim2), each area filling has N_PE/ N bar k-space line, the data of every k-space line are counted as Dim1.Phase code cycle-index is N_PE/ N, preliminary phases is compiled Code gradient G_p0Amplitude from zero progressively increasing or decreasing until phase encoding gradient maximum (G_P) 1/N, stepping is ± G_p/ N_PE, and phase encoding gradient G is set_Δp=± G_P/ N, here the positive sign correspondence k-space first half, negative sign correspondence k-space lower half, G_P0Determine the original position of k-space line, G_P0+i·G_Δp(i=0 to N-1) determines the position of current k-space line.Often organize 4 points Dixon sequence units gathers four Dixon echoes, and first group of echo fills central area, and second group of echo fills immediate area, By that analogy, until k-space has been filled.

Then, data processing module from k-space file by single echo data count (i.e. Dim1) extract first with Phase echo data, first anti-phase echo data, second homophase echo data, second anti-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 Dimension plural number array (With), and rightWithPhase is carried out in the following manner after taking complex conjugate and time reversal Bit correction:

A. corresponding k in four arrays is chosen_yThe row vector of=0, is designated asWith

B. calculateWithBetween phase difference φ₁AndWithBetween phase difference and Δ φ₂；

C.WithIt is multiplied by respectivelyWith

Then, rightWithCarry out one-dimensional inverse Fourier transform along phase-encoding direction respectively and obtain four figures Image field two-dimensional complex number array (With), each array size is Dim1 2N_PE。

As N=1, with the data analysis of phasor and anti-phase figure based on following formula:

$S_0^1=(S_w+S_f)e^{-{\mathrm{i\φ}}_0}---\left(1\right)$

$S_1^1=(S_w-S_f)A\·e^{-i({\mathrm{\φ}}_0+\mathrm{\φ})}---\left(2\right)$

$S_0^2=(S_w+S_f)A^2\·e^{-i({\mathrm{\φ}}_0+2\mathrm{\φ})}---\left(3\right)$

$S_1^2=(S_w-S_f)A^3\·e^{-i({\mathrm{\φ}}_0+3\mathrm{\φ})}---\left(4\right)$

Here, subscript 0 represents homophase, 1 represent anti-phase,WhereinIt it is apparent T2 constant. In the case of N=1, A can measure based on above two each image pixel intensities with phasor, i.e.Meanwhile, according toAcquisition can be calculatedDistribution map.

Can get according to formula (1) and (2)Calculated by four-quadrant arctan functionPhase place solution is carried out by conventional fitting of a polynomial or region growth method Twine.Again willWithIt is multiplied by respectivelyEliminate initial phase, and be multiplied by e respectively^i·φ、e^i·2φAnd e^i·3φThus eliminate Field inhomogeneous broadening effect.After eliminating phase errorCalculateFor determining that water or fat pixel are being handed over Ownership at boundary.

Then, water picture and fat picture carry out separating and distinguishing cumulative mean according to the following formula:

$S_w=\frac{S_0^1}{2A^0}+\frac{\mathrm{\κ}\·S_1^1}{2A^1}+\frac{S_0^2}{2A^2}+\frac{\mathrm{\κ}\·S_1^2}{2A^3}---\left(5\right)$

$S_f=\frac{S_0^1}{2A^0}-\frac{\mathrm{\κ}\·S_1^1}{2A^1}+\frac{S_0^2}{2A^2}-\frac{\mathrm{\κ}\·S_1^2}{2A^3}---\left(6\right)$

As N > 1 time, as long as first group of echo fills k-space center line (i.e. T₁Weighting situation), with phasor and anti-phase figure still Data analysis can be carried out based on formula (1) to formula (4), and obtain water picture and fat picture based on formula (5) and formula (6):

As N > 1 time, if N group echo fill k-space center line (i.e.Weighting situation), then

$S_0^1=(S_w+S_f)A^{2N-2}\·e^{-i\[{\mathrm{\φ}}_0+(2N-2)\mathrm{\φ}\]}---\left(7\right)$

$S_1^1=(S_w-S_f)A^{2N-1}\·e^{-i\[{\mathrm{\φ}}_0+(2N-1)\mathrm{\φ}\]}---\left(8\right)$

$S_0^2=(S_w+S_f)A^{2N}\·e^{-i\[{\mathrm{\φ}}_0+2N\·\mathrm{\φ}\]}---\left(9\right)$

$S_1^2=(S_w-S_f)A^{2N+1}\·e^{-i\[{\mathrm{\φ}}_0+(2N+1)\mathrm{\φ}\]}---\left(10\right)$

Above formula reflection is mainly determined by k-space center line with phasor and the amplitude of anti-phase figure and phase property.By formula (7) and Formula (9) can obtainAccording toCan be calculatedParameter distribution figure.It addition, by four-quadrant anyway Cut function to calculateAnd by conventional fitting of a polynomial or region growth method Carry out phase unwrapping, and according to Δ B₀=φ/(2 π γ Δ τ) obtains field pattern.WillWithIt is multiplied by respectively e^i·(2N-2)φ、e^i·(2N-1)φ、e^i·(2N)φAnd e^i·(2N+1)φ, thus eliminate that field is uneven and local magnetic susceptibility effect, then pass throughCalculate initial phase φ₀, thenWithIt is multiplied by respectivelyThus disappear Except initial phase.After eliminating phase errorCalculateFor determining that water or fat pixel are having a common boundary The ownership at place.It practice, Δ B during each Δ τ in sequence₀Extra phase error phi and extra amplitude fading will be produced A, if being incorporated to φ by (2N-2) φ in formula (7) to (10)₀, A^2N-2It is merged into (S_w+S _f ), then formula (7) to (10) is in form On still can be equal to formula (1) to (4), therefore also can carry out data process by aforementioned manner.Finally, according to formula (5) and formula (6) by water Picture and fat are as carrying out separating and distinguishing cumulative mean.

This water fat isolation technics can improve scan efficiency 4N times, obtains water picture and fat picture that signal to noise ratio strengthens, also simultaneously Can obtainParameter distribution figure, it is adaptable to various clinical practice environment, including infant and hyperactivity patient profiles.

Sequence shown in Fig. 4 and Fig. 5 is the three-dimensional version of this water fat isolation technics, except needs are selecting layer direction to carry out Fourier Outside conversion, available similar data processing method obtains pellicular water fat separate picture.It addition, sequence shown in Fig. 6 and Fig. 7 is noise The ratio water fat separation sequence of enhancement mode, spin echo or gradient echo imaging mode carry out phase code and k-space is filled out routinely Fill, gained respectively organize same phasor (With) and anti-phase figure (With) data process can be carried out by formula (1) to (4) equally, And it is as follows to finally obtain water fat separate picture:

$S_w=\underset{m=1}{\overset{N}{\mathrm{\Σ}}}(\sqrt{\frac{\left|S_1^m\right|}{A^{2m-2}}\frac{\left|S_3^m\right|}{A^{2m}}}+\mathrm{\κ}\·\sqrt{\frac{\left|S_2^m\right|}{A^{2m-1}}\frac{\left|S_4^m\right|}{A^{2m+1}}})---\left(11\right)$

$S_f=\underset{m=1}{\overset{N}{\mathrm{\Σ}}}(\sqrt{\frac{\left|S_1^m\right|}{A^{2m-2}}\frac{\left|S_3^m\right|}{A^{2m}}}-\mathrm{\κ}\·\sqrt{\frac{\left|S_2^m\right|}{A^{2m-1}}\frac{\left|S_4^m\right|}{A^{2m+1}}})---\left(12\right).$

Two, embodiment

Embodiment 1

Sequence shown in Stowage Plane one on 1.5T magnetic resonance imaging system, and parameter list is set, wherein Dim1=256, Dim2=192, N=4, Δ τ=2.3ms, TR=160ms.Performing sequence and gather 4 groups of echoes of T1 weighting, often group is by four Dixon echo is constituted.K-space is pressed echo group number and is divided 4 regions, and zone number j is from 1 to 4, and each area filling has N_PE/ N= Article 24, k-space line.

The k-space first half is filled, preliminary phases gradient G is set_P0For phase encoding gradient maximum G_p1/4, phase Position coding is divided into N_PE/ N=24 walks, and cycle-index i is from 1 to 24, and first group of echo fills central area, and phase encoding gradient is i·(G_P/N)/(N_PE/ N)=i G_P/96；Jth group echo fills periphery jth region, and phase encoding gradient is i G_P/96+ (j-1)·G_Δp, wherein G_Δp=G_p/4.K-space lower half is filled, G is set_P0The 1/4 of maximum is born for phase encoding gradient ?.

In the case of part Fourier gathers, N is set_PE=Dim2 X%=192 (wherein X%=100%), X% here It it is phase code actual execution step number.

Then, perform data processing module, from k-space file by single echo data count (256) extract first Homophase echo data, first anti-phase echo data, second homophase echo data and second anti-phase echo data, respectively structure Making four two-dimensional complex number arrays, size is 256 × 192, carries out one-dimensional discrete inverse Fourier transform also along frequency coding direction Oppisite phase data is carried out in the manner aforesaid phasing, then carries out one-dimensional discrete inverse Fourier transform along phase-encoding direction and obtain ArriveWithCalculate A and κ, back-pushed-type (5) and formula (6) in the manner aforesaid) obtain water picture and fat picture.Sequence It is 0.16 × 192/4 × 100%=7.7 (s) that row perform sweep time once.

Embodiment 2:

Sequence shown in Stowage Plane one on 3.0T magnetic resonance imaging system, and parameter list is set, wherein Dim1=256, Dim2=192, N=8, Δ τ=1.1ms, TR=160ms.Performing sequence and gather 4 groups of echoes of T1 weighting, often group is by four Dixon echo is constituted.K-space is pressed echo group number and is divided 8 regions, and zone number j is from 1 to 8, and each area filling has N_PE/ N= Article 12, k-space line.

The k-space first half is filled, preliminary phases gradient G is set_P0For phase encoding gradient maximum G_P1/8, phase Position coding is divided into N_PE/ N=12 walks, and cycle-index i is from 1 to 12, and first group of echo fills central area, and phase encoding gradient is i·(G_P/N)/(N_PE/ N)=i G_P/96；Jth group echo fills periphery jth region, and phase encoding gradient is i G_P/96+ (j-1)·G_Δp, wherein G_Δp=G_p/8.K-space lower half is filled, G is set_P0The 1/8 of maximum is born for phase encoding gradient ?.

In the case of part Fourier gathers, N is set_PE=Dim2 X%=192 (wherein X%=100%), X% here It it is phase code actual execution step number.

Then, perform data processing module, from k-space file by single echo data count (256) extract first Homophase echo data, first anti-phase echo data, second homophase echo data and second anti-phase echo data, respectively structure Making four two-dimensional complex number arrays, size is 256 × 192, carries out one-dimensional discrete inverse Fourier transform also along frequency coding direction Oppisite phase data is carried out in the manner aforesaid phasing, then carries out one-dimensional discrete Fourier transform along frequency coding direction to space Frequency domain, then by PCSS mode part Fourier reconstruction, obtainsWithIn the manner aforesaid calculate A and κ, back-pushed-type (5) and formula (6)) obtain water picture and fat picture.Sequence perform sweep time once be 0.16 × 192/8 × 60%=2.3 (s).

Three, innovative point of the present invention

In the present invention, water fat isolation technics includes single-shot water fat separation sequence and the data processing method of miscellaneous editions, It is mainly used in strengthening signal to noise ratio and adding fast scan speed to obtain and to eliminate the same phasor of an inhomogeneous broadening effect, anti-phase simultaneously Figure, water picture and fat picture and acquisition field pattern Δ B₀AccuratelyDistribution map.

Whole single-shot water fat separation sequence uses soft pulse single gtadient echo or spin echo mode, by N group sequence Column unit is constituted, and often group sequence units gathers the Dixon echo of one group of four phase code (such as 0, π, 2 π, 3 π).

Selecting layer pulse to use little angle soft pulse or spin echo soft pulse, frequency encoding gradient is by a preparation gradient and The equally spaced trapezoidal gradient of series is constituted, and adjacent trapezoidal gradient integral area is equal but opposite polarity；Phase encoding gradient Gradient G is encoded by preliminary phases_p0Gradient G is encoded with a series of opposite polarity triangular phase_ΔpConstitute, each phase code Gradient G_ΔpIt is placed in the middle position of adjacent two frequency encoding gradient；Each sequence repetition unit is at bipolarity frequency coding One group of Dixon echo is gathered under gradient effect.

This single-shot water fat separation sequence can use supper-fast scan mode to carry out fractional scanning, and single-shot produces N group Dixon echo carries out phase code respectively, organizes interior four echoes and shares a step phase code.

First group of echo fills central area, and second group of echo fills immediate area, by that analogy, until k-space is filled Complete, obtain four k-space complex matrixs altogether, two of the most corresponding T1 weighting with phasor and two anti-phase figures.

N group echo fills central area, and second group of echo fills immediate area, by that analogy, until k-space is filled Complete, obtain four k-space complex matrixs, the most corresponding T altogether₂ ^*Two of weighting with phasor and two anti-phase figures.

Four k-space complex matrixs, first carry out one-dimensional inverse Fourier transform respectively and obtain four and mix along frequency coding direction Conjunction space two-dimensional plural number array (With), and rightWithCorresponding k in four arrays is chosen after taking complex conjugate_y The row vector of=0, is designated asWithCalculateWithBetween phase difference φ₁AndWithBetween phase difference and Δ φ₂；WithIt is multiplied by respectivelyWithThen, rightWithAlong phase Position coding direction carry out respectively one-dimensional inverse Fourier transform obtain two same phasors (With) and two anti-phase figures (With)。

With phasor and anti-phase figure according toWith Produce the water fat separate picture of signal to noise ratio enhancing respectively and shorten sweep time N times.

Single-shot water fat separation sequence may be used without 3-D scanning mode, increases an extra phase place selecting layer direction Coding gradient also presses the same manner collection signal, and supporting data processing module increases an edge and selects layer direction when image reconstruction One-dimensional discrete Fourier transform, then carry out phasing by the same manner and obtain pellicular water fat separate picture.

Single-shot water fat separation sequence may be used without signal noise ratio (snr) of image and strengthens scan mode, carries out phase place in the usual way Coding, each scanning aspect acquisition same phasor of N group (With) and anti-phase figure (With), and obtain N group water picture and fat Picture, i.e.WithLogical Crossing and cumulative realizing signal to noise ratio and be remarkably reinforced.

Last it is noted that various embodiments above is only in order to illustrate technical scheme, it is not intended to limit；To the greatest extent The present invention has been described in detail by pipe with reference to foregoing embodiments, it will be understood by those within the art that: it is right Technical scheme described in foregoing embodiments is modified, or the most some or all of technical characteristic is carried out equivalent replaces Change, do not make the essence of appropriate technical solution depart from the scope of various embodiments of the present invention technical scheme.

Claims (5)

1. 4 Dixon method for separate imaging of water and fat of a supper-fast single-shot, it is characterised in that described supper-fast single swashs Send out 4 Dixon method for separate imaging of water and fat to comprise 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 Column unit is constituted, and often group sequence units gathers the Dixon echo of one group of four phase code；

Step S200: first group of echo fills central area, second group of echo fills immediate area, by that analogy, until k-space Having filled, obtained four k-space complex matrixs altogether, two of the most corresponding T1 weighting with phasor and two anti-phase figures；Or

N group echo fills central area, and second group of echo fills immediate area, by that analogy, until k-space has been filled, altogether Obtain four k-space complex matrixs, the most corresponding T₂ ^*Two of weighting with phasor and two anti-phase figures；

Step S300: four k-space complex matrixs, first carrying out one-dimensional inverse Fourier transform respectively along frequency coding direction obtains four Individual blending space two-dimensional complex number arrayWithAnd it is rightWithChoose in four arrays corresponding after taking complex conjugate k_yThe row vector of=0, is designated asWithCalculateWithBetween phase difference φ₁AndWithBetween phase difference and Δ φ₂；WithIt is multiplied by respectivelyWithThen, rightWithEdge Phase-encoding direction carries out one-dimensional inverse Fourier transform respectively and obtains two same phasorsWith two anti-phase figures

Step S400: with phasor and anti-phase figure according toWith (whereinA⁰=1, )；Produce respectively Give birth to the water fat separate picture of signal to noise ratio enhancing and shorten sweep time N times.

4 Dixon method for separate imaging of water and fat of supper-fast single-shot the most according to claim 1, it is characterised in that The choosing layer pulse of step S100 uses little angle soft pulse or spin echo soft pulse, frequency encoding gradient by a preparation gradient and A series of equally spaced trapezoidal gradients are constituted, and adjacent trapezoidal gradient integral area is equal but opposite polarity；Phase code ladder Degree is encoded gradient G by preliminary phases_p0Gradient G is encoded with a series of opposite polarity triangular phase_ΔpConstituting, each phase place is compiled Code gradient G_ΔpIt is placed in the middle position of adjacent two frequency encoding gradient；Each sequence repetition unit is compiled in bipolarity frequency One group of Dixon echo is gathered under code gradient effect.

4 Dixon method for separate imaging of water and fat of supper-fast single-shot the most according to claim 1, it is characterised in that Single-shot water fat separation sequence uses supper-fast scan mode to carry out fractional scanning, the N group Dixon echo that single-shot produces Carry out phase code respectively, organize interior four echoes and share a step phase code.

4 Dixon method for separate imaging of water and fat of supper-fast single-shot the most according to claim 1, it is characterised in that Single-shot water fat separation sequence uses 3-D scanning mode, increases an extra phase encoding gradient selecting layer direction and presses The same manner gathers signal, and supporting data processing module increases an edge and selects one-dimensional discrete Fu in layer direction when image reconstruction Vertical leaf transformation, then carries out phasing by the same manner and obtains pellicular water fat separate picture.

4 Dixon method for separate imaging of water and fat of supper-fast single-shot the most according to claim 1, it is characterised in that Single-shot water fat separation sequence uses signal noise ratio (snr) of image to strengthen scan mode, carries out phase code in the usual way, each sweeps Aspect of retouching obtains the same phasor of N groupWith anti-phase figureAnd obtain N group water picture and fat picture, i.e.WithWherein,M represents integer, and span is from 1 to N；Realize signal to noise ratio by adding up to be remarkably reinforced.