CN106324537B - A kind of supper-fast segmented single-shot water rouge separation method - Google Patents
A kind of supper-fast segmented single-shot water rouge separation method Download PDFInfo
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Abstract
The invention discloses a kind of supper-fast segmented single-shot water rouge separation method, is twined by supper-fast chemical shift imaging sequence, signal analysis model, echo amplitude attenuation compensation method and the quick solution of phase and accurate alignment technique is used to realize the separation enhancing scanning of water rouge and thin layer separate imaging of water and fat on magnetic resonance imaging system；Image artifacts are eliminated by phasing while scan efficiency can be increased substantially；Two-dimentional version allows chemical shift imaging to realize clinical application in enhancing scanning for the first time, it can also be used to baby and hyperactivity patient scan.
Description
Technical field
The present invention relates to medical nuclear magnetic resonance imaging technical field more particularly to a kind of supper-fast segmented single-shot water rouge
Separation method.
Background technique
In medical magnetic resonance imaging (MRI), chemical shift imaging (also known as spectrum imaging) is than conventional selected fat magnetic
Change saturation, water selective excitation and short TI and restore (STIR) pressure rouge imaging technique and is more advantageous to the clear of lesion and its surrounding tissue
It has been shown that, to radiofrequency field B1Uniformity and magnetic field strength there is no particular/special requirement not lose signal noise ratio (snr) of image yet, group can also be measured
Knit the relative scale of middle fat and water.Dixon water rouge isolation technics is one of chemical shift imaging technology, based on spin echo
Two o'clock and three point Dixon separate imaging of water and fat technologies clinically apply it is relatively broad, but sweep time be routine T1 weight sweep
Twice or three times retouched reduces the efficiency of clinical scanning and diagnosis.Currently, using single-shot simultaneously acquire two with mutually and
Three point Dixon technologies of one reverse phase echo have replaced the imaging system of traditional Dixon technology at home and abroad several famous brand names
On put it over and realize routine clinical application, but so far, separate imaging of water and fat technology is difficult to control due to sweep time
System is never clinically applied to T1 weighting enhancing scanning within 10 seconds, can not also be existed by supper-fast scanning mode
The interference that motion artifacts are avoided in infant and hyperactivity patient imaging procedure, so that the technology is relative to other pressure rouge technologies
Advantage be clinically unable to give full play.In fact, the excitation of long echo string and acquisition mode are conducive to accelerate scanning speed,
It is just applied in fast spin echo (FSE) and echo-planar imaging (EPI) decades ago, but this excitation and acquisition side
The adjoint phase error of formula can cause a variety of image artifacts, this be once FSE and EPI routinize using the difficult point that faces and by compared with
The development efforts of long-term just solve.For separate imaging of water and fat, the phase of the magnetization vector of water and fat constituent and its time
Dependent request radio-frequency pulse and gradient pulse technology accurately control, and the excitation of long echo string and acquisition mode are due to hardware
Not perfect property and vortex field and Maxwell's field-effect can generate significantly larger phase error accumulation.Magnet system and gradient
As soon as the process modification of system has a more very long maturation also limitation by current industrial basis, this needs strong
Data processing technique solve these technical problems.
Summary of the invention
The object of the present invention is to provide a kind of three-dimensional segmented single-shot N point Dixon water realized based on gtadient echo
Rouge method for separate imaging can increase substantially scan efficiency and eliminate image artifacts by phase correction techniques.
The present invention provides a kind of supper-fast segmented single-shot water rouge separation methods to include the following steps：
Step S100：According to prescan needs, apparent laterally relaxation is loaded on industrial personal computer sequencer by console
The Henan timeCycle tests.
Step S200：Two-dimensional chemical displacement imaging sequence module is loaded on sequencer by console.
It is formed using the alternate frequency encoding gradient of 2N positive-negative polarity by N group water in 2-dimensional gradient echo sequence basis
The gtadient echo string that rouge is alternately constituted with phase echo and reverse phase echo；N number of same phase echo is carrying out Gradient Phase coding respectively, with
Correspondingly k-space be divided into N number of region, first echo fills central area, and next echo is sequentially filled immediate area,
And same phasor is reconstructed using part Fourier mode；N number of reverse phase echo carries out Gradient Phase coding respectively, correspondingly
K-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled immediate area, and uses portion
Fourier mode is divided to reconstruct reverse phase figure.
It is formed using the alternate frequency encoding gradient of 2N positive-negative polarity by N number of water in 3-dimensional gradient echo sequence basis
The gtadient echo string that rouge is alternately constituted with phase echo and N number of reverse phase echo；N number of same phase echo carries out Gradient Phase coding respectively,
Correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled close to area
Then domain carries out 3 d-dem inverse Fourier transform and generates a series of same phasors of thin layer；N number of reverse phase echo carries out gradient phase respectively
Position coding, correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled
Then immediate area carries out 3 d-dem inverse Fourier transform and generates a series of same phasors of thin layer.
Step S300：Using the general theoretical model established in spatial frequency domain and image area to gtadient echo string, to penetrating
Influence of the magnetic field bump to phase of echo and amplitude is corrected during the TE that frequency pulse excitation is formed to first echo：
Wherein, t refers to current phase code circulation step, and N arrives the round numbers of 2L range, φ 10It (r) is proton magnetization vector
Initial phase, φ (r) is the phase error mainly generated by Magnetic field inhomogeneity effect, T2 *Item is excellent for carrying out to echo amplitude
Change compensation.
SwAnd SfWater and fat components in image pixel are respectively indicated, they and MwAnd MfIt is directly proportional,Including reverse phase figure
Initial phase and the phase error that field inhomogeneities, vortex field and Maxwell field generate during TE and (2N-2) Δ τ,Mainly by first reverse phase echo (i.e. ky=0 line) phase error during TE determines.
Mw(r) and Mf(r) the proton magnetization vector for respectively indicating water and fat in imaging region, in three-dimensional space encoding strip
It can be described as under part：
Step S400：Water is as SwWith fat as SfIt calculates and generates according to the following formula：
In step S100, apparent lateral relaxation time of the echo amplitude based on imaging regionTest value compensates school
Just, used test sequence includes the units such as slice selective gradient, frequency encoding gradient and echo acquirement, and water mould is placed in imaging area
Domain range is directly positioned in human body as upper selection imaging thick-layer, and setting echo time TE takes different time between 1ms and 1s
Numerical value simultaneously meets TE=n/f condition, and n is natural number, and it is non-thread to be then based on single exponential function progress to the echo amplitude of different TE
Property fitting obtain
In step S200, k-space center line is selected to be greater than maximum value 10% to amplitude after one-dimensional inverse Fourier transform
The phase of complex data point carries out primary phase correction by linear fit method.
In step S300, from reverse phase echo I2N-2Or with phase echo I2N-1Middle selection two of them are in frequency encoding gradient pole
Property is positive in negative situation, the k-space center line k acquired respectivelyy=0 carries out one-dimensional discrete along frequency coding direction becomes against Fourier
After changing, the phase error of center line is obtained by complex operation, then accordingly to all k-space lines in one-dimensional discrete against Fourier
Phasing is carried out after transformation, to eliminate the non-equilibrium effect of bipolarity frequency encoding gradient.
In step 300, from reverse phase echo I2N-2Or with phase echo I2N-1Middle selection two of them are in frequency encoding gradient polarity
It is positive in negative situation, acquires central area k-space line respectively, carry out one-dimensional discrete respectively along frequency coding direction and become against Fourier
Phase error and the averaging of each line in central area are obtained by complex operation after changing, then accordingly to all k-space lines one-dimensional
Phasing is carried out after discrete inverse Fourier transform, eliminates the non-equilibrium effect of bipolarity frequency encoding gradient.
In step S300, the same phase echo and the corresponding k-space data of reverse phase echo that acquire twice are carried out respectively
Image reconstruction and the separation of water rouge, then water picture and fat eliminate irreducible phase errors as being overlapped respectively.
Beneficial effect：The present invention is mended by supper-fast chemical shift imaging sequence, signal analysis model, echo amplitude decaying
Compensation method and the quick solution of phase twine and accurate alignment technique is used to realize the separation enhancing scanning of water rouge on magnetic resonance imaging system
With thin layer separate imaging of water and fat；Image artifacts are eliminated by phasing while scan efficiency can be increased substantially；Two-dimentional version
Chemical shift imaging is allowed to realize clinical application in enhancing scanning for the first time, it can also be used to which baby and hyperactivity patient sweep
It retouches.
Detailed description of the invention
The T of Fig. 1 embodiment of the present invention2 *Cycle tests.
Wherein, TE=n/ Δ f, Δ f are water rouge chemical shift difference, and n is natural number, TE value between 1ms and 1s.
The two-dimentional segmented single-shot water rouge separation sequence of Fig. 2 embodiment of the present invention.
Wherein, sequence start-up portion acquires one group of two o'clock Dixon echo, and subsequent repetitive unit acquires N-1 group two o'clock Dixon
Echo is the TE=Δ Δ f/2 of τ=1/ with the time interval of phase echo and reverse phase echo, applies phase before each group echo samples and compile
Code gradient, applies the phase encoding gradient of polarity reversion after sampling, in three gradient directions after last group of echo acquirement
Apply luffing damage phase gradient to eliminate remaining transverse magnetization vector.
The three-dimensional segmented single-shot water rouge separation sequence of Fig. 3 embodiment of the present invention.
Wherein, sequence start-up portion acquires one group of two o'clock Dixon echo, and subsequent repetitive unit acquires N-1 group two o'clock Dixon
Echo is the TE=Δ Δ f/2 of τ=1/ with the time interval of phase echo and reverse phase echo, applies phase before each group echo samples and compile
Code and selects layer direction phase encoding gradient at gradient, applies the phase encoding gradient of polarity reversion after sampling and layer direction phase is selected to compile
Code gradient applies luffing in three gradient directions after last group of echo acquirement and damages phase gradient to eliminate remaining transverse magnetic
Change vector.
Fig. 4 clinical scanning workflow of the present invention.
The quick accurate phase unwrapping algorithm flow chart of Fig. 5 present invention.
The k-space filling mode of each imaging level in the case of the enhancing scanning of Fig. 6 embodiment of the present invention.
Wherein, the solid line of signal acquisition part indicates that reverse phase gradient echo, dotted line are indicated with phase gradient echo.
The k-space filling mode of each imaging level in the case of the non-reinforcing scanning of Fig. 7 embodiment of the present invention.
Wherein, the solid line of signal acquisition part indicates that reverse phase gradient echo, dotted line are indicated with phase gradient echo.
Fig. 8 two dimension segmented single-shot water rouge separation sequence of the embodiment of the present invention.
Wherein, sequence start-up portion acquires one group of three point Dixon echo, and subsequent repetitive unit acquires N-1 group two o'clock Dixon
Echo is the TE=Δ Δ f/2 of τ=1/ with the time interval of phase echo and reverse phase echo, applies phase before each group echo samples and compile
Code gradient, applies the phase encoding gradient of polarity reversion after sampling, in three gradient directions after last group of echo acquirement
Apply luffing damage phase gradient to eliminate remaining transverse magnetization vector.
The three-dimensional segmented single-shot water rouge separation sequence of Fig. 9 embodiment of the present invention.
Wherein, sequence start-up portion acquires one group of three point Dixon echo, and subsequent repetitive unit acquires N-1 group two o'clock Dixon
Echo is the TE=Δ Δ f/2 of τ=1/ with the time interval of phase echo and reverse phase echo, applies phase before each group echo samples and compile
Code and selects layer direction phase encoding gradient at gradient, applies the phase encoding gradient of polarity reversion after sampling and layer direction phase is selected to compile
Code gradient applies luffing in three gradient directions after last group of echo acquirement and damages phase gradient to eliminate remaining transverse magnetic
Change vector.
Specific embodiment
To keep the technical problems solved, the adopted technical scheme and the technical effect achieved by the invention 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 limiting the invention.It also should be noted that for ease of description, attached drawing
In only some but not all of the content related to the present invention is shown.
One, the principle of the present invention
Medical magnetic resonance imaging instrument usually by magnet, industrial personal computer, console, gradient coil, radio-frequency coil, RF power amplification and
The hardware cells such as gradient power amplifier are constituted.Pulse train module shown in figure one to figure three is loaded into industrial personal computer by console to control
Each hardware cell realizes excitation, space encoding and the acquisition of human body magnetic resonance signal, the data processing installed on console host
Module carries out primary phase correction, image reconstruction, phase unwrapping and field inhomogeneities (Δ B to magnetic resonance signal0) correction, amplitude
Correction is separated with water rouge.Entire data acquisition and processing (DAP) process executes automatically according to scanning process shown in figure four.
Firstly, according to prescan needs, by console on industrial personal computer sequencer shown in loading figure one it is apparent
Lateral relaxation timeCycle tests, the sequence include the units such as slice selective gradient, frequency encoding gradient and echo acquirement.
First in human body positioning as upper selection imaging thick-layer, setting echo time TE takes different time numerical value and is met between 1ms and 1s
TE=n/ Δ f condition (n is natural number), then the echo amplitude of different TE acquisition is based onCarry out Nonlinear Quasi
It closes and obtainsHere I is the magnetization vector of water rouge, I0For I equilibrium state initial value.Then, according to the vortex of gradient system
Field characteristic carries out preemphasis to gradient waveform.
Then, loaded on sequencer by console three dimensional chemical shown in Fig. 3 displacement imaging sequence module or
Two-dimensional chemical shown in Fig. 2 is displaced imaging sequence module.The module includes 900Excitation pulse, slice selective gradient Gs, phase code ladder
Spend Gp2, positive-negative polarity frequency encoding gradient GrAnd the units such as echo acquisition, wherein three-dimensional version further includes selecting layer direction phase
Encode gradient Gp1, echo time TE=1/ Δ f/2, and the time interval Δ being arranged between positive-negative polarity gradient are set in sequence
The Δ of τ=1/ f/2.Same phase (or reverse phase) the echo string length that single-shot is arranged in sequential parameter table is L, and frequency coding is arranged
Direction, phase-encoding direction and to select the data point in layer direction be respectively Dim1, Dim2 and Dim3, other imaging parameters can refer to often
Advise the setting of GRE T1WI imaging requirements.The chemical shift imaging sequence carries out fractional scanning, each reverse phase with multiple mode of excitation
(or same phase) echo carries out phase code by mode shown in figure six or figure seven, and the total degree of phase code circulation is Dim2/
L.K-space is divided into L region by L value, and first same phase (or reverse phase) echo fills k-space central area, second same phase
(or reverse phase) echo fills immediate area, and subsequent each same phase (or reverse phase) echo is sequentially filled each region in periphery.In addition, reading ladder
Spend k-space center line (k under polarity turn around conditiony=0) or central area or entire k-space repeated acquisition are primary and separately store
For a R-matrix.With phase images and the corresponding k-space data of reverse phase image, storage is two-dimensional complex number respectively on console
Matrix (Dim1 × Dim2) or three-dimensional complex matrix (Dim1 × Dim2 × Dim3).For three-dimensional version, console data processing mould
Block first along selecting layer direction to carry out one-dimensional discrete Fourier transform, obtains the k-space complex matrix of each imaging level.For every
A imaging level, reverse phase echoWith same phase echoTheoretical modeling it is as follows：
T refers to current phase code circulation step in above formula, and N arrives the round numbers of 2L range, φ 10It (r) is proton magnetization vector
Initial phase, φ (r) is the phase error mainly generated by Magnetic field inhomogeneity effect,Item is excellent for carrying out to echo amplitude
Change compensation, Mw(r) and Mf(r) the proton magnetization vector for respectively indicating water and fat in imaging region, in three-dimensional space encoding condition
Under can be described as：
Field inhomogeneities effect in formula (1) and (2) during TE is not ignored, this is because TE is needing many imagings
Actually it can not usually reach several milliseconds even ten milliseconds or more close to zero in system, and gtadient echo can neither reunion
Displacement study effect can not meet again an inhomogeneous broadening effect.Under the conditions of the TE=Δ Δ f/2 of τ=1/, formula (1) and (2) are reduced to
In above formula,
Here we defineIt is measured based on frontA can be calculated in value.
In addition, can determine that the first two echo and the relationship of other echoes are as follows from formula (5) to (8)：
As it can be seen thatWithBetween amplitude and phase relationship be quite analogous toWithBetween amplitude and phase
Relationship, therefore similar data processing side can be used with reverse phase echo with phase to each group in the echo of each radio-frequency drive
Formula.
Data processing module starting in the case where gradient system lacks vortex field and Maxwell field inhibits function is primary
Phase correction module, first to reverse phase echoWith same phase echoIt is preliminary to carry out vortex field and Maxwell's field phase school
Just, implementation is as described below：
A. it selectsKy=0 line is after the one-dimensional discrete inverse Fourier transform of frequency coding direction and calculates amplitude and is greater than
The phase of the 10% complex data point of maximum value.
B. linear fit is carried out to gained phase value in step A, obtains slope Δ φ respectively0With intercept θ0。
C. it selectsKy=0 line calculates amplitude after the one-dimensional discrete inverse Fourier transform of frequency coding direction and is greater than most
The phase for the 10% complex data point being worth greatly.
D. linear fit is carried out to gained phase value in step C automatically, obtains slope Δ φ respectively1With intercept θ1。
E. to allAlong frequency coding direction carry out one-dimensional discrete inverse Fourier transform after multiplied byAgain
One-dimensional discrete Fourier transform is carried out, is updated allWherein n is numbered at frequency coding direction number strong point.
F. to allAlong frequency coding direction carry out one-dimensional discrete inverse Fourier transform after multiplied byAgain
It carries out one-dimensional discrete Fourier transform and carries out time reversal and calculate conjugate complex number, update all
Then, from reverse phase (or same phase) echo(or) in choose two of them in frequency encoding gradient polarity
K-space center line (the k acquired respectively in the negative situation that is positivey=0) one-dimensional discrete is carried out along frequency coding direction to become against Fourier
Array P and P` are obtained after changing, and are calculatedHereIndicate Pi,jConjugate complex number, i and j are respectively indicated
Number of the data point along frequency coding and phase-encoding direction.By reverse phase (or same phase) echo(or) filling k it is empty
Between array along frequency coding direction carry out one-dimensional discrete inverse Fourier transform and multiplied byIt is carried out again along phase-encoding direction
One-dimensional discrete inverse Fourier transform, the reverse phase image S after obtaining phasing0(or with phase images S1), it is finally (or anti-to same phase
Phase) echo(or) the k-space array of filling carries out the same phase images that are updated of two-dimensional discrete inverse Fourier transform
S1(or reverse phase image S0)。
The probability of happening of above-mentioned phasing wound the purpose is to reduce phase is to guarantee that phase unwrapping algorithm is sufficiently effective
And operation time is reduced, because the common phase unwrapping algorithm in the field MRI (such as cut by polynomial fitting method, region growth method and branch
Method etc.) efficiency is relatively low and is insufficient effective when noise and insufficient sampled point.Then, data processing module starts
Phase unwrapping and correction module, theoretical basis and implementation are as described below：
Since there are amplitude fading occurs during an additional Δ τ for each reverse phase echo previous compared with phase echo
A and phase error phi, reverse phase figure S0With same phasor S1It can be described as：
Here SwAnd SfWater and fat components in image pixel are respectively indicated, they and MwAnd MfIt is directly proportional,Including reverse phase
The initial phase of figure and the phase that field inhomogeneities, vortex field and Maxwell field generate during TE and (2N-2) Δ τ
Error,Mainly by first reverse phase echo (i.e. ky=0 line) phase error during TE determines.
By the phase in formula (11)By algorithm stream shown in figure five
The quick accurate phase unwrapping of Cheng Jinhang, then to reverse phase image S0It eliminatesIt is as follows：
When with κ=Re (S`0)/|S`0| determine (Sw-Sf) symbol when, formula (13) can also be written as
S`0=κ | S0|=Sw-Sf (14)
And to same phase images S1It is as follows to eliminate phase：
S`1=| S1|=(Sw+Sf)·A (15)
Then, water rouge separation module is based on formula (14) and formula (15) calculates and generates water as SwWith fat as SfIt is as follows：
In this way, four sub-pictures of our available elimination Magnetic field inhomogeneity effects, i.e., with phasor S`0, reverse phase figure S`1, water
As SwWith fat as Sf。
The spatial distribution of A is generally negligible in formula (16) and (17), but in high field intensity equipment local magnetic susceptibility effect compared with
In the case where big, the spatial distribution of A can not be ignored, and otherwise may cause the separation of water rouge not exclusively, for this purpose, pulse train module
Sequence shown in offer figure eight and figure nine is spare, and the start-up portion of the sequence designs the Dixon echo of three phases for measuring A
Distribution, wherein third echo is only filled with the k-space line of k-space central area Dim2/N, and data processing module is still pressed aforementioned
Mode carries out phasing and discrete inverse Fourier transform, as a result as follows：
Meanwhile after aforementioned phasingWithMiddle Dim2/L k-space line in extraction k-space central area,
It is obtained after discrete inverse Fourier transform：
It is as follows that low resolution A distribution map is obtained from formula (18) and formula (19)：
Then it is Dim1 × Dim2 matrix by A linear interpolation, is achieved with water rouge based on formula (16) and formula (17) in this way and fills
Divide isolated image.It is filled with twice since the corresponding k-space center of reverse phase figure is practical, therefore signal noise ratio (snr) of image obtains further
It improves.
Above-mentioned chemical shift imaging technology is greatly improved the scan efficiency of chemical shift imaging and overcomes MRI machine
Hardware deficiency adverse effect.
Two, embodiment
It is installed at water rouge discrete pulse block and data on the console host of 1.5T medical magnetic resonance imager
Manage module, including primary phase correction, image reconstruction, phase unwrapping and correction, amplitude correction and water rouge such as separate at the submodules, press
It is executed automatically according to scanning process shown in figure four.
Firstly, passing through console apparent lateral relaxation time shown in loading figure one on industrial personal computer sequencer
(T2*) cycle tests, first in human body positioning as upper selection imaging thick-layer, setting echo time TE takes difference between 1ms and 1s
Time numerical value simultaneously meets TE=n/ Δ f condition (n is natural number), then is based on to the echo amplitude of different TE acquisitionCarry out nonlinear fitting acquisitionThen, gradient waveform is carried out according to the vortex field characteristic of gradient system
Preemphasis.Then, water rouge separate picture is generated after water rouge discrete pulse sequence and data processing module successively execute.
Embodiment 1：Enhancing scanning, two-dimensional imaging mode.
When enhancing scanning, referring to the representative value of clinically routine SPGR sweep parameter, shown in setting figure two at
As sequential parameter, such as Dim1=192, Dim2=161, TR=160ms, L=4, X%=60%, TE=Δ τ=4.4ms.Operation
The two-dimensional imaging sequence simultaneously acquires data by mode shown in figure six, and wherein the k-space filling mode of reverse phase echo is with the feelings of L=4
It is described as follows for condition：
The space A1.k is divided into four storage areas (C, S, P and V), stores central area data and the week of k-space respectively
Each area data in side, as shown in figure 6.
A2. the central area that first reverse phase echo filling k-space C is indicated.
A3. the neighboring area that second reverse phase echo filling k-space S is indicated.
A4. the neighboring area that third reverse phase echo filling k-space P is indicated.
A5. the neighboring area that the 4th reverse phase echo filling k-space V is indicated.
Correspondingly, the PE system of reverse phase echo as shown in figure 6, is described as follows：
B1. phase code sum is set as Dim2=2m+1, while setting k-space filling proportion as X%, then for upper half of k
Space, coded number shared by each region in periphery are m/4, and coded number shared by central area is m/4+1.Each region phase code ladder
Degree variation range is respectively labeled as by order from top to bottom：PM—Pm-m/4+1；Pm-m/4—Pm-m/2+1；Pm-m/2—Pm-3m/4+1；
Pm-3m/4—P1.Phase encoding gradient amplitude is from PmTo P1Successively successively decrease, stepping is-Gp/m/2.Then, first reverse phase is returned
Wave, phase code is gradually set as P when each phase code recyclesm-3m/4To P1；For second reverse phase echo, each phase
Phase code is gradually set as P when coding cyclem-m/2To Pm-3m/4+1；For third reverse phase echo, each phase code circulation
When phase code be gradually set as Pm-m/4To Pm-m/2+1；For the 4th reverse phase echo, phase is compiled when each phase code recycles
Code is gradually set as PmTo Pm-m/4+1。
B2. for lower half of k-space, it has been only filled with central area C, remaining region does not refill；Each phase code is followed
Phase code is gradually set as P when ring2To Pmm, mm=Round [(2m+1) X%]；In the case where needing to provide state of signal-to-noise, in
C repeatable acquisition in heart district domain is primary and is refilled with, and is added up and be averaged with the data of preceding one acquisition.
B3. phase code recycles execution order：In order to alleviate the influence of systematic jitters, the phase code in each region from
It gradually executes, and is alternately performed in upper half of k-space and lower half of k-space, every of acquisition outward close to k-space center
K-space line sequentially stores, and obtains the matrix that two sizes are Dim1 × mm, respectively constitutes the real part and void of a plural array K
Portion.
B4. when it is zero that phase code, which goes to gradient amplitude, i.e. kyGradient is read in=0 the case where, the interior setting of imaging sequence
Polarity reversion is carried out, and acquires echo data again, progress complex conjugate, which is separately stored, after one-dimensional discrete inverse Fourier transform is
One one-dimensional plural array P.
Equally, for same phase echo, we can still carry out phase code and k-space filling using aforesaid way, and only the
Four steps save, and vice versa.
Then, the k-space line (including real and imaginary parts) sequentially stored is arranged again by above-mentioned PE system
The plural array K` that a size is Dim1 × Dim2 is arranged and constructed, tentatively carries out vortex field and Maxwell field in the manner aforesaid
Phasing, and phasing is further carried out in the following manner：
C1. one-dimensional discrete inverse Fourier transform is carried out along frequency coding direction to array K`, extracts corresponding ky=0 row arrow
Amount obtains one-dimensional plural array P`.
C2. the phase error of array P and P` each element is set as Δ φij, can obtain(i=0,1,
2,…,Dim1；J=0).
It C3. will along frequency coding directionMultiplied by each row vector of array K`, and carry out one-dimensional discrete Fourier transform
Array K is updated afterwards.
Finally, image reconstruction can zeroize in usual manner carries out inverse Fourier transform again, here using following manner into
Row：
D1. the k-space line for corresponding to k-space central area C is chosen from K` array, and is carried out inverse Fourier transform and obtained
Array A.
D2. inverse Fourier transform is directly carried out to K` array obtain array B.
D3. to each element of array A and B according to Ci,j=exp [- iangle (Ai,j)]Bi,jObtain new array C.
D4. Fourier transform is carried out to array C, and symmetry principle is conjugated according to k-space and chooses corresponding upper half of k-space
K-space line, seek its complex conjugate and fill array C remainder, obtain new array D.
D5. inverse Fourier transform is carried out to array D and completes image reconstruction.
D6. the separation of water rouge is carried out according to formula (11)-(17).
Sweep time calculates as follows：
M, L and X% are selected according to the timing node of enhancing scanning, realizes image resolution ratio under conditions of guaranteeing signal-to-noise ratio
Optimization.
Separate imaging of water and fat technology of the invention may be implemented completely enhancing scanning in application, either low field at
As in system or High-Field imaging system.Also, in 1.5T imaging system, due to echo time TE=2.2ms, we can be with
N=16 is set, and other parameters are same as above, then Tscan=0.96 (second), this may be implemented separate imaging of water and fat technology of the invention and exists
Application in abdominal contrast enhancement scanning.
Embodiment 2：Non-reinforcing scanning, three-dimensional imaging mode.
In non-reinforcing scanning, referring to the representative value of clinically routine 3D SPGR sweep parameter, it is arranged shown in figure three
Three-dimensional imaging sequential parameter, such as Dim1=256, Dim2=160, Dim3=32, L=4, TR=60ms, TE=Δ τ=
4.4ms, the time span of phase encoding gradient are limited within Δ τ/2.It runs the three-dimensional imaging sequence and acquires k-space number
According to wherein the k-space filling mode of reverse phase echo is described as follows in case where M=4：
A1. by selecting layer direction phase code order to extract two-dimentional k-space, four storage areas (C, S, P and V) point are divided into
Each region of central area data and periphery that k-space Yong Yu not stored, as shown in figure seven.
A2. the central area that first reverse phase echo filling k-space C is indicated.
A3. the neighboring area that second reverse phase echo filling k-space S is indicated.
A4. the neighboring area that third reverse phase echo filling k-space P is indicated.
A5. the neighboring area that the 4th reverse phase echo filling k-space V is indicated.
Correspondingly, the PE system of reverse phase echo is described as follows as shown in figure seven：
B1. phase code sum is set as Dim2=2m+1, then for upper half of k-space, each region in periphery is shared to be compiled
Yardage is m/4, and coded number shared by central area is m/4+1.Each region phase encoding gradient variation range is by order from top to bottom
It is respectively labeled as：Pm—Pm-m/4+1；Pm-m/4—Pm-m/2+1；Pm-m/2—Pm-3m/4+1；Pm-3m/4—P1.Phase encoding gradient amplitude is from Pm
To P1Successively successively decrease, stepping is-Gp/m/2.Then, for first reverse phase echo, phase code when each phase code recycles
Gradually it is set as Pm-3m/4—P1；For second reverse phase echo, phase code is gradually set as when each phase code recycles
Pm-m/2—Pm-3m/4+1；For third reverse phase echo, phase code is gradually set as P when each phase code recyclesm-m/4—
Pm-m/2+1；For the 4th reverse phase echo, phase code is gradually set as P when each phase code recyclesm—Pm-m/4+1。
B2. for lower half of k-space, each region phase encoding gradient variation range is marked respectively by order from top to bottom
For：P2—P3m/4；Pm-3m/4+1—Pm-m/2；Pm-m/2+1—Pm-m/4；Pm-m/4+1—Pm.Phase encoding gradient amplitude is from P2To PmSuccessively
It is incremented by, stepping is+Gp/m/2.Then, for first reverse phase echo, phase code is gradually arranged when each phase code recycles
For P2—Pm-3m/4；For second reverse phase echo, phase code is gradually set as P when each phase code recyclesm-3m/4+1—
Pm-m/2；For third reverse phase echo, phase code is gradually set as P when each phase code recyclesm-m/2+1—Pm-m/4；For
4th reverse phase echo, phase code is gradually set as P when each phase code recyclesm-m/4+1—Pm。
B3. phase code recycles execution order：In order to alleviate the influence of systematic jitters, the phase code in each region from
It gradually executes, and is alternately performed in upper half of k-space and lower half of k-space, every of acquisition outward close to k-space center
K-space line sequentially stores, obtain size be Dim1 × Dim2 complex matrix K, real and imaginary parts size be Dim1 ×
Dim2。
B4. central area C repeats a phase code circulation, and is arranged and reads gradient progress polarity reversion, adopts again
Collect echo data, separately storing after one-dimensional discrete inverse Fourier transform is array P.
B5. under three-dimensional imaging mode, for each phase loop (outer circulation), execution selects the phase code in layer direction to follow
Ring (interior circulation), each amplitude incremented by successively for selecting layer direction phase encoding gradient reach Dim3 until cycle-index, obtain big
Small is Dim1 × Dim2 × Dim3 complex matrix K, and real and imaginary parts size is Dim1 × Dim2 × Dim3.
Equally, for same phase echo, we still phase code can be carried out using aforesaid way and k-space is filled, but the
Four steps save, and vice versa.
Finally, being arranged again by above-mentioned PE system the k-space line (including real and imaginary parts) sequentially stored
A new plural array K` is arranged and constructed, vortex field and Maxwell field phasing is tentatively carried out in the manner aforesaid, goes forward side by side
One step carries out phasing in the following manner：
C1. one-dimensional discrete inverse Fourier transform is carried out along frequency coding direction to array K`, is extracted along frequency coding direction
The first row vector of central area C carries out complex conjugate, obtains one-dimensional plural array P`.
C2. the phase error of array P and P` each element is set as Δ φij, can obtain(i=0,1,2 ...,
Dim1；J=0), and one-dimension array X1 is constituted.
C3. to central area, remaining each row vector repeats above-mentioned (1)-(2) data handling procedure, obtains a series of arrays
X1, X2, X3......, then storing after being averaged to these arrays is array X.
C4. array X multiplied by each row vector of array K` and is subjected to one-dimensional discrete Fourier transform along frequency coding direction
Array K` is updated afterwards.
Finally, carrying out image reconstruction by two dimension or 3 d-dem inverse Fourier transform to array K`, and according to formula (11)-
(17) separation of water rouge is carried out.
The case where being set as other values for L, we can equally be quickly obtained water rouge separate picture in a similar way, imaging
Time shorten to the 1/N of usual manner.In general, vortex field and field inhomogeneities will not be led in the case where L smaller (such as L=4)
Cause image that apparent geometric distortion occurs.In the imaging system of gradient system for being equipped with anti-vortex function, L may be configured as 8 very
To 16, there is no obvious geometric distortion.Sweep time calculates as follows：
Three, innovative point of the invention
In the present invention, using supper-fast chemical shift imaging sequence, signal analysis model, echo amplitude attenuation compensation method
It is twined with the quick solution of phase and accurate alignment technique is used to realize that water rouge separates enhancing scanning and thin layer on magnetic resonance imaging system
Separate imaging of water and fat.
It is formed using the alternate frequency encoding gradient of 2N positive-negative polarity by N group water in 2-dimensional gradient echo sequence basis
The gtadient echo string that rouge is alternately constituted with phase echo and reverse phase echo.N number of same phase echo is carrying out Gradient Phase coding respectively, with
Correspondingly k-space be divided into N number of region, first echo fills central area, and next echo is sequentially filled immediate area,
And same phasor is reconstructed using part Fourier mode, to improve N times of scan efficiency.N number of reverse phase echo carries out ladder respectively
Phase code is spent, correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is successively
Immediate area is filled, and reverse phase figure is reconstructed using part Fourier mode, to improve N times of scan efficiency.
It is formed using the alternate frequency encoding gradient of 2N positive-negative polarity by N number of water in 3-dimensional gradient echo sequence basis
The gtadient echo string that rouge is alternately constituted with phase echo and N number of reverse phase echo.N number of same phase echo carries out Gradient Phase coding respectively,
Correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled close to area
Then domain carries out 3 d-dem inverse Fourier transform and generates a series of same phasors of thin layer.N number of reverse phase echo carries out gradient phase respectively
Position coding, correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled
Then immediate area carries out 3 d-dem inverse Fourier transform and generates a series of same phasors of thin layer；
General theoretical model is established to gtadient echo string in spatial frequency domain and image area respectively：
Respectively to describe influence of the magnetic field bump to spatial frequency domain and image area signal amplitude and phase, and
Magnetic field bump is to phase of echo and amplitude during the TE that above-mentioned model is energized into the formation of first echo to radio-frequency pulse
Influence is corrected.
Apparent lateral relaxation time of the echo amplitude based on imaging regionTest value compensates correction, survey used
Try sequence include the units such as slice selective gradient, frequency encoding gradient and echo acquirement, and by water mould be placed in imaging region range or
It directly positions in human body as upper selection imaging thick-layer, setting echo time TE takes different time numerical value and expired between 1ms and 1s
Sufficient TE=n/ Δ f condition (n is natural number) is then based on single exponential function to the echo amplitude of different TE and carries out nonlinear fitting
It obtains
K-space center line is selected to be greater than the complex data point of maximum value 10% to amplitude after your one-dimensional Fourier transformation
Phase carries out primary phase correction by linear fit method；
From reverse phase (or same phase) echo I2N-2(or I2N-1) in choose two of them and be positive and forsake one's love in frequency encoding gradient polarity
K-space center line (the k acquired respectively under conditiony=0) pass through after frequency coding direction progress one-dimensional discrete inverse Fourier transform
Complex operation obtains the phase error of center line, then laggard in one-dimensional discrete inverse Fourier transform to all k-space lines accordingly
Row phasing, to eliminate the effect of anisotropy of bipolarity frequency encoding gradient；
From reverse phase (or same phase) echo I2N-2(or I2N-1) in choose two of them and be positive and forsake one's love in frequency encoding gradient polarity
Central area k-space line is acquired under condition respectively, along frequency coding direction carry out one-dimensional discrete inverse Fourier transform respectively after pass through
Complex operation obtains the phase error of each line in central area and averaging, then accordingly to all k-space lines in one-dimensional discrete against Fu
Phasing is carried out after vertical leaf transformation, to eliminate the effect of anisotropy of bipolarity frequency encoding gradient；
Image reconstruction and water are carried out respectively to the same phase echo and the corresponding k-space data of reverse phase echo that acquire twice
Rouge separation, then water picture and fat as being overlapped respectively, to thoroughly eliminate irreducible phase errors.
The related phase error of magnetic field bump carries out phase by a kind of exact algorithm based on discontinuous path integral
Position solution is eliminated by the plural number operation of same phasor and reverse phase figure again after twining, and then water is as SwWith fat as SfIt counts according to the following formula
It calculates and generates：
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, those skilled in the art should understand that：Its is right
Technical solution documented by foregoing embodiments is modified, or is equally replaced to some or all of the technical features
It changes, the range for technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution.
Claims (6)
1. a kind of supper-fast segmented single-shot water rouge separation method, which is characterized in that the supper-fast segmented single swashs
Shampoo rouge separation method includes the following steps：
Step S100：According to prescan needs, through console when loading apparent transverse relaxation on industrial personal computer sequencer
BetweenCycle tests；
Step S200：Two-dimensional chemical displacement imaging sequence module is loaded on sequencer by console；
It is same by N group water rouge using the alternate frequency encoding gradient formation of 2N positive-negative polarity in 2-dimensional gradient echo sequence basis
The gtadient echo string that phase echo and reverse phase echo are alternately constituted；N number of same phase echo carries out Gradient Phase coding respectively again, therewith phase
Ground k-space is answered to be divided into N number of region, first echo fills central area, and next echo is sequentially filled immediate area, and adopts
Same phasor is reconstructed with part Fourier mode；N number of reverse phase echo carries out Gradient Phase coding respectively, and correspondingly k is empty
Between be divided into N number of region, first echo fills central area, and next echo is sequentially filled immediate area, and uses part
Fourier mode reconstructs reverse phase figure；Or
It is same by N number of water rouge using the alternate frequency encoding gradient formation of 2N positive-negative polarity in 3-dimensional gradient echo sequence basis
The gtadient echo string that phase echo and N number of reverse phase echo are alternately constituted；N number of same phase echo carries out Gradient Phase coding respectively, therewith
Correspondingly k-space is divided into N number of region, and first echo fills central area, and next echo is sequentially filled immediate area, so
3 d-dem inverse Fourier transform is carried out afterwards generates a series of same phasors of thin layer；N number of reverse phase echo carries out Gradient Phase volume respectively
Code, correspondingly k-space is divided into N number of region, and first echo fills central area, next echo be sequentially filled close to
Then region carries out 3 d-dem inverse Fourier transform and generates a series of same phasors of thin layer；
Step S300：Using the general theoretical model established in spatial frequency domain and image area to gtadient echo string, radio frequency is corrected
Influence of the magnetic field bump to phase of echo and amplitude during the TE that pulse excitation is formed to first echo：
Wherein, the Δ f/2 of Δ τ=1/, Δ f indicate that the resonance frequency difference of fat and water, t refer to current phase code circulation step, N
The round numbers of 2L range, φ are arrived 10(r) be proton magnetization vector initial phase, φ (r) is mainly by Magnetic field inhomogeneity effect
The phase error of generation,Item is for optimizing compensation to echo amplitude；
SwAnd SfWater and fat components in image pixel are respectively indicated, they and MwAnd MfIt is directly proportional,It indicates to include reverse phase figure
Initial phase and the phase error that field inhomogeneities, vortex field and Maxwell field generate during TE and (2N-2) Δ τ,Mainly by filling K space center line, i.e. ky=0 line, first reverse phase echo, the phase error during TE determine；
Mw(r) and Mf(r) the proton magnetization vector for respectively indicating water and fat in imaging region, under three-dimensional space encoding condition
It can be described as：
Here,WithRespectively indicate Mw(r) and Mf(r) initial value, Gx, GyAnd GzThe gradient for respectively referring to x, y and z directionss is strong
Degree；
Step S400：Water is as SwWith fat as SfIt calculates and generates according to the following formula：
Hereκ indicates (Sw-Sf) symbol.
2. a kind of supper-fast segmented single-shot water rouge separation method according to claim 1, which is characterized in that step
In S100, apparent lateral relaxation time of the echo amplitude based on imaging regionTest value compensates correction, used test sequence
Column include slice selective gradient, frequency encoding gradient and echo acquirement unit, and water mould is placed in imaging region range or is directly existed
Thick-layer is imaged as upper selection in human body positioning, and setting echo time TE takes different time numerical value between 1ms and 1s and meets TE=
N/f condition, n are natural number, are then based on single exponential function to the echo amplitude of different TE and carry out nonlinear fitting acquisition
3. a kind of supper-fast segmented single-shot water rouge separation method according to claim 1, which is characterized in that step
In S200, k-space center line is selected to be greater than the complex data point of maximum value 10% to amplitude after one-dimensional inverse Fourier transform
Phase carries out primary phase correction by linear fit method.
4. a kind of supper-fast segmented single-shot water rouge separation method according to claim 1, which is characterized in that step
In S300, from reverse phase echo I2N-2Or with phase echo I2N-1Middle selection two of them are positive condition of forsaking one's love in frequency encoding gradient polarity
The lower k-space center line k acquired respectivelyy=0 after frequency coding direction progress one-dimensional discrete inverse Fourier transform, passes through plural number
Operation obtains the phase error of center line, and phase is then carried out after one-dimensional discrete inverse Fourier transform to all k-space lines accordingly
Bit correction, to eliminate the non-equilibrium effect of bipolarity frequency encoding gradient.
5. a kind of supper-fast segmented single-shot water rouge separation method according to claim 1, which is characterized in that step
In 300, from reverse phase echo I2N-2Or with phase echo I2N-1Middle selection two of them are positive condition of forsaking one's love in frequency encoding gradient polarity
Under, acquire central area k-space line respectively, along frequency coding direction carry out one-dimensional discrete inverse Fourier transform respectively after by multiple
Number operations obtain phase error and the averaging of each line in central area, then accordingly to all k-space lines in one-dimensional discrete against Fourier
Phasing is carried out after leaf transformation, eliminates the non-equilibrium effect of bipolarity frequency encoding gradient.
6. a kind of supper-fast segmented single-shot water rouge separation method according to claim 1, which is characterized in that step
In S300, image reconstruction and water are carried out respectively to the same phase echo and the corresponding k-space data of reverse phase echo that acquire twice
Rouge separation, then water picture and fat eliminate irreducible phase errors as being overlapped respectively.
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