CN102727201B - Magnetic resonance system and water-fat separation imaging method and device thereof - Google Patents
Magnetic resonance system and water-fat separation imaging method and device thereof Download PDFInfo
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Abstract
The invention discloses a magnetic resonance system and a water-fat separation imaging method and device thereof. The method comprises the following steps of: collecting the magnetic resonance images of water and fat in the body tissue of a patient; using at least two anti-phase or same-phase magnetic resonance images to calculate an additional phase; selecting any one of the images to carry out signal judgment on the image to identify a signal point; unwrapping the additional phase of the identified signal point; and combining the anti-phase images in the magnetic resonance images after being unwrapped with the same-phase images to obtain the images of water and fat. The magnetic resonance system and the water-fat separation imaging method and device thereof can increase the speed of phase unwrapping, thereby quickly generating separated water images and fat images.
Description
Technical field
The present invention relates to a kind of magnetic resonance system, relate in particular to method for separate imaging of water and fat, the device of magnetic resonance system.
Background technology
In nuclear magnetic resonance, the hydrogen proton in the fat in tissue is different with the residing molecule environment of hydrogen proton in other non-fat, makes their resonant frequency have fine difference, is called chemical shift.Dixon proposes to utilize chemical shift effect to obtain water images and the fat image in nuclear magnetic resonance the earliest.Dixon side's ratio juris is that each voxel in hypothesis human body only has water and two kinds of compositions of fat, thereby each pixel in magnetic resonance image (MRI) is synthetic by the macroscopic magnetization vector of the macroscopic magnetization vector fat of water.According to chemical shift principle, the hydrogen proton in water and fat is subject to after radio-frequency pulse excitation simultaneously, and their relaxation time is also different, and in different echo time acquired signal, water and fat show different signal intensitys.Thereby on conventional spin-echo sequence basis, by regulating the different echo times, can in theory accurately obtain any angle of water and two magnetization vectors of fat.
And in practical engineering application due to system noise, eddy current effect, main field inhomogeneities, Maxwell follow and tissue between, between tissue and air, pcrmeability variation etc. all can cause Magnetic field inhomogeneity, the inhomogeneities in magnetic field can cause again the serious distortion of phase place, and impact therefore how to eliminate these errors becomes the key of Dixon algorithm success or failure.
As the improvement to Dixon method, a kind of line-of-sight course of the phase error correction based on non-uniform field is suggested, the party's ratio juris is to obtain two width magnetic resonance image (MRI) of water and the synchronous secondary magnetic resonance image (MRI) of fat and antiphase, according to two width magnetic resonance image (MRI) of antiphase, calculate the additive phase that magnetic field bump causes, then try to achieve water images and fat image together with synchronous image.Line-of-sight course also can adopt the image of a width antiphase and two synchronous images to carry out water fat separation of images.
The weak point of this line-of-sight course is: it is separated that the additive phase of being tried to achieve by the image of two width antiphases can not directly be used for carrying out water fat, because the additive phase for being caused by Magnetic field inhomogeneity may surpass a territory, for example surpass ± π, there is phase-wrapping phenomenon, therefore must go to reel to phase place.For phase place being gone to reel, in prior art, the additive phase of each point in image is taken turns doing to reel and process, speed is very slow.
Summary of the invention
The main technical problem to be solved in the present invention is, a kind of magnetic resonance system and method for separate imaging of water and fat thereof, device are provided, and improves the speed of phase unwrapping, thereby generates quickly separated water images and fat image.
According to an aspect of the present invention, provide a kind of method for separate imaging of water and fat of magnetic resonance system, comprising:
Water in collection patient body tissue and fatty magnetic resonance image (MRI), described magnetic resonance image (MRI) comprises the magnetic resonance image (MRI) of the synchronous magnetic resonance image (MRI) of at least one pair and at least two width antiphases, or described magnetic resonance image (MRI) comprises magnetic resonance image (MRI) and at least two synchronous magnetic resonance image (MRI) of at least one secondary antiphase;
Utilize at least two width antiphases or at least two synchronous magnetic resonance image (MRI) to calculate additive phase;
Choose and appoint piece image, image is carried out to signal judgement, identify signaling point;
The additive phase of the signaling point identifying is gone to reel;
The image of the antiphase in the magnetic resonance image (MRI) of going after coiling is drawn to water images and fat image in conjunction with synchronous image.
According to a further aspect in the invention, provide a kind of separate imaging of water and fat device of magnetic resonance system, comprising:
Image capture module, for gathering the water of patient body tissue and fatty magnetic resonance image (MRI), described magnetic resonance image (MRI) comprises the magnetic resonance image (MRI) of the synchronous magnetic resonance image (MRI) of at least one pair and at least two width antiphases, or described magnetic resonance image (MRI) comprises magnetic resonance image (MRI) and at least two synchronous magnetic resonance image (MRI) of at least one secondary antiphase;
Additive phase computing module, for utilizing at least two width antiphases or at least two synchronous magnetic resonance image (MRI) to calculate additive phase;
Signaling point identification module, appoints piece image for choosing, and image is carried out to signal judgement, identifies signaling point;
Go the module of reeling, for the additive phase of the signaling point identifying is gone, reel;
Water fat separation module, for going the image of the antiphase of the magnetic resonance image (MRI) after coiling to draw water images and fat image in conjunction with synchronous image.
The present invention also provides a kind of magnetic resonance system, comprises above-mentioned separate imaging of water and fat device.
Accompanying drawing explanation
Fig. 1 is the structural representation of magnetic resonance system in an embodiment of the present invention;
Fig. 2 is the structured flowchart of separate imaging of water and fat device in an embodiment of the present invention;
Fig. 3 removes to reel the structured flowchart of module in an embodiment of the present invention;
Fig. 4 is the structured flowchart of region growing unit in an embodiment of the present invention;
Fig. 5 is the flow chart of separate imaging of water and fat in an embodiment of the present invention;
Fig. 6 is that in an embodiment of the present invention, region growing method is removed the flow chart of reeling;
Fig. 7 is the flow chart of signaling point identification in an embodiment of the present invention.
The specific embodiment
Below by the specific embodiment, by reference to the accompanying drawings the present invention is described in further detail.
Please refer to Fig. 1, in one embodiment, magnetic resonance system 100 comprises magnet system 110, gradient magnetic system 120, radio system 130 and control and processing system 140.Magnet system 110 comprises magnet 111, gradient magnetic field coil 112, transmitting coil 113 and receiving coil 114, magnet 111 can adopt permanent magnet, superconducting magnet or resistive magnet, for for example, providing a constant main field to object under test (patient), gradient magnetic field coil 112 is for producing a gradient magnetic at three dimensions, transmitting coil 113 is for providing radio frequency (RF) pulse to excite nuclear spin in object under test, and receiving coil 114 is for detection of the echo-signal of being sent by determinand.Gradient magnetic system 120 is connected with control and processing system 140, for driving gradient magnetic field coil 112 under the control in control and processing system.Radio system 130 is connected with control and processing system 140, for producing RF pulse after-applied to transmitting coil 113 through processing and amplifying under the control in control and processing system.
Control and processing system 140 are both for controlling each several part, also for echo-signal is processed.The echo-signal that receiving coil 114 is detected is transferred to be controlled and processing system 140, control and processing system 140 comprise separate imaging of water and fat device, according to echo-signal, obtain magnetic resonance image (MRI), magnetic resonance image (MRI) is processed to the separated water images of rear acquisition and fat image.
In embodiments of the present invention, the principle of water fat separation is: adopt two width images of antiphase and the piece image of synchronous piece image or synchronous two width images and antiphase, if there is no the error that magnetic resonance system Magnetic field inhomogeneity causes, by antiphase or synchronous two width image additions, subtract, can obtain the image of water and fatty image.But due to magnetic resonance system Magnetic field inhomogeneity or other reasons, can on the macroscopic magnetization vector of water macroscopic magnetization vector fat, produce an additive phase, by antiphase or synchronous two width images, can try to achieve additive phase, after additive phase is gone to reel, again the image of antiphase be drawn to water images and fat image in conjunction with synchronous image.Before additive phase being removed to coiling, first the signaling point in image is identified, in all pixels of image, identify signaling point and noise spot, signaling point is the synthetic of water signal and fat signal, in the follow-up processing of going to reel, only the additive phase of signaling point is gone to reel, saved the time of removing coiling on the one hand, on the other hand, reduced noise spot to follow-up impact of removing coiling, avoided these noise spots going the error propagation of winding process, so the embodiment of the present invention also can effectively suppress the propagation of error, thereby improved the success rate of water fat separation.
Figure 2 shows that the structured flowchart of separate imaging of water and fat device in a kind of embodiment, separate imaging of water and fat device 200 comprises image capture module 210, additive phase computing module 220, signaling point identification module 270, module 230 and water fat separation module 240 go to reel.Image capture module 210 is for gathering the water of patient body tissue and fatty magnetic resonance image (MRI), described magnetic resonance image (MRI) comprises the magnetic resonance image (MRI) of the synchronous magnetic resonance image (MRI) of at least one pair and at least two width antiphases, or described magnetic resonance image (MRI) comprises magnetic resonance image (MRI) and at least two synchronous magnetic resonance image (MRI) of at least one secondary antiphase.Additive phase computing module 220 is for utilizing at least two width antiphases or at least two synchronous magnetic resonance image (MRI) to calculate additive phase.Signaling point identification module 270 is appointed piece image for choosing, and image is carried out to signal judgement, first identifies signaling point.The module 230 of going to reel is reeled for the additive phase of the signaling point identifying is gone.Water fat separation module 240 is for going the image of the antiphase of the magnetic resonance image (MRI) after coiling to draw water images and fat image in conjunction with synchronous image.
In one embodiment, as shown in Figure 3, signaling point identification module 270 comprises amplitude judging unit 271, amplitude judging unit 271 is for comparing the amplitude of the pixel of image and final amplitude threshold, if the amplitude of pixel is more than or equal to final amplitude threshold, think that this pixel is signaling point, if the amplitude of pixel is less than final amplitude threshold, think that this pixel is not signaling point.In another embodiment, as shown in Figure 3, signaling point identification module 270 also comprises phase place judging unit 272, and phase place judging unit 272 is for comparing the phase place of neighbor between two, if both comparative results are less than phase threshold, think that neighbor is signaling point.In a kind of instantiation, phase place judging unit 272 comprises chooses initial seed subelement 272a, seed growth subelement 272b, signaling point number judgment sub-unit 272c and the first phase place threshold increment subelement 272d.Initial seed subelement 272a is used for according to imposing a condition selection initial seed, then the initial seed of acquisition is transferred to seed and increases subelement 272b, seed increases subelement 272b and take initial seed as starting point, according to the first phase threshold of setting, start region growing, the pixel being increased thinks signaling point.Signaling point number judgment sub-unit 272c often completes circulation at seed growth subelement 272b and obtains after signaling point number, whether the signaling point number that judgement adopts phase place determining method to obtain meets the requirements, if undesirable, control the first phase place threshold increment subelement 272d and change the first phase threshold, then control initial seed subelement 272a and seed and increase subelement 272b task again.
In one embodiment, as shown in Figure 3, described in the module 230 of going to reel comprise matching unit 250, described matching unit 250 is for adopting polynomial fitting method to go to reel to additive phase.Signaling point identification module 270 is appointed piece image for choosing, image is carried out to signal judgement, first identify signaling point, the additive phase of the signaling point that then matching unit 250 only identifies signaling point identification module 270 when adopting polynomial fitting method to go to reel to additive phase goes to reel.
In improved embodiment, described in the module 230 of going to reel comprise matching unit 250 and region growing unit 260, described matching unit 250 goes to reel for the additive phase of the signaling point that adopts polynomial fitting method signaling point identification module 270 is identified; Described region growing unit 260 is processed for adopting region growing method to go to reel in the result of going at polynomial fitting method to reel.
In another kind of embodiment, the module 230 of going to reel does not comprise matching unit 250, but adopts the phase place of the 260 pairs of signaling points that identify in region growing unit to go the processing of reeling.
In a kind of instantiation of embodiment as shown in Figure 4, described region growing unit 260 comprises that selected seed subelement 261, seed amplitude judgment sub-unit 262, seed phase place adjust subelement 263, increase go to reel subelement 264 and signaling point and increase judgment sub-unit 265.Selected seed subelement 261 is for the signaling point selected seed definite, and the seed of choosing is delivered to seed amplitude judgment sub-unit 262 judge, if the seed of choosing meets the requirements, seed is delivered to seed phase place and adjusted subelement 263, according to pre-defined rule, the phase place of seed is adjusted, and the phase place after adjusting is as the phase place of seed.By adjusting seed after phase place, deliver to and increase the subelement 264 that goes to reel and carry out region growing according to pre-defined rule.At the growth subelement 264 that goes to reel, increase rear signaling point and increase judgment sub-unit 265 and judge whether that all signaling points are all increased, if finish to increase, otherwise controlled 261 work of selected seed subelement, continued selected seed in not increasing signaling point.
Based on above-mentioned separate imaging of water and fat device, describe the method for separate imaging of water and fat of magnetic resonance system below in detail.
In one embodiment, as shown in Figure 5, method for separate imaging of water and fat comprises the following steps:
Step S1, gather respectively water in patient body tissue and the magnetic resonance image (MRI) of fatty same phase and antiphase, same phase and antiphase refer to the angle between water signal and fat signal in the signal collecting, for example gather the magnetic resonance image (MRI) of a secondary same phase magnetic resonance image (MRI) and two width antiphases, water and fatty phase angle are (π, 0, π) certainly, also can gather the magnetic resonance image (MRI) of several synchronous magnetic resonance image (MRI) and Geng Duo antiphase.Due to Magnetic field inhomogeneity or other poor prognostic causes of magnetic resonance system, will cause image to have an additive phase, additive phase φ
0represent, water and the fatty relative angle gathering be (π, 0, π) three width magnetic resonance image (MRI) are as follows:
Step S2, utilizes the magnetic resonance image (MRI) of two width antiphases to calculate additive phase.By I
1can obtain
, by this value, process (1) formula and just obtain:
I by the two width antiphases of (2) formula
0' and I
2' be divided by, can obtain additive phase, expression formula is as follows:
e
i2φ＝I′
2*conj(I′
0)----------------------------(3)
Step S3, chooses and appoints piece image, and image is carried out to signal judgement, identifies signaling point.For entire image, some pixels are the signaling points being produced by patient's echo, sort signal point comprises the signal of water and fatty signal, synthetic by both, and some pixels be by disturbing (for example patient moves, external interference or system unstable) noise spot that causes.If each pixel is gone to reel, the inevitable used time is longer, and the processing time that causes reeling is long.In the present embodiment, first in all pixels, identify signaling point, while going to reel, only the additive phase of the signaling point identifying is gone to reel.
Step S4, goes to reel to additive phase, while going to reel, only the additive phase of the signaling point identifying is gone to reel.The additive phase causing due to Magnetic field inhomogeneity may surpass a territory, for example, surpass ± π, and phase-wrapping phenomenon occurs, and therefore must go to reel to 2 φ angles in formula (3).When going to reel, can adopt the existing method for winding that goes, also can adopt the method in the present embodiment, first adopt polynomial fitting method to go to reel to additive phase, in the result of then going to reel at polynomial fitting method, adopt region growing method to go to reel and process.
When adopting polynomial fitting method to go to reel to additive phase, can adopt existing multinomial to carry out matching, the prerequisite of polynomial fitting method phase unwrapping is that the phase place of the signaling point in hypothesis image is slowly to change, and it can be obtained by multistage fitting of a polynomial.In the present embodiment, adopt quadratic polynomial fitting formula to be:
2φ
w＝ax+bx
2+cy+dy
2+exy+f -------------(4)
In above formula, x, y are the coordinates in two dimensional image, and a, b, c, d, e, f are fitting coefficients.Concrete implementation procedure is:
(1) first with atan function, obtain 2 φ that reel
wphase place:
2φ
w＝atan(I
3)--------------(5)
(2) formula (4) is obtained to formula (6) to x, y differentiate respectively
(3) front by data fitting formula (6), first with the kurtosis in data after threshold value T0=pi/2 rejecting differentiate, (object is to reject 2 φ
win discrete value), then carry out fitting of a polynomial, what matching adopted is method of least square.F=mean (2 φ wherein
w) (meansigma methods of picture signal point phase place).
(4) obtain after match value, calculate of=2 φ
w-(ax+bx
2+ cy+dy
2+ exy+f), the integral multiple of then according to this phase contrast of, the coiling phase place of signaling point being added and subtracted to 2 π makes of reach minimum.
Adopt polynomial fitting method to go the phase diagram obtaining after coiling to have block discontinuity zone to additive phase, produce island effect, in the result of therefore at polynomial fitting method, additive phase being gone to reel, then adopt region growing method to go to additive phase the processing of reeling.
Region growing method goes the flow process of reeling as shown in Figure 6, comprises the following steps:
Step S41, selected seed step.Selected seed subelement 261 selecting range maximum and adjoint point in not increasing signaling point are that the additive phase point of not reeling is as seed.For initial seed, if do not find satisfactory signaling point, select not increase time large and adjoint point of amplitude in signaling point and be point that additive phase do not reel as seed.
Step S42, seed amplitude determining step.Seed amplitude judgment sub-unit 262 compares the amplitude peak value in the amplitude of the seed of newly choosing and signaling point, if comparative result meets the second predetermined condition, finishes to increase, and does not meet the second predetermined condition and carries out step S43.In a kind of instantiation, calculate the amplitude of seed and difference or the ratio of the amplitude peak value in signaling point newly chosen, when the amplitude of the seed of newly choosing is far smaller than the amplitude peak value in signaling point, the amplitude of the seed of for example newly choosing be less than amplitude peak value 1% or other any can think to be far smaller than value time, think that the seed of newly choosing can not be the signaling point needing, so finish to increase.Certainly, it will be understood by those skilled in the art that the second predetermined condition can also be other conditions of setting as the case may be.
Step S43, by the most contiguous phase bit comparison that increases signaling point of the phase place of the seed of newly choosing and its, if phase place comparative result does not meet the 3rd predetermined condition, performs step S44.Otherwise execution step S45.Phase bit comparison in this step can be phase contrast or the ratio that calculates the phase place of the seed of newly choosing and its most contiguous phase place that increases signaling point, preferably calculate both phase contrasts, the 3rd predetermined condition also can be set with experience as the case may be according to the mode difference comparing, for example, when calculating the phase place of the seed newly choose and it is the most contiguous while increasing the phase contrast of signaling point, the 3rd predetermined condition can be to judge whether phase contrast is greater than 2 π, when being greater than 2 π, phase contrast performs step S44, seed phase place is adjusted, otherwise directly with this seed, carry out region growing.
Step S44, adjusts seed phase place.Seed phase place is adjusted subelement 263 and for the phase place of seed that this is newly chosen, is added/subtract the phase place adjustment of 2 π integral multiples.When the phase place of seed is entered to horizontal phasing control, the multiple that specifically adds/subtract 2 π can be selected according to phase contrast, object be make the phase place of seed newly chosen and the phase contrast of its most contiguous phase place that increases signaling point minimum, for example phase contrast is 5 π, need the phase place of seed to add/subtract the adjustment of 4 π, the phase place after adjusting is as the phase place of the seed of newly choosing.If phase place comparative result meets the 3rd predetermined condition, using the seed of newly choosing as the seed increasing, in step, with this seed, carry out region growing below.
Step S45, increases and goes the step of reeling.Increase and remove to reel subelement 264 for the phase place of the phase place of the seed of growth and its periphery adjacent signaling point is compared successively, if the comparative result of the phase place of the phase place of seed and a certain adjacent signaling point is less than the second phase threshold of setting, this adjacent signaling point is increased, and this adjacent signaling point is classified as to one of seed of next round growth.Phase bit comparison in this step can be the phase difference value that calculates both, can be also the phase place ratio that calculates both, and the second phase threshold also can be set with experience as the case may be according to the mode difference comparing.In a kind of instantiation, calculate the phase contrast of the phase place of seed and the phase place of its periphery adjacent signaling point, the second phase threshold GrowT is an empirical value, such as GrowT, is π/4 or π/8 etc., when phase contrast is less than GrowT, this adjacent signaling point is increased.
If the phase place of seed increasing and the comparative result of the phase place of a certain adjacent signaling point are more than or equal to the second phase threshold of setting, the phase place of this adjacent signaling point is added/subtracts 2 π integral multiples, the multiple that specifically adds/subtract 2 π can be selected according to phase contrast, object is to make both phase contrasts minimum, and then the phase place that adds/subtract after 2 π integral multiples of the phase place of seed and a certain adjacent signaling point is compared, judge whether new comparative result is less than the second phase threshold of setting, if it is will increase/subtract phase place after the 2 π integral multiples new phase as this adjacent signaling point, this adjacent signaling point is increased, and this adjacent signaling point is classified as to one of seed that next round increases.
In this step, the seed for region growing (for comparing) will be excluded when next round increases, and not be used further to comparison and the region growing of next round.
After adopting the seed increasing completeer, this step recirculation once, adopts the seed of the next round growth obtaining in circulation last time to carry out the comparison of adjacent signaling point, and qualified signaling point is increased, and is listed in one of seed that more next round increases.So circulation until do not have adjacent signaling point to be increased, then performs step S46.
Step S46, signaling point increases judgment sub-unit 265 and judges whether that all signaling points are all increased, if finish to increase, otherwise turns to step S41, continues selected seed in not increasing signaling point.
After the scheme that adopts the present embodiment goes 2 φ angles in formula (3) to reel, obtain:
p＝coSθ，θ＝arg(e
iφ)----------------------------(7)
Step S 5, will go the image of two width antiphases after coiling to draw water images and fat image in conjunction with a secondary synchronous image.By I
0' and I
2' multiply each other, and by I ' and formula (7) substitution, obtain water images and fat image is as follows.
Adopting fitting of a polynomial to go the prerequisite of reeling is that in hypothesis image, the phase place of signaling point is slowly to change, after matching, can be the phase unwrapping of 4 π or 6 π to reeling, but still there is the phase-wrapping of 2 π, these exist the place of phase-wrapping can cause last result images is one one, cause island effect, thereby cause the water fat of follow-up mistake separated, making has water signal in fat image, on water images, there is fat signal, be unfavorable for doctor's diagnosis.When result that fitting of a polynomial is gone to reel is updated in an embodiment of the present invention that disclosed region growing goes in method for winding, because removing method for winding, this region growing do not suppose that in image, the phase place of signaling point is slowly to change, can for coiling, be the phase unwrapping of 2 π, island effect is just in time removed in the combination of two kinds of methods, can improve the correctness of follow-up water fat separation, for doctor provides water images and fat image more accurately.
In a further embodiment, going to reel also can adopt separately polynomial fitting method and region growing method, also can adopt existing any phase unwrapping method.
The present embodiment is going first to identify signaling point before coiling, so the accuracy of the signaling point that assurance identifies just becomes extremely important.In instantiation of the present invention, can adopt amplitude determining method to carry out identification signal point, also can adopt phase place determining method to carry out identification signal point, also can adopt the method for both combinations to carry out identification signal point.
Amplitude determining method is that the amplitude of the pixel in image and final amplitude threshold are compared, if the amplitude of pixel is more than or equal to final amplitude threshold, think that this pixel is signaling point, if the amplitude of pixel is less than final amplitude threshold, think that this pixel is not signaling point.
Phase place determining method is that the phase place of neighbor is compared, if both comparative results are less than phase threshold, thinks that neighbor is signaling point.
Describe in detail below amplitude determining method and phase place determining method in conjunction with the embodiment that carries out signaling point identification, its flow process as shown in Figure 7, comprises the following steps:
Step S31, calculates initial amplitude threshold step.Described initial amplitude threshold value equals amplitude peak value in image and the meansigma methods of minimum amplitude value, i.e. initial amplitude threshold estimation value T=(max (I)+min (I))/2, and I is picture amplitude data, then performs step S32.
Step S32, adopts amplitude threshold to carry out segmentation step to pixel.The range value of all pixels in image or gray value and initial amplitude threshold value are compared, obtain first group of collection of pixels G1 and second group of collection of pixels G2, first group of collection of pixels G1 is the collection of pixels that is more than or equal to initial amplitude threshold value, in this set, be signaling point, thereby can obtain the number of signaling point.Second group of collection of pixels G2 is the collection of pixels that is less than initial amplitude threshold value, is noise point.When carrying out pixel segmentation for the first time, the pixel that G1 is greater than T by all gray values forms, and the pixel that G2 is less than T by all gray values forms.
Step S33, middle amplitude threshold calculation procedure.Calculate respectively the averaged amplitude value U1 of first group of collection of pixels G1 and the averaged amplitude value U2 of second group of collection of pixels G2, using the meansigma methods of the averaged amplitude value U2 of the averaged amplitude value U1 of first group of collection of pixels and second group of collection of pixels amplitude threshold, i.e. new middle amplitude threshold Tnew=(U1+U2)/2 in the middle of current.
Step S34, in the middle of the middle amplitude threshold newly calculating is previous with it, amplitude threshold compares, for example compare both difference or ratio, judge whether comparative result is less than predefined parameter, if this current middle amplitude threshold is final amplitude threshold, end loop, carries out phase place determining method if follow-up, continue execution step S35.If comparative result is not less than predefined parameter, turn to execution step S32, in step S32, the range value of all pixels in image and this middle amplitude threshold newly calculating are compared, adopt the middle amplitude threshold newly calculating to carry out pixel segmentation, circulation step S 32 to S 34, until the comparative result of the middle amplitude threshold newly calculating middle amplitude threshold previous with it is less than predefined parameter.The number of the pixel in the first group of collection of pixels G1 obtaining after cutting apart is exactly the number of the signaling point that obtains of employing amplitude determining method.
Step S35, chooses initial seed step.The pixel of choosing amplitude maximum in initial seed subelement 272a selection image is initial seed.Because the amplitude of signaling point is generally large than the amplitude of noise, thus first suppose that the pixel of amplitude maximum is signaling point, and take that it carries out region growing as initial seed.
Step S36, seed growth steps.Seed increases subelement 272b for the phase place of the phase place of the seed of growth and its periphery neighbor pixel is compared successively, for example compare both difference or ratio, if phase place comparative result is less than the first phase threshold, this neighbor pixel is increased, one of and the seed increasing this neighbor pixel as next round, circulation increases until do not have neighbor pixel to be increased, and there is no new growth seed, and after loop ends, the set of seed is the set of signaling point.The first phase threshold initial in this step can be set according to mode and experience relatively, for example, according to the performance setting of magnetic resonance system.
Step S37, the signaling point number that signaling point number judgment sub-unit 272c draws after growth in step S36 is finished compares with the signaling point number that the amplitude of employing determining method draws, for example compare both difference or ratio, judge whether comparative result meets the first predetermined condition, if, adopting the signaling point that phase place determining method finally draws is final result, for follow-up additive phase, goes to reel.Otherwise execution step S38.In a kind of instantiation of this step, whether the signaling point number that in determining step S36, growth draws after finishing meets the first predetermined condition with the ratio of the signaling point number that the amplitude of employing determining method draws, the first predetermined condition is empirical value.
Step S38, the first phase place threshold increment subelement 272d, for the first phase threshold is recalculated, increases progressively the first phase threshold according to setting step-length, and setting step-length is empirical value.Value after increasing progressively, as the first new phase threshold, then turns to execution step S35, and circulation is until the comparative result of the signaling point number that the signaling point number drawing and amplitude judging unit draw meets the first predetermined condition.
The handling process that separately employing amplitude determining method or phase place determining method carry out identification signal point is the above-mentioned corresponding step of reference respectively.
By coming identification signal point can revise the image border signal error in judgement problem causing due to range signal judgement amplitude determining method and the combination of phase place determining method, obtain good effect.On the one hand, edge effect due to radio-frequency coil, fringe magnetic field is inhomogeneous, cause the image signal amplitude of marginal point little, in the amplitude of employing determining method process, be easily mistaken for noise, and phase place determining method is to judge based on phase place, do not consider amplitude, therefore the marginal point that meets phase condition can be judged as to signaling point.On the other hand, in magnetic resonance testing process, due to the impact of external environment, on image, may occur the noise that brightness is larger, if according to amplitude determining method, noise will be judged to be broken into signaling point.But the phase place of this noise like is conventionally more mixed and disorderly, consecutive points phase contrast is larger, and therefore, in follow-up phase place determining method, much noise can be excluded, and can not be identified as signaling point.Therefore, phase place determining method has just in time made up the deficiency of amplitude determining method.
In addition, the present embodiment is also proofreaied and correct the recognition result of phase place determining method after phase place determining method identification signal point, because may cause phase error in picture coding process, cause adopting phase place determining method to cause erroneous judgement, therefore by the result of amplitude determining method, the recognition result of phase place determining method is proofreaied and correct, effectively avoided employing phase place determining method to cause erroneous judgement.
In a further embodiment, a secondary antiphase magnetic resonance image (MRI) that gathers respectively water in patient body tissue and fat and two synchronous magnetic resonance image (MRI) adopt the scheme in the embodiment of the present invention can realize equally water with fatty separated, water and fatty phase angle are (0 in such cases, π, 2 π), formula (1) becomes:
Formula (2) becomes:
Formula (3) becomes:
e
i2φ＝I′
2-------------------------(3′)
In above-described embodiment, the initial seed of choosing while adopting region growing method, except the above-mentioned scheme of obtaining of mentioning, initial seed also can adopt other acquisition methods and constraints.
Above-described embodiment can be applicable in the magnetic resonance system of any magnetic field intensity, and especially, for low magnetic resonance system, effect is more obvious.
Phase place determining method identification signal point in above-described embodiment also can be applicable to other image identification system, and the angle that region growing goes method for winding also to can be applicable to other field is gone to reel and processed.
Above content is in conjunction with concrete embodiment further description made for the present invention, can not assert that specific embodiment of the invention is confined to these explanations.For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, can also make some simple deduction or replace, all should be considered as belonging to protection scope of the present invention.
Claims (10)
1. the method for separate imaging of water and fat of magnetic resonance system, is characterized in that comprising:
Water in collection patient body tissue and fatty magnetic resonance image (MRI), described magnetic resonance image (MRI) comprises the magnetic resonance image (MRI) of at least one synchronous magnetic resonance image (MRI) and at least two width antiphases, or described magnetic resonance image (MRI) comprises magnetic resonance image (MRI) and at least two synchronous magnetic resonance image (MRI) of at least one width antiphase;
Utilize at least two width antiphases or at least two synchronous magnetic resonance image (MRI) to calculate additive phase;
Choose and appoint piece image, image is carried out to signal judgement, identify signaling point;
The additive phase of the signaling point identifying is gone to reel;
The image of the antiphase in the magnetic resonance image (MRI) of going after coiling is drawn to water images and fat image in conjunction with synchronous image;
Describedly image carried out to signal judgement comprise:
Amplitude determining step, the amplitude of the pixel in image and final amplitude threshold are compared, if the amplitude of pixel is more than or equal to final amplitude threshold, think that this pixel is signaling point, if the amplitude of pixel is less than final amplitude threshold, think that this pixel is not signaling point;
Described final amplitude threshold is chosen by following steps:
Calculate the step of initial amplitude threshold value, described initial amplitude threshold value equals amplitude peak value in image and the meansigma methods of minimum amplitude value;
Pixel segmentation step, the range value of all pixels in image and initial amplitude threshold value are compared, obtain first group of collection of pixels and second group of collection of pixels, first group of collection of pixels is the collection of pixels that is more than or equal to initial amplitude threshold value, and second group of collection of pixels is the collection of pixels that is less than initial amplitude threshold value;
Middle amplitude threshold calculation procedure, calculate respectively the averaged amplitude value of first group of collection of pixels and the averaged amplitude value of second group of collection of pixels, using the meansigma methods of the averaged amplitude value of the averaged amplitude value of first group of collection of pixels and second group of collection of pixels amplitude threshold in the middle of current;
Final amplitude threshold identification step, in the middle of this is current, amplitude threshold middle amplitude threshold previous with it compares, judge whether comparative result is less than predefined parameter, if this current middle amplitude threshold is final amplitude threshold, otherwise turn to, carry out pixel segmentation step, the range value of all pixels in image and this current middle amplitude threshold are compared.
2. the method for claim 1, is characterized in that, describedly image is carried out to signal judgement also comprises:
Phase place determining step, compares the phase place of neighbor, if both comparative results are less than phase threshold, thinks that neighbor is signaling point.
3. method as claimed in claim 2, is characterized in that, described phase place determining step comprises:
Choose initial seed step, selecting the pixel of amplitude maximum in image is initial seed;
Seed growth steps, the seed of growth and its periphery neighbor pixel are carried out to phase bit comparison successively, if phase place comparative result is less than the first phase threshold, this neighbor pixel is increased, one of and the seed increasing this neighbor pixel as next round, this step that circulates is until rise to and there is no seed, and after loop ends, the set of seed is the set of signaling point.
4. method as claimed in claim 3, is characterized in that, described phase place determining step also comprises:
The signaling point number drawing in the signaling point number drawing after seed growth steps and amplitude determining step is compared, judge whether comparative result meets the first predetermined condition, if so, the signaling point drawing in phase place determining step of take is final result, otherwise carries out following steps;
According to setting step-length, the first phase threshold is increased progressively rear as the first new phase threshold, circulation is carried out and is chosen initial seed step and seed growth steps until the comparative result of the signaling point number drawing in the signaling point number drawing in phase place determining step and amplitude determining step meets the first predetermined condition.
5. the method as described in any one in claim 1 to 4, is characterized in that, the additive phase of the signaling point identifying is gone to reel comprises the step that adopts region growing method to remove coiling, and described region growing method goes coiling to comprise:
Selected seed step, in increasing signaling point, selecting range maximum and adjoint point are not that the additive phase point of not reeling is as seed, for initial seed, if do not find satisfactory signaling point, select not increase time large and adjoint point of amplitude in signaling point and be point that additive phase do not reel as seed;
Seed amplitude determining step, amplitude peak value in the amplitude of the seed of newly choosing and signaling point is compared, if the amplitude of the seed of newly choosing be less than amplitude peak value 1% or other any can think to be far smaller than value time; finish to increase, otherwise carry out following steps;
Seed phase place set-up procedure, by the most contiguous phase bit comparison that increases signaling point of the phase place of the seed of newly choosing and its, if phase contrast is greater than 2 π, the phase place of the seed that this is newly chosen adds/subtracts the phase place adjustment of 2 π integral multiples, so that both phase contrasts are minimum, otherwise using the seed of newly choosing as the seed increasing;
Increase and go the step of reeling, for the phase place of the phase place of the seed of growth and its periphery adjacent signaling point is compared successively, if comparative result is less than the second phase threshold of setting, this adjacent signaling point is increased, and this adjacent signaling point is classified as to one of seed of next round growth; If comparative result is more than or equal to the second phase threshold of setting, after this adjacent signaling point being increased/subtract 2 π integral multiples, again judge whether new comparative result is less than the second phase threshold of setting, if it is will increase/subtract phase place after the 2 π integral multiples new phase as this adjacent signaling point, and this adjacent signaling point is classified as to one of seed of next round growth, this step that circulates is not until have adjacent signaling point to be increased;
Judge whether that all signaling points are all increased, if finish to increase, otherwise turn to selected seed step.
6. the separate imaging of water and fat device of magnetic resonance system, is characterized in that comprising:
Image capture module, for gathering the water of patient body tissue and fatty magnetic resonance image (MRI), described magnetic resonance image (MRI) comprises the magnetic resonance image (MRI) of at least one synchronous magnetic resonance image (MRI) and at least two width antiphases, or described magnetic resonance image (MRI) comprises magnetic resonance image (MRI) and at least two synchronous magnetic resonance image (MRI) of at least one width antiphase;
Additive phase computing module, for utilizing at least two width antiphases or at least two synchronous magnetic resonance image (MRI) to calculate additive phase;
Signaling point identification module, appoints piece image for choosing, and image is carried out to signal judgement, identifies signaling point; Go the module of reeling, for the additive phase of the signaling point identifying is gone, reel;
Water fat separation module, for going the image of the antiphase of the magnetic resonance image (MRI) after coiling to draw water images and fat image in conjunction with synchronous image;
Described signaling point identification module comprises:
Amplitude judging unit, for the amplitude of the pixel of image and final amplitude threshold are compared, if the amplitude of pixel is more than or equal to final amplitude threshold, think that this pixel is signaling point, if the amplitude of pixel is less than final amplitude threshold, think that this pixel is not signaling point;
Described amplitude judging unit also, for choosing final amplitude threshold, is specially: described amplitude judging unit is for first calculating initial amplitude threshold value, and described initial amplitude threshold value equals amplitude peak value in image and the meansigma methods of minimum amplitude value; Then the range value of all pixels in image and initial amplitude threshold value are compared, obtain first group of collection of pixels and second group of collection of pixels, first group of collection of pixels is the collection of pixels that is more than or equal to initial amplitude threshold value, and second group of collection of pixels is the collection of pixels that is less than initial amplitude threshold value; Then calculate respectively the averaged amplitude value of first group of collection of pixels and the averaged amplitude value of second group of collection of pixels, using the meansigma methods of the averaged amplitude value of the averaged amplitude value of first group of collection of pixels and second group of collection of pixels amplitude threshold in the middle of current; In the middle of this is current, amplitude threshold middle amplitude threshold previous with it compares, judge whether comparative result is less than predefined parameter, if this current middle amplitude threshold is final amplitude threshold, otherwise continue the range value of all pixels in image and this current middle amplitude threshold to compare, obtain first group of collection of pixels and second group of collection of pixels.
7. device as claimed in claim 6, is characterized in that, described signaling point identification module also comprises:
Phase place judging unit, for the phase place of neighbor is compared, if both comparative results are less than phase threshold, thinks that neighbor is signaling point.
8. device as claimed in claim 7, is characterized in that, described phase place judging unit comprises:
Choosing initial seed subelement, is initial seed for selecting the pixel of image amplitude maximum;
Seed increases subelement, for the seed of growth and its periphery neighbor pixel are carried out to phase bit comparison successively, if phase place comparative result is less than the first phase threshold, this neighbor pixel is increased, one of and the seed increasing this neighbor pixel as next round, control seed and increase subelement work until rise to and there is no seed, after loop ends, the set of seed is the set of signaling point.
9. device as claimed in claim 8, is characterized in that, described phase place judging unit also comprises:
Signaling point number judgment sub-unit, for seed being increased to the signaling point number that signaling point number that subelement draws and amplitude judging unit draw, compare, judge whether comparative result meets the first predetermined condition, it is final result that the seed of if so, take increases the signaling point that subelement draws;
The first phase place threshold increment subelement, when the signaling point number drawing for the signaling point number that draws when seed growth subelement and amplitude judging unit does not meet the first predetermined condition, according to setting step-length, the first phase threshold is increased progressively rear as the first new phase threshold, control and choose that initial seed subelement and seed increase subelement work and meet the first predetermined condition until seed increases the comparative result of the signaling point number that signaling point number that subelement draws and amplitude judging unit draw.
10. the device as described in any one in claim 6 to 9, is characterized in that, described in the module of going to reel comprise that described region growing unit comprises for adopting region growing method the phase place of signaling point to be gone to the region growing unit of reeling and processing:
Selected seed subelement, for being that the additive phase point of not reeling is as seed not increasing signaling point selecting range maximum and adjoint point, for initial seed, if do not find satisfactory signaling point, select not increase time large and adjoint point of amplitude in signaling point and be point that additive phase do not reel as seed;
Seed amplitude judgment sub-unit, for the amplitude peak value of the amplitude of the seed of newly choosing and signaling point is compared, if the amplitude of the seed of newly choosing be less than amplitude peak value 1% or other any can think to be far smaller than value time; finish growth;
Seed phase place is adjusted subelement, when not being far smaller than the amplitude peak of signaling point when the amplitude of the seed of newly choosing by the most contiguous phase bit comparison that increases signaling point of the phase place of the seed of newly choosing and its, if phase contrast is greater than 2 π, the phase place of the seed that this is newly chosen adds/subtracts the phase place adjustment of 2 π integral multiples, so that both phase contrasts are minimum, otherwise using the seed of newly choosing as the seed increasing;
Increase and remove the subelement of reeling, for the phase place of the phase place of the seed of growth and its periphery adjacent signaling point is compared successively, if comparative result is less than the second phase threshold of setting, this adjacent signaling point is increased, and this adjacent signaling point is classified as to one of seed of next round growth; If comparative result is more than or equal to the second phase threshold of setting, after this adjacent signaling point being increased/subtract 2 π integral multiples, again judge whether new comparative result is less than the second phase threshold of setting, if it is will increase/subtract phase place after the 2 π integral multiples new phase as this adjacent signaling point, and this adjacent signaling point is classified as to one of seed of next round growth, control to increase and goes to reel subelement periodic duty until do not have adjacent signaling point to be increased;
Signaling point increases judgment sub-unit, for judging whether that all signaling points are all increased, if finish to increase, otherwise controls the work of selected seed subelement, continues selected seed in not increasing signaling point.
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| CN103549954B (en) * | 2013-10-29 | 2016-04-06 | 华东师范大学 | A kind of nuclear magnetic resonance three dimensional Phase unfolding method and device thereof |
| CN105809661B (en) * | 2014-12-30 | 2018-08-07 | 中国科学院深圳先进技术研究院 | The image water fat separation method and system of magnetic resonance imaging |
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