CN108876769A - A kind of left auricle of heart CT image partition method - Google Patents

A kind of left auricle of heart CT image partition method Download PDF

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CN108876769A
CN108876769A CN201810553854.0A CN201810553854A CN108876769A CN 108876769 A CN108876769 A CN 108876769A CN 201810553854 A CN201810553854 A CN 201810553854A CN 108876769 A CN108876769 A CN 108876769A
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image
sequence
heart
left auricle
indicate
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CN108876769B (en
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黄晓阳
张耀丹
苏茂龙
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Xiamen University
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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/0002Inspection of images, e.g. flaw detection
    • G06T7/0012Biomedical image inspection
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/10Segmentation; Edge detection
    • G06T7/11Region-based segmentation
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/10Segmentation; Edge detection
    • G06T7/136Segmentation; Edge detection involving thresholding
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00Image analysis
    • G06T7/10Segmentation; Edge detection
    • G06T7/187Segmentation; Edge detection involving region growing; involving region merging; involving connected component labelling
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/10Image acquisition modality
    • G06T2207/10072Tomographic images
    • G06T2207/10081Computed x-ray tomography [CT]
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/20Special algorithmic details
    • G06T2207/20112Image segmentation details
    • G06T2207/20156Automatic seed setting
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06TIMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00Indexing scheme for image analysis or image enhancement
    • G06T2207/30Subject of image; Context of image processing
    • G06T2207/30004Biomedical image processing
    • G06T2207/30048Heart; Cardiac

Abstract

A kind of left auricle of heart CT image partition method, it is related to Medical Image Processing, noise reduction process is carried out to left auricle of heart CT image first, using the boundary information of priori knowledge building left auricle of heart missing, using area growth algorithm obtains individual initial segmentation image as individual label figure of Atlas;The Atlas segmentation that individual is marked and the information relationship of left auricle of heart CT flanking sequence improves is recycled, initial segmentation sequence is obtained;Using the profile information in initial segmentation sequence as the initial profile of level set algorithm, and the approximate Euclidean distance information for obtaining left auricle of heart CT sequence chart is inputted as feature, accurate segmentation result sequence is obtained finally by quick level set algorithm, to achieve the purpose that left auricle of heart CT image segmentation.

Description

A kind of left auricle of heart CT image partition method
Technical field
The present invention relates to Medical Image Processings, more particularly, to a kind of left auricle of heart CT image partition method.
Background technique
Left auricle of heart is the component part in human body atrium sinistrum, and function is auxiliary pump blood.The multiple-limb knot of left auricle of heart itself Structure tends to interfere with blood backflow, when left auricle of heart just cannot produce contraction, atrial pressure is caused to increase, and causes atrial fibrillation, left auricle of heart knot Structure has a major impact cardiovascular and cerebrovascular disease.When carrying out blocking operation to left auricle of heart, the shape for how being directed to left auricle of heart selects to close Suitable plugging device is the basis of successful surgery.Therefore, left auricle of heart CT image segmentation is to carry out left auricle of heart image analysis, processing One of basis is of great significance.However because left auricle of heart with atrium sinistrum to be adhered part non-boundary, left auricle of heart CT image texture-free The features such as feature, left auricle of heart CT image segmentation have certain difficulty.The research of existing left auricle of heart image segmentation is also fewer, with Maximally related the method for the present invention is that (yellow contain Cape jasmine, Han Luyi, Liu Qi, text of an annotated book Juan, Deng Lihua, what insults the left heart of ultrasound to yellow contain Cape jasmine et al. The profile of ear image automatically extracts [J] Sichuan University journal (engineering science version), 2016,48 (03):87-93.) one proposed The partitioning algorithm of kind left auricle of heart ultrasound image, the algorithm realize the dividing function of left auricle of heart ultrasound image, from individual ultrasound figure Left auricle of heart Accurate Segmentation is realized as in, which first passes through the position identification of two steps, then by close to the initial of true edge Profile obtains precisely segmentation using movable contour model, and the position determination of first two steps needs to rely on priori knowledge, algorithm robustness It is low.And this method carries out left auricle of heart image dividing processing for ultrasound image, can not be directly used in left auricle of heart CT image segmentation.
Left auricle of heart changeable, complicated anatomical features with shape.Left auricle of heart CT image has following features:It is left Auricle and atrium sinistrum are adhered substantially texture-free feature of part non-boundary, left auricle of heart etc., therefore the boundary of left auricle of heart CT image can not It directly obtains, it is bad using traditional image segmentation algorithm effect.
Summary of the invention
It is an object of the invention to In view of the above shortcomings of the prior art, provide a kind of image segmentation side left auricle of heart CT Method.
The present invention carries out noise reduction process to left auricle of heart CT image first, utilizes the boundary of priori knowledge building left auricle of heart missing Information, using area growth algorithm obtain individual initial segmentation image as individual label figure of Atlas;Recycle individual label with And the Atlas segmentation that the information relationship of left auricle of heart CT flanking sequence improves, obtain initial segmentation sequence;By initial segmentation sequence Initial profile of the profile information as level set algorithm in column, and obtain the approximate Euclidean distance information of left auricle of heart CT sequence chart It is inputted as feature, accurate segmentation result sequence is obtained finally by quick level set algorithm, to reach left auricle of heart CT image The purpose of segmentation.
The present invention includes the following steps:
1) left auricle of heart CT sequence image A is inputted;
2) noise reduction process is carried out to the sequence image A in step 1), obtains sequence image B;
3) selecting step 2) in sequence image B in individual CT scheme Bi, residue sequence image is denoted as B ';
4) individual CT according to obtained in step 3) schemes BiThe position feature information of middle left auricle of heart manually chooses two features Point, the boundary information of building left auricle of heart missing, obtains image C;
5) to image C using area growth algorithm obtained in step 4), image L is obtainedi
6) the image L obtained with step 5)iFor initial markup image, the image B ' Atlas for carrying out adjacent registration is divided, Obtain initial segmentation sequence L;
7) to the sequence image B in step 2), all foreground points is calculated to the approximate Euclidean distance of background dot, obtain distance Image sequence D;
8) profile for the initial segmentation sequence L for obtaining step 6) is as initial profile, by distance obtained in step 7) Image sequence D carries out the accurate of left auricle of heart CT sequence image to sequence image B as characteristic image, using quick level set algorithm Segmentation.
In step 2), the sequence image A carries out noise reduction process, and the specific method for obtaining sequence image B can be:
(1) image of i-th image after t iterative filtering is denoted as I in sequence image At,i, use curvature anisotropy Diffusion equation recalculates:
Wherein, c (| x |) indicates specific conductance,▽ expression takes gradient, and t indicates the number of iterations, I (x, y, I) i-th image in sequence image A is indicated;
(2) the process n times of iterative step (1), i-th image after obtaining noise reduction;
(3) it is incremented by i, enables i=i+1, execute step (1), obtains the image sequence B after retaining edge noise reduction;
In step 3), the selecting step 2) in sequence image B in individual CT scheme BiSpecific method can be:
(1) the image number n in left auricle of heart CT sequence image A is calculated;
(2) i-th image is chosen as figure Bi, wherein i is the maximum integer no more than n/2.
In step 4), described individual CT according to obtained in step 3) schemes BiThe position feature information of middle left auricle of heart, people Work chooses two characteristic points, the boundary information of building left auricle of heart missing, and the specific method for obtaining image C can be:
(1) two seed points manually chosen are set as p1(x1, y1)、p2(x2, y2), this two o'clock can determine a logical coordinates Straight line in systemIn physical coordinates system,It can be by from point p1To point p2The pixel fitting extended one by one is constituted, then point p1's Next pixel position is expressed as:
Wherein, N0Indicate the position of next pixel, N1, N2Indicate position candidate, d1, d2Respectively indicate N1, N2To logic The distance of next point on coordinate;
(2) according to the positional relationship straight line in left auricle of heart anatomical structureSlope k meet:K ∈ (- 45 °, 0 °) ∪ (- 90 °, -45 °), then its corresponding N1, N2It is expressed as:
(3) when the slope k of straight line meets k ∈ (- 45 °, 0 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy is indicated in logic Vertical missing value, according to pi+1Value can determine the result of next coordinate:
Work as straight lineSlope k when meeting k ∈ (- 90 °, -45 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy is indicated in logic Vertical missing value.According to pi+1Value can determine the result of next coordinate:
(4) image B is modifiediMiddle coordinate N0The gray value of place pixel:
I(N0)=0
Obtain image C.
It is described to image C using area growth algorithm obtained in step 4) in step 5), obtain image LiIt is specific Method can be:
(1) position according to left auricle of heart in image C selects a pixel as seed point s, setting in image C When the seed point of input meets following threshold values seed point set seed is added in point s by threshold value thresholding:
I0(s)∈[lower,upper]
Wherein, I0(s) indicate that the gray value of seed point s in image C, lower indicate that the lower limit of gray value, upper indicate The upper limit of gray value;
(2) to each si∈ seed calculates siEight connected region U, by all elements U in eight connected regioni∈ U meets Seed point set seed is all added in the point of given threshold condition in above-mentioned steps (1), repeats step (2) until not new point is added Seed point set seed obtains image Li
In step 6), with the image L obtained in the step 5)iFor initial markup image, phase is carried out to image sequence B ' The Atlas segmentation of neighbour's registration, the specific method for obtaining initial segmentation sequence L can be:
(1) serial number of the image Bi in sequence image B is denoted as i, and next image in sequence image B is denoted as Bi+1, by Bi The image L obtained with step 5)iLabel is denoted as to (Bi, Li), by BiAs floating image, Bi+1Image is carried out for fixed image to match Standard obtains transformation parameter fi+1.Image registration using elastix tool (S.Klein, M.Staring, K.Murphy, M.A.Viergever,J.P.W.Pluim,"elastix:atoolboxforintensitybasedmedical image registration,"IEEE TransactionsonMedicalImaging,vol.29,no.1,pp.196-205, January2010 it) realizes, specific step is as follows:
(a) pyramid model is used, by image Bi, Bi+1It is divided into three accuracy classes;
(b) by image Bi, Bi+1It is mapped in logical coordinates from physical coordinates by interpolation method;
(c) with the mode of stochastical sampling respectively from image Bi, Bi+1Middle several sample points of selection, it is whole as representing Sample point set Si, Si+1
(d)Si, Si+1Between similarity indicated using mutual information;
(e) optimization algorithm being registrated uses adaptive gradient descent algorithm;
(f) use multi-level registration strategies, successively with rigid transformation, affine transformation, B-spline transformation (D.Rueckert, L.I.Sonoda,C.Hayes,D.L.G.Hill,M.O.Leach,and D.J.Hawkes.Nonrigidregistrationusing free-formdeformations: ApplicationtobreastMRimages.IEEETrans.Med.Imag.,18(8):712-721,1999) three kinds of transformation sides Formula obtains transformation parameter fi+1
(2) by transformation parameter fi+1Act on tag image Li, obtain Bi+1Tag image Li+1
(3) by Bi+1With Li+1As new label to (Bi+1, Li+1), it repeats step (1) and (2), until terminating;
(4) by image BiAs an image B upper in floating image, with sequence image Bi-1According to side described in step (1) Method carries out image registration, wherein Bi-1For fixed image, transformation parameter f is obtainedi-1
(5) by transformation parameter fi-1Act on tag image Li, obtain Bi-1Tag image Li-1
(6) by Bi-1With Li-1As new label to (Bi-1, Li-1), it repeats step (4) and (5), until terminating.
In step 7), the sequence image B in step 2), calculate all foreground points to background dot approximate Euclidean Distance, the specific method for obtaining range image sequence D can be:(referring to document:Akmal B M,Maragos P.Optimum design of chamfer distance transforms.[J].IEEE Transactions on Image Processing A Publication of the IEEE Signal Processing Society,1998,7(10): 1477-84.):
(1) each image in sequence image B is handled as follows:Range conversion template is pressed from left to right from upper Sequence sliding under and successively calculates each pixel to the minimum euclidean distance of background, obtains intermediate distance image sequence Bd
(2) to intermediate distance image sequence BdEach image be handled as follows:Range conversion template is pressed from the right side To left sequence sliding from bottom to top, each pixel is successively calculated to the minimum euclidean distance of background, obtains distance feature image Sequence D.
In step 8), the profile of the initial segmentation sequence L that step 6) is obtained is as initial profile, by step 7) Obtained in range image sequence D as characteristic image, left auricle of heart CT sequence is carried out to sequence image B using quick level set algorithm The accurate segmentation of column image, specific method can be for (referring to documents:Anon.Insight segmentation and registration Toolkit[EB/OL].[2008-07-06].http://www.itk.org.):
(1) each image Di (i=1,2,3 ... ..n) in characteristic image sequence D of adjusting the distance, wherein n is distance feature The sum of image sequence D is calculated using sigmoid function, forms the input feature vector DS of quick level set algorithmi(i=1, 2,3 ... ..n), wherein sigmoid function is:
Wherein, I indicates image Di, Max, Min are image D respectivelyiMiddle maximum, minimum gradation value, α indicate image DiBrightness The width (window width) of range, β indicate the brightness (window position) at range center, and I ' indicates output image, i.e. DSi;All DSi(i= 1,2,3 ... ..n) it is quick level set algorithm characteristic sequence, it is denoted as DS;
(2) using the sequence L obtained in step 6) as the initial profile sequence of quick level set algorithm, in step 8) a) The DS obtained in the process is as quick level set algorithm characteristic sequence, to every image Li, i=1,2,3 ... the ..n in sequence L, Li is arranged to the zero level collection an of high-dimension function by level set algorithm, this high-dimension function is called level set function:Y (X, t), Then level set function movement becomes a differential equation, by extracting zero level collection G ((X), t)={ Y (X, t) from output =0 } come the profile moved, the update of a level set equation computing differential solution of equation ψ is used:
Wherein, A (x) indicates that advection coefficient, P (x) indicate propagation coefficient (being also the coefficient of expansion), and Z (x) indicates curvature The space regulator coefficient of mean value, α, β, γ indicate the weight of each parameter, are constants.
The present invention carries out left auricle of heart image segmentation to image for the left auricle of heart feature of image of boundary information missing, right first Image sequence carries out noise reduction process, and reducing noise bring influences;Then in order to obtain initial profile Model sequence, first to individual Image obtains individual initial segmentation image comprising skeleton pattern information by the boundary information of supplement missing;Again by this individual The corresponding gray level image of initial segmentation image forms initial Atlas label pair, is obtained by being first registrated the Atlas algorithm divided again Obtain sequence of partitions;Atlas flag sequence is the initial segmentation sequence for including initial profile model, successively inputs profile information Level set algorithm obtains its corresponding segmentation result sequence.The present invention is finally reached the purpose being split to image left auricle of heart, The left auricle of heart that segment boundary lacks is separated from the left ventriculography picture being attached thereto.
For individual left auricle of heart initial segmentation process by priori knowledge, building is adhered the boundary missing of parts of images missing, then Individual initial segmentation is obtained using partitioning algorithm;Using improved Atlas algorithm from individual initial segmentation image to initial segmentation Sequence image, it is similar using adjacent image in sequence image, meet requirement of the Atlas algorithm to label centering grayscale image, uses The adjacent grayscale image in position is registrated individual initial segmentation grayscale image obtained in the sequence with it, by the transformation results of registration Atlas label (initial segmentation image) is acted on, the Atlas label of neighboring gradation image is obtained, and is combined into new Atlas mark Note pair, the iteration step can form complete Atlas flag sequence;Accurate Segmentation replaces grayscale image to obtain using distance map The differentiation information of left auricle of heart and atrium sinistrum, then by the quick level set algorithm of initial profile information input, it is finally reached Accurate Segmentation Purpose.
Compared with the existing technology, beneficial effects of the present invention are:
1, the present invention is directed to left auricle of heart CT characteristics of image, carries out information supplement to boundary lack part using priori knowledge, The outgrowth defect for compensating for the algorithm of region growing of connection thresholding successfully obtains first initial point comprising profile information It cuts.
2, the present invention uses improved Atlas algorithm, now combines the corresponding grayscale image of individual initial segmentation image For initial markers pair, the grayscale image for recycling the grayscale image of just label centering adjacent with its sequence location is registrated, will be registrated Transformation results act on Atlas label (initial segmentation image), obtain the Atlas label of neighboring gradation image, and be combined into New Atlas label pair, the iteration step can form complete Atlas flag sequence, reach automatic obtain and believe comprising profile The purpose of the initial segmentation sequence of breath.
3, improved Atlas algorithm used in the present invention is using the correlation between sequence, solves similar marker to obtaining Difficult problem is taken, the segmentation precision of traditional list Atlas algorithm is not only increased, is also greatly reduced in more Atlas algorithms and matches Quasi-, fusion time complexity.
4, the present invention replaces gray level image to increase location information using range image, and set algorithm of improving the standard is in weak boundary point Cut the Boundary Recognition ability in problem;And the precision that segmentation is improved by the profile diagram that improved Atlas algorithm obtains is combined, Realize the Accurate Segmentation of left auricle of heart sequence.
5, the present invention increases the boundary information lacked in left auricle of heart CT sequence image by three steps, improves segmentation essence Degree, these methods complement each other, all linked with one another, be used in combination with can more accurate Ground Split go out left auricle of heart image, have The advantages of segmentation precision height, strong robustness.
The present invention is directed to the left auricle of heart feature of image of boundary information missing, and point multiple steps are handled, analyzed, reach from Precisely divide the purpose of left auricle of heart image in CT image.Individual label of the invention obtains, Atlas obtains initial profile sequence, Distance feature obtains, the several steps of quick level-set segmentation can functionally complement each other, and single label, which obtains, mainly utilizes priori The boundary information of information combination priori knowledge supplement missing, recycles the algorithm of region growing of connection thresholding to obtain segmentation, algorithm Simply, time complexity is low;Improved Atlas algorithm obtains initial profile sequence, for level set algorithm provide as close possible to The initial profile of real border, reduces the time complexity of level set algorithm, and has prompted the boundary position information of missing, mentions High segmentation accuracy;Distance feature can improve the problem of boundary information deficiency in gray level image, and set algorithm of improving the standard is boundless The accuracy of profile at boundary improves robustness;Quick level set algorithm can actively generate closed outline, and in initial profile information And with the help of distance feature, accurately segmentation result sequence image is generated.Relative to the immediate prior art, have bright Aobvious distinguishing characteristics, and have the advantages that obvious:Method of the invention can generate sequences segmentation as a result, practical, also not Need excessive manual intervention, it is only necessary to which the i.e. producible accurately left auricle of heart sequences segmentation of three points of artificial selection is as a result, accurate It is more superior in property and robustness.
Detailed description of the invention
Fig. 1 is basic flow chart of the invention;
Fig. 2 is one of the left auricle of heart CT image sequence of the embodiment of the present invention;
Fig. 3 is the range conversion template of the embodiment of the present invention;
Fig. 4 is one of the final segmentation result image sequence of the embodiment of the present invention.
Specific embodiment
Present invention is further described in detail with reference to the accompanying drawings and examples, and embodiment is according to flow chart shown in Fig. 1 It explains in detail.
The present invention includes the following steps:
1) left auricle of heart CT sequence image A is inputted;
2) noise reduction process is carried out to the sequence image A in step 1), obtains sequence image B;
3) selecting step 2) in sequence image B in individual CT scheme Bi, residue sequence image is denoted as B ';
4) the image B according to obtained in step 3)iThe position feature information of middle left auricle of heart manually chooses two characteristic points, The boundary information of left auricle of heart missing is constructed, image C is obtained;
5) to image C using area growth algorithm obtained in step 4), image L is obtainedi
6) the image L obtained with step 5)iFor initial markup image, the image B ' Atlas for carrying out adjacent registration is divided, Obtain initial segmentation sequence L.
7) to the sequence image B in step 2), all foreground points is calculated to the approximate Euclidean distance of background dot, obtain distance Image sequence D;
8) profile for the initial segmentation sequence L for obtaining step 6) is as initial profile, by distance obtained in step 7) Image sequence D carries out the accurate of left auricle of heart CT sequence image to sequence image B as characteristic image, using quick level set algorithm Segmentation.
One of left auricle of heart CT image sequence of the embodiment of the present invention is referring to fig. 2.
In step 2), the sequence image A carries out noise reduction process, and the specific method for obtaining sequence image B can be:
(1) image of i-th image after t iterative filtering is denoted as I in sequence image At,i, use curvature anisotropy Diffusion equation recalculates:
Wherein, c (| x |) indicates specific conductance, wherein▽ expression takes gradient, and t indicates the number of iterations, I (x, y, i) indicates i-th image in sequence image A;
In the present embodiment, the value of parameters is as follows:C=5, t=4.
(2) the process n times of iterative step (1), i-th image after obtaining noise reduction;
(3) it is incremented by i, enables i=i+1, execute step (1), obtains the image sequence B after retaining edge noise reduction;
In step 3), individual CT schemes B in the selection sequence image BiSpecific method be:
(1) the image number n in left auricle of heart CT sequence image A is calculated;
(2) i-th image is chosen as figure Bi, wherein i is the maximum integer no more than n/2;
In the present embodiment, the value of parameters is as follows:N=60, i=30 choose the 30th image.
In step 4), two characteristic points, building left auricle of heart missing are manually chosen from the image Bi obtained in step 3) Boundary information, obtain image C specific method be:
(1) two seed points manually chosen are set as p1(x1, y1)、p2(x2, y2), this two o'clock can determine a logical coordinates Straight line in systemIn physical coordinates system,It can be by from point p1To point p2The pixel fitting extended one by one is constituted, then point p1's Next pixel position is expressed as:
Wherein, N0Indicate the position of next pixel, N1, N2Indicate position candidate, d1, d2Respectively indicate N1, N2To logic The distance of next point on coordinate;
(2) according to the positional relationship straight line in left auricle of heart anatomical structureSlope k meet:K ∈ (- 45 °, 0 °) ∪ (- 90 °, -45 °), then its corresponding N1, N2It is expressed as:
(3) when the slope k of straight line meets k ∈ (- 45 °, 0 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy is indicated in logic Vertical missing value.According to pi+1Value can determine the result of next coordinate:
Work as straight lineSlope k when meeting k ∈ (- 90 °, -45 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy is indicated in logic Vertical missing value.According to pi+1Value can determine the result of next coordinate:
(4) image B is modifiediMiddle coordinate N0The gray value of place pixel:
I(N0)=0
Obtain image C;
In the present embodiment, the value of parameters is as follows:
P1 (x1, x2)=(115,66), p2 (x2, y2)=(166,110)
It is described to image C using area growth algorithm obtained in step 4) in step 5), obtain image LiIt is specific Method is:
(1) position according to left auricle of heart in image C selects a pixel as seed point s, setting in image C When the seed point of input meets following threshold values seed point set seed is added in point s by threshold value thresholding:
I0(s)∈[lower,upper]
Wherein, I0(s) indicate that the coordinate value of seed point s in image C, lower indicate that the lower limit of gray value, upper indicate The upper limit of gray value.
(2) to each si∈ seed calculates siEight connected region U, by all elements U in eight connected regioni∈ U meets Seed point set seed is all added in the point of given threshold condition in above-mentioned (1), repeats (2) until seed point set is added in not new point Seed, the image L of acquisitioni
In the present embodiment, the value of parameters is as follows:Lower=137, upper=255, s=(152,85).
In step 6), with the image L obtained in the step 5)iFor initial markup image, phase is carried out to image sequence B ' The Atlas segmentation of neighbour's registration, the specific method for obtaining initial segmentation sequence L are:
(1) serial number of the image Bi in sequence image B is denoted as i, and next image in sequence image B is denoted as Bi+1.By Bi The image L obtained with step 5)iLabel is denoted as to (Bi, Li), by BiAs floating image, Bi+1Image is carried out for fixed image to match Standard obtains transformation parameter fi+1.Image registration using elastix tool (S.Klein, M.Staring, K.Murphy, M.A.Viergever,J.P.W.Pluim,"elastix:atoolboxforintensitybasedmedical image registration,"IEEE TransactionsonMedicalImaging,vol.29,no.1,pp.196-205, January2010 it) realizes, specific step is as follows:
(a) pyramid model is used, by image Bi, Bi+1It is divided into three accuracy classes;
(b) by image Bi, Bi+1It is mapped in logical coordinates from physical coordinates by interpolation method;
(c) use the mode of stochastical sampling from separated image Bi, Bi+1Middle several sample points of selection, it is whole as representing Sample point set Si, Si+1
(d)Si, Si+1Between similarity indicated using mutual information (referring to document:P.Th′ evenazandM.Unser.Optimizationofmutualinformationformultiresolutionimageregist ration.IEEETrans.Image Process.,9(12):2083–2099,2000.);
Mutual information can be expressed as:
Wherein, LFAnd LMIt is the set at aturegularaintervals intensity distribution center, p is discrete joint probability, and pFAnd pMPoint It is not the edge discrete probabilistic of the fixation and moving image by summing to m and f.Joint probability uses B-spline Parzen Window is estimated:
Wherein, ωFAnd ωMIndicate fixed and mobile B-spline Parzen window.Scaling constants σFAnd σMEqual to by LFAnd LM The intensity case width of definition.These are directly according to IFAnd IMIntensity value ranges and the quantity of histogram case specified of user | LF | and | LM|;
(e) optimization algorithm being registrated uses adaptive gradient descent algorithm (bibliography:S.Klein, J.P.W.Pluim,M.Staring,and M.A.Viergever.Adaptive stochastic gradient descent optimisationfor image registration.International Journal ofComputer Vision,81 (3):227–239,March 2009);
(f) multi-level registration strategies are used, successively convert (bibliography with rigid transformation, affine transformation, B-spline: D.Rueckert,L.I.Sonoda,C.Hayes,D.L.G.Hill,M.O.Leach,and D.J.Hawkes.Nonrigidregistrationusing free-form deformations:Application to breast MR images.IEEE Trans.Med.Imag.,18(8):712-721,1999.) three kinds of mapping modes, are become Change parameter fi+1
First using the position between rigid transformation adjustment floating image and fixed image:
Wherein, R (x) indicates spin matrix, and C indicates rotation center, and t indicates original transformation parameter group, μ expression parameter to Amount, by Eulerian angles (rad) and translation set of vectors at being made of length for 3 vector μ, wherein θzIt indicates around perpendicular to figure The rotation of the axis of picture, tx、tyRespectively indicate the translation on the direction x, y;
It reuses affine transformation and adjusts global shape:
Wherein, C indicates that rotation center, t indicate original transformation parameter group, μ expression parameter vector, and A (x) indicates can be achieved flat It moves, rotation, the matrix of scaling and shearing, parameter vector μ is by matrix element aijWith translation vector tx、tyComposition, tx、tyTable respectively Show the translation on the direction x, y;
The deformation of part is finally carried out using B-spline transformation:
Wherein, xkIndicate control point, β3(x) multidimensional B-spline multinomial (M.Unser.Splines three times is indicated: Aperfect fit for signal and image processing.IEEE Signal Process.Mag.,16(6): 22-38,1999.), pkIt indicates B-spline coefficient vector (control point displacement), σ indicates B-spline control point spacing, NxIt indicates by by B The point set of x point control constraints in batten;Control point mesh is defined σ=(σ by the amount of space between control point1..., σd) (its Middle d indicates picture size), each direction can be different;The quantity P=(P1 ..., Pd) at control point passes through M= (P1 × ... × Pd) × d determines the quantity of parameter M;Parameter vector is as follows:μ=(p1x, p2x..., pP1, p1y, p2y..., pP2)T;To obtain transformation parameter fi+1
(2) by transformation parameter fi+1Act on tag image Li, obtain Bi+1Tag image Li+1
(3) by Bi+1With Li+1As new label to (Bi+1, Li+1), it repeats step (1) and (2), until terminating;
(4) by image BiAs an image B upper in floating image, with sequence image Bi-1According to side described in step (1) Method carries out image registration, wherein Bi-1For fixed image, transformation parameter f is obtainedi-1
(5) by transformation parameter fi-1Act on tag image Li, obtain Bi-1Tag image Li-1
(6) by Bi-1With Li-1As new label to (Bi-1, Li-1), it repeats step (4) and (5), until terminating;
In the present embodiment, the value of parameters is as follows:N=2048, N=3, Iter (Iterr, Itera, IterB)= (800,1200,1000), | LF|=| LM|=(16,32,64)
In step 7), the sequence image B in step 2), calculate all foreground points to background dot approximate Euclidean Distance, the specific method for obtaining range image sequence D are:(referring to document:Akmal B M,Maragos P.Optimum design of chamfer distance transforms.[J].IEEE Transactions on Image Processing A Publication of the IEEE Signal Processing Society,1998,7(10): 1477-84.):
(1) each image in sequence image B is handled as follows:Range conversion template is pressed from left to right from upper Sequence sliding under and successively calculates each pixel to the minimum euclidean distance of background, obtains intermediate distance image sequence Bd
(2) to intermediate distance image sequence BdEach image be handled as follows:Range conversion template is pressed from the right side To left sequence sliding from bottom to top, each pixel is successively calculated to the minimum euclidean distance of background, obtains distance feature image Sequence D;
In the present embodiment, range conversion template is as shown in figure 3, wherein the value of parameters is as follows:A=5, b=7, c= 11;
In step 8), the profile of the initial segmentation sequence L that step 6) is obtained is as initial profile, by step 7) Obtained in range image sequence D as characteristic image, left auricle of heart CT sequence is carried out to sequence image B using quick level set algorithm The accurate segmentation of column image, specific method are (referring to document:Anon.Insight segmentation and registration Toolkit[EB/OL].[2008-07-06].http://www.itk.org.):
(1) each image Di (i=1,2,3 ... ..n) in characteristic image sequence D of adjusting the distance, wherein n is distance feature The sum of image sequence D is calculated using sigmoid function, forms the input feature vector DS of quick level set algorithmi(i=1, 2,3 ... ..n), wherein sigmoid function is:
Wherein I indicates image Di, Max, Min are image D respectivelyiMiddle maximum, minimum gradation value, α indicate image DiBrightness model The width (window width) enclosed, β indicate the brightness (window position) at range center, and I ' indicates output image, i.e. DSi;All DSi(i=1, 2,3 ... ..n) it is quick level set algorithm characteristic sequence, it is denoted as DS;
(2) using the sequence L obtained in step 6) as the initial profile sequence of quick level set algorithm, in step 8) a) The DS obtained in the process as quick level set algorithm characteristic sequence, in sequence L every image Li (i=1,2,3 ... ..n), Li is arranged to the zero level collection an of high-dimension function by level set algorithm, this high-dimension function is called level set function:Y (X, t), then level set function movement becomes a differential equation, by extracting zero level collection G ((X), t)={ Y from output (X, t)=0 } come the profile that is moved.Use the update of a level set equation computing differential solution of equation ψ:
Wherein, A (x) indicates that advection coefficient, P (x) indicate propagation coefficient (being also the coefficient of expansion), and Z (x) indicates curvature The space regulator coefficient of mean value, α, β, γ indicate the weight of each parameter, are constants;
In the present embodiment, the value of parameters is as follows:The quick level set that P (x) is obtained using (1) process in step 8) Algorithm characteristics sequence D S.α, β, γ are set as the default value in ITK development kit (referring to document:Anon.Insight segmentation and registration Toolkit[EB/OL].[2008-07-06].http:// www.itk.org.).The final result images for obtaining left auricle of heart CT image segmentation, as shown in Figure 4.

Claims (8)

1. a kind of left auricle of heart CT image partition method, it is characterised in that include the following steps:
1) left auricle of heart CT sequence image A is inputted;
2) noise reduction process is carried out to the sequence image A in step 1), obtains sequence image B;
3) selecting step 2) in sequence image B in individual CT scheme Bi, residue sequence image is denoted as B ';
4) individual CT according to obtained in step 3) schemes BiThe position feature information of middle left auricle of heart manually chooses two characteristic points, structure The boundary information of left auricle of heart missing is built, image C is obtained;
5) to image C using area growth algorithm obtained in step 4), image L is obtainedi
6) the image L obtained with step 5)iFor initial markup image, the image B ' Atlas for carrying out adjacent registration is divided, is obtained Initial segmentation sequence L;
7) to the sequence image B in step 2), all foreground points is calculated to the approximate Euclidean distance of background dot, obtain range image Sequence D;
8) profile for the initial segmentation sequence L for obtaining step 6) is as initial profile, by range image obtained in step 7) Sequence D carries out precisely dividing for left auricle of heart CT sequence image to sequence image B as characteristic image, using quick level set algorithm It cuts.
2. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that in step 2), the sequence chart As A progress noise reduction process, the specific method for obtaining sequence image B is:
(1) image of i-th image after t iterative filtering is denoted as I in sequence image At,i, use curvature anisotropy parameter Equation recalculates:
Wherein, c (| x |) indicates specific conductance,▽ expression takes gradient, and t indicates the number of iterations, I (x, y, i) table Show i-th image in sequence image A;
(2) the process n times of iterative step (1), i-th image after obtaining noise reduction;
(3) it is incremented by i, enables i=i+1, execute step (1), obtains the image sequence B after retaining edge noise reduction.
3. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that in step 3), the selection step It is rapid 2) in sequence image B in individual CT scheme BiSpecific method be:
(1) the image number n in left auricle of heart CT sequence image A is calculated;
(2) i-th image is chosen as figure Bi, wherein i is the maximum integer no more than n/2.
4. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that described according to step in step 4) It is rapid 3) obtained in individual CT scheme BiThe position feature information of middle left auricle of heart, manually chooses two characteristic points, and building left auricle of heart lacks The boundary information of mistake, the specific method for obtaining image C are:
(1) two seed points manually chosen are set as p1(x1, y1)、p2(x2, y2), this two o'clock determines straight in a logical coordinates system of pulse train Line l, in physical coordinates system, l is by from point p1To point p2The pixel fitting extended one by one is constituted, then point p1Next picture Vegetarian refreshments position is expressed as:
Wherein, N0Indicate the position of next pixel, N1, N2Indicate position candidate, d1, d2Respectively indicate N1, N2Onto logical coordinates The distance of next point;
(2) met according to the slope k of the positional relationship straight line l in left auricle of heart anatomical structure:K ∈ (- 45 °, 0 °) ∪ (- 90 °, -45 °), then its corresponding N1, N2It is expressed as:
(3) when the slope k of straight line meets k ∈ (- 45 °, 0 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy indicates vertical in logic Deviation, according to pi+1Value determine the result of next coordinate:
When the slope k of straight line l meets k ∈ (- 90 °, -45 °):
Wherein, pi+1Indicate the selection criteria of the next position, dx indicates horizontal departure value in logic, and dy indicates hanging down in logic Straight deviation.According to pi+1Value determine the result of next coordinate:
(4) image B is modifiediMiddle coordinate N0The gray value of place pixel:
I(N0)=0
Obtain image C.
5. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that described to step in step 5) 4) image C using area growth algorithm obtained in obtains image LiSpecific method be:
(1) position according to left auricle of heart in image C selects a pixel as seed point s, given threshold in image C When the seed point of input meets following threshold values seed point set seed is added in point s by thresholding:
I0(s)∈[lower,upper]
Wherein, I0(s) indicate that the gray value of seed point s in image C, lower indicate that the lower limit of gray value, upper indicate gray value The upper limit;
(2) to each si∈ seed calculates siEight connected region U, by all elements U in eight connected regioni∈ U, meets step (1) seed point set seed is all added in the point of given threshold condition in, repeats step (2) until seed point set is added in not new point Seed obtains image Li
6. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that in step 6), with from step 5) Obtained in image LiFor initial markup image, the image sequence B ' Atlas for carrying out adjacent registration is divided, initial segmentation is obtained The specific method of sequence L is:
(1) serial number of the image Bi in sequence image B is denoted as i, and next image in sequence image B is denoted as Bi+1, by BiWith step The rapid image L 5) obtainediLabel is denoted as to (Bi, Li), by BiAs floating image, Bi+1Image registration is carried out for fixed image, Obtain transformation parameter fi+1;Image registration realizes that specific step is as follows using elastix tool:
(a) pyramid model is used, by image Bi, Bi+1It is divided into three accuracy classes;
(b) by image Bi, Bi+1It is mapped in logical coordinates from physical coordinates by interpolation method;
(c) with the mode of stochastical sampling respectively from image Bi, Bi+1Middle several sample points of selection, as the sample point for representing entirety Collect Si, Si+1
(d)Si, Si+1Between similarity indicated using mutual information;
(e) optimization algorithm being registrated uses adaptive gradient descent algorithm;
(f) multi-level registration strategies are used, successively three kinds of mapping modes is converted with rigid transformation, affine transformation, B-spline, obtains Obtain transformation parameter fi+1
(2) by transformation parameter fi+1Act on tag image Li, obtain Bi+1Tag image Li+1
(3) by Bi+1With Li+1As new label to (Bi+1, Li+1), it repeats step (1) and (2), until terminating;
(4) by image BiAs an image B upper in floating image, with sequence image Bi-1According to method described in step (1) into Row image registration, wherein Bi-1For fixed image, transformation parameter f is obtainedi-1
(5) by transformation parameter fi-1Act on tag image Li, obtain Bi-1Tag image Li-1
(6) by Bi-1With Li-1As new label to (Bi-1, Li-1), it repeats step (4) and (5), until terminating.
7. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that described to step in step 7) 2) the sequence image B in calculates all foreground points to the approximate Euclidean distance of background dot, obtains the specific of range image sequence D Method is:
(1) each image in sequence image B is handled as follows:Range conversion template is pressed from left to right from top to bottom Sequence sliding, successively calculate each pixel arrive background minimum euclidean distance, acquisition intermediate distance image sequence Bd
(2) to intermediate distance image sequence BdEach image be handled as follows:Range conversion template is pressed from right to left certainly Sequence sliding on down successively calculates each pixel to the minimum euclidean distance of background, obtains distance feature image sequence D.
8. a kind of left auricle of heart CT image partition method as described in claim 1, it is characterised in that described by step in step 8) 6) profile of the initial segmentation sequence L obtained is as initial profile, using range image sequence D obtained in step 7) as feature Image, the accurate segmentation of left auricle of heart CT sequence image is carried out using quick level set algorithm to sequence image B, and specific method is:
(1) each image Di, i=1,2 in characteristic image sequence D of adjusting the distance, 3 ... ..n, wherein n is distance feature image The sum of sequence D is calculated using sigmoid function, forms the input feature vector DS of quick level set algorithmi, i=1,2, 3 ... ..n, wherein sigmoid function be:
Wherein, I indicates image Di, Max, Min are image D respectivelyiMiddle maximum, minimum gradation value, α indicate image DiBrightness range Width, β indicate range center brightness, I ' indicate output image, i.e. DSi;All DSiFor quick level set algorithm feature Sequence is denoted as DS, wherein i=1,2,3 ... ..n;
(2) a) process using the sequence L obtained in step 6) as the initial profile sequence of quick level set algorithm, in step 8) The DS of middle acquisition is as quick level set algorithm characteristic sequence, and to every image Li, i=1,2 in sequence L, 3 ... ..n are horizontal Li is arranged to the zero level collection an of high-dimension function by set algorithm, this high-dimension function is called level set function:Y (X, t), then Level set function movement becomes a differential equation, by extracting zero level collection G ((X), t)={ Y (X, t)=0 } from output The profile moved uses the update of a level set equation computing differential solution of equation ψ:
Wherein, A (x) indicates that advection coefficient, P (x) indicate that propagation coefficient, Z (x) indicate the space regulator system of curvature mean value Number, it is constant that α, β, γ, which indicate the weight of each parameter,.
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