CN103473805A - Method for measuring size of three-dimensional reconstruction liver model on basis of improved region growing algorithm - Google Patents

Abstract

The invention discloses a method for measuring the size of a three-dimensional reconstruction liver model on the basis of an improved region growing algorithm. The method includes the steps that seed point selection and growth criteria in a traditional region growing algorithm are improved by means of a quasi-Monte Carlo method, and an abdomen CT image is segmented by means of an improved region growing segmentation method to extract a liver area; a segmented binary image is used for three-dimensional reconstruction to obtain the three-dimensional reconstruction liver model only provided with a surface mesh, and the model is sealed; a regular square bounding box is arranged, the bottommost face of the bounding box is provided with a projection plane, the sizes of pentahedrons defined by a triangle patch on the reconstruction model and a projection projected by the triangle patch on the projection plane in an enclosed mode are calculated, wherein the triangle patch is provided with a normal vector in the positive direction and a normal vector in the negative direction; finally, the algebraic sum of the sizes of the pentahedrons is the size of the liver model. The method can well represent the shape of the liver, and therefore size measurement is effectively carried out on the three-dimensional reconstruction liver model. Besides, the size of a part of the liver can be measured, and measurement precision is high.

Description

Method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume

Technical field

The present invention relates to a kind of method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume, relating to medical image processes and two technical fields of Computer Applied Technology, mainly according to the processing power of computing machine, abdominal CT images is cut apart, then carried out three-dimensional reconstruction and realize cubing.

Background technology

Because China belongs to the liver diseases hotspot, in the process for the treatment of liver diseases, the doctor need to obtain liver volume data relatively accurately usually.Liver volume is measured not only can the quantitative evaluation liver size, can also indirectly reflect the liver function situation, there is extensive and important clinical value, all significant in postevaluation and liver transfer operation are selected, performed the operation to assessment cirrhosis Hepatic Functional Reserve, liver neoplasm modus operandi, the accuracy that therefore preoperative liver volume is measured directly affects the selection of operation plan.

Because liver is erose organ, for a long time, most liver volume measuring method is for two dimensional image, carry out the integral and calculating volume by the area of asking for liver area in image series, but this method is merely able to estimate liver volume according to formula, its measurement precision need further raising.

The three-dimensional reconstruction hepatic model has form structure preferably, and the doctor just can carry out the liver morphological analysis, and the cubing accuracy of Three-dimension Reconstruction Model is that doctors are confessed.

Through existing technology retrieval is found, Chinese patent literature CN102663819A, open day 2012-09-12, put down in writing " the liver volume measuring method based on ultrasonoscopy and three-dimensional model ", although being the liver to three-dimensional reconstruction, the method carried out cubing, but its core concept is to carry out liver segmentation for X-Y scheme, calculate the product of the spacing of the area sum of all liver sections and adjacent two sections, the volume using result of calculation as liver.Asking in the method the tomography area is that each section is divided into to a plurality of triangles, by asking a plurality of leg-of-mutton area sums, obtains the area of section.This method need to just can more approach actual value by the less liver area area that adds up out of the area of triangle subdivision, so the process of subdivision relatively wastes time and energy, and the error of computed tomography area is larger.In addition, the method is to carry out the liver volume measurement for two dimensional image, and the measurement result of the method the integrated straight of three-dimensional liver reconstruction model not to be tapped into to capable measurement result more satisfactory.

At " medical equipment information " 22 volumes 12 in 2007 in interim " research of the volume of intracranial hematoma measuring method based on the CT image ", doctor Li Qiang and Wu Juan have been used integral method in measuring volume of hematoma, every layer of hemotoncus of sequence C T image all split, then ask for hemotoncus region area in every one deck according to pixel size and quantity, finally according to the product of areas of bed thickness and every layer, calculate the volume of hemotoncus.Mentioned standardization liver volume measuring method in the Zhao Jing of University Of Qingdao Master's thesis " application in children's's liver tumor operation of CT three-dimensional reconstruction and Future liver volume ":

(1) standardization liver volume=706.2 * body surface area+2.4;

(2) children's's 30kg body surface area (m ²)=body weight (kg) * 0.035+0.1;

(3) children's's 30kg body surface area (m ²body weight)=[(kg)-30] * 0.02+1.05.

By the calculating of standard liver volume, can roughly understand normal person's liver volume size, but the liver volume of generation illness can not be calculated and obtain with this formula.These two pieces of articles are similar with " the liver volume measuring method based on ultrasonoscopy and three-dimensional model ", all indirectly to carry out cubing for two dimensional image, different is to calculate region area in " research of the volume of intracranial hematoma measuring method based on the CT image " not need zone is divided into to several triangles, but calculate after each pixel size pixels whole in the zone of adding up out and, finally carry out the integration cube.

In document " Stereology:a novel technique for rapid assessment of liver volume " (Insights Imaging (2012) 3:387 – 393), the author has proposed the area that a kind of method based on stereology is measured liver area on two dimensional image, by the single image zone is divided into to several square nets, then add up the number of grid that liver area comprises, and then carry out cubing by integral formula.And at document " Validation study of a fast; accurate; and precise brain tumor volume measurement " (Computer methods and programs in biomedicine, (2013)), the author is in carrying out cubing to brain tumor, at first obtain cutting apart image by improving Level Set Method, then image area is calculated, finally by integration, try to achieve gross tumor volume.And at document " CT liver volumetry using three-dimensional image data in living donor liver transplantation:Effects of slice thickness on volume calculation " (Liver Transpl.2011December; 17 (12): 1427 – 1436.) in, the author is central bay impact on cubing apart from size for different image layer spacings, and in this article the computing method of volume still for two dimensional image, calculate the liver area area by number of pixels and pixel size in the statistics liver area, then carry out integration and ask liver volume.

Asking for volume method in related medical science in above-mentioned document is all measured indirectly for two dimensional image, there is certain Subjective Factors, and said method is all to carry out cubing for whole object, can not carry out local measurement, be subject to certain restrictions, and its measurement precision need further raising.

Summary of the invention

The technical issues that need to address of the present invention just are to overcome the defect of prior art, a kind of method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume is provided, the inventive method is directly to carry out cubing for Three-dimension Reconstruction Model, and can directly to the model regional area, be measured, also there is effect preferably aspect measurement precision.

For addressing the above problem, the present invention adopts following technical scheme:

The invention provides a kind of method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume, described method comprises the following steps:

1), CT image pre-service;

2), area-of-interest, Quasi-Monte-Carlo method selection Seed Points are set;

3), cut apart liver area;

4), cut apart post processing of image;

5), liver three-dimensional reconstruction;

6), bounding box is set, and tri patch normal vector consistance is adjusted;

7), the tri patch projection, ask pentahedron volume cumulative sum, obtain volume data.

Be specially: at first use quasi Monte Carlo method to choose with the criterion of growing and improved the Seed Points in traditional algorithm of region growing, and with the region growing dividing method after improving, abdominal CT images is cut apart to extract liver area; Secondly utilizing the bianry image split to carry out three-dimensional reconstruction obtains only having the three-dimensional reconstruction hepatic model of surface mesh and model being sealed; The square bounding box of rule finally is set, the bottom surface of bounding box is set to projection plane, calculate on reconstruction model and have the tri patch of positive and negative direction method vector and the pentahedron volume that its projection on projection plane surrounds, the algebraic sum that finally calculates all pentahedron volumes is exactly the volume of hepatic model.

Concrete steps are:

The first step: use nonlinear mapping technique to improve the contrast of liver area in abdominal CT images, alternatively arrange one than large rectangle zone, i.e. region of interest ROI in liver area;

Second step: use the quasi Monte Carlo method random point that distributes in ROI, then screened suitable Seed Points;

The 3rd step: region growing adopts neighbours territory method to be grown, and by the gray-scale value of pixel and the variation of Grad, the growth criterion is set, and at first with the Robert operator, calculates the average gradient value in area-of-interest

when algorithm of region growing judges whether some pixels meet growth conditions, if this grey scale pixel value meet as shown in the formula, this pixel is included in growth district so, otherwise judges next pixel.

$G_{\mathrm{ave}}-a\stackrel{\&OverBar;}{\&dtri;T}<G_i<G_{\mathrm{ave}}+a\stackrel{\&OverBar;}{\&dtri;T}$

Wherein, a is the regulation and control parameter;

The 4th step: use improved algorithm of region growing to be cut apart and obtain liver area continuous abdominal CT images, then carry out aftertreatment and obtain continuous liver area bianry image;

Post-processing step comprises: according to morphological method, image is carried out to empty filling, use the canny operator to obtain liver contour images preferably, then with the flood-fill algorithm, the liver contour images is filled, finally obtained thering is the liver image than smooth contoured;

Then the liver image of these being cut apart is used classical Marching Cube algorithm to carry out the surface rendering reconstruction, because this method is to carry out cubing for the Three-dimension Reconstruction Model sealed, so can there be the surface hole defect on some spaces in the model after rebuilding, need to carry out the repairing of surface hole defect to the model after rebuilding, so just can obtain the hepatic model that only there is surperficial triangle gridding of sealing;

The 5th step: at first, the rectangle bounding box of a rule is set according to this reconstruction hepatic model volume coordinate distance, and the bottom surface of bounding box is set to projection plane Z, its normal vector is N.Six faces of this bounding box can change by man-machine interactively the size of bounding box, so that carry out the measurement of liver local volume.

Secondly, because process of reconstruction intermediate cam dough sheet normal vector direction is not unified, direction is inside and outside inconsistent.So need the surperficial tri patch of the whole hepatic model of traversal, the normal vector of tri patch carried out to the unification adjustment.：

1), obtain an initial tri patch Δ ABC normal vector n,

The normal vector n of the tri patch that 2), traversal is adjacent with Δ ABC _iif, n*n _i<0, n _iwith the n opposite direction, so just change normal vector n _idirection, consistent with the n direction; If n*n _i0, n _iidentical with the n direction, proceed traversal adjustment;

3), the tri patch after the normal vector unification is classified: normal vector inner product that first kind tri patch is its normal vector and projection plane Z is greater than 0; Normal vector inner product that the Equations of The Second Kind tri patch is its normal vector and projection plane Z is less than 0; Normal vector inner product that the 3rd class tri patch is its normal vector and projection plane Z equals 0.

The 6th step: by bounding box is come internal model is intercepted alternately, carry out the cubing of regional area;

The 7th step: liver volume is calculated, by tri patch is projected on projecting plane and forms pentahedron, calculated that sorted pentahedron volume is cumulative asks poor.

The present invention proposes a kind of volume measuring method of CT 3-dimensional reconstruction liver, the method improves to be partitioned into liver area by the region growing method to traditional, then obtain the three-dimensional reconstruction hepatic model, finally by the projection volume algebraic sum, liver volume is calculated.The present invention not only carries out cubing to liver and has higher calculating accuracy, but also can measure local liver volume.

Innovative point of the present invention has:

1. the present invention is cut apart liver image by the algorithm of region growing that uses improved Seed Points selection course and region growing criterion.Adopt first quasi Monte Carlo method to come liver area image selected seed point, the method can be carried out statistical computation to the liver area Pixel Information according to the random point be distributed in liver area, then selects suitable Seed Points and makes the region growing criterion that meets this area information.

2. in medical science, the cubing of histoorgan is all measured for whole object, and also for how carrying out local liver volume measurement, designs in the present invention.By the liver image to after cutting apart, use Marching Cube algorithm to carry out three-dimensional reconstruction, and the regular square bounding box of an applicable reconstruction model size is set.Owing to can bounding box being carried out to the size that man-machine interactively operates to change bounding box, therefore can intercept the part liver by bounding box, then carry out local measurement.

3. medically liver volume being measured to great majority is to carry out integral and calculating for two dimensional image to carry out measurement volumes indirectly, the present invention directly carries out cubing to the hepatic model of three-dimensional reconstruction, and the three-dimensional reconstruction hepatic model is directly carried out to cubing has more accurate measurement result.Core of the present invention is the liver volume that the pentahedron volume of having used tri patch with positive and negative direction method vector and its projection on projection plane to surround sues for peace to ask for three-dimensional reconstruction.In the present invention, use Marching Cube algorithm to carry out to liver image the three-dimensional reconstruction hepatic model that three-dimensional reconstruction obtains only having surperficial triangle gridding, the tri patch normal vector is being carried out after the unification adjustment, tri patch being classified, the normal vector inner product that is divided into tri patch normal vector and projection plane is greater than 0, be less than 0 and equal 0 three kinds, the third situation volume projection is 0, therefore ignores.Finally the first two kind tri patch is projected on the projection plane arranged and obtains pentahedron, then pentahedron is split into to three tetrahedrons, by asking three tetrahedral volumes and obtaining this pentahedron volume.Finally the pentahedron volume of the three groups of tri patch projections read group total that adds up is obtained to final three-dimensional reconstruction hepatic model volume.

The accompanying drawing explanation

Fig. 1 is process flow diagram of the present invention.

Fig. 2 for selecting the schematic diagram of ROI the random point that distributes in liver area, and wherein white portion is the area-of-interest of setting, and the point in white portion is the random point of low difference distribution.

Fig. 3 is for through over-segmentation the liver bianry image that carries out aftertreatment.

Fig. 4 is three-dimensional reconstruction liver Local map, and this part is the part liver obtained through after the bounding box intercepting, and this model is the liver partial model that only has surperficial triangle gridding.

Fig. 5 is reconstruction model cubing principle schematic, and Y means reconstruction model, and arrow n means tri patch normal vector direction on model, and y means the projection of Y on projection plane Z, and N means view plane normal's amount.

Fig. 6 is that pentahedron forms schematic diagram, pentahedron P ₁p ₂p ₃q ₁q ₂q ₃can subdivision be three tetrahedrons, be respectively: P ₁q ₁q ₂q ₃, P ₁p ₂p ₃q ₂with P ₁p ₃q ₂q ₃.Ask three tetrahedron volumes and be exactly pentahedral volume by formula 6.

Embodiment

As shown in Figure 1, the invention provides a kind of method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume, described method comprises the following steps:

1), CT image pre-service;

2), area-of-interest, Quasi-Monte-Carlo method selection Seed Points are set;

3), cut apart liver area;

4), cut apart post processing of image;

5), liver three-dimensional reconstruction;

6), bounding box is set, and tri patch normal vector consistance is adjusted;

7), the tri patch projection, ask pentahedron volume cumulative sum, obtain volume data.

Concrete steps are:

The first step: use nonlinear mapping technique to improve the contrast of liver area in abdominal CT images, alternatively arrange one than the large rectangle zone in liver area, i.e. area-of-interest (ROI), as shown in Figure 2.

The present invention selects nonlinear mapping technique to be processed abdomen images, and it is by the gray-scale value g of input image pixels (x, y) _in(x, y) is converted to the gray-scale value g of output image by mapping function F (x, y) _out(x, y).Realize this process with the Sigmoids function, the Sigmoids function as shown in Equation (1):

$P^{\&prime;}=(\mathrm{Max}-\mathrm{Min})\&CenterDot;\frac{1}{1+e^{-\frac{p-\mathrm{\&beta;}}{\mathrm{\&alpha;}}}}+\mathrm{Min}---\left(1\right)$

Wherein, P is the gray-scale value of input pixel, and P ' is the gray-scale value of output pixel, the minimum value that Min and Max are the output image gray scale and maximal value.The regulation and control parameter that α is the input gray level scope, β is around the gray scale in center range.This process can improve picture contrast.Due to the liver peripheral region adhesion of abdominal CT many muscle and mucous membranes, be difficult to effectively differentiate by naked eyes, through after Nonlinear Mapping, can improve preferably the abdomen images contrast, make the liver area profile can become clear, be conducive to the follow-up of liver and cut apart.

Then the square ROI of a rule is set on the liver area of abdominal CT images by the mode of man-machine interactively, this region area is included in liver area the largelyst, so more is conducive to add up the liver area Pixel Information and selects Seed Points and the growth criterion is set;

Second step: use the quasi Monte Carlo method random point that distributes in ROI, then screen suitable Seed Points.

Hang down the random point of difference distribution by using quasi Monte Carlo method to distribute in ROI, the more uniform point of this process need distribution is statistical picture information exactly, realizes quasi Monte Carlo method with the Halton algorithm in the present invention and generate equally distributed low difference random point.Because each random point is corresponding with the liver area pixel respectively, therefore can add up the half-tone information in liver area by the corresponding pixel of these random points.And these random points are by being used to the Seed Points in algorithm of region growing after screening, be conducive to like this to reduce the impact that artificial selected seed point brings (such as the artificial Seed Points of selecting is a noise spot, or the Seed Points institute respective pixel gray-scale value of selecting and liver area gray average difference is excessive etc. that factor all can exert an influence to the effect of algorithm of region growing).

The Seed Points screening is as shown in formula 2,3:

$G_{\mathrm{ave}}=\frac{1}{M-m}\underset{i=1}{\overset{M-m}{\mathrm{\&Sigma;}}}{G}_i---\left(2\right)$

$\frac{|G_j-G_{\mathrm{ave}}|}{G_{\mathrm{ave}}}\&le;u---\left(3\right)$

Wherein: G _ifor the respective pixel P of random point institute _igray-scale value, G _avefor whole random point institute respective pixel gray average in the ROI come out.The quantity of the random point of the low difference distribution that M is the quasi Monte Carlo method generation.M is singular point quantity, and singular point refers to the small holes occurred in pretreated CT image for liver zone, and some random point correspondences these small holes, so this institute's respective pixel gray-scale value is 0, so these points need to be excluded.U is numeric ratio, is used for controlling suitable Seed Points quantity;

The 3rd step: selecting suitable growth criterion is the committed step in algorithm of region growing, and the present invention is set the growth criterion by the gray-scale value of pixel and the variation of Grad.At first calculate the average gradient value in area-of-interest with the Robert operator

when algorithm of region growing judges whether some pixels meet growth conditions, if this grey scale pixel value meets formula 4, this pixel is included in growth district so, otherwise judges next pixel.

$G_{\mathrm{ave}}-a\stackrel{\&OverBar;}{\&dtri;T}<G_i<G_{\mathrm{ave}}+a\stackrel{\&OverBar;}{\&dtri;T}---\left(4\right)$

Wherein, a is the regulation and control parameter;

The 4th step: use improved algorithm of region growing to be cut apart and obtain liver area continuous abdominal CT images, then carry out aftertreatment and obtain continuous liver area bianry image.Post-processing step comprises: according to morphological method, image is carried out to empty filling; Use the canny operator to obtain liver contour images preferably, then with the flood-fill algorithm, the liver contour images is filled, finally obtain thering is the liver image than smooth contoured, as shown in Figure 3;

Then the liver image of these being cut apart is used classical Marching Cube algorithm to carry out the surface rendering reconstruction, because the Three-dimension Reconstruction Model that the present invention be directed to sealing carries out cubing, so can there be the surface hole defect on some spaces in the model after rebuilding, so need to carry out the repairing of surface hole defect to the model after rebuilding, so just can obtain the hepatic model that only there is surperficial triangle gridding of sealing, as shown in Figure 4;

The 5th step: at first, the rectangle bounding box of a rule is set according to this reconstruction hepatic model volume coordinate distance, and the bottom surface of bounding box is set to projection plane Z, its normal vector is N.Six faces of this bounding box can change by man-machine interactively the size of bounding box, so that carry out the measurement of liver local volume.

Secondly, because process of reconstruction intermediate cam dough sheet normal vector direction is not unified, direction is inside and outside inconsistent.So need the surperficial tri patch of the whole hepatic model of traversal, the normal vector of tri patch carried out to the unification adjustment.At first choose a tri patch Δ ABC, its normal vector is n, as initial normal vector.The normal vector n of the tri patch that then traversal is adjacent with Δ ABC _iif, n*n _i<0, n _iwith the n opposite direction, so just change normal vector n _idirection, consistent with the n direction; If n*n _i0, n _iidentical with the n direction, proceed traversal adjustment.Finally, the tri patch after the normal vector unification is classified: normal vector inner product that first kind tri patch is its normal vector and projection plane Z is greater than 0; Normal vector inner product that the Equations of The Second Kind tri patch is its normal vector and projection plane Z is less than 0; Normal vector inner product that the 3rd class tri patch is its normal vector and projection plane Z equals 0;

The 6th step: because the bounding box around reconstruction model can change size by man-machine interactively, therefore, by bounding box is come reconstruction model is intercepted alternately, obtain the liver partial model, so just can carry out local cubing to hepatic model.Because the coordinate range of six faces in space coordinates of bounding box is confirmable, and, when the face to bounding box intercepts the part hepatic model alternately, in mutual process, the coordinate of six faces of bounding box also can change in space coordinates.When carrying out the liver local measurement, need which tri patch of judgement in the bounding box scope, because the tri patch that only has the local hepatic model after intercepting is in the scope of bounding box.Judge tri patch whether the method in the bounding box scope be: the traversal tri patch, judge that the coordinate of three points of tri patch is whether all in the bounding box coordinate range, if the coordinate of a point of tri patch is not in the bounding box coordinate range, illustrate that this triangle and bounding box intersect or, outside the bounding box coordinate range, this tri patch just is left in the basket and does not carry out calculating so; Otherwise it is upper that tri patch is projected to projecting plane Z, according to the 7th step, carries out volume calculating;

The 7th step: liver volume is calculated: form a pentahedron by tri patch being projected on projecting plane, calculate sorted pentahedron volume cumulative sum, then ask poor and calculate.

It is upper that first-selection need to project to respectively plane Z to tri-point coordinate of tri patch Δ ABC of traversal, obtains projected triangle Δ abc.Now Δ ABC and Δ abc form a pentahedron, then this pentahedron are carried out to subdivision, obtain three tetrahedrons (as shown in Figure 6).Finally according to formula 5, calculate each tetrahedral volume:

$V\left(P_1{Q}_1{Q}_2{Q}_3\right)=\frac{1}{6}*\left|\begin{array}{cccc}1& 1& 1& 1\\ x_1& x_2& x_3& x_4\\ y_1& y_2& y_3& y_4\\ z_1& z_2& z_3& z_4\end{array}\right|---\left(5\right)$

(x wherein ₁, y ₁, z ₁), (x ₂, y ₂, z ₂) (x ₃, y ₃, z ₃) (x ₄, y ₄, z ₄) be respectively tetrahedron P ₁q ₁q ₂q ₃four point coordinate, cumulative three tetrahedral volumes and be exactly the pentahedron volume after projection then.

Minute two class situations in the process of finally calculating at whole hepatic model volume: a kind of is that the normal vector inner product of tri patch normal vector and projection plane Z is greater than 0, and the pentahedron volume cumulative sum after these tri patch projections is V ₁; Normal vector inner product that another kind of tri patch is its normal vector and projection plane Z is less than 0, and the pentahedron volume cumulative sum after these tri patch projections is V ₂.Equaling 0 the projection of tri patch on projection plane Z due to the normal vector inner product of normal vector and projection plane Z is straight line, and its volume is 0, so ignore.Finally obtain the volume of three-dimensional reconstruction hepatic model as shown in Equation (6).

V _liver=| V ₁-V ₂| (6)

Finally it should be noted that: obviously, above-described embodiment is only for example of the present invention clearly is described, and is not the restriction to embodiment.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without also giving all embodiments.And the apparent variation of being amplified out thus or change are still among protection scope of the present invention.

Claims (3)

1. the method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume, is characterized in that, described method comprises the following steps:

1), CT image pre-service;

2), area-of-interest, quasi Monte Carlo method selection Seed Points are set;

3), cut apart liver area;

4), cut apart post processing of image;

5), liver three-dimensional reconstruction;

6), bounding box is set, and tri patch normal vector consistance is adjusted;

7), the tri patch projection, ask pentahedron volume cumulative sum, obtain volume data.

2. the method based on improving algorithm of region growing and measure three-dimensional reconstruction hepatic model volume as claimed in claim 1, it is characterized in that, be specially: at first use quasi Monte Carlo method to choose with the criterion of growing and improved the Seed Points in traditional algorithm of region growing, and with the region growing dividing method after improving, abdominal CT images is cut apart to extract liver area; Secondly utilizing the bianry image split to carry out three-dimensional reconstruction obtains only having the three-dimensional reconstruction hepatic model of surface mesh and model being sealed; The square bounding box of rule finally is set, the bottom surface of bounding box is set to projection plane, calculate on reconstruction model and have the tri patch of positive and negative direction method vector and the pentahedron volume that its projection on projection plane surrounds, the algebraic sum that finally calculates all pentahedron volumes is exactly the volume of hepatic model.

3. the method based on improving algorithm of region growing measurement three-dimensional reconstruction hepatic model volume as claimed in claim 2, is characterized in that, concrete steps are:

The first step: use nonlinear mapping technique to improve the contrast of liver area in abdominal CT images, rectangular area, i.e. a region of interest ROI alternatively are set in liver area;

Second step: use the quasi Monte Carlo method random point that distributes in ROI, then screen suitable Seed Points;

The 3rd step: region growing adopts neighbours territory method to be grown, and by the gray-scale value of pixel and the variation of Grad, the growth criterion is set, and at first with the Robert operator, calculates the average gradient value in area-of-interest

when algorithm of region growing judges whether some pixels meet growth conditions, if this grey scale pixel value meets following formula, this pixel is included in growth district so, otherwise judges next pixel;

$G_{\mathrm{ave}}-a\stackrel{\&OverBar;}{\&dtri;T}<G_i<G_{\mathrm{ave}}+a\stackrel{\&OverBar;}{\&dtri;T}$

Wherein, a is the regulation and control parameter;

The 4th step: use improved algorithm of region growing to be cut apart and obtain liver area continuous abdominal CT images, then carry out aftertreatment and obtain continuous liver area bianry image;

Post-processing step comprises: according to morphological method, image is carried out to empty filling, use the canny operator to obtain liver contour images preferably, then with the flood-fill algorithm, the liver contour images is filled, finally obtained thering is the liver image than smooth contoured;

Then the liver image of these being cut apart is used classical Marching Cube algorithm to carry out the surface rendering reconstruction, because this method is to carry out cubing for the Three-dimension Reconstruction Model sealed, so can there be the surface hole defect on some spaces in the model after rebuilding, need to carry out the repairing of surface hole defect to the model after rebuilding, so just can obtain the hepatic model that only there is surperficial triangle gridding of sealing;

The 5th step: at first, the rectangle bounding box of a rule is set according to this reconstruction hepatic model volume coordinate distance, and the bottom surface of bounding box is set to projection plane Z, its normal vector is N; Six faces of this bounding box can change by man-machine interactively the size of bounding box, so that carry out the measurement of liver local volume;

Secondly, because process of reconstruction intermediate cam dough sheet normal vector direction is not unified, direction is inside and outside inconsistent; So need the surperficial tri patch of the whole hepatic model of traversal, the normal vector of tri patch carried out to the unification adjustment:

1), obtain an initial tri patch Δ ABC normal vector n, as initial normal vector;

The normal vector n of the tri patch that 2), traversal is adjacent with Δ ABC _iif, n*n _i<0, n _iwith the n opposite direction, so just change normal vector n _idirection, consistent with the n direction; If n*n _i0, n _iidentical with the n direction, proceed traversal adjustment;

3), the tri patch after the normal vector unification is classified: normal vector inner product that first kind tri patch is its normal vector and projection plane Z is greater than 0; Normal vector inner product that the Equations of The Second Kind tri patch is its normal vector and projection plane Z is less than 0; Normal vector inner product that the 3rd class tri patch is its normal vector and projection plane Z equals 0;

The 6th step: by bounding box is come internal model is intercepted alternately, carry out the cubing of regional area;

The 7th step: liver volume is calculated, by tri patch being projected on projecting plane, formed a pentahedron, calculate sorted pentahedron volume cumulative sum, then ask poor and calculate.

Images