CN100447816C - 3D analysis and analog method for CT projection data - Google Patents

Abstract

The invention relates to the rebuilding method of a CT projecting image. The CT projecting data three dimensional analog method comprises determining the definition method for the module and scanning, setting analog program inside the computer, with the above to generate CT projecting data pjk. Changing the module definition and scanning parameter in an interactive way, it realizes the quick acquisition of analytical analog projecting data.

Description

CT data for projection 3 D analysis and analog method

Technical field

The present invention relates to the method that the CT projected image is rebuild, particularly the analogy method of CT projected image reconstruction.

Background technology

The CT technology is widely used in industrial nondestructive testing (NDT), medical diagnosis and scientific research field.Must use the CT data for projection in the research process of CT reconstruction algorithm.

The source of CT data for projection can have two kinds: 1) from actual CT system acquisition; 2) produce by computer Simulation calculation.

Since actual CT system price costliness, the CT system that most research units are unactual.In addition, for the data for projection of the performance need particular model of studying reconstruction algorithm, must corresponding model customized during recording projection data in actual CT system, expense is very big, and is subjected to the restriction of actual manufacturing capacity, and some model can't create.For these reasons, the computer Simulation calculation data for projection is widely adopted in CT reconstruction algorithm research process.

The method of computer Simulation calculation data for projection has two classes: 1) analysis and analog method; 2) method for numerical simulation.Analysis and analog method directly calculates the acquisition analog projection data by mathematic(al) representation, required model definition directly writes in the computer program code, change model if desired and then must write the simulated projections calculation procedure again, but its analog projection data is desirable, does not contain the discretize noise.Method for numerical simulation is then with the process of aggregation of model as pixel, simulation process is for calculating each pixel and the result being merged to obtain analog projection data, model can be by pixel definition one by one, and the change model need not to change the simulated projections calculation procedure, and is therefore very easy to use.But method for numerical simulation has 2 deficiencies: 1) computing velocity is slow; 2) introduced the discretize noise in the projection process.The method that reduces the discretize noise is to reduce Pixel Dimensions, but then can cause the one-tenth cube multiplication of computing time long like this.For the CT algorithm research, do not wish to have the discretize noise in the analog projection data, the simulated projections computing method of actual selection then need according to compromising between computing time, this three of convenience to the degrees of tolerance of discretize noise, model change, select suitable computing method, at present under the condition computing velocity of analysis and analog method be generally method for numerical simulation tens to hundred times.

Summary of the invention

(1) technical matters that will solve

The purpose of this invention is to provide a kind of computing velocity fast, be convenient to revise the CT data for projection 3 D analysis and analog method of model, thereby can obtain the analog projection data of the no discretize noise of various models easily and quickly.

(2) technical scheme

In order to achieve the above object, the present invention takes following scheme: comprising: 1) determine the model definition method; 2) determine the scan mode define method; 3) the analytic simulation program is set in computing machine; 4) by 1), 2), 3) produce CT data for projection p ^Jk

Wherein, described model definition method comprises: A is by a plurality of models of combination definition of the basic body of attenuation coefficient separately of having specified; B establishes a model by i basic body M _iForm, the attenuation coefficient of each basic body is m _iC carries out model definition by the computer interactive interface.

Wherein, described scan mode define method comprises:

The simulated projections process that a is complete is made of j projection;

B specifies the radiographic source center of this projection for each projection

The detector center

C specifies the probe unit of detector to count k and each detector cells center

Relative detector center

Geometric relationship;

Amount of radiation l, each bar ray starting point that d specifies each detector cells to receive

Relative radiographic source center Geometric relationship and each bar ray and detector intersection point Relative detector cells center

Geometric relationship, each bar ray to the contribution weight w of the simulated projections numerical value of detector cells _Jkl, weight should be normalized, promptly

E carries out the definition of scan mode by the computer interactive interface.

Wherein, described analytic simulation program comprises:

The analog physical factor for the treatment of that a) will be provided with is divided into to the influence of ray position with to two classes that influence of projection value.According to starting point and the terminal point coordinate of the influence of ray position being adjusted ray, according to projection value influenced the final simulated projections value of adjustment.

B) by coordinate conversion ray starting point, terminal point coordinate are transformed into the solid local coordinate system, in the solid local coordinate system, calculate the intersecting point coordinate of ray and solid.

C),, calculate attenuation coefficient subsequently by the coordinate Calculation intersection length in the solid local coordinate system to direct stack combinations mode.

D) to replacing array mode, intersecting point coordinate is transformed into system coordinate system, in system coordinate system, calculates the distance of two intersection points, calculate attenuation coefficient subsequently to the ray starting point.

Wherein, described CT data for projection p _JkComprise:

A) the simulated projections numerical value p of a ray _JklBe line segment ${\stackrel{r}{r}}_{\mathrm{jkl}}={\stackrel{r}{d}}_{\mathrm{jkl}}-{\stackrel{r}{s}}_{\mathrm{jkl}}$ Go up the integration of all attenuation coefficient m, that is:

$p_{\mathrm{jkl}}={\stackrel{`}{O}}_{{\stackrel{r}{r}}_{\mathrm{jkl}}}\mathrm{du}$

B) the simulated projections numerical value p of each detector cells _JkFor:

C) p _JklThe computing method and the attenuation coefficient of model relevant, the attenuation coefficient of model is made up by certain mode by the attenuation coefficient of each solid and obtains, different array modes must use different computing method to calculate p _Jkl

Wherein, described array mode comprises: directly adding up of each solid attenuation coefficient, that is: establish a bit in the model

Be positioned at m solid forming this model, then the attenuation coefficient of this point of model is

P under this array mode _JklComputing method be:

Calculate line segment earlier Intersection length L with each solid of composition model _Ijkl, calculate simulated projections numerical value p then _Jkl:

Wherein, described array mode comprises: the replacement of each solid attenuation coefficient is made up, and establishes in the model a bit that is:

Be positioned at m solid forming this model, then the attenuation coefficient of this point of model is $m{r}_r=m_m,$ P under this array mode _JklComputing method be: establish line segment

There are two intersection points of two intersection points and n solid to be positioned at the n layer with N solid in i the solid of composition model, arrive

Distance be respectively a _JklnAnd b _Jkln, establish a _Jkln＜b _Jkln

a _jkl0＝0， $b_{\mathrm{jkl}0}=\left|{\stackrel{r}{r}}_{\mathrm{jkl}}\right|,$ m ₀＝0。The 0th layer is line segment The line segment of each layer all may be divided into shorter line segment by more high-rise intersection point, and the attenuation coefficient value of each point is the attenuation coefficient value of the solid of the top line segment correspondence under it.Can calculate simulated projections numerical value p thus _Jkl

(3) beneficial effect

1) is used for changing model definition and sweep parameter definition owing to offering with alternant way, be implemented under the situation that need not to write again the simulated projections program and define various models and sweep parameter as required, thereby obtain the analytic simulation data for projection quickly and easily.2) computing velocity is fast, can obtain the analog projection data of the no discretize noise of various models.

Description of drawings

Fig. 1 is the simulated projections value calculation flow chart of replacement when combination ray of each solid attenuation coefficient of the present invention;

Fig. 2 is an analytic simulation projection process synoptic diagram of the present invention;

Fig. 3 is a model definition interactive interface synoptic diagram of the present invention;

Fig. 4 is that simulated projections parameter of the present invention is provided with the interactive interface synoptic diagram.

Fig. 5 is an analytic simulation projection program calculation flow chart of the present invention.

1) embodiment

Following examples are used to illustrate the present invention, but are not used for limiting the scope of the invention.

The present invention adopts when implementing, and comprises step: 1) determine the model definition method; 2) determine the scan mode define method; 3) the analytic simulation program is set in computing machine; 4) by step 1), step 2), step 3) produces CT data for projection p _Jk

As shown in Figure 2, exemplary embodiments of the present invention comprises the disposal route that computer interactive interface and analytic simulation program are imported the user.Use two coordinate systems among the embodiment: system coordinate system and solid local coordinate system.Model center is positioned at the system coordinate system initial point, and radiographic source position, detector position all define in system coordinate system.Solid is centered close to solid local coordinate system initial point, and axis of symmetry overlaps with coordinate axis.

The interactive interface of model definition as shown in Figure 3, the user determines the coordinate (x of solid center in system coordinate system of composition model _i, y _i, z _i) and the angle of inclination a of axis of symmetry in system coordinate system of solid _i, f _i, determine solid attenuation coefficient m simultaneously _iAnd array mode.

The interactive interface that the simulated projections parameter is provided with as shown in Figure 4, the physical influence factor that the user determines scan mode and will simulate.

The flow process of analytic simulation program to the disposal route of user input is as shown in Figure 5:

1) the physical influence factor that will simulate is decomposed into two classes: to the influence of ray position (as various skews etc.) and to the influence of ray upslide shadow value (as noise etc.).

2) calculate the starting point coordinate of each bar ray according to sweep parameter setting and the physical factor setting that influences ray position

And terminal point coordinate

3) starting point coordinate and terminal point coordinate are obtained the starting point coordinate of each bar ray in the local coordinate system of each solid by coordinate conversion And terminal point coordinate

4) in the local coordinate system of each solid, calculate the intersecting point coordinate of ray and solid: do not have two intersection points (no intersection point or an intersection point is only arranged); Two intersection points are perhaps arranged

With

If the attenuation coefficient of solid calculates ray and each solid intersection length L by direct accumulate mode combination according to the distance between two points formula _Ijkl, can calculate the projection value p of each bar ray then _Jklp _JklComputing method be:

Calculate line segment earlier Intersection length L with each solid of composition model _Ijkl, calculate simulated projections numerical value p then _Jkl:

If the attenuation coefficient of solid then obtains its coordinate in system coordinate system with intersecting point coordinate by coordinate conversion by the substitute mode combination

With

Calculate again intersection point to the ray starting point apart from a _IjklAnd b _Ijkl, can calculate the projection value p of each bar ray then _Jkl

The corresponding calculated formula is:

$a_{\mathrm{ijkl}}=\sqrt{{(x_{a_{\mathrm{ijkl}}}-x_{s_{\mathrm{jkl}}})}^2+{(y_{a_{\mathrm{ijkl}}}-y_{s_{\mathrm{jkl}}})}^2+{(z_{a_{\mathrm{ijkl}}}-z_{s_{\mathrm{jkl}}})}^2},$

$b_{\mathrm{ijkl}}=\sqrt{{(x_{b_{\mathrm{ijkl}}}-x_{s_{\mathrm{jkl}}})}^2+{(y_{b_{\mathrm{ijkl}}}-y_{s_{\mathrm{jkl}}})}^2+{(z_{b_{\mathrm{ijkl}}}-z_{s_{\mathrm{jkl}}})}^2}.$

Each bar ray is to the contribution weight w of the simulated projections numerical value of detector cells _JklMay be selected to be:

$w_{\mathrm{jkl}}=\frac{1}{l}$

As shown in Figure 1, under the above-mentioned substitute mode combination, p _JklComputing method be:

If line segment

There are two intersection points of two intersection points and n solid to be positioned at the n layer with N solid in i the solid of composition model, arrive

Distance be respectively a _JklnAnd b _Jkln, establish a _Jkln＜b _Jklna _jkl0＝0， $b_{\mathrm{jkl}0}=\left|{\stackrel{r}{r}}_{\mathrm{jkl}}\right|,$ m ₀＝0。The 0th layer is line segment

The line segment of each layer all may be divided into shorter line segment by more high-rise intersection point, and the attenuation coefficient value of each point is the attenuation coefficient value of the solid of the top line segment correspondence under it.Calculate simulated projections numerical value p by method shown in Figure 1 thus _JklWith all intersection points by arriving

Distance series arrangement from small to large, search with this then and be each positioned at top line segment.Use a variable p _JklPreserve the simulated projections value, initial value is changed to 0.Use variable S _c, E _cPreserve current line segment starting point, final position of handling, variable n _cPreserve line segment place layer when pre-treatment.

S _cSince 0, search corresponding E by the following method _cAnd n _cIf: as the line segment starting point S of pre-treatment _cBe a _JklnClass point (i.e. n layer middle distance

Nearer point), then calculate E earlier _c, E _cFor all are higher than as anterior layer n _cAnd greater than S _cA _JklnClass point and as the b of anterior layer correspondence _JklnClass point (i.e. n layer middle distance

Point far away) b _JlncMiddle minimum point recomputates then as anterior layer n _c, with n _cBe changed to E _cThe place layer; If line segment starting point S when pre-treatment _cBe b _JklnThe class point then recomputates earlier as anterior layer n _c, with n _cBe changed to and satisfy corresponding a _JklnClass point is less than S _c, corresponding b _JklnClass point is less than E _c(be the line segment terminal point of preceding single treatment this moment) and the number of plies own are less than n _cAll layers in maximal value, calculate line segment terminal point E then when pre-treatment _c, E _cFor all are higher than as anterior layer n _cAnd greater than S _cA _JklnClass point and as the b of anterior layer correspondence _JklnClass point (i.e. n layer middle distance

Point far away) b _JklncMiddle minimum point.Search subsequently as anterior layer n _cCorresponding attenuation coefficient m _Nc, then with (E _c-S _c) ' m _NcBe added to p _JklIn, so just finished a line segment and handled.The line segment terminal point of single treatment before will working as pre-treatment line segment starting point subsequently and being changed to repeats above line segment processing procedure then, up to starting point arrive the maximal value b in having a few _Jkl0The time finish calculating.

Claims (5)

1, CT data for projection 3 D analysis and analog method is characterized in that comprising:

1) determines the model definition method;

2) determine the scan mode define method, described scan mode define method comprises:

The simulated projections process that a is complete is made of j projection;

B specifies the radiographic source center of this projection for each projection The detector center

C specifies the probe unit of detector to count k and each detector cells center

Relative detector center

Geometric relationship;

Amount of radiation l, each bar ray starting point that d specifies each detector cells to receive

Relative radiographic source center

Geometric relationship and each bar ray and detector intersection point

Relative detector cells center Geometric relationship, each bar ray to the contribution weight w of the simulated projections numerical value of detector cells _Jkl, weight should be normalized, promptly

E carries out the definition of scan mode by the computer interactive interface;

3) the analytic simulation program is set in computing machine;

4) by 1), 2), 3) produce CT data for projection p _Jk

2, CT data for projection 3 D analysis and analog method as claimed in claim 1 is characterized in that described model definition method comprises: A is by a plurality of models of combination definition of the basic body of attenuation coefficient separately of having specified; Model of B is by i basic body M _iForm, the attenuation coefficient of each basic body is m _iC carries out model definition by the computer interactive interface.

3, CT data for projection 3 D analysis and analog method as claimed in claim 1 is characterized in that described analytic simulation program comprises:

The analog physical factor for the treatment of that a) will be provided with is divided into to the influence of ray position with to two classes that influence of projection value, according to starting point and the terminal point coordinate of the influence of ray position being adjusted ray, according to projection value influenced the final simulated projections value of adjustment;

B) by coordinate conversion ray starting point, terminal point coordinate are transformed into the solid local coordinate system, in the solid local coordinate system, calculate the intersecting point coordinate of ray and solid;

C),, calculate attenuation coefficient subsequently by the coordinate Calculation intersection length in the solid local coordinate system to direct stack combinations mode;

D) to replacing array mode, intersecting point coordinate is transformed into system coordinate system, in system coordinate system, calculates the distance of two intersection points, calculate attenuation coefficient subsequently to the ray starting point.

4, CT data for projection 3 D analysis and analog method as claimed in claim 2 is characterized in that described array mode comprises: directly the adding up of each solid attenuation coefficient, promptly in the model a bit

Be positioned at m solid forming this model, then the attenuation coefficient of this point of model is

P under this array mode _JklComputing method be:

Calculate line segment earlier Intersection length L with each solid of composition model _Ijkl, calculate simulated projections numerical value p then _Jkl:

5, CT data for projection 3 D analysis and analog method as claimed in claim 2 is characterized in that described array mode comprises: the replacement combination of each solid attenuation coefficient, i.e. a bit in the model

Be positioned at m solid forming this model, then the attenuation coefficient of this point of model is P under this array mode _JklComputing method be:

Line segment

There are two intersection points of two intersection points and n solid to be positioned at the n layer with N solid in i the solid of composition model, arrive

Distance be respectively a _JklnAnd b _Jkln, a _Jkln＜b _Jkln, a _Jkl0=0,

m ₀The=0,0th layer is line segment

The line segment of each layer all is divided into shorter line segment by more high-rise intersection point, and the attenuation coefficient value of each point is the attenuation coefficient value of the solid of the top line segment correspondence under it, calculates simulated projections numerical value p thus _Jkl

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