CN204520733U - A kind of die body and use the CBCT system of this die body - Google Patents

Abstract

This utility model provides a kind of die body and uses the CBCT system of this die body, this system comprises radiographic source, detector, load carrier and die body, the structure of die body is simple, process the subpoint needed for three, can be x-ray source and the static placement of detector in scanning process, object stage rotates; Also can be that radiographic source and detector are fixed on rotation wall, then be suspended on support.In scanning process, the relative position of radiographic source and detector is constant, can form a position known coordinate system, i.e. x-ray source-detector coordinates system.By scanning die body in this system, thus obtaining the position relationship between die body coordinate system and x-ray source-detector coordinates system, improving the quality of rebuilding image.The die body used in this system is more simple, can go out can be applicable to the parameter matrix of back projection by direct solution, the reconstructed image quality under the condition of rocking is significantly improved, and under can be generalized to the condition of half detector.

Description

A kind of die body and use the CBCT system of this die body

Technical field

This utility model relates to imaging field, specifically a kind of die body and use the CBCT system of this die body.

Background technology

CBCT is the abbreviation of Cone beam CT, i.e. conical beam CT, that cone beam is thrown according to computer restructuring fault image equipment, to be x-ray generator do annular digital throwing photograph around throwing according to body with lower quantity of X-rays X to its principle, then by around throw according to body repeatedly numeral throw recombinate in a computer according to the data obtained in rear " commons factor " after so that acquisition 3-D view.CBCT has very high isotropic space resolving power, and the imaging definition of acquisition is high.

Because conical beam CT (CBCT) can obtain by the high-precision three-dimensional image of scan patients, play an important role in imaging etc. in oral disease diagnosis and treatment, operation.In dentistry CT, major part all uses conical beam CT, adopts flat panel detector to detect X-ray dampening information.Under this scheme, XX radiographic source and flat panel detector are integrally suspended on crossbeam, but in the process that x-ray source rotates, likely center of gravity does not overlap with hitch point, overarm Moment changes always, thus causes the twisting of overarm, and this twisting can affect the order of accuarcy of back projection, introduce geometry artifact, reduce the precision of rebuilding image.Therefore, how to measure and to eliminate this twisting, making back projection's process more accurate, dentistry is rebuild and has great significance.

Solution back projection accurately problem mainly contains two thinkings, the first mechanically adjusts, the center of gravity of x-ray source detector can be overlapped with hitch point by trim and eliminate moment, more advanced material is used to reduce the twisting degree of cantilever, make the rotational case of x-ray source detector very little with the difference in design, but this method can improve the cost of product greatly; The second thinking is, utilizes die body to demarcate x-ray source and to rebuild the position relationship of coordinate system, then according to actual nominal data but not theoretical value carries out back projection accurately.

As disclosed a kind of method and system eliminating CT image geometry artifact in number of patent application CN201110051997, the method comprises carries out CT scan to die body, obtain the projection coordinate of barycenter on CT detector of die body, according to the projection coordinate of barycenter on CT detector of die body, determine geometric parameter, geometric parameter is substituted into reconstruction formula, and wherein, geometric parameter can determine the relative position between x-ray source focus in CT, turntable center of rotation, CT detector; Treat imaging object and carry out CT scan, obtain the fan-beam projection data of object to be imaged, utilize the fan-beam projection data of reconstruction formula process object to be imaged, obtain the CT view data of object to be imaged.

But the parameter of demarcating in the program is too many, and all parameters are not disposable obtaining, and often obtain a parameter, all can increase the uncertainty of parameter, make correction accuracy decline.And die body of the prior art, be only used in such scheme.

Utility model content

For this reason, technical problem to be solved in the utility model is the method for elimination geometry artifact of the prior art, the parameter of demarcating is many, calculation of complex, precision are not high, thus proposes a kind of die body being applicable to eliminate simply, easily in the method for geometry artifact and the CBCT system using this die body.

For solving the problems of the technologies described above, the CBCT system a kind of die body being provided and using this die body of the present utility model.

This utility model provides the die body in a kind of CBCT system under half detector, comprise a lateral connection arm, be respectively arranged with at the two ends of described lateral connection arm and be parallel to each other and two vertical arm connected vertically with described lateral connection arm, described two vertical arm form three holes triangular in shape.

This utility model also provides the die body in a kind of CBCT system under half detector, comprise a lateral connection arm, described lateral connection arm is provided with four be parallel to each other and vertical arm vertical with this lateral connection arm respectively, adjacent two vertical linking arms form three holes triangular in shape.

Preferably, described three holes are equilateral triangle.

Preferably, steel ball is provided with in each hole.

This utility model also provides a kind of CBCT system, comprising:

Radiographic source, sends ray;

Detector, is oppositely arranged with described radiographic source, and fixes with described radiogenic relative position;

Load carrier, is arranged between radiographic source and detector;

Die body described in claim 1-4, is arranged between radiographic source and detector.

Preferably, the position of described radiographic source and described detector is fixed, and described load carrier can rotate around its center of rotation,

Preferably, described radiographic source and described detector are fixed on equal turning arm, keep described radiographic source and described detector relative position to fix, rotate.

Technique scheme of the present utility model has the following advantages compared to existing technology,

(1) this utility model provides a kind of die body and uses the CBCT system of this die body, comprise: radiographic source, detector, load carrier and die body, the structure of die body is simple, process the subpoint needed for three, can be x-ray source and the static placement of detector in scanning process, object stage rotates; Also can be that radiographic source and detector are fixed on rotation wall, then be suspended on support.In scanning process, the relative position of radiographic source and detector is constant, can form a position known coordinate system, i.e. x-ray source-detector coordinates system.By scanning die body in this system, known parameters and scanning result is utilized to solve the position of die body gauge point under x-ray source-detector coordinates system, thus the position relationship obtained between die body coordinate system and x-ray source-detector coordinates system, by in its application back projection process, improve the quality of rebuilding image.The die body used in this system is more simple, can go out can be applicable to the parameter matrix of back projection by direct solution, the reconstructed image quality under the condition of rocking is significantly improved, and under can be generalized to the condition of half detector.

Accompanying drawing explanation

In order to make content of the present utility model be more likely to be clearly understood, below according to specific embodiment of the utility model also by reference to the accompanying drawings, this utility model is described in further detail, wherein

The die body of Fig. 1 for using under the full detector in embodiment 1.

The die body of Fig. 2 for using under half detector in embodiment 1.

Fig. 3 is the structural representation of the CBCT system in embodiment 1.

Fig. 4 is in the die body of embodiment 13 perspective view under x-ray source-detector coordinates system;

Fig. 5 is method schematic diagram used when solving coordinate under x-ray source-detector coordinates system of three points in die body in embodiment 2;

Fig. 6 is the flow chart eliminating the method for geometry artifact in CBCT of embodiment 2.

Detailed description of the invention

embodiment 1:

Die body under half detector in a kind of CBCT system is provided in the present embodiment, as shown in Figure 1, comprise a lateral connection arm 1, be respectively arranged with at the two ends of described lateral connection arm 1 and be parallel to each other and two vertical arm 2 and 3 connected vertically with described lateral connection arm, described two vertical arm 2,3 form three holes 4,5,6 triangular in shape.As preferred embodiment, in hole 4,5,6 in equilateral triangle, and be provided with steel ball in each hole, being convenient to projection is accurate location.

This die body can be used in CBCT system under half detector, is projected by above-mentioned subpoint 4,5,6.

embodiment 2:

Die body under half detector in a kind of CBCT system is provided in the present embodiment, as shown in Figure 2, comprise a lateral connection arm 11, described lateral connection arm 11 is provided with four be parallel to each other and vertical arm 12,13,14,15 vertical with this lateral connection arm respectively, on adjacent two vertical linking arms, form three holes triangular in shape, i.e. molding porose 16 in vertical arm 12, molding porose 17,18 in vertical arm 13, its mesopore 16,17,18 is in equilateral triangle.Molding porose 14 in vertical arm 19, molding porose 20,21 in vertical arm 15, its mesopore 19,20,21 one-tenth equilateral triangles.Steel ball is provided with in each hole.

embodiment 3:

There is provided a kind of CBCT system in the present embodiment, structure as shown in Figure 3, is characterized in that, comprising:

Radiographic source C1, sends ray.

Detector C 2, is oppositely arranged with described radiographic source C1, and fixes with described radiogenic relative position.

Load carrier is object stage, is arranged between radiographic source and detector, for arranging die body C2 or object under test;

Die body C2, can select the die body in embodiment 1 or 2 as required.For full detector, select die body in embodiment 1, the die body in embodiment 2 is selected for half detector.This die body is arranged between radiographic source C1 and detector C 3, at least forms three subpoints, projects on detector plane, as shown in Figure 4 by radiogenic ray by subpoint.During scanning, the position of described radiographic source and described detector is fixed, and described load carrier rotates around center of rotation.Also can be set to described radiographic source and described detector is fixed on equal turning arm, keep described radiographic source and described detector relative position to fix, rotate.

This CBCT system can be x-ray source and the static placement of detector in scanning process, and object stage rotates; Also can be that radiographic source and detector are fixed on rotation wall, then be suspended on support.In scanning process, the relative position of radiographic source and detector is constant, can form a position known coordinate system, i.e. x-ray source-detector coordinates system.

Above-mentioned die body, for scanning die body in advance, known parameters and scanning result is utilized to solve the position of die body gauge point under x-ray source-detector coordinates system, thus the position relationship obtained between die body coordinate system and x-ray source-detector coordinates system, by in its application back projection process, improve the quality of rebuilding image.Die body under full detector as shown in Figure 1, comprises three subpoints that three become equilateral triangle.In this system, the die body used is more simple, can go out can be applicable to the parameter matrix of back projection by direct solution, the reconstructed image quality under the condition of rocking is significantly improved, and under can be generalized to the condition of half detector, the die body under half detector as shown in Figure 2.

In other embodiments, in half detector, the die body used is two parallel equilateral triangles, can ensure that under any angle detector detects the projection information on one group of equilateral triangle summit, as shown in Figure 2, again according to corresponding geometrical relationship, the spin matrix under all angles and translation matrix can be obtained.Computing Principle detailed in Example 4.

CBCT system in visible the present embodiment, the die body used is more simple, can go out can be applicable to the parameter matrix of back projection by direct solution, the reconstructed image quality under the condition of rocking is significantly improved, and under can be generalized to the condition of half detector.

embodiment 4:

A kind of method eliminating geometry artifact in CBCT is provided in the present embodiment, use above-mentioned die body and the CBCT system with above-mentioned die body, mainly comprise two processes, being first obtain spin matrix under all angles and translation matrix by the mode of die body, is then the process that FDK rebuilds.Because the coordinate conversion relation between any two orthogonal coordinate systems can represent by a spin matrix and a translation matrix, therefore, after the spin matrix obtained between reconstruction coordinate system and x-ray source-detector coordinates system and translation matrix, the coordinate in x-ray source-detector coordinates system can just be calculated by the coordinate of reconstruction point in reconstruction coordinate system.

First, the method calculating spin matrix under all angles and translation matrix is provided.

If three points of conllinear, rebuilding the coordinate under coordinate system and x-ray source-detector coordinates system, just can not obtain the spin matrix under this angle and translation matrix under the known a certain angle of S11.Use die body to obtain this coordinate of 3 in the present embodiment, die body processes accurate three holes, position, and little steel ball is put into hole, three position coordinateses of little steel ball center in die body can be known clearly.Then by die body, the correct position be placed on object stage scans, and can obtain dampening information on the detector, and can extract three little steel ball center projected positions on the detector.

Three positions one of little steel ball under x-ray source-detector coordinates system have 9 unknown numbers, each subpoint can list two equations, altogether can list 6 equations, and three little steel balls in space between two distance be known, 3 equations can be listed, so 9 equations altogether can be listed.Unknown number number is equal with equation number, and this problem can solve, and equation is as follows:

$\left\{\begin{array}{c}\frac{L}{L-u_z}{u}_x=U_x\\ \frac{L}{L-u_z}{u}_y=U_y\\ \frac{L}{L-v_z}{v}_x=V_x\\ \frac{L}{L-v_z}{v}_y=V_y\\ \frac{L}{L-w_z}{w}_x=W_x\\ \frac{L}{L-w_z}{w}_y=W_y\\ (u_x-v_x)2^{}+{(u_y-v_y)}^2+{(u_z-v_z)}^2=r_1^2\\ (u_x-w_x)2^{}+{(u_y-w_y)}^2+{(u_z-w_z)}^2=r_2^2\\ (w_x-v_x)2^{}+{(w_y-v_y)}^2+{(w_z-v_z)}^2=r_3^2\end{array}\right.$

Above in equation, (u _x, u _y, u _z) position of representative point u in x-ray source-detector coordinates system, (U _x, U _y) represent its projection on detector plane.Point v and some w is similar, (v _x, v _y, v _z) position of representative point v in x-ray source-detector coordinates system, (V _x, V _y) projection of representative point v on detector plane; (w _x, w _y, w _z) position of representative point w in x-ray source-detector coordinates system, (W _x, W _y) projection of representative point w on detector plane.(r ₁, r ₂, r ₃) represent the distance between three points in die body coordinate system respectively.Solve an equation and can adopt trial and error method, u _zdensity search in limited range, for each u _z, according to Fig. 5, by solving quadratic equation, can obtain possible v1 and v2, w1 and w2, then calculate v1 and w1, v1 and w2 respectively, v2 and w1, if the distance of the point in these four kinds of situations of v2 and w2 is also r, then correct result has been obtained in representative.

In above process, when angle θ solves little ball position, adopt trial and error method, u _zdensity search in limited range, checks other unknown numbers whether to meet equation, just obtains the result of equation.

By solving above-mentioned equation group, the coordinate of u, v, w 3 in x-ray source-detector coordinates system can be obtained, be respectively (u _x, u _y, u _z), (v _x, v _y, v _z), (w _x, w _y, w _z), the coordinate of three somes u, v, w in x-ray source-detector coordinates system under angle θ is designated as u _θ, v _θ, w _θ, u _θ, v _θ, w _θit is all the matrix of 3 × 1.

Generally, when selecting three points on die body, three points, that is r in equilateral triangle can be selected ₁=r ₂=r ₃=r.

Step 12, under angle θ, according to three some u, v, w coordinate u under x-ray source-detector coordinates system _θ, v _θ, w _θ, calculate spin matrix M _θwith translation matrix T _θformula as follows:

$T_{\mathrm{\θ}}=\frac{u_{\mathrm{\θ}}+v_{\mathrm{\θ}}+w_{\mathrm{\θ}}}{3}$

$a_{1\mathrm{\θ}}=\frac{u_{\mathrm{\θ}}-T_{\mathrm{\θ}}}{r/\sqrt{3}}$

$a_{2\mathrm{\θ}}=(\frac{v_{\mathrm{\θ}}-T_{\mathrm{\θ}}}{r/\sqrt{3}}+\frac{a_{1\mathrm{\θ}}}{2})*\frac{2}{\sqrt{3}}$

a _3θ＝a _1θ×a _2θ

M _θ＝[a _1θa _2θa _3θ]

In above formula, r represents the distance between equilateral triangle two summit, the T tried to achieve _θfor the translation matrix under angle θ, M _θfor the spin matrix under angle θ.

After die body scanning one circle, just can be obtained (the M under each angle θ by step 11 and step 12 _θ, T _θ), for each reconstruction point, the coordinate in x-ray source-detector coordinates system under each angle θ can be calculated, and then obtain the position of subpoint, thus carry out accurately back projection's process.

When after the spin matrix under calculating all angles and translation matrix, carry out coordinate reconstruction for reconstruction point, flow chart as shown in Figure 6, comprises the steps:

S21: obtain reconstruction point and rebuilding the coordinate in coordinate system.Reconstruction point is rebuilding the coordinate in coordinate system herein, directly can obtain according to the position of reconstruction point in reconstruction coordinate system.

S22, according to spin matrix and the translation matrix of rebuilding coordinate system and x-ray source-detector coordinates system, calculate the coordinate of described reconstruction point in x-ray source-detector coordinates system.Computing formula is as follows:

$\begin{array}{c}{S}_4\\ S_5\\ S_6\end{array}=M_{\mathrm{\θ}}*\begin{array}{c}{S}_1\\ S_2\\ S_3\end{array}+T_{\mathrm{\θ}}$

Wherein (S ₁, S ₂, S ₃) be the coordinate rebuilding 1 S in coordinate system, (S ₄, S ₅, S ₆) be the coordinate of this S under x-ray source-detector coordinates system; T _θfor the translation matrix under angle θ, M _θfor the spin matrix under angle θ.

S23, according to the coordinate of the above-mentioned reconstruction point calculated in x-ray source-detector coordinates system, calculate the subpoint of this reconstruction point on detector plane, computing formula is as follows:

$\left\{\begin{array}{c}{S}_{\mathrm{x\θ}}=\frac{L}{L-S_6}{S}_4\\ S_{\mathrm{y\θ}}=\frac{L}{L-S_6}{S}_5\end{array}\right..$

Wherein, (S ₄, S ₅, S ₆) be the coordinate of this S under x-ray source-detector coordinates system, (S _{x θ}, S _{y θ}) be the subpoint of this reconstruction point on detector plane, L is the distance between x-ray source and detector plane.

S24, reconstructed value according to back projection's formulae discovery reconstruction point, this computing formula is as follows:

$f\left(s\right)=\frac{1}{2}{\∫}_0^{2\mathrm{\π}}\frac{1}{U^2}\tilde{p}(\mathrm{\θ},S_{\mathrm{x\θ}},S_{\mathrm{y\θ}})\mathrm{d\β}$

Wherein, the reconstructed value of f (S) representative point S in above formula, filtered data, (S _{x θ}, S _{y θ}) representative point S is under θ angle, the projected position on detector plane, U is weight coefficient, under x-ray source-detector coordinates system s ₆for the z durection component of a S, L is the distance between x-ray source and detector plane. filtered function, θ, S _{x θ}, S _{y θ}be the variable of this function, filter function herein and back projection's formula all belong to prior art, and those skilled in the art know.

Pass through said process, the reconstruction of reconstruction point under a reconstruction coordinate system can be completed, according to the accurate projection position of reconstruction point under different angles, and carry out data for projection superposition according to formula, complete the reconstruction of reconstruction point, thus the reconstruction image of the geometry artifact that has been eliminated, and improve the quality of rebuilding image.

The method of the elimination geometry artifact in the present embodiment, first obtains the spin matrix under all angles and translation matrix, then calculates reconstruction point by Coordinate Conversion and is rebuilding the reconstructed value under coordinate system.The program can carry out single demarcation on the whole, obtains spin matrix and translation matrix, easy to use, formula is simple, calculate quick, and the situation of half detector can be extended to, solve cause due to mechanical reason rock problem, utilize die body to demarcate to rock, and these parameters are applied in process of reconstruction, not only eliminate geometry artifact, and decrease the parameter in whole process, reduce data operation quantity, improve the quality of processing speed and reconstruction image.

Obviously, above-described embodiment is only for clearly example being described, and the restriction not 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 the need to also giving all embodiments.And thus the apparent change of extending out or variation be still among the protection domain that this utility model creates.

Claims (7)

1. the die body in a CBCT system under half detector, it is characterized in that, comprise a lateral connection arm, be respectively arranged with at the two ends of described lateral connection arm and be parallel to each other and two vertical arm connected vertically with described lateral connection arm, described two vertical arm form three holes triangular in shape.

2. the die body in a CBCT system under half detector, it is characterized in that, comprise a lateral connection arm, described lateral connection arm is provided with four and is parallel to each other and vertical arm vertical with this lateral connection arm respectively, adjacent two vertical linking arms form three holes triangular in shape.

3. die body according to claim 1 and 2, is characterized in that, described three holes are equilateral triangle.

4. die body according to claim 3, is characterized in that, is provided with steel ball in each hole.

5. a CBCT system, is characterized in that, comprising:

Radiographic source, sends ray;

Detector, is oppositely arranged with described radiographic source, and fixes with described radiogenic relative position;

Load carrier, is arranged between radiographic source and detector;

Die body described in claim 1-4, is arranged between radiographic source and detector.

6. system according to claim 5, is characterized in that, the position of described radiographic source and described detector is fixed, and described load carrier can rotate around its center of rotation.

7. system according to claim 5, is characterized in that, described radiographic source and described detector are fixed on equal turning arm, keeps described radiographic source and described detector relative position to fix, rotates.