CN103006251A - Calibration phantom, calibration device and calibration method for calibrating geometric parameters in CT (Computed Tomography) system - Google Patents

Abstract

The invention relates to a calibration phantom used for calibration of geometric parameters in a CT system, which comprises two identical calibration plates and small balls arranged in parallel. The two calibration plates are correspondingly provided with a number of identical small holes, so that There are at least four small balls and they are respectively installed in the small holes on the two calibration plates. The invention relates to a calibration device used for calibrating geometric parameters in a CT system, which includes a CT system composed of a light source, a rotary table and a detector, and the calibration device also includes a rotary table vertically placed between the light source and the detector Calibration phantom on . In addition, the invention also provides a calibration method for geometric parameter calibration in the CT system. The above calibration device and calibration method can simultaneously calibrate all seven geometric parameters of the CT system with only one projection of the calibration phantom, which is easy to operate and greatly satisfies the image correction of the subsequent CT system.

Description

Be used for the CT system and demarcate demarcation phantom, caliberating device and the scaling method of geometric parameter

Technical field

The present invention relates to the demarcation of geometric parameter in the CT system, relate in particular to a kind of demarcation phantom, caliberating device and scaling method for CT system geometrical parameter calibration.

Background technology

Computer tomography (CT) is a kind of important imaging means that obtains internal structure of body information by lossless manner, and it has the inferior many merits of high-resolution, high sensitivity and multilamellar, is widely used in each medical clinical examination field.Geometrical parameter calibration is the important component part of micro-CT system debug, also is the precondition that obtains accurate reconstruction CT image.

The geometrical parameter calibration method of system " a kind of X ray gated cone-beam computed tomography " that Chinese patent application numbers 201210148432.8 proposes.The method reappears geometry site between x-ray source, flat panel detector and the rotating shaft in the cone-beam CT system by the camera calibration technology, thereby geometric parameter and error thereof to Cone-Beam CT are carried out direct solution, it is a kind of systematized measurement method for solving, can with Cone-Beam CT abstract be basic camera system model, thereby be mutually related simultaneously a plurality of geometric parameters in the solving system.

But the geometrical parameter calibration method of above-mentioned disclosed CT system can not be demarcated whole 7 geometric parameters of CT system simultaneously; And the CT system that can not be applicable to simultaneously exsomatize (demarcate the phantom rotation, light source and detector are motionless) and vivo CT system (demarcate phantom and fix, light source and detector rotation); In addition, the parameter calibration process is complicated, need to carry out multiple projections to demarcating phantom, is difficult to repeatedly repeat realize.

Summary of the invention

Based on this, be necessary the defective that the calibration system for geometric parameter in the above-mentioned CT system exists, a kind of demarcation phantom that can demarcate simultaneously geometric parameter in the CT system is provided.

A kind of demarcation phantom for CT system geometrical parameter calibration, comprise: comprise two the identical scaling board that be arranged in parallel and beads, correspondingly respectively on described two scaling boards offer some identical apertures, described bead is at least four and be installed on respectively in the aperture on described two scaling boards.

The present invention also provides a kind of caliberating device for CT system geometrical parameter calibration, comprise the CT system that is formed by light source, turntable and detector, described caliberating device also comprises the demarcation phantom on the turntable that vertically is placed between described light source and the detector, described demarcation phantom comprises two the identical scaling board that be arranged in parallel and beads, correspondingly respectively on described two scaling boards offer some identical apertures, described bead is at least four and be installed on respectively in the aperture on described two scaling boards; Described demarcation phantom rotates with described turntable, and described detector is used for the center point coordinate of the projected image of each bead of collection; And image processing module, be used for making up the first projection matrix according to the center point coordinate of described projected image, described image processing module also is used for calculating respectively each bead at the locus of described CT system coordinate system coordinate according to geometry and the described demarcation phantom geometry of described CT system, and make up the second projection matrix according to described locus coordinate, calculate the projection centre point coordinates of detector plane according to described the first projection matrix and described the second projection matrix, light source is to the distance of detector, the torsion angle of detector, the inclination angle of detector, the anglec of rotation of detector and light source are to the distance of turntable rotating shaft.

In addition, the present invention also provides the scaling method of geometric parameter in a kind of CT system, described CT system comprises light source, turntable and detector, described scaling method comprises the steps: that vertical the placement demarcated phantom on the turntable between described light source and the detector, described demarcation phantom comprises two the identical scaling board that be arranged in parallel and beads, correspondingly respectively on described two scaling boards offer some identical apertures, described bead is at least four and be installed on respectively in the aperture on described two scaling boards; Described demarcation phantom is rotated with described turntable, gather abscissa and the vertical coordinate of central point of the projected image of each bead by described detector; Center point coordinate according to described projected image makes up the first projection matrix; Calculate respectively the locus coordinate of each bead in described CT system coordinate system according to the geometric relationship of described CT system and the geometric relationship of demarcating phantom; Make up the second projection matrix according to described locus coordinate; According to described the first projection matrix and described the second projection matrix calculate the projection centre point coordinates, light source of detector plane to the inclination angle of the torsion angle of the distance of detector, detector, detector, the anglec of rotation of detector and light source be to the distance of turntable rotating shaft.

Above-mentioned caliberating device and scaling method for CT system geometric parameter, adopt the simple phantom of demarcating, rotate at turntable, demarcate the center point coordinate of the projected image of each bead on the phantom by the detector collection, center point coordinate according to projected image makes up the first projection matrix, geometry and demarcation phantom geometry according to the CT system calculate respectively the locus coordinate of each bead in described caliberating device coordinate system, and make up the second projection matrix according to described locus coordinate, calculate the projection centre point coordinates of detector plane according to the first projection matrix and the second projection matrix, light source is to the distance of detector, the torsion angle of detector, the inclination angle of detector, the anglec of rotation of detector and light source are to the distance of turntable rotating shaft.

Above-mentioned caliberating device and scaling method only need carry out whole 7 geometric parameters that 1 projection just can be demarcated the CT system simultaneously to demarcating phantom, and be simple to operate, greatly satisfied the image rectification of follow-up CT system; In addition, above-mentioned caliberating device and scaling method can be applicable to exsomatize CT system and vivo CT system, wide adaptability simultaneously; Simultaneously, above-mentioned nominal volume mode structure is simple, preparation cost is cheap, is easy to obtain.

Description of drawings

The sketch map of the demarcation phantom that is used for CT system geometrical parameter calibration that Fig. 1 provides for the embodiment of the invention one.

The structural representation of the aperture of offering on the scaling board that Fig. 2 provides for embodiment one provided by the invention.

The structural representation of the caliberating device that is used for CT system geometrical parameter calibration that Fig. 3 provides for the embodiment of the invention two.

The flow chart of the scaling method of geometric parameter in the CT system that Fig. 4 provides for the embodiment of the invention three.

Fig. 5 passes through the flow chart of steps of center point coordinate that detector gathers the projected image of each bead for what embodiment three provided by the invention provided.

Fig. 6 calculates respectively the locus coordinate flow chart of steps of each bead in the CT system coordinate system for what the embodiment of the invention three provided according to the geometric relationship of CT system and the geometric relationship of demarcation phantom.

The projected image that when embedding 18 prills on the demarcation phantom, obtains that Fig. 7 provides for the embodiment of the invention four.

The specific embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and the specific embodiments, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, is not intended to limit the present invention.

Embodiment one:

See also Fig. 1 and Fig. 2, the sketch map of the demarcation phantom that is used for CT system geometrical parameter calibration that provides for the embodiment of the invention one.

Demarcate phantom 100 and comprise scaling board 110 and bead 120.

The quantity of scaling board 110 is that two and structure are identical.Two scaling boards 110 over against and be arranged in parallel.In embodiment provided by the invention, the spacing of two scaling boards is preferably 46mm, and the width of each scaling board is preferably 150mm, thickness is preferably 2mm.Correspondingly respectively on two scaling boards 110 offer some identical apertures 111.Aperture 111 is the square formation formula and is distributed on the scaling board.See also Fig. 2, the structural representation of the aperture 111 of offering on the scaling board 110 that provides for embodiment one provided by the invention, the square formation that aperture 111 is 7*7 is distributed on the scaling board 110, and the diameter of aperture 111 is preferably 1mm, hole depth is preferably 0.5mm, and spacing is preferably 20mm between the adjacent holes.

Bead 120 is at least four.Bead 120 is installed on respectively in two apertures 111 on the scaling board 110, namely on any one scaling board 110 bead 120 is installed all.The quantity that is appreciated that aperture 120 can also be 6 or other more quantity.

In embodiment provided by the invention, the material of scaling board 110 is preferably vinyon.Bead 120 is preferably the rustless steel bead.

Embodiment two:

See also Fig. 3, the structural representation of the caliberating device that is used for CT system geometrical parameter calibration that Fig. 3 provides for the embodiment of the invention two.

Caliberating device 200 comprises CT system, demarcation phantom 100 and the image processing module (not shown) that is comprised of light source 210, turntable (not shown) and detector 230.

Be provided with turntable between light source 210 and the detector 230.Demarcating phantom 100 is vertically installed on the turntable.Demarcating phantom 100 rotates with turntable.Detector 230 is used for gathering the center point coordinate of the projected image of demarcating each bead 120 in the aperture 111 of offering on the phantom 100.The center point coordinate that is appreciated that the projected image of bead 120 on imaging plane does not all overlap.

Image processing module is used for making up the first projection matrix according to the center point coordinate of projected image.Image processing module also is used for according to the geometry of CT system and demarcates phantom 100 geometries and calculate respectively each bead 120 at the locus of CT system coordinate system coordinate, and makes up the second projection matrix according to the locus coordinate.Image processing module calculates the projection centre point coordinates on detector 230 planes, the distance that light source 210 arrives detector 230, the torsion angle of detector 230, the inclination angle of detector 230, the anglec of rotation of detector 230 and the distance that light source 210 arrives the turntable rotating shaft according to the first projection matrix and the second projection matrix.

Embodiment three:

See also Fig. 3 and Fig. 4, the flow chart of the scaling method of geometric parameter in the CT system that provides for the embodiment of the invention three of Fig. 4 wherein, wherein the CT system comprises light source 210, turntable and detector 230, specifically comprises the steps:

Step S310: the vertical placement demarcated phantom 100 on the turntable between light source 210 and the detector 230.In embodiment provided by the invention, it is identical with the demarcation phantom that the embodiment of the invention one provides to demarcate phantom 100.Be appreciated that bead 120 is at least four and be installed on respectively in two apertures 111 on the scaling board 110, namely demarcate on two scaling boards 110 of phantom 100 and all will place bead 120.

Step S320: will demarcate phantom 100 with turntable rotation, and gather abscissa and the vertical coordinate of central point of the projected image of each beads 120 by detector 230.

See also Fig. 5, pass through the flow chart of steps of center point coordinate that detector 230 gathers the projected image of each beads for what embodiment three provided by the invention provided, it comprises the steps:

Step S321: the plane at definition detector 230 places is as coordinate plane.Wherein take detector 230 lower left corners as zero, orientation U, the V of pixel is respectively axis of abscissas and axis of ordinates on the detector 230.

Step S322: will demarcate phantom 100 and rotate with turntable.Be appreciated that the bead 120 of demarcating in the aperture 111 of offering on the phantom 100 at the uniform velocity rotates with turntable, carries out projection by 210 pairs of beads of light source 120, and obtains projected image.In embodiment provided by the invention, the number of times of projection is preferably 1 time, is appreciated that the number of times of projection can also be for repeatedly, and when the number of times of projection was more, the geometric parameter of the CT system that finally obtains was more accurate.

Step S323: detector 230 gathers the projected image of each bead 120.Be appreciated that each projection bead all obtains 1 projected image at detector 230, namely bead is all obtaining projected image take detector 230 place coordinate planes as imaging plane.

Step S324: the central point that obtains successively each bead 120 projected images by the edge extracting processing method is with the plane at detector 230 places abscissa and the vertical coordinate as coordinate plane.The center point coordinate that is appreciated that the projected image of bead 120 on imaging plane does not all overlap.

Step S330: central point abscissa and vertical coordinate according to projected image make up the first projection matrix.In embodiment provided by the invention, it is specific as follows to make up the first projection matrix according to the central point abscissa of projected image and vertical coordinate:

With the abscissa of the central point of the projected image of each bead 120 and vertical coordinate substitution matrix [u, v, 1] respectively ^TIn, make up the first projection matrix [u, v, 1] ^T, wherein, u and v represent respectively abscissa and the vertical coordinate of bead 120 projected centre point, [u, v, 1] ^TBe the matrix of 3xN, N is the bead number.

Step S340: calculate respectively the locus coordinate of each bead in the CT system coordinate system according to the geometric relationship of CT system and the geometric relationship of demarcation phantom.

See also Fig. 6, calculate respectively the locus coordinate flow chart of steps of each bead 120 in the CT system coordinate system for what the embodiment of the invention three provided according to the geometric relationship of CT system and the geometric relationship of demarcation phantom 100, specifically comprise the steps:

Step S341: definition coordinate system (X, Y, Z), wherein Y-axis is the rotating shaft of turntable, Z axis is that light source 210 is to the ray of rotating shaft.

Step S342: the axis at the central point place of demarcating phantom 100 is overlapped with rotating shaft.In another embodiment of demarcation phantom 100 provided by the invention, the axis that the central point place of phantom 100 is demarcated on the edge is provided with a metal cylinder, and this metal cylinder overlaps with rotating shaft, and this metal cylinder can rotate around rotating shaft.

Step S343: the rotation turntable makes the plane parallel at two scaling boards 110 and detector 230 places, can obtain the locus coordinate (x, y, z) of each bead on coordinate system (X, Y, Z).Be appreciated that because to demarcate the structure of phantom 100 be known, demarcate like this relative tertiary location of each bead 120 on the phantom 100 and determine, will demarcate phantom 100 and be fixed on the turntable, and make that metal cylinder overlaps with the rotating shaft Y-axis in the demarcation phantom 100.The rotation turntable, so that the plane at two scaling board 110 places of demarcation phantom 100 and the plane parallel at detector 230 places, light source 210 is respectively the center on two planes at the vertical point of two scaling boards 110 demarcating phantom 100, can obtain rustless steel bead 120 at coordinate system (X, Y, Z) the locus coordinate (x, y, z) on.

Step S350: make up the second projection matrix according to the locus coordinate.In embodiment provided by the invention, wherein, according to rustless steel bead 120 at coordinate system (X, Y, Z) the locus coordinate (x, y, z) on makes up the second projection matrix, specifically comprise the steps: the locus coordinate (x with each bead, y, z) difference substitution matrix [x, y, z, 1] ^TIn, make up the second projection matrix [x, y, z, 1] ^TWherein, x, y, z are the locus coordinate (x, y, z) of each bead.

Step S360: according to the first projection matrix and the second projection matrix calculate the projection centre point coordinates, light source of detector plane to the inclination angle of the torsion angle of the distance of detector, detector, detector, the anglec of rotation of detector and light source be to the distance of turntable rotating shaft.

According to the first projection matrix and the second projection matrix calculate the projection centre point coordinates, light source of detector plane to the inclination angle of the torsion angle of the distance of detector, detector, detector, the anglec of rotation of detector and light source be to the flow chart of steps of the distance of turntable rotating shaft, specifically comprise the steps:

Definition coordinate system (X, Y, Z), wherein Y-axis is the rotating shaft of turntable, Z axis is that light source 210 is to the ray of rotating shaft.

Definition detector 230 lower left corners are zero, and U, V are the orientation of pixel on the detector 230, and λ is the size, (u of detector pixel ₀, v ₀) be the projection centre point coordinates on detector 230 planes, D is the distance that light source 210 arrives detector 230, and α is that the torsion angle of detector 230, inclination angle, the γ that β is detector 230 are the anglec of rotation of detector 230, and R is that light source 210 is to the distance of rotating shaft.

According to the first projection matrix [u, v, 1] ^TAnd the second projection matrix [x, y, z, 1] ^TMake up formula a[u, v, 1] ^T=A[x, y, z, 1] ^T, wherein, A is sytem matrix, a is coefficient.Be appreciated that a can rule of thumb choose.

According to formula A=Φ [ζ | ω] and calculate Φ, ζ, wherein,

$\mathrm{\φ}=\left[\begin{array}{ccc}\frac{D}{\mathrm{\λ}}& 0& u_0\\ 0& \frac{D}{\mathrm{\λ}}& v_0\\ 0& 0& 1\\ & & \end{array}\right]$

$\mathrm{\ζ}=\left[\begin{array}{ccc}\cos \mathrm{\β}\cos \mathrm{\γ}& \sin \mathrm{\α}\sin \mathrm{\β}\cos \mathrm{\γ}-\cos \mathrm{\α}\sin \mathrm{\γ}& \sin \mathrm{\α}\sin \mathrm{\γ}+\cos \mathrm{\α}\sin \mathrm{\β}\cos \mathrm{\γ}\\ \cos \mathrm{\β}\sin \mathrm{\γ}& \cos \mathrm{\α}\cos \mathrm{\γ}+\sin \mathrm{\α}\sin \mathrm{\β}\sin \mathrm{\γ}& \cos \mathrm{\α}\sin \mathrm{\β}\sin \mathrm{\γ}-\sin \mathrm{\α}\cos \mathrm{\γ}\\ -\sin \mathrm{\β}& \sin \mathrm{\α}\cos \mathrm{\β}& \cos \mathrm{\α}\cos \mathrm{\β}\end{array}\right]$

$\mathrm{\ω}=\left[\begin{array}{c}{\mathrm{\ω}}_1\\ {\mathrm{\ω}}_2\\ {\mathrm{\ω}}_3\end{array}\right]$

ω ₁＝A ₃₄、ω ₂＝(A ₂₄-Φ ₂₃A ₃₄)/Φ ₂₃、ω ₂＝(A ₂₄-Φ ₂₃A ₃₄)/Φ ₂₃、ω ₂＝(A ₁₄-Φ ₁₃A ₃₄-ω ₂A ₁₂)/Φ ₁₁。In the above-mentioned formula, D is that light source is to the distance of detector, (u ₀, v ₀) be light source 210 at the projection centre point coordinates on detector 230 planes, λ is the size of detector 230 pixels, α is that the torsion angle of detector 230, inclination angle, the γ that β is detector 230 are the anglec of rotation of detector 230.

Be appreciated that and obtain first the locus coordinate (x of N bead 120 on coordinate system (X, Y, Z) _i, y _i, z _i), i=1,2,3 ... N and with the plane at detector 230 places abscissa and the vertical coordinate (u as coordinate plane _i, v _i), i=1,2,3 ... N.By formula a[u, v, 1] ^T=A[x, y, z, 1] ^T, following equation is arranged:

u _ia _i＝A ₁₁x _i+A ₁₂y _i+A ₁₃z _i+A ₁₄

v _ia _i＝A ₂₁x _i+A ₂₂y _i+A ₂₃z _i+A ₂₄

ω _i＝A ₃₁x _i+A ₃₂y _i+A ₃₃z _i+A ₃₄

Coefficient a disappears _i, obtain following two equations:

A ₁₁x _i+A ₁₂y _i+A ₁₃z _i+A ₁₄-u _i(A ₃₁x _i+A ₃₂y _i+A ₃₃z _i+A ₃₄)＝0

A ₂₁x _i+A ₂₂y _i+A ₂₃z _i+A ₂₄-v _i(A ₃₁x _i+A ₃₂y _i+A ₃₃z _i+A ₃₄)＝0

Write above equation as matrix form, obtained: HA*=0, wherein,

$H=\left[\begin{array}{cccccccccccc}{x}_i& y_i& z_i& 1& 0& 0& 0& 0& -u_i{x}_i& {-u}_i{y}_i& -u_i{z}_i& -u_i\\ 0& 0& 0& 0& x_i& y_i& z_i& 1& -v_i{x}_i& -v_i{y}_i& -v_i{z}_i& -v_i\end{array}\right]$

$A^{*}=\left[\begin{array}{c}{A}_{11}\\ A_{12}\\ A_{13}\\ A_{14}\\ A_{21}\\ A_{22}\\ A_{23}\\ A_{24}\\ A_{31}\\ A_{32}\\ A_{33}\\ A_{34}\end{array}\right]$

For equation HA*=0, can pass through singular value decomposition method, matrix H is decomposed, obtain A*, get final product to get sytem matrix A.

According to formula A=Φ [ζ | ω], can obtain A _{3 * 3}=Φ ζ (namely having removed the last string of the 3x4 of matrix A), because Φ is upper triangular matrix, can be to matrix A _{3 * 3}Carry out " QR decomposition " and obtain Φ, ζ.

According to formula o=[o _x, o _y, o _z] ^T=-ζ ^Tω, calculating XYZ coordinate is center point coordinate o _x, o _yAnd o _z

Wherein, in the above-mentioned formula, ζ can be obtained by above-mentioned steps,

$\mathrm{\ω}=\left[\begin{array}{c}{\mathrm{\ω}}_1\\ {\mathrm{\ω}}_2\\ {\mathrm{\ω}}_3\end{array}\right]$

ω ₁＝A ₃₄、ω ₂＝(A ₂₄-Φ ₂₃A ₃₄)/Φ ₂₃、ω ₂＝(A ₂₄-Φ ₂₃A ₃₄)/Φ ₂₃、ω ₂＝(A ₁₄-Φ ₁₃A ₃₄-ω ₂A ₁₂)/Φ ₁₁。

Projection centre point coordinates (the u on calculating detector 230 planes ₀, v ₀), light source 210 arrives the distance B of detector 230, the anglec of rotation γ of the torsion angle α of detector 230, the angle of inclination beta of detector 230, detector 230, and light source 210 is to the distance R of rotating shaft.

Be appreciated that ζ and XYZ coordinate are center point coordinate o according to Φ obtained above _x, o _yAnd o _z, can calculate the projection centre point coordinates (u on detector 230 planes ₀, v ₀), light source 210 arrives the distance B of detector 230, the anglec of rotation γ of the torsion angle α of detector 230, the angle of inclination beta of detector 230, detector 230, and light source 210 is to the distance R of rotating shaft.

Wherein, the projection centre point coordinates (u on detector 230 planes ₀, v ₀) computing formula be: u ₀=Φ ₁₃, v ₀=Φ ₂₃, Φ ₁₃The 1st row of representing matrix Φ and element corresponding to the 3rd row, Φ ₂₃The 1st row of representing matrix Φ and element corresponding to the 3rd row.

Light source 210 to the computing formula of the distance B of detector 230 is: D=Φ ₁₁λ, Φ ₁₁The 1st row of representing matrix Φ and element corresponding to the 1st row.

The computing formula of the torsion angle α of detector 230 is: α=Arctan2 (ζ ₃₂, ζ ₃₃), ζ ₃₂The 3rd row of representing matrix ζ and element corresponding to the 2nd row, ζ ₃₃The 3rd row of representing matrix ζ and element corresponding to the 3rd row.

The computing formula of the angle of inclination beta of detector 230 is: β=sin ^-1(ζ ₃₁), ζ ₃₁The 3rd row of representing matrix ζ and element corresponding to the 1st row.

The computing formula of the anglec of rotation γ of detector 230 is: γ=Arctan2 (ζ ₁₂, ζ ₃₁), ζ _{, 12}The 1st row of representing matrix ζ and element corresponding to the 2nd row, ζ ₃₁The of representing matrix ζ, 3 row and element corresponding to the 1st row.

Light source 210 to the computing formula of the distance R of rotating shaft is: o _x, o _y, o _zFor XYZ coordinate is center point coordinate.

Embodiment four:

See also Fig. 7, for the embodiment of the invention four provide on demarcating phantom, embed 18 prills the time projected image that obtains.Situation when demarcating 18 prills of phantom 100 embeddings.Each correspondence is put into 9 beads, the projected image that obtains on two scaling boards up and down respectively.For the effectiveness of verification algorithm, press extreme case, only carried out 1 projection (equaling 1).In theory, when value was larger, the result can be more close to actual value.System's geometric parameter analogue value that the above-mentioned scaling method Calculation Simulation of foundation obtains and actual value are as shown in Table 1.As can be seen from the results, the method precision is very high.

Form 1

?	R	D	α	β	γ	u 0	v 0
								Actual value	570	1005	-1.5708	-1.5708	0.00	257	257
Value of calculation	571.7760	1008.5622	-1.5708	-1.5705	0.00	257	255.0620
								Error	0.312％	0.354％	0％	0.019％	0％	0％	0.754％

The scaling method of geometric parameter and caliberating device adopt and demarcate the phantom rotation in the above-mentioned CT system, and light source and detector are motionless, thereby realize the demarcation of geometric parameter in the CT system; Be appreciated that the demarcation that can realize equally geometric parameter in the CT system for vivo CT system (demarcate phantom and fix, light source and detector rotation).

Above-mentioned caliberating device and scaling method for CT system geometric parameter, adopt the simple phantom of demarcating, rotate at turntable, demarcate the center point coordinate of the projected image of each bead on the phantom by the detector collection, center point coordinate according to projected image makes up the first projection matrix, geometry and demarcation phantom geometry according to the CT system calculate respectively the locus coordinate of each bead in described caliberating device coordinate system, and make up the second projection matrix according to described locus coordinate, calculate the projection centre point coordinates of detector plane according to the first projection matrix and the second projection matrix, light source is to the distance of detector, the torsion angle of detector, the inclination angle of detector, the anglec of rotation of detector and light source are to the distance of turntable rotating shaft.

Above-mentioned caliberating device and scaling method only need carry out whole 7 geometric parameters that 1 projection just can be demarcated the CT system simultaneously to demarcating phantom, and be simple to operate, greatly satisfied the image rectification of follow-up CT system; In addition, above-mentioned caliberating device and scaling method can be applicable to exsomatize CT system and vivo CT system, wide adaptability simultaneously; Simultaneously, above-mentioned nominal volume mode structure is simple, preparation cost is cheap, is easy to obtain.

The above, it only is preferred embodiment of the present invention, be not that the present invention is done any pro forma restriction, although the present invention discloses as above with preferred embodiment, yet be not to limit the present invention, any those skilled in the art, within not breaking away from the technical solution of the present invention scope, when the technology contents that can utilize above-mentioned announcement is made a little change or is modified to the equivalent embodiment of equivalent variations, in every case be not break away from the technical solution of the present invention content, any simple modification that foundation technical spirit of the present invention is done above embodiment, equivalent variations and modification all still belong in the scope of technical solution of the present invention.

Claims (13)

1. A calibration phantom for calibrating geometric parameters in a CT system, characterized in that, said calibration phantom comprises two identical calibration plates and bead arranged in parallel, and said two calibration plates are correspondingly set up respectively There are several identical small holes, and there are at least four small balls installed in the small holes on the two calibration plates. 2. The calibration phantom for calibrating geometric parameters in a CT system according to claim 1, wherein the distance between the two calibration plates is 46mm, the width of the calibration plate is 150mm, and the thickness is 2mm. 3 . The calibration phantom for calibrating geometric parameters in a CT system according to claim 1 , wherein the small holes are distributed on the calibration plate in a square matrix. 4 . 4. The calibration phantom for calibrating geometric parameters in a CT system according to claim 3, wherein the small holes are distributed on the calibration plate in a 7*7 square matrix, and the small holes The diameter of the hole is 1mm, the hole depth is 0.5mm, and the distance between adjacent holes is 20mm. 5 . The calibration phantom for calibrating geometric parameters in a CT system according to claim 1 , wherein the calibration plate is made of polyethylene plastic, and the ball is made of stainless steel. 6. A calibration device for geometric parameters in a CT system, comprising a CT system made up of a light source, a rotary table and a detector, characterized in that the calibration device also includes a rotary device vertically placed between the light source and the detector The calibration phantom on the platform, the calibration phantom includes two identical calibration plates and small balls arranged in parallel, the two calibration plates are respectively provided with several identical small holes, and the small balls are at least four one and respectively installed in the small holes on the two calibration plates; the calibration phantom rotates with the turntable, and the detector is used to collect the center point coordinates of the projection images of each small ball; and An image processing module, configured to construct a first projection matrix according to the coordinates of the center point of the projection image, and the image processing module is also configured to calculate each small ball according to the geometric structure of the CT system and the geometric structure of the calibration phantom The spatial position coordinates in the CT system coordinate system, and constructing a second projection matrix according to the spatial position coordinates, and calculating the projection center point coordinates of the detector plane according to the first projection matrix and the second projection matrix , the distance from the light source to the detector, the torsion angle of the detector, the inclination angle of the detector, the rotation angle of the detector and the distance from the light source to the rotation axis of the turntable. 7 . The calibration device for geometric parameters in the CT system according to claim 6 , wherein the center point coordinates of the projected images of the small ball on the imaging plane do not coincide. 8 . 8. A calibration method of geometric parameters in a CT system, said CT system comprising a light source, a rotary table and a detector, is characterized in that said calibration method comprises the steps of: Place the calibration phantom vertically on the rotating platform between the light source and the detector, the calibration phantom includes two identical calibration plates and small balls arranged in parallel, and the two calibration plates are respectively provided with a number of The same small holes, the small balls are at least four and are respectively installed in the small holes on the two calibration plates; Rotate the calibration phantom with the turntable, and collect the abscissa and ordinate of the center point of the projected image of each small ball through the detector; Constructing a first projection matrix according to the abscissa and ordinate of the center point of the projected image; Calculate the spatial position coordinates of each small ball in the coordinate system of the CT system according to the geometric structure relationship of the CT system and the geometric structure relationship of the calibration phantom; Constructing a second projection matrix according to the spatial position coordinates; According to the first projection matrix and the second projection matrix, the coordinates of the projection center point of the detector plane, the distance from the light source to the detector, the twist angle of the detector, the tilt angle of the detector, the rotation angle of the detector, and The distance from the light source to the axis of rotation of the turntable. 9. The calibration method of geometric parameters in the CT system according to claim 8, wherein the step of collecting the center point coordinates of the projection images of each small ball through the detector specifically comprises: Define the plane where the detector is located as a coordinate plane; wherein the lower left corner of the detector is the coordinate origin, and the arrangement directions U and V of the pixels on the detector are the abscissa axis and the ordinate axis respectively; rotating the calibration phantom with the turntable; The detector collects projection images of each small ball; The abscissa and ordinate of the center point of each small ball projection image on the plane where the detector is located as a coordinate plane are sequentially obtained through an edge extraction processing method. 10. The calibration method of geometric parameters in the CT system according to claim 8 or 9, wherein, the step of constructing the first projection matrix according to the center point coordinates of the projection image specifically comprises: Substitute the abscissa and ordinate of the center point of the projected image of each small ball into the matrix [u, v, 1] ^T respectively to construct the first projection matrix [u, v, 1] ^T , where u and v represent The abscissa and ordinate of the center point of the ball projection. 11. The calibration method of geometric parameters in the CT system according to claim 8, wherein, according to the geometric structure relationship of the CT system and the geometric structure relationship of the calibration phantom, the spatial position coordinates of each small ball are calculated respectively , including the following steps: Define a coordinate system (X, Y, Z), wherein the Y axis is the rotation axis of the turntable, and the Z axis is the ray from the light source to the rotation axis; Make the axis where the center point of the calibration phantom is located coincide with the rotation axis; The space position coordinates (x, y, z) of each small ball on the coordinate system (X, Y, Z) can be obtained by rotating the turntable so that the two calibration plates are parallel to the plane where the detector is located. 12. The calibration method of geometric parameters in the CT system according to claim 8 or 11, wherein, constructing a second projection matrix according to the spatial position coordinates comprises the steps of: The spatial position coordinates (x, y, z) of each small ball are respectively substituted into the matrix [x, y, z, 1] ^T to construct the second projection matrix [x, y, z, 1] ^T . 13. The calibration method of geometric parameters in the CT system according to claim 8, wherein, according to the first projection matrix [u, v, 1] ^T and the second projection matrix [x, y , z, 1] ^T Calculate the coordinates of the projection center point of the detector plane, the distance from the light source to the detector, the torsion angle of the detector, the inclination angle of the detector, the rotation angle of the detector and the distance from the light source to the rotation axis of the turntable , including the following steps: Define a coordinate system (X, Y, Z), wherein the Y axis is the rotation axis of the turntable, and the Z axis is the ray from the light source to the rotation axis; Define the lower left corner of the detector as the coordinate origin, U and V are the arrangement direction of the pixels on the detector, λ is the size of the detector pixels, (u ₀ , v ₀ ) is the projection center point of the detector plane Coordinates, D is the distance from the light source to the detector, α is the twist angle of the detector, β is the inclination angle of the detector, γ is the rotation angle of the detector, R is the distance from the light source to the rotation axis; Construct the formula a[u, v, ^{1] T =} A[x ^, y, z, 1] ^T , where A is the system matrix and a is the coefficient; According to the formula A=Φ[ζ|ω] and calculate Φ, ζ, where, $\mathrm{\&phi;}=\left[\begin{array}{ccc}\frac{\mathrm{D.}}{\mathrm{\&lambda;}}& 0& u_0\\ 0& \frac{\mathrm{D.}}{\mathrm{\&lambda;}}& v_0\\ 0& 0& 1\\ & & \end{array}\right]$ $\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\\ \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}& \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}\end{array}\right]$ $\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}\end{array}\right]$ ω ₁ =A ₃₄ , ω ₂ =(A ₂₄ -Φ ₂₃ A ₃₄ )/Φ ₂₃ , ω ₂ =(A ₂₄ -Φ ₂₃ A ₃₄ )/Φ ₂₃ , ω ₂ =(A ₁₄ -Φ ₁₃ A ₃₄ - ω ₂ A ₁₂ )/Φ ₁₁ ; _Calculate the coordinates o _x , o _y and o _z of the center point of the XYZ coordinate system according ^to the formula o=[o _x , o y , o _z ] T =-ζ ^T ω; Calculate the projection center point coordinates (u ₀ , v ₀ ) of the detector plane, the distance D from the light source to the detector, the torsion angle α of the detector, the inclination angle β of the detector, the rotation angle γ of the detector, the distance from the light source to the detector The distance R of the axis of rotation; Among them, the calculation formula of the projection center point coordinates (u ₀ , v ₀ ) of the detector plane is: u ₀ = Φ ₁₃ , v ₀ = Φ ₂₃ , and Φ ₁₃ represents the elements corresponding to the first row and the third column of the matrix Φ , Φ ₂₃ represents the elements corresponding to the first row and the third column of the matrix Φ, The calculation formula for the distance D from the light source to the detector is: D=Φ ₁₁ λ, Φ ₁₁ represents the elements corresponding to the first row and the first column of the matrix Φ, The calculation formula of the torsion angle α of the detector is: α=Arctan2(ζ ₃₂ , ζ ₃₃ ), ζ ₃₂ represents the elements corresponding to the 3rd row and the 2nd column of the matrix ζ, and ζ ₃₃ represents the 3rd row and the 2nd column of the matrix ζ 3 columns corresponding to the elements, The calculation formula of the inclination angle β of the detector is: β=sin ^-1 (-ζ ₃₁ ), ζ ₃₁ represents the elements corresponding to the 3rd row and the 1st column of the matrix ζ, The calculation formula of the rotation angle γ of the detector is: γ=Arctan2(ζ ₁₂ , ζ ₃₁ ), ζ _{, 12} represents the elements corresponding to the first row and the second column of the matrix ζ, and ζ ₃₁ represents the third row of the matrix ζ and the element corresponding to column 1, The formula for calculating the distance R from the light source to the rotation axis is:

o _x , o _y , and o _z are the coordinates of the center point of the XYZ coordinate system.

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