CN100570343C - Wide view-field three-D CT imaging method - Google Patents

Abstract

Wide view-field three-D CT imaging method, step is: (1) carries out single circular orbit cone-beam CT scan first time, obtains first group of digital radial projection image sequence; (2) the vertical principal ray direction of the inspection platform translation certain distance of carrying object carries out single circular orbit cone-beam CT scan second time, obtains second group of digital radial projection image sequence; (3) two groups of digital radial projected images are carried out dark current and inconsistency correction; (4) the recording ray source is to detector distance, inspection stage translation distance, detector level detection passage number; (5) according to above-mentioned parameter, the projection shuffle algorithm that utilizes the present invention to study is rearranged into complete class collimated beam ray projection image sequence with above-mentioned incomplete two groups of cone-beam x-ray projection digital image sequences; (6) image sequence that obtains according to step (5), the class collimated beam ray reconstruction algorithm that utilizes the present invention to study is rebuild the three dimensional CT image of scanning area.The present invention can be extended to the imaging visual field of single circular orbit cone-beam scan original 3 times by twice single circular orbit cone-beam scan of inspection platform, and the scanner uni process of reconstruction is simple, and is efficient.

Description

Wide view-field three-D CT imaging method

Technical field

The present invention relates to a kind of wide view-field three-D CT imaging method, belong to the x-ray ct technology field.

Background technology

In the X ray CT system, x-ray source sends X ray, pass a certain zone of object to be detected from different perspectives, the detector that is positioned over the radiographic source opposite is accepted in respective angles, then according to each angle ray decay in various degree, utilize certain reconstruction algorithm and computing machine to carry out computing, reconstruct object and be scanned regional ray line attenuation coefficient distribution map image, thereby realize nondestructively reproducing the features such as Media density, composition and structural form of object in this zone by reconstruction from projections imaging.

In existing typical cone-beam x-ray 3D-CT imaging, for satisfying Tuy, Smith and Grangeat data condition for completeness, series of effective scan mode and reconstruction algorithm thereof have been developed in succession, as orthogonal scanning, spiral scan and correction spiral scan etc.For the consideration of sweep velocity and algorithm computation amount, present 3D-CT mainly is based on the technology of single circular orbit cone-beam scan mode and FDK reconstruction algorithm.Shown in Fig. 2 (a), under this scan mode, only object returns around turning axle and circles, and can reconstruct by x-ray source S the object that cone-beam that detector is opened covers is treated the chromatography part according to the data of FDK algorithm and flat panel detector collection.Shown in Fig. 2 (b), but this kind 3D-CT technology inspected object maximum rotating diameter is r.For the three-dimensional chromatography of the bigger member of tactical diameter and the high amplification ratio micro tomography of small test specimen, limited by scanning field of view, above-mentioned scanning technique all is difficult to carry out.

Along with going deep into of research, wide view-field three-D tomography problem has obtained increasing concern of CT circle and research.Enlarging the method for three-D CT imaging scope at present, mainly is the big visual field of two dimension CT formation method to be similar to be applied in the small-angle three-D CT imaging.Different with reconstruction algorithm by scan mode, projection preprocess method, these big visual field of two dimension CT formation methods can be divided three classes substantially: projection splicing method, pseudo-data fitting method and redundant data mining method.Projection splicing method scanning field of view is big, and projection pre-service and reconstruction algorithm are simple, but the scanning system complex structure, scan efficiency is low; Pseudo-data fitting method scan efficiency height, Project Realization is convenient, but scanning field of view can only improve 0.5～1 times, and the reconstruction precision is low.So, really can be for practical application also should consider the redundant data mining method.The data for projection redundancy feature that the redundant data mining method utilizes the single circular orbit cone-beam scan of standard to exist by improving scan mode, enlarges scanning field of view.More representational redundant data mining method is Fu Jian etc., the three-dimensional big field of view industrial CT imaging research of cone-beam x-ray, 2006, optical technology, 32 (2): the inspection platform offsetting that proposes in 209～212.Its scan mode such as Fig. 3 (c) at first examine the platform horizontal translation, so that its rotation center is positioned on the ray that connects ray source focus and detector end points, examines platform then and revolve three-sixth turn, finish scanning.It is applied to non-central plane by revising radiographic source to detector distance with the data for projection symmetry that only exists at central plane, and data are carried out pre-service, utilizes standard FDK algorithm to rebuild at last.Although the redundant data mining method has scan efficiency and rebuilds advantage of high precision, its scanning field of view still can only enlarge 0.5～1 times.

Summary of the invention

Technology of the present invention is dealt with problems and is: have the little problem of scanning field of view at present three dimensional CT based on single circular orbit cone-beam scan and FDK reconstruction algorithm, a kind of wide view-field three-D CT imaging method based on twice biasing of inspection platform scanning is provided, solve the quick three-dimensional chromatography of large-size member and the high amplification ratio micro tomography of small test specimen, reset processing by inspection twice single circular orbit cone-beam scan of platform and class collimated beam, the imaging visual field of single circular orbit cone-beam scan is extended to original 3 times, and the scanner uni process of reconstruction is simple, and is efficient.

Technical solution of the present invention: wide view-field three-D CT imaging method, its characteristics are may further comprise the steps:

(1) carries out single circular orbit cone-beam CT scan first time, obtain first group of digital radial projection image sequence;

(2) the vertical principal ray direction of the inspection platform translation certain distance of carrying object carries out single circular orbit cone-beam CT scan second time, obtains second group of digital radial projection image sequence;

(3) two groups of digital radial projected images are carried out dark current and inconsistency correction;

(4) the recording ray source is to detector distance, inspection stage translation distance, detector level detection passage number;

(5) according to above-mentioned parameter, the projection shuffle algorithm that utilizes the present invention to study is rearranged into complete class collimated beam ray projection image sequence with above-mentioned incomplete two groups of cone-beam x-ray projection digital image sequences;

(6) image sequence that obtains according to step (5), the class collimated beam ray reconstruction algorithm that utilizes the present invention to study is rebuild the three dimensional CT image of scanning area.

Scanning theory of the present invention such as Fig. 4: during scanning, the inspection platform at first 1 is done one time 360 degree revolving scanning in the position, examines the platform tangential movement then to the position 2, tries again 360 to spend revolving scannings, can finish the scanning chromatography, and can examine the member tactical diameter is r ₁And can examining the member tactical diameter, single circular orbit cone-beam scan CT is r to the maximum ₂, the same redundant data mining method that adopts the inspection platform to setover and scan can be examined the member tactical diameter and be r to the maximum ₃

Class collimated beam shuffle algorithm of the present invention is as follows, and derivation graph is seen Fig. 5:

P(t，θ，s)＝F(β，m，n，i)， $m=\frac{R\·t}{\sqrt{R^2-t^2}}$

If $\left|m\right|\≤\frac{L_1}{2},$ $\mathrm{\β}=\mathrm{\θ}+\arcsin \left(\frac{t}{R}\right),$ $m=\frac{R\·t}{\sqrt{R^2-t^2}},$ $\left|\mathrm{mn}\right|=\frac{\left|\mathrm{Sm}\right|\·\left|\mathrm{st}\right|}{\left|\mathrm{St}\right|},$

|St|＝R·cos(γ)，|Sm|＝R·tan(γ)

If $\left|m\right|>\frac{L_1}{2},$ β＝θ+γ ₁-γ ₂； $m=\frac{t}{\cos ({\mathrm{\γ}}_1-{\mathrm{\γ}}_2)}-L,$ ${\mathrm{\γ}}_1=\arcsin \left(\frac{t}{\sqrt{R^2+L^2}}\right),$ ${\mathrm{\γ}}_2=\arcsin \left(\frac{L}{\sqrt{R^2+L^2}}\right)$

$\left|\mathrm{St}\right|=\sqrt{R^2+L^2}\·\cos \left({\mathrm{\γ}}_1\right),$ |Sm|＝|St|-|t|·tan(φ)，φ＝γ ₂-γ ₁

(θ, t is s) for resetting the class collimated beam projection image sequence that generates, F (β, m, n, i) two groups of single circular orbit cone-beam scan projection image sequence of gathering for detector, L for P ₁Represent the detector level to visit first number, θ is value between 0～2 π, represents the revolving scanning angle, R is the distance of radiographic source to detector plane, and L is inspection stage translation distance, and i is 1 or 2, two scanning positions of representative inspection platform, other parameter meanings as illustrated in Figures 5 and 6.

Reconstruction algorithm of the present invention is as follows:

$\mathrm{\μ}(x,y,z)={\∫}_0^{2\mathrm{\π}}\tilde{P}(\mathrm{\θ},t(x,y,\mathrm{\θ}),s(x,y,z,\mathrm{\θ}))d_{\mathrm{\θ}}$

$\tilde{P}(\mathrm{\θ},t,s)=(\frac{\left|\mathrm{St}\right|}{\left|\mathrm{Ss}\right|}\·P(\mathrm{\θ},t,s))*h\left(t\right),$ t(x，y，θ)＝y·cos(θ)-x·sin(θ)， $m=\frac{t\·R}{\sqrt{R^2-t^2}}$

If $\left|m\right|\≤\frac{L_1}{2},$ Then $s(x,y,z,\mathrm{\θ})=\frac{z\·\sqrt{R^2-t^2(x,y,\mathrm{\θ})}}{\sqrt{R^2-t^2(x,y,\mathrm{\θ})}-(x\·\cos \left(\mathrm{\θ}\right)+y\·\sin \left(\mathrm{\θ}\right))}$

If $\left|m\right|>\frac{L_1}{2},$ Then $s(x,y,z,\mathrm{\θ})=\frac{z\·\sqrt{R^2+L^2-t^2(x,y,\mathrm{\θ})}}{\sqrt{R^2+L^2-t^2(x,y,\mathrm{\θ})}-(x\·\cos \left(\mathrm{\θ}\right)+y\·\sin \left(\mathrm{\θ}\right))}$

Wherein, μ (x, y z) treat the value of reconstruction point for the space,

Be space ray and its included angle cosine in the surface level projection, h (t) is an one dimension Shepp-Logan filter function.

Scanning imagery of the present invention visual field approximate formula is as follows: $x_2=R\·\frac{(\frac{L_1}{2}+L)}{\sqrt{R^2+{(\frac{L_1}{2}+L)}^2}}$

(R=1463, L=240, L under the typical ct findings image-forming condition ₁=256), scanning field of view radius x of the present invention ₂=356.6, and the single circular orbit scanning of standard 3D-CT scanning field of view radius is 127.51.As seen, scanning field of view of the present invention can scan more than 2.8 times of 3D-CT by the single circular orbit of standard up to standard, under the limiting case, can reach 3 times.

The present invention's advantage compared with prior art is as follows:

(1) the present invention so Scan Architecture is simple, is easy to the system compatible with existing standard list circular orbit cone-beam scan 3D-CT owing to only need the inspection platform to carry out a translation along the principal ray direction;

(2) the present invention only need carry out twice rotation sweep, so the scan efficiency height;

(3) 3 times of can the standard up to standard single circular orbit scanning of scanning field of view of the present invention 3D-CT.

Description of drawings

Fig. 1 is a wide view-field three-D CT imaging method process flow diagram of the present invention;

Fig. 2 (a) is the 3D-CT technology to analyze principle based on single circular orbit cone-beam scan mode and FDK reconstruction algorithm, and Fig. 2 (b) is the scanning theory vertical view;

Fig. 3 (a) is the big visual field of a pseudo-data fitting method CT technology to analyze principle, and Fig. 3 (b) is the big visual field of a detector offsetting CT technology to analyze principle, and Fig. 3 (c) is the big visual field of inspection platform offsetting CT technology to analyze principle;

Fig. 4 is a wide view-field three-D CT scanning theory vertical view of the present invention;

Fig. 5 is the class collimated beam shuffle algorithm derivation graph of wide view-field three-D CT of the present invention;

Fig. 6 is a 3D-CT experimental provision of the present invention, and the single circular orbit cone-beam scan of its standard visual field is 180mm;

Fig. 7 is the subassembly of 500mm is finished wide view-field three-D CT imaging on Fig. 7 experimental provision process and result for the tactical diameter that constitutes with three workpiece.Fig. 7 (a) is 1 projection of gathering in the position of 0 detector when spending for scanning angle, Fig. 7 (b) is 2 projections of gathering in the position of 0 detector when spending for scanning angle, Fig. 7 (c) is the projection sinogram of detector middle layer 1 and 2 generations in the position in the 360 degree circumferential scanning processes, Fig. 7 (d) is the projection sinogram of detector middle layer after finishing the class collimated beam and resetting, Fig. 7 (e) is the corresponding class collimated beam projection sinogram of detector middle layer after the filtering, Fig. 7 (f) is the middle layer CT reconstructed image that utilizes class parallel beam reconstruction algorithm to obtain, and Fig. 7 (g) is the three dimensional CT reconstructed image (successively showing) of the member scanning area utilizing class parallel beam reconstruction algorithm and obtain.

Embodiment

As Fig. 1, concrete implementation step of the present invention is as follows:

(1) scanned object is positioned over cone-beam CT scan system rotation inspection platform, guarantees to examine the platform rotation center and be positioned on the principal ray;

(2) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains first group of two-dimensional digital image sequence;

(3) when the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the first time;

(4) the inspection platform of carrying object is from finishing the position vertical principal ray direction translation certain distance of single circular orbit cone-beam scan for the first time.This distance should be less than the planar array detector lateral dimension, and guarantees object in scanning process, has only a direction to exceed planar array detector imaging scope;

(5) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains second group of two-dimensional digital image sequence;

(6) when the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the second time;

(7) during no ray, (2) and (3) method forms the details in a play not acted out on stage, but told through dialogues projection image sequence set by step, and the details in a play not acted out on stage, but told through dialogues projection image sequence is averaged, and obtains two-dimentional details in a play not acted out on stage, but told through dialogues projected image D;

(8) object is removed from scan table, guaranteed no any object between radiographic source and linear array detector;

(9) set by step (2) and (3) method forms the bright field projected image, and the bright field projection image sequence is averaged, and obtains two-dimentional bright field projected image L;

(10) L is deducted D, finish the bright field dark current correction, obtain L1;

(11) ask the mean value of L1,, obtain two-dimensional array U with mean value each value divided by L1;

(12) the every width of cloth view data with two groups of projection image sequence all deducts D, finishes dark current correction;

(13) the every width of cloth view data with two groups of projection image sequence multiply by U, finishes inconsistency and proofreaies and correct;

(14) provide the scan geometry parameter by scanister machinery digital control system, promptly radiographic source is to detector distance, inspection stage translation distance and detector level detection passage number;

(15) set scanning angle θ, horizontal projection position t and the vertical projection position s of class collimated beam ray projection image sequence correspondence, calculate scanning angle β, horizontal projection position m, vertical projection position n and the scanning position i of corresponding cone-beam scan projection image sequence correspondence;

(16) utilize the Tri linear interpolation formula, from cone-beam scan projection image sequence F (β, m, n, i) reset obtain class collimated beam ray projection image sequence P (θ, t, s);

(17) repeat above-mentioned steps (15) and (16), reach 360 degree up to scanning angle θ.

(18) the scanning angle θ of setting class collimated beam ray projection image sequence correspondence obtains under this scanning angle, space ray and its included angle cosine in the surface level projection, and (θ, t s) carry out the product weighting to projected image P to utilize it;

(19) repeat above-mentioned steps (18), reach 360 degree up to angle θ;

(20) set the scanning angle θ of class collimated beam ray projection image sequence correspondence, utilize the Shepp-Logan filter function to weighting after projected image P (θ, t s) carry out filtering line by line, obtain projected image after the filtering

(21) repeat above-mentioned steps (20), reach 360 degree up to angle θ;

(22) (x, y z), obtain its respective projection address t and s to given reconstruction point volume coordinate under each scanning angle θ;

(23) with under all θ angles

Carry out sum-average arithmetic, obtain space (x, y, reconstructed value z);

(24) repetition above-mentioned steps (22) and (23) is all calculated until each spatial point of scanning area, thereby finishes the three-dimensional tomographic reconstruction of scanning area.

Fig. 7 has provided the wide view-field three-D CT imaging example that the tactical diameter that is made of three kinds of workpiece is the subassembly of 500mm.Fig. 7 (a)～(f) has illustrated data handling procedure of the present invention with behavior example in the middle of the detector.Wherein, Fig. 7 (a) is 1 projection of gathering in the position of 0 detector when spending for scanning angle, Fig. 7 (b) is 2 projections of gathering in the position of 0 detector when spending for scanning angle, Fig. 7 (c) is the projection sinogram of detector middle layer 1 and 2 generations in the position in the 360 degree circumferential scanning processes, Fig. 7 (d) is the projection sinogram of detector middle layer after finishing the class collimated beam and resetting, Fig. 7 (e) is the corresponding class collimated beam projection sinogram of detector middle layer after the filtering, the middle layer CT reconstructed image of Fig. 7 (f) for utilizing class parallel beam reconstruction algorithm to obtain.The three dimensional CT reconstructed image (successively show) of Fig. 7 (g) for utilizing the member scanning area that class parallel beam reconstruction algorithm obtains.Fig. 7 result shows that scanning theory of the present invention and reconstruction algorithm are correct.

Claims (5)

1, wide view-field three-D CT imaging method is characterized in that comprising the following steps:

(1) carries out single circular orbit cone-beam CT scan first time, obtain first group of digital radial projection image sequence;

(2) the vertical principal ray direction of the inspection platform translation certain distance of carrying object carries out single circular orbit cone-beam CT scan second time, obtains second group of digital radial projection image sequence;

(3) two groups of digital radial projected images are carried out dark current and inconsistency correction;

(4) the recording ray source is to detector distance, inspection stage translation distance, detector level detection passage number;

(5), utilize the projection shuffle algorithm that above-mentioned incomplete two groups of cone-beam x-ray projection digital image sequences are rearranged into complete class collimated beam ray projection image sequence according to above-mentioned parameter; The step of described projection shuffle algorithm is:

A. set scanning angle θ, horizontal projection position t and the vertical projection position s of class collimated beam ray projection image sequence correspondence, calculate scanning angle β, horizontal projection position m, vertical projection position n and the scanning position i of corresponding cone-beam scan projection image sequence correspondence;

B. utilize the Tri linear interpolation formula, from cone-beam scan projection image sequence F (β, m, n, i) reset obtain class collimated beam ray projection image sequence P (θ, t, s);

C. repeat above-mentioned steps a and step b, reach 360 degree up to scanning angle θ;

(6) image sequence that obtains according to step (5) utilizes class collimated beam ray reconstruction algorithm, rebuilds the three dimensional CT image of scanning area; The step of described class collimated beam three-dimensional reconstruction algorithm is:

A. set the scanning angle θ of class collimated beam ray projection image sequence correspondence, obtain under this scanning angle, space ray and its included angle cosine in the surface level projection, (θ, t s) carry out the product weighting to projected image P to utilize it;

B. repeat above-mentioned steps a, reach 360 degree up to angle θ;

C. set the scanning angle θ of class collimated beam ray projection image sequence correspondence, utilize the Shepp-Logan filter function to weighting after projected image P (θ, t s) carry out filtering line by line, obtain projected image after the filtering

D. repeat above-mentioned steps c, reach 360 degree up to angle θ;

E. (x, y z), obtain its respective projection address t and s to given reconstruction point volume coordinate under each scanning angle θ;

F. with under all θ angles

Carry out sum-average arithmetic, obtain space (x, y, reconstructed value z);

G. repeat above-mentioned steps e and f, all calculated, thereby finish the three-dimensional tomographic reconstruction of scanning area until each spatial point of scanning area.

2, wide view-field three-D CT imaging method according to claim 1 is characterized in that: carry out single circular orbit cone-beam CT scan first time in the described step (1), the step that obtains set of number ray projection image sequence is:

(1) scanned object is positioned over cone-beam CT scan system rotation inspection platform, guarantees to examine the platform rotation center and be positioned on the principal ray;

(2) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains first group of two-dimensional digital image sequence;

(3) when the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the first time.

3, large scale three-D CT imaging method according to claim 1 is characterized in that: carry out single circular orbit cone-beam CT scan second time in the described step (2), the step that obtains set of number ray projection image sequence is:

(1) the inspection platform of carrying object is from finishing the position vertical principal ray direction translation certain distance of single circular orbit cone-beam scan for the first time, this distance should be less than the planar array detector lateral dimension, and guarantee object in scanning process, have only a direction to exceed planar array detector imaging scope;

(2) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains second group of two-dimensional digital image sequence;

(3) when the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the second time.

4, wide view-field three-D CT imaging method according to claim 1 is characterized in that: in the described step (3) two groups of digital radial projected images being carried out the step that dark current and inconsistency proofread and correct is:

(1) during no ray, with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains first group of two-dimensional digital image sequence; When the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finish single circular orbit cone-beam CT scan for the first time, form the details in a play not acted out on stage, but told through dialogues projection image sequence, the details in a play not acted out on stage, but told through dialogues projection image sequence is averaged, obtain two-dimentional details in a play not acted out on stage, but told through dialogues projected image D;

(2) object is removed from scan table, guaranteed radiographic source and no any object between planar array detector;

(3) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains first group of two-dimensional digital image sequence; When the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the first time, formed the bright field projected image, and the bright field projection image sequence is averaged, and obtained two-dimentional bright field projected image L;

(4) L is deducted D, finish the bright field dark current correction, obtain L1;

(5) ask the mean value of L1,, obtain two-dimensional array U with mean value each value divided by L1;

(6) with the cone-beam x-ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, crosses the ray projection of object by planar array detector with the transmission of fixed sample speed continuous acquisition, obtains first group of two-dimensional digital image sequence; When the inspection platform revolved three-sixth turn, planar array detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finished single circular orbit cone-beam CT scan for the first time, and every width of cloth view data of two groups of projection image sequence obtaining all deducts D, finishes dark current correction;

(7) every width of cloth view data of two groups of projection image sequence that step (6) is obtained multiply by U, finishes inconsistency and proofreaies and correct.

5, wide view-field three-D CT imaging method according to claim 1 is characterized in that, radiographic source provides by scanister machinery digital control system to detector distance, inspection stage translation distance and detector level detection passage number in the described step (4).

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