CN102253061B - Vertical cone beam CT (Computed Tomography) imaging calibration system and method applying same - Google Patents
Vertical cone beam CT (Computed Tomography) imaging calibration system and method applying same Download PDFInfo
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Abstract
The invention relates to a vertical cone beam CT (Computed Tomography) imaging calibration system and a method applying the system. The calibration system provided by the invention comprises an X ray source (100), a detector (106) a certain distance far away from the X ray source (100), an objective table (102) arranged between the X ray source (100) and the detector (106), a rotating shaft (315) for fixing the objective table (102) and a metal ball calibration model (104) fixed on the objective table (102). The method provided by the invention comprises the following steps: measuring the rotating center of a rotating shaft in the rotating process; measuring the rotating consistency of the rotating shaft; measuring the consistency of the rotating shaft in the vertical moving process; and measuring the consistency of the rotating shaft in the horizontal moving process. By the adoption of the invention, the reconstruction efficiency and reconstruction quality of the system are improved.
Description
Technical field
The present invention relates to a kind of vertical Cone-Beam CT (Computer Tomography, the computer tomography technology) method of system calibration, refer in particular to radiographic source and detector is fixed, by make sample with objective table with turning axle rotation, move forward and backward the calibration steps of the cone-beam CT system that obtains scan-data up and down, related to a kind of cone-beam CT system Calibration Method of rebuilding with the FDK algorithm more specifically.The FDK algorithm is Feldkamp, Davis, the filtered back projection's reconstruction algorithm based on cone beam projection that Kress proposed in 1984.
Background technology
Cone-beam CT system has the spatial resolution height, distinguishing features such as acquisition time weak point and ray utilization factor height.General reconstruction algorithm commonly used is the FDK algorithm in the cone-beam CT system.The FDK algorithm is Feldkamp, Davis, the filtered back projection's reconstruction algorithm based on cone beam projection that Kress proposed in 1984, be characterized in that theoretical construct is simple, reconstruction speed is fast, is easy to practical application, especially can obtain to rebuild preferably structure under the less situation of cone angle.Yet, the system that the FDK algorithm requires to use this algorithm satisfies certain imaging geometry structure: in the cone-beam CT system, and process radiogenic plane vertical with detector is called midplane, and turning axle is vertical with midplane, and the while is parallel with the column direction of detector pixel array, line direction is vertical; Cross cone-beam x-ray source focus and do the straight line of vertical probe, this straight line is through turning axle; It is stable that the rotation of turning axle keeps, and remains vertical with midplane in rotary course; Radiographic source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
Yet because the limited and alignment error of parts machining accuracy, after the cone-beam CT system installation, the system imaging geometry can't accurately satisfy the requirement of FDK algorithm, even through algorithm geometry correction correction, quality of reconstructed images also can descend to some extent.A kind of vertical cone-beam CT system calibration steps that the present invention proposes is assessed the imaging geometry structure of current system, and provides the instruction of system mechanics fine setting.Cone-beam CT system mechanically reaches a more accurate ground imaging geometry structure after adjusting, reduce the burden of geometry correction in the reconstruction algorithm.The imaging geometry structure that the imaging geometry structure of cone-beam CT system more requires near the FDK algorithm, the reconstruction efficient of system is more high, and quality of reconstructed images is also more high.So the cone-beam CT system calibration can effectively improve reconstruction efficient and the reconstructed image quality of system.
Summary of the invention
Technical matters:The technical problem to be solved in the present invention is to have carried the vertical cone-beam CT system calibration steps that supplies a kind of vertical cone-beam CT system calibration system and use this system, to improve reconstruction efficient and the reconstruction quality of system
Technical scheme:For solving the problems of the technologies described above, the invention provides a kind of vertical cone-beam CT system calibration system, this system comprise x-ray source, and x-ray source at a distance of the detector of certain distance and be arranged on x-ray source and detector between objective table, be used for fixing objective table turning axle, be fixed on the Metal Ball calibrating patterns on the objective table; Wherein the Metal Ball calibrating patterns rotates with turning axle with objective table in scanning process; X-ray source and position of detector maintain static, and obtain data for projection by the objective table rotation; Fix a Metal Ball on the Metal Ball calibrating patterns; Metal Ball calibrating patterns, objective table and turning axle constitute sample system.
Preferably, the Metal Ball calibrating patterns is the cylindrical cup that organic glass is made, the coboundary fixing metal ball of cup.
The present invention also provides a kind of vertical Cone-Beam CT calibration steps, and this method may further comprise the steps: measure the rotation center of turning axle in rotary course; Measure the rotation consistance of turning axle; Described rotation consistance is to instigate sample system to be fixed on certain position, make the Metal Ball calibrating patterns be positioned at suitable rotation sampled point, 360 ° of Metal Ball calibrating patterns rotations M time, M is natural number, in the position of each rotation back calculating prill, the consistance of prill position is exactly the rotation consistance of turning axle respectively; Measure the consistance of turning axle in vertical moving process; The consistance of described turning axle in vertical moving process refers to the consistance of rotation center in the process that turning axle moves up and down; Measure the consistance of turning axle in the process of moving horizontally, the consistance of described turning axle in the process of moving horizontally refers to the consistance of rotation center in the process that turning axle moves forward and backward;
Realize the calibration of three-dimensional Cone-Beam CT calibration system according to above-mentioned number.
Preferably, the measuring method of the rotation center of described turning axle is: make sample system be fixed on certain position, the Metal Ball calibrating patterns rotates with turning axle, gets N rotation sampled point equably and gets its projected image on detector; The data for projection that rotates a circle according to the Metal Ball calibrating patterns calculates the rotation center of turning axle, and N is even number.
Preferably, the conforming measuring method of the rotation of described measurement turning axle is: make sample system be fixed on certain position, the Metal Ball calibrating patterns rotates with turning axle, gets N rotation sampled point equably and gets its projected image on detector, and N is even number; In relatively rotating for M time, the skew of the projected position of same position prill and rotation center projected position is namely known the rotation consistance of turning axle according to side-play amount, and M is natural number.
Preferably, the conforming measuring method of turning axle in vertical moving process is: in the vertical direction, sample system moves up and down and makes complete the dropping on the detector of Metal Ball calibrating patterns projected footprint of prill in rotary course, in this vertical range, choose V sampled point, V is even number, wherein V/2 vertical sampled point is positioned at the midplane top, and V/2 vertical sampled point is positioned at the midplane below; At each vertical sampled point, the Metal Ball calibrating patterns rotates with turning axle, get its projection N evenly spaced position, N is even number, calculate the projected position of each rotation sampled point prill on detector, and calculate the projected position of rotating shaft center's point on detector, the consistance of turning axle in vertical moving process namely known in relatively V skew that vertical sampled point calculates the rotary middle point of gained.
Preferably, the conforming measuring method of turning axle in the process of moving horizontally is: in the horizontal direction, sample system moves horizontally gets H horizontal sampled point in the scope, and H is natural number; At each horizontal sampled point, measure the vertical mobile consistance of this horizontal level turning axle respectively, according to rotating shaft center's projection that this horizontal level V vertical sampled point calculates, V is even number, calculates the subpoint of this horizontal level ray source focus on detector; The consistance of turning axle in the process of moving horizontally namely known in the skew of the projection of the ray source focus that H horizontal sampling point position of comparison calculates.
Preferably, described vertical cone-beam CT system adopts the FDK algorithm to rebuild; The requirement of the imaging geometry structure of the vertical cone-beam CT system of FDK algorithm is: turning axle is vertical with midplane, and the while is parallel with the column direction of detector pixel array, line direction is vertical; Cross the x-ray source focus and do the straight line of vertical probe, this straight line is through turning axle; It is stable that the rotation of turning axle keeps, and remains vertical with midplane in rotary course; X-ray source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
Preferably, the Metal Ball calibrating patterns is the cylindrical cup of an organic glass system, and the coboundary of cup is fixed a Metal Ball.
Beneficial effect:
A kind of vertical cone-beam CT system calibration system and method that the present invention proposes are got several sample points in sample system tangential movement scope, each sample position is measured the consistance that the objective table vertical direction moves, and obtains each position rotation center curve.The rotation center curve that in same plane, shows all horizontal sampling locations.It should be noted that sample system near detector position to the process that moves near the radiographic source position, the enlargement factor of system imaging is big from little change, the represented physical length of pixel is from diminishing greatly on the detector.So before relatively each horizontal level rotation center is offset, the rotation center position need be converted to identical unit of quantity.When there is small deviation in system geometries, be near actual value at the projected position of ray source focus on detector of the most close detector position estimation, and depart from actual value farthest in the focus projection value of the most close radiographic source position estimation, relatively the deviation of two extreme positions just can be determined direction and the size of radiographic source skew.
The skew of horizontal level rotation center shows that the relative geometrical relation of the horizontal guide rail of radiographic source in the system, detector and objective table does not satisfy the geometry that the FDK algorithm requires in the cone-beam CT system.According to the measurement of system imaging geometry, radiographic source or CCD are finely tuned accordingly.Remeasure the imaging geometry structure of system after the adjustment, whether the adjustment direction before the checking is correct.Repeatedly measure and be adjusted to can't be by the accurate system of mechanical means the imaging geometry structure.
Description of drawings
Fig. 1: the Scan Architecture of vertical cone-beam CT system;
Fig. 2 a: the side of the Metal Ball calibrating patterns that vertical cone-beam CT system calibration is used;
Fig. 2 b: the vertical view of the Metal Ball calibrating patterns that vertical cone-beam CT system calibration is used;
Fig. 3: the perspective view of Metal Ball calibrating patterns;
Fig. 4: the process flow diagram of vertical cone-beam CT system calibration process;
Embodiment
The present invention will be further described below in conjunction with accompanying drawing.
In order more at large to explain the technical scheme of foregoing invention, below list specific embodiment technique effect is described.It is emphasized that these embodiment do not limit the scope of the invention for explanation the present invention.
The present invention proposes a kind of vertical Cone-Beam CT calibration system and be applied to the method for this system, especially radiographic source and detector maintain static, objective table rotates with turning axle, the calibration steps of the imaging geometry structure of the cone-beam CT system that the integral body that objective table and turning axle constitute can move up and down.
What particularly point out is the reconstruction algorithm employing FDK algorithm of this cone-beam CT system, this algorithm is by Feldkamp, the filtered back projection's reconstruction algorithm based on cone beam projection that Davis and Kress proposed in 1984, rolled up the 6th phase 612 to 619 pages of articles of delivering " practical cone-beam reconstruction algorithm " with reference to them in June the 1st in 1984 in " U.S.'s optics meeting will, A collects: optics, image science and vision ".
The FDK reconstruction algorithm has certain requirement to the imaging geometry structure of system: turning axle is vertical with the midplane in cone-beam x-ray source, and the while is parallel with the column direction of detector pixel array, line direction is vertical; Cross cone-beam x-ray source focus and do the straight line of vertical probe, this straight line is through turning axle; It is stable that the rotation of turning axle keeps, and remains vertical with midplane in rotary course; Radiographic source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
The present invention proposes a kind of vertical cone-beam CT system calibration steps, the calibration steps of the imaging geometry structure of the cone-beam CT system that especially radiographic source and detector maintain static, objective table moves up and down with turning axle rotation, what particularly point out is that the reconstruction algorithm of this cone-beam CT system adopts the FDK algorithm.The FDK reconstruction algorithm has certain requirement to the imaging geometry structure of system: turning axle is vertical with the midplane in cone-beam x-ray source, and the while is parallel with the column direction of detector pixel array, line direction is vertical; Cross cone-beam x-ray source focus and do the straight line of vertical probe, this straight line is through turning axle; It is stable that the rotation of turning axle keeps, and remains vertical with midplane in rotary course; Radiographic source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
Referring to Fig. 1-Fig. 4, vertical cone-beam CT system calibration provided by the invention system comprise x-ray source 100, with x-ray source 100 at a distance of the detector 106 of certain distance and be arranged on x-ray source 100 and detector 106 between objective table 102, for the turning axle 315 of fixing objective table 102, be fixed on the Metal Ball calibrating patterns 104 on the objective table 102.
Said midplane refers among the present invention: be called midplane with detector 106 planes vertical and process x-ray source 100 in the vertical Cone-Beam CT calibration system.
Wherein Metal Ball calibrating patterns 104 rotates with turning axle 315 with objective table 102 in scanning process; X-ray source 100 is motionless with the stationkeeping of detector 106, obtains data for projection by objective table 102 rotations; Fix a Metal Ball 105 on the Metal Ball calibrating patterns 104; Metal Ball calibrating patterns 104, objective table 102 and turning axle 315 constitute sample system 201.
Metal Ball calibrating patterns 104 is cylindrical cups that organic glass is made, the coboundary fixing metal ball 105 of cup.
Vertical Cone-Beam CT calibration steps provided by the invention may further comprise the steps: measure the rotation center of turning axle 315 in rotary course; Measure the rotation consistance of turning axle 315; Described rotation consistance is to instigate sample system 201 to be fixed on certain position, make Metal Ball calibrating patterns 104 be positioned at suitable rotation sampled point, 360 ° of Metal Ball calibrating patterns 104 rotations M time, M is natural number, in the position of each rotation back calculating prill 105, the consistance of prill 105 positions is exactly the rotation consistance of turning axle respectively; Measure the consistance of 315 turning axles in vertical moving process; The consistance of described turning axle 315 in vertical moving process refers to the consistance of rotation center in the process that turning axle moves up and down; Measure the consistance of turning axle 315 in the process of moving horizontally, the consistance of described turning axle 315 in the process of moving horizontally refers to the consistance of rotation center in the process that turning axle moves forward and backward; Realize the calibration of three-dimensional Cone-Beam CT calibration system according to above-mentioned number.
The measuring method of the rotation center of described turning axle is: make sample system 201 be fixed on certain position, Metal Ball calibrating patterns 104 is got N rotation sampled point equably and is got its projected image on detector 106 with turning axle 315 rotations; The data for projection that rotates a circle according to Metal Ball calibrating patterns 104 calculates the rotation center of turning axle, and N is even number.
The conforming measuring method of the rotation of described measurement turning axle is: make sample system 201 be fixed on certain position, Metal Ball calibrating patterns 104 is with turning axle 315 rotations, get N rotation sampled point equably and get its projected image on detector 106, N is even number; In relatively rotating for M time, the skew of the projected position of same position prill 105 and rotation center projected position is namely known the rotation consistance of turning axle according to side-play amount, and M is natural number.
The conforming measuring method of turning axle in vertical moving process is: in the vertical direction, sample system 201 moves up and down that the projected footprint that makes Metal Ball calibrating patterns 104 prill 105 in rotary course is complete to be dropped on the detector 106, in this vertical range, choose V sampled point, V is even number, wherein V/2 vertical sampled point is positioned at the midplane top, and V/2 vertical sampled point is positioned at the midplane below; At each vertical sampled point, Metal Ball calibrating patterns 104 is with turning axle 315 rotations, get its projection N evenly spaced position, N is even number, calculate the projected position of each rotation sampled point prill 105 on detector 106, and calculate the projected position of rotating shaft center's point on detector, the consistance of turning axle in vertical moving process namely known in relatively V skew that vertical sampled point calculates the rotary middle point of gained.
The conforming measuring method of turning axle in the process of moving horizontally is: in the horizontal direction, sample system 201 moves horizontally gets H horizontal sampled point in the scope, and H is natural number; At each horizontal sampled point, measure the vertical mobile consistance of this horizontal level turning axle respectively, according to rotating shaft center's projection that this horizontal level V vertical sampled point calculates, V is even number, calculates the subpoint of this horizontal level ray source focus on detector; The consistance of turning axle in the process of moving horizontally namely known in the skew of the projection of the ray source focus that H horizontal sampling point position of comparison calculates.
Described vertical cone-beam CT system adopts the FDK algorithm to rebuild; The requirement of the imaging geometry structure of the vertical cone-beam CT system of FDK algorithm is: turning axle 315 is vertical with midplane, and the while is parallel with the column direction of detector 106 pixel arrays, line direction is vertical; Cross x-ray source 100 focuses and do the straight line of vertical probe 106, this straight line is through turning axle 315; It is stable that the rotation of turning axle 315 keeps, and remains vertical with midplane in rotary course; X-ray source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
Metal Ball calibrating patterns 104 is cylindrical cups of an organic glass system, and the coboundary of cup is fixed a Metal Ball 105.
As follows in detail: Fig. 1 is the Scan Architecture of vertical cone-beam CT system, and the ingredient of vertical cone-beam CT system comprises little focal spot x-ray source 100, objective table 102, Metal Ball calibrating patterns 104 and detector 106.Metal Ball calibrating patterns 104 is fixed on the objective table 102, and objective table 102 is fixed on the turning axle 315.Metal Ball calibrating patterns 104 and objective table 102 can be with turning axle 315 rotations in this system.Metal Ball calibrating patterns 104, objective table 102 and turning axle 315 constitute sample system 201.Sample system 201 can move forward and backward along horizontal guide rail, moves up and down along vertical guide rail.X-ray source 100 immobilizes after system's installation with the position of detector 106, but can finely tune as required.
Fig. 2 a is the side of the used Metal Ball calibrating patterns 104 of vertical cone-beam CT system calibration; Fig. 2 b is the vertical view of the used Metal Ball calibrating patterns 104 of vertical cone-beam CT system calibration.Metal Ball calibrating patterns 104 is cylindrical cups of an organic glass system, and the coboundary of cup has a prill 105.Relative position difference between x-ray source 100, sample system 201 and the detector 106, the enlargement factor of system is different, namely when sample system 201 during near detector 106 system's enlargement factor less, and system's enlargement factor is bigger when the close x-ray source 100 of sample system 201.Therefore, in order to allow the projected image of metal calibrating patterns 104 fill up detector 106 planes as far as possible, the metal calibrating patterns 104 of different-diameter when sample system 201 is positioned at the varying level position, the closer to the position of x-ray source 100, the diameter of Metal Ball calibrating patterns 104 cups is just more little.
Fig. 3 is that the Metal Ball calibrating patterns is in the bead perspective view of rotary course.Prill 105 is small-sized with respect to metal calibrating patterns 104, can be considered as particle.With in turning axle 315 rotary courses, the movement locus of bead particle 312 is circles to metal calibrating patterns 104 with objective table 102.In cone beam projection, if particle rotates in circular trace, the track of its projection 314 is exactly an ellipse.The projection one at circular trace center fixes on the projection line of turning axle.In the process of bead particle 312 rotation, 180 ° the bead particle line of two positions of being separated by necessarily passes through rotation center.Because the projection of straight line on detector remains straight line in the cone beam projection, so 180 ° the line that is projected on the detector of bead particle of two positions of being separated by must be through the circle projection of track center on detector.The bead particle is even number through 360 ° rotation at N(N) individual evenly spaced position gets its projection.Be separated by 180 ° the projection join line of bead particle of two positions through the projection of rotating shaft center, can try to achieve the rotation center of turning axle by least square method according to N/2 bar straight-line equation.
Fig. 4 is the process flow diagram of the calibration process of vertical cone-beam CT system.
The calibration process of vertical cone-beam CT system mainly comprises the measurement of the rotation center of turning axle; The rotation consistance of turning axle; The consistance of turning axle in vertical moving process; The consistance of turning axle in the process of moving horizontally.
The measuring method of the rotation center of turning axle is as follows: Metal Ball calibrating patterns 104 rotates with turning axle 315 with objective table 102, gathers a width of cloth perspective view, the subpoint of calculating prill 105 on detector every 360/N °.
Calculate bead in the method for subpoint on the detector: in perspective view, because the gray scale of the organic glass cup of Metal Ball calibrating patterns 104 and background is higher, the gray scale of prill 105 is lower, can use thresholding method that Metal Ball is split.Then the data of the Metal Ball scope that splits are preserved, and with gray-scale value normalization, even the grey value profile of all pixels is between 0-255 in the image.If the point coordinate in the Metal Ball zone that is partitioned into is
, the gray-scale value of respective pixel is
, wherein
, P is the number of pixels in the Metal Ball zone that is partitioned into.Make the subpoint coordinate of prill be
, then this coordinate can calculate by following formula:
Calculate the computing method of rotation center: obtain N evenly spaced little spheric projection after Metal Ball calibrating patterns 104 rotates 360 °.With
Expression bead particle is at the subpoint coordinate of i position, and 180 ° the subpoint of bead particle of two positions of being separated by is
With
, wherein
, can be expressed as by the straight line of these two points:
Wherein
The subpoint coordinate of expression rotation center.
Because N is even number, total N/2 of such equation, the least square solution of finding the solution these equations just can obtain the subpoint coordinate of rotation center
Specific practice is: equation (2) is rewritten as following form:
Wherein,
Then system of equations can be written as:
System of equations (5) is called the overdetermined equation group, the least square solution of separating this equation get final product the subpoint coordinate of rotation center
The conforming measuring method of the rotation of turning axle is as follows: Metal Ball calibrating patterns 104 is even number through 360 ° rotation at N(N) individual evenly spaced position gets its projection.Sample system 201 is fixed on certain position, and 360 ° of M(M of Metal Ball calibrating patterns 104 rotation are natural number) inferior, preserve respectively in each rotation N position the bead particle projected position and calculate the projected position of this position rotation center.Relatively in M the rotation, the rotation consistance of turning axle is namely known in the skew of same position bead particle projected position and rotation center projected position according to the side-play amount of analysis gained.
The conforming measuring method of turning axle in vertical moving process is as follows: in the vertical direction, moving up and down sample system 201 makes the bead particle complete the dropping on the detector of projected footprint of rotary course, choosing V(V in this vertical range is even number) individual sampled point, wherein V/2 vertical sampled point is positioned at above the radiographic source midplane, and V/2 vertical sampled point is positioned at below the radiographic source midplane.At each vertical sampled point, Metal Ball calibrating patterns 104 is even number through 360 ° rotation at N(N) individual evenly spaced position gets its projection.Record the projected position of each rotation sampled point bead particle on detector, and calculate the projected position of rotating shaft center's point on detector.Ideally, the line of the subpoint of V vertical sampled point rotating shaft center is the straight line that column direction is parallel, line direction is vertical of a parallel detector image plane element array.The result of actual measurement, the line of the subpoint of V vertical sampled point rotating shaft center and the column direction of detector plane pixel array have an angle, illustrate that namely turning axle moves up and down instability in the process in sample system 201, its rotation center is along certain direction skew.
The conforming measuring method of turning axle in the process of moving horizontally is as follows: in the horizontal direction, getting H(H in the sample system 201 front and back mobile ranges is natural number) individual horizontal sampled point.At each horizontal sampled point, measure the vertical mobile consistance of this horizontal level turning axle respectively, be even number according to this horizontal level V(V) projection of individual rotating shaft center, calculate the subpoint of this horizontal level ray source focus on detector.
Calculate the method for the subpoint of ray source focus on detector: sample system is measured the rotary middle point projection coordinate of calculating at certain horizontal level and is expressed as
, wherein
The subpoint coordinate of this position ray source focus on detector is
, then this coordinate can calculate by following formula:
Wherein,
Wherein
The minor axis of representing i vertical sampling location bead particle elliptical orbit.The minor axis of bead particle elliptical path of its projection in rotary course changes along with the change in location of sample system: sample system is the closer to midplane, and the minor axis of the elliptical orbit of bead particle is more short; Sample system is more away from midplane, and the minor axis of the elliptical orbit of bead particle is more long.So along the column direction of detector, the subpoint of i rotation center is directly proportional with the minor axis of i bead particle elliptical orbit with the distance of the subpoint of ray source focus, as described in equation (7).Owing to V is the both sides that the individual vertical sampled point of even number and V/2 lays respectively at midplane, can calculate V/2 ray source focus projection ordinate according to equation (7)
, be averaged again and just obtain the ordinate of ray source focus projection more accurately
In theory, the line of the ray source focus subpoint of all H horizontal sampling locations is parallel with the center line of cone-beam X-ray, vertical with detector plane.The result of actual measurement, the line of the ray source focus subpoint of all H horizontal sampling locations and detector plane out of plumb but certain included angle is arranged.According to the relative position of the relative radiographic source with objective table of this angle and detector, can estimate radiogenic deviation post.
Claims (3)
1. vertical cone-beam computer tomography calibration steps, it is characterized in that: this method is based on a kind of vertical cone-beam computer tomography calibration system, this system comprise x-ray source (100), and x-ray source (100) is oppositely arranged and discontiguous detector (106) and be arranged on x-ray source (100) and detector (106) between objective table (102), be used for fixing objective table (102) turning axle (315), be fixed on the Metal Ball calibrating patterns (104) on the objective table (102);
Wherein Metal Ball calibrating patterns (104) rotates with turning axle (315) with objective table (102) in scanning process; X-ray source (100) is motionless with the stationkeeping of detector (106), obtains data for projection by objective table (102) rotation; Fix a Metal Ball (105) on the Metal Ball calibrating patterns (104); Metal Ball calibrating patterns (104), objective table (102) and turning axle (315) constitute sample system (201);
Metal Ball calibrating patterns (104) is the cylindrical cup that organic glass is made, the coboundary fixing metal ball (105) of cup;
This method may further comprise the steps:
Measure the rotation center of turning axle (315) in rotary course;
Measure the rotation consistance of turning axle (315); Described rotation consistance is to instigate sample system (201) to be fixed on certain position, make Metal Ball calibrating patterns (104) be positioned at suitable rotation sampled point, 360 ° of Metal Ball calibrating patterns (104) rotations M time, M is natural number, in the position of each rotation back calculating Metal Ball (105), the consistance of Metal Ball (105) position is exactly the rotation consistance of turning axle respectively;
Measure the consistance of (315) turning axle in vertical moving process; The consistance of described turning axle (315) in vertical moving process refers to the consistance of rotation center in the process that turning axle moves up and down;
Measure the consistance of turning axle (315) in the process of moving horizontally, the consistance of described turning axle (315) in the process of moving horizontally refers to the consistance of rotation center in the process that turning axle moves forward and backward;
Realize the calibration of vertical Cone-Beam CT calibration system according to above-mentioned steps;
The measuring method of the rotation center of described turning axle is: make sample system (201) be fixed on certain position, Metal Ball calibrating patterns (104) is got N rotation sampled point equably and is got its projected image on detector (106) with turning axle (315) rotation; The data for projection that rotates a circle according to Metal Ball calibrating patterns (104) calculates the rotation center of turning axle, and N is even number;
The conforming measuring method of the rotation of described measurement turning axle is: make sample system (201) be fixed on certain position, Metal Ball calibrating patterns (104) rotates with turning axle (315), get N rotation sampled point equably and get its projected image on detector (106), N is even number; In relatively rotating for M time, the projected position of same position Metal Ball (105) and the skew of rotation center projected position are namely known the rotation consistance of turning axle according to side-play amount, and M is natural number;
The conforming measuring method of turning axle in vertical moving process is: in the vertical direction, sample system (201) moves up and down that the projected footprint that makes Metal Ball calibrating patterns (104) Metal Ball (105) in rotary course is complete to be dropped on the detector (106), in this vertical range, choose V sampled point, V is even number, wherein V/2 vertical sampled point is positioned at the midplane top, and V/2 vertical sampled point is positioned at the midplane below; At each vertical sampled point, Metal Ball calibrating patterns (104) rotates with turning axle (315), get its projection N evenly spaced position, N is even number, calculate the projected position of each rotation sampled point Metal Ball (105) on detector (106), and calculate the projected position of rotating shaft center's point on detector, the consistance of turning axle in vertical moving process namely known in relatively V skew that vertical sampled point calculates the rotary middle point of gained;
The conforming measuring method of turning axle in the process of moving horizontally is: in the horizontal direction, sample system (201) moves horizontally gets H horizontal sampled point in the scope, and H is natural number; At each horizontal sampled point, measure the vertical mobile consistance of this horizontal level turning axle respectively, according to rotating shaft center's projection that this horizontal level V vertical sampled point calculates, V is even number, calculates the subpoint of this horizontal level ray source focus on detector; The consistance of turning axle in the process of moving horizontally namely known in the skew of the projection of the ray source focus that H horizontal sampling point position of comparison calculates.
2. vertical cone-beam computed tomography imaging system calibration steps according to claim 1 is characterized in that: described vertical Cone-Beam CT calibration system adopts the FDK algorithm to rebuild; The requirement of the imaging geometry structure of the vertical Cone-Beam CT calibration system of FDK algorithm is: turning axle (315) is vertical with midplane, and the while is parallel with the column direction of detector (106) pixel array, line direction is vertical; Cross x-ray source (100) focus and do the straight line of vertical probe (106), this straight line is through turning axle (315); It is stable that the rotation of turning axle (315) keeps, and remains vertical with midplane in rotary course; X-ray source is center for the projected image of rebuilding to the intersection point of the vertical line of detector.
3. vertical cone-beam computed tomography imaging system calibration steps according to claim 1 and 2, it is characterized in that: Metal Ball calibrating patterns (104) is the cylindrical cup of an organic glass system, and the coboundary of cup is fixed a Metal Ball (105).
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| CN106706675B (en) * | 2015-07-16 | 2019-08-27 | 中国科学院高能物理研究所 | A kind of bearing calibration based on computer demixing scan imaging CL system |
| WO2018126335A1 (en) * | 2017-01-03 | 2018-07-12 | 苏州海斯菲德信息科技有限公司 | Method for evaluating and correcting geometric parameters of cone-beam ct system based on glomerulus motif |
| CN107507257B (en) * | 2017-08-11 | 2021-01-29 | 重庆真测科技股份有限公司 | Large-view-field indexing offset reconstruction method and system |
| CN108030501B (en) * | 2017-11-14 | 2019-12-13 | 深圳先进技术研究院 | geometric calibration device and method for static cone-beam CT imaging system |
| JP6988732B2 (en) * | 2018-08-02 | 2022-01-05 | 株式会社島津製作所 | Radiation image processing equipment and radiation image processing method |
| CN113945174B (en) * | 2021-10-21 | 2023-10-17 | 中国工程物理研究院激光聚变研究中心 | X-ray projection measurement image size calibration method |
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| US6459754B1 (en) * | 1999-10-27 | 2002-10-01 | Ge Medical Systems Global Technology Company, Llc | Methods and apparatus for cone beam multislice CT correction |
| JP2005241575A (en) * | 2004-02-27 | 2005-09-08 | Toshiba Corp | X-ray computed tomography system and three-dimensional perspective image forming apparatus |
| CN101832954B (en) * | 2010-03-15 | 2012-06-20 | 中国工程物理研究院应用电子学研究所 | Method for carrying out image reconstruction and coordinate system origin calibration by using same in cone-beam XCT system |
| CN101936720B (en) * | 2010-07-30 | 2012-03-21 | 北京航空航天大学 | Method for calibrating detector torsion angle applied to cone-beam XCT system |
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