CN103800032B - The corrective system corrected for cone-beam CT system geometric position and bearing calibration thereof - Google Patents
The corrective system corrected for cone-beam CT system geometric position and bearing calibration thereof Download PDFInfo
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Abstract
The invention discloses a kind of corrective system for the correction of cone-beam CT system geometric position and bearing calibration thereof.Positioner of the present invention, collimator apparatus and axis adjustment device; Wherein, positioner comprises supporter, the first and second alignment marks, and the shape and size of the first and second alignment marks are identical, is set in parallel in positioner on supporter and is placed with before radiographic source; Collimator apparatus comprises ventilating hole plate and bracing frame, and the center of ventilating hole plate has through hole, and ventilating hole plate is placed before the detectors by bracing frame; Axis adjustment device comprises adjustable stem and pedestal, and adjustable stem is arranged on pedestal, and axis adjustment device is placed on a spinstand.Corrective system of the present invention, first determine the position of central ray, carry out the adjustment of the geometry position error of detector again, make the face outward turning corner of central beam position on the detector and detector out relatively independent, reduce the adjustment difficulty of geometric correction, reach the object of quick adjustment cone-beam CT system.
Description
Technical field
The present invention relates to biomedical imaging field, be specifically related to a kind of corrective system for the correction of cone-beam CT system geometric position and bearing calibration thereof.
Background technology
CT technology CT(ComputedTomography) in current nucleus medical image, play very important effect, especially in multi-modality imaging field, CT provides structural information and correction for attenuation information for other mode.Can say so, the reconstruction precision of CT determines image reconstruction effect and the image syncretizing effect of other mode to a great extent.At present, 3 D pyramidal CT generally adopts FDK(Feldkamp) analytic reconstruction algorithm, but the three-dimensional reconstruction effect of FDK algorithm is very responsive to the geometric parameter of 3 D pyramidal CT system, it requires that the relative geometry position of radiographic source, detector and turntable is in perfect condition, namely radiographic source central ray vertically injects detector center, and rotating shaft is orthogonal with central ray coplanar orthogonal.Therefore carry out geometric correction to 3 D pyramidal CT to have very important significance.
Traditional geometric correction method is broadly divided into asynchronous correction, and nonlinear least square method synchronous correction.So-called asynchronous correction, be exactly that each step only corrects one or several parameter, synchronous correction is exactly all parameters of disposable correction.
The people such as YiSun propose a kind of method of asynchronous correction in " ACalibrationMethodforMisalignedScannerGeometryinCone-bea mComputedTomography " literary composition: four summits four identical high density balls being placed in square poly (methyl methacrylate) plate, then just can obtain four balls projected position on the detector.The various geometrical offset parameter of detector can be calculated successively by the relative geometry position relation between four projections.But this method all calculates based on other parameter ideal situations in each step, and some operation requirements are difficult to realize, and such as require that radiographic source central ray vertical sand shooting is to the symmetrical centre of four points.And the method needs to measure the distance of radiographic source to detector, and in fact cannot determine due to ray source focus position and be difficult to obtain this parameter.
The people such as Smekal propose a kind of method of inlaying two circle steel balls on low density material in " Accuratetechniqueforcompletegeometriccalibrationofcone-b eamcomputedtomographysystem ".A cylinder inlays upper and lower two-layer steel ball, and each 12 up and down, be circumferentially uniformly distributed, the relative position between steel ball is known, carries out geometric parameter correction by the relative position of its projection centre on the detector.But projection is easy to obscure with the corresponding relation of raw steel pearl in the method.
Patent CN202104929U improves said method, between two-layer steel ball, add again one or more positioning ball, makes the corresponding relation of projection and raw steel pearl definitely, and the method is computationally easier simultaneously.But the precision of these two kinds of methods is subject to the interference of several factors, such as, correct the certainty of measurement etc. of the relative position between the machining accuracy of imitative body used, steel ball.
All asynchronous correction methods, need to measure radiographic source to the distance of detector and radiographic source to rotating shaft or correct the distance of imitating body, these distance parameters are not only difficult to measurement, and inevitably introduce measurement error.
BJ University of Aeronautics & Astronautics provides a kind of method of synchronous correction in Non-linearleastsquareestimationofgeometricalparametersfo rCone-beamthreedimensionalcomputedtomography.Place a steel ball on a spinstand, obtain the projection of this steel ball under all angles through 360 degree of rotations.By the projection centre extracted under each angle and the functional relationship set up between projection centre and geometric parameter, namely by nonlinear least square method, matching estimation is carried out to geometric parameter, thus reach the disposable object solving all geometric parameters.The method has carried out too much hypothesis in formulation process, as detector rotates without in face, without face external rotation, rotating shaft non-angular error, only has offset error etc., thus inapplicable for practical situation.
Geometric correction of the prior art is in trimming process, and several geometric correction parameters can change simultaneously, thus add the difficulty of correction.Corrective system of the present invention and method, make the face outward turning corner of central beam position on the detector and detector out relatively independent, reduce the adjustment difficulty of geometric correction, reach the object of quick adjustment cone-beam CT system.
Summary of the invention
In order to overcome problems of the prior art, the invention provides a kind of corrective system for the correction of cone-beam CT system geometric position and bearing calibration thereof, the determination of central ray position can be realized, thus can quick adjustment cone-beam CT system geometric error.
One object of the present invention is to provide a kind of corrective system corrected for cone-beam CT system geometric position.
Corrective system for the correction of cone-beam CT system geometric position of the present invention comprises: positioner, collimator apparatus and axis adjustment device; Wherein, positioner comprises supporter, the first alignment mark and the second alignment mark, and the first alignment mark is identical with the shape and size of the second alignment mark, is set in parallel on supporter, and positioner is placed with before radiographic source; Collimator apparatus comprises ventilating hole plate and bracing frame, and the center of ventilating hole plate has through hole, and ventilating hole plate is placed before the detectors by bracing frame, and the axle of through hole is perpendicular to detector; Axis adjustment device comprises adjustable stem and pedestal, and adjustable stem is arranged on pedestal, and axis adjustment device is placed on a spinstand.
Cone-beam CT system comprises detector, turntable, radiographic source, detector platform, adjustable base and radiographic source platform; Wherein, detector platform, adjustable base and radiographic source platform are located along the same line; Radiographic source platform and detector platform lay respectively at two ends, and radiographic source is positioned on radiographic source platform; Detector is placed on detector platform; Adjustable base is between detector platform and radiographic source platform, and turntable is arranged on adjustable base.
Detector platform has 6 degree of freedom, can move along three mutually perpendicular axis, and can rotate around three mutually perpendicular axis.Radiographic source platform has 6 degree of freedom, can move along three mutually perpendicular axis, and can rotate around three mutually perpendicular axis.Adjustable base has 3 degree of freedom, can move along three mutually perpendicular axis.
Positioner is placed with before radiographic source, for determining the position of central ray, and for regulating the displacement error of detector, makes central ray incide the imaging center of detector.The line at the center of the first and second alignment marks is parallel to central ray.First and second alignment marks of positioner adopt the material that attenuation quotient is larger, as tungsten, copper, lead and zirconium etc.; Supporter adopts the material that attenuation quotient is lower, as lucite etc.; The attenuation quotient of the material that the first and second alignment marks adopt is greater than the attenuation quotient of supporter.
Collimator apparatus is placed before the detectors, for regulate detector face outside angular error.Ventilating hole plate needs to have certain thickness, and adopts the material that attenuation quotient is larger, as lead, steel, ferrum and copper etc., can obtain the projection of through hole during to meet and to project to ventilating hole plate, namely clearly can tell the edge of the projection speckle of through hole in projection.The thickness of ventilating hole plate is directly proportional to the aperture of through hole, and the thickness of the linear attenuation coefficient of ventilating hole plate and ventilating hole plate is inversely proportional to.
Axis adjustment device place on a spinstand, according to axis adjustment device projection on the detector, adjust the position of turntable, thus make the rotating shaft of turntable and central ray coplanar.Axis adjustment device adopts the material that attenuation quotient is larger, as lead, steel, ferrum and copper etc.
Another object of the present invention is to provide a kind of bearing calibration corrected for cone-beam CT system geometric position.
The bearing calibration corrected for cone-beam CT system geometric position of the present invention, comprises the following steps:
1) central ray is determined:
A) positioner is placed with before radiographic source, launches cone-beam x-ray from radiographic source, project on detector through positioner;
B) position of regulating positioning device before radiographic source, makes the center superposition of the first and second alignment marks projection on the detector, and now central ray is through the center of the first and second alignment marks;
2) offset deviation of detector is regulated:
Central ray is through the center of the first and second alignment marks, then the first and second alignment marks projection centre is on the detector exactly central ray position on the detector, according to the position of the projection centre pixel on the detector of the first and second alignment marks, by the position of detector platform adjustment detector, the imaging center of detector is moved to the center of the projection of the first and second alignment marks, central ray is incident to the imaging center of detector, and now detector does not exist offset deviation;
3) regulate detector face outside angular error:
A) placed before the detectors by collimator apparatus, and ventilating hole plate is close to detector, the axle of through hole is perpendicular to detector, and the position of adjustment ventilating hole plate, makes the imaging center being centrally located at detector of through hole, removed by positioner from radiographic source;
B) collimation device projects, and observes through hole projection on the detector, and by the angle of detector platform adjustment detector, make the through hole circle being projected as rule on the detector, now detector does not exist angular deviation outside face;
4) rotating shaft of turntable is regulated;
Collimator apparatus is disassembled, axis adjustment device is placed on a spinstand, turntable rotates a circle, project to adjustable stem, the shape of projection is about vertical axisymmetric tetragon, and the axis of symmetry of tetragon is exactly the projection of rotating shaft, according to adjustable stem projection on the detector, by the displacement of adjustable base adjustment turntable, make the imaging center of detector drop on the axis of symmetry of the projection of adjustable stem, now the rotating shaft of turntable and central ray coplanar.
Advantage of the present invention:
Accompanying drawing explanation
Fig. 1 is the structural representation of cone-beam CT system of the present invention;
Fig. 2 is the principle schematic of cone-beam CT system of the present invention;
Fig. 3 is the schematic diagram of the geometry position error situation of several detector, and wherein, (a) and (b), for detector is in the projection of XZ plane, (c) and (d), for detector is in the projection of XY plane, (e) is for detector is in the projection of YZ plane;
Fig. 4 is the schematic diagram of an embodiment of the corrective system for the correction of cone-beam CT system geometric position of the present invention, wherein, and the schematic diagram that (a) is positioner, the schematic diagram that (b) is collimator apparatus, the schematic diagram that (c) is axis adjustment device;
Fig. 5 is the schematic diagram of the projection of the positioner of corrective system of the present invention, wherein, a centered by (), ray is not through the center of the first and second alignment marks, the schematic diagram of the projection of the first and second alignment marks, b centered by (), ray is through the center of the first and second alignment marks, the schematic diagram of the first and second alignment marks projection on the detector;
Fig. 6 is the schematic flow sheet of the bearing calibration for the correction of cone-beam CT system geometric position of the present invention;
Fig. 7 is the schematic diagram of the axis adjustment device projection on the detector of geometric correction system of the present invention, wherein, and the situation that (a) vertically places for adjustable stem, the situation that (b) does not vertically place for adjustable stem.
Detailed description of the invention
Below in conjunction with accompanying drawing, by embodiment, the present invention will be further described.
As shown in Figure 1, the cone-beam CT system of the present embodiment comprises detector 1, rotation 2, radiographic source 3, detector platform 4, adjustable base 5 and radiographic source platform 6; Wherein, detector platform 4, adjustable base 5 and radiographic source platform 6 are positioned at same straight line and are arranged on optical table 10; Radiographic source platform 6 and detector platform 4 lay respectively at two ends, and detector 1 is placed on detector platform 4, and radiographic source 3 is positioned on radiographic source platform 6; Adjustable base 5 is between detector platform 4 and radiographic source platform 6, and turntable 2 is arranged on adjustable base 5.
In the present embodiment, the table top flatness of optical table 10 is 0.10mm/m
2, surface uniform distribution standard M6 screw.The pixel size of detector 1 is 74.8um, and pel array is 1944 × 1536.Turntable 2 is fixed on optical table 10 by adjustable base 5, and adjustable base 5 is provided with motor, by the conputer controlled anglec of rotation, can realize continuously, be interrupted rotation, minimum step value 0.5 degree.Radiographic source 3 is point source, and focal spot size is 40um.Detector platform 4 and radiographic source platform 6 can realize the adjustment of 6 degree of freedom respectively by spiral button, comprise regulating along X, Y and Z-direction displacement and around X, Y and Z-direction angle, degree of regulation is 0.02mm.Adjustable base 5 is for fixing and adjustment turntable 2, angular error due to turntable 2 can sum up the angular error η to detector 1, therefore adjustable base only need realize the adjustment of 3 degree of freedom, the displacement namely along X, Y and Z-direction regulates, and degree of regulation is 0.02mm.
As shown in Figure 2, S represents light source, and central ray is propagated along X-axis, and XYZ coordinate system is the space coordinates set up with central ray and rotating shaft, and O is initial point.UV coordinate system is capable with the imaging center of actual detector and the plane coordinate system of central series foundation, and ideally, this plane is parallel to YOZ, and O
2be positioned in X-axis, U is parallel to Y, and V is parallel to Z.Detector to be adjusted is positioned at VO
2u plane, O
2for the imaging center of detector to be adjusted.
Because artificial installation accuracy is limited, all there is certain geometric position deviation in cone-beam CT system substantially, and these deviations can be divided into three parts: radiogenic deviation, the deviation of turntable and the deviation of detector.These three parts can be summed up as 5 parameter errors of detector: angular error η in displacement error Δ v, Δ u dough-making powder outer angular error β (angle of pitch), θ (side corner) and face.Fig. 3 is the schematic diagram of the geometric error situation of several detector.Wherein, (a) and (b) are for detector is in the projection of XOZ plane, and as shown in Fig. 3 (a), detector rotates θ around U axle; As shown in Figure 3 (b), the imaging center O of detector
2Δ V is differed apart from along V wheelbase from O.Figure (c) and (d) are for detector is in the projection of XOY plane, and as shown in Figure 3 (c), detector rotates β around V axle; As shown in Fig. 3 (d), the imaging center O of detector
2Δ U is differed apart from along U wheelbase from O.As shown in Fig. 3 (e), detector rotates η around X-axis, for the adjustment of this internal rotation angle degree, can be summed up as the adjustment of rotating shaft.
As shown in Figure 4 (a), positioner A comprises supporter A3, the first and second alignment mark A1 and A2, in the present embodiment, supporter A3 is the flat board with two surfaces parallel to each other, the shape and size of the first and second alignment marks are identical, be embedded in respectively on the surface parallel to each other of supporter A3, and the line at the two center be parallel to supporter bottom surface and perpendicular to the surface at place.First and second alignment mark A1 and A2 are respectively filament annulus, are provided with two mutually orthogonal filaments in the inside of filament annulus.The line at the center of the first and second alignment mark A1 and A2 is parallel to the bottom surface of supporter and perpendicular to the surface be parallel to each other of supporter, makes the line at the center of the first and second alignment mark A1 and A2 be parallel to central ray.In the present embodiment, the center of the first and second alignment mark A1 and A2 is the center of circle of filament annulus, the cross point of namely mutually orthogonal filament.
As shown in Figure 4 (b), collimator apparatus B comprises ventilating hole plate B1 and bracing frame B3, and the center of ventilating hole plate B1 has through hole B2.As shown in Figure 4 (c), axis adjustment device C comprises adjustable stem C1 and pedestal C2.
The bearing calibration corrected for cone-beam CT system geometric position of the present embodiment, comprises the following steps:
1) central ray is determined:
A) positioner A is placed with before radiographic source 3, as shown in Figure 6 (a), launches cone-beam x-ray from radiographic source, project on detector 1 through positioner A;
B) observe the image obtained on the detector, if the center of circle of two filament annulus overlaps, i.e. the cross point of orthogonal filament, shows that central ray is on two determined straight lines in the center of circle; If the center of circle of two filament annulus does not overlap, then show that central ray is without two centers of circle.
Such as, in the vertical direction, if be projected in two below straight lines that the center of circle is determined, then the position relationship that the image obtained has is as shown in Fig. 5 (a).11 is detector plane, A1 ' for ray through the first alignment mark A1(according to Similar Principle of Triangle, diameter projected is larger) central projection, A2 ' for ray less through the second alignment mark A2(diameter projected, the convenient difference of diameter projected's difference of two circles) central projection, the projection A2 ' of the second alignment mark A2 is in the bottom of the projection A1 ' of the first alignment mark A1.Now, the height of reduction positioner A can reduce the distance between A1 ' and A2 '.Repeatedly regulate, A1 ' and A2 ' can be made at sustained height.In like manner, if be projected in two more than straight lines that the center of circle is determined, reduce the height of positioner A, A1 ' and A2 ' can be made at sustained height.As for the adjustment on left and right directions in like manner.The position of regulating positioning device A before radiographic source, until the center superposition of the first and second alignment marks projection on the detector, as shown in Fig. 5 (b).
Now, central ray is through the center of the first and second alignment marks, and the projection on the detector of the center of the first and second alignment marks is exactly central ray position on the detector.
2) offset deviation Δ v and the Δ u of detector is regulated:
Central ray is through the center of the first and second alignment marks, then the center of the first and second alignment marks projection is on the detector exactly the position that central ray incides on detector, according to the projection centre of the first and second alignment marks in the position of detector pixel point, by the position of detector platform adjustment detector, the imaging center of detector is moved to the center of the projection of the first and second alignment marks.
Such as, read the coordinate at the center of the first and second alignment marks, the coordinate of the imaging center of detector is (number of lines of pixels/2, pixel columns/2), according to the difference of two coordinates, detector platform repeatedly can be regulated to adjust the position of detector, Two coordinate is overlapped.
Now, central ray is incident to the imaging center of detector, and now detector does not exist offset deviation.
3) regulate detector face outside angular error β and θ:
A) before collimator apparatus B being placed on detector 1, and ventilating hole plate is close to detector, and the axle of through hole is perpendicular to detector, the position of adjustment ventilating hole plate, make the imaging center being centrally located at detector of through hole, positioner is removed from radiographic source, as shown in Figure 6 (b);
B) collimation device projects, and observes through hole projection on the detector, if there is not probe angle error β and θ, is then projected as a regular circle.If there is any one angular error, then this view field just goes out to present an ellipse.
Such as, during adjusting pitch angle error β, by the luffing angle of detector platform adjustment detector, projection imaging, reads oval vertically long axis direction shared pixel count on the detector.When pixel count reaches maximum, show now to have essentially eliminated luffing angle error β.In like manner, by the side gyration of detector platform adjustment detector, projection imaging, reads the pixel count that oval horizontal long axis direction is shared on the detector.When pixel count reaches maximum, show now to have essentially eliminated side gyration error theta.After these two angular adjustment are good, be projected as a regular circle.Now, there is not angular deviation outside face in detector.
4) rotating shaft of turntable is regulated;
Collimator apparatus B is disassembled, axis adjustment device C is placed on the optional position of the table top of the level of turntable 2, as shown in Figure 6 (c), turntable 2 rotates a circle, and projects to adjustable stem C1, and the shape of projection is about vertical axisymmetric tetragon, the axis of symmetry of tetragon is exactly the projection of rotating shaft, according to adjustable stem projection on the detector, by the displacement of adjustable base adjustment turntable, in two kinds of situation:
A () adjustable stem C1 is vertically placed on the table top of the level of turntable, by allowing turntable 2 rotate a circle, obtaining the multi-angle projection of adjustable stem C1, is a rectangle.By finding projection distance V axle distance farthest in the u-direction, as shown in Figure 7 (a), such as adjustable stem C1 is 50 pixel sizes at the positive direction distance V axle maximum distance of U, be 30 pixels in the negative direction of U apart from V axle maximum distance, we just can learn that rotating shaft has error along Y-axis positive direction like this, then regulate adjustable base 5 to make its opposite direction along Y-axis move (50-30)/4*pixel_size.Wherein pixel_size is the pixel size of detector, as detector pixel size 74.8um. repeated trials can be adjusted to ideal position turntable 2 ~ 3 times.
If b () adjustable stem C1 does not place vertically, projection is an isosceles trapezoid.The two ends farthest of isosceles trapezoid are the straight lines tilted, as shown in Figure 7 (b) shows, but bearing calibration is substantially the same, we are by finding distance V axle straight line farthest, then their axis of symmetry is drawn, so just can calculate offset Δ U, then regulate turntable adjustable base system to make its opposite direction along Y-axis mobile Δ U/4, repeated trials can be adjusted to ideal position rotating shaft 2 ~ 3 times.
Now, the rotating shaft of turntable and central ray coplanar.By axis adjustment device C, the rotating shaft of turntable and central ray coplanar after, face internal rotation angle degree has just regulated, and namely now there is not face internal rotation angle degree deviation.
It is finally noted that, the object publicizing and implementing mode is to help to understand the present invention further, but it will be appreciated by those skilled in the art that: without departing from the spirit and scope of the invention and the appended claims, various substitutions and modifications are all possible.Therefore, the present invention should not be limited to the content disclosed in embodiment, and the scope that the scope of protection of present invention defines with claims is as the criterion.
Claims (10)
1., for the corrective system that cone-beam CT system geometric position corrects, described cone-beam CT system comprises detector (1), turntable (2), radiographic source (3), detector platform (4), adjustable base (5) and radiographic source platform (6); Wherein, described detector platform (4), adjustable base (5) and radiographic source platform (6) are located along the same line; Described radiographic source platform (6) and detector platform (4) lay respectively at two ends, and described radiographic source (3) is positioned on radiographic source platform (6); Described detector (1) is placed on detector platform (4); Described adjustable base (5) is positioned between detector platform (4) and radiographic source platform (6), turntable (2) is arranged on adjustable base (5), it is characterized in that, described corrective system comprises: positioner (A), collimator apparatus (B) and axis adjustment device (C); Wherein, described positioner (A) comprises supporter (A3), the first alignment mark and the second alignment mark (A1 and A2), first alignment mark is identical with the shape and size of the second alignment mark (A1 with A2), be set in parallel on supporter (A3), positioner (A) is placed with at radiographic source (3) front; Described collimator apparatus (B) comprises ventilating hole plate (B1) and bracing frame (B3), the center of ventilating hole plate (B1) has through hole (B2), it is front that ventilating hole plate (B1) is placed on detector (1) by bracing frame (B3), and the axle of through hole is perpendicular to detector; Described axis adjustment device (C) comprises adjustable stem (C1) and pedestal (C2), and adjustable stem is arranged on pedestal, and axis adjustment device (C) is placed on turntable (2).
2. corrective system as claimed in claim 1, it is characterized in that, the line at the center of described first and second alignment marks (A1 and A2) is parallel to central ray.
3. corrective system as claimed in claim 1, it is characterized in that, the attenuation quotient of the material that described first and second alignment marks (A1 and A2) adopt is greater than the attenuation quotient of supporter (A3).
4. corrective system as claimed in claim 1, it is characterized in that, the thickness of described ventilating hole plate (B1) is directly proportional to the aperture of through hole, and the linear attenuation coefficient of described ventilating hole plate (B1) and the thickness of ventilating hole plate (B1) are inversely proportional to.
5. corrective system as claimed in claim 3, is characterized in that, the material of described first and second alignment marks adopts the one in tungsten, copper, lead and zirconium; The material of supporter adopts lucite.
6. corrective system as claimed in claim 1, is characterized in that, the material of described ventilating hole plate adopts the one in lead, steel, ferrum and copper; The material of described axis adjustment device adopts the one in lead, steel, ferrum and copper.
7. corrective system as claimed in claim 1, it is characterized in that, described supporter (A3) is for having the flat board on two surfaces parallel to each other, described first and second alignment marks (A1 and A2) are embedded on the surface parallel to each other of supporter (A3) respectively, and the line at the two center be parallel to supporter (A3) bottom surface and perpendicular to the surface at place.
8. corrective system as claimed in claim 1, it is characterized in that, described first and second alignment marks (A1 and A2) are respectively filament annulus, are provided with two mutually orthogonal filaments in the inside of filament annulus.
9., for the bearing calibration that cone-beam CT system geometric position corrects, it is characterized in that, described bearing calibration comprises the following steps:
1) central ray is determined:
A) positioner is placed with before radiographic source, launches cone-beam x-ray from radiographic source, project on detector through positioner;
B) position of regulating positioning device before radiographic source, makes the center superposition of the first and second alignment marks projection on the detector, and now central ray is through the center of the first and second alignment marks;
2) offset deviation of detector is regulated:
Central ray is through the center of the first and second alignment marks, then the first and second alignment marks projection centre is on the detector exactly central ray position on the detector, according to the position of the projection centre pixel on the detector of the first and second alignment marks, by the position of detector platform adjustment detector, the imaging center of detector is moved to the center of the projection of the first and second alignment marks, central ray is incident to the imaging center of detector, and now detector does not exist offset deviation;
3) regulate detector face outside angular error:
A) placed before the detectors by collimator apparatus, and ventilating hole plate is close to detector, the axle of through hole is perpendicular to detector, and the position of adjustment ventilating hole plate, makes the imaging center being centrally located at detector of through hole, removed by positioner from radiographic source;
B) collimation device projects, and observes through hole projection on the detector, and by the angle of detector platform adjustment detector, make the through hole circle being projected as rule on the detector, now detector does not exist angular deviation outside face;
4) rotating shaft of turntable is regulated;
Collimator apparatus is disassembled, axis adjustment device is placed on a spinstand, turntable rotates a circle, project to adjustable stem, the shape of projection is about vertical axisymmetric tetragon, and the axis of symmetry of tetragon is exactly the projection of rotating shaft, according to adjustable stem projection on the detector, by the displacement of adjustable base adjustment turntable, make the imaging center of detector drop on the axis of symmetry of the projection of adjustable stem, now the rotating shaft of turntable and central ray coplanar.
10. bearing calibration as claimed in claim 9, is characterized in that, in step 4) in, according to adjustable stem projection on the detector, by the displacement of adjustable base adjustment turntable, in two kinds of situation:
If a () adjustable stem is vertically placed on the table top of the level of turntable, by allowing turntable rotate a circle, obtaining the multi-angle projection of adjustable stem, is a rectangle, then regulates adjustable base to make the imaging center of detector drop on the axis of symmetry of rectangle;
If b () adjustable stem is not vertically placed on the table top of level of turntable, by allowing turntable rotate a circle, obtaining the multi-angle projection of adjustable stem, being one trapezoidal, then regulating adjustable base that the imaging center of detector is dropped on trapezoidal axis of symmetry.
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