CN100488457C - Conical beam CT accurate filtering back projection reproducing method based on spiral saddle line - Google Patents
Conical beam CT accurate filtering back projection reproducing method based on spiral saddle line Download PDFInfo
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- CN100488457C CN100488457C CNB2007101732774A CN200710173277A CN100488457C CN 100488457 C CN100488457 C CN 100488457C CN B2007101732774 A CNB2007101732774 A CN B2007101732774A CN 200710173277 A CN200710173277 A CN 200710173277A CN 100488457 C CN100488457 C CN 100488457C
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Abstract
The invention relates to a cone beam CT precision filtering back-projection reconstruction method based on a screw saddle line in the technical field of biological medicine imaging. The invention comprises adopting single X-ray source which is scanned in the path of screw saddle line, choosing a plane to be reconstructed, calculating the crossing point of the plane and the path of screw saddle line, choosing the crossing point, deciding the direction of filtering, filtering the projection date which is received through scanning, and carrying through the back-projection reconstruction of the data which is filtered to obtain reconstructed images. The invention has fast imaging speed and high imaging precision, and can directly display reconstructed images without transforming coordinates, which not only is suitable for the imaging of long objects, but also is suitable for the fast imaging and continuous observation of dynamic objects.
Description
Technical field
What the present invention relates to is a kind of method of biomedical imaging technical field, specifically, is a kind of conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line.
Background technology
The X ray bulb of conical beam CT sends the cone beam X ray on one point, after passing measurand, the X ray of decay is detected by the detector of offside, and X-ray is converted into the signal of telecommunication, deliver to the analog-digital converter and the data acquisition unit of computer, be converted into digital signal and be stored in the computer.This just finishes once exposure and gatherer process, and in order to obtain rebuilding the required data for projection of measurand, x-ray source needs along certain track scanning, and finishes single exposure and data acquisition in each position.X-ray source scan mode commonly used has two kinds at present, and a kind of is that referential is observed with the testee, and the track of x-ray source is a single-screw, and helical cone beam CT is recording projection data quickly, realizes the volume reconstruction of long materials; Another is that referential is observed with the testee, and the track of x-ray source is the saddle line, has periodic characteristics based on the conical beam CT of saddle line, can realize the fast imaging of dynamic object such as heart and observes continuously.
Find through literature search prior art, A.Katsevich is in Advances in AppliedMathematics[applied mathematics progress] (2004 the 32nd phases, the 681st page to 697 pages) on " Improved exact FBP algorithm for spiral CT " [the improved spiral CT accurate filtering back projection algorithm] delivered, a kind of conical beam CT accurate filtering back projection method for reconstructing based on helix has been proposed.Concrete implementation method is to allow x-ray source and detector simultaneously along spiral motion, and the data for projection that obtains on the detector is carried out filtering earlier, carries out backprojection reconstruction along the PI line then.Described PI line is meant on the helix 2 line, and the difference of angle parameter of representing these 2 positions is less than 360 °.The advantage of this method is that image taking speed is fast, the imaging precision height, and the big and imaging precision of vertical axis Z coverage has nothing to do with pitch; The shortcoming of this method is that backprojection reconstruction must carry out along the PI line, and the image of reconstruction also needs to carry out coordinate transform could be discerned by the ordinary people, and this method only is suitable for helical cone beam CT, can not be used for along the conical beam CT of saddle line sweep.
Summary of the invention
The objective of the invention is to overcome deficiency of the prior art, a kind of conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line is proposed, it is fast to make it have an image taking speed, the imaging precision height, the image of rebuilding does not need just can directly show through coordinate transform, and, also be applicable to the fast imaging of dynamic object and observation continuously both applicable to the imaging of long materials.
The present invention realizes by following technical method, the present invention adopts single x-ray source, at first x-ray source scans with the helix saddle thread path, select the plane of desire reconstruction then, calculate the intersection point of this plane and helix saddle line scanning pattern, select to satisfy the intersection point of certain condition, determine the direction of filtering, the data for projection that scanning is obtained carries out filtering, at last the data of filtering is carried out backprojection reconstruction, obtains the image of rebuilding.
The inventive method may further comprise the steps:
The first step, x-ray source are sent the cone beam X ray on one point, pass measurand after, the X ray of decay is detected by the detector of offside.
In second step, the line of x-ray source and detector centre is perpendicular to vertical axis Z.
In the 3rd step, x-ray source and detector rotate around vertical axis Z simultaneously, do the helix saddle line motion with respect to testee.Detector and corresponding data for projection acquisition system recording projection data.The parameter of selected helix saddle line will guarantee arbitrary process testee and be not less than 4 perpendicular to the plane of vertical axis Z and the intersection point of helix saddle line.
Described helix saddle line is meant: helix and the saddle line linear superposition on vertical axis Z direction, promptly satisfy
Function curve, wherein ρ is the three-dimensional coordinate of any point on the helix saddle line, s is an angle parameter, R (s) is that helix saddle line upper angle parameter is that of s projects to distance between initial point on X-Y plane (perpendicular to the plane of vertical axis Z), A (s) is the amplitude of saddle line, and H (s) is the pitch of helix, and the scope of s surpasses 2 π, R (s) will obtain and be wide enough so that the face of cylinder at helix saddle line place surrounds testee, and A (s), H (s) are non-minus real number.
The amplitude of described saddle line is meant: the saddle line departs from the distance of X-Y plane in vertical axis Z direction.
The pitch of described helix is meant: helix is in the distance between adjacent two bung flanges on the vertical axis Z direction.
Described data for projection acquisition system is meant gets off the data record on the detector and changes into the system that digital signal is passed to Computer Processing.
The 4th step, select one through testee and perpendicular to the plane of vertical axis Z, calculate the intersection point of this plane and helix saddle line, be designated as P1, P2, P3 ..., PN, N 〉=4.
In the 5th step, in this N intersection point, select 4 intersection points that satisfy following condition: the zone that line surrounded between the intersection point must cover the tomography aspect of testee, and another is that the difference of angle parameter between the intersection point must be less than 360 °.According to the size of these 4 intersection point angle parameters, be designated as PA respectively, PB, PC, PD.
The 6th step, these 4 intersection points are divided into 5 sections with helix saddle line, are respectively: angle parameter is less than the part of PA, the part of angle parameter between PA and PB, the part of angle parameter between PB and PC, angle parameter between PC and PD part and angle parameter greater than the part of PD.Wherein the filtering direction of the data for projection between PA and PB is to be starting point with PA, and PB is the vector of terminal point; The filtering direction of the data for projection between PB and PC is to be starting point with PB, and PC is the vector of terminal point; The filtering direction of the data for projection between PC and PD is to be starting point with PC, and PD is the vector of terminal point; The filtering direction of the data for projection between PA and PD is to be starting point with PD, and PA is the vector of terminal point.
The 7th step, on helix saddle line, each the some P that begins from a PA, there is a series of plane process point P and is parallel to the pairing filtering direction of a P, do the intersection of these planes and detector plane, along these intersections the data for projection that obtains on the detector is carried out filtering: the Hilbert transform computing.
The 8th step, the data of filtering are carried out backprojection reconstruction, obtain the two-dimensional ct image of the reconstruction under the rectangular coordinate system.
Described data to filtering are carried out backprojection reconstruction, are meant: the intersection point of selected angle parameter minimum is as lower limit of integral, and the intersection point of angle parameter maximum carries out the process of integration as upper limit of integral to filtered data.
The 9th step changed the planar position that desire is rebuild, and repeated the 5th and went on foot for the 6th step, obtained a series of two-dimensional ct image.
The tenth step, with the 2-d reconstruction image under these a series of rectangular coordinate systems, the 3-D view of the measurand of generation under the rectangular coordinate system, high-resolution 3-D view or two-dimensional ct image after in specified scope, demonstrating reconstruction.
The principle of the invention is: when data for projection was carried out filtering, the direction of filtering was in same plane, and each filtering direction is end to end, and therefore vector and be 0 can directly rebuild this plane; And when data for projection being carried out filtering based on the accurate filtering back projection method for reconstructing of helix, the direction of filtering is determined by the PI line, also must be during reconstruction along the PI line, therefore what obtain is reconstructed image under the PI coordinate system, also needs to carry out Coordinate Conversion and just can obtain reconstructed image under the rectangular coordinate system.
The present invention is with respect to the advantage based on the conical beam CT accurate filtering back projection method for reconstructing of helix: the image that (1) rebuilds does not need just can show directly that through coordinate transform time consumption reduces more than 30%; (2) scan mode is flexible, by the amplitude of change saddle line and the pitch of helix, makes this method for reconstructing both applicable to the imaging of long materials, also is applicable to the fast imaging of dynamic object and observation continuously.
Description of drawings
Fig. 1 is the sketch map of data for projection filtering direction in the embodiment of the invention
The specific embodiment
Below in conjunction with accompanying drawing embodiments of the invention are elaborated: present embodiment is being to implement under the prerequisite with the technical solution of the present invention, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.
Embodiment implements according to following steps:
1. a biological specimen is placed and can do on the linear uniform motion bed along vertical axis Z direction, x-ray source sends the cone beam X ray on one point, through collimator, after passing Mus alive, the X ray of decay is detected by the flat-panel detector of offside, detector is rectangular plane, is made up of 128 detecting units of 512 x.
2.X radiographic source is apart from vertical axis Z75cm, detector distance vertical axis Z60cm, and the central vertical of x-ray source and detector is in vertical axis Z.
3.X radiographic source and detector move with uniform velocity along the saddle line around vertical axis Z, gather a data for projection every 0.3 °.Biological specimen is along with edge of bed vertical axis Z does rectilinear motion.The amplitude of saddle line is 10cm when initial, and the pitch of helix is 10cm.At record during data for projection, also answer the locus of writing scan device and other after necessary relevant information in the image reconstruction, comprising: the vertical axis Z position of X ray emission source; The position of each detector cell when obtaining data in each detector set etc.
4. select through biological specimen and with the vertical plane Z=0 of vertical axis Z, calculate the intersection point of it and helix saddle line, be designated as P1, P2, P3 ..., PN, N 〉=4.
5. in this N intersection point, select 4 points, according to the size of these 4 intersection point angle parameters, be designated as PA respectively, PB, PC, PD.These 4 points will meet the following conditions: the quadrilateral area that 4 points surround must cover the tomography aspect that biological specimen is positioned at Z=0, and the difference of PD and PA angle parameter must be less than 360 °.
6. these 4 intersection points are divided into 5 sections with helix saddle line, be respectively the part of angle parameter less than PA, the part of angle parameter between PA and PB, the part of angle parameter between PB and PC, angle parameter between PC and PD part and angle parameter greater than the part of PD.Wherein the filtering direction of the data for projection between PA and PB is to be starting point with PA, and PB is the vector of terminal point; The filtering direction of the data for projection between PB and PC is to be starting point with PB, and PC is the vector of terminal point; The filtering direction of the data for projection between PC and PD is to be starting point with PC, and PD is the vector of terminal point; The filtering direction of the data for projection between PA and PD is to be starting point with PD, and PA is the vector of terminal point.Helix saddle line tracking when solid line is exactly x-ray source and detector scanning among Fig. 1, the direction of arrow indication is the filtering direction of each part,
7. on helix saddle line, from a PA, every increase by 0.3 degree of angle parameter is just selected a some P, selectes a some Q simultaneously on vertical axis Z, and some P is identical with the coordinate of some Q on vertical axis Z direction.The relation of the plane Z=0 that judging point Q and desire are rebuild: (1) is if put Q on the Z=0 of plane, then will put Q moves down, each mobile 1mm, the plane W that does to pass through a some P, some Q and be parallel to the pairing filtering direction of a P, plane W and flat-panel detector have intersection L, along intersection L the data for projection that obtains on the detector is carried out Hilbert transform, transfer point Q always is not till plane W and flat-panel detector have intersection; (2) if put Q under the Z=0 of plane, then will put Q up moves, each mobile 1mm, the plane W that does to pass through a some P, some Q and be parallel to the pairing filtering direction of a P, plane W and flat-panel detector have intersection L, along intersection L the data for projection that obtains on the detector is carried out filtering: Hilbert transform, transfer point Q always is not till plane W and flat-panel detector have intersection.According to as above method respectively to from a PA to a PB, some PB to a PC, some PC to a PD, some PA carries out filtering to the data for projection a PD.
8. filtered data for projection is carried out back projection, reconstruct the image of biological specimen tomography 512 * 512 under the rectangular coordinate system.Specifically, be exactly to calculate 4 integrations earlier, first integration is that lower limit of integral, some PB are upper limit of integral with a PA, second integration is that lower limit of integral, some PC are upper limit of integral with a PB, the 3rd integration is that lower limit of integral, some PD are upper limit of integral with a PC, the 4th integration is that lower limit of integral, some PA are upper limit of integral with a PD, these 4 integrations all carry out integral operation along helix saddle line to filtered data for projection, these 4 integral linearities are stacked up promptly obtain the volume data of reconstruction then.
9. the image of Chong Jianing is presented on the high-resolution medical display by visual software.
Such embodiment, needing in the A.Katsevich exact reconstruction methods to have avoided volume data is rebuild fully, then with volume data from the PI coordinate system transformation behind Cartesian coordinates, the defective that reconstructed image could show, do not need carrying out coordinate transform and can directly show to reconstructed image, accelerated image taking speed greatly, implementation result is that time consumption has reduced by 45%.
Claims (7)
1, a kind of conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line is characterized in that, may further comprise the steps:
The first step, x-ray source are sent the cone beam X ray on one point, pass measurand after, the X ray of decay is detected by the detector of offside;
In second step, the line of x-ray source and detector centre is perpendicular to vertical axis Z;
The 3rd step, x-ray source and detector rotate around vertical axis Z simultaneously, do the helix saddle line motion with respect to testee, detector and corresponding data for projection acquisition system recording projection data, the parameter of selected helix saddle line to guarantee arbitrary through testee and perpendicular to the intersection point of the plane of vertical axis Z and helix saddle line more than or equal to 4;
The 4th step, select one through testee and perpendicular to the plane of vertical axis Z, calculate the intersection point of this plane and helix saddle line, be designated as P1, P2, P3 ..., PN, N 〉=4;
The 5th step, in this N intersection point, select 4 intersection points that satisfy following condition: the zone that line surrounded between the intersection point must cover the tomography aspect of testee, another is that the difference of angle parameter between the intersection point must be less than 360 °, according to the size of these 4 intersection point angle parameters, these 4 intersection points are designated as PA, PB, PC and PD respectively;
The 6th step, these 4 intersection points are that PA, PB, PC and PD are divided into 5 sections with helix saddle line, be respectively: angle parameter is less than the part of PA, the part of angle parameter between PA and PB, the part of angle parameter between PB and PC, angle parameter between PC and PD part and angle parameter greater than the part of PD;
The 7th step, on helix saddle line, each the some P that begins from a PA, there is a series of plane process point P and is parallel to the pairing filtering direction of a P, do the intersection of these planes and detector plane, the data for projection that obtains on the detector is carried out filtering with the Hilbert transform computing along these intersections;
The 8th step, the data of filtering are carried out backprojection reconstruction, obtain the two-dimensional ct image of the reconstruction under the rectangular coordinate system;
The 9th step changed the planar position that desire is rebuild, and repeated the 5th and went on foot for the 8th step, obtained a series of two-dimensional ct image;
The tenth step, with the two-dimensional ct image under these a series of rectangular coordinate systems, the 3-D view of the measurand of generation under the rectangular coordinate system, 3-D view or two-dimensional ct image after in specified scope, demonstrating reconstruction.
2, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 1 is characterized in that described helix saddle line is meant: helix and the saddle line linear superposition on vertical axis Z direction, promptly satisfy
Function curve, wherein ρ is the three-dimensional coordinate of any point on the helix saddle line, s is an angle parameter, R (s) is that helix saddle line upper angle parameter is that of s is perpendicular to the distance between initial point of projecting on the X-Y plane of vertical axis Z, A (s) is the amplitude of saddle line, and H (s) is the pitch of helix, and the scope of s surpasses 2 π, R (s) will obtain and be wide enough so that the face of cylinder at helix saddle line place surrounds testee, and A (s), H (s) are non-minus real number.
3, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 2 is characterized in that the amplitude of described saddle line is meant: the saddle line departs from distance perpendicular to the X-Y plane of vertical axis Z in vertical axis Z direction.
4, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 2 is characterized in that the pitch of described helix is meant: helix is in the distance between adjacent two bung flanges on the vertical axis Z direction.
5, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 1, it is characterized in that described data for projection acquisition system is meant gets off the data record on the detector and change into the system that digital signal is passed to Computer Processing.
6, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 1, it is characterized in that, described 4 intersection points are that PA, PB, PC and PD are divided into 5 sections with helix saddle line, wherein: the filtering direction of the data for projection between PA and PB is to be starting point with PA, and PB is the vector of terminal point; The filtering direction of the data for projection between PB and PC is to be starting point with PB, and PC is the vector of terminal point; The filtering direction of the data for projection between PC and PD is to be starting point with PC, and PD is the vector of terminal point; The filtering direction of the data for projection between PA and PD is to be starting point with PD, and PA is the vector of terminal point.
7, the conical beam CT accurate filtering back projection method for reconstructing based on helix saddle line according to claim 1, it is characterized in that, described data to filtering are carried out backprojection reconstruction, be meant: the intersection point of selected angle parameter minimum is as lower limit of integral, the intersection point of angle parameter maximum carries out the process of integration as upper limit of integral to filtered data.
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| JP5317580B2 (en) * | 2008-08-20 | 2013-10-16 | 株式会社東芝 | X-ray CT system |
| EP2945123A1 (en) * | 2014-05-12 | 2015-11-18 | Agfa Healthcare | Computerized tomographic image exposure and reconstruction method |
| CN106228584B (en) * | 2016-07-20 | 2019-08-13 | 中国人民解放军信息工程大学 | Cone-Beam CT circle plus straight path backprojection-filtration method for reconstructing |
| CN113123177B (en) * | 2019-12-31 | 2023-03-14 | 比亚迪股份有限公司 | Antiskid steel plate, machining method thereof and track beam |
| CN111768858A (en) * | 2020-06-30 | 2020-10-13 | 上海联影医疗科技有限公司 | Method, system and computer equipment for displaying scanning pitch parameters |
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