CN102692423B - Non-scanning method for acquiring CT (Computer Tomography) projection data - Google Patents
Non-scanning method for acquiring CT (Computer Tomography) projection data Download PDFInfo
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- CN102692423B CN102692423B CN201210206908.9A CN201210206908A CN102692423B CN 102692423 B CN102692423 B CN 102692423B CN 201210206908 A CN201210206908 A CN 201210206908A CN 102692423 B CN102692423 B CN 102692423B
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Abstract
The invention relates to a non-scanning method for acquiring CT (Computer Tomography) projection data, and the non-scanning method is suitable for measuring sectional images of a measured object which is in rapid change and rapid motion and inappropriate for long-term beam irradiation. According to the non-scanning method for acquiring the CT projection data, the measured object and a plurality of CT measurement components are not required for rotation and translation. The CT measurement components consist of linear diffusion beam sources, beam deflectors and planar detectors; beams shot from the linear diffusion beam sources pass through the measured object and are then deflected by the beam deflectors; two-dimensional flux density distribution is formed on the planar detectors; the two-dimensional flux density distribution comprises a number of groups of parallel beam lines, a number and spacing distance of the parallel beam lines of each group, and projection angle information corresponding to the parallel beam lines of each group; and the information is the CT projection data. One CT measurement component can be used for measuring data in a range of a certain projection angle, and a CT measurement system consisting of the CT measurement components can be used for measuring the projection data in the range of 180 DEG. When pulse beams are used, the pulse duration is beam irradiation time.
Description
Technical field
The present invention relates to a kind of measured object and CT measurement component and all need not rotate the method gathering CT data for projection with the non-scanning type of translation.
Background technology
In existing CT technology, the beam no matter inciding measured object is straight line, fan-shaped or taper, no matter detector is single, linear array or face battle array, be all with the scan method rotating measured object or CT measurement component obtain different angles data for projection (YXLON International X-ray GmbH. the CT method for recording projection data: China, 200610140311.3 [P] .2007-05-30; Shanghai Inst. of Applied Physics Chinese Academy of Sciences. a kind of rapid X-ray fluorescence CT method: China, 201010171983.7 [P] .2010-10-20), the single beam pulse of duration very short (within such as one millisecond) cannot be used to gather the CT data for projection of 180 ° of projection angle range.In CT measures, the rotational speed of physical construction is generally less than 50 cycle per seconds, if measured object changes in measuring process or move, will cause rebuilding image error.Some measured object should not be subject to beam exposure for a long time, and rotating scanner method also should not be used to measure.
Summary of the invention
In order to measure Rapid Variable Design, rapid movement and the image in selected cross section in moment should not determined by the object of beam exposure for a long time, under CT measurement component and the non-rotary situation of measured object, carry out CT projection, the invention provides a kind of measured object and CT measurement component and all need not rotate the method gathering CT data for projection with the non-scanning type of translation.
Principle of work of the present invention is, CT measurement component is formed by linear diffusion beam source, beam deflector and planar detector, the beam of linear diffusion beam source outgoing deflects through beam deflector through after measured object, planar detector is formed the distribution of two-dimentional flux density, described two-dimentional flux density distribution comprises parallel-beam line group number, often organizes parallel-beam line quantity and spacing, often organizes projection angle information corresponding to parallel-beam line, and described information is the CT data for projection needing to gather.
As shown in Figure 1, spot beam source 1, shaping lens group 2, diffuser 3, exit slit 4, entrance slit 5, deflection lens 6, planar detector 7 are arranged along X-direction, take X-axis as axis of symmetry.Wherein spot beam source 1, shaping lens group 2, diffuser 3 and exit slit 4 form linear diffusion beam source, and entrance slit 5 and deflection lens 6 form beam deflector.
After shaping lens group 2 shaping, being irradiated to diffuser 3 by the beam of spot beam source 1 outgoing and exit slit 4 outgoing by being close to diffuser 3, forming linear diffusion beam source.The beam of exit slit 4 outgoing from length along Y direction is through measured object, being incided by the entrance slit 5 parallel with exit slit 4 is close in the deflection lens 6 of entrance slit 5, deflect into through deflection lens 6 again on the receiving plane of planar detector 7, the receiving plane of planar detector 7 is formed the Two dimensional Distribution of beam flux density, and the Two dimensional Distribution of the beam flux density on receiving plane is converted to electric signal and carries out record by computing machine by planar detector 7.A CT measurement component can be measured necessarily
the data for projection of angular range, forms CT measuring system by multiple CT measurement component, can make
measurement range reach 180 °, calculate measured object cross section by CT reconstruction algorithm and the absorption coefficient of beam distribute, acquisition measured object cross-sectional image.
Deflection lens 6 is as beam deflector, its structure is different from known imaging len, the constituted mode in the cross section of the length direction perpendicular to entrance slit 5 of deflection lens 6 is as follows: when the imaging len that the focal length of an anaberration is f moves along the Width of entrance slit 5, when the center different distance of the optical axis distance entrance slit 5 of described imaging len, select the cross section perpendicular to the center different distance apart from entrance slit 5 of the length direction of entrance slit 5 on described imaging len, along with the Width of described imaging len along entrance slit 5 moves, the cross section of the length direction perpendicular to entrance slit 5 of these section constitution deflection lens 6 selected.The focal distance f of the imaging len of anaberration is defined as the focal length of deflection lens 6.Because the optical axis that the different cross section being parallel to XOZ plane of deflection lens 6 is corresponding has different Z values, so there is different angles from YOZ plane at the beam being parallel to the different cross section of XOZ plane being incident upon deflection lens 6 in XOY plane from diffuser 3 after deflection lens 6 deflects.
The invention has the beneficial effects as follows, use method provided by the invention, use single beam pulse just can obtain the CT data for projection in measured object cross section, in Measuring Time, CT measurement component and measured object do not need to rotate, Measuring Time is only determined by the beam pulse duration, is applicable to the measured object cross-sectional image measured Rapid Variable Design, rapid movement and should not be subject to beam exposure for a long time.
Accompanying drawing explanation
Fig. 1 is principle of work of the present invention and equipments layout scheme figure.
Fig. 2 is the perspective view of deflection lens 6 in YOZ plane, for illustration of the architectural feature of deflection lens 6.
1. spot beam source, 2. shaping lens group, 3. diffuser, 4. exit slit, 5. entrance slit, 6. deflection lens, 7. planar detectors in figure.
Embodiment
Be that axis of symmetry is arranged by shown in accompanying drawing 1 with X-axis by spot beam source 1, shaping lens group 2, diffuser 3, exit slit 4, entrance slit 5, deflection lens 6, planar detector 7, form a CT measurement component, wherein exit slit 4 is close to diffuser 3, entrance slit 5 is close to deflection lens 6, and test zone is between exit slit 4 and entrance slit 5.A CT measurement component can be measured necessarily
the data for projection of angular range, forms CT measuring system by multiple CT measurement component, can make
measurement range reach 180 °, meet the requirement of image reconstruction to projection angle.During measurement, spot beam source 1 sends a branch of beam, described beam is irradiated on the receiving plane of planar detector 7 after shaping lens group 2, diffuser 3, exit slit 4, measured object, entrance slit 5 and deflection lens 6, the Two dimensional Distribution of the beam flux density on receiving plane is converted to electric signal by computer recording by planar detector 7, calculate measured object cross section by CT reconstruction algorithm to distribute to the absorption coefficient of beam, obtain measured object cross-sectional image.
The beam that spot beam source 1 sends can be continuous beam, for measuring Rapid Variable Design, rapid movement or should not for a long time by the measured object of beam exposure, also can be Wavelength stabilized continuous beam, static, stable and can for a long time by the measured object of beam exposure for measuring, also can be the time dependent frequency sweep beam of wavelength, for measuring the absorbing state of measured object to different wave length.
Radiation beam wavelength is determined according to measurement demand, can be to be in X ray to any one within the scope of microwave region or several wavelength and one or several wave bands, uses corresponding spot beam source 1.Shaping lens group 2, diffuser 3, exit slit 4, entrance slit 5, deflection lens 6 and planar detector 7, according to the corresponding material of beam operation wavelength chooses, make their service band comprise beam operation wavelength.
If the beam of spot beam source 1 outgoing matches at the length direction of exit slit 4 and the subtended angle of Width and slit 4, also can not use shaping lens group 2 and directly irradiate diffuser 3 by spot beam source 1.
According to focal length, beam energy, the beam operation wavelength of CT measurement component size, deflection lens 6, planar detector 7 can be a planar array detector, also can be that the arrangement of multiple planar array detector forms.When planar array detector do not meet in size, sensitivity, operation wavelength measurement require time, planar detector 7 also can be the combination of imaging lens and planar array detector, also can be the combination of plane fluorescent material, imaging lens and planar array detector, also can be the combination of imaging lens, image intensifier and planar array detector, also can be the combination of plane fluorescent material, image intensifier, imaging lens and planar array detector.Described planar array detector also can be replaced by the photosensitive material such as film, dry plate.Planar detector 7 also can comprise auxiliary ones, the element such as making beam reflect, support and fixedly use element.
Become linear diffusion beam source from diffuser 3 by the beam of exit slit 4 outgoing, each point in described linear diffusion beam source can regard a point-like diffusion beam source as.Entrance slit 5, as the incident diaphragm of deflection lens 6, jointly forms a space with exit slit 4 and cuts into slices, and the beam being only positioned at the section of described space just can incide in deflection lens 6, is irradiated on planar detector 7 after deflection lens 6 deflects.When exit slit 4 is identical with the width of entrance slit 5, the thickness of described space section is exit slit width.
Deflection lens 6 realizes the key component that beam forms the distribution of two-dimentional flux density on planar detector, and its architectural feature is understood by accompanying drawing 2.A cross section of the cross section a that each of deflection lens 6 is parallel to XOZ plane to be the focal length of an anaberration be the imaging len of f, the optical axis of described imaging len is perpendicular to YOZ plane and meet at B point with Z axis, cross section a and Y-axis meet at A point, the line of AB and Y-axis angle theta, the Y-coordinate y of A point
awith the Z coordinate z of B point
bduring jack per line, θ is just.Work as y
avalue when changing, z
balso respective change, ensures that θ is constant.
As shown in Figure 1, the object space interarea distance s of exit slit 4 and deflection lens 6, the receiving plane of planar detector 7 and the image space interarea distance t of deflection lens 6, be mapped to the beam deflection of the P point in deflection lens 6 to the Q point on the receiving plane of planar detector 7 from the M point diffuser 3.If the coordinate of M point is (-s, y
m, 0), the coordinate of P point is (0, y
p, 0), Q point coordinate is (t, y
q, z
q), then
If the length of exit slit 4 is L
m, the length of entrance slit 5 is L
p, then Q point coordinate scope is
Formula (1) and formula (2) show, the effect of deflection lens 6 is the components making the Incident beams in XOY plane have Z-direction after deflection, in the plane being parallel to YOZ plane, there is two-dimentional Illumination Distribution, each organize parallel Incident beams formed in YOZ plane one with the line segment of Y-axis angle α, α is calculated by formula (1) and formula (2):
Preferred parameter one is:
l
m=2s, L
p=2s,
α=-45 °, the Y-direction size of the receiving plane of planar detector 7
the Z-direction size of the receiving plane of planar detector 7
test zone center point coordinate
the adjacent picture elements distance δ of the receiving plane of planar detector 7, gets line number (along the Y-direction) N by beam exposure
yhalf as parallel lines number, then test zone diameter
take measurement of an angle scope
now:
Formula (6) and formula (7) illustrate: after deflection lens 6 deflects, form the line segment that one is parallel to Z axis from the beam of any point M outgoing diffuser 3 at the receiving plane of planar detector 7; The beam of diffuser 3 outgoing forms the line segment that is parallel to Y-axis after any point P in deflection lens 6 deflects on the receiving plane of planar detector 7; The one group of parallel-beam being mapped to deflection lens 6 from diffuser 3 forms the line segment of and Y-axis angle 45 ° after deflection lens 6 deflects at the receiving plane of planar detector 7.
For preferred parameter one, use two CT measurement component composition CT measuring systems, first CT measurement component is measured
measured object cross section projection in scope, the direction of measurement of second CT measurement component and first CT measurement component is perpendicular, measures
measured object cross section projection in scope, the measured object cross section data for projection that described CT measuring system obtains covers 180 ° of scopes, can obtain measured object cross-sectional image by reconstruction algorithm, rebuilds the spatial resolution of image
significantly impact is produced on measurement result, the width d of exit slit 4 for avoiding space slice thickness
4with the width d of entrance slit 5
5value is
Preferred parameter two is:
l
m=2s, L
p=2s, t=f, α=90 °, the Y-direction size L of the receiving plane of planar detector 7
y>=2f, the Z-direction size L of the receiving plane of planar detector 7
z>=2f, test zone center point coordinate
the adjacent picture elements distance δ of the receiving plane of planar detector 7, gets line number (along the Y-direction) N by beam exposure
yhalf as parallel lines number, then test zone diameter
take measurement of an angle scope
now:
Formula (8) and formula (9) illustrate: the beam of diffuser 3 outgoing forms the line segment that is parallel to Y-axis after any point P in deflection lens 6 deflects on the receiving plane of planar detector 7; The one group of parallel-beam being mapped to deflection lens 6 from diffuser 3 forms at the receiving plane of planar detector 7 line segment that is parallel to Z axis after deflection lens 6 deflects; After deflection lens 6 deflection, form the line segment of and Y-axis angle 45 ° at the receiving plane of planar detector 7 from the beam of any point M outgoing diffuser 3.
For preferred parameter two, use two CT measurement component composition CT measuring systems, first CT measurement component is measured
measured object cross section projection in scope, the direction of measurement of second CT measurement component and first CT measurement component is perpendicular, measures
measured object cross section projection in scope, the measured object cross section data for projection that described CT measuring system obtains covers 180 ° of scopes, can obtain measured object cross-sectional image by reconstruction algorithm, rebuilds the spatial resolution of image
significantly impact is produced on measurement result, the width d of exit slit 4 for avoiding space slice thickness
4with the width d of entrance slit 5
5value is
The shaping lens group 2 occurred in above content, deflection lens 6, imaging len, imaging lens, the lens wherein related to not are the optical lens being applicable to visible light wave range of narrow sense, but the lens of the broad sense that irradiation beam is thereon deflected, the element that the effect namely making the deflecting action of beam and optical lens that visible ray is deflected in service band is identical.
Spot beam source 1 involved in the present invention, not refering in particular to beam-emergence end is infinitesimal point, but the beam source that general reference exit end size is very little compared with the length of exit slit 4.
Diffuser 3 involved in the present invention can be transmission-type, also can be reflection-type, the beam that difference is only to incide diffuser 3 with from the beam of diffuser 3 outgoing at the homonymy of the diffusing surface of diffuser 3 or heteropleural, accompanying drawing 1 can not be restrictions of transmission-type as diffuser 3.
Deflection lens 6 involved in the present invention also can be replaced by the deflection mirror with certain surface curvature distribution, and described surface curvature distribution should meet the requirement of formula (1) and formula (2).Deflection lens 6 is replaced by described deflection mirror; only that the mode of beam deflection is become reflection from refraction; do not change the function of beam deflector of the present invention; principle of work of the present invention is not departed from yet; deflection lens 6 is only the embodiment realizing beam deflector function; as the restriction to beam deflector form, the beam deflection element of deflection lens 6 by described deflection mirror or other form any can not be replaced, all falls into protection scope of the present invention.
Claims (8)
1. the method for a non-scanning type collection CT data for projection, it is characterized in that: form CT measurement component by linear diffusion beam source, beam deflector and planar detector, the beam of linear diffusion beam source outgoing deflects through beam deflector through after measured object, planar detector is formed the distribution of two-dimentional flux density, described two-dimentional flux density distribution comprises parallel-beam line group number, often organizes parallel-beam line quantity and spacing, often organizes projection angle information corresponding to parallel-beam line, and described information is described CT data for projection;
Described beam deflector is made up of deflection lens and entrance slit, deflection lens is as follows perpendicular to the section constitution mode of described entrance slit length direction: a cross section of the cross section a that each of deflection lens (6) is parallel to XOZ plane to be the focal length of an anaberration be the imaging len of f, when the imaging len of described anaberration moves along described entrance slit width direction, when the optical axis of described imaging len is apart from described entrance slit center different distance, select the cross section apart from described entrance slit center different distance perpendicular to described entrance slit length direction on described imaging len, along with described imaging len moves along described entrance slit width direction, the cross section perpendicular to described entrance slit length direction of deflection lens described in these section constitutions selected.
2. method according to claim 1, linear diffusion beam source operation wavelength is in X ray within the scope of microwave region.
3. method according to claim 1, linear diffusion beam source is continuous beam source.
4. method according to claim 1, linear diffusion beam source is the time dependent frequency sweep beam of operation wavelength.
5. method according to claim 1, linear diffusion beam source is made up of spot beam source, shaping lens group, diffuser and exit slit.
6. method according to claim 1, the service band of beam deflector and planar detector comprises described linear diffusion beam source operation wavelength.
7. method according to claim 6, planar detector is planar array detector.
8. method according to claim 6, planar detector forms primarily of plane fluorescent material, image intensifier, imaging lens and planar array detector.
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