CN104424654B - The method and system of automatic Calibration CT center offsets - Google Patents
The method and system of automatic Calibration CT center offsets Download PDFInfo
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Abstract
Disclose a kind of method and system of automatic Calibration CT center offsets.This method includes：The initial sinusoids figure represented with matrix is read, the initial sinusoids figure is that the data rotated a circle based on detector collection turntable are obtained；Calculate the cross-correlation coefficient between the preceding half son row of each row in initial sinusoids figure and rear half son row；Determine that the projection of CT working regions on the detector is interval；It is determined that the sequence number of the detector cells corresponding to the maximum of the interval cross-correlation coefficient of projection；And CT center offsets are determined based on the interval and described sequence number of projection.It is high with regard to center offset, reliability can be obtained using only sinogram using the scheme of above-described embodiment, it is not affected by noise, CT image indexes of system etc. can be improved.
Description
Technical field
The application is related to CT technologies, and in particular to one kind is in CT scan and process of reconstruction, automatic Calibration center offset
Method and system.
Background technology
Industrial CT system includes radiographic source, detector, Mechanical course and computer etc..Radiographic source sends X-ray, turntable rotation
Three-sixth turn, the projected image of detector collection all angles simultaneously uploads computer, and computer carries out CT image weights according to perspective view
Build.The parameter of most critical is center offset during CT is rebuild, and the parameter directly influences the picture matter of CT images.Center offset is
Pixel-shift amount of the projected position of turntable pivot on the detector relative to detector center.At present, it is determined that in
The method of heart offset has：Try in advance, LUT Method, sinogram measuring method etc..
Chinese patent application discloses the projection rotating center measurement that CN101303225 describes a kind of 2D-CT scanning systems
Method.This method needs to rotate the data for projection obtained for one week using turntable and turntable is remained stationary as and radiographic source and detector turn
Move both data for projection obtained for one week to calculate center offset, it is easy to by noise or the shadow of the precision of other specification
Ring.
United States Patent (USP) US8259897B2 describes a kind of determination method and device of CT imaging centers offset, this method
Propose to carry out two processes of coarse search and fine search to calculate center offset.Equally, this method due to by noise or its
The influence of its parameters precision, center offset result of calculation can be affected.
The content of the invention
In view of one or more problems of the prior art, it is proposed that a kind of method of automatic Calibration CT center offsets
And system.
In one aspect of the invention, it is proposed that a kind of method of automatic Calibration CT center offsets, including step：Read
The initial sinusoids figure represented with matrix, the initial sinusoids figure is that the data rotated a circle based on detector collection turntable are obtained
's；Calculate the cross-correlation coefficient between the preceding half son row of each row in initial sinusoids figure and rear half son row；Determine CT working regions
Projection on the detector is interval；Determine detector cells corresponding to the maximum of the interval cross-correlation coefficient of the projection
Sequence number；And CT center offsets are determined based on the interval and described sequence number of projection.
In another aspect of this invention, it is proposed that a kind of system of automatic Calibration CT center offsets, including：Read with square
The device of the initial sinusoids figure of matrix representation, the initial sinusoids figure is that the data rotated a circle based on detector collection turntable are obtained
's；Calculate the device of the cross-correlation coefficient between the preceding half son row of each row in initial sinusoids figure and rear half son row；Determine CT works
Make the interval device of the projection of region on the detector；Corresponding to the maximum for determining the interval cross-correlation coefficient of the projection
The device of the sequence number of detector cells；And the device of CT center offsets is determined based on the interval and described sequence number of projection.
In another aspect of the invention, it is proposed that a kind of method of automatic Calibration CT center offsets, including step：Read
The initial sinusoids figure represented with matrix, the initial sinusoids figure is that the data rotated a circle based on detector collection turntable are obtained
's；K point of the interpolation of any two point, obtains the sinogram of resampling in initial sinusoids figure each row of data；Calculating is adopted again
Cross-correlation coefficient in the sinogram of sample between the preceding half son row and rear half son row of each row；Determine CT working regions in detector
On projection it is interval；Determine the sequence number of the detector cells corresponding to the maximum for the cross-correlation coefficient that the projected area is asked；With
And asked based on the K values, the projected area and the sequence number determines CT center offsets.
In still another aspect of the invention, it is proposed that a kind of system of automatic Calibration CT center offsets, including：Read with square
The device of the initial sinusoids figure of matrix representation, the initial sinusoids figure is that the data rotated a circle based on detector collection turntable are obtained
's；K point of the interpolation of any two point, obtains the device of the sinogram of resampling in initial sinusoids figure each row of data；Meter
Calculate the device of the cross-correlation coefficient between the preceding half son row of each row in the sinogram of resampling and rear half son row；Determine that CT works
The interval device of the projection of region on the detector；Determine the spy corresponding to the maximum of the interval cross-correlation coefficient of the projection
Survey the device of the sequence number of device unit；And CT center offsets are determined based on the K values, the interval and described sequence number of the projection
Device.
It is high with regard to center offset, reliability can be obtained using only sinogram using the scheme of above-described embodiment, not by noise
Influence, can improve CT image indexes of system etc..
Brief description of the drawings
Following accompanying drawing indicates embodiments of the present invention.These drawings and embodiments are with non-limiting, non exhaustive
Property mode provide some embodiments of the present invention, wherein：
Fig. 1 shows the sine used in the technology of automatic Calibration CT center offsets according to an embodiment of the invention
Figure；
Fig. 2 shows the structural representation of the system of automatic Calibration CT center offsets according to an embodiment of the invention
Figure；
Fig. 3 is the flow chart for the method for describing automatic Calibration CT center offsets according to an embodiment of the invention；
Fig. 4 is shown in the technologies of automatic Calibration CT center offsets according to another embodiment of the present invention to initial sinusoids
The sinogram for the row resampling that figure enters obtained by row interpolation in the row direction；And
Fig. 5 is the flow chart for the method for describing automatic Calibration CT center offsets according to another embodiment of the present invention.
Embodiment
The specific embodiment of the present invention is described more fully below, it should be noted that the embodiments described herein is served only for citing
Illustrate, be not intended to limit the invention.In the following description, in order to provide thorough understanding of the present invention, a large amount of spies are elaborated
Determine details.It will be apparent, however, to one skilled in the art that：This hair need not be carried out using these specific details
It is bright.In other instances, in order to avoid obscuring the present invention, known circuit, material or method are not specifically described.
Throughout the specification, meaning is referred to " one embodiment ", " embodiment ", " example " or " example "
：It is comprised in reference to special characteristic, structure or the characteristic that the embodiment or example are described at least one embodiment of the invention.
Therefore, in each local phrase " in one embodiment " occurred, " in embodiment ", " example " of entire disclosure
Or " example " is not necessarily all referring to same embodiment or example.Furthermore, it is possible to will be specific with any appropriate combination and/or sub-portfolio
Feature, structure or property combination in one or more embodiments or example.In addition, those of ordinary skill in the art should manage
Solution, term "and/or" used herein includes any and all combination for the project that one or more correlations are listed.
Center offset is very important technical parameter during three generations CT is rebuild, and directly influences the picture matter of CT images.
In industry CT scanning means, what turntable repetitive positioning accuracy, detector repetitive positioning accuracy, detector and X-ray machine were synchronized with the movement
Mechanically deform when depth of parallelism index and equipment long-term use etc. can cause the change of center offset, and real in engineering
This change is inevitable in trampling, and the central passage offset change when high amplification ratio is imaged of Microfocus X-ray system is especially tight
Weight.
For problems of the prior art, embodiments of the invention propose a kind of automatic Calibration CT center offsets
Method, it determines work using any one group of projection correlation at 180 degree angle is differed by turntable center during CT scan
The position of industry CT center offsets.For example, the data rotated a circle according to some embodiments, detector collection turntable, are being calculated
During, computer reads the initial sinusoids figure represented with matrix, calculates the preceding half son row of each row in initial sinusoids figure with after
Cross-correlation coefficient between half son's row.Then, it is determined that the projection of CT working regions on the detector is interval, and determine projected area
Between cross-correlation coefficient maximum corresponding to detector cells sequence number.After above-mentioned data are obtained, based on the projected area
Between and the sequence number determine CT center offsets.According to such scheme, CT centers only can be just calibrated using only sinogram inclined
Shifting amount, it is to avoid the influence of noise or other specification to measurement accuracy.
Fig. 1 shows the sine used in the technology of automatic Calibration CT center offsets according to an embodiment of the invention
Figure.In the embodiment shown in fig. 1, initial sinusoids figure is divided into 0-180 degree and 180 to 360 degree two parts, and sinogram
Data are stored with a matrix type.In the illustrated embodiment, arranged by calculating the preceding half son of each row in sinogram with after
The cross-correlation coefficients asked of half son's row determines center offset.
Fig. 2 shows the structural representation of the system of automatic Calibration CT center offsets according to an embodiment of the invention
Figure.As shown in Figure 2, it is illustrated that the system of the automatic Calibration CT center offsets of embodiment includes radiographic source 110, turntable 120, detection
Device 130, control and tomography computer 140.Radiographic source 110 sends X-ray, and turntable 120 is rotated by 360 °, and detector 130 is gathered respectively
The projected image of individual angle simultaneously uploads control and tomography computer 140.Control and tomography computer 140 demarcate CT according to perspective view
Center offset.Center offset is projected position 131 of the pivot of turntable 120 on detector 130 relative to detection
The pixel-shift amount of device center 132.
Fig. 3 is the flow chart for the method for describing automatic Calibration CT center offsets according to an embodiment of the invention.Such as
Shown in Fig. 3, in step S310, control and tomography computer 140 read the initial sinusoids figure represented with matrix, the initial sinusoids
Figure is that the data rotated a circle based on detector collection turntable are obtained.For example.Turntable 120 is rotated by 360 °, and detector 130 is adopted
Collect data, obtain initial sinusoids figure p (β, s), β=122M, s=12N, as shown in Figure 1.(β s) is Two-Dimensional Moment to p
Battle array, wherein β represents that projection angle is numbered in sinogram, is matrix line number, and s represents that detector is numbered in sinogram, is rectangular array
Number.
In step S320, the cross correlation between the preceding half son row of each row in initial sinusoids figure and rear half son row is calculated
Number.Each row in sinogram are for example divided into two son row, i.e., M point of preceding 180 projection angle is a row, rear 180 projection
M point of angle is a row, for example, first row is divided into：U1 (β)=p (β, 1), β=12M and v1 (β)=p (β, 1), β=M+
12···2M.U1 (β) and v1 (β) cross-correlation coefficient R (1) are calculated using formula, sinogram first row coefficient value is used as；Together
Manage, the coefficient value that can obtain any one row of sinogram is：R(s)s=12···（N-1)*K+1.
In step S330, determine that the projection of CT working regions on the detector is interval.For example, by sinogram p（β, s) owns
Row addition is averaged, and obtains a line signal：
Wherein, using p (s) left side air value standard deviations as reference, the part in signal more than 5 times of standard deviations is defined as
Workpiece area, now corresponding Qu Wenwei [s1s2] ∈ [1 (N-1) * K+1].According to other embodiment, other can also be used
The standard deviation of multiple is used as workpiece area, such as 3 times.
In step S340, it is determined that the sequence number of the detector cells corresponding to the maximum of the interval cross-correlation coefficient of projection.
For example, software statistics and the maximum R (s) of each row coefficient of workpiece area sinogram is automatically extracted, when recording acquirement maximum
Detector sequence number X, X represent projected pixel position of the pivot of turntable 120 on detector 130, i.e.,：S=X, R (X)=
Max { R (s), s=s1s2 }.
In step S350, CT center offsets are determined based on projection interval and the sequence number.For example will be by the sequence number and institute
The difference stated between the interval midpoint of projection is defined as CT center offsets.
, can also be to original although being described above demarcating CT center offsets for original sinogram
The encryption that sinogram carries out line direction samples to improve precision.
Fig. 4 is shown in the technologies of automatic Calibration CT center offsets according to another embodiment of the present invention to initial sinusoids
The sinogram for the row resampling that figure enters obtained by row interpolation in the row direction.Fig. 5 is that description is according to another embodiment of the present invention
The flow chart of the method for automatic Calibration CT center offsets.
In step S510, control and tomography computer 140 read the initial sinusoids figure represented with matrix, the initial sinusoids
Figure is that the data rotated a circle based on the collection turntable 120 of detector 130 are obtained.For example, turntable 120 is rotated by 360 °, detector
130 gathered datas, obtain initial sinusoids figure p（β, s), β=122M, s=12N.p（β, s) is two-dimensional matrix, its
Middle β represents that projection angle is numbered in sinogram, is matrix line number, and s represents that detector is numbered in sinogram, is matrix row number.
In step S520, K point of the interpolation of any two point, obtains resampling in initial sinusoids figure each row of data
Sinogram.For example, to sinogram p（β, s) by K point of linear interpolation insertion, (K is more than between any two point in each row of data
Equal to 1), obtain row encryption resampling sinogram g (β, s), β=122M, s=12 (N-1) * K+1.
In step S530, the cross-correlation between the preceding half son row of each row in the sinogram of resampling and rear half son row is calculated
Coefficient.For example, each row in resampling sinogram are divided into two son row, i.e., M point of preceding 180 projection angle is a row,
M point of 180 projection angles is a row afterwards, for example, first row is divided into：U1 (β)=g (β, 1), β=12M and v1 (β)=g
(β, 1), β=M+122M.U1 (β) and v1 (β) cross-correlation coefficient R (1) are calculated using formula, it is sinusoidal as resampling
Figure first row coefficient value；Similarly, the coefficient value that can obtain any one row of resampling sinogram is：R（s)s=12···(N-1)*
K+1。
In step S540, determine that the projection of CT working regions on the detector is interval.For example it is row encryption resampling is sinusoidal
Scheme g（β, s) all rows additions are averaged, and obtain a line signal：
Wherein, using p (s) left side air value standard deviations as reference, the part in signal more than 5 times of standard deviations is defined as
Workpiece area, now corresponding Qu Wenwei [s1s2] ∈ [1 (N-1) * K+1].According to other embodiment, other can also be used
The standard deviation of multiple is used as workpiece area, such as 3 times.
In step S550, the sequence number of the detector cells corresponding to the maximum for the cross-correlation coefficient that projected area is asked is determined.
For example software statistics and automatically extract the maximum R of each row coefficient of workpiece area sinogram（S), record when obtaining maximum
Detector sequence number X, X represent the projected pixel position of turntable pivot on the detector, i.e.,：S=X, R (X)=Max R (s), s=
s1···s2}。
In step S560, CT center offsets are determined based on the K values, the interval and described sequence number of the projection.For example,
The business that difference divided by K between the sequence number and the interval midpoint of the projection is obtained is defined as CT center offsets.Or,
Center offset is represented with following formula：
OffsetX=(X-((N-1)*K+1+1)/2)/K……(3)
Although being described in above embodiment for arc linear array detector, those skilled in the art can
To recognize, the scheme of the above embodiment of the present invention can apply to the D fan perspective view of linear linear array detector acquisition
The processing for the 3 D cone-beam projected image that picture and planar array detector are obtained.
It is high with regard to center offset, reliability can be obtained using only sinogram using embodiments of the invention, not by noise shadow
Ring.
Detailed description above has elaborated automatic Calibration CT centers by using block diagram, flow chart and/or example
Numerous embodiments of the method and system of offset.One or more functions are included in this block diagram, flow chart and/or example
And/or in the case of operation, it will be understood by those skilled in the art that each function in this block diagram, flow chart or example and/
Or operation can be by various hardware, software, firmware or substantially their any combination come independent and/or common realization.
In one embodiment, if the stem portion of theme described in embodiments of the invention can pass through application specific integrated circuit (ASIC), scene
Programmable gate array (FPGA), digital signal processor (DSP) or other integrated forms are realized.However, people in the art
Member is it should be understood that some aspects of embodiments disclosed herein can be realized equally in integrated electricity on the whole or partly
Lu Zhong, the one or more computer programs for being embodied as running on one or more computer (for example, be embodied as at one or
The one or more programs run in multiple stage computers system), be embodied as running on the one or more processors one or
Multiple programs (for example, being embodied as the one or more programs run in one or more microprocessors), are embodied as firmware, or
Person is substantially embodied as any combination of aforesaid way, and those skilled in the art are according to the disclosure, will be provided with designing circuit
And/or the ability of write-in software and/or firmware code.In addition, it would be recognized by those skilled in the art that theme described in the disclosure
Mechanism can be distributed as the program product of diversified forms, and no matter actually be used for performing the signal bearing medium of distribution
Particular type how, the exemplary embodiment of theme described in the disclosure is applicable.The example of signal bearing medium is included but not
It is limited to：Recordable-type media, such as floppy disk, hard disk drive, compact-disc (CD), digital universal disc (DVD), digital magnetic tape, calculating
Machine memory etc.；And transmission type media, such as numeral and/or analogue communication medium are (for example, optical fiber cable, waveguide, wire communication
Link, wireless communication link etc.).
Although exemplary embodiment describing the present invention with reference to several, it is to be understood that, term used is explanation and shown
Example property and nonrestrictive term.Because the present invention can be embodied without departing from the spiritual or real of invention in a variety of forms
Matter, it should therefore be appreciated that above-described embodiment is not limited to any foregoing details, and the spirit that should be limited in appended claims
With widely explained in scope, therefore the whole changes fallen into claim or its equivalent scope and remodeling all should be the power of enclosing
Profit requires to be covered.
Claims (10)
1. a kind of method of automatic Calibration CT center offsets, including step：
The initial sinusoids figure represented with matrix is read, the initial sinusoids figure is to gather the number that turntable rotates a circle based on detector
According to what is obtained；
Calculate the cross-correlation coefficient between the preceding half son row of each row in initial sinusoids figure and rear half son row；
Determine that the projection of CT working regions on the detector is interval；
Determine the sequence number of the detector cells corresponding to the maximum of the interval cross-correlation coefficient of the projection；And
CT center offsets are determined based on the interval and described sequence number of projection.
2. the method for claim 1, wherein the detector is specially that arc linear array detector or linear linear array are visited
Survey device or planar array detector.
3. the method for claim 1, wherein the difference between the sequence number and the interval midpoint of the projection is determined
For CT center offsets.
4. the method for claim 1, wherein determine the interval step bag of the projection of CT working regions on the detector
Include：
All rows of initial sinusoids figure are added and are averaged, a line signal is obtained；
Using the standard deviation of the row signal left side air value as reference value, the part in signal more than 5 times of standard deviations is defined as
The projection of CT working regions on the detector is interval.
5. a kind of system of automatic Calibration CT center offsets, including：
The device of the initial sinusoids figure represented with matrix is read, the initial sinusoids figure is based on detector collection turntable rotation one
What the data in week were obtained；
Calculate the device of the cross-correlation coefficient between the preceding half son row of each row in initial sinusoids figure and rear half son row；
Determine the interval device of the projection of CT working regions on the detector；
Determine the device of the sequence number of detector cells corresponding to the maximum of the interval cross-correlation coefficient of the projection；And
The device of CT center offsets is determined based on the interval and described sequence number of projection.
6. a kind of method of automatic Calibration CT center offsets, including step：
The initial sinusoids figure represented with matrix is read, the initial sinusoids figure is to gather the number that turntable rotates a circle based on detector
According to what is obtained；
K point of the interpolation of any two point, obtains the sinogram of resampling in initial sinusoids figure each row of data；
Calculate the cross-correlation coefficient between the preceding half son row of each row in the sinogram of resampling and rear half son row；
Determine that the projection of CT working regions on the detector is interval；
Determine the sequence number of the detector cells corresponding to the maximum of the interval cross-correlation coefficient of the projection；And
CT center offsets are determined based on the K values, the interval and described sequence number of projection.
7. method as claimed in claim 6, wherein, the detector is specially that arc linear array detector or linear linear array are visited
Survey device or planar array detector.
8. method as claimed in claim 6, wherein, by the difference between the sequence number and the interval midpoint of the projection divided by
The business that K is obtained is defined as CT center offsets.
9. method as claimed in claim 6, wherein it is determined that the interval step bag of the projection of CT working regions on the detector
Include：
All rows of the sinogram of resampling are added and are averaged, a line signal is obtained；
Using the standard deviation of the row signal left side air value as reference value, the part in signal more than 5 times of standard deviations is defined as
The projection of CT working regions on the detector is interval.
10. a kind of system of automatic Calibration CT center offsets, including：
The device of the initial sinusoids figure represented with matrix is read, the initial sinusoids figure is based on detector collection turntable rotation one
What the data in week were obtained；
K point of the interpolation of any two point, obtains the device of the sinogram of resampling in initial sinusoids figure each row of data；
Calculate the device of the cross-correlation coefficient between the preceding half son row of each row in the sinogram of resampling and rear half son row；
Determine the interval device of the projection of CT working regions on the detector；
Determine the device of the sequence number of detector cells corresponding to the maximum of the interval cross-correlation coefficient of the projection；And
The device of CT center offsets is determined based on the K values, the interval and described sequence number of projection.
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| CN101825433A (en) * | 2010-03-31 | 2010-09-08 | 北京航空航天大学 | Measuring method of offset of rotating center of rotating table of fan beam 2D-CT scanning system |
| EP2357613A2 (en) * | 2009-12-15 | 2011-08-17 | General Electric Company | Method for computed tomography motion estimation and compensation |
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|---|---|---|---|---|
| CN101027677A (en) * | 2004-06-24 | 2007-08-29 | 维森盖特有限公司 | Method for correction of relative object-detector motion between successive views |
| CN101303225A (en) * | 2008-07-09 | 2008-11-12 | 北京航空航天大学 | Projection rotating center measurement method suitable for 2D-CT scanning system |
| EP2357613A2 (en) * | 2009-12-15 | 2011-08-17 | General Electric Company | Method for computed tomography motion estimation and compensation |
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