CN107563972A - A kind of CT data correcting methods and a kind of ladder test block - Google Patents
A kind of CT data correcting methods and a kind of ladder test block Download PDFInfo
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Abstract
The invention discloses a kind of CT data correcting methods, by a kind of ladder test block, obtain the detector dosage natural logrithm value under different equivalent steel thickness.And by fitting of a polynomial, fit true ray integral curve.Then ideal ray integral curve is obtained.Finally by the corresponding relation of two curves, the gamma correction to CT data is realized.Ray hardened by multipotency so as to solve, CT data caused by the physics such as ray scattering and detector nonlinearity or system reason are in nonlinear problem.And then realize to hardening, scattering, the Data correction of detector nonlinearity.The invention also discloses a kind of ladder test block for CT Data corrections, the test block possesses some equivalent steel thick layers, and its density is equal to standard steel.
Description
Technical field
The present invention relates to Medical Imaging Technology field, more particularly to a kind of CT data correcting methods.
Background technology
19 end of the centurys, William roentgen are found that X ray.After this, internal structure of body is examined using X ray
Survey a kind of important means become for Non-Destructive Testing.With the development of computer technology, computer application gradually penetrates into
Among every subjects.CT (Computed Tomography) Computed tomography, is exactly computer science and high energy thing
A kind of brand-new nondestructiving detecting means that Neo-Confucianism intersects to form.The technology realize testee faultage image scanning with again
Build.And it is widely used in the field such as medical science and industry.
Because of X ray physical characteristic or system self reason, CT reconstruction images can have image quality issues, it is necessary to CT numbers
Handled according to being corrected.
Detector under the details in a play not acted out on stage, but told through dialogues without X ray, has doses value because of its electronic device reason.Each detector
Details in a play not acted out on stage, but told through dialogues dose value has difference, and can accumulate in CT data.Therefore details in a play not acted out on stage, but told through dialogues variable can influence CT reconstructed image qualities.Having
In the case of X ray, for each detector in detector array when obtaining same X-ray dose, its dose value still can table
Reveal otherness, cause inconsistency be present between detector.
Existing CT data correction schemes carry following problem：1) only natural logrithm is according to progress dark field correction, Air correction phase
To simple correcting mode, image caused by multi-power spectrum ray is hardened, and the calibration result of the image problem such as ray scattering
It is poor；2) lack wide applicability, be only capable of to specific CT data, or specific CT image problems carry out Data correction.
Dark field correction is used to remove each detector electronics of CT system caused spuious error in itself, its bearing calibration
For：In the case of x-ray bombardment, each detector of CT system subtracts corresponding spy in the data that the testing conditions of different set are gathered
Survey the details in a play not acted out on stage, but told through dialogues data that device gathers when without x-ray bombardment；
Air correction is used to remove each detector cells of CT system institute's actual detection biography under the x-ray bombardment of same dose
Defeated dose error, its bearing calibration are：The number that each probe unit of CT system gathers in the case of the x-ray bombardment of no-raster part
According to for air data, the dose value after being averaged to it i.e. as X-ray irradiation；The air data value of each probe unit collection
Modifying factor is obtained compared with dose value；The ratio between data and modifying factor of detector collection are corresponded to during x-ray bombardment scanned copy
Data value as after Air correction；When carrying out details in a play not acted out on stage, but told through dialogues Air correction, the air data of collection then first carries out dark field correction.
According to Beer law, the density integral on the path that ray penetrates object is naturally right with detector dose value
Inversely, and the size of generally scanned copy is not single for number, and X ray is when ray energy is higher, its continuum
Problem can be highlighted.The ray attenuation that the ray of X ray under i.e. each energy corresponds to penetrator density is different, causes X
Ray presentation is a certain degree of non-linear, and the phenomenon is referred to as beam hardening.This problem can be more serious influence CT rebuild figure
As quality, it is therefore desirable to which correlation method is corrected.
The content of the invention
To solve the above problems, the invention discloses a kind of CT data correcting methods, pass through a kind of CT of the present invention
Data correcting method, the staged gamma correction to CT data can be realized, reach the problems such as removing beam hardening, ray scattering
The purpose for the nonlinear error of CT data brought.
A kind of CT data correcting methods, including dark field correction and Air correction, in addition to CT data gamma corrections, it is described
CT data gamma correction is for removing beam hardening, the error that ray scattering is brought, the side of the CT data gamma correction
Method is to be done X-ray scanning using the test block with different equivalent thickness and obtained its data to make reference value, is penetrated with reference to X ray
Physical relation existing for obstacle dose value and obstacle thickness, establishes that reference value is corresponding with calculated value to contrast mathematical modulo
Type, and the data obtained by correspondingly contrasting mathematical modeling to part to be measured scanning are carried out according to correction；The correspondence contrasts mathematical modulo
Type, which is forgiven, to be carried out natural logrithm computing to reference value, fitting of a polynomial is carried out to natural logrithm operational data, to fitting of a polynomial
Curve is differentiated, and the index inverse operation of natural logrithm.
Further, the CT data gamma correction comprises the following steps：
1) the ladder CT data of ladder test block are gathered by the detector of CT system；Even if ladder test block abuts ray
Source, since top layer ladder, X ray is allowed to sequentially pass through each layer of ladder test block, by detector gathered data, acquisition
The gathered data of corresponding different layers ladder test block is ladder CT data；
2) the CT data to be corrected of part to be measured are gathered by the detector of CT system；
3) take natural logrithm to obtain logarithm ladder CT data to ladder CT data, treat correcting CT data and take natural logrithm to obtain
To logarithm CT data to be corrected；
4) fitting of a polynomial is carried out to logarithm ladder CT data, obtains logarithm step function；
5) matched curve of logarithm step function is made, determines aim curve slope, makes correction aim curve；
6) inverse function of Fitted logistic step function is utilized, asks for equivalent steel thickness corresponding to logarithm CT data to be corrected
Value；
7) according to the corresponding equivalent steel thickness value and correction aim curve, logarithm correcting CT data are obtained；
8) index processing is done to logarithm correcting CT data, obtains correcting CT data.
Further, 5 ranks are carried out to logarithm ladder CT data in step 4 or 6 rank multinomials is fitted.
Further, the determination method of the step 5 lieutenant colonel positive goal slope of curve is in matched curve maximum equivalent steel thickness
Within value 15%, five thickness values at equal thicknesses interval are taken, ask matched curve oblique in the slope of five thickness values, gained
The average value of rate is aim curve slope.
The invention also discloses a kind of ladder test block, including some equivalent steel thick layers, it is close that its density is equal to standard steel
Degree, the width double altitudes of each equivalent steel thick layer is equal, and equivalent steel thick layer orlop thickness is more than CT system radiographic source
The maximum equivalent steel thickness penetrated；The width of the equivalent steel thick layer is more than detector width, the equivalent steel thick layer
Highly it is more than 3 times of detector collimation height.
Compared to prior art, the present invention has the advantages that：
1st, it is caused the problems such as beam hardening and ray scattering except being corrected to details in a play not acted out on stage, but told through dialogues data and air data
CT data inaccuracy also can be corrected effectively.
2nd, the correcting mode that the present invention uses has universal applicability, not for a certain specific CT scan pair
As, and a certain specific CT image problems.But effective Data correction can be carried out to most CT data.
Brief description of the drawings
Accompanying drawing 1 is a kind of flow chart of CT data correcting methods of the present invention.
Accompanying drawing 2 is aim curve and Fitted logistic step function curve synoptic diagram.
Accompanying drawing 3 is ladder test block schematic diagram.
Accompanying drawing 4 is the air data and details in a play not acted out on stage, but told through dialogues data of detector cells collection.
Embodiment
The particular content that the invention will now be described in detail with reference to the accompanying drawings.
The invention discloses a kind of CT data correcting methods, including dark field correction, Air correction and the non-linear school of CT data
Just, comprise the following steps that：
1st, details in a play not acted out on stage, but told through dialogues data and air data are gathered with CT system；
In the case of without X ray, details in a play not acted out on stage, but told through dialogues data DARK (i) is gathered by the detector of CT system, wherein i represents detection
Device is numbered, have X ray but without part to be measured in the case of, air data AIR (i), wherein i are gathered by the detector of CT system
Represent detector numbering.Each detector cells correspond to a details in a play not acted out on stage, but told through dialogues data and an air data, therefore, details in a play not acted out on stage, but told through dialogues data and
Air data is two data sequences, as shown in Figure 4.
2nd, ladder test block is scanned with CT system, gathers ladder CT data；
Ladder test block is successively scanned with X ray, test block is tried one's best close to radiographic source, obtains the scanning number of each test layer
According to, each detector cells read different data in the ladder test block of different-thickness, therefore, the ladder CT finally given
Data are a data matrix L adder (Dk, i), wherein the thickness degree of ladder test block is Dk, i expression detector numberings.
3rd, part to be measured is scanned with CT system, gathers CT data CTData (i) to be corrected；
With X-ray scanning part to be measured, CT data CTData (i) to be corrected are gathered, CT data to be corrected are a data sequences
Row, wherein i represent detector numbering.
4th, dark field correction and Air correction are carried out to ladder CT data；
LadderAD(Dk, i) and=(Ladder (Dk,i)-DARK(i))/(AIR(i)-DARK(i))*meani(AIR(i)-
DARK (i)) wherein LadderAD (Dk, i) be details in a play not acted out on stage, but told through dialogues Air correction after ladder CT data, meani(AIR (i)-DARK (i)) is
The average value of the difference of all detector air datas and details in a play not acted out on stage, but told through dialogues data, i represent detector numbering.
5th, correcting CT data are treated and carry out dark field correction and Air correction；
CTDataAD (i)=(CTData (i)-DARK (i))/(AIR (i)-DARK (i)) * meani(AIR(i)-DARK
(i))
Wherein CTDataAD (i) be details in a play not acted out on stage, but told through dialogues Air correction after CT data to be corrected, meani(AIR (i)-DARK (i)) is
The average value of the difference of all detector cells air datas and details in a play not acted out on stage, but told through dialogues data, i represent detector numbering.
6th, natural logrithm processing is carried out to the ladder CT data after correction, logarithm ladder CT data is obtained, after correction
CT data to be corrected carry out natural logrithm processing, obtain logarithm CT data；
Ladder_Ln(Dk, i) and=ln (AIR (i)-DARK (i)/LadderAD (Dk,i))
CTData_Ln (i)=ln (AIR (i)-DARK (i)/CTDataAD (i))
Wherein Ladder_Ln (Dk, i) and it is logarithm ladder CT data, wherein CTData_Ln (i) is logarithm CT data, AIR
(i) it is air data, DARK (i) is details in a play not acted out on stage, but told through dialogues data, DkFor ladder test block thickness degree, i represents detector numbering.
According to Beer law I=I0e-μx, the density integral on the path that ray penetrates object, with detector dose value
Natural logrithm inversely, formula is：
Wherein L represents to penetrate path length, I0Incident CT values are represented, I represents outgoing CT values.Therefore, to ladder CT data
Natural logrithm is taken, can make it that linear relationship be presented with equivalent steel thickness in principle.
7th, the logarithm ladder CT data are carried out with 5 ranks or 6 rank multinomials is fitted, obtain Fitted logistic step function, made
Go out Fitted logistic step function curve, as shown in Figure 2.
F(Dk, i) and=Polyfit ({ Ladder_Ln (D1,i),Ladder_Ln(D2,i),......Ladder_Ln(Dk,
i)})
Wherein F (Dk, i) and it is logarithm step function, Ladder_Ln (D1, i) and it is logarithm ladder CT data, DkTested for ladder
The thickness degree of part, i represent detector numbering.
8th, according to Fitted logistic step function curve, correction aim curve is made, as shown in Figure 2.
The part within matched curve maximum equivalent steel thickness value 15% is chosen, the partial linear is preferable, can be used as school
The basis for selecting of positive goal curve.Five thickness values at equal thicknesses interval, D are taken in the part1, D2, D3, D4, D5.Ask fitting
Curve is in the slope of these thickness values, the slope using its average as correction aim curve.Formula is as follows：
CorLine(Dk, i) and=Grad (i) Dk
Wherein Grad (i) be slope average value, CorLine (Dk, i) and it is to correct aim curve, DkFor ladder test block layer
Thickness, i represent detector numbering.
9th, according to the inverse function of Fitted logistic step function, equivalent steel thickness corresponding to logarithm CT data to be corrected is asked for
Value.F-1(CTData_Ln (i))=InverseFun c (F (Dk,i))
D (i)=F-1(CTData_Ln(i))
Wherein F-1(CTData_Ln (i)) is the inverse function of logarithm step function, and CTData_Ln (i) is logarithm CT to be corrected
Data, D (i) are the equivalent steel thickness value in matched curve, and i represents detector numbering.
10th, according to the thickness value asked for, corresponding logarithm correcting CT data are obtained, formula is as follows：
CTCorData_Ln (i)=CorLine (D (i))=Grad (i) D (i)
Wherein CTCorData_Ln (i) is logarithm correcting CT data, and Grad (i) is the average value of slope, CorLine (D)
To correct aim curve, i represents detector numbering.
Handled by the way that logarithm correcting CT data are entered with row index, obtain correcting CT data.Formula is as follows：
Wherein CTCorData (i) is correcting CT data.
The invention also discloses a kind of ladder test block, the test block is used for CT data gamma corrections.A kind of ladder is surveyed
Test specimen, including some equivalent steel thick layers, its density are equal to standard steel density, the width double altitudes of each equivalent steel thick layer
It is equal, as shown in Figure 2.
Equivalent steel thick layer orlop thickness DNThe maximum equivalent steel thickness penetrated more than CT system radiographic source.
The width of equivalent steel thick layer is more than detector width.
The height of equivalent steel thick layer is more than 3 times of detector collimation height, to avoid interfering for longitudinal ray.
Accompanying drawing 3 is the stereogram of ladder test block, and in test process, detector is parallel to the ladder test block.
Finally illustrate, the above embodiments are merely illustrative of the technical solutions of the present invention and it is unrestricted, although with reference to compared with
The present invention is described in detail good embodiment, it will be understood by those within the art that, can be to the skill of the present invention
Art scheme is modified or equivalent substitution, and without departing from the objective and scope of technical solution of the present invention, it all should cover at this
Among the right of invention.
Claims (5)
1. a kind of CT data correcting methods, including dark field correction and Air correction, it is characterised in that：It is non-linear also to include CT data
Correction, the CT data gamma correction is for removing beam hardening, the error that ray scattering is brought, and the CT data are non-linear
The method of correction is to be done X-ray scanning using the test block with different equivalent thickness and obtained its data to make reference value, with reference to X
Ray penetrates obstacle dose value and I=I be present with obstacle thickness0e-μxPhysical relation, establish reference value and calculated value
Correspondence contrast mathematical modeling, and the data obtained are scanned to part to be measured by correspondingly contrasting mathematical modeling and carried out according to correction；Institute
State to correspond to forgive according to mathematical modeling and natural logrithm computing is carried out to reference value, multinomial plan is carried out to natural logrithm operational data
Close, polynomial fitting curve is differentiated, and the index inverse operation of natural logrithm.
2. a kind of CT data correcting methods as claimed in claim 1, it is characterised in that the CT data gamma correction includes
Following steps：
1) ladder CT data are gathered by the detector of CT system；Ladder test block is set to abut radiographic source, since top layer ladder,
X ray is allowed to sequentially pass through each layer of ladder test block, by detector gathered data, the corresponding different layers ladder test of acquisition
The gathered data of part is ladder CT data；
2) the CT data to be corrected of part to be measured are gathered by the detector of CT system；
3) take natural logrithm to obtain logarithm ladder CT data to ladder CT data, treat correcting CT data and take natural logrithm to obtain pair
Number CT data to be corrected；
4) logarithm ladder CT data are subjected to fitting of a polynomial, obtain logarithm step function；
5) matched curve of logarithm step function is made, determines aim curve slope, makes correction aim curve；
6) inverse function of Fitted logistic step function is utilized, asks for equivalent steel thickness value corresponding to logarithm CT data to be corrected；
7) according to the corresponding equivalent steel thickness value and correction aim curve, logarithm correcting CT data are obtained；
8) logarithm correcting CT data are done into index processing, obtains correcting CT data.
A kind of 3. CT data correcting methods as claimed in claim 2, it is characterised in that：To logarithm ladder CT data in step 4
Carry out 5 ranks or the fitting of 6 rank multinomials.
A kind of 4. CT data correcting methods as claimed in claim 2, it is characterised in that：Step 5 lieutenant colonel's positive goal slope of curve
Determination method be within matched curve maximum equivalent steel thickness value 15%, take five thickness values at equal thicknesses interval, ask
In the slope of five thickness values, the average value of gained slope is aim curve slope for matched curve.
A kind of 5. ladder test block, applied to a kind of CT data correcting methods described in claim 1, it is characterised in that：Including
Some equivalent steel thick layers, its density are equal to standard steel density, and the width double altitudes of each equivalent steel thick layer is equal, equivalent
Steel thick layer orlop thickness is more than the maximum equivalent steel thickness that CT system radiographic source penetrates；The width of the equivalent steel thick layer
More than detector width, the height of the equivalent steel thick layer is more than 3 times of detector collimation height.
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