CN101584587B - Automatic calibration method for CT projection center - Google Patents
Automatic calibration method for CT projection center Download PDFInfo
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- CN101584587B CN101584587B CN2008101121934A CN200810112193A CN101584587B CN 101584587 B CN101584587 B CN 101584587B CN 2008101121934 A CN2008101121934 A CN 2008101121934A CN 200810112193 A CN200810112193 A CN 200810112193A CN 101584587 B CN101584587 B CN 101584587B
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Abstract
The invention provides an automatic calibration method for a CT projection center, which comprises the following steps of: 1) using CT to perform all-round scanning on a measured object to obtain original projection data of the measured object in various detector units of a detector array under different angles; 2) performing data processing on the original projection data to find the positions ofprojection points of the edges of the measured object in the detector array; and 3) calculating the CT projection center according to the positions of the projection points of the edges of the measur ed object in the detector array, and calibrating the original projection data to obtain final two-dimensional tomography data. The method can calibrate the central projection position of the CT without adopting a special die body and moving the measured objects; and various calibration steps of the method can be established into a reconstruction pre-processing program to automatically run so as tosave measurement time, and prolong the effective service life of diographic sources and detectors.
Description
Technical field
The invention belongs to technical field of nondestructive testing, specifically, the present invention relates to a kind of method of correcting CT projection centre.
Background technology
Computer tomography (CT) is widely used in fields such as medical image, industrial nondestructive testing, its ultimate principle is that radiographic source is launched high-energy ray, through behind the testee, detect ray signal after the decay by detector, by the projection information of the ray under the collection different angles to measured object, use corresponding algorithm for reconstructing, calculate the two-dimensional signal of measured section.Difference according to the motion image data mode of radiographic source-detector can be divided into CT for five generations, the third generation scan pattern for the first generation scan pattern of translation-rotation and rotation-rotation comparatively commonly used at present.
Accurate reconstruction goes out the two-dimensional signal of measured section, need obtain CT projection geometry accurately, and wherein the center of one dimension projection is a very important parameter.Projection centre overlaps with the center cell of detector in theory, but be difficult in the installation process of CT the two is adjusted unanimity fully, therefore, the detector center does not often overlap with projection centre in the practical application, if this parameter is not proofreaied and correct, will there be pseudo-shadow in resulting reconstructed image.
Bearing calibration to projection centre at present is divided into the direct method of measurement and model tuning method.The direct method of measurement is to determine the projection centre of detector by the center of rotation of the source-detector of direct measurement CT and turntable, and this method is subject to measurement error, difficult realization the in the practical application; The model tuning rule adopts special-purpose needle-like model, earlier calibration model is scanned, and determines projection centre by iterative computation, then measured object is formally measured, and the projection centre data of using special purpose model to measure gained are proofreaied and correct formal measurement data.Be applied to big scale fixed equipments for CT, as the measurement of multiphase flow reactor, the enforcement of special purpose model method need remove tested pipeline section from the CT field of view (FOV), just can just carry out die for special purpose sports school, and is comparatively loaded down with trivial details.Gauged another shortcoming that uses a model is to have increased scanning times and Measuring Time, has expended the life-span of radiographic source and detector.And, industry CT is under a few thing condition, detector or radiographic source can be because little moving take place in temperature or other reason, naked eyes are difficult to tell that this type of is unusual from reconstructed image, therefore and the pseudo-shadow that forms, the model tuning method can't be finished the correction of projection centre automatically, causes the measurement result of distortion.
Summary of the invention
The objective of the invention is, avoid using special-purpose correction die body,, and the initial data of gathering carried out simple calculations, realize the correction of projection centre fast, thereby a kind of method of automatic correcting CT projection centre is provided by direct scanning measured object.
For achieving the above object, the automatic bearing calibration of CT projection centre provided by the invention comprises the steps:
1) uses CT that measured object is carried out full week (360 degree) scanning, obtain under the different angles measured object in the original projection data of each detector cells of detector array;
2) described original projection data is carried out date processing, find out the position of described measured object marginal point (apart from scanning center's utmost point far point) in described detector array;
3) go out the CT projection centre according to the position calculation of subpoint in described detector array at described measured object edge and described original projection data is proofreaied and correct, carry out image reconstruction then, obtain final two-dimensional ct image.
In the technique scheme, described step 2) comprise following substep:
21) find out maximum p in all original projection data
Max
22) according to this maximum p
MaxDraw the decay threshold value p that does not block scanning
Valve
23) when the original projection data of detector cells less than decay threshold value p
ValveThe time, judge that this detector cells detects described measured object; Find out the detector cells that in all detect the detector cells of measured object projection, is positioned at the detector array two ends.
In the technique scheme, described step 21) also comprise: with the form access of initial data with matrix P, the element among the described matrix P is with p
AbExpression; The vectorial a of row is the data of different detector cells under the same angle among the described matrix P, and column vector b is the data under the same detector cells different angles; Described step 22) also comprises: the threshold value coefficient k of not blocking scanning is set, described decay threshold value p
Valve=kp
Max
In the technique scheme, described step 23) also comprise: Ergodic Matrices P, try to achieve eligible (p
Ab＜p
Valve) time, the minimum b of b
MinWith maximum b
Max
In the technique scheme, described step 3) comprises following substep:
31) calculate projection centre p
Center(b
Max+ b
Min)/2;
32) calculate N
Offset=p
Center-d/2, d are the sum of detector cells, N
OffsetInitial data is carried out the columns of interpolation for need;
33) original projection data matrix P is carried out interpolation, interpolation method is: insert (a N in matrix P
Offset* b) interpolating matrix, the value of all elements equals p in this interpolating matrix
MaxN
OffsetBe timing, be illustrated in the right-hand member interpolation of matrix P, N
OffsetWhen negative, then be illustrated in the left end interpolation of matrix P.
34) matrix after the interpolation is carried out logarithm operation, the line number of going forward side by side value is rebuild, and obtains final two-dimentional layer data.
In the technique scheme, described attenuation quotient k is 0.8.It should be noted that k value is not limited to certain particular value, according to survey object difference, the span of k is: 0.5＜k＜1.Can choose optimum parameter value according to concrete measuring object.The rule of determining of k value is, the measured object bigger (density is bigger) to the X-attenuation coefficient, the k value value is corresponding can be smaller, the measured object (density less) less to X-ray error coefficient, the k value value needs big, can obtain and proofread and correct the result preferably.
The present invention has following technique effect:
The present invention need not to adopt special-purpose die body, need not mobile measured object, can proofread and correct, and each aligning step of the present invention can enroll and rebuilds pre-treatment program and move automatically the central projection position of CT, save Measuring Time, prolonged the useful working life of radiographic source and detector.
Description of drawings
Below, describe embodiments of the invention in conjunction with the accompanying drawings in detail, wherein:
Fig. 1 is CT projection to the measurement pipeline section under first angle.
Fig. 2 is the gray-scale map of CT to the initial data of the measuring section scanning of recirculating fluidized bed, and its abscissa is a probe access, and vertical coordinate is the anglec of rotation, and gray scale is represented projection value.
Fig. 3 be in the scanning space (left side) on the measured object apart from center pole far point f (x, y) and initial data sinogram (right side) go up corresponding b
MaxWith b
Min, b
MaxWith b
MinBe respectively the maximum and the minimum of the probe access that meets decision condition.
Fig. 4 is the 2-d reconstruction figure without the projection centre parameter correction.Measuring object is the fluid bed blank pipe.
Fig. 5 is the 2-d reconstruction figure that adopts after the scheme that the present invention proposes.
Fig. 6 is reconstruction figure the 512nd row, and 700-1000 column data comparison diagram, abscissa are the probe access number, and vertical coordinate is the CT reconstructed value.
Fig. 7 is the program realization flow figure of one embodiment of the invention; T represents True among the figure, and F represents False.
Fig. 8 is that 1-1024 column data figure, measuring object are the lucite disk model without the 2-d reconstruction figure (left side) of projection centre parameter correction and the 512nd row thereof.
Fig. 9 is disk model 2-d reconstruction figure and the 512nd row thereof after the scheme of employing the present invention proposition is proofreaied and correct, 1-1024 column data figure.
The specific embodiment
The present invention can be used for various CT Non-Destructive Testings field, and the detection that distributes with cross section material in the circulating fluid bed reactor is an example below, and each ins and outs of the present invention are described.
Circulating fluid bed reactor is widely used in fields such as petroleum refining, boiler, metallurgy, cross section material distribution situation is an important indicator of reactor operation conditions in the reactor, CT can not insert glitch-free measurement reactor content distribution sectional view, has caused the great interest of industry in recent years.This embodiment promptly is that the riser entrance that CT is applied to recirculating fluidized bed is measured.
Use the CT machine to belong to third generation X ray CT in this embodiment, detector adopts uniform line-array to arrange, and has 1536 detector cells; The running voltage of x-ray source is 65kV, and operating current is 6.5mA; The CT machine carries out full weeks 360 degree sampling, and sampling step length is 0.1 degree, and single pass is adopted 3600 groups of data for projection altogether.
When ray passed measured object, its intensity decayed, and this process is followed the Lambert-beer law:
I＝I
0e
-μl
I
0Be incident X-rays intensity, I is an outgoing X ray intensity, and μ is the linear attenuation coefficient of measured object, and l is the thickness that ray penetrates this material.
Therefore, under a the angle, the projection p of b passage
AbCan be expressed as:
p
ab＝I
0e
∫ L μ l dl
L is under a the angle in the formula, and the ray of b passage correspondence passes the path of measured object.
Fig. 1 is the 1st angle, the projection value of 1536 probe access.
Adopting data are preserved with the two-dimensional matrix form, a=3600 in this example, b=1536:
Transfer matrix to gray-scale map (as shown in Figure 2) and be the scanning sinogram.
Ask the greatest member value p of this matrix
Max, the corresponding transmitted intensity of this value, i.e. I without the measured object decay
0, threshold value p
Valve=kp
Max, Ergodic Matrices is obtained eligible p
Ab≤ p
ValveIn the matrix element, the minima b of b
MinWith maximum b
MaxIn this example, k gets 0.8, it should be noted that, k value is not limited to certain particular value, and according to survey object difference, the span of k is: 0.5＜k＜1.Can choose optimum parameter value according to concrete measuring object.The rule of determining of k value is, the measured object bigger (density is bigger) to the X-attenuation coefficient, the k value value is corresponding can be smaller, the measured object (density less) less to X-ray error coefficient, the k value value needs big, can obtain and proofread and correct the result preferably.The effect of this threshold value is the marginal information of identification measured object (being the riser outer wall in this example).
Projection centre and correction offset are asked for by following formula:
p
center＝(b
min+b
max)/2
N
offset＝p
center-d
center
N
OffsetBe need interpolation columns, promptly need to insert (N
Offset* 3600) matrix, the value of matrix element equal the transmitted intensity value without the measured object decay.N
OffsetBe timing, need at projection matrix right-hand member interpolation, N
OffsetWhen negative, need in the left end interpolation.
In this example, p
Max=13800, p
Valve=11074, b
Min=210, b
Max=1374, p
Center=792.And the detector central passage is d
Center=1536/2=768, N
Offset=p
Center-d
Cdnter=24.Then need to insert (24 * 3600) matrix at matrix P right-hand member, the value of matrix element is 13800.
After the projection centre correction, sampled data is carried out processing such as logarithm operation, hardening correcting, adopt filtered back projection's method (FBP) to carry out 2-d reconstruction then, reconstruction figure is of a size of the 1024*1024 pixel.
Fig. 4 is without the gauged reconstructed results of projection centre, and Fig. 5 is for adopting the present invention, through the gauged reconstructed results of projection centre.As can be seen from Figure, the present invention can effectively proofread and correct the projection centre skew, disappears therefore and the pseudo-shadow that forms.To rebuilding figure the 512nd row, the 700-1000 row compare, as shown in Figure 6.
This trimming process can be enrolled in the pre-treatment program of CT reconstruction, and that realizes projection centre automatically determines that its flow chart as shown in Figure 6.
Fig. 8, Fig. 9 are respectively without the CT reconstruction figure (left side) of projection centre calibration and process the present invention calibration and the 512nd row grey scale curve figure (right side), and measuring object is a disk model.As can be seen, rebuild figure (Fig. 7) without the CT of calibrate and have tangible pseudo-shadow, use the present invention to carry out (Fig. 8) after the cent(e)ring, picture quality is significantly improved, and has effectively eliminated because of projection centre and has been forbidden the pseudo-shadow that causes.
The automatic correction method of projection centre that the present invention proposes is compared with existent method, has the advantage of the time of using manpower and material resources sparingly, need not to adopt the special correcting circuit model, need not measured object is moved, and can finish the correction of projection centre fast.
Should be noted that the present invention is not limited to the detection that the cross section material distributes in the reactor, the present invention can also be used for other CT Non-Destructive Testing field, and this is that those of ordinary skills understand easily.
At last; above-described specific embodiment; purpose of the present invention, technical scheme and beneficial effect are further described; institute is understood that; the above is specific embodiments of the invention only, is not limited to the present invention, and is within the spirit and principles in the present invention all; any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (2)
1. the automatic bearing calibration of a CT projection centre comprises the steps:
1) uses CT that measured object is carried out full week scanning, obtain under different angles measured object in the original projection data of each detector cells of detector array;
2) described original projection data is carried out date processing, find out the position of subpoint in described detector array at described measured object edge;
3) go out the CT projection centre according to the position calculation of subpoint in described detector array at described measured object edge and described original projection data is proofreaied and correct, obtain final two-dimentional layer data;
Described step 2) comprise following substep:
21) with the form access of original projection data with matrix P, the element among the described matrix P is with p
AbExpression; The vectorial a of row is the data of different detector cells under the same angle among the described matrix P, and column vector b is the data under the same detector cells different angles; Find out the maximum p in all original projection data
Max
22) according to this maximum p
MaxDraw the decay threshold value p that does not block scanning
ValveThe threshold value coefficient k of not blocking scanning is set, described decay threshold value p
Valve=kp
Max
23) when the original projection data of detector cells less than decay threshold value p
ValveThe time, judge that this detector cells detects described measured object; Ergodic Matrices P tries to achieve eligible p
Ab＜p
ValveThe time, the minimum b of b
MinWith maximum b
Max
Described step 3) comprises following substep:
31) calculate projection centre p
Center=(b
Max+ b
Min)/2;
32) calculate N
Offset=p
Center-d/2, d are the sum of detector cells, N
OffsetInitial data is carried out the columns of interpolation for need;
33) original projection data matrix P is carried out interpolation, interpolation method is: insert a N in matrix P
OffsetThe interpolating matrix of * b, the value of all elements equals p in this interpolating matrix
MaxN
OffsetBe timing, be illustrated in the right-hand member interpolation of matrix P, N
OffsetWhen negative, then be illustrated in the left end interpolation of matrix P;
34) matrix after the interpolation is carried out logarithm operation, the line number of going forward side by side value is rebuild, and obtains final two-dimentional layer data.
2. the automatic bearing calibration of CT projection centre according to claim 1 is characterized in that, the span of described threshold value coefficient k is: 0.5＜k＜1.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| RU2589292C2 (en) * | 2011-05-24 | 2016-07-10 | Конинклейке Филипс Н.В. | Device and method for formation of attenuation correction map |
| CN102512140B (en) * | 2011-11-29 | 2013-07-24 | 中国科学院自动化研究所 | Method for locating optical projection tomography imaging rotation center |
| CN104181177B (en) * | 2013-05-24 | 2017-08-22 | 上海联影医疗科技有限公司 | CT detector location bearing calibrations |
| CN103606144A (en) * | 2013-10-17 | 2014-02-26 | 中国科学院过程工程研究所 | Method and apparatus for determining center of rotation of projection of computed tomography (CT) |
| CN103654833B (en) * | 2013-11-19 | 2015-10-28 | 中国科学院过程工程研究所 | The determination method and apparatus at CT detector deflection angle |
| CN105653392A (en) * | 2014-11-12 | 2016-06-08 | 上海西门子医疗器械有限公司 | Method backing up and recovering computer tomoscan original data and corresponding equipment thereof |
| CN108333197B (en) * | 2018-02-01 | 2019-10-22 | 北京航空航天大学 | Bias industrial CT system turntable rotation center scaling method under scan pattern |
| CN112233030B (en) * | 2020-10-15 | 2023-01-03 | 上海优医基医疗器械技术有限公司 | CT projection geometric correction method based on deep learning |
| CN112666704B (en) * | 2020-12-29 | 2022-05-13 | 中国科学院长春光学精密机械与物理研究所 | Structural design method of first-elimination stray light hood in optical system |
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|---|---|---|---|---|
| CN1657011A (en) * | 2005-03-22 | 2005-08-24 | 东软飞利浦医疗设备系统有限责任公司 | X-ray computerised tomograph capable of automatic eliminating black false image |
| CN1692889A (en) * | 2005-01-28 | 2005-11-09 | 大连理工大学 | Scale template used for pyramidal tract x-rays CT system |
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| CN1692889A (en) * | 2005-01-28 | 2005-11-09 | 大连理工大学 | Scale template used for pyramidal tract x-rays CT system |
| CN1657011A (en) * | 2005-03-22 | 2005-08-24 | 东软飞利浦医疗设备系统有限责任公司 | X-ray computerised tomograph capable of automatic eliminating black false image |
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|---|
| JP昭62-284250A 1987.12.10 |
| JP特开2006-25868A 2006.02.02 |
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