CN103654833A - Method and device for determining detector deflection angle of CT - Google Patents

Abstract

The invention discloses a method and device for determining the detector deflection angle of a CT. The method comprises the steps that the CT to be detected is used for completely scanning an object to be measured to obtain the first limiting position D1 and the second limiting position D2, in a detector array, of the edge subpoint of the object to be measured; a coordinate system is established with the position D0, in the detector array, of the COR subpoint of the CT to be detected as the original point and with the line where the detector array is located as the X axis, and the X-axis coordinate value q1 of the D1 and the X-axis coordinate value q2 of the D2 are calculated; the distance RD between the radiation source focus of the CT to be detected and the D0 is calculated; the detector deflection angle gamma of the CT to be detected is determined according to the RD, q1 and q2. The technical effect of fast and accurately determining the detector deflection angle of the CT to be detected can be achieved by directly scanning the object to be measured and carrying out simple operation on the collected original data without using a special sizing die.

Description

Definite method and apparatus at CT detector deflection angle

Technical field

The present invention relates to Digital imaging in medicine and technical field of nondestructive testing, relate in particular to definite method and apparatus at a kind of CT detector deflection angle.

Background technology

CT(Computed Tomography, computed tomography) be applied to the earliest medical image, be introduced into subsequently industrial nondestructive testing field, due to its non-insertion, glitch-free detection characteristic, CT has also obtained good application in fields such as agriculture and forestry, geophysics, chemical industry.According to the difference of the motion image data mode of radiographic source-detector, CT can be divided into five generations, that comparatively commonly uses at present writes on one's behalf and restraints the third generation fan-beam scan pattern of scan pattern and rotation-rotation for first of translation-rotation.Wherein, third generation fan-beam scan pattern is divided into again two classes according to the distribution situation of detector: a kind of is the equidistant fan-beam scanning of linear array detectors, and another kind is the isogonism fan-beam scanning that arc line shaped detector array is corresponding.In engineering application, equidistant fan-beam scan pattern is most widely used.Scanning corresponding FBP(Filtering Back Projection, filtered back projection with third generation fan-beam) algorithm for reconstructing is owing to having taken into account two CT performance indications of reconstruction time and reconstruction quality, is widely used.

For equidistant fan-beam scan pattern, standard FBP algorithm for reconstructing requires scanning system to meet two conditions simultaneously: 1, the center of rotation of turntable is on the line of ray source focus and central detector; 2, central ray (line of ray source focus and center of rotation) is perpendicular to the straight line at detector place.But because machine error is inevitable, or because the reasons such as movement of turntable all can make CT device be difficult to accurately meet above-mentioned two conditions, thereby cause CT to rebuild image, there is artifact in the installation process of CT.Existing a lot of CT projection rotating center (Center Of Rotation, COR), the namely bearing calibration of the subpoint of center of rotation can be determined the detector position coordinate that central ray is corresponding, try to achieve the projection address of center of rotation on detector, thereby data for projection can be offset to certain distance and eliminate the artifact causing due to center of rotation skew.

But, even if proofreaied and correct the position of COR, while using FBP algorithm for reconstructing, still require the line of radiographic source and center of rotation perpendicular to detector place straight line.When this condition cannot meet, be equivalent to detector and depart from an angle around center of rotation subpoint rotation, and drift angle is when larger, even COR is proofreaied and correct, the image reconstructing according to canonical algorithm will still there will be artifact, and the interpretation of image is rebuild in impact to CT.

Summary of the invention

In view of this, the invention provides definite method and apparatus at a kind of CT detector deflection angle, without using special-purpose correction die body, only by directly scanning testee, and the initial data gathering is carried out to simple calculations, can determine fast and accurately the detector deflection angle of CT to be measured.

In first aspect, the embodiment of the present invention provides definite method at a kind of CT detector deflection angle, comprising:

Use CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂;

Position D with the center of rotation subpoint COR of CT to be measured in detector array ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂;

Calculate ray source focus and the D of CT to be measured ₀between distance R _d;

According to R _d, q ₁and q ₂, determine the detector deflection angle of described CT to be measured _γ.

In the possible implementation of the first, described use CT to be measured carries out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of testee in detector array ₁with the second extreme position D ₂.

Further, the position D of the COR of described CT to be measured in detector array ₀acquisition methods specifically comprises:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N], m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT in detector array ₀.

In the possible implementation of the second, ray source focus and the D of described calculating CT to be measured ₀between distance R _dspecifically comprise:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line, M be intersection point detector array in position;

According to formula: $\left\{\begin{array}{c}\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}=\frac{D_1{D}_0}{D_0{D}_2}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

In the third possible implementation, described according to R _d, q ₁and q ₂, determine that the detector deflection angle γ of described CT to be measured specifically comprises:

According to formula: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*R_D}{2*q_1{q}_2},$ Calculate the value of γ.

In the 4th kind of possible implementation, described method also comprises: according to definite result at the detector deflection angle of described CT to be measured, original projection value to each detector pixel point of described CT to be measured is calibrated, and according to the data for projection after calibration, generates the corresponding image of rebuilding.

In second aspect, the embodiment of the present invention provides the determining device at a kind of CT detector deflection angle, comprising:

Edge projection point position acquisition unit, for using CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit, for the center of rotation subpoint COR with CT to be measured at the position of detector array D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂;

Metrics calculation unit, for calculating ray source focus and the D of CT to be measured ₀between distance R _d;

Detector deflection angle determining unit, for according to R _d, q ₁and q ₂, determine the detector deflection angle γ of described CT to be measured.

In the possible implementation of the first, described edge projection point acquiring unit specifically for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of testee in detector array ₁with the second extreme position D ₂.

Further, described device also comprises COR position acquisition unit, for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT in detector array ₀.

In the possible implementation of the second, described metrics calculation unit specifically for:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line, M be intersection point detector array in position;

According to formula: $\left\{\begin{array}{c}\frac{D_1{D}_0}{D_0{D}_2}=\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

In the third possible implementation, described detector deflection angle determining unit specifically for:

According to formula: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*R_D}{2*q_1{q}_2},$ Calculate the value of γ.

In the 4th kind of possible implementation, described device also comprises:

Calibration and reconstruction unit, for according to definite result at the detector deflection angle of described CT to be measured, calibrate the original projection value of each detector pixel point of described CT to be measured, according to the data for projection after calibration, generates the corresponding image of rebuilding.

The embodiment of the present invention is by being used CT to be measured to scan testee, the edge projection point that obtains testee detector array in the first extreme position D ₁with the second extreme position D ₂; With the COR of CT to be measured detector array in position D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂; Calculate ray source focus and the D of CT to be measured ₀between distance R _d; And according to R _d, q ₁and q ₂and then the technological means of the detector deflection angle γ of definite described CT to be measured, realized without using special-purpose correction die body, only pass through directly scanning testee, and the initial data gathering is carried out to simple calculations, can determine fast and accurately the technique effect at the detector deflection angle of CT to be measured, according to this detector deflection angle, can further to data for projection, proofread and correct, optimize FBP algorithm for reconstructing, further eliminate the artifact of rebuilding in image.

Accompanying drawing explanation

Fig. 1 is the geometrical relationship schematic diagram of relevant parameter in the CT scan of first embodiment of the invention;

Fig. 2 is the flow chart that method is determined at a kind of CT detector deflection angle of first embodiment of the invention;

Fig. 3 is the all-round scan-data projection sinogram that porous disc is measuring object of take of second embodiment of the invention;

Fig. 4 is the only correction COR of second embodiment of the invention, uses the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

Fig. 5 is the only correction COR of second embodiment of the invention, uses the partial enlarged drawing of the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

When Fig. 6 is second embodiment of the invention, proofread and correct COR and detector deflection angle, use the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

When Fig. 7 is second embodiment of the invention, proofread and correct COR and detector deflection angle, use the partial enlarged drawing of the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

Fig. 8 is the structure chart of determining device at a kind of CT detector deflection angle of third embodiment of the invention.

The specific embodiment

In order to make the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, the specific embodiment of the invention is described in further detail.Be understandable that, specific embodiment described herein is only for explaining the present invention, but not limitation of the invention.It also should be noted that, for convenience of description, in accompanying drawing, only show part related to the present invention but not full content.

The first embodiment

Figure 1 illustrates the geometrical relationship schematic diagram of relevant parameter in the CT scan of first embodiment of the invention.Wherein, the CT machine under third generation fan-beam scan pattern has been shown in Fig. 1.As shown in Figure 1, this three generations CT comprises radiographic source 110 and detector array 120, wherein, transmitting of radiographic source 110 has certain subtended angle, typical subtended angle angular range is, 30～45 °, detector array 120 is arranged at radiographic source 110 and transmits within the segment angle covering, detector array 120 comprises a plurality of detector cells, and each detector cells is a detector pixel point.In when scanning, radiographic source 110 and detector array 120 synchronous round center of rotation O, 150 are rotated.Wherein, by the focus S of radiographic source 110,130 do the straight line perpendicular to detector array 120, hand over detector array 120 in a M, 180.

In theory, detector focus S, 130, center of rotation O, 150 and intersection point M, 180 should be positioned on straight line, but in actual applications,, due to various actual cause, cannot accomplish accurately to meet above condition, for example, in Fig. 1, center of rotation O, 150 projection values in detector array 120 are positioned at D ₀, 190 positions.Detector focus S, 130, center of rotation O, 150 and D ₀, 190 are positioned on straight line, that is to say, and actual XY coordinate system, is equivalent to, by desirable X1Y1 coordinate system, be offset γ angle.Wherein, XY coordinate is that to take detector array 120 place straight lines be X-axis, with D ₀coordinate system for initial point foundation; X1Y1 coordinate is with SD ₀place straight line is Y1 axle, the coordinate system that the straight line vertical with Y1 axle of take set up as X1 axle.Now, if rebuild image with XY coordinate system, can there is artifact.Therefore, XY coordinate system need to be proofreaied and correct as X1Y1 coordinate system, wherein, γ angle is that coordinate system XY is with respect to the deflection angle of coordinate system X1Y1.

In theory, for the scan-data not blocking (the measurement fan-beam of CT can envelope testee completely), can obtain apart from center of rotation O, 150 farthest a bit, establishing this point is A, this some projection positional distance D on detector array 120 ₀, 190 corresponding positions farthest time are respectively an A, and 160 and some A', 140 (wherein A' point be rotated counterclockwise the position after certain angle for A point), put A, and 160 subpoints on detector array 120 are a D ₂, 1A0; Point A', 140 subpoints on detector array 120 are a some D ₁, 170, these two points are corresponding to certain crest and trough in CT rotation sweep data projection sinogram.

As shown in Figure 1, SD ₀for angle ∠ D ₁sD ₂for angular bisector, according to angular bisector character, can draw:

$\frac{D_1{D}_0}{D_0{D}_2}=\frac{{\mathrm{SD}}_1}{{\mathrm{SD}}_2};$

$\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_1\right)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_2\right)}^2}}=\frac{D_1{D}_0}{D_0{D}_2};$

And: ${\mathrm{SD}}_0=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2};$

If D ₁, 170 coordinates in XY coordinate system are (q ₁, 0), D ₂, the coordinate of 1A0 in XY coordinate system is (q ₂, 0); Cross SD ₁straight line and X1 axle meet at S ₁, 1B0 point, SD ₂meet at S with X1 axle ₂, 1C0 point, establishes S ₁, the coordinate of 1B0 in X1Y1 coordinate system is (p ₁, 0), S ₂, the coordinate of 1C0 in X1Y1 coordinate system is (p ₂, 0);

Equally according to SD ₀for angle ∠ D ₁sD ₂for angular bisector, obtain: p ₁=-p ₂;

Further, according to the character of coordinate transform, can obtain:

$p_1=\frac{{\mathrm{SD}}_0*q_1\cos \mathrm{\&gamma;}}{{\mathrm{SD}}_0-q_1*\sin \mathrm{\&gamma;}}$ With $p_2=\frac{{\mathrm{SD}}_0*q_2\cos \mathrm{\&gamma;}}{{\mathrm{SD}}_0-q_2*\sin \mathrm{\&gamma;}};$

And then obtain: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*{\mathrm{SD}}_0}{2*q_1{q}_2}.$

γ is the detector deflection angle of CT to be measured.

The first embodiment

Fig. 2 is the flow chart of definite method at a kind of CT detector deflection angle of first embodiment of the invention, the method of the present embodiment can be carried out by the determining device at CT detector deflection angle, this device can be realized by the mode of hardware and/or software, generally can be integrated in CT machine inner.The method of the present embodiment specifically comprises the steps:

Step 110, use CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂.

In the present embodiment, can be by using CT to be measured testee to be carried out to the mode of all-round scanning (360 ° of scanning), the position of the edge projection point that obtains testee in detector array.

Wherein, the edge of testee refers to the utmost point far point of testee distance C T center of rotation, the first extreme position D of the edge projection point of testee in detector array ₁with the second extreme position D ₂refer to the pixel position of proximity detector both sides at the subpoint place at testee edge.

Typically, using the subpoint at testee edge in the pixel position in proximity detector left side as the first extreme position D ₁; Using the subpoint at testee edge in the pixel position on proximity detector right side as the second extreme position D ₂.

For example, detector comprises 1-2048 detector pixel point, these 2048 detector pixel points order on detector is arranged, CT measures testee by the mode of rotation sweep, wherein, the edge Q(utmost point far point of testee) projection value on detector lays respectively at: No. 3 pixels, No. 128 pixels, No. 459 pixels ..., on No. 2011 pixels, because the two ends (No. 1 pixel and No. 2048 pixels) of No. 3 pixels and No. 2011 proximity detectors of pixel, therefore, using No. 3 pixel positions as D ₁, using the position at No. 2011 pixel places as D ₂.

The first extreme position D of the edge projection point that can obtain above-mentioned testee by variety of way in the present embodiment in detector array ₁with the second extreme position D ₂, for example, can directly read pixel corresponding to pixel that maximum crest value in CT rotation sweep data projection sinogram is corresponding and minimum trough value etc., this is not limited.

One of the present embodiment preferred embodiment in, use CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of testee in detector array ₁with the second extreme position D ₂.

Step 120, the position D with the center of rotation subpoint COR of CT to be measured in detector array ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂.

In the present embodiment, D ₀, D ₁and D ₂all be positioned in X-axis, therefore,

q ₁＝-D ₁D ₀,q ₂＝D ₀D ₂；

Wherein, D ₁d ₀for D ₁and D ₀between distance, D ₀d ₂for D ₀and D ₂between distance.

The position D of the COR that in the present embodiment, can take calculated in various ways CT to be measured in detector array ₀, such as: the direct method of measurement, model tuning method and symmetrical relations method etc. do not limit this.

One of the present embodiment preferred embodiment in, use cross-correlation method to obtain above-mentioned D ₀.Wherein, the position D of the COR of described CT to be measured in detector array ₀acquisition methods specifically comprise:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT to be measured in detector array ₀.

Step 130, the ray source focus that calculates CT to be measured and D ₀between distance R _d.

In the present embodiment, obtaining D ₀after position, can obtain by the mode of direct measurement ray source focus and the D of CT to be measured ₀between distance R _d, also can derive R by triangular relationship _dvalue, this is not limited.

One of the present embodiment preferred embodiment in, ray source focus and the D of described calculating CT to be measured ₀between distance R _dspecifically comprise:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line; M be intersection point detector array in position;

Wherein, vertical dimension SM can directly measure by instruments such as set squares.

According to formula: $\left\{\begin{array}{c}\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}=\frac{D_1{D}_0}{D_0{D}_2}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

Step 140, according to R _d, q ₁and q ₂, determine the detector deflection angle γ of described CT to be measured.

In the present embodiment, can be according to formula:

calculate the value of γ.

The embodiment of the present invention is by being used CT to be measured to scan testee, the edge projection point that obtains testee detector array in the first extreme position D ₁with the second extreme position D ₂; With the COR of CT to be measured detector array in position D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂; Calculate ray source focus and the D of CT to be measured ₀between distance R _d; And according to R _d, q ₁and q ₂and then the technological means of the detector deflection angle γ of definite described CT to be measured, realized without using special-purpose correction die body, only pass through directly scanning testee, and the initial data gathering is carried out to simple calculations, can determine fast and accurately the technique effect at the detector deflection angle of CT to be measured, according to this detector deflection angle, can further to data for projection, proofread and correct, optimize FBP algorithm for reconstructing, further eliminate the artifact of rebuilding in image.

On the basis of technique scheme, described method also comprises: according to definite result at the detector deflection angle of described CT to be measured, original projection value to each detector pixel point of described CT to be measured is calibrated, and according to the data for projection after calibration, generates the corresponding image of rebuilding.

The second embodiment

On the basis of above-described embodiment, in the present embodiment, adopt the equidistant fan beam CT of the third generation as CT to be measured.It is bright that the high tension generator of radiographic source system is that German Yxlon(looks according to section) produce, model is MGG40, X-ray tube is Philips(Philip) company produces, model is Y-TU/100-D01; The equidistant array that detector is produced for generation (Beijing) scientific & technical corporation that stablizes the country, model is LSC-412, scintillator material is GOS(Gadolinium Oxysulfide, gadolinium oxysulfide), detector array has 1536 detector cells, also be 1536 detector pixel points, pixel is of a size of 0.3*0.6mm, and pel spacing is 0.4mm.The x ray running voltage that this experiment adopts is 100kVp, and electric current is 2.2mA, step motor drive object stage, and rotating 360 degrees is sampled, and the incremental steps of sampling angle is 0.1 °.Testee adopts porous organic glass model.Algorithm for reconstructing adopts the FBP algorithm of standard, uses S-L(Shepp-Logan, and desirable V-type wave filter is multiplied by SIN function) wave filter.All reconstructed results, therefore can the definite truth of effecting reaction projection rotating center all without post processing of image.

This experiment makes the center of rotation of CT to be measured along the larger distance in rectilinear direction offset detection device center, detector place artificially, this situation can be equivalent to detector and rotate an angle around center of rotation subpoint, and the distance of radiographic source and center of rotation subpoint increases.

According to the incremental steps of 0.1 °, use above-mentioned CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0,3600], m ∈ [1,1536], the original projection data sinogram of the all-round scanning of not passing through logarithm operation collecting, as shown in Figure 3.

According to following steps, determine the detector deflection angle of this CT to be measured:

1) the vertical dimension SM=1000mm of actual measurement ray source focus S and detector array.

2) use CT to be measured to carry out all-round scanning to testee, under different rotary angle, the projection value of each detector pixel point forms a matrix P, the original projection data p (n θ, m) that each element in P obtains corresponding to CT scan to be measured,

Wherein, the row vector of matrix P represents under the same anglec of rotation, 1536 1536 projection values that detector pixel point is corresponding; The column vector of matrix P represents under 3600 different anglecs of rotation, 3600 projection values that same detector pixel point is corresponding.

For example, the maximum p that Ergodic Matrices P tries to achieve _max=13107, choose predetermined coefficient k=0.8, obtain projection threshold value p _value=0.8*13107=10485.6;

Ergodic Matrices P again, meeting p (n θ, m) in each pixel of < 10485.6, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of described testee in detector array ₁with the second extreme position D ₂.For example, D ₁be positioned at detector pixel point position No. 19, D ₂be positioned at detector pixel point position No. 1098, these 2 downside farthest boundary points corresponding to the original projection data sinogram shown in Fig. 3 and upside farthest boundary point position.

Wherein, if directly read maximum and detector pixel point corresponding to minima in the original projection data sinogram shown in Fig. 3, can bring very large error because of the impact of random noise.

3) the position D of the COR that the cross-correlation method that utilizes the first embodiment preferred implementation to propose calculates CT to be measured in detector array ₀, for example, D ₀be positioned at detector pixel point position No. 568.

4) utilize formula: $\left\{\begin{array}{c}\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}=\frac{D_1{D}_0}{D_0{D}_2}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate ray source focus S and the position D of COR in detector array ₀distance R _d=1003.2mm, wherein, D ₁d ₀=(568-19) * 0.4mm; D ₀d ₂=(1098-568) * 0.4mm.

5) according to formula: q ₁=-D ₁d ₀, q ₂=D ₀d ₂, calculate q ₁and q ₂.

6) utilize formula:

calculate detector equivalence deflection angle γ=4.7 ° of CT to be measured.

In the present embodiment, if only COR is proofreaied and correct, that is: get No. 568 detector pixel point position as the accurate location of COR, the 2-d reconstruction figure of employing standard FBP algorithm for reconstructing and the partial enlarged drawing of 2-d reconstruction figure are as shown in Figure 4 and Figure 5, in Fig. 4 and Fig. 5, can find out, in 2-d reconstruction image, have visible artefacts;

If COR and detector deflection angle are proofreaied and correct simultaneously, that is: get No. 568 detector pixel point position as the accurate location of COR, by 4.7 ° of substitution updating formulas of deflection angle, the 2-d reconstruction figure of employing standard FBP algorithm for reconstructing and the partial enlarged drawing of 2-d reconstruction figure are as shown in Figure 6 and Figure 7, at Fig. 6 and Fig. 7, can find out, artifact has obtained obvious correction.

It should be noted that the present invention is not limited to the measurement of disk model effective, the present invention can also be for other CT field of non destructive testing, and it is intelligible that this is that those of ordinary skills hold.

The 3rd embodiment

Fig. 8 is the structure chart of determining device of a kind of CT detector anglec of rotation of third embodiment of the invention.As shown in Figure 8, described device comprises:

Edge projection point position acquisition unit 81, for using CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit 82, for the center of rotation subpoint COR with CT to be measured at the position of detector array D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂;

Metrics calculation unit 83, for calculating ray source focus and the D of CT to be measured ₀between distance R _d;

Detector deflection angle determining unit 84, for according to R _d, q ₁and q ₂, determine the detector deflection angle γ of described CT to be measured.

The embodiment of the present invention is by being used CT to be measured to scan testee, the edge projection point that obtains testee detector array in the first extreme position D ₁with the second extreme position D ₂; With the COR of CT to be measured detector array in position D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂; Calculate ray source focus and the D of CT to be measured ₀between distance R _d; And according to R _d, q ₁and q ₂and then the technological means of the detector deflection angle γ of definite described CT to be measured, realized without using special-purpose correction die body, only pass through directly scanning testee, and the initial data gathering is carried out to simple calculations, can determine fast and accurately the technique effect at the detector deflection angle of CT to be measured, according to this detector deflection angle, can further to data for projection, proofread and correct, optimize FBP algorithm for reconstructing, further eliminate the artifact of rebuilding in image.

On the basis of the various embodiments described above, described edge projection point acquiring unit specifically for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, as the edge projection point of described testee detector array in the first extreme position D ₁with the second extreme position D ₂.

On the basis of the various embodiments described above, described device also comprises COR position acquisition unit, for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT to be measured in detector array ₀.

On the basis of the various embodiments described above, described metrics calculation unit specifically for:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line; M is the position of intersection point in detector array;

According to formula: $\left\{\begin{array}{c}\frac{D_1{D}_0}{D_0{D}_2}=\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

On the basis of the various embodiments described above, described detector deflection angle determining unit specifically for:

According to formula: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*R_D}{2*q_1{q}_2},$ Calculate the value of γ.

On the basis of the various embodiments described above, described device also comprises:

Calibration and reconstruction unit, for according to definite result at the detector deflection angle of described CT to be measured, calibrate the original projection value of each detector pixel point of described CT to be measured, according to the data for projection after calibration, generates the corresponding image of rebuilding.

Definite method of the CT detector anglec of rotation that the determining device of the CT detector anglec of rotation that the embodiment of the present invention provides can provide for execution any embodiment of the present invention, possesses corresponding functional module, reaches same technique effect.

Obviously, those skilled in the art should be understood that, the embodiment of the present invention can realize by the executable program of computer installation, thereby they can be stored in storage device and be carried out by processor, described program can be stored in a kind of computer-readable recording medium, the above-mentioned storage medium of mentioning can be read only memory, disk or CD etc.; Or they are made into respectively to each integrated circuit modules, or a plurality of modules in them or step are made into single integrated circuit module realize.Like this, the present invention is not restricted to the combination of any specific hardware and software.

The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, to those skilled in the art, the present invention can have various changes and variation.All any modifications of doing, be equal to replacement, improvement etc., within protection scope of the present invention all should be included within spirit of the present invention and principle.

Claims (12)

1. definite method at CT detector deflection angle, is characterized in that, comprising:

Use CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂;

Position D with the center of rotation subpoint COR of CT to be measured in detector array ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂;

Calculate ray source focus and the D of CT to be measured ₀between distance R _d;

According to R _d, q ₁and q ₂, determine the detector deflection angle γ of described CT to be measured.

2. definite method at CT detector deflection according to claim 1 angle, is characterized in that, described use CT to be measured carries out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of testee in detector array ₁with the second extreme position D ₂.

3. definite method at CT detector deflection according to claim 1 and 2 angle, is characterized in that, the position D of the COR of described CT to be measured in detector array ₀acquisition methods specifically comprises:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT in detector array ₀.

4. definite method at CT detector deflection according to claim 1 angle, is characterized in that, ray source focus and the D of described calculating CT to be measured ₀between distance R _dspecifically comprise:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line, M be intersection point detector array in position;

According to formula: $\left\{\begin{array}{c}\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}=\frac{D_1{D}_0}{D_0{D}_2}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

5. definite method at CT detector deflection according to claim 1 angle, is characterized in that, described according to R _d, q ₁and q ₂, determine that the detector deflection angle γ of described CT to be measured specifically comprises:

According to formula: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*R_D}{2*q_1{q}_2},$ Calculate the value of γ.

6. definite method at CT detector deflection according to claim 1 angle, it is characterized in that, described method also comprises: according to definite result at the detector deflection angle of described CT to be measured, original projection value to each detector pixel point of described CT to be measured is calibrated, according to the data for projection after calibration, generate the corresponding image of rebuilding.

7. the determining device at CT detector deflection angle, is characterized in that, comprising:

Edge projection point position acquisition unit, for using CT to be measured to carry out all-round scanning to testee, the first extreme position D of the edge projection point that obtains testee in detector array ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit, for the center of rotation subpoint COR with CT to be measured at the position of detector array D ₀for initial point, the detector array place straight line of take is X-axis, sets up coordinate system, calculates D ₁x-axis coordinate figure q ₁and D ₂x-axis coordinate figure q ₂;

Metrics calculation unit, for calculating ray source focus and the D of CT to be measured ₀between distance R _d;

Detector deflection angle determining unit, for according to R _d, q ₁and q ₂, determine the detector deflection angle γ of described CT to be measured.

8. the determining device at CT detector deflection according to claim 7 angle, is characterized in that, described edge projection point acquiring unit specifically for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle, the projection original value p (n θ, m) of each detector pixel point, forms projection matrix, wherein, and n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain the maximum p in described projection matrix _max, according to formula p _value=kp _maxcalculate projection threshold value p _value, wherein, k is predetermined coefficient, k ∈ (0.5,1);

Meeting p (n θ, m) < p _valueeach pixel in, select the pixel position at proximity detector array two ends, the first extreme position D as the edge projection point of testee in detector array ₁with the second extreme position D ₂.

9. according to the determining device at the CT detector deflection angle described in claim 7 or 8, it is characterized in that, described device also comprises COR position acquisition unit, for:

According to predetermined incremental steps θ, use CT to be measured to be rotated scanning to testee, obtain under different rotary angle the projection value p of each detector pixel point (n θ, m); Wherein, n, m and N are integer, n ∈ [0, N],

m ∈ [1, M], total number that M is detector pixel point, M is greater than 1 integer;

Obtain detector pixel point m each projection value under described different rotary angle, described each projection value is divided into First ray p _m(k θ) and the second sequence p _m(k θ+180 °), wherein, k is integer,

Calculate respectively the First ray p in each detector pixel point _m(k θ) and the second sequence p _mcross-correlation coefficient between (k θ+180 °), forms cross correlation Number Sequence R (m);

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with maximum in R (m) sequence, the position D of the COR using this detector pixel point position as described CT in detector array ₀.

10. the determining device at CT detector deflection according to claim 7 angle, is characterized in that, described metrics calculation unit specifically for:

Measure the vertical dimension SM of CT ray source focus to be measured and detector array place straight line, M be intersection point detector array in position;

According to formula: $\left\{\begin{array}{c}\frac{D_1{D}_0}{D_0{D}_2}=\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate described R _dvalue, wherein: D ₁d ₀for D ₁and D ₀between distance; D ₀d ₂for D ₀and D ₂between distance; MD ₀for M and D ₀between distance.

The determining device at 11. CT detector deflection according to claim 7 angles, is characterized in that, described detector deflection angle determining unit specifically for:

According to formula: $\mathrm{\&gamma;}=\arcsin \frac{(q_1+q_2)*R_D}{2*q_1{q}_2},$ Calculate the value of γ.

The determining device at 12. CT detector deflection according to claim 7 angles, is characterized in that, described device also comprises:

Calibration and reconstruction unit, for according to definite result at the detector deflection angle of described CT to be measured, calibrate the original projection value of each detector pixel point of described CT to be measured, according to the data for projection after calibration, generates the corresponding image of rebuilding.

Images