CN103654833B - The determination method and apparatus at CT detector deflection angle - Google Patents

Abstract

The invention discloses a kind of determination method and apparatus of CT detector deflection angle.Described method comprises: use CT to be measured to carry out all-round scanning to testee, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂; With the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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.Present invention achieves without the need to using special correction die body, by means of only directly scanning testee, and simple calculations being carried out to the initial data gathered, the technique effect at the detector deflection angle of CT to be measured can be determined fast and accurately.

Description

The determination 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, particularly relate to a kind of determination method and apparatus of CT detector deflection angle.

Background technology

CT(Computed Tomography, computed tomography) be applied to medical image the earliest, be introduced into industrial nondestructive testing field subsequently, due to its non-intrusive, glitch-free examine repair, CT have also been obtained good application in fields such as agriculture and forestry, geophysics, chemical industry.According to the difference of the motion pick data mode of radiographic source-detector, CT can be divided into for five generations, the third generation fan-delta sandbody pattern of scan pattern and rotation-rotation is restrainted in writing on one's behalf for first of translation-rotation of comparatively commonly using at present.Wherein, third generation fan-delta sandbody pattern is divided into again two classes according to the distribution situation of detector: a kind of is the equidistant fan-delta sandbody that linear array detector is corresponding, and another kind is the isogonism fan-delta sandbody that arc line shaped detector array is corresponding.In engineer applied, equidistant fan-delta sandbody model application is the most extensive.The FBP(Filtering BackProjection corresponding with third generation fan-delta sandbody, filtered back projection) algorithm for reconstructing owing to having taken into account reconstruction time and reconstruction quality two CT performance indications, be widely used.

For equidistant fan-delta sandbody pattern, standard FBP algorithm for reconstructing requires that scanning system meets 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 in the installation process of CT, or CT device all can be made to be difficult to accurately meet above-mentioned two conditions due to the reason such as movement of turntable, thus cause CT to rebuild image occurring artifact.Existing a lot of CT projection rotating center (Center Of Rotation, COR), the namely bearing calibration of the subpoint of center of rotation can determine the detector position coordinate that central ray is corresponding, namely try to achieve center of rotation projection address on the detector, thus data for projection can be offset certain distance and eliminate because center of rotation offsets the artifact caused.

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

Summary of the invention

In view of this, the invention provides a kind of determination method and apparatus of CT detector deflection angle, without the need to using special correction die body, by means of only directly scanning testee, and simple calculations is carried out to the initial data gathered, the detector deflection angle of CT to be measured can be determined fast and accurately.

In first aspect, embodiments provide a kind of defining method of CT detector deflection angle, comprising:

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

With the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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 implementation that the first is possible, described use CT to be measured carries out all-round scanning to testee, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as the first extreme position D of edge projection point in detector array of testee 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, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, the projection value p (n θ, m) of each detector pixel point; Wherein, n, m and N are integer, n ∈ [0, N], m ∈ [1, M], M are total number of detector pixel point, M be greater than 1 integer;

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

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

In the implementation that the second is possible, the ray source focus of described calculating CT to be measured and D 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 implementation that the third is possible, 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 the determination result at the detector deflection angle of described CT to be measured, the original projection value of each detector pixel point of described CT to be measured is calibrated, according to the data for projection after calibration, generates and rebuild image accordingly.

In second aspect, embodiments provide a kind of determining device 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, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit, for the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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 implementation that the first is possible, described edge projection point acquiring unit specifically for:

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂.

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

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

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

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

In the implementation that the second is possible, 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 implementation that the third is possible, 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 the determination result at the detector deflection angle according to 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 and rebuild image accordingly.

The embodiment of the present invention by use CT to be measured testee is scanned, obtain testee edge projection point 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, with detector array place straight line for X-axis, set up coordinate system, calculate 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 determine the technological means of detector deflection angle γ of described CT to be measured, achieve without the need to using special correction die body, by means of only directly scanning testee, and simple calculations being carried out to the initial data gathered, the technique effect at the detector deflection angle of CT to be measured can be determined fast and accurately, according to this detector deflection angle, can correct data for projection further, optimize FBP algorithm for reconstructing, eliminate the artifact of rebuilding in image further.

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 of a kind of CT detector deflection angle defining method of first embodiment of the invention;

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

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;

Correct COR and detector deflection angle while that Fig. 6 being second embodiment of the invention, use the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

Correct COR and detector deflection angle while that Fig. 7 being second embodiment of the invention, use the partial enlarged drawing of the 2-d reconstruction figure of standard FBP algorithm for reconstructing;

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

Detailed description of the invention

In order to make the object, technical solutions and advantages of the present invention clearly, 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, illustrate only part related to the present invention in accompanying drawing but not full content.

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-delta sandbody 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 be arranged at radiographic source 110 transmit cover segment angle within, detector array 120 comprises multiple detector cells, and each detector cells is a detector pixel point.Scan time, radiographic source 110 and detector array 120 synchronous round center of rotation O, 150 rotate.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, and 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, 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, and that is, actual XY coordinate system, is equivalent to, by desirable X1Y1 coordinate system, offset by γ angle.Wherein, XY coordinate is with detector array 120 place straight line for X-axis, with D ₀for the coordinate system that initial point is set up; X1Y1 coordinate is with SD ₀place straight line is Y1 axle, the coordinate system set up for X1 axle with the straight line vertical with Y1 axle.Now, if rebuild image with XY coordinate system, artifact can be there is.Therefore, need XY coordinate system to be corrected to X1Y1 coordinate system, wherein, γ angle is the deflection angle of coordinate system XY relative to coordinate system X1Y1.

In theory, for the scan-data blocked (the measurement fan-beam of CT can envelope testee completely), distance center of rotation O can be obtained, 150 farthest a bit, if this point is A, then this point projects positional distance D on detector array 120 ₀, 190 farthest time corresponding position be respectively an A, 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 in CT rotation sweep data projection sinogram and trough.

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

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

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

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 ₂s is met at X1 axle ₂, 1C0 point, if 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);

Same 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.

First embodiment

Fig. 2 is the flow chart of the defining method at a kind of CT detector deflection angle of first embodiment of the invention, the method of the present embodiment can be performed by the determining device at CT detector deflection angle, this device realizes by the mode of hardware and/or software, and general accessible site is inner in CT machine.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, obtain the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂.

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

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

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

For example, detector comprises 1-2048 detector pixel point, the order arrangement on the detector of these 2048 detector pixel points, CT measures testee by the mode of rotation sweep, wherein, Q(pole, the edge far point of testee) projection value on the detector lays respectively at: No. 3 pixels, No. 128 pixels, No. 459 pixel ..., on No. 2011 pixels, because No. 3 pixels and No. 2011 pixels are closest to the two ends (No. 1 pixel and No. 2048 pixels) of detector, 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 edge projection point in detector array of above-mentioned testee can be obtained in the present embodiment by various mode ₁with the second extreme position D ₂, such as, directly can read pixel corresponding to maximum crest value in CT rotation sweep data projection sinogram and pixel etc. corresponding to minimum trough value, 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, obtain the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂.

Step 120, with the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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.

In the present embodiment, various method can be taked to calculate the position D of COR in detector array of CT to be measured 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, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, the projection value p (n θ, m) of each detector pixel point; Wherein, n, m and N are integer, n ∈ [0, N], m ∈ [1, M], M are total number of detector pixel point, M be greater than 1 integer;

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

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

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

In the present embodiment, D is being obtained ₀after position, ray source focus and the D of CT to be measured can be obtained by the mode directly 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, the ray source focus of described calculating CT to be measured and D 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 directly can be measured 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 according to formula: calculate the value of γ.

The embodiment of the present invention by use CT to be measured testee is scanned, obtain testee edge projection point 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, with detector array place straight line for X-axis, set up coordinate system, calculate 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 determine the technological means of detector deflection angle γ of described CT to be measured, achieve without the need to using special correction die body, by means of only directly scanning testee, and simple calculations being carried out to the initial data gathered, the technique effect at the detector deflection angle of CT to be measured can be determined fast and accurately, according to this detector deflection angle, can correct data for projection further, optimize FBP algorithm for reconstructing, eliminate the artifact of rebuilding in image further.

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

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, and X-ray tube is Philips(Philip) company produces, model is Y-TU/100-D01; The equidistant array that detector is produced for the generation that stablizes the country (Beijing) scientific & technical corporation, 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, and use S-L(Shepp-Logan, desirable V-type wave filter is multiplied by SIN function) wave filter.All reconstructed results, therefore can the truth determined 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 deviation detector center, detector place artificially, this situation can be equivalent to detector and have rotated 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 °, above-mentioned CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, the projection value p (n θ, m) of each detector pixel point; Wherein, n, m and N are integer, n ∈ [0,3600], m ∈ [1,1536], the Raw projection data sinogram of the all-round scanning without logarithm operation collected, as shown in Figure 3.

The detector deflection angle of this CT to be measured is determined according to following steps:

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, and each element in P corresponds to the Raw projection data p (n θ, m) that CT scan to be measured obtains,

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

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

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

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

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

4) formula is utilized: $\left\{\begin{array}{c}\frac{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_1{D}_0-{\mathrm{MD}}_0)}^2}}{\sqrt{{\left(\mathrm{SM}\right)}^2+{(D_0{D}_2+{\mathrm{MD}}_0)}^2}}=\frac{D_1{D}_0}{D_0{D}_2}\\ R_D=\sqrt{{\left(\mathrm{SM}\right)}^2+{\left({\mathrm{MD}}_0\right)}^2}\end{array}\right.,$ Calculate the position D of ray source focus S and 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) formula is utilized: calculate detector equivalence deflection angle γ=4.7 ° of CT to be measured.

In the present embodiment, if only corrected COR, that is: the accurate location of No. 568 detector pixel point position as COR is got, 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, can find out to there is visible artefacts in 2-d reconstruction image in figures 4 and 5;

If corrected COR and detector deflection angle simultaneously, that is: the accurate location of No. 568 detector pixel point position as COR is got, deflection angle 4.7 ° is substituted into updating formula, 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, can find out at Fig. 6 and Fig. 7, artifact obtains 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 used in other CT field of non destructive testing, and this is those of ordinary skill in the art's easy understand.

3rd embodiment

Fig. 8 is the structure chart of the 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, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit 82, for the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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 by use CT to be measured testee is scanned, obtain testee edge projection point 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, with detector array place straight line for X-axis, set up coordinate system, calculate 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 determine the technological means of detector deflection angle γ of described CT to be measured, achieve without the need to using special correction die body, by means of only directly scanning testee, and simple calculations being carried out to the initial data gathered, the technique effect at the detector deflection angle of CT to be measured can be determined fast and accurately, according to this detector deflection angle, can correct data for projection further, optimize FBP algorithm for reconstructing, eliminate the artifact of rebuilding in image further.

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

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as described testee edge projection point 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, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, the projection value p (n θ, m) of each detector pixel point; Wherein, n, m and N are integer, n ∈ [0, N], m ∈ [1, M], M are total number of detector pixel point, M be greater than 1 integer;

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

Travel through described cross correlation Number Sequence R (m), search the detector pixel point corresponding with the maximum in R (m) sequence, using the COR position D in detector array of this detector pixel point position as described CT to be measured 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 the determination result at the detector deflection angle according to 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 and rebuild image accordingly.

The determining device of the CT detector anglec of rotation that the embodiment of the present invention provides may be used for the defining method performing the CT detector anglec of rotation that any embodiment of the present invention provides, and 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, thus they storages can be performed by processor in the storage device, described program can be stored in a kind of computer-readable recording medium, the above-mentioned storage medium mentioned can be read only memory, disk or CD etc.; Or they are made into each integrated circuit modules respectively, or the multiple module in them or step are made into single integrated circuit module to 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 change and change.All do within spirit of the present invention and principle any amendment, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (12)

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

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

With the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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. the defining method at CT detector deflection angle according to claim 1, is characterized in that, described use CT to be measured carries out all-round scanning to testee, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂specifically comprise:

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂.

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

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

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

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

4. the defining method at CT detector deflection angle according to claim 1, is characterized in that, the ray source focus of described calculating CT to be measured and D 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. the defining method at CT detector deflection angle according to claim 1, 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. the defining method at CT detector deflection angle according to claim 1, it is characterized in that, described method also comprises: according to the determination result at the detector deflection angle of described CT to be measured, the original projection value of each detector pixel point of described CT to be measured is calibrated, according to the data for projection after calibration, generate and rebuild image accordingly.

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, obtains the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂;

Edge projection point coordinates acquiring unit, for the position D of center of rotation subpoint COR in detector array of CT to be measured ₀for initial point, with detector array place straight line for X-axis, set up coordinate system, calculate 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 angle according to claim 7, is characterized in that, described edge projection point position acquisition unit specifically for:

According to predetermined incremental steps θ, CT to be measured is used to carry out rotation sweep to testee, under obtaining different rotary angle, projection original value p (the n θ of each detector pixel point, m), form projection matrix, wherein, n, m and N is integer, n ∈ [0, N] m ∈ [1, M], M are total number of detector pixel point, M be 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 closest to detector array two ends, as the first extreme position D of edge projection point in detector array of testee ₁with the second extreme position D ₂.

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

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

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

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

10. the determining device at CT detector deflection angle according to claim 7, 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 angles according to claim 7, 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 angles according to claim 7, it is characterized in that, described device also comprises:

Calibration and reconstruction unit, for the determination result at the detector deflection angle according to 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 and rebuild image accordingly.