CN100381101C - Method for determining effective section width of CT unit - Google Patents

Abstract

The present invention relates to a method for determining the effective slicing width of a CT machine. The method comprises the following steps that an initial coordinate system is established to determine the effective region range of receiving X-rays on Z-axis; a start coordinate and a terminate coordinate of the region receiving the X-rays on the Z-axis are calculated, and the width range of each point for receiving the X-rays on the Z-axis is further calculated; a slicing photoreception section curve on the theory is drawn out and corrected, and subsequently, the full width at half maximum of the curve is the effective width of the slicing. The method of the present invention has simple operation and accurate results, and consequently, the method provides the reference for the design of the opening width of an upper sluice gate and a lower sluice gate of the CT machine. Furthermore, the present invention calculates the utilization rate of the effective X-rays in a quantitative way.

Description

The method of the effective slice width of a kind of definite CT machine

Technical field

The invention belongs to technical field of medical instruments, the method for the effective slice width of particularly a kind of definite CT machine.

Background technology

Effectively slice width is an important performance indexes of CT machine, controls effective slice width size exactly and is very important for the data scanning of CT machine.Effective slice width of present CT machine is by regulating the last tail gates A/F of machine, undertaken by the section die body again that actual measurement obtains, if effective slice width value of measuring does not adhere to specification, then need to repeat the adjusting of tail gates A/F, reach designing requirement with this.The method complicated operating process of this manual adjustment, inefficiency.

Summary of the invention

At deficiency of the prior art, the invention provides the method for the effective slice width of a kind of definite CT machine.Come to determine to go up the size design of tail gates by this method.The inventive method is according to the straightline propagation character of light, calculate the dosage that each point of Z axle can receive effective X ray quantitatively, draw out the x-ray dose distribution curve of Z axle, obtain the halfwidth degree again and be effective slice width, compare by effective slice width with actual measurement, verify the effectiveness of this method, had actual application value.

The inventive method comprises the steps:

(1) set up the initialization coordinate system:

With the Z axle is that abscissa, Y-axis are that vertical coordinate is set up plane right-angle coordinate, the Z shaft position is corresponding with CT machine testing device center of rotation shaft position, the X source filament places Y-axis forward or negative sense optional position, upper lock gate is the optional position between filament of light source and Z axle, tail gates are positioned at Y-axis negative sense or forward optional position, and promptly upper lock gate lays respectively at Z axle both sides.

(2) determine on the Z axle, can accept the effective coverage scope of X ray, promptly determine coordinate figure (Z _i ³, Y _i ³), to calculate by the geometric distribution relation of filament, upper lock gate, Z axle, tail gates, step is as follows:

A, with (Z ₁ ¹, Y ₁ ¹), (Z ₁ ⁴, Y ₁ ⁴) point be the first and last point of line segment, set up straight line L equation, calculated line L and upper lock gate, the collinear intersection point (Z in Z axle place ₁ ²', Y ₁ ²), (Z ₁ ³', Y ₁ ³), when ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{2^{\&prime;}}\&GreaterEqual;{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2$ The time, then ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}}={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3,$ Forward d to,

B, when ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{2^{\&prime;}}<{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2$ The time, then with (Z ₁ ², Y ₁ ²), (Z ₁ ⁴, Y ₁ ⁴) be the first and last point of line segment, set up straight line L equation, calculated line L and focus, the collinear intersection point (Z in Z axle place ₁ ¹', Y ₁ ¹), (Z ₁ ³', Y ₁ ³), when ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{1^{\&prime;}}\&le;{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^1$ The time, then ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}},$ Forward d to,

C, when ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{1^{\&prime;}}<{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^1$ The time, then with (Z ₂ ¹, Y ₂ ¹), (Z ₁ ², Y ₁ ²) be the first and last point of line segment, set up straight line L equation, the collinear intersection point (Z in calculated line L and Z axle place ₁ ³', Y ₁ ³), ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}},$ Forward d to,

D, above be the computational process of left side coordinate figure, right side coordinate figure computational methods are identical therewith.

(3) calculate the point coordinates at the whole story that Z is coupling and is subjected to the X ray zone by step (2), further calculate the irradiating width scope that each point on the Z axle can be accepted X ray.

(4) abscissa with each point of Z axle is an abscissa, and the irradiating width that can accept X ray with each point on the Z axle is a vertical coordinate, draws out theoretical SSP (section sensitization section) curve.

(5) proofread and correct SSP (section sensitization section) curve with the point spread function convolution algorithm, the halfwidth degree of proofreading and correct the back curve is exactly effective slice width.

Described Z shaft position is corresponding with CT machine testing device center of rotation shaft position.The data of described point spread function obtain by the pearl image calculation that is used for measurement space resolution in the die body.Described effective slice width can be verified by the actual slice width that AAPM die body (measuring the various performance die bodys of CT machine) measures, need adopt square wave function that theoretical curves is carried out convolution algorithm during checking.

This method compared with prior art, and is simple to operate; The effective slice width that obtains by Theoretical Calculation and effective slice width of actual measurement compare, and result of calculation is accurately, has actual application value; Use the inventive method and can design the satisfactory tail gates A/F size that goes up by the mode of search; Simultaneously, use the utilization rate that the inventive method can also be determined effective X ray quantitatively.

Description of drawings

Fig. 1: for determining the flow chart of the effective slice width of CT machine;

Fig. 2: be coordinates computed sketch map among the embodiment;

Wherein, 1 filament, 2 upper lock gate open areas, 3 tail gates open areas;

Fig. 3: in embodiment $Z_{}^{}$ ${}_1^{2^{\&prime;}}\&GreaterEqual;{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2$ The time determine Z axle computation interval scope sketch map;

Wherein, 1 filament, 2 upper lock gate open areas, 3 tail gates open areas;

Fig. 4: in embodiment $Z_{}^{}$ ${}_1^{2^{\&prime;}}<{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2$ The time determine Z axle computation interval scope sketch map;

Wherein, 1 filament, 2 upper lock gate open areas, 3 tail gates open areas;

Fig. 5: in embodiment $Z_{}^{}$ ${}_1^{2^{\&prime;}}>{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2$ The time determine Z axle computation interval scope sketch map;

Wherein, 1 filament, 2 upper lock gate open areas, 3 tail gates open areas;

Fig. 6: be (Z among the embodiment _i, 0) and the effective optical width calculating of some sketch map;

Wherein, 1 filament, 2 upper lock gate open areas, 3 tail gates open areas;

Fig. 7: be the calculating sketch map of point spread function among the embodiment;

Fig. 8: be the curve of point spread function among the embodiment; (the pearl image calculation by the Catfan die body obtains)

Fig. 9: be the figure as a result of embodiment 1 effective slice width and X utilization rate;

Wherein, Fig. 9 a is the Theoretical Calculation result, and Fig. 9 b is an actual measured results; (the section die body in the AAPM die body, measurement result)

Figure 10: be the figure as a result of embodiment 2 effective slice width and X ray utilization rate;

Wherein, Figure 10 a is the Theoretical Calculation result, and Figure 10 b is an actual measured results;

Figure 11: be the figure as a result of embodiment 3 effective slice width and X ray utilization rate;

Wherein, Figure 11 a is the Theoretical Calculation result, and Figure 11 b is an actual measured results.

The specific embodiment

Below in conjunction with accompanying drawing the present invention is described in further detail:

The light intensity of supposing the X source filament is a uniform distribution, and the geometric distribution of filament, upper lock gate open area, Z axle, tail gates open area has determined effective slice width of CT machine.

1) sets up initialization coordinates computed system (as shown in Figure 2);

With the Z axle is that abscissa (the Z shaft position is corresponding with CT machine testing device center of rotation shaft position), Y-axis are that vertical coordinate is set up plane right-angle coordinate, the X source filament places Y-axis forward optional position and parallel Z axle, upper lock gate is optional position and parallel with the Z axle between filament of light source and Z axle, and tail gates are positioned at optional position and parallel with the Z axle, Z axle below; (Z _i ^k, Y _i ^k) be respectively filament zone, upper lock gate open area, Z and be coupling and be subjected to the first and last point position coordinates of X-ray line zone, tail gates open area.Wherein i=1 is a starting point coordinate, and i=2 is the end point coordinate; Be the coordinate of filament during k=1, k=2 is the coordinate of upper lock gate, and k=3 is the coordinate of Z axle, and k=4 is the coordinate of tail gates; l _kBe solid (comprise filament zone, upper lock gate open area, Z are coupling be subjected to light zone, tail gates open area) length, h _kBe the distance of solid to the Z axle; First and last point is marked respectively: (Z ₁ ^k, Y ₁ ^k) coordinate be (l _k/ 2, h _k), point (Z ₂ ^k, Y ₂ ^k) coordinate be (l _k/ 2, h _k), at coordinate (Z _i ³, Y _i ³) in, ${\mathrm{<figure-callout\; id="3"\; label="Y\; i"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Y</figure-callout>}}_i^{}=0,{\mathrm{<figure-callout\; id="3"\; label="Z\; i"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_i^{}$ Value in step 2) in determine.

2) determine on the Z axle, can accept the valid interval scope of X ray, just determine coordinate figure (Z _i ³, Y _i ³), the geometric distribution by filament, upper lock gate, Z axle, tail gates concerns to be calculated;

A, as shown in Figure 3 is with (Z ₁ ¹, Y ₁ ¹), (Z ₁ ⁴, Y ₁ ⁴) point be the first and last point of line segment, set up straight line L equation.Calculated line L and upper lock gate, the collinear intersection point (Z in Z axle place ₁ ²', Y ₁ ²), (Z ₁ ³', Y ₁ ³).If ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{2^{\&prime;}}\&GreaterEqual;{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2,$ Then $({\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}}={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3),$ Forward d to;

B, as shown in Figure 4, if ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{2^{\&prime;}}<{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2,$ Then with (Z ₁ ², Y ₁ ²), (Z ₁ ⁴, Y ₁ ⁴) be the first and last point of line segment, set up straight line L equation, calculated line L and focus, the collinear intersection point (Z in Z axle place ₁ ¹', Y ₁ ¹), (Z ₁ ³', Y ₁ ³).If ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{1^{\&prime;}}\&le;{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^1,$ Then ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}},$ Forward d to;

C, as shown in Figure 5, if ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{1^{\&prime;}}<{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^1,$ Then with (Z ₂ ¹, Y ₂ ¹), (Z ₁ ², Y ₁ ²) be the first and last point of line segment, set up straight line L equation, the collinear intersection point (Z in calculated line L and Z axle place ₁ ³', Y ₃ ¹), ${\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^3={\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^{3^{\&prime;}},$ Forward d to;

D, above be the computational process of left side coordinate figure, right side coordinate figure computational methods are identical therewith.

3) calculate Z by step 2 and be coupling and be subjected to the point coordinates at the whole story in X-ray line zone, further calculate the irradiating width scope that each point on the Z axle can be accepted the X-ray line.The calculating of at first given Z axle is counted, and for example set to calculate that to count be 1000 points, (Z _i, 0) and be i calculation level (i=0 ... 999), (Z then _i, 0) coordinate figure be (Z ₁ ³+ (Z ₂ ³-Z ₁ ³) ÷ 999 * i, 0).Calculate (Z more arbitrarily _i, 0) and put the irradiating width of accepting the X-ray line, as shown in Figure 6.

Angle on the left of a, the calculating earlier: ${\mathrm{\&alpha;}}_1=a\tan ((Z_i-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^1)/h_1),$ ${\mathrm{\&alpha;}}_2=a\tan ((Z_i-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^2)/h_2),$ ${\mathrm{\&alpha;}}_3=\mathrm{athn}(({\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^4-Z_i)/h_4),{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">h</figure-callout>}}_1,{\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">h</figure-callout>}}_2,{\mathrm{<figure-callout\; id="4"\; label="h"\; filenames="C20041002123000142.png"\; state="\{\{state\}\}">h</figure-callout>}}_4$ Be respectively filament, upper lock gate, tail gates distance to the Z axle, all be on the occasion of.α＝min{α ₁，α ₂，α ₃}。

B, calculating right side angle: ${\mathrm{\&beta;}}_1=a\tan (({\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^1-Z_i)/h_1),$ ${\mathrm{\&beta;}}_2=a\tan (({\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2^2-Z_i)/h_2),$ ${\mathrm{\&beta;}}_3=a\tan ((Z_i-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1^4)/h_4),{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="C20041002123000111.png,C20041002123000112.png"\; state="\{\{state\}\}">h</figure-callout>}}_1,{\mathrm{<figure-callout\; id="2"\; label="h"\; filenames="C20041002123000102.png,C20041002123000111.png"\; state="\{\{state\}\}">h</figure-callout>}}_2,{\mathrm{<figure-callout\; id="4"\; label="h"\; filenames="C20041002123000142.png"\; state="\{\{state\}\}">h</figure-callout>}}_4$ Be respectively filament, upper lock gate, tail gates distance to the Z axle, all be on the occasion of.β＝min{β ₁，β ₂，β ₃?}。

C, Z _iThe irradiating width that point is accepted filament is h ₁* (tan (β)+tan (α)).

4) with each (Z _i, 0) abscissa be abscissa, with each (Z _i, 0) and the irradiating width of accepting the X-ray line is vertical coordinate, draws out theoretical SSP (section sensitization section) curve, its halfwidth degree is exactly effective slice width;

5), also to add the point spread function convolutional calculation and proofread and correct SSP (section sensitization section) curve for to make the realistic effective slice width value of the theoretical value that obtains.The data of point spread function obtain by the pearl image calculation that is used for measurement space resolution in the catfan die body (measuring the various performance die bodys of CT machine).Constant in order to guarantee total X-ray emittance, integral kernel is wanted normalization.

The introduction that point spread function calculates:

The CT machine is an imaging system, and the response that an impulse function passes through after the CT imaging system is impulse response.Can simulate the impulse response function of CT imaging system by the pearl image of catfan die body.Fig. 7 is the enlarged drawing of catfan die body pearl image.Point among the figure is the maximum point of CT value, and putting with this is that circle is drawn at the center, increases progressively with a pitch of pixels, asks for the meansigma methods of picture element CT value on the different circumference.So just can obtain a level and smooth point spread function curve.As the point spread function curve that the curve among Fig. 8 calculates for Fig. 7, zone, the rear section of point spread function is a smooth region, casts out.Each point of function curve is deducted the minima of this function curve, make minima make zero.Calculate the accumulated value of each point of this function curve again, be worth point spread function normalization with this then.

The accuracy of effective slice width of calculating for proof theory need at first record actual effective slice width.If actual effective slice width is to obtain with the metal pattern bulk measurement, the sheet metal width that is used to measure effective slice width can cause error to actual measured results, so adopt square wave function that theoretical curves is carried out convolution algorithm, Theoretical Calculation result and actual measured results better met.

Below lift effectiveness and the practicality that several object lessons illustrate the method.

Embodiment 1

In accompanying drawing 9, upper lock gate A/F 0.4mm, during tail gates mouth width 4mm, by effective slice width (the being Z axle halfwidth degree) FWHM=1.6819mm that calculates, and the effective slice width FWHM=1.6618mm that measures by the AAPM die body; The utilization rate of X ray is 61.83%, and the utilization rate of the X ray that obtains by integration is 58.01%;

Embodiment 2

In accompanying drawing 10, upper lock gate A/F 0.8mm, during tail gates mouth width 22mm, by effective slice width (the being Z axle halfwidth degree) FWHM=2.7973mm that calculates, and the effective slice width FWHM=2.7882mm that measures by the AAPM die body; The utilization rate of X ray is 100.00%, and the utilization rate of the X-ray line that obtains by integration is 100.00%;

Embodiment 3

In accompanying drawing 11, upper lock gate A/F 0.8mm, during tail gates A/F 4mm, by effective slice width (the being Z axle halfwidth degree) FWHM=1.6907mm that calculates, and the effective slice width FWHM=1.6934mm that measures by the AAPM die body; The utilization rate of X-ray line is 58.01%, and the utilization rate of the X-ray line that obtains by integration is 55.95%;

Effective slice width value after overcorrect compares through the effective slice width with the AAPM actual measurement, and result of calculation is accurate, has actual application value;

Use above method,, just can select the mechanical dimension that meets effective slice width designing requirement, thereby provide foundation for the last tail gates A/F size design of CT machine by search.Simultaneously, because X dosage that the utilization rate of X ray is a detector to be accepted and the ratio that shines the X dosage that gets off by upper lock gate, this method can also calculate the utilization rate of effective X ray quantitatively, by comparing the accuracy rate height with the X ray utilization rate that obtains through integral operation.

Claims (5)

1. the method for the effective slice width of definite CT machine is characterized in that following steps are arranged:

(1) sets up the initialization coordinate system;

With the Z axle is that abscissa, Y-axis are that vertical coordinate is set up plane right-angle coordinate, and the Z shaft position is corresponding with CT machine testing device center of rotation shaft position, and the X source filament places Y-axis forward or negative sense optional position, and promptly upper lock gate and tail gates lay respectively at Z axle both sides; (Z _i ^k, Y _i ^k) be respectively filament zone, upper lock gate open area, Z and be coupling and be subjected to the first and last point position coordinates of X-ray line zone, tail gates open area.Wherein i=1 is a starting point coordinate, and i=2 is the end point coordinate; Be the coordinate of filament during k=1, k=2 is the coordinate of upper lock gate, and k=3 is the coordinate of Z axle, and k=4 is the coordinate of tail gates; l _kBe solid length, solid comprises: filament zone, upper lock gate open area, Z are coupling and are subjected to light zone, tail gates open area, h _kFor the distance of solid, first and last point is marked respectively: (Z to the Z axle ₁ ^k, Y ₁ ^k) coordinate be (l _k/ 2, h _k), point (Z ₂ ^k, Y ₂ ^k) coordinate be (l _k/ 2, h _k), at coordinate (Z _i ³, Y _i ³) in, $Y_i^3=0,$ Z _i ³Value in step (2), determine;

(2) determine on the Z axle, can accept the effective coverage scope of X ray, promptly determine coordinate figure (Z _i ³, Y _i ³); Geometric distribution relation by filament, upper lock gate, Z axle, tail gates is calculated, and step is as follows: a, with (Z ₁ ¹, Y ₁ ¹), (Z ₁ ⁴, Y ₁ ⁴) point be the first and last point of line segment, set up straight line L equation, calculated line L and upper lock gate, the collinear intersection point (Z in Z axle place ₁ ²', Y ₁ ²), (Z ₁ ³', Y ₁ ³): when $Z_1^{2^{\&prime;}}\&GreaterEqual;Z_1^2$ The time, then $Z_1^{3^{\&prime;}}=Z_1^3,$ Forward d to,

B, when $Z_1^{2^{\&prime;}}<Z_1^2$ The time, then with (Z ₁ ², Y ₁ ²), (Z ₁ ⁴, Y ₁ ⁴) be the first and last point of line segment, set up straight line L equation, calculated line L and focus, the collinear intersection point (Z in Z axle place ₁ ¹', Y ₁ ¹), (Z ₁ ³', Y ₁ ³), when $Z_1^{1^{\&prime;}}\&le;Z_2^1$ The time, then $Z_1^3=Z_1^{3^{\&prime;}},$ Forward d to,

C, when $Z_1^{1^{\&prime;}}<Z_{2,}^1$ Then with (Z ₂ ¹, Y ₂ ¹), (Z ₁ ², Y ₁ ²) be the first and last point of line segment, set up straight line L equation, the collinear intersection point (Z in calculated line L and Z axle place ₁ ³', Y ₁ ³), $Z_1^3=Z_1^{3^{\&prime;}},$ Forward d to,

D, above be the computational process of left side coordinate figure, right side coordinate figure computational methods are identical therewith;

(3) calculate the point coordinates at the whole story that Z is coupling and is subjected to the light zone by step (2), further calculate the width range that each point on the Z axle can be accepted X ray;

(4) abscissa with each point of Z axle is an abscissa, and the irradiating width that can accept filament with each point on the Z axle is a vertical coordinate, draws out theoretical section sensitization section curve;

(5) proofread and correct section sensitization section curve with the point spread function convolution algorithm, the halfwidth degree of proofreading and correct the back curve is exactly effective slice width.

2. the method for the effective slice width of definite CT machine according to claim 1 is characterized in that the data of point spread function in the described step (5) obtain by measuring the pearl image calculation that is used for measurement space resolution in the various performance die bodys of CT machine.

3. the method for the effective slice width of definite CT machine according to claim 1 is characterized in that effective slice width that section sensitization section curve halfwidth kilsyth basalt shows in the described step (5) can be by relatively verifying with the effective slice width of reality.

4. the method for the effective slice width of definite CT machine according to claim 3 is characterized in that effective slice width that described section sensitization section curve halfwidth kilsyth basalt shows can relatively verify by the actual effectively slice width that measures with the AAPM die body.

5. the method for the effective slice width of definite CT machine according to claim 4, it is actual effectively when slice width compares checking that effective width that the sensitization section curve halfwidth kilsyth basalt that it is characterized in that cutting into slices shows and AAPM die body measure, needs at first with square wave function section sensitization section curve convolution algorithm.

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