CN104809750A - Linear scanning CT system and image reconstructing method - Google Patents

Abstract

The invention relates to a linear scanning CT system and image reconstructing method and belongs to the technical field of CT scanning. The system comprises an X ray source, a detector, a detection object, a data acquisition system, an image reconstruction displaying computer system, a control system and a mechanical system. The detector is an area array planar detector, in the scanning process, the X ray source and the detector perform opposite parallel linear movements surrounding the detection object. According to the system, a slide ring component and a large-vision multi-layer detection system are omitted; the system has the advantages of simple structure, low cost and mobility/portability; the invention further provides a precision reconstruction algorithm applied to projection data of the system for image construction, the noise immunity is fine, and the computing speed is high.

Description

A kind of rectilinear scanning CT system and image rebuilding method

Technical field

The invention belongs to CT scan technical field, relate to a kind of rectilinear scanning CT system and image rebuilding method.

Background technology

Since 20 century 70s come out, X ray computer tomography (Computed Tomography, be called for short CT) become the gordian technique of medical diagnostic image, the quantity of CT system configuration quantity, CT scan imaging is always in the trend of growth.Statistics display in 2007, global in-service CT system is more than 45000 covers, and the U.S. CT of a year detects number more than 7,000 ten thousand person-times.

" Chinese CT Analysis on Market Development report " display that Chinese medicine equipment association provides, within 2010, China CT machine owning amount is 11 242, and the owning amount of every a population of one million CT machine is increased to 8.6 in 2010 from 2006 5.5.In the world, the every a population of one million of Japan in 2006 has CT machine and reaches 98, and Australia is 51.Although the owning amount of China every a population of one million CT machine maintains growth level faster, compared with developed countries, owning amount is still on the low side.Therefore, should " report " point out, China has a high potential to CT system requirements.Correspondingly, other developing countries and regions, as India, Africa, Latin America etc., also has large market.

In recent years, the research and development of CT system in directions such as sweep velocity, low dosage, picture qualities drops into many.Such as adopt the system in multilayer, large fan angle scanning, multiray source, connected applications High Rotation Speed slip ring, expects to meet the demand of quick-speed large-scale scanning clinically.But existing Medical CT system is all the scanning rotated around detected object based on x-ray source and detector, many employing filtered backprojection image reconstruction algorithm, need overall full angle (360 °) or half angle (>=180 °) image data.Correspondingly, slip ring has become critical component indispensable in CT system.And slip ring manufactures complicated, be difficult to simplify CT system architecture.Therefore, modern Medical CT system price is expensive, and request for utilization is high, only has the larger medical mechanism of developed country or developing country to be equipped with, and the CT equipment that many developing country, remote districts etc. are needed badly is difficult to possess.According to the latest news, U.S. Department of Defense have subscribed the New X radiation imaging system of 70,000,000 dollars of removable, transmission of wireless signals in January, 2014, for solving Military Medical demand, illustrates that the special dimension such as military, wartime is medical also needs new CT equipment badly.

Therefore, follow the tracks of advanced CT formation method, carry out the research of new CT technical foundation, and then development structure is simple, low cost, removable/portable new CT system are very necessary and urgent.

Summary of the invention

In view of this, the object of the present invention is to provide a kind of rectilinear scanning CT system and image rebuilding method, this system does not adopt the slide ring portion of conventional CT system and large visual field multilayer detection system, have that structure is simple, low cost, the advantage such as removable/portable, additionally provide a kind of exact reconstruction algorithm, the data for projection that can directly apply to this system carries out image reconstruction, has good anti-noise ability and arithmetic speed is very fast.

An object of the present invention is to provide a kind of rectilinear scanning CT system; Two of object of the present invention is to provide the image rebuilding method of a kind of rectilinear scanning CT.

An object of the present invention is achieved through the following technical solutions: a kind of rectilinear scanning CT system, and this system comprises x-ray source, detector, detected object, data acquisition system (DAS), image reconstruction Display control computer system, control system and mechanical system;

Described x-ray source sends X ray penetration-detection object, and arrive detector, dampening information is converted to electric signal and imports computer system into through data acquisition system (DAS) by detector, and machine system shows after carrying out image reconstruction process as calculated; Described detector is face Array Plate detector; In scanning process, x-ray source and detector do parallel lines in opposite directions around detected object and move.

Further, the projection angle θ of the relative x-axis of X ray through visual field in this scanning system is:

$\mathrm{\&theta;}=\left\{\begin{array}{c}{\tan }^{-1}\left(\frac{S_D}{x_D-x_i}\right),x_i<0,x_i\&NotEqual;x_D\\ \frac{\mathrm{\&pi;}}{2},x_i=x_D\\ \mathrm{\&pi;}-{\tan }^{-1}\left(\frac{S_D}{x_i-x_D}\right),x_i\&GreaterEqual;0,x_i\&NotEqual;x_D\end{array}\right.;$

Wherein, S _dfor radiographic source is along the distance of y-axis and detector; x _dthat scanning field of view center is along the distance between x-axis and detector cells; x _ifor radiographic source position, i=1 ..., I, projection number when wherein I is radiographic source rectilinear motion.

Further, in this scanning system through the X ray of visual field and the distance l of projection centre ray be:

$l={(x_i^2+S_O^2)}^{\frac{1}{2}}\sin \mathrm{\&gamma;};$

Wherein, x _ifor radiographic source position, i=1 ..., I, projection number when wherein I is radiographic source rectilinear motion; S _ofor radiographic source is along the distance at y-axis and scanning field of view center; γ is projected through the ray at scanning field of view center and the angle of this ray, γ=β-θ, β=θ _(l=0)for the angle of the ray and x-axis that are projected through scanning field of view center O; The span of l is [-R, R], and R is the radius of scanning field of view.

Further, described system adopts the mode of repeatedly straight line parallel moving sweep to scan.

Further, described system adopts the mode of isogonism repeatedly parallel lines scanning to scan, and obtains the data for projection being not less than 180 ° around scanning field of view.

Further, the mode of described isogonism repeatedly parallel lines scanning comprises the rectilinear scanning of 2 orthogonal rectilinear scanning or 3 even circumferential distributions.

Further, when described system adopts the isogonism mode that repeatedly parallel lines scans to scan, obtain the data for projection relative to scanning field of view even circumferential by the radiographic source projection of non-equidistance, i.e. isogonism sample mode, and isogonism sampling plan is:

${\mathrm{\&beta;}}_1={\tan }^{-1}(-\frac{S_O}{x_1});{\mathrm{\&beta;}}_I=\mathrm{\&pi;}-{\tan }^{-1}\left(\frac{S_O}{x_I}\right);$

$\mathrm{\&Delta;\&beta;}=\frac{1}{I-1}({\mathrm{\&beta;}}_I-{\mathrm{\&beta;}}_1);x_i=-S_O\cot [{\mathrm{\&beta;}}_1+(i-1)\mathrm{\&Delta;\&beta;}];$

Wherein, β=θ _(l=0), be the angle of the ray and x-axis that are projected through scanning field of view center O; S _ofor radiographic source is along the distance at y-axis and scanning field of view center; △ β is the angle between twice projection, and △ β is according to the start position x of radiographic source movement ₁with final position x _icalculate;

Two of object of the present invention is achieved through the following technical solutions: the image rebuilding method of a kind of rectilinear scanning CT, and the method comprises the following steps:

S1: carry out fan beam projections data weighting by following formula:

P ^a(x _i,x _D)＝|cosγ|*P(x _i,x _D)；

Wherein, P (x _i, x _d) be the data for projection gathered, P ^a(x _i, x _d) be the data for projection after weighting; x _ifor radiographic source position; x _dfor scanning field of view center is along the distance between x-axis and detector cells, γ is projected through the ray at scanning field of view center and the angle of this ray;

S2: by following formula to weighted projection data filtering:

P ^b(x _i,x _D)＝P ^a(x _i,x _D)*h(x _D)；

Wherein, p ^b(x _i, x _d) be filtered data for projection, h (x _d) be the ramp filter in spatial domain;

S3: back projection:

$f(x,y)={\&Integral;}_0^T{\&Integral;}_{x_0}^{x_I}\frac{1}{L^2}{P}^b(x_i,x_D,\mathrm{\&eta;}){\mathrm{dx}}_i\mathrm{d\&eta;};$

Wherein, for back projection's coefficient, T is rectilinear scanning number of times, η=1 ..., T.

Further, described data for projection is the data for projection relative to scanning field of view even circumferential of the radiographic source projection acquisition of non-equidistance; Employing isogonism repeatedly parallel lines scan pattern scans, a rectilinear scanning can obtain I X-ray projection data, one time CT scan is realized by T rectilinear scanning, and the projection number M of a CT scan is evenly distributed on equivalence and is not less than in the projection angle of 180 °, and reconstruction image array is N × N; Wherein,

Beneficial effect of the present invention is: a kind of rectilinear scanning CT system provided by the invention, adopt radiographic source and face Array Plate detector parallel lines moving sweep, simulation radiographic source and detector are around the rotation sweep of detected object, do not adopt the slide ring portion of conventional CT system and large visual field multilayer detection system, can simplied system structure and reduction system cost.Rectilinear scanning CT imaging, when detector size is constant, its field of detection changes with scanning process, different from conventional CT image reconstruction algorithm, therefore present invention also offers the image exact reconstruction algorithm of a kind of rectilinear scanning CT, the data for projection that can directly apply to this system carries out image reconstruction, has good anti-noise ability and arithmetic speed is very fast.

Accompanying drawing explanation

In order to make the object, technical solutions and advantages of the present invention clearly, below in conjunction with accompanying drawing, the present invention is described in further detail, wherein:

Fig. 1 is rectilinear scanning CT system model of the present invention;

Fig. 2 is the two-dimensional geometry model of phantom in the CT scan of system of the present invention;

Fig. 3 is isogonism repeatedly parallel lines scan mode schematic diagram;

Fig. 4 is the reconstructing parameters figure of fladellum;

The Shepp-Logan model that Fig. 5 (a) adopts for experiment 1;

The CT image that Fig. 5 (b) obtains for 2T scan mode FBP image reconstruction algorithm in experiment 1;

The CT image that Fig. 5 (c) obtains for 3T scan mode FBP image reconstruction algorithm in experiment 1;

Fig. 6 (a) tests the newly-designed model 2 of 2 employings;

Fig. 6 (b) tests the CT image that in 2,2T scan mode FBP image reconstruction algorithm obtains;

Fig. 6 (c) tests the CT image that in 2,3T scan mode FBP image reconstruction algorithm obtains;

Wherein, 1 is x-ray source, and 2 is detected object, and 3 is detector, and 4 is data acquisition system (DAS), and 5 is image reconstruction Display control computer system, and 6 is that control system, 7 is for mechanical system.

Embodiment

Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.

A kind of rectilinear scanning CT system provided by the invention, its model as shown in Figure 1, x-ray source 1, detected object 2, detector 3, and data acquisition system (DAS) 4, image reconstruction Display control computer system 5, control system 6 and mechanical system 7.

X-ray source sends X ray penetration-detection object, and arrive detector, the information after X-ray attenuation is converted to electric signal and imports computer system into through data acquisition system (DAS) by detector, and machine system shows after carrying out image reconstruction process as calculated; Detector is face Array Plate detector; In scanning process, x-ray source and detector do parallel lines in opposite directions around detected object and move.

The present invention is directed to medium line detector array fladellum two-dimension image rebuild to study, and can be generalized to three-dimensional image reconstruction.As shown in Figure 2, detector is by equidistantly placing, and theoretical analysis can suppose that detector column is endless, and radiographic source kinematic axis is parallel with detector plane, detected object is placed between radiographic source and detector, and the central point of xoy coordinate system is fixed on the central point that radius is the scanning field of view of R.Given radiographic source position x _i(i=1 ..., I), projection number when wherein I is radiographic source rectilinear motion, the ray being arrived detector cells by scanning field of view center is called position x _ithe central ray at place, θ is the projection angle of the relative x-axis of certain ray under this projection, and γ is the angle of central ray and this ray.S _oradiographic source along the distance at y-axis and scanning object center, S _dradiographic source along the distance of y-axis and detector.Radiographic source is parallel with x-axis with the rectilinear motion of detector.So in 2 dimensional planes, the projection angle θ of the relative x-axis of the X ray through visual field is:

$\mathrm{\&theta;}=\left\{\begin{array}{c}{\tan }^{-1}\left(\frac{S_D}{x_D-x_i}\right),x_i<0,x_i\&NotEqual;x_D\\ \frac{\mathrm{\&pi;}}{2},x_i=x_D\\ \mathrm{\&pi;}-{\tan }^{-1}\left(\frac{S_D}{x_i-x_D}\right),x_i\&GreaterEqual;0,x_i\&NotEqual;x_D\end{array}\right.,---\left(1\right)$

X _dthat scanning field of view center is along the distance between x-axis and detector cells.

If γ=β is-θ, be the angle of the ray and this ray that are projected through scanning field of view center, β=θ _(l=0)for the angle of the ray and x-axis that are projected through scanning field of view center O; Through the X ray of visual field and the distance l of projection centre ray be then:

$l={(x_i^2+S_O^2)}^{\frac{1}{2}}\sin \mathrm{\&gamma;},---\left(2\right)$

In formula (2), the span of parameter l is [-R, R].

The necessary condition that parallel beam CT structure realizes CT image Exact Reconstruction obtains to be no less than 180 ° of parallel projections around scanning field of view.But 1 time straight line parallel moving sweep pattern obviously can not obtain the data for projection being no less than 180 ° of degree scopes.For this reason, the method for available repeatedly straight line parallel moving sweep.Such as, scanned by the isogonism mode that repeatedly parallel lines scans.As shown in Figure 3, we can adopt rectilinear scanning (3T) acquisition of 2 orthogonal rectilinear scannings (2T) or 3 even circumferential distributions to be not less than the data for projection of 180 ° around scanning field of view, wherein Fig. 3 (a) is 2T pattern, and Fig. 3 (b) is 3T pattern.

Radiographic source, detector parallel lines motion CT scan pattern are around the rotary motion of field of detection by radiographic source, detector parallel lines motion simulation radiographic source-detector.Dot in Fig. 3 on each straight line represents a radiogenic projected position of rectilinear scanning motion, and radiographic source projected position is equidistant mode.Obviously, the projection relative scanning visual field that the equidistant projection mode of radiographic source obtains is circumferentially uneven, unfavorable to image reconstruction.Therefore, we obtain the data for projection relative to scanning field of view even circumferential by the radiographic source projection of non-equidistance, i.e. isogonism sample mode.

For isogonism repeatedly parallel lines scan pattern, set a rectilinear scanning and can obtain I X-ray projection data, one time CT scan is realized by T parallel lines scanning, assuming that the projection number M of a CT scan is evenly distributed in the projection angle of equivalence 180 °, reconstruction image array is N × N, then

$I=\frac{M}{T},---\left(3\right)$

$\frac{M}{N}\&ap;\frac{\mathrm{\&pi;}}{2},---\left(4\right)$

If β=θ _(l=0), be the angle of the ray and this ray that are projected through scanning field of view center O.Then can obtain sampling plan:

${\mathrm{\&beta;}}_1={\tan }^{-1}\left(\frac{S_o}{-x_1}\right),---\left(5\right)$

${\mathrm{\&beta;}}_I={\mathrm{\&pi;}-\tan }^{-1}\left(\frac{S_o}{x_I}\right),---\left(6\right)$

$\mathrm{\&Delta;\&beta;}=\frac{1}{I-1}({\mathrm{\&beta;}}_I-{\mathrm{\&beta;}}_1),---\left(7\right)$

x _i＝-S _ocot[β ₁+(i-1)△β]， (8)

Wherein, △ β is the angle between twice projection, and △ β is according to the start position x of radiographic source movement ₁with final position x _icalculate.

Present invention also offers the image rebuilding method of a kind of rectilinear scanning CT.Collimated beam X ray can be represented by line integral through the decay that object is total, even works as conversion

Wherein f (x, y) represents object (or attenuation coefficient distribution of X ray); represent that scanning angle is projection ray and initial point distance are the data for projection of l; δ () represents carat function or impulse function in Di; represent the projection line of X ray.By the Central slice theorem of Fourier transform (FT), namely projection angle is data for projection fourier transform equal the Fourier transform of center slice

F (x, y) can by inverse Fourier transform (1FT) if or antithesis when transform reconstruction out, as follows:

Wherein represent and rebuild image; | w| is called as " jump " wave filter in frequency field; Ramp filter be | the Fourier inversion of w|.

As shown in Figure 4, in fladellum situation, every bar fan beam projections ray corresponding with parallel beam projection ray g (γ, β) of equidirectional, corresponding relation is

Then have

Cartesian coordinates (x, y) is represented, i.e. x=rcos α, y=rsin α with polar coordinates (r, α), and then

What replace variable can specific factor be by formula (12), (13)

$f(r,\mathrm{\&alpha;})={\&Integral;}_{-\frac{\mathrm{\&pi;}}{2}}^{\frac{\mathrm{\&pi;}}{2}}{\&Integral;}_{-\&infin;}^{\&infin;}g(\mathrm{\&gamma;},\mathrm{\&beta;})h(r\cos (\mathrm{\&gamma;}-\mathrm{\&beta;}-\mathrm{\&alpha;}+\frac{\mathrm{\&pi;}}{2})-\sqrt{(x_i^2+S_O^2)}\cos \mathrm{\&gamma;})\sqrt{(x_i^2+S_O^2)}\cos \mathrm{\&gamma;d\&gamma;d\&beta;},---\left(15\right)$

Formula (15) is Fan-beam Reconstruction algorithm.

An image rebuilding method of rectilinear scanning CT, comprises the following steps:

S1: fan beam projections data weighting:

P ^a(x _i,x _D)＝|cosγ|*P(x _i,x _D)， (16)

Wherein P (x _i, x _d) be the data for projection gathered, P ^a(x _i, x _d) be data for projection after weighting.

S2: to weighted projection data filtering:

P ^b(x _i,x _D)＝P ^a(x _i,x _D)*h(x _D)， (17)

Wherein P ^b(x _i, x _d) be filtered data for projection, h (x _d) be ramp filter in spatial domain,

S3: be not less than the back projection in [0, π] scope:

$f(x,y)={\&Integral;}_0^T{\&Integral;}_{x_0}^{x_I}\frac{1}{L^2}{P}^b(x_i,x_D,\mathrm{\&eta;}){\mathrm{dx}}_i\mathrm{d\&eta;}---\left(18\right)$

Wherein, be back projection's coefficient, T is rectilinear scanning number of times, η=1 ..., T.

Utilize MATLAB, we simulate fan beam projections and the FBP image reconstruction of parallel lines CT scan, and table 1 is simulation scanning parameter.

Experiment 1:

Emulation experiment image adopts Shepp-Logan model, as shown in Fig. 5 (a).The field number of scan image is 256mm, and rebuilding image array size is 512 × 512.Obtain following result through simulation scanning and image reconstruction, Fig. 5 (b), (c) are the CT image that 2T and 3T scan mode FBP image reconstruction algorithm obtains respectively.

Experiment 2:

Emulation experiment image adopts newly-designed model 2, and as shown in Fig. 6 (a), the circular hole that the interval striped that model image has several width different is different with several diameter, smallest circle bore dia is a pixel.The field number of scan image is 256mm, and rebuilding image array size is 512 × 512.Obtain following result through simulation scanning and image reconstruction, Fig. 6 (b), (c) are the CT image that 2T and 3T scan mode FBP image reconstruction algorithm obtains respectively.

Emulation experiment confirms FBP image reconstruction feasibility.

Table 1. simulation scanning parameter

What finally illustrate is, above preferred embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although by above preferred embodiment to invention has been detailed description, but those skilled in the art are to be understood that, various change can be made to it in the form and details, and not depart from claims of the present invention limited range.

Claims (9)

1. a rectilinear scanning CT system, is characterized in that: this system comprises x-ray source, detector, detected object, data acquisition system (DAS), image reconstruction Display control computer system, control system and mechanical system;

Described x-ray source sends X ray penetration-detection object, and arrive detector, dampening information is converted to electric signal and imports computer system into through data acquisition system (DAS) by detector, and machine system shows after carrying out image reconstruction process as calculated; Described detector is face Array Plate detector; In scanning process, x-ray source and detector do parallel lines in opposite directions around detected object and move.

2. a kind of rectilinear scanning CT system according to claim 1, is characterized in that: in this scanning system through the projection angle θ that the X ray of visual field is relative be:

$\mathrm{\&theta;}=\left\{\begin{array}{c}{\tan }^{-1}\left(\frac{S_D}{x_D-x_i}\right),x_i<0,x_i\&NotEqual;x_D\\ \frac{\mathrm{\&pi;}}{2},x_i=x_D\\ \mathrm{\&pi;}-{\tan }^{-1}\left(\frac{S_D}{x_i-x_D}\right),x_i\&GreaterEqual;0,x_i\&NotEqual;x_D\end{array}\right.;$

Wherein, S _dfor radiographic source is along the distance of y-axis and detector; x _dthat scanning field of view center is along the distance between x-axis and detector cells; x _ifor radiographic source position, i=1 ..., I, projection number when wherein I is radiographic source rectilinear motion.

3. a kind of rectilinear scanning CT system according to claim 1, is characterized in that: in this scanning system through the X ray of visual field and the distance l of projection centre ray be:

$l={(x_i^2+S_O^2)}^{\frac{1}{2}}\sin \mathrm{\&gamma;};$

Wherein, x _ifor radiographic source position, i=1 ..., I, projection number when wherein I is radiographic source rectilinear motion; S _ofor radiographic source is along the distance at y-axis and scanning field of view center; γ is projected through the ray at scanning field of view center and the angle of this ray, γ=β-θ, β=θ _(l=0)for the angle of the ray and x-axis that are projected through scanning field of view center O; The span of l is [-R, R], and R is the radius of scanning field of view.

4. a kind of rectilinear scanning CT system according to claim 1, is characterized in that: described system adopts the mode of repeatedly straight line parallel moving sweep to scan.

5. a kind of rectilinear scanning CT system according to claim 4, is characterized in that: described system is scanned by the mode of isogonism repeatedly parallel lines scanning, obtains the data for projection being not less than 180 ° around scanning field of view.

6. a kind of rectilinear scanning CT system according to claim 5, is characterized in that: the mode of described isogonism repeatedly parallel lines scanning comprises the rectilinear scanning of 2 orthogonal rectilinear scanning or 3 even circumferential distributions.

7. a kind of rectilinear scanning CT system according to claim 6, it is characterized in that: when described system adopts the isogonism mode that repeatedly parallel lines scans to scan, the data for projection relative to scanning field of view even circumferential is obtained by the radiographic source projection of non-equidistance, i.e. isogonism sample mode, and isogonism sampling plan is:

${\mathrm{\&beta;}}_1={\tan }^{-1}\left(\frac{S_O}{-x_1}\right);{\mathrm{\&beta;}}_I=\mathrm{\&pi;}-{\tan }^{-1}\left(\frac{S_O}{x_I}\right);$

$\mathrm{\&Delta;\&beta;}=\frac{1}{I-1}({\mathrm{\&beta;}}_I-{\mathrm{\&beta;}}_1);$ x _i＝-S _Ocot[β ₁+(i-1)Δβ]；

Wherein, β=θ _(l=0), be the angle of the ray and x-axis that are projected through scanning field of view center O; Δ β is the angle between twice projection, and Δ β is according to the start position x of radiographic source movement ₁with final position x _icalculate.

8. an image rebuilding method of rectilinear scanning CT, is characterized in that: the method comprises the following steps:

S1: carry out fan beam projections data weighting by following formula:

P ^a(x _i,x _D)＝|cosγ|*P(x _i,x _D)；

Wherein, P (x _i, x _d) be the data for projection gathered, P ^a(x _i, x _d) be the data for projection after weighting; x _ifor radiographic source position; x _dfor scanning field of view center is along the distance between x-axis and detector cells, γ is projected through the ray at scanning field of view center and the angle of this ray;

S2: by following formula to weighted projection data filtering:

P ^b(x _i,x _D)＝P ^a(x _i,x _D)*h(x _D)；

Wherein, p ^b(x _i, x _d) be filtered data for projection, h (x _d) be the ramp filter in spatial domain;

S3: back projection:

$f(x,y)={\&Integral;}_0^T{\&Integral;}_{x_0}^{x_I}\frac{1}{L^2}{P}^b(x_i,x_D,\mathrm{\&eta;}){\mathrm{dx}}_i\mathrm{d\&eta;};$

Wherein, for back projection's coefficient, T is rectilinear scanning number of times, η=1 ..., T.

9. the image rebuilding method of a kind of rectilinear scanning CT according to claim 8, is characterized in that: described data for projection is the data for projection relative to scanning field of view even circumferential that the radiographic source projection of non-equidistance obtains; Employing isogonism repeatedly parallel lines scan pattern scans, X ray once projects and can obtain I detection data, one time CT scan is realized by T parallel lines scanning, and the projection number M of a CT scan is evenly distributed on equivalence and is not less than in the projection angle of 180 °, and reconstruction image array is N × N; Wherein,