CN103900931A - Multi-energy-spectrum CT imaging method and imaging system - Google Patents

Abstract

The invention discloses a multi-energy-spectrum CT imaging method and an imaging system. The multi-energy-spectrum CT imaging method comprises the following steps: scanning the object to be detected, and reconstructing the density image of a basic material so as to finally obtain the electron density and equivalent atomic number distribution of the object to be detected or linear attenuation coefficient distribution of the object under the radiation of mono-energetic X-rays. The multi-energy-spectrum CT reconstruction method comprises the following steps: assigning an initial value for the density image of a basic material to be reconstructed; carrying out orthographic projection on an estimated image so as to obtain a projection estimated value; estimating the error of the reconstructed image; updating the image by utilizing the estimated error of the reconstructed image, and repeating the steps mentioned above until the reconstructed density image is convergent. The multi-energy-spectrum CT imaging system comprises a scanning module, a reconstruction module, and a statistics module, wherein the reconstruction module comprises an initializing module, a projecting module, a correcting module, and an updating module.

Description

A kind of multi-power spectrum CT formation method and imaging system

Technical field

The present invention relates to radiant image field, be specifically related to a kind of multi-power spectrum X ray CT formation method.

Background technology

Traditional X-ray ray CT uses an X-ray energy spectrum to scan testee.Rebuild the CT value of image relevant with material, the density of testee, also relevant with the power spectrum of X ray.So the reconstruction image of different material may have same or analogous CT value.This just makes traditional CT to distinguish it.But multi-power spectrum CT uses multiple power spectrums to scan testee, therefore can obtain the information of more testees.Utilize these information can rebuild testee equivalent atom ordinal sum electron density image, or rebuild the density image of sill.Multi-power spectrum CT is in bone density measurement, PET attenuation correction, marrow constituent analysis, and the fields such as oil core analysis, safety inspection are with a wide range of applications.

Multi-power spectrum CT Problems of Reconstruction is a nonlinear problem.The research of relevant method for reconstructing starts from eighties of last century the seventies.Comparatively conventional method for reconstructing has at present: pre-treatment method for reconstructing and aftertreatment method for reconstructing.Pre-treatment method for reconstructing is the projection value that the first multi-power spectrum projection being obtained by reality estimates sill density image, then utilizes classic method to rebuild to obtain the density image of sill.Aftertreatment method for reconstructing is that the many groups multi-power spectrum projection first reality being obtained is rebuild respectively, then carries out linear combination to obtain the density image of sill to rebuilding image.In these two class methods, all adopt the method for fitting of a polynomial to estimate the projection value of sill density image or the density image of sill.The precision of matching can be subject to the impact of the factors such as die body shape, size, material, and therefore reconstruction quality is difficult to ensure.

Summary of the invention

The object of the invention is to solve the not high problem of reconstruction quality existing in existing multi-power spectrum CT image reconstruction process, a kind of multi-power spectrum CT formation method and imaging system that can accurately realize image reconstruction is provided.

For reaching above-mentioned purpose, the present invention proposes a kind of multi-power spectrum CT formation method, comprises the following steps:

S1: utilize multi-power spectrum X ray to scan testee, obtain polychrome projection actual value;

S2: according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee;

S3: the electron density, the equivalent atom ordinal number that obtain testee according to the reconstruction density image of each sill distribute or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry.

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, described step S2 comprises:

S21: be the reconstruction density image initialize of each sill, as the reconstruction density image estimated value of each sill;

S22: the reconstruction density image estimated value to described each sill is carried out orthogonal projection, obtains the polychrome projection estimated value of each sill;

S23: calculate the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill;

S24: utilize the error update of the reconstruction density image estimated value of the each sill of gained to rebuild the density image of each sill;

S25: repeating step S22-S24, until the convergence of the density image of each sill of rebuilding.

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, it described in step S21, is the reconstruction density image initialize of each sill, refer to that the image of selecting based on projection or the reconstruction of the method for reconstructing based on image is as initial pictures, or using 0 as initial pictures, in image, each pixel value is 0.

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, the orthogonal projection process of step S22 is nonlinear, its formula is

$p_{k,i}^{\left(n\right)}=-\ln \underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}},$

Wherein

with

be respectively the estimated value of two kinds of sill density images, R _ifor the projection vector corresponding to i article of ray,

represent the discrete form of k normalization power spectrum, M _krepresent the number of element after k power spectrum discretize,

with

represent respectively the discrete form of two kinds of sill mass attenuation coefficients.

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, utilizes projection P in step S23 _{k, i}the error formula of the reconstruction image of estimating is

${\stackrel{\→}{e}}_g^{\left(n\right)}=\frac{{\mathrm{\Φ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

${\stackrel{\→}{e}}_g^{\left(n\right)}=\frac{{\mathrm{\Θ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

Wherein

${\mathrm{\Φ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\φ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

${\mathrm{\Θ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\θ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, the formula that upgrades reconstruction image in step S24 is

${\stackrel{\→}{f}}^{(n+1)}={\stackrel{\→}{f}}^{\left(n\right)}+{\stackrel{\→}{e}}_f^{\left(n\right)},$

${\stackrel{\→}{g}}^{(n+1)}={\stackrel{\→}{g}}^{\left(n\right)}+{\stackrel{\→}{e}}_g^{\left(n\right)}.$

A kind of multi-power spectrum CT formation method that the present invention proposes, wherein, in step S3, the formula of electron gain density image and equivalent atom ordinal number image is

$\stackrel{\→}{\mathrm{\ρ}}=\stackrel{\→}{f}\·{\mathrm{\ρ}}_f+\stackrel{\→}{g}\·{\mathrm{\ρ}}_g$

$\stackrel{\→}{Z}=\stackrel{\→}{f}\·Z_f+\stackrel{\→}{g}\·Z_g$

Wherein represent the electron density image of testee, ρ _fand ρ _grepresent respectively the electron density of sill;

the equivalent atom ordinal number that represents testee distributes, Z _fand Z _grepresent respectively the atomic number of sill;

The formula of the Single energy X ray absorptionmetry linear attenuation coefficient that acquisition testee is E to energy is

$\stackrel{\→}{l}\left(E\right)=\stackrel{\→}{f}\·a_f\left(E\right)+\stackrel{\→}{g}\·a_g\left(E\right)$

Wherein a _fand a (E) _g(E) be respectively the mass attenuation coefficient of sill.

Meanwhile, the present invention also proposes a kind of multi-power spectrum CT imaging system, comprising:

Scan module, to testee scanning, to obtain polychrome projection actual value;

Rebuild module, be connected with described scan module, according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee;

Statistical module: be connected with described reconstruction module, obtain electron density and the distribution of equivalent atom ordinal number or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry of testee according to the reconstruction density image of each sill.

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, described reconstruction module comprises:

Initialization module is the reconstruction density image initialize of each sill, as the reconstruction density image estimated value of each sill;

Projection module, is connected with described initialization module, and the reconstruction density image estimated value of described each sill is carried out to orthogonal projection, obtains the polychrome projection estimated value of each sill;

Correction module, is connected with described projection module, calculates the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill;

Update module, is connected with described correction module, utilizes the error of the reconstruction density image estimated value of the each sill of gained, upgrades the density image of rebuilding each sill through iteration repeatedly.

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, described initialization module is by selecting the image of rebuilding based on projection or based on the method for reconstructing of image as initial pictures, or carrys out initialize using 0 as initial pictures.

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, the orthogonal projection process of described projection module is nonlinear, its formula is

$p_{k,i}^{\left(n\right)}=-\ln \underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}},$

Wherein

with

be respectively the estimated value of two kinds of sill density images, R _ifor the projection vector corresponding to i article of ray,

represent the discrete form of k normalization power spectrum, M _krepresent the number of element after k power spectrum discretize,

with

represent respectively the discrete form of two kinds of sill mass attenuation coefficients.

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, utilizes projection P in described correction module _{k, i}the error formula of the reconstruction image of estimating is

${\stackrel{\→}{e}}_f^{\left(n\right)}=\frac{{\mathrm{\Φ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

${\stackrel{\→}{e}}_g^{\left(n\right)}=\frac{{\mathrm{\Θ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

Wherein

${\mathrm{\Φ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\φ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

${\mathrm{\Θ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\θ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, the formula that upgrades reconstruction image in described update module is

${\stackrel{\→}{f}}^{(n+1)}={\stackrel{\→}{f}}^{\left(n\right)}+{\stackrel{\→}{e}}_f^{\left(n\right)},$

${\stackrel{\→}{g}}^{(n+1)}={\stackrel{\→}{g}}^{\left(n\right)}+{\stackrel{\→}{e}}_g^{\left(n\right)}.$

A kind of multi-power spectrum CT imaging system that the present invention proposes, wherein, in described statistical module, the formula of electron gain density image and equivalent atom ordinal number image is

$\stackrel{\→}{\mathrm{\ρ}}=\stackrel{\→}{f}\·{\mathrm{\ρ}}_f+\stackrel{\→}{g}\·{\mathrm{\ρ}}_g$

$\stackrel{\→}{Z}=\stackrel{\→}{f}\·Z_f+\stackrel{\→}{g}\·Z_g$

Wherein

represent the electron density image of testee, ρ _fand ρ _grepresent respectively the electron density of sill;

the equivalent atom ordinal number that represents testee distributes, Z _fand Z _grepresent respectively the atomic number of sill;

The formula of the Single energy X ray absorptionmetry linear attenuation coefficient that acquisition testee is E to energy is

$\stackrel{\→}{l}\left(E\right)=\stackrel{\→}{f}\·a_f\left(E\right)+\stackrel{\→}{g}\·a_g\left(E\right)$

Wherein a _fand a (E) _g(E) be respectively the mass attenuation coefficient of sill.

Compared with prior art, beneficial effect of the present invention is:

The present invention has taken into full account that X-ray machine sends the energy spectrum characteristics of X ray, and is joined in reconstruction algorithm, thereby can Exact Reconstruction goes out the image of testee sill.By utilizing iteration characteristic, the inventive method can be used in conventional various scan patterns.In addition, the inventive method has the concurrency of height, is suitable for graphic process unit or other hardware devices and accelerates.

Brief description of the drawings

Fig. 1 is the process flow diagram of multi-power spectrum CT formation method of the present invention;

Fig. 2 is the process flow diagram of reconstruction density image method of the present invention;

Fig. 3 is experiment FAULT MODEL image.

The polychrome data for projection gathering under the different tube voltages of Fig. 4, wherein (a) data for projection for gathering under 80kV tube voltage; (b) data for projection for gathering under 140kV tube voltage

Fig. 5 is experiment X-ray energy spectrum.

Fig. 6 density is 1.0g/cm ³water and density be 1.8g/cm ³the mass attenuation coefficient curve of bone.

The sill density image that Fig. 7 rebuilds, wherein (a) is water base image, is (b) bone base image.This figure is the reconstructed results after completing steps A2.

Fig. 8 is the linear attenuation coefficient image corresponding to 50keV energy X ray.

Fig. 9 is the composition structural drawing of multi-power spectrum CT imaging system of the present invention.

Description of reference numerals: 10-scan module; 20-rebuilds module; 21-initialization module; 22-projection module; 23-correction module; 24-update module; 30-statistical module.

Embodiment

Below in conjunction with accompanying drawing, just above-mentioned technical characterictic and the advantage with other of the present invention is described further.

Refer to Fig. 1, the process flow diagram of multi-power spectrum CT formation method proposing for the present invention.As seen from Figure 1, multi-power spectrum formation method of the present invention comprises the following steps:

S1: utilize multi-power spectrum X ray to scan testee, obtain polychrome projection actual value;

S2: according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee;

S3: the electron density, the equivalent atom ordinal number that obtain testee according to the reconstruction density image of each sill distribute or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry.

The multi-power spectrum CT formation method that the present invention proposes is actually the mode that pushes away correction by counter, progressively approaches, thereby reaches the object of rebuilding image.First by step S1, testee is scanned, to obtain the projection value of testee reality.Then taking this actual projection value as benchmark, carry out the density image process of reconstruction of each sill by step S2.Finally, according to the sill density image of rebuilding, the information such as further electron density, the distribution of equivalent atom sequence or the linear attenuation coefficient distribution to Single energy X ray absorptionmetry of calculating acquisition testee, thus carry out various analysis judgements according to above-mentioned information.

Wherein, multi-power spectrum of the present invention refers to the X ray containing two or more power spectrums.Multi-power spectrum CT formation method of the present invention is a kind of nonlinear iteration method for reconstructing, is applicable to how much one situations of making peace how much inconsistent scannings.So-called how much consistent scannings, refer to the scanning that can obtain the projection under the different power spectrums in every X ray path.

Please continue to refer to Fig. 2, for rebuilding the detail flowchart of density image process described in above-mentioned steps S2.As shown in Figure 2, the reconstruction density image that obtains each sill in testee mainly comprises the following steps:

S21: be the reconstruction density image initialize of each sill, as the reconstruction density image estimated value of each sill;

S22: the reconstruction density image estimated value to described each sill is carried out orthogonal projection, obtains the polychrome projection estimated value of each sill;

S23: calculate the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill;

S24: utilize the error update of the reconstruction density image estimated value of the each sill of gained to rebuild the density image of each sill;

S25: repeating step S22-S24, until the convergence of the density image of each sill of rebuilding.

The specific implementation process of multi-power spectrum CT formation method of the present invention is described by a specific embodiment below.

Fig. 3 is die body shape used in the present embodiment.The present embodiment adopts the mode of twice sweep to obtain two groups of polychrome data for projection.The tube voltage that first X-ray tube is set is 80kV, and scanning testee obtains first group of polychrome data for projection, as shown in Figure 4 (a); Then the tube voltage of adjusting X-ray tube is 140kV, installs 1mm copper filter plate additional before X-ray tube simultaneously, again scans testee and obtains second group of polychrome data for projection, as shown in Figure 4 (b).

The X-ray energy spectrum that in twice sweep, X-ray tube sends as shown in Figure 5.The sweep parameter of system is: radiographic source is 1300mm to the distance of detector, and radiographic source is 1000mm to the distance at turntable center, and line detector is made up of the spy unit of 1024 0.03mm.Every group of polychrome data for projection is of a size of 1024 × 720.

Complete after scanning, carry out density image reconstruction according to the method described in S2.First choose suitable sill, what in the present embodiment, sill was selected is that density is 1.0g/cm ³water and density be 1.8g/cm ³bone, rebuilding image size is 1024 × 1024.Respectively X-ray energy spectrum and sill mass attenuation coefficient (see figure 6) are sampled and obtained with the sampling interval of 1kV and 1keV

with

Concrete implementation step is as follows:

1) be image initialize to be reconstructed

2) establish through the inferior iteration of n (>=0) and tried to achieve

with

to given power spectrum k and ray i, will

with

substitution formula (1) and formula (3), calculate

with

3) will try to achieve

with

substitution formula (2), calculates

with

4) will try to achieve

with

substitution formula (4) obtains the new estimated value of two kinds of sill images

with

5) to different power spectrum k and ray i, repeating step 2)-4) until two kinds of sill image convergences.

The sill image of rebuilding as shown in Figure 7.So far, the present embodiment has successfully obtained the Exact Reconstruction density image of water and bone.

Further, utilize the sill density image of rebuilding can calculate the linear attenuation coefficient image of testee to Single energy X ray absorptionmetry.Method is by the product summation of the water base image of rebuilding and the product of the x-ray photon mass attenuation coefficient of water to prescribed energy and the bone base image of reconstruction and the x-ray photon mass attenuation coefficient of bone to prescribed energy.Fig. 8 has provided the linear attenuation coefficient image of the photon that model is 50keV about energy.

In addition, the present invention also provides a kind of multi-power spectrum CT imaging system.Referring to Fig. 9, is the composition structural drawing of multi-power spectrum CT imaging system of the present invention, comprises scan module 10, rebuilds module 20 and statistical module 30.Wherein scan module 10 is for testee being carried out to the scanning of multi-power spectrum X ray, to obtain the actual value of polychrome projection; Rebuild module 20 and be connected with described scan module 10, according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee; Statistical module 30 is connected with described reconstruction module 20, obtains electron density and the distribution of equivalent atom ordinal number or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry of testee according to the reconstruction density image of each sill.

Particularly, rebuild module 20 and comprise again initialization module 21, projection module 22, correction module 23 and update module 24.Wherein initialization module 21 is used to the reconstruction density image initialize of each sill, using the reconstruction density image estimated value as each sill; Be generally by selecting the image of rebuilding based on projection or based on the method for reconstructing of image as initial pictures, or carry out initialize using 0 as initial pictures.

Projection module 22 is connected with described initialization module 21, and the reconstruction density image estimated value of described each sill is carried out to orthogonal projection, obtains the polychrome projection estimated value of each sill.Described orthogonal projection process is nonlinear.

Correction module 23 is connected with described projection module 22, calculates the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill.

Update module 24 is connected with described correction module, utilizes the error of the reconstruction density image estimated value of the each sill of gained, upgrades the density image of rebuilding each sill through iteration repeatedly.

More than explanation is just illustrative for the purpose of the present invention, and nonrestrictive, those of ordinary skill in the art understand; in the case of not departing from the spirit and scope that following claims limit, can make many amendments, change; or equivalence, but all will fall within the scope of protection of the present invention.

Claims (14)

1. a multi-power spectrum CT formation method, is characterized in that, comprises the following steps:

S1: utilize multi-power spectrum X ray to scan testee, obtain polychrome projection actual value;

S2: according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee;

S3: obtain electron density and the distribution of equivalent atom ordinal number or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry of testee according to the reconstruction density image of each sill.

2. a kind of multi-power spectrum CT formation method according to claim 1, is characterized in that, described step S2 comprises:

S21: be the reconstruction density image initialize of each sill, as the reconstruction density image estimated value of each sill;

S22: the reconstruction density image estimated value to described each sill is carried out orthogonal projection, obtains the polychrome projection estimated value of each sill;

S23: calculate the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill;

S24: utilize the error update of the reconstruction density image estimated value of the each sill of gained to rebuild the density image of each sill;

S25: repeating step S22-S24, until the convergence of the density image of each sill of rebuilding.

3. a kind of multi-power spectrum CT formation method according to claim 2, it is characterized in that, it described in step S21, is the reconstruction density image initialize of each sill, refer to that the image of selecting based on projection or the reconstruction of the method for reconstructing based on image is as initial pictures, or using 0 as initial pictures, in image, each pixel value is 0.

4. a kind of multi-power spectrum CT formation method according to claim 2, is characterized in that, the orthogonal projection process of step S22 is nonlinear, and its formula is

$p_{k,i}^{\left(n\right)}=-\ln \underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}},---\left(1\right)$

Wherein

with

be respectively the estimated value of two kinds of sill density images, R _ifor the projection vector corresponding to i article of ray, represent the discrete form of k normalization power spectrum, M _krepresent the number of element after k-power spectrum discretize,

with

represent respectively the discrete form of two kinds of sill mass attenuation coefficients.

5. a kind of multi-power spectrum CT formation method according to claim 2, is characterized in that, utilizes projection P in step S23 _k,ithe error formula of the reconstruction image of estimating is

${\stackrel{\→}{e}}_f^{\left(n\right)}=\frac{{\mathrm{\Φ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

$\left(2\right)$

${\stackrel{\→}{e}}_g^{\left(n\right)}=\frac{{\mathrm{\Θ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

Wherein

${\mathrm{\Φ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\φ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

$\left(3\right)$

${\mathrm{\Θ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\θ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

represent vectorial R _itransposition.

6. a kind of multi-power spectrum CT formation method according to claim 2, is characterized in that, the formula that upgrades reconstruction image in step S24 is

${\stackrel{\→}{f}}^{(n+1)}={\stackrel{\→}{f}}^{\left(n\right)}+{\stackrel{\→}{e}}_f^{\left(n\right)},$

$\left(4\right)$

${\stackrel{\→}{g}}^{(n+1)}={\stackrel{\→}{g}}^{\left(n\right)}+{\stackrel{\→}{e}}_g^{\left(n\right)}.$

7. a kind of multi-power spectrum CT formation method according to claim 1, is characterized in that, in step S3, the formula of electron gain density image and equivalent atom ordinal number image is

$\stackrel{\→}{\mathrm{\ρ}}=\stackrel{\→}{f}\·{\mathrm{\ρ}}_f+\stackrel{\→}{g}\·{\mathrm{\ρ}}_g---\left(5\right)$

$\stackrel{\→}{Z}=\stackrel{\→}{f}\·Z_f+\stackrel{\→}{g}\·Z_g---\left(6\right)$

Wherein

represent the electron density image of testee, ρ _fand ρ _grepresent respectively the electron density of sill; the equivalent atom ordinal number that represents testee distributes, Z _fand Z _grepresent respectively the atomic number of sill;

The formula of the Single energy X ray absorptionmetry linear attenuation coefficient that acquisition testee is E to energy is

$\stackrel{\→}{l}\left(E\right)=\stackrel{\→}{f}\·a_f\left(E\right)+\stackrel{\→}{g}\·a_g\left(E\right)---\left(7\right)$

Wherein a _fand a (E) _g(E) be respectively the mass attenuation coefficient of sill.

8. a multi-power spectrum CT imaging system, is characterized in that, comprising:

Scan module, to testee scanning, to obtain polychrome projection actual value;

Rebuild module, be connected with described scan module, according to real polychrome data for projection, obtain the reconstruction density image of each sill in testee;

Statistical module: be connected with described reconstruction module, obtain electron density and the distribution of equivalent atom ordinal number or the linear attenuation coefficient distribution of testee to Single energy X ray absorptionmetry of testee according to the reconstruction density image of each sill.

9. a kind of multi-power spectrum CT imaging system according to claim 8, is characterized in that, described reconstruction module comprises:

Initialization module is the reconstruction density image initialize of each sill, as the reconstruction density image estimated value of each sill;

Projection module, is connected with described initialization module, and the reconstruction density image estimated value of described each sill is carried out to orthogonal projection, obtains the polychrome projection estimated value of each sill;

Correction module, is connected with described projection module, calculates the error between polychrome projection estimated value and the polychrome projection actual value of each sill, to obtain the error of reconstruction density image estimated value of each sill;

Update module, is connected with described correction module, utilizes the error of the reconstruction density image estimated value of the each sill of gained, upgrades the density image of rebuilding each sill through iteration repeatedly.

10. a kind of multi-power spectrum CT imaging system according to claim 9, it is characterized in that, described initialization module is by selecting the image of rebuilding based on projection or based on the method for reconstructing of image as initial pictures, or carrys out initialize using 0 as initial pictures.

11. a kind of multi-power spectrum CT imaging systems according to claim 9, is characterized in that, the orthogonal projection process of described projection module is nonlinear, and its formula is

$p_{k,i}^{\left(n\right)}=-\ln \underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}},$

Wherein

with

be respectively the estimated value of two kinds of sill density images, R _ifor the projection vector corresponding to i article of ray,

represent the discrete form of k normalization power spectrum, M _krepresent the number of element after k power spectrum discretize,

with

represent respectively the discrete form of two kinds of sill mass attenuation coefficients.

12. a kind of multi-power spectrum CT imaging systems according to claim 9, is characterized in that, in described correction module, utilize projection P _{k, i}the error formula of the reconstruction image of estimating is

${\stackrel{\→}{e}}_f^{\left(n\right)}=\frac{{\mathrm{\Φ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

${\stackrel{\→}{e}}_g^{\left(n\right)}=\frac{{\mathrm{\Θ}}_{k,i}^{\left(n\right)}}{{\left({\mathrm{\Φ}}_{k,i}^{\left(n\right)}\right)}^2+{\left({\mathrm{\Θ}}_{k,i}^{\left(n\right)}\right)}^2}\frac{R_i^{\mathrm{\τ}}{q}_{k,i}^{\left(n\right)}(p_{k,i}-p_{k,i}^{\left(n\right)})}{{\left|R_i\right|}^2},$

Wherein

${\mathrm{\Φ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\φ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

${\mathrm{\Θ}}_{k,i}^{\left(n\right)}=\underset{m=1}{\overset{M_k}{\mathrm{\Σ}}}{S}_{k,m}{\mathrm{\θ}}_m{e}^{-{\mathrm{\φ}}_m{R}_i{\stackrel{\→}{f}}^{\left(n\right)}-{\mathrm{\θ}}_m{R}_i{\stackrel{\→}{g}}^{\left(n\right)}}$

13. a kind of multi-power spectrum CT imaging systems according to claim 9, is characterized in that, the formula that upgrades reconstruction image in described update module is

${\stackrel{\→}{f}}^{(n+1)}={\stackrel{\→}{f}}^{\left(n\right)}+{\stackrel{\→}{e}}_f^{\left(n\right)},$

${\stackrel{\→}{g}}^{(n+1)}={\stackrel{\→}{g}}^{\left(n\right)}+{\stackrel{\→}{e}}_g^{\left(n\right)}.$

14. a kind of multi-power spectrum CT imaging systems according to claim 8, is characterized in that, in described statistical module, the formula of electron gain density image and equivalent atom ordinal number image is

$\stackrel{\→}{\mathrm{\ρ}}=\stackrel{\→}{f}\·{\mathrm{\ρ}}_f+\stackrel{\→}{g}\·{\mathrm{\ρ}}_g$

$\stackrel{\→}{Z}=\stackrel{\→}{f}\·Z_f+\stackrel{\→}{g}\·Z_g$

Wherein

represent the electron density image of testee, ρ _fand ρ _grepresent respectively the electron density of sill;

the equivalent atom ordinal number that represents testee distributes, Z _fand Z _grepresent respectively the atomic number of sill;

The formula of the Single energy X ray absorptionmetry linear attenuation coefficient that acquisition testee is E to energy is

$\stackrel{\→}{l}\left(E\right)=\stackrel{\→}{f}\·a_f\left(E\right)+\stackrel{\→}{g}\·a_g\left(E\right)$

Wherein a _fand a (E) _g(E) be respectively the mass attenuation coefficient of sill.

Images