CN105675631A - Fast fan-beam geometric phase contrast CT imaging device and method - Google Patents

Abstract

The invention discloses a fast fan-beam geometric phase contrast CT imaging device and method. The phase contrast CT imaging device comprises an X light source, a phase grating, a sample platform, an analysis grating and a detector. The device and the method provided by the invention adopt a cylindrical optical element, and can realize large view-field imaging under the illumination of a conventional X light source. By utilizing the cylindrical optical element geometrically matching with light rays, the problem of blockage of large-incident angle rays can be avoided, the imaging view field is greatly improved, at the same time, by combining the dimetric projection idea, under a traditional CT scanning mode, the phase information of an object can be successfully extracted, and fast phase contrast CT imaging can be completed.

Description

A kind of quickly fan-beam geometric phase contrast CT image-forming apparatus and method

Technical field

The present invention relates to X-ray technical field of imaging, particularly to one quick fan-beam geometric phase contrast CT image-forming apparatus and method.

Background technology

Since roentgen finds X-ray, X-ray is widely used in the field such as medical image, industrial nondestructive testing, but, traditional X-ray light absorbs imaging, and the soft-tissue imaging effect that atomic is low is undesirable. Under X-ray irradiates, the refractive index of object can be n=1-δ-i β with complex representation, and wherein δ is refractive index real part reduction amount, β is imaginary index. Along with atomic reduces, δ and β reduces therewith, and so at hard X-ray wave band, the refractive index real part reduction amount δ of low atomic soft tissue is about 1000 times of imaginary index β. Therefore, the phase information utilizing object can obtain the image higher than absorption image contrast in theory.

At present, X-ray phase contrast imaging has been developed in five kinds of formation methods: coaxial phase-contrast imaging method, crystal interferometer formation method, analyzing crystal formation method, optical grating contrast formation method and edge light formation method. Optical grating contrast formation method, owing to light source coherence is required the features such as relatively low and imaging viewing field is bigger, is widely studied in recent years. Traditional optical grating contrast formation method utilizes phase stepping method to complete information and separates and extract, but phase stepping method needs transverse shifting grating and CT scan mode incompatible, cause the drawbacks such as phase contrast CT imaging time length, dosage are high, it is impossible to dynamic organization's imagings such as hearts. 2010, Zhu Peiping researchers etc. publish a kind of quick optical grating contrast formation method (PNAS107 of table in institute of NAS, 13576 13581,2010) i.e. positive back projection method, the method successfully applies for a patent CN102325498B simultaneously, right the method can be only applied to parallel beam illumination geometry, is generally synchrotron radiation X light source, largely limits its practical application. If positive back projection thought can be applied to the illumination of fan-beam geometry, the application of phase contrast CT will be greatly promoted.

Summary of the invention

It is an object of the invention to propose a kind of quickly fan-beam geometric phase contrast CT image-forming apparatus and method, be particularly suited for imaging of medical and food inspection. Under conventional CT scans mode, it is obtained in that phase contrast information, and then realizes quick phase contrast CT.

The technical solution used in the present invention is:

A kind of quickly fan-beam geometric phase contrast CT image-forming device, for object carries out three-dimensional phase contrast imaging, this device includes X source, example platform, phase grating, analysis grating and detector successively along light path, wherein:

X source, for launching X-ray to object to be detected;

Example platform, is used for fixing object;

Phase grating, for π phase-shifted grating or pi/2 phase shift grating, for modulating the Wave-front phase of incident X-rays;

Analyze grating, for absorption grating, produce large period Moire fringe with phase grating from image, it is simple to low resolution detector detecting object information;

Detector, for recording the X-ray intensity by object and optical system.

Preferably, described X source is hard X-ray discharger.

Preferably, described phase grating, analyze screen periods less than 10 μm.

Described detector pixel unit size ranges for 20 μm～100 μm.

Preferably, phase grating, analyze grating dutycycle be 0.5.

Phase grating, analysis grating and detector are cylindrical optical element.

The radius of curvature of phase grating is R₁, be positioned at X source be initial point, R₁For on the circular arc of radius, the radius of curvature analyzing grating is R₂, and be positioned at X source be initial point, R₂For on the circular arc of radius.

Further, phase grating and analysis screen periods meetRelation, wherein d₁For phase grating cycle, d₂For analyzing screen periods, R₁And R₂Respectively X source is to phase grating and phase grating to the distance analyzed between grating. Phase grating and analysis grating space R₂Meet Talbot distance $R_2=\frac{{\mathrm{Nd}}_1{d}_2}{2\mathrm{\η}\mathrm{\λ}}N=1,3,5,\mathrm{7...}$

When phase grating produces pi/2 phase shift, η=1; When phase grating produces π phase shift, η=2. N is that Talbot is from imaging level time, d₁For phase grating cycle, d₂For analyzing screen periods, λ is X-ray wavelength.

A kind of quickly fan-beam geometric phase contrast CT image-forming method, comprises the steps:

A) do not put in object situation, along the equidistant travel(l)ing phase grating (G of one Cycle Length of place circular arc₁) or η Cycle Length equidistantly mobile analysis grating (G₂), it is thus achieved that displacement and intensity image, useRepresent, wherein x_gFor the relative displacement between phase grating and analysis grating;

B) find the median point of displacement curve, and phase grating is transferred to, with analyzing grating relative position, the abscissa positions x that median point is corresponding₀;

C) object is fixed on example platform, rotation platform or the whole imaging device beyond platform one week, at interval of 1 degree, detector records subject image;

D) after device and object rotate against one week, can calculating each projection view angles, projection view angles scope is more than π+2 α_maxAccurate Reconstruction can be realized, the absorption image A and refraction image θ of object_r

$\begin{array}{c}{\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\mathrm{\μ}(x,y,z)dr=1n\left(\frac{2S\left({\mathrm{\α}}_g\right)I_0}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}\right)=A(\mathrm{\α},\mathrm{\φ},z)\\ -{\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\frac{\∂\mathrm{\δ}(x,y,z)}{r\∂\mathrm{\ϵ}}dr=\frac{R_1}{{\mathrm{CR}}_0}\frac{I(\mathrm{\α},\mathrm{\φ},z)-I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)})={\mathrm{\θ}}_r(\mathrm{\α},\mathrm{\φ},z)\end{array}$

Wherein, μ is the linear absorption coefficient of object, and δ is object refractive index real part reduction amount, α and α_gFor fan angle, α_maxFor maximum fan-angle, φ is rotary viewing angle, I₀Detector (D) direct-recording intensity during for not having any optical element and object in the middle of light source (S) and detector (D), the intensity that when I is image objects, detector (D) records,It it is a constant;

E) filtered back-projection method or other three-dimensional reconstruction method is used to rebuild absorption image and refraction image.

Preferably, step (a) intermediate reach moves step number more than three.

Beneficial effect:

The present invention utilizes and the cylindrical optical element of fan-beam geometric match, it is to avoid the problem that big angle of incidence ray is blocked, and substantially increases imaging viewing field. In combination with dimetric projection thought, under conventional CT scans pattern, successfully extract the phase information of object, and then complete quick phase contrast CT imaging.

Accompanying drawing explanation

Fig. 1 quick fan-beam geometric phase contrast CT image-forming device schematic diagram;

Fig. 2 is quick fan-beam geometric phase contrast CT image-forming method flow diagram;

Fig. 3 is conjugation ray schematic diagram calculation of the present invention;

Fig. 4 object model constituent figure;

Fig. 5 three-dimensional reconstruction analog result figure;

Fig. 6 is dotted line position theoretical value and extraction of values comparison diagram in refraction angle projection sinogram 5 (c);

Fig. 7 is for absorbing dotted line position theoretical value and extraction of values comparison diagram in projection sinogram 5 (d);

Fig. 8 is dotted line position theoretical value and reconstruction value comparison diagram in refractive index real part reduction amount reconstruction result 5 (e);

Fig. 9 is dotted line position theoretical value and reconstruction value comparison diagram in imaginary index reconstruction result 5 (f).

Detailed description of the invention

When the hard X-ray illumination of optical grating contrast imaging, the absorption grating in imaging system needs bigger thickness, causes that depth-width ratio is very big. During the illumination of fan-beam geometry, large ratio of height to width plane grating will stop big angle of incidence ray, seriously restrict imaging viewing field.

As it is shown in figure 1, the quick fan-beam geometric phase contrast imaging device of the present invention includes X source S, phase grating G₁, example platform P, analyze grating G₂And detector D. Phase grating G₁, analyze grating G₂It is cylinder elements with detector D, and its radius of curvature is equal to the distance between itself and light source.

Quick fan-beam geometric phase contrast imaging method of the present invention can be completed by flow process shown in Fig. 2: first under not putting object situation, along analyzing grating G within η cycle₂Place circular arc is equidistantly mobile analyzes grating G₂20 steps, record detector image, and with relative position for abscissa, light intensity is that vertical coordinate obtains displacement curve; Find displacement curve median point position, grating relative position is fixed on this some correspondence abscissa positions; Whole imaging device beyond rotating object platform P or object platform P one week, records the intensity image of detector at interval of 1 degree of angle; As shown in Figure 3 ray I (α, φ, z) and ray I (-α, φ+π+2 α, z) conjugate relation each other, rotary sample, after one week, can calculate the absorption image A and refraction image θ of object under each projection view angles φ by following formula_r,

$\begin{array}{c}{\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\mathrm{\μ}(x,y,z)dr=1n\left(\frac{2S\left({\mathrm{\α}}_g\right)I_0}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}\right)=A(\mathrm{\α},\mathrm{\φ},z)\\ -{\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\frac{\∂\mathrm{\δ}(x,y,z)}{r\∂\mathrm{\α}}dr=\frac{R_1}{{\mathrm{CR}}_0}\frac{I(\mathrm{\α},\mathrm{\φ},z)-I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)})={\mathrm{\θ}}_r(\mathrm{\α},\mathrm{\φ},z)\end{array}$

Finally, the 3-D view of following filtered back-projection method reconstruct refractive index real part reduction amount and imaginary part is used.

$\mathrm{\μ}(x,y,z)=\underset{0}{\overset{2\mathrm{\π}}{\∫}}\frac{I}{L^2}\[A(\mathrm{\α},\mathrm{\φ},z)R_{0}cos\mathrm{\α}\]*\frac{{\mathrm{\α}}^2}{{\sin }^2\left(\mathrm{\α}\right)}H\left(\mathrm{\α}\right){|}_{\mathrm{\α}={\mathrm{\α}}_0}d\mathrm{\φ}$

$\mathrm{\δ}(x,y,z)=-\underset{0}{\overset{2\mathrm{\π}}{\∫}}\frac{I}{L}\[{\mathrm{\θ}}_r(\mathrm{\α},\mathrm{\φ},z)R_{0}cos\mathrm{\α}\]*\frac{1}{sin\left(\mathrm{\α}\right)}I\left(\mathrm{\α}\right){|}_{\mathrm{\α}=\mathrm{\α}0}d\mathrm{\φ}$

$L=\sqrt{{R^2}_0+x^2+y^2+2R_0(xsin\mathrm{\φ}-ycos\mathrm{\φ})}$

$H\left(\mathrm{\α}\right)=\underset{-\mathrm{\∞}}{\overset{\mathrm{\∞}}{\∫}}\left|\mathrm{\ρ}\right|e^{j2\mathrm{\π}\mathrm{\α}\mathrm{\ρ}}d\mathrm{\ρ}$

$I\left(\mathrm{\α}\right)=\underset{-\mathrm{\∞}}{\overset{\mathrm{\∞}}{\∫}}\frac{\left|\mathrm{\ρ}\right|}{2\mathrm{\π}j\mathrm{\ρ}}{e}^{j2\mathrm{\π}\mathrm{\α}\mathrm{\ρ}}d\mathrm{\ρ}$

${\mathrm{\α}}_0=arcsin\frac{xcos\mathrm{\φ}+ysin\mathrm{\φ}}{L}$

Fig. 4 gives a common physical model, its different piece filler respectively background water 1, polymethyl methacrylate 2, Merlon 3, polypropylene 4 and mylar 5. Table 1 lists the different constituent refractive index real part reduction amount when the X-ray that energy is 25keV irradiates and imaginary values and the relative value with water. By the present invention, finally give the three-dimensional reconstruction result shown in Fig. 5. In Fig. 5, (a), (b) are theoretical image, and (c), (d) are sinogram, and (e), (f) attach most importance to composition picture.

Image such as Fig. 6 and Fig. 7 shows that extraction of values and theoretical calculation are very good. Fig. 8 is dotted line position theoretical value and reconstruction value comparison diagram in refractive index real part reduction amount reconstruction result 5 (e); Fig. 9 is dotted line position theoretical value and reconstruction value comparison diagram in imaginary index reconstruction result 5 (f). Relatively known reconstruction result is very identical with theoretical model, further demonstrate that the correctness of extracting method.

Table 1: object model constituent and refractive index parameter: δ, β be material refractive index real part reduction amount and imaginary part respectively, the value of Δ δ, Δ β respectively material refractive index real part reduction amount water relative to imaginary part.

The above is specific embodiments of the present invention, it is noted that the program is not used to the limited present invention, all under principles of the invention thought premise, any amendment made, equivalent replacement or improvement, all should be contained within protection scope of the present invention.

Claims (10)

1. a quick fan-beam geometric phase contrast CT image-forming device, for carrying out three-dimensional phase contrast imaging, it is characterised in that this device includes X source (S), example platform (P), phase grating (G successively along light path to object₁), analyze grating (G₂) and detector (D), wherein:

X source (S), for launching X-ray to object to be detected;

Example platform (P), is used for fixing object;

Phase grating (G₁), for π phase-shifted grating or pi/2 phase shift grating, for modulating the Wave-front phase of incident X-rays;

Analyze grating (G₂), for absorption grating, with phase grating (G₁) produce large period Moire fringe from image, it is simple to low resolution detector detecting object information;

Detector (D), for recording the X-ray intensity by object and optical system.

2. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁), analyze grating (G₂) dutycycle be 0.5.

3. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁), analyze grating (G₂) and detector (D) be cylindrical optical element.

4. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁) radius of curvature be R₁, be positioned at X source (S) be initial point, R₁For, on the circular arc of radius, analyzing grating (G₂) radius of curvature be R₂, and be positioned at X source (S) be initial point, R₂For on the circular arc of radius.

5. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁) and analyze grating (G₂) cycle less than 10 μm.

6. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that detector (D) Pixel Dimensions ranges for 20 μm～100 μm.

7. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁) and analyze grating (G₂) cycle meetRelation, wherein, d₁For phase grating (G₁) cycle, d₂For analyzing grating (G₂) cycle, R₁And R₂Respectively X source (S) is to phase grating (G₁) and phase grating (G₁) to analyzing grating (G₂) distance, as phase grating (G₁) produce pi/2 phase shift time, η=1; As phase grating (G₁) produce π phase shift time, η=2.

8. quick fan-beam geometric phase contrast CT image-forming device according to claim 1, it is characterised in that phase grating (G₁) and analyze grating (G₂) spacing R₂Meet Talbot distanceN=1,3,5,7...

N is that Talbot is from imaging level time, d₁For phase grating (G₁) cycle, d₂For analyzing grating (G₂) cycle, λ is X-ray wavelength.

9. a quick fan-beam geometric phase contrast CT image-forming method, it is characterised in that comprise the steps:

A) do not put in object situation, along the equidistant travel(l)ing phase grating (G of one Cycle Length of place circular arc₁) or η Cycle Length equidistantly mobile analysis grating (G₂), with grating relative position be abscissa, light intensity obtain displacement curve for vertical coordinate, useRepresent, wherein x_gFor phase grating (G₁) and analyze grating (G₂) between relative displacement;

B) median point of displacement curve is found, and phase grating (G₁) and analyze grating (G₂) relative position is transferred to the abscissa positions x that median point is corresponding₀;

C) object is fixed on example platform (P), whole quick fan-beam geometric phase contrast CT image-forming device beyond rotary sample platform (P) or example platform (P), at interval of certain angle, record the subject image on detector (D);

D) quickly fan-beam geometric phase contrast CT image-forming device and object rotate against at least π+2 α_maxAfter radian, calculate the absorption image A and refraction image θ of each projection view angles object_r, computing formula is as follows:

${\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\mathrm{\μ}(x,y,z)dr=\ln \left(\frac{2S\left({\mathrm{\α}}_g\right)I_0}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}\right)=A(\mathrm{\α},\mathrm{\φ},z)$

$-{\∫}_{-\mathrm{\∞}}^{\mathrm{\∞}}\frac{\∂\mathrm{\δ}(x,y,z)}{r\∂\mathrm{\α}}dr=\frac{R_1}{{\mathrm{CR}}_0}\frac{I(\mathrm{\α},\mathrm{\φ},z)-I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}{I(\mathrm{\α},\mathrm{\φ},z)+I(-\mathrm{\α},\mathrm{\φ}+\mathrm{\π}+2\mathrm{\α},z)}={\mathrm{\θ}}_r(\mathrm{\α},\mathrm{\φ},z)$

Wherein, μ is the linear absorption coefficient of object, and δ is object refractive index real part reduction amount, α and α_gFor fan angle, α_maxFor maximum fan-angle, φ is rotary viewing angle, I₀Detector (D) direct-recording intensity during for not having any optical element and object in the middle of light source (S) and detector (D), the intensity that when I is image objects, detector (D) records,It it is a constant;

E) three-dimensional reconstruction method is used to rebuild absorption image and refraction image.

10. quick fan-beam geometric phase contrast CT image-forming method according to claim 9, it is characterized in that, step (a) intermediate reach moves step number more than three, and the three-dimensional reconstruction method described in step (e) is filtered back-projection method or iterative reconstruction method.