CN106618623A - Imaging method of hard X-ray grating interferometer with single exposure - Google Patents
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Abstract
The invention discloses an imaging method of a hard X-ray grating interferometer with single exposure. The imaging method is characterized by including the steps of 1, moving any grating, and fixing a working point of the hard X-ray grating interferometer at a left half waist and right half waist position of a light intensity curve; 2, obtaining a background projection image and a projection image of an imaged object respectively; 3, obtaining the normalized projection image of the imaged object, and conducting logarithm process on the normalized projection image; 4, constructing an expression formula to conduct one-dimensional Fourier transform according to the logarithm process result; 5, utilizing one-dimensional inverse Fourier transform to extract absorption of the imaged object and a relative phase shift signal respectively according to the result of the Fourier transform. According to the imaging method of the hard X-ray grating interferometer with the single exposure, the data collection procedure of the hard X-ray grating interferometer is simplified, the imaged object is subjected to single exposure, the imaging efficiency is improved, the radiation damage risk is reduced, and thus a new path of the development of a future fast and low-radiation-dose clinical medical imaging technology is provided.
Description
Technical field
The present invention relates to hard x-ray imaging physics and method field, the hard X ray light of specifically a kind of single exposure
The imaging method of grating interferometer.
Background technology
Over nearly more than 100 years, x-ray imaging methods and techniques are in Imaging physics mechanism, data acquisition plan, cross sectional reconstruction
The aspects such as algorithm constantly obtain new progress, and material science, clinical medicine, archaeology science, public peace are had been developed as at present
The indispensable important tool in congruent field.Particularly in clinical medicine domain, x-ray imaging method and apparatus, including X-ray
Projection imaging art (X-ray Radiography) and X ray computer tomography technology (X-ray Computed
Tomography), the major contribution that can not be substituted is made that to modern humans' health, social development.
From for Imaging physics mechanism, existing x-ray imaging methods and techniques are that the light intensity after object is penetrated based on X-ray
Difference in attenuation.Object to the heavy elements such as metal, bone composition, X-ray has obvious light intensity attenuation after penetrating.Therefore,
When to these strong absorption image objects, very high image contrast is obtained in that so that be clearly observed internal structure.But
It is, the object such as the human body soft tissue in clinical medicine imaging, the polymer in material science, mainly by the low atom such as carbon, hydrogen, oxygen
The light element composition of ordinal number.Due to decay of these light elements to X-ray it is very weak, cannot be effective using existing X imaging techniques
It was observed that these objects being made up of light element.Therefore, it is necessary to it is existing to overcome to develop new x-ray imaging methods and techniques
The limitation of x-ray imaging method.
The interaction of X-ray and material is reviewed, is found at hard X ray wave band (10-100keV), as soft tissue, gathered
The refractive index real part (mutually transplanting) of the elements such as the main component of the weak absorbing object such as compound, carbon, hydrogen, oxygen is imaginary index
More than 1000 times of (i.e. Absorption Terms).Therefore, measure X-ray and pass through phase shift information during object than detecting light intensity dampening information more
Plus effectively.X-ray phase contrast imaging technology is exactly based on record X-ray and forms image contrast through the phase in-migration after object
's.Compared with existing absorption-contrast imaging technology, when to weak absorbing image objects, X-ray phase contrast imaging technology energy
It is enough to obtain higher image contrast, higher measurement sensitivity, lower dose of radiation.Since the nineties in last century, carry successively
Go out and developed four kinds of Hard X-Ray Phase-Contrast Imaging methods：Crystal interferometer, phase propagation imaging, diffraction enhanced imaging, light
Grating interferometer.Wherein, hard X ray grating interferometer despite gradually growing up later for 2002, but is presently believed to be
Most one of X-ray phase contrast imaging method of application prospect.Compared with other imaging methods, hard X ray grating interferometer
It is the currently the only method that directly can obtain phase contrast using conventional X-ray source, thus in clinical medicine diagnosis and treatment, material supply section
The fields such as, public safety detection have broad application prospects.Hard X ray grating interferometer has very high measurement sensitive
Degree, can simultaneously obtain absorption, phase shift and the dispersion image of object from one group of data for projection.Three kinds of different subject images are mutual
For supplement, the internal structural information of object is reflected from different perspectives.These advantages cause hard X ray grating interferometer to become near
One of study hotspot in x-ray imaging field over year.
In hard X ray grating interferometer, the project objects image of detector record contains absorption, the phase of object simultaneously
Shifting and scattered signal, i.e. image contrast come from the mixing contribution of object absorption signal, phase shift signalling, scattered signal.And in reality
Border application in, such as quantitative analysis and research internal structure of body, projected image recognize, Computerized three-dimensional cross sectional reconstruction, will
Ask and obtain independent, pure object absorption, phase shift and scattered signal.Therefore, how quickly, accurately to carry from project objects image
It is one of study hotspot in recent years to take pure absorption, phase shift and scattered signal.At present, hard X ray grating interferometer is universal
Experimental data collection is carried out using phase stepping method and object information is extracted.This method requires complicated horizontal step-scan light
Grid, cause the data acquisition time grown very much, reduce conventional efficient；It is (experimentally many that requirement gathers several project objects images
In 4), increased the dose of radiation and radiation injury risk of object.These limitation hinder hard X ray grating interferometer and exist
The popularization and application in the fields such as clinical medicine diagnosis.Therefore, develop new imaging method, overcome phase stepping method grating stepping to sweep
Retouch, multiple object exposure limitation, have been developed as the bottle that must be solved in hard X ray grating interferometer practicalization
One of neck problem.
The content of the invention
The present invention is the weak point for avoiding existing imaging method, proposes a kind of hard X ray grating interference of single exposure
The imaging method of instrument, to can thoroughly abandon loaded down with trivial details grating step-scan, simplifies the data acquisition of hard X ray grating interferometer
Flow process, and imaging efficiency is improved, the time for exposure is reduced, dose of radiation and radiation injury risk are reduced, so as to quick, low to realize
The Hard X-Ray Phase-Contrast Imaging of dose of radiation provides new way.
To achieve the above object of the invention, the present invention is adopted the following technical scheme that：
A kind of imaging method of the hard X ray grating interferometer of single exposure of the present invention, the hard X ray grating interferometer
Including：X-ray source, source grating, phase grating, analysis grating, detector；Arrange between the x-ray source and phase grating
There are the source grating and the object to be imaged；The source grating is close to the x-ray source and is arranged；The object to be imaged is close to described
The inner side of phase grating is arranged；The analysis grating is provided with the outside of the phase grating；It is described analysis grating with it is described
Axial distance between phase grating is d；The detector is close to the outside of the analysis grating；Be characterized in, it is described into
Image space method is carried out as follows：
Any two grating in step 1, the fixation source grating, phase grating and analysis grating, and move along direction
3rd grating is moved into the screen periods of itself a quarter so that the operating point of the hard X ray grating interferometer is fixed
At the waist of a left side half of light intensity curve or right half waist position；The moving direction is the side both perpendicular to optical axis and grating grizzly bar
To；
Step 2, the startup x-ray source and detector, the setting time for exposure is t；
Background projection image I is obtained using the detector according to the time for exposure t0Afterwards, the x-ray source is closed；
Step 3, the visual field central authorities that the object to be imaged is placed into the phase grating, start the x-ray source, and
Projected image I of the object to be imaged is obtained according to the time for exposure t using the detectorDAfterwards, the X-ray is closed
Source；
Step 4, projected image I to the object to be imagedDBackground normalization process is carried out, normalized projection is obtained
Image I 'D, wherein I 'D=ID/I0；
Step 5, to normalized projected image I 'DProcess of taking the logarithm is carried out, result ln (I ' is obtainedD)；
Step 6, to expression formula K1-ln(I′D) make one-dimensional Fourier transform, obtain transformation results F1；K1It is for constant and full
Sufficient K1=lnS (p2/ 4) or K1=lnS (- p2/ 4), wherein p2It is the cycle of the analysis grating；S(p2/ 4) it is the hard X ray
The light intensity curve of grating interferometer is in p2Numerical value at/4；
Step 7, according to transformation results F1, in one-dimensional Fu of the phase shift signalling that the object to be imaged is obtained using formula (1)
Leaf transformation result F2：
F2=F1/(1/γ+iK2λu/M) (1)
In formula (1), γ is the ratio of the refractive index real part with imaginary part of the object to be imaged；I represents imaginary unit, i2
=-1；K2For constant, and meetOrWherein S ' (p2/ 4) it is the hard X ray
The first derivative of the light intensity curve of grating interferometer is in p2Numerical value at/4, d is the phase grating to the analysis grating
Axial distance；λ is the EWL of the x-ray source；U is spatial frequency；M is the geometry of the hard X ray grating interferometer
Magnifying power；
Step 8, the absorption signal T that the object to be imaged is extracted using formula (2)：
In formula (2),Represent one-dimensional inverse Fourier transform；
Step 9, the phase shift signalling Φ that the object to be imaged is extracted using formula (3)：
Using the absorption signal T and phase shift signalling Φ of the object to be imaged as the result of the imaging method.
Compared with the prior art, the invention has the beneficial effects as follows：
1st, present invention utilizes the refractive index real part of hard X ray wave band, biologic soft tissue etc. is approximate with imaginary part is directly proportional
Characteristic, based on light intensity curve half waist position linear approximation, it is proposed that single exposure be imaged new method, solve single exposure
Lower object absorbs, the quantitative extraction problem of phase shift information, overcomes grating step-scan, the multiexposure, multiple exposure of existing phase stepping method
Limitation, simplify data acquisition flow, it is to avoid high dose of radiation, realize quick, the hard X ray phase of low radiation dose
Position contrast imaging；
2nd, compared with existing phase stepping method, the present invention when subject image is obtained, by by hard X ray grating interference
Instrument is fixed at the waist of a left side half of light intensity curve or right half waist position, has abandoned loaded down with trivial details grating step-scan, is greatly simplified
Data acquisition flow, improves conventional efficient；
3rd, compared with existing phase stepping method, the present invention is using the refractive index real part of the object to be imaged and the ratio of imaginary part
γ keeps constant characteristic, and light intensity curve to simplify imaging equation in the linear approximation of half waist position, so as to only need to be to object
Carry out single exposure and obtain 1 project objects image, it becomes possible to the quantitative absorption for extracting object and phase shift signalling, it is to avoid be right
The multiexposure, multiple exposure of object simultaneously obtains multiple projected images, effectively reduces dose of radiation, reduces radiation injury risk；Subtract simultaneously
Lack experimental period, improve conventional efficient；
4th, the present invention has abandoned loaded down with trivial details grating step-scan, only needs to obtain 1 project objects under each projection angle
Image, enabling with computed tomography directly in conjunction with, realize the linear absorption coefficient of object, phase coefficient it is fast
Fast three-dimension disclocation is rebuild；
5th, compared with Traditional x-ray imaging method, the phase shift signalling that the present invention passes through acquisition object can be more clearly from
The fine structure of observation human body soft tissue etc., more accurately difference is normally and pathological tissues；
6th, imaging new method proposed by the present invention is equally applicable to two-dimentional hard X ray grating interferometer, neutron grating interference
Instrument, is widely used, strong applicability.
Description of the drawings
Fig. 1 is one-dimensional hard X ray grating interferometer schematic diagram in prior art；
Fig. 2 is the light intensity curve figure of hard X ray grating interferometer in prior art；
Fig. 3 is the refractive index real part of lucite and imaginary part ratio figure in prior art；
Fig. 4 is the extraction result figure of the absorption signal of the object to be imaged 6 in the present invention；
Fig. 5 is the extraction result figure of the phase shift signalling of the object to be imaged 6 in the present invention；
Label in figure：1X radiographic sources；2 source gratings；3 phase gratings；4 analysis gratings；5 detectors；6 object to be imaged.
Specific embodiment
As shown in figure 1, hard X ray grating interferometer includes：X-ray source 1, source grating 2, phase grating 3, analysis grating 4,
Detector 5；Source grating 2 and the object to be imaged 6 are provided between x-ray source 1 and phase grating 3；Source grating 2 is close to X-ray
Source 1 is arranged；The object to be imaged 6 is close to the inner side of phase grating 3 and is arranged；The outside of phase grating 3 is provided with analysis grating 4；
Axial distance between analysis grating 4 and phase grating 3 is d；Detector 5 is close to the outside of analysis grating 4；The present embodiment
In, the imaging method of the hard X ray grating interferometer of single exposure is to carry out as follows：
Any two grating in step 1, fixation source grating 2, phase grating 3 and analysis grating 4, and move along direction general
3rd grating moves the screen periods of itself a quarter so that the operating point of hard X ray grating interferometer is fixed on light intensity
At the waist of a left side half of curve or right half waist position (arrow indicating positions in Fig. 2)；Moving direction is both perpendicular to optical axis and grating
The direction of grizzly bar；
Hard X ray grating interferometer is fixed at the waist of a left side half of light intensity curve or right half waist position, has not only been abandoned loaded down with trivial details
Grating step-scan, and cause the measurement sensitivity of phase shift signalling of the object to be imaged 6 to reach maximum, so as to more accurate
Extract the absorption of the object to be imaged 6 and phase shift signalling in ground.
Step 2, startup x-ray source 1 and detector 5, the setting time for exposure is t；
Background projection image I is obtained using detector 5 according to time for exposure t0Afterwards, for the perspective view of the object to be imaged 6
The normalized of picture, closes x-ray source 1；
Step 3, the visual field central authorities that the object to be imaged 6 is placed into phase grating 3, start x-ray source 1, and using detection
Device 5 obtains projected image I of the object to be imaged 6 according to time for exposure tDAfterwards, x-ray source 1 is closed；
Right half waist position p is operated in hard X ray grating interferometer2As a example by/4.The object to be imaged 6 that detector 5 is obtained
Projected image IDMeet：
In formula (3.1), T is the absorption signal of the object to be imaged 6；S () is the light intensity curve of hard X ray grating interferometer
(shown in Fig. 2)；p2It is the cycle for analyzing grating 4；λ is the EWL of x-ray source 1；D is phase grating 3 to analysis grating 4
Axial distance；M is the geometry magnifying power of hard X ray grating interferometer；Represent first differential computing；Φ is the object to be imaged
6 phase shift signalling.
Step 4, projected image I to the object to be imaged 6DBackground normalization process is carried out, normalized perspective view is obtained
As I 'D, wherein I 'D=ID/I0；
Step 5, to normalized projected image I 'DProcess of taking the logarithm is carried out, result ln (I ' is obtainedD)；
Right half waist position p is operated in hard X ray grating interferometer2As a example by/4.According to formula (3.1), normalized projection
Image I 'DLogarithm process result ln (I 'D) meet：
In the refracted signal to hard X ray such as the applications such as clinical medicine imaging, biologic soft tissue
It is very little, generally meetsHard X ray grating interferometer is operated in light intensity by step 1
At the waist of a left side half of curve or right half waist position, for little refraction signal, first-order linear reasonably can be made to light intensity curve approximately,
It is linear imaging equation by nonlinear imaging equation simplification,
Formula (5.2) substitutes into formula (5.1) and is obtained,
K in formula (5.3)1For constant, and meet K1=lnS (p2/ 4), wherein p2It is the cycle for analyzing grating 4；S(p2/ 4) be
The light intensity curve of hard X ray grating interferometer is in p2Numerical value at/4；K2For constant, and meetWherein S '
(p2/ 4) for hard X ray grating interferometer light intensity curve first derivative in p2Numerical value at/4, d is phase grating 3 to analysis
The axial distance of grating 4；λ is the EWL of x-ray source 1；Represent first differential computing.
T is the absorption signal of the object to be imaged 6 to be extracted, is proportional to the imaginary part of object refractive index；Φ is to be extracted
The phase shift signalling of the object to be imaged 6, is proportional to the real part of object refractive index.The things such as the soft tissue for clinical medicine imaging field
Body, its refractive index real part is approximate with imaginary part proportional.By taking the equivalent substitution thing-lucite of human body soft tissue as an example, such as
Shown in Fig. 3, in hard X ray in energy range 27-41keV, its refractive index real part is held essentially constant with the ratio γ of imaginary part, than
The average of value γ is 2469, and fluctuating range is less than 3%.Then the phase shift signalling Φ and absorption signal T of the object to be imaged 6 are approximate
Meet proportional relation,
Formula (5.4) substitutes into formula (5.3) and is obtained,
Step 6, to expression formula K1-ln(I′D) make one-dimensional Fourier transform, obtain transformation results F1；K1It is for constant and full
Sufficient K1=lnS (p2/ 4) or K1=lnS (- p2/ 4), wherein p2It is the cycle for analyzing grating 4；S(p2/ 4) dry for hard X ray grating
The light intensity curve of interferometer is in p2Numerical value at/4；
One-dimensional Fourier transform is made to formula (5.5), transformation results F are obtained1：
In formula (6.1),Represent one-dimensional Fourier transform；F2Be the object to be imaged 6 one-dimensional Fu of phase shift signalling in
Leaf transformation result；I represents imaginary unit, i2=-1；U is spatial frequency.
Step 7, transformation results F according to formula (6.1)1, using formula (1) phase shift signalling of the object to be imaged 6 is obtained
One-dimensional Fourier transform result F2：
F2=F1/(1/γ+iK2λu/M) (1)
In formula (1), γ is the ratio of the refractive index real part with imaginary part of the object to be imaged 6；I represents imaginary unit, i2=-1；
K2For constant, and meetOrWherein S ' (p2/ 4) it is hard X ray grating interferometer
Light intensity curve first derivative in p2Numerical value at/4, d is axial distance of the phase grating 3 to analysis grating 4；λ is X-ray
The EWL in source 1；U is spatial frequency；M is the geometry magnifying power of hard X ray grating interferometer；
Step 8, according to formula (5.4), one-dimensional Fourier transform result F of the absorption signal of the object to be imaged 6TMeet：
Formula (1) substitutes into formula (8.1) and obtains,
One-dimensional inverse Fourier transform is made to formula (8.2), so as to extract the absorption signal T of the object to be imaged 6 using formula (2)：
In formula (2),Represent one-dimensional inverse Fourier transform；
Fig. 4 is the extraction result figure of the absorption signal of the object to be imaged 6.The object to be imaged 6 is organic glass of 4 millimeters of diameter
Glass rod；The effective energy of x-ray source 1 is 35keV.According to Fig. 4, the absorption signal extracted using formula (2) and theoretical calculation
Very well, it was confirmed that the present invention can quantitatively extract the absorption signal of the object to be imaged 6.
Step 9, one-dimensional inverse Fourier transform is made to formula (1), so as to extract the phase shift letter of the object to be imaged 6 using formula (3)
Number Φ：
Fig. 5 is the extraction result figure of the phase shift signalling of the object to be imaged 6, and the object to be imaged 6 is organic glass of 4 millimeters of diameter
Glass rod；The effective energy of x-ray source 1 is 35keV.According to Fig. 5, the phase shift signalling extracted using formula (3) has been coincide well reason
By value, it was confirmed that the present invention can quantitatively extract the phase shift signalling of the object to be imaged 6.
Using the absorption signal T and phase shift signalling Φ of the object to be imaged 6 as the result of imaging method.
Claims (1)
1. a kind of imaging method of the hard X ray grating interferometer of single exposure, the hard X ray grating interferometer includes：X is penetrated
Line source (1), source grating (2), phase grating (3), analysis grating (4), detector (5)；In the x-ray source (1) and phase place light
The source grating (2) and the object to be imaged (6) are provided between grid (3)；The source grating (2) is close to the x-ray source (1) and is set
Put；The object to be imaged (6) is close to the inner side of the phase grating (3) and is arranged；Arrange in the outside of the phase grating (3)
There is analysis grating (4)；Axial distance between analysis grating (4) and the phase grating (3) is d；The detection
Device (5) is close to the outside of analysis grating (4)；It is characterized in that, the imaging method is carried out as follows：
Any two grating in step 1, the fixation source grating (2), phase grating (3) and analysis grating (4), and move along
3rd grating is moved in direction the screen periods of itself a quarter so that the operating point of the hard X ray grating interferometer
It is fixed at the waist of a left side half of light intensity curve or right half waist position；The moving direction is both perpendicular to optical axis and grating grizzly bar
Direction；
Step 2, the startup x-ray source (1) and detector (5), the setting time for exposure is t；
Background projection image I is obtained using the detector (5) according to the time for exposure t0Afterwards, the x-ray source (1) is closed；
Step 3, the visual field central authorities that the object to be imaged (6) is placed into the phase grating (3), start the x-ray source
(1), and using the detector (5) projected image I of the object to be imaged (6) is obtained according to the time for exposure tDAfterwards,
Close the x-ray source (1)；
Step 4, projected image I to the object to be imaged (6)DBackground normalization process is carried out, normalized perspective view is obtained
As I 'D, wherein I 'D=ID/I0；
Step 5, to normalized projected image I 'DProcess of taking the logarithm is carried out, result ln (I ' is obtainedD)；
Step 6, to expression formula K1-ln(I′D) make one-dimensional Fourier transform, obtain transformation results F1；K1For constant, and meet K1=
lnS(p2/ 4) or K1=lnS (- p2/ 4), wherein p2It is the cycle of analysis grating (4)；S(p2/ 4) it is the hard X ray light
The light intensity curve of grating interferometer is in p2Numerical value at/4；
Step 7, according to transformation results F1, the one-dimensional Fourier of the phase shift signalling of the object to be imaged (6) is obtained using formula (1)
Transformation results F2：
F2=F1/(1/γ+iK2λu/M) (1)
In formula (1), γ is the ratio of the refractive index real part with imaginary part of the object to be imaged (6)；I represents imaginary unit, i2=-
1；K2For constant, and meetOrWherein S ' (p2/ 4) it is the hard X ray grating
The first derivative of the light intensity curve of interferometer is in p2Numerical value at/4, d is the phase grating (3) to analysis grating (4)
Axial distance；λ is the EWL of the x-ray source (1)；U is spatial frequency；M is the hard X ray grating interferometer
Geometry magnifying power；
Step 8, the absorption signal T that the object to be imaged (6) is extracted using formula (2)：
In formula (2),Represent one-dimensional inverse Fourier transform；
Step 9, the phase shift signalling Φ that the object to be imaged (6) is extracted using formula (3)：
Using the absorption signal T and phase shift signalling Φ of the object to be imaged (6) as the result of the imaging method.
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