CN109035359A - A kind of frequency domain iteration phase abstracting method absorbing duality based on phase shift - Google Patents
A kind of frequency domain iteration phase abstracting method absorbing duality based on phase shift Download PDFInfo
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Abstract
The present invention relates to a kind of frequency domain iteration phase abstracting methods that duality is absorbed based on phase shift, include the following steps: the exposure parameter that digital radiation imaging system is set, edge of a knife utensil is placed in object plane position to be imaged, acquisition obtains edge of a knife image, the edge of a knife cross section curve of different location is obtained from image, then edge of a knife cross section curve is averaged, it differentiates again to averaged curve, obtain the line spread function of corresponding characterization system performance, the line spread function is rotated a circle in rectangular coordinate system, two-dimensional points spread function is calculated, then Fourier transformation is asked to obtain itImaging object is placed, imaging parameter constant is kept, to image objects, obtains phase contrast imaging resultGo out Absorption Terms by phase bit extraction analytical method solvingAs initial value, iterative calculation obtains the Fourier transformation that phase contrast imaging absorbs item of imageFind out the phase information image of characterization internal structure of body。
Description
Technical field
The invention belongs to biomedical engineering and Medical Imaging fields, are related to a kind of frequency that duality is absorbed based on phase shift
Domain iterative phase abstracting method.
Background technique
Osteoporosis is one of common ailment of middle-aged and old, first of the big disease illness rate of the elderly five placed in the middle, is seriously affected
The quality of life of the elderly.Statistics shows that there are about 200,000,000 people to suffer from osteoporosis in the whole world at present, and sclerotin is dredged at present for China
Loose patient is about 90,000,000.1997, annual October 20 was set to " world's osteoporosis day " by the World Health Organization, meaning
People are being improved to the understanding of this disease of osteoporosis.China is developing country, as China steps into aging society
Meeting prevents and treats osteoporosis and has become the social concern of urgent need to resolve, and realizing its early diagnosis is to solve this
One of key of problem.
X ray image method is the main conventional method of current diagnosing osteoporosis, this method by directly observation or
Measurement different parts skeleton density, shape, the shape of bone trabecula and distribution are diagnosed.But this X ray image method
Be by organizer's different parts density variation degree of being contrasted, therefore can only when bone mass loss is larger could efficient diagnosis,
Be not suitable for the assessment of early stage osteoporosis.
Until last century Mo, X-ray phase contrast imaging theory (X-ray phase contrast imaging, XPCI)
Proposition, broken traditional x-ray imaging theory, to realize that ideal early stage diagnosing osteoporosis brings new dawn.
Studies have shown that the contrast resolution of phase contrast imaging improves 10 times compared with traditional x-ray absorption-contrast imaging under identical dose of radiation
The image visibility of the bone tissue imaging to lesion early stage (normal tissue and lesion density variation are smaller) can be improved in left and right.
In currently available X-ray phase contrast technology, in-line X-ray phase contrast imaging technology introduces additional optics dress due to not needing
It sets, imaging optical path designs relatively easy stabilization, it is considered to be most suitable for realizing the aobvious of clinical medicine application conversion under conditions present
One of micro- imaging technique.
In in-line X-ray phase contrast imaging measurement, after object, corrugated is distorted incident X-ray, after distortion
Corrugated interferes effect after continuing to travel to certain distance, by being overlapped with the corrugated not being distorted.In this way, X-ray is logical
After crossing object, by the Free propagation of certain distance, phase change information can be converted to it is modulated after strength information lead to
It crosses as plane is shown.In-line X-ray phase contrast imaging uses the system parameter setting of Fresnel near field diffraction pattern, at this time in image planes
The Diffraction intensity distribution of acquisition is proportional to the Laplacian transformation of phase change amount, and the phase change two dimension of indirect reflection
Distribution, so phase distribution information is obtained from obtained intensity signal by mathematical method, it is this by ionization meter Lai extensive
The inverse process of multiple object phase Information Problems is exactly phase bit extraction.Up to the present, many scholars carry out ideal feelings
The phase bit extraction research of in-line X-ray phase contrast imaging, achieves valuable achievement under condition.
But so far, X-ray in-line X-ray phase contrast imaging still without being applied on diagnosing osteoporosis, learn by major part
Person is all based on the approximate model expansion research of weakly absorbing material (soft tissue) foundation, is not suitable for having larger absorption to X-ray
Bone tissue.In addition, the phase extraction model of currently used all kinds of in-line X-ray phase contrast imagings is built upon ideal imaging system
On system and imaging process, and the factor for causing image quality to deteriorate in real system is not fully considered, is not more adopted
Measure is taken to exclude the degradation effects in imaging results.Although by using the micro- focal spot x-ray source of high brightness and a large amount
The detector of sub- detection efficiency is expected largely to improve the above problem, but under present condition, High Performance X-ray source and
Detector is still in development phase, even if these equipment are applied, image quality degradation factors still can not exclude completely.
In addition, being bound to cause system cost raising, lead to in-line X-ray phase contrast imaging popularizes advantage if introducing high-performance equipment
Very big weakening.
Therefore, critical issue major embodiment of the restricting current line phase-contrast imaging technique in osteoporosis clinical application
At two aspects: 1. existing phase contrast imaging phase extraction models are the approximate models established based on weakly absorbing material, are not suitable for
In the phase bit extraction of bone tissue phase contrast imaging；2. there is defects for imaging system aspect itself, for example X source is not ideal point
Source, detector performance are limited by factors such as itself resolution ratio and point spread functions, and there are all kinds of hazardous noises etc. for system.
Since the in-line X-ray phase contrast imaging based on Microfocus X-ray source is the imaging technique for being suitble to diagnosing osteoporosis to promote and apply,
Therefore, the accurate extraction of bone tissue phase information is realized for the imaging technique, obtains the phase of characterization bones structural information
Bit image has significant research and application value.Traditional phase abstracting method, by establishing line to soft tissue phase contrast imaging
Property approximate model, the analytic solutions of phase is obtained with this, this method is not suitable for the bone tissue of high-selenium corn, and for existing defects
Imaging system, this phase abstracting method based on linear approximation model tends not to accurately obtain phase information.Therefore, it sends out
A kind of frequency domain iteration phase abstracting method for absorbing duality based on phase shift is put on display, realizes strong absorption interior of articles structural information
Accurate phase extracts, this has a very important significance application of the phase contrast imaging in terms of diagnosing osteoporosis and popularization.
Summary of the invention
Purport of the invention is to propose a kind of frequency domain iteration phase abstracting method that duality is absorbed based on phase shift, the present invention
From the exact non-linear model of Microfocus X-ray source in-line X-ray phase contrast imaging, considers the strong absorption characteristic of bone tissue and combine phase shift
It is theoretical to absorb duality, by the phase information of alternative manner approaching to reality, ensure that and accurately obtained under non-ideal imaging system
The phase information for being absorbed object by force is the clinical application of in-line X-ray phase contrast imaging system and technology in diagnosing osteoporosis
Favourable conditions are provided.Technical solution is as follows:
A kind of frequency domain iteration phase abstracting method absorbing duality based on phase shift, including the following steps:
1. X-ray in-line X-ray phase contrast imaging parameter setting；
2. the exposure parameter of digital radiation imaging system is arranged, edge of a knife utensil is placed in object plane position to be imaged, is adopted
Collection obtains edge of a knife image, and the edge of a knife cross section curve of different location is obtained from image, then edge of a knife cross section curve is averaged,
It differentiates again to averaged curve, obtains the line spread function of corresponding characterization system performance, which is sat at right angle
It rotates a circle in mark system, two-dimensional points spread function is calculated, then asks Fourier transformation to obtain it
3. placing imaging object, imaging parameter constant is kept, to image objects, obtains phase contrast imaging result
4. going out Absorption Terms by phase bit extraction analytical method solvingAs initial value, then calculate separately HereSymbolIndicate Fourier transformation operator,Indicate gradient
Operator and Laplace operator, λ are X-ray wavelength, re=2.82 × 10-15M is classical electron radius, σKNFor Compton scattering
Section,For spatial frequency, M is imaging amplification factor, can be passed throughIt calculates, R1, R2Respectively object
To the distance of light source and detector.
5. above-mentioned calculated result is substituted into following iterative formulaHere IinIndicate incidence X
Transmitted intensity, ε are regularization parameter, and numerical value can be set as the inverse of practical phase contrast image signal-to-noise ratio, | | it is transported for modulus
It calculates, No. * is to take conjugate complex number, when less than default error, i.e., iteration reaches preset times or the adjacent error of iteration result twice
Obtain the Fourier transformation that phase contrast imaging absorbs item of image
6. to Absorption TermsInverse Fourier transform is carried out, is obtainedThen utilize Absorption TermsWith phase informationBetween relationship, find out characterization internal structure of body
Phase information imageHereFor shadow density.
Detailed description of the invention
The line spread function of Fig. 1 in-line X-ray phase contrast imaging system.
The phase contrast imaging result of Fig. 2 cicada slough.
The phase bit extraction result obtained under Fig. 3 classics analytic method.
The present invention is based on the results of the frequency domain iteration phase abstracting method of phase shift absorption duality by Fig. 4.
Specific embodiment
The present invention will be described in terms of several below.
1. digital X-ray imaging system
Experiment is using the Microfocus X-ray source digital radiation imaging system voluntarily constructed.The detector of the system is 1024 × 1024
Ccd array, pixel size be 50 μm of 50 μ m, 14 grades of gray scales.The spatial resolution of transverse direction and longitudinal direction is every millimeter of 20 pictures
Element.The focal spot size of X-ray tube is 50 μm.In experiment, the operating voltage of x-ray source is 70kVp, operating current 0.5mA.At
As object is used with the cicada slough absorbed more by force.The distance of experimental setup x-ray source to object is 100cm, and corresponding object arrives
The distance of detector is 100cm.Under arrangement above, light source on the detector at focal spot picture be 50 μm.Due to imaging system
Point spread function be detector point spread function and light source point spread function convolution, in above-mentioned experimental setup, need
Consider that detector and light source spot size point spread function ask the degradation effects and system noise of in-line X-ray phase contrast imaging result
Topic is finally directed to imaging system characteristic, realizes a kind of frequency domain iteration phase abstracting method that duality is absorbed based on phase shift.
2. absorbing the frequency domain iteration phase bit extraction principle of duality based on phase shift
In X-ray in-line X-ray phase contrast imaging, transmission function of the object to incident X-raysIt can be expressed as
WhereinIt is the coordinate position on object plane, i is imaginary unit,WithObject is respectively corresponded to entering
Penetrate the absorption and phase shift effect of X-ray.
After X-ray passes through object, Fresnel diffraction effect, X-ray corrugated table occur in continuing communication process for related light
It is shown as:
Wherein subscript d indicate object to detector distance,For linear convolution operator,It is Fresnel diffraction
Operator:
In this way, being (assuming that incident X-rays intensity is to be uniformly distributed) by final detector acquired image
Under the near-axial condition of in-line X-ray phase contrast imaging, above-mentioned coordinateIt needs to useIt replaces, M here
For amplification factor is imaged, can pass throughTo calculate (R1, R2Respectively object to light source and detector away from
From).
Under sigmatron, since the photoelectric effect of X-ray is reduced, the radiation injury of human body is reduced, therefore realizes high
The phase contrast imaging of energy X-ray is of great significance.When consideration sigmatron situation (60-500keV), the phase and absorption of object
Meet phase shift and absorb duality theory, i.e.,
Here λ is X-ray wavelength,For shadow density, re=2.82 × 10-15M is classical electron radius,
σKNFor Compton scattering section, can be calculated with following formula
Here η=E/511keV, E are X-ray energy.
It is theoretical according to paraxial fresnel diffraction, and in view of the phase of tissue different location is not in mutation
Situation, the Fourier transformation expression formula of intensity signal on available detector
HereSymbolIndicate Fourier transformation operator,WithRespectively indicate gradient operator and La Pu
Laplacian operater, IinIndicate incident X-rays intensity,For spatial frequency,Ssystem transfer function is represented, is depended primarily on
X-ray source focal spot size and detector point spread function.
Duality theory is absorbed according to phase shift, available following relationship:
It realizes accurate phase bit extraction, formula (8) can be converted to a least square fitting problem, i.e.,
Here For disturbance term.
The corresponding solution of minimization problem of formula (11) can be indicated with following formula
HereIndicate (n+1)th iteration result, when practical iteration,Initial value can be by traditional
Phase bit extraction analytic method obtains.
Traditional phase bit extraction analytic method is the low-density characteristics simplified model based on the object to be imaged, i.e., to formula
(12) it is approximate to have made many hypothesis, nonlinear terms therein have been ignored, sine termIt is approximately 0, cosine termIt is approximately 1, the model for thus obtaining traditional phase bit extraction analytic method is as follows:
Since system noise influences, actually measured ssystem transfer functionThere are zeros, due in formula (12)Positioned at denominator, denominator be zero will lead to phase bit extraction failure.Therefore it needs for formula (12) to be modified to
Here ε is regularization parameter, and numerical value can be set as the inverse of practical phase contrast image signal-to-noise ratio, | | it is modulus
Operation, No. * is to take conjugate complex number.
It is less than default error when iteration reaches preset times or the adjacent error of iteration result twice to get having arrived object
The Fourier transformation of absorption imageThe absorption image of corresponding spatial domain is obtained by inverse Fourier transform again
It is finally theoretical (formula (5), (6)) according to phase and absorption duality, the phase bit extraction result of phase contrast image can be obtained
3. a kind of techniqueflow for the frequency domain iteration phase abstracting method for absorbing duality based on phase shift
A kind of process of frequency domain iteration phase abstracting method being absorbed duality based on phase shift of the invention is described as follows:
1) X-ray in-line X-ray phase contrast imaging parameter setting: in the present invention, the distance of setting light source to object is 100cm, with
The distance of this corresponding object to detector is 100cm.
2) exposure parameter of digital radiation imaging system is set, places edge of a knife utensil in object plane position to be imaged, adopts
Collection obtains edge of a knife image, and the edge of a knife cross section curve of different location is obtained from image, then edge of a knife cross section curve is averaged,
It differentiates again to averaged curve, obtains the line spread function of corresponding characterization system performance, which is sat at right angle
It rotates a circle in mark system, two-dimensional points spread function is calculated, then asks Fourier transformation to obtain it
3) place imaging object, the present invention in use cicada slough for test articles, holding be imaged parameter constant, to the object at
Picture obtains phase contrast imaging result
4) Absorption Terms are gone out by traditional phase bit extraction analytical method solvingAs initial value, then calculate separately HereSymbolIndicate Fourier transformation operator,Indicate gradient
Operator and Laplace operator, λ are X-ray wavelength, re=2.82 × 10-15M is classical electron radius, σKNFor Compton scattering
Section,For spatial frequency, M is imaging amplification factor, can be passed throughTo calculate (R1, R2Respectively object arrives
The distance of light source and detector).
5) above-mentioned calculated result is substituted into following iterative formulaHere IinIndicate incidence X
Transmitted intensity, ε are regularization parameter, and numerical value can be set as the inverse of practical phase contrast image signal-to-noise ratio, | | it is transported for modulus
It calculates, No. * is to take conjugate complex number, when less than default error, i.e., iteration reaches preset times or the adjacent error of iteration result twice
The Fourier transformation that phase contrast imaging absorbs item of image is obtained
6) to Absorption TermsInverse Fourier transform is carried out, is obtainedThen utilize Absorption TermsWith phase informationBetween relationship, find out characterization internal structure of body
Phase information imageHereFor shadow density.
The present invention is using the Microfocus X-ray source digital radiation imaging system voluntarily constructed.System is obtained by knife edge device first
The transmission function of detector.Fig. 1 gives the system line spread function obtained by knife-edge method measurement, and what thus measurement obtained is
The halfwidth of system line function curve is 80 microns.The line spread function is rotated a circle in rectangular coordinate system, can be obtained pair
The point spread function answered.
Cicada slough is imaged, Fig. 2 gives the phase contrast imaging result figure of the cicada slough obtained under non-ideal phase contrast imaging system, can
To find out, due to the influence of noise and ssystem transfer function, phase contrast image quality is unsatisfactory.
Phase bit extraction is carried out to the phase contrast imaging result of Fig. 2 using formula (13) corresponding classical analytic method, is obtained
As a result as shown in Figure 3.It can be seen that since imaging model is to having the cicada slough absorbed more by force to be not appropriate for, so the phase obtained
Bit image is second-rate.
Using the frequency domain iteration phase abstracting method proposed by the present invention for absorbing duality based on phase shift, it is contemplated that object
Absorption characteristic avoids linear approximation bring error, is approached by iteration optimization, can obtain phase letter as shown in Figure 4
Breath extracts as a result, better than phase bit extraction result under classical analytic method.
Final result shows that the phase extraction model of in-line X-ray phase contrast imaging can not be accurate under current engineering specifications
The problem of obtaining to absorb object phase information by force under non-ideal imaging system is based on phase shift using one kind of the invention and absorbs two
The frequency domain iteration phase abstracting method of member, in the case of can effectively improve non-ideal system, to the strong phase contrast figure for absorbing object
Accuracy as carrying out phase bit extraction result.Since imaging object of the present invention is using cicada slough, there is biggish suction to X-ray
It receives, is unsatisfactory for low absorption object model used by traditional phase contrast imaging, it is believed that there are similar characteristics with skeletal structure, because
This research achievement of the invention can further effective one point in actual clinical for the coaxial of osteoporosis early diagnosis
In phase contrast imaging system.The application of this method will provide technical support for the diagnosis of effectively realization early stage osteoporosis, be deep
The clinical practice and research for being carried out in the line phase-contrast imaging of osteoporosis provide strong support.
Claims (1)
1. a kind of frequency domain iteration phase abstracting method for absorbing duality based on phase shift, including the following steps:
1. X-ray in-line X-ray phase contrast imaging parameter setting；
2. the exposure parameter of digital radiation imaging system is arranged, edge of a knife utensil is placed in object plane position to be imaged, acquisition obtains
Edge of a knife image is obtained, the edge of a knife cross section curve of different location is obtained from image, then edge of a knife cross section curve is averaged, then right
Averaged curve is differentiated, and the line spread function of corresponding characterization system performance is obtained, by the line spread function in rectangular coordinate system
In rotate a circle, two-dimensional points spread function is calculated, then asks Fourier transformation to obtain it
3. placing imaging object, imaging parameter constant is kept, to image objects, obtains phase contrast imaging result
4. going out Absorption Terms by phase bit extraction analytical method solvingAs initial value, then calculate separately HereSymbolIndicate Fourier transformation operator, ▽2Indicate gradient
Operator and Laplace operator, λ are X-ray wavelength, re=2.82 × 10-15M is classical electron radius, σKNFor Compton scattering
Section,For spatial frequency, M is imaging amplification factor, can be passed throughIt calculates, R1, R2Respectively object arrives
The distance of light source and detector；
5. above-mentioned calculated result is substituted into following iterative formulaHere IinIndicate incidence X
Transmitted intensity, ε are regularization parameter, and numerical value can be set as the inverse of practical phase contrast image signal-to-noise ratio, | | it is transported for modulus
It calculates, No. * is to take conjugate complex number, when less than default error, i.e., iteration reaches preset times or the adjacent error of iteration result twice
Obtain the Fourier transformation that phase contrast imaging absorbs item of image
6. rightInverse Fourier transform is carried out, is obtainedThen utilize Absorption Terms
With phase informationBetween relationship, find out characterization internal structure of body phase information imageThis
InFor shadow density.
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| CN110376222A (en) * | 2019-07-04 | 2019-10-25 | 天津大学 | A kind of more material phase abstracting methods towards the imaging of non-ideal line phase-contrast |
| CN112179926A (en) * | 2020-09-24 | 2021-01-05 | 首都师范大学 | Coaxial CT-based phase-absorption inversion and material quantitative imaging method |
| CN112484658A (en) * | 2019-09-12 | 2021-03-12 | 卡尔蔡司Smt有限责任公司 | Method for detecting object structure and apparatus for carrying out the method |
| CN112735342A (en) * | 2020-12-30 | 2021-04-30 | 深圳Tcl新技术有限公司 | Backlight light type processing method and device and computer readable storage medium |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110376222A (en) * | 2019-07-04 | 2019-10-25 | 天津大学 | A kind of more material phase abstracting methods towards the imaging of non-ideal line phase-contrast |
| CN110376222B (en) * | 2019-07-04 | 2021-10-12 | 天津大学 | Multi-material phase extraction method for nonideal coaxial phase contrast imaging |
| CN112484658A (en) * | 2019-09-12 | 2021-03-12 | 卡尔蔡司Smt有限责任公司 | Method for detecting object structure and apparatus for carrying out the method |
| US11892769B2 (en) | 2019-09-12 | 2024-02-06 | Carl Zeiss Smt Gmbh | Method for detecting an object structure and apparatus for carrying out the method |
| CN112179926A (en) * | 2020-09-24 | 2021-01-05 | 首都师范大学 | Coaxial CT-based phase-absorption inversion and material quantitative imaging method |
| CN112735342A (en) * | 2020-12-30 | 2021-04-30 | 深圳Tcl新技术有限公司 | Backlight light type processing method and device and computer readable storage medium |
| CN112735342B (en) * | 2020-12-30 | 2022-05-03 | 深圳Tcl新技术有限公司 | Backlight light type processing method and device and computer readable storage medium |
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