CN107432749B - A kind of phase abstracting method of X-ray phase contrast - Google Patents
A kind of phase abstracting method of X-ray phase contrast Download PDFInfo
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- CN107432749B CN107432749B CN201710543821.3A CN201710543821A CN107432749B CN 107432749 B CN107432749 B CN 107432749B CN 201710543821 A CN201710543821 A CN 201710543821A CN 107432749 B CN107432749 B CN 107432749B
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
- A61B6/5205—Devices using data or image processing specially adapted for radiation diagnosis involving processing of raw data to produce diagnostic data
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/48—Diagnostic techniques
- A61B6/484—Diagnostic techniques involving phase contrast X-ray imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/50—Clinical applications
- A61B6/502—Clinical applications involving diagnosis of breast, i.e. mammography
Abstract
The present invention relates to a kind of phase abstracting methods of X-ray phase contrast, comprising: the exposure parameter of digital radiation imaging system is arranged in setting X-ray in-line X-ray phase contrast imaging parameter, places imaging object in object plane position to be imaged；To the image objects, it is imaged when obtaining imaging results, and obtaining without object；Construct corresponding finite element fission space；The nonlinear model of phase contrast imaging is converted into finite element model；Finite element model is iteratively solved using algebraic reconstruction technique, then obtains the phase information of characterization internal structure of body.
Description
Technical field
The invention belongs to biomedical engineering and Medical Imaging field, the phase for being related to a kind of X-ray phase contrast is taken out
Take new method.
Background technique
Breast cancer is current women first big " killer ", according to recent statistics data in 2015, whole world patient with breast cancer people
Several and death toll increased to 1,700,000 and 520,000 in 2012 respectively, and 25% and the cancer for respectively accounting for all female cancer cases are dead
Die 15% several [2].China human mortality is numerous, and breast cancer illness rate is in obvious ascendant trend in recent years, and the diagnosis and treatment of breast cancer are
As increasingly heavy and urgent need to resolve social concern, and realizing its early diagnosis is to solve this social concern, improve patient
The key of survival rate and quality of life.
The main means of current mammary gland routine inspection are molybdenum (rhodium) target X-ray breast imaging art, however long-term clinical practice
Show the technology in sensitivity, specific, safety and comfort etc. have great shortcoming: on the one hand the technology is deposited
In the up to omission factor of 10-15%；It on the other hand is positive and final biopsy diagnosis rate is 25-29% by the diagnosis of technique.
Especially the serious is cause diagnostic accuracy seriously to reduce since the breast of young woman is excessively fine and close.
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 breast cancer anatomy imaging diagnostic techniques is brought
New dawn.Studies have shown that under identical dose of radiation, the contrast resolution of phase contrast imaging compared with traditional x-ray absorb contrast at
As improving 10 times or so, the image visibility of soft-tissue imaging is significantly improved.In currently available X-ray phase contrast technology
In, in-line X-ray phase contrast imaging technology introduces additional Optical devices due to not needing, and imaging optical path designs relatively easy stabilization, quilt
It is considered to be most suitable for realizing one of the micro-imaging technique of clinical medicine application conversion under conditions present.
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 the weak phase shifted samples of thin layer weak absorbing, by the Free propagation of certain distance, phase change information can be converted to through adjusting
Strength information after system as plane by showing.The system using Fresnel near field diffraction pattern that in-line X-ray phase contrast imaging uses
Parameter setting, the Diffraction intensity distribution obtained in image planes at this time are proportional to the Laplacian transformation of phase change amount, and non-straight
The reversed phase change Two dimensional Distribution reflected, so to obtain phase distribution letter from obtained intensity signal by mathematical method
Breath, this inverse process for restoring object phase Information Problems by ionization meter is exactly phase bit extraction.Up to the present, had
Many scholars have carried out the phase bit extraction research of ideally in-line X-ray phase contrast imaging, achieve valuable achievement.But so far
Until the present, the phase extraction model of currently used all kinds of in-line X-ray phase contrast imagings is built upon ideal image system and was imaged
It on the basis of the linear approximation of journey, is very restricted in practical applications, for the Microfocus X-ray source phase contrast under non-ideal system
Imaging system, phase bit extraction result do not reach expected result.
Since the in-line X-ray phase contrast imaging based on Microfocus X-ray source is the imaging technique for being more suitable for realizing clinical application, because
This, realizes the accuracy that phase information extracts for the imaging technique, obtains the phase image of characterization internal structure of body information
With significant research and application value.Traditional phase abstracting method is carried out by the second dervative model to phase contrast imaging
Approximation obtains the analytic solutions of phase with this, and this method can obtain effective phase information under high quality imaging contexts, but
It is the imaging system for existing defects, this phase abstracting method based on second dervative approximate model tends not to accurately obtain
Take phase information.
Summary of the invention
For under current engineering specifications, X source, imperfection and system noise of detector etc. cause phase contrast image matter
Amount deteriorates, and phase contrast reduces, and realizes that phase bit extraction not can guarantee phase information and extract based on traditional second dervative approximate model
As a result accuracy.One kind proposed by the present invention can guarantee the X-ray phase of the phase information of the object to be imaged accurately obtained
Serve as a contrast the phase bit extraction new method of imaging.The invention is based on the accurate subdivision of finite element and realizes X-ray phase contrast model linearization, protects
The accurate acquisition of the phase information of the object to be imaged is demonstrate,proved.Technical solution is as follows:
A kind of phase abstracting method of X-ray phase contrast, including the following steps:
(1) be arranged X-ray in-line X-ray phase contrast imaging parameter, be arranged digital radiation imaging system exposure parameter, at
Place imaging object in the object plane position of picture；
(2) to the image objects, imaging results I is obtainedd(x, y), and obtain without object when be imaged；
(3) according to IdThe dimension size of (x, y) constructs corresponding finite element fission space: being equal to detector picture using area
The square finite element of element, and by the finite element node locating heart within the pixel, according to image IdThe direction of the row of (x, y) matrix is
Sequentially, the serial number of finite element node is set；After completing finite element fission, it is 4 corresponding finally to obtain each square finite element
The coordinate of node ID and area and each node, number of nodes D are IdThe summation of pixel number in (x, y)；
(4) by the nonlinear model of phase contrast imagingBe converted to finite element model Kh
=Q, Iin(x, y) is incident X-rays intensity,For the phase information of standard item internal structure to be asked, λ is X-ray
Wavelength, d distance between testee and detector, ▽2For Laplace operator, h=[h in finite element model1(x,y),
h2(x,y),…hD(x,y)]TFor finite element basic function ui(x, y) to the characterization of phase information, i.e.,K is that D × D ties up matrix, and Q is the n dimensional vector n of D × 1, and corresponding element is respectivelyQi=∫Ωui(x,y)q0(x, y) d Ω, wherein ▽ ui(x, y) is to finite element
Basic function ui(x, y) calculates gradient, and the selection of finite element basic function is square finite element,
(5) finite element model Kh=Q is iteratively solved to obtain h using algebraic reconstruction technique, recycles phaseAnd h
Relationship, obtain characterization internal structure of body phase information.
Detailed description of the invention
Fig. 1 fibre columns and fibrous nodules imitate the phase contrast imaging result figure of body
Fig. 2 imitates the phase bit extraction result of body using the fiber goalpost that conventional method obtains
The phase section curve and true phase that Fig. 3 is obtained using conventional method compare
Fig. 4 imitates the phase bit extraction result of body using the fiber goalpost that the method for the present invention obtains
The corresponding phase section curve of Fig. 5 and true phase comparing result
Specific embodiment
For in X-ray in-line X-ray phase contrast imaging, realize that phase bit extraction can not based on traditional second dervative approximate model
Guarantee that phase information extracts the accuracy of result, the present invention proposes a kind of phase bit extraction new method of X-ray phase contrast, with this
Under the conditions of solving current engineering technology, the phase information based on in-line X-ray phase contrast imaging extracts faced critical issue, finally
Obtained technical solution is as follows:
1. X-ray in-line X-ray phase contrast imaging parameter is arranged: the distance of light source to object is 80cm, and object correspondingly arrives
The distance of detector is 80cm.2. the exposure parameter of digital radiation imaging system is arranged, placed in object plane position to be imaged
Imaging object, the imitative body that uses is respectively 100 μm, 50 μm, 20 μm and 5 μm of polyethylene fibre column by diameter in the present invention, with
And diameter is respectively that 100 μm, 50 μm, 20 μm and 5 μm of polyethylene fibre ball is constituted.To the image objects, imaging knot is obtained
Fruit Id(x,y).3. according to IdThe dimension size of (x, y) constructs corresponding finite element fission space: being equal to detector using area
The square finite element of pixel, and by the finite element node locating heart within the pixel, according to image IdThe direction of the row of (x, y) matrix
For sequence, the serial number of finite element node is set；After completing finite element fission, each square finite element corresponding 4 is finally obtained
The coordinate of a node ID and area and each node, number of nodes D are IdThe summation of pixel number in (x, y).4. by phase contrast
The nonlinear model of imagingBe converted to finite element model Kh=Q, Iin(x, y) is incidence
X-ray intensity,For the phase information of standard item internal structure to be asked, λ is the wavelength of X-ray, and d is measured object
Distance between body and detector, ▽2For Laplace operator.H=[h in finite element model1(x,y),h2(x,y),…hD(x,
y)]TFor finite element basic function ui(x, y) to the characterization of phase information, i.e.,K is D × D
Matrix is tieed up, Q is the n dimensional vector n of D × 1, and corresponding element is respectively Kij=∫Ωκ·▽ui(x,y)·▽uj(x, y) d Ω, Qi=∫Ωui
(x,y)q0(x,y)dΩ.Wherein ▽ ui(x, y) is to finite element basic function ui(x, y) calculates gradient, the selection of finite element basic function
Be square finite element,5. using algebra weight to finite element model Kh=Q
The method of building iteratively solves to obtain h, recycles phaseWith the relationship of hIt can be obtained
Characterize the phase information of internal structure of body.
Below with reference to embodiment, further illustrate.
1 digital X-ray imaging system
Experiment imaging system is 100 toy digital radiation imaging system of Pixarray, by U.S.'s BIOPTICS corporation
It makes.The ccd array that the detector of the system is 1024 × 1024, pixel size are 50 μm of 50 μ m, 14 grades of gray scales.It is lateral and vertical
To spatial resolution be every millimeter of 20 pixels.The focal spot size of X-ray tube is 50 μm.In experiment, the work electricity of x-ray source
Pressure is 33kVp, operating current 0.5mA.It is respectively 100 μm, 50 μm, 20 μm and 5 μm of polyethylene that imaging object, which uses diameter,
Fibre columns and diameter are respectively 100 μm, 50 μm, 20 μm and 5 μm of polyethylene fibre ball.Experimental setup x-ray source is to object
Distance be 80cm, the distance of corresponding object to detector is 80cm.
The phase bit extraction principle of 2 in-line X-ray phase contrast imagings
In X-ray in-line X-ray phase contrast imaging, object can be expressed as the transmission function T (x, y) of incident X-rays
Wherein (x, y) is the coordinate position on object plane, and j is imaginary unit, μ (x, y) andRespectively correspond object pair
The absorption and phase shift effect of incident X-rays.
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:
W (x, y)=T (x, y) * Pd(x,y) (2)
Wherein subscript d indicates object to the distance of detector, and * is linear convolution operator, Pd(x, y) is Fresnel diffraction
Operator:
Here λ is the wavelength of X-ray.In this way, being (assuming that incident X-rays intensity by final detector acquired image
To be uniformly distributed)
Id(x, y)=| T (x, y) * Pd(x,y)|2 (4)
The near-axial condition of in-line X-ray phase contrast imaging is substituted into above formula, light intensity and object phase information on available detector
Relational expression:
Here Iin(x, y) is incident X-rays intensity,For the phase information of standard item internal structure to be asked.
We defineSurplus can be defined according to formula (5) at this time
Certain testing function in Selection experiment space, is weighted surplus, i.e., above-mentioned surplus is flat to the weighting of testing function
It is zero
Here Ω is test space, and Ψ (x, y) is testing function.Consider based on identity derived from green theorem
HereFor the boundary of test space, n is the direction of spatial surface exterior normal, for x-ray imaging, considers side
X-ray out-of-bounds does not contribute imaging, and null boundary condition can be used
Formula (8) and (9) are substituted into (7), can be obtained
In order to be matched with the flat panel detector that phase contrast imaging uses, space Ω is divided into L and mutually disjoints and covers Ω
Unit ωl(l=1,2 ..., L), vertex constitute D finite element node Ni(i=1,2 ..., D), finite element selection are square
Shape is matched with this with detector pixel.By the finite element node locating heart within the pixel, according to image IdThe row of (x, y) matrix
Direction be sequence, be arranged finite element node serial number.After completing finite element fission, each square finite element pair is finally obtained
The coordinate of 4 node ID and area and each node answered.
Testing function Ψ (x, y) is taken as finite element basic function collection { ui(x, y), i=1,2,3 ..., D }, then formula (10)
It is converted to
Meanwhile according to finite element fission model, phase contrast imaging solution to model can be expressed as the linear combination of basic function collection
Phase contrast imaging model can be expressed as matrix form equation by (12) substitution (11)
Kh=Q (13)
Here h=[h1(x,y),h2(x,y),…hD(x,y)]TFor amount to be asked, K is that D × D ties up matrix, and Q is the dimension arrow of D × 1
Amount, corresponding element are respectively
Kij=∫Ωκ·▽ui(x,y)·▽uj(x,y)dΩ
(14)
Qi=∫Ωui(x,y)q0(x,y)dΩ (15)
For each square finite elements, coordinate origin is located at centroid, then can obtain corresponding K of the finite elements
Matrix, K=1/6* [4-1-2-1；-1 4 -1 -2；-2 -1 4 -1；-1 -2 -1 4].All K submatrixs are superimposed,
K matrix can be obtained.And matrix Q is by by q0The value of (x, y) is interpolated on corresponding finite element node and realizes.
Hereby it is achieved that by finite element method, converting the nonlinear model (formula (5)) of phase contrast imaging to
Linear model (13) is then iteratively solved to obtain h using algebraic reconstruction technique, recycles phaseWith the relationship of hIt can be obtained the phase information of characterization internal structure of body.
A kind of 3 techniqueflows of the phase bit extraction new method of X-ray phase contrast
A kind of process of X-ray phase imaging method based on imaging system characteristic 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 80cm, with
The distance of this corresponding object to detector is 80cm.
2) exposure parameter of digital radiation imaging system is set, places imaging object in object plane position to be imaged, this
The imitative body used in invention is respectively by the polyethylene fibre column and diameter that diameter is respectively 100 μm, 50 μm, 20 μm and 5 μm
100 μm, 50 μm, 20 μm and 5 μm of polyethylene fibre ball is constituted.To the image objects, imaging results I is obtainedd(x,y).Together
When be imaged when will be without object
3) according to IdThe dimension size of (x, y) constructs corresponding finite element fission space: being equal to detector picture using area
The square finite element of element, and by the finite element node locating heart within the pixel, according to image IdThe direction of the row of (x, y) matrix is
Sequentially, the serial number of finite element node is set；After completing finite element fission, it is 4 corresponding finally to obtain each square finite element
The coordinate of node ID and area and each node, number of nodes D are IdThe summation of pixel number in (x, y).
4) by the nonlinear model of phase contrast imagingBe converted to finite element model Kh
=Q: h=[h in model1(x,y),h2(x,y),…hD(x,y)]TFor finite element basic function ui(x, y) to the characterization of phase information,
I.e.K is that D × D ties up matrix, and Q is the n dimensional vector n of D × 1, and corresponding element is respectively Kij=∫Ω
κ·▽ui(x,y)·▽uj(x, y) d Ω, Qi=∫Ωui(x,y)q0(x,y)dΩ.Wherein
5) finite element model Kh=Q is iteratively solved to obtain h using algebraic reconstruction technique, recycles phaseAnd h
RelationshipIt can be obtained the phase information of characterization internal structure of body.
It is similar using 100 toy digital radiation imaging device of the Pixarray building of BIOPTICS company, U.S. production
Axis phase contrast imaging system.Fig. 1 gives through this system in low x-ray dose (45kV tube voltage, 0.5mA tube current, when exposure
Between 5 seconds) under phase contrast imaging as a result, signal noise ratio (snr) of image is calculated as 10dB.
Approximation is carried out to phase contrast imaging second dervative model using conventional method first, then realizes phase bit extraction, as a result
As shown in Figure 2.Provide the section curves of fibre columns simultaneously, and according to the material composition and its diameter for using fiber in imitative body,
The true phase for extrapolating imitative body compares, as shown in Figure 3.
When constructing linear model using finite element method of the invention, then realizes phase bit extraction, Fig. 4 institute can be obtained
The phase bit extraction result shown.Corresponding phase section curve and true phase comparing result are equally provided, as shown in Figure 5.Pass through
Comparison, it can be seen that fibre columns lesser for diameter and fibrous nodules, the method for the present invention can obtain more accurate phase bit extraction
As a result.
Claims (1)
1. a kind of phase abstracting method of X-ray phase contrast, including the following steps:
(1) X-ray in-line X-ray phase contrast imaging parameter is set, the exposure parameter of digital radiation imaging system is set, to be imaged
Place imaging object in object plane position；
(2) to the image objects, imaging results I is obtainedd(x, y), and obtain without object when be imaged；
(3) according to IdThe dimension size of (x, y) constructs corresponding finite element fission space: being equal to detector pixel just using area
Rectangular finite element, and by the finite element node locating heart within the pixel, according to image IdThe direction of the row of (x, y) matrix is sequence,
The serial number of finite element node is set；After completing finite element fission, the corresponding 4 node sequences of each square finite element are finally obtained
Number and area and each node coordinate, number of nodes D be IdThe summation of pixel number in (x, y)；
(4) by the nonlinear model of phase contrast imagingFinite element model Kh=Q is converted to,
Iin(x, y) is incident X-rays intensity,For the phase information of standard item internal structure to be asked, λ is the wave of X-ray
It is long, d distance between testee and detector,For Laplace operator, h=[h in finite element model1(x,y),h2(x,
y),…hD(x,y)]TFor finite element basic function ui(x, y) to the characterization of phase information, i.e.,K is that D × D ties up matrix, and Q is the n dimensional vector n of D × 1, and corresponding element is respectivelyQi=∫Ωui(x,y)q0(x, y) d Ω, whereinIt is to finite element
Basic function ui(x, y) calculates gradient, and the selection of finite element basic function is square finite element,
(5) finite element model Kh=Q is iteratively solved to obtain h using algebraic reconstruction technique, recycles phaseWith the pass of h
System obtains the phase information of characterization internal structure of body.
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