CN108022272A - The computer program and CT system reduced for the metal artifacts based on segmentation and spectrum - Google Patents
The computer program and CT system reduced for the metal artifacts based on segmentation and spectrum Download PDFInfo
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- G—PHYSICS
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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T11/00—2D [Two Dimensional] image generation
- G06T11/003—Reconstruction from projections, e.g. tomography
- G06T11/008—Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
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- G06T2207/10072—Tomographic images
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Abstract
The metal artifacts based on segmentation and spectrum are applied to reduce (MAR) system and program in polychrome X ray CT systems, wherein using the priori of the high Z metals caused in known X ray energy spectrums in the sample of main artifact.Decomposed using basic material, which solves the problems, such as to be used only in the single sweep operation of the sample performed under the X ray energies of selection to reduce or eliminate the metal artifacts associated with beam hardening.Specifically, thickness based on the metal in each projection angle and the X ray attenuations in each projection angle, concentrated from the high Z volume datas of segmentation and generate high Z set of projections, by these set normalization, and the tomography volumetric data sets of correction are then created using low Z projections and high Z set of projections.
Description
Background technology
X-ray computer tomography (CT) is a kind of non-destructive for the internal structure for being used to check and analyze sample
Technology.In general, when X-ray passes through sample, X-ray is absorbed by the sample or scatters.Do not absorbed or scattered off
X-ray be transmitted through sample, and be then detected by device system detectio.It is referred to as X- in the image that detector system is formed
Ray projection.Via the CT algorithm for reconstructing of standard tomography volume number is rebuild from a series of these projections in different angle
According to collection.X-ray tomograph system often by these tomography volumes be presented on tomography volumetric data sets two dimension,
In cross sectional image or " section ".
Some X-ray tomograph systems are projected using polychromatic X-ray beam with generating X-ray.Wrap in polychromatic X-ray source
Include X-ray pipe (laboratory source) or white synchrotron beam, or the source based on accelerator.The advantages of polychromatic X-ray beam, exists
In for given source, they are usually more powerful than monochromatic beam, because the wave filter of energy consumption need not be damaged.
When using polychromatic beam, because the energy relatively low when beam passes through object is absorbed first, the X-ray of transmission is strong
Degree is general no longer proportional to material thickness.As a result, when projecting using polychromatic beam generation X-ray, often occur to be claimed
For the phenomenon of beam hardening (BH).Beam hardening with when X-ray passes through sample towards the Transmission X-penetrate of more high x-ray energy
The change of line spectrum is associated.
Beam hardening often produces artifact in the tomography reconstruction with polychromatic X-ray.Knot as beam hardening
Fruit generates typical artifact, including cupping artifact and jail-bar artifacts., can be effectively by absorbing the linearisation to material thickness
Correction only includes a kind of beam hardening of the object of material.But for mixing material object, especially comprising low-density (it is low-
Z) the object of material and high density (height-Z) material, this method is not effective.Because such as metal or such as iron (Fe) and
Low-the Z of height-Z element ratios such as silicon (Si), carbon (C), nitrogen (N) and the oxygen (O) with element of the atomicity higher than 18 of golden (Au)
The more X-rays of element absorption, it is pseudo- that metallic element structure generally produces more serious beam hardening when exposed to X-ray
Shadow.These artifacts are also referred to as " metal artifacts ".In addition, factor such as X-ray scattering, the Poisson in addition to beam hardening are made an uproar
Sound, and movement and edge effect can cause the establishment of metal artifacts.
The current method that metal artifacts reduce in X-ray CT images is generally divided into three groups.First group, group 1, uses N- ranks
Fitting of a polynomial carries out beam hardening correction to reduce metal artifacts.Here our this methods are referred to as " BHC (beam hardening schools
Just) ".Second group, group 2, emphasis is the segmentation/subtract shadow of metal in projection, followed by analysis or the Method Of Accomplishment of iterative algorithm.The
Three groups, or group 3, using based on spectrum or Method of Physical Modeling to reduce statistically and iteratively or suppress artifact.
Every kind of artifact, which reduces method, shortcoming.Group 1MAR methods only can substantially reduce artifact and only to a kind of metal
Normal work.The part that group 2MAR methods usually only provide artifact suppresses, and metallic perimeter may introduce newly in the sample
Blurring artefact.This is because the information on the structure in the sample that is covered by metal is wiped free of.Opposite, group 3MAR method reasons
Preferably deposited by can above reduce or eliminate most metals artifact and usually realize as a result, not wiped in projection because of them
Information.But since it is desired that substantial amounts of iterative processing steps, the computational efficiency for organizing 3 methods are low.
Recently, it is PCT/US that the PCT Application No. of WO 2015/168147A1 is submitted and be published as on April 28th, 2015
In 2015/0280323, the MAR methods based on segmentation and spectrum using basic material decomposable process are described.This method only makes
The single sweep operation of the sample performed used in known X-ray power spectrum, solves the reduction of the artifact associated with beam hardening or disappears
Except the problem of, while will not wipe by metal cover information.Which improve current group 2 and the MAR methods of group 3.
This method combines some advantages of group 2 and group 3MAR methods, while avoids their some shortcomings.It is different
In organizing 1 method, which can be used for various metals.Different from organizing 2 methods, which can minimize any new
The introducing of artifact, and the details on the metal structure in the CT reconstruction images of sample is provided., should different from organizing 3 methods
MAR methods can be non-iterative or alternatively only need totally 2 or 3 iteration (that is, low to calculate consumption), and in theory can be with
Beam hardening physics based on spectral correlation removes metal artifacts.
The MAR methods are utilized on the spectral power distribution (that is, spectrum) of polychromatic X-ray that is incident on sample (here
Power spectrum be also combined with the detection sensitivity of detector) priori and contribute to main artifact establishment sample in one
The physical characteristic of the main height-Z metals of kind.
First, original projection is considered as base line projection.Using the base line projection of sample, this method can for example via
The baseline tomography of the filtered back projection of standard/Field Kemp-Davis-Cray this (FBP/FDK) algorithm for reconstructing generation sample
Photography volumetric data sets.
Next, to concentrate the height-Z metals of selection to create the height-Z metallic objects of segmentation from baseline tomography volume data
Volume data collection.Then by by the generation of the height-Z metal volume data sets forward projection of segmentation only with the associated throwing of height-Z metal phases
Photograph album, that is to say, that create the height-Z metal shadowings of forward projection.The height-Z projects what is concentrated with the height-Z volume datas of segmentation
It is associated in the thickness of the height-Z elements of the segmentation of each projection angle.
The concept of basic material decomposition is employed in the method.It is assumed that other materials of the sample in addition to height-Z metals
Material can also be claimed by a kind of selection or hypothesis low-Z elements/material (i.e. silicon (Si) or carbon (C)) " expression " or representative
For " equivalent low-Z elements ".As a result, sample is preferably modeled as including several, such as two kinds of basic materials：Height-Z
Metallic element and equivalent low-Z elements, include the identical base line projection of the X-ray spectrum for selection.
Using the relation between base line projection and two kinds of basic materials, this method calculates the thickness with equivalent low-Z elements
Associated set of projections, such as formed during the CT scan of sample in X-ray beam during rotation sample in each projection angle
's.These are also referred to as equivalent low-Z elements set of projections.Display look-up table (LUT) technology is to determine the most universal of this relation
Method.
Then MAR methods utilize equivalent low-Z elements to project to create the tomography body of the beam hardening correction of sample
Volume data collection, the tomography volumetric data sets also referred to as corrected.
Finally, the MAR methods using the selection of image projection combination monochromatic x-rays energy value to generate the beam of sample
The tomography volumetric data sets of hardening correcting.For this purpose, this method normalizes and obscures first height-Z set of projections.So
Afterwards, monochromatic x-rays energy of this method based on selection merges equivalent low-Z projections and normalized height-Z projections, with wound
It build the monochromatic fusion projection of the correction of the X-ray energy of selection in.Then, this method is weighed from the monochromatic fusion projection of correction
Positive tomography volumetric data sets for school building.
The content of the invention
The present invention relates to the further of the MAR based on segmentation and spectrum is improved.Specifically, from the height-Z metals of segmentation
Volumetric data sets create multiple set of projections.These are projected the thickness based on the metal in different angle and are decayed based on X-ray
To create.This, which is realized, more accurately characterizes metal.
Preferably, these set of projections are combined.In one case, declined by the way that two set of projections normalization are created height-Z
Subtract set of projections.
In general, according to one side, it is a feature of the present invention that a kind of be used in X-ray computer tomography
Computer system on the computer program for being used for data acquisition and image reconstruction that performs.The baseline of the program creation sample is thrown
Photograph album, the baseline tomography volumetric data sets of sample are created from base line projection collection, and will come from baseline tomography body
Height-Z the segmentation of structures of volume data collection is to create the height-Z volumetric data sets of segmentation.According to the present invention, based in each projected angle
The thickness of the metal of degree and the X-ray decay in each projection angle, life is concentrated by program from the height-Z volume datas of segmentation
Into multiple high-Z set of projections.The power spectrum of X-ray beam is considered, by program using one or more height-Z set of projections to generate
Low-Z the set of projections of effect.Finally, the tomography volume of correction is generated using equivalent low-Z set of projections and height-Z set of projections
Data set.
In one example, thrown by program by the way that the X-ray based on the X-ray decay in each projection angle is decayed
Photograph album and height-Z thickness set of projections based on the metal thickness in each projection angle are normalized, and create normalized height-Z
Set of projections.
Preferably, the monochromatic x-rays energy of the selection of the power spectrum based on X-ray beam, equivalent low-Z is projected with returning
One height-Z projection the fusions changed, to create the monochromatic fusion set of projections in the X-ray energy of selection.
Finally, the tomography volumetric data sets of correction are rebuild from monochromatic fusion projection.
In general, according to one side, it is a feature of the present invention that X-ray CT system.The system include X-ray into
As system, which generates base line projection collection by rotating against sample in X-ray beam；And computer
System, the computer system generate the baseline tomography volumetric data sets of sample from base line projection collection, will break from baseline
Height-Z the segmentation of structures of layer photography volumetric data sets is to create the height-Z volumetric data sets of segmentation.
According to the present invention, thickness based on the metal in each projection angle and decline in the X-ray of each projection angle
Subtract, height-Z set of projections is generated from the height-Z volumetric data sets of segmentation.The one or more height of power spectrum use of consideration X-ray beam-
Z set of projections creates equivalent low-Z set of projections.Finally school is generated using equivalent low-Z elements projection and height-Z set of projections
Positive tomography volumetric data sets.
Above and other feature of the present invention includes various novel structure details and component combination, below with reference to accompanying drawings
And more detailed description is done to further advantage in claim and is indicated.It should be appreciated that implement the certain party of the present invention
Method and device are shown by example, rather than limitation of the present invention.Without departing from the scope of the invention, the principle of the present invention
It can be applied to feature in a variety of different embodiments.
Brief description of the drawings
In the accompanying drawings, reference numeral indicates identical part by different views.Attached drawing is not necessarily drawn to scale；
Focus on that the principle of the present invention is shown.In figure：
Figure 1A to 1F shows the beam hardening and metal artifacts of the sample scanned with polychromatic X-ray, wherein Figure 1A displayings
Include the design of Simulation of the exemplary sample of height-Z metallic element structures；Figure 1B respectively show in 70KV (low energy) and
Two kinds of X-ray power spectrums of 150KV (high-energy), include the influence of detector sensitivity；Fig. 1 C and Fig. 1 D, which respectively show, to be come from
Metal artifacts in the tomographic image that low energy scans and high-energy scans；And Fig. 1 E and 1F respectively show and linearly decline
Subtract the curve of the function of line distribution of the coefficient as low energy tomographic image and high-energy tomographic image in sample,
Metal artifacts in low energy tomographic image are more serious than the metal artifacts in high-energy tomographic image；
Fig. 2 is the schematic diagram of the applicable X-ray CT system of the present invention；
Fig. 3 is the flow of the preferred embodiment for the MAR of the present invention for showing the program execution by performing on the computer systems
Figure；
Fig. 4 A and 4B are illustrated for determining base line projection and the relation under the energy of selection between two kinds of basic materials
Exemplary look-up table (LUT), wherein similar LUT can be utilized in the step 916 of the flow chart of Fig. 3；And
Fig. 5 A to 5E illustrate the associated image of the output phase of the different illustrative steps from MAR's, and wherein Fig. 5 A are illustrated
The base line projection collection of CT scan from sample；The baseline tomography for the sample that Fig. 5 B shows are created from the base line projection of Fig. 5 A is taken the photograph
Shadow image；Fig. 5 C illustrate the height-Z metal images of the segmentation subtracted from the baseline tomographic image of Fig. 5 B；Fig. 5 D are shown
Height-Z the projections created from the forward projection of the height-Z metal images of the segmentation of Fig. 5 C；And Fig. 5 E illustrate with it is equivalent
Equivalent low-Z the set of projections that the thickness of low-Z elements is associated.
Embodiment
The present invention is described more fully with now with reference to attached drawing, the illustrative embodiment of the present invention is illustrated in attached drawing.So
And the present invention may be implemented in many different forms, and it should not be construed as limited to embodiments described herein；On the contrary,
It will be detailed and complete to these embodiments are provided so that the disclosure, and this will be fully passed on to those skilled in the art
The scope of invention.
As it is used herein, term "and/or" includes any and all of one or more associated Listed Items
Combination.Further, it is to be understood that it ought be included in the present specification using term, included including and/or comprising specified described
Feature, integer, step, operation, the presence of element and/or component, but one or more of the other feature is not precluded the presence or addition of,
Integer, step, operation, element, component and/or combinations thereof.However, it should be understood that working as includes component or subsystem
Element be referred to as and/or be expressed as being connected or when being coupled to another element, it can be connected or coupled to another
A element, or there may be intermediary element.
For monochromatic x-rays, Beer law describes the X-ray when X-ray is by pure object and will be attenuated：
I=I0e-μt
Wherein I0The X-ray intensity being incident upon on object, t are object thicknesses, and I is the X-ray intensity of transparent objects,
μ is attenuation coefficient (including photoelectric absorption and the effect of Compton scattering, and if X-ray energy of object>1.02MeV when electricity
Sub- pairing effect), it depends on sample rate ρ, atomic number Z, atomic mass A and X-ray ENERGY E.
Above-mentioned formula can be rewritten with integrated form：
I=I0e-∫μ(l)dl, and
∫ μ (l) dl=-ln (I/I0)
Wherein l is the beam path through object.This has fully met the line integral demand of CT algorithm for reconstructing.As a result,
Beam hardening (BH) artifact is not introduced for monochromatic x-rays.
On the other hand, polychromatic X-ray source generates X-ray on spectrum D (E).For the sake of simplicity, D (E) also includes detection
The influence of device sensitivity.The downstream intensity I of object is given by：
I=I0∫D(E)e-∫μ(E,I)dldE
μ (E) is typically the nonlinear function of E, is given by：
Wherein
N ≈ 4 (photoelectric absorption part), and
(Compton scattering part), wherein fKNIt is Ke Lai-benevolence section formula.
Since μ (E) is typically the nonlinear function of ENERGY E, the transmission of the X-ray from polychromatic X-ray source cannot expire
The line integral demand of sufficient CT algorithm for reconstructing.μhigh-energy<μlow-energy, it is meant that the material is inhaled relative to height-Energy X-ray
Receive " more " it is low-Energy X-ray.Seem to be difficult to " move " by the output spectrum of the X-ray of the decay of sample transmission,
It is referred to as beam hardening (BH).Height-Z metal materials have more serious beam hardening problem, cause to rebuild in the CT of sample disconnected
There are typical metal artifacts in layer photographs.
Figure 1A to Fig. 1 F shows that the beam as caused by the BH in the two kinds of different X-ray energy of the invention utilized is hard
Change problem and metal artifacts 106.
Figure 1A illustrates the design of Simulation of the sample 114 including a variety of high-Z and low-Z elements.Element includes manganese (Mn), iron
(Fe), nickel (Ni), copper (Cu), cobalt (Co) and carbon (C).
Figure 1B illustrates two kinds of polychromatic X-rays spectrum in low energy@70KV and high-energy@150KV.
Fig. 1 C and Fig. 1 D are illustrated due to beam hardening and the reconstruction image of the sample 114 including uncorrected artifact 106.
Fig. 1 C are created using the low energy polychromatic X-ray source operated in 70KV.On the other hand, Fig. 1 D use the height in 150KV operations
Energy polychromatic X-ray source creates.
Fig. 1 E and 1F illustrate the distribution ratio of the linear attenuation coefficient in low energy and the reconstruction image of high-energy scanning
Compared with.As shown in the figure, the metal and BH artifacts in reconstruction image are that energy is relevant.Metal and BH artifacts ratio in low energy CT
It is more serious in high-energy CT.For example, low energy attenuation coefficient shows as height-Z elements in uniform low-Z packing materials
The wave crest and trough 154 of edge.
Fig. 2 is the schematic diagram of the applicable X-ray CT system 200 of the present invention.The X-ray CT system 200 includes X-ray
Imaging system, it has the X-ray source system 102 of generation polychromatic X-ray beam 103, and turntable 110, it, which has, is used to protect
Hold the sample retainer 112 of sample 114.Image or X-ray are projected through detector system 118 and catch.Computer system 124
These images are usually received and handled, and the general control of system 200 is provided.
Source 102 is preferably " laboratory X-ray source ", because its ubiquitous and relatively low cost.Nevertheless,
Synchrotron source or source based on accelerator are another selections.
Source 102 can be X-ray pipe, and wherein electronics by electric field acceleration and injects metallic target piece in a vacuum, with electricity
Son slows down and launches X-ray in a metal.In general, the type depending on used metallic target, such source produces and at certain
The continuous spectrum of the background X-ray of the intensity sharp peak combination of a little energy, feature of some energy from the target 104 of selection
Line obtains.In addition, X-ray beam is scattered, and lack room and time coherence.
In one example, source 102 is the rotary anode type with tungsten target or micro- focusing source.Can also use include molybdenum,
Gold, platinum, silver or copper target.Preferably, using transmittance structure, wherein electron beam thin target 104 is hit from the dorsal part of thin target 104.From target
The X-ray of 104 opposite side transmitting is used as beam 103.
In another example particularly, source 102 is the Anode X-ray source of structuring, such as on October 28th, 2008
License to described in the U.S. Patent number 7443953 of Yun et al., its content is incorporated herein by reference in their entirety.In this feelings
Under condition, source 102 is with the thin top layer made of desired target and by low atomic number and low-density with good thermal property
Thick bottom made of material.Anode can include, for example, being deposited on the copper with optimum thickness on beryllium or diamond basalis
Layer.
The X-ray for producing the radiation with the energy for being suitable for tomography application as described herein can also be used to swash
Light device.
In yet another example, source 102 is metal jet X-ray source, for example, can from the ExcillumAB of Sweden,
Obtained at Kista.Such source is managed using micro- focus on, its Anodic is liquid-metal jet stream.Therefore, anode is continuous
It is regenerated and melted.
Source 102 be preferably placed at can separately adjustable source to sample distance (202) source Z- axis platforms on.
The X-ray beam 103 generated by source 102 has the power spectrum usually controlled by the operating parameter in source.In laboratory source
In the case of, dominating parameter includes target and accelerating potential.Power spectrum is also by suppressing any of unwanted energy or radiation wavelength
Wave filter is adjusted to dominate.For example, using such as energy filter 107 (designed for selecting desired X-ray wave-length coverage (band
It is wide)) eliminate or decay the undesirable wavelength being present in beam.However, wave filter 107 does not reduce transmitted beam 103 substantially
Gross energy or bandwidth.For example, wave filter 107, which preferably reduces the power in beam 103, is not more than 50%.In preferred embodiment
In, it, which reduces the power in beam, is not more than 30%.Correlation is the most of polychromatic X-ray quilts generated by X-ray source 102
Retain with irradiating sample 114.In general, the band of used X-ray is wider than 40%, such as passes through the half of X-ray energy band
What peak overall with (FWHM) and the ratio of center X-ray energy were limited.For example, for the central energy of 50KeV, using around
The energy band of central energy at least 20KeV.In general, bandwidth is at least 20%, because otherwise the available flux in source is cut
Too serious, it reduces performance and/or slows down operation.
When sample 114 is exposed to X-ray beam 103, the X-ray photon for being transmitted through sample is formed by detector system
The X-ray beam 105 of 118 decay received.In some other example examples, object lens are used for the inspection in X-ray imaging system
Survey in device system 118 and form image.
Amplified using geometry, the amplification projected image of sample 114 with equal to source to sample distance 202 and source to detector away from
The magnifying power of inverse ratio between from 204 is formed on detector system 118.In general, the geometry magnifying power of X-ray platform is 2
And between 100, or bigger.In this case, the resolution ratio of X-ray image is subject to the focus ruler of X-ray source system 102
The limitation of very little or dimensions of virtual.
In order to realize high-resolution, the present example of X-ray CT system 200 is further using very high-resolution
Detector system 118, X-ray source system 102 is positioned close to reference to by sample 114.In one implementation, scintillator 119 with
Between micro objective 121 is used in combination to provide 2 and 100, or the addition power of bigger.
In order to adjust geometry magnifying power, operator adjusts source using the user-interface application 126 in computer system 124
To sample distance 202 and source to detector distance 204.Operator adjusts these distances to realize desired geometry magnifying power.
Be typically based on the parameter of operator's restriction, the controller 122 of computer system 124 indicate turntable 110 relative to
Beam 103 rotates sample, to perform CT scan via controller 122.According to some realizations, x-ray detector system 118 also carries
The ability of the visual field of sample 114 is adjusted for use by the pixel size in x-ray detector system 118 is changed.
Detector system 118 creates the X-ray beam from the decay interacted with the scintillator 119 in detector system 118
Graphical representation in the pixel of 105 X-ray photon.The image formed at detector system 118 is referred to as X-ray throwing
Shadow or X-ray projected image.
In one example, computer system 124 includes image processor 120 and user-interface application 126.It is connected to meter
The display device 136 of calculation machine system 124, shows usually in the user-interface application 126 of computer system 124 and comes from X-ray
The information of CT system 200.The input unit 142 of such as touch-screen or computer mouse is realized in operator, computer system 124
Interaction between display device 136.
Computer system 124 is carried out load information from the database 150 for being connected to computer system 124 and is stored information into
Database 150.Controller 122 has controller interface 130, it allows operator to be controlled via computer system 124 in software
Component in lower control and management X-ray CT system 200.
Component of the control of controller 122 with controller interface 130.Component with controller interface 130 includes image
Processor 120, detector system 118, turntable 110 and X-ray source system 102.
Using user-interface application 126, operator limits/selects CT scan parameter 232.These are included with X-ray source system
The X-ray voltage that scanning and the X-ray power spectrum of time for exposure on system 102 limit is set.Operator usually also selects other
Set, such as incide the visual field of X-ray beam 103 on sample 114, the number of the X-ray projected image created for sample 114
The angle of the turntable 110 of mesh and the sample 114 for rotating the X-ray CT scan in X-ray beam 103.
Computer system 124, by means of its image processor 120, receives from detector system 118 and sample 114
Each rotation angle image or projection information that are associated.Image processor 120 creates for each rotation angle of sample 114
Single projected image, and believed using CT algorithm for reconstructing combination projected images with creating three-dimensional tomographic volume for sample
Breath.
Fig. 3 is to provide the journey by for example being performed in computer system 124 or another computer system or computing resource
The flow chart of the details of MAR performed by sequence.
In step 902, identification promotes the height-Z metals in the sample 114 of main artifact 106.It generally, there are sample
Promote to create the priori of the appearance of the height-Z elements of main artifact 106 and the type of these elements in 114, and therefore, this
A little information are inputted by operator or received from database (for example, 150).For example, in most of semiconductor fabrications, member
Plain component is known and well limits.In other examples, these information by the graphical analysis of image processor 120 come really
It is fixed.It is typically chosen one or more height-Z metals.
In step 904, program allows the operator to the X- of influence of the sensitivity that selection includes detector system 118 and penetrates
The voltage of line source 102 is set.The operation also referred to as limits available energy spectrum.In this example, the selection of effective power spectrum also with selection
The wave filter 107 of sweep parameter 232 is associated.Power spectrum can pass through physical measurement or the mould performed by image processor 120
Intend program measurement in advance and/or estimation.
According to step 906, X-ray CT system 200 is being selected under the control of computer system 124 according to sweep parameter 232
The X-ray power spectrum selected performs the CT scan of sample 114.In response to scanning, in step 908, program causes image processor
120 can create sample by rotating sample in the X-ray beam 103 of the X-ray source 102 from X-ray CT system 200
The base line projection collection 502 of product 114.In addition, in general, any scanning track, including spiral-fault photography can be used, wherein
Sample 114 is together with other continuous or discrete tracks by rotation and translation at the same time.But in some implementations, at image
Reason device 120 further creates beam hardening correction (BHC) set of projections by using N rank multinomials fitting algorithm, is come from correction
The beam hardening effect of original baseline projection.Then, BHC is projected and then can be provided improvement in step 910 for metal segmentation
Reconstruction.But original baseline projection stills need to be used for basic material decomposition step 916, including it is following herein.
Exemplary base line projection 502 is illustrated in Fig. 5 A.Pay attention to the projection based on one-dimensional (1D) parallel beam of use
Simulation.When using one-dimensional parallel beam, base line projection collection/image 502 is also referred to as " sinogram ".In other more typical scenes
In, illumination X-ray beam has cone shape, such as the X-ray beam 103 described in Fig. 2.
In step 910, image processor 120 creates the baseline tomography volume data of sample from base line projection 502
Collection 504, or create BHC baseline tomography volumetric data sets 504-1 from BHC base line projections 502.Baseline tomography volume
Data set 504 is often uncorrected artifact.Here it is possible to use standard CT algorithm for reconstructing, including filtered back projection and FDK side
Method (FBP/FDK).In all follow-up steps, the volumetric data sets 504/504-1 that will be created as the result of step 910
It is referred to as the baseline tomography volumetric data sets 504 of sample 114.
Schematic diagram of Fig. 5 B shows from baseline tomography volumetric data sets 504.It is included from height-Z material structures
The obvious artifact 106 sent.
According to step 912, split height-Z metals from baseline tomography volumetric data sets 504 to create the height-Z of segmentation gold
Belong to volumetric data sets 506.In a manner of similar to other MAR methods based on segmentation, one or more threshold values are used with from base
Line tomography volumetric data sets 504 split height-Z metal parts, to create the height-Z metal volumes data set 506 of segmentation.It is standby
Selection of land, can use other dividing methods to isolate height-Z metallicities.
Fig. 5 C illustrate the height-Z metal volumes data set 506 of example division.It is it is characterized in that (more in height-Z materials
It is a) position at white point.
Step 914-1 and 914-2 receive the height-Z metal volumes data set 506 of segmentation as input, and to segmentation
Height-Z metallic datas collection 506 performs different forward projection's operations.
In step 914-1, program performs segmentation based on the thickness of the height-Z metals cut in the punishment of each projection angle
Height-Z metal volumes data set 506 forward projection (FP), with create with the height-Z metals that cut of each projection angle punishment
The height-Z thickness set of projections 508/FP that is associated of thicknesst.Height-Z thickness set of projections 508/FPtGenerally include and sample 114
The information that large fracture in height-Z structures is associated, because small crack is cleared away by thickness threshold value.Each height-Z set of projections 508/FPt
There is provided with being used when obtaining base line projection 502 in X-ray beam 103 during rotation sample 114 at each projection angle
The information that the thickness of height-Z metals is associated.
Fig. 5 D are illustrated from height-Z set of projections 508/FPtExemplary synthesis height-Z projection.In more generally pencil-beam
In geometry, the height-Z gold of three-dimensional segmentation is created from three-dimensional height-Z cone-beam projections using three-dimensional cone beam forward projection technology
Belong to volumetric image.
In practice, actual X-ray CT system 200 is limited with resolution ratio, causes the object edge in image can quilt
Obscure (compared with the idealization step function characteristic at edge).It is therefore preferred that perform the height-Z metal shadowings collection of forward projection
Gaussian Blur, to match actual systemic resolution limitation.As a result, height-Z projects 508/FPtEdge also can be by
It is fuzzy.
In step 914-2, MAR programs based on the X-ray of height-Z metals cut in the punishment of each projection angle decay come
The forward projection of the height-Z metal volumes data set 506 of segmentation is performed, to create height-Z X-ray attenuation projection collection 508/FPa。
Different from height-Z thickness set of projections 508/FPt, because not utilizing thickness threshold value, height-Z X-ray attenuation projection collection 508/FPa
It can include the information of all slits in the height-Z structures of sample 114.
Step 915 receives height-Z thickness set of projections FPtWith height-Z X-ray attenuation projection collection FPaAs input.Height-Z declines
Subtract set of projections 508/FPaExtraly with height-Z thickness set of projections FPtNormalization, and be then blurred with create it is normalized it is high-
Z set of projections 508-1.
In step 916, according to base line projection 502 and two or more preferable basic materials under the energy of selection
Relation, 508/FP is projected with reference to height-Z thicknesstPerform basic material to decompose, projected with generating equivalent low-Z (nonmetallic) element
Collection 510.It is also important that it is noted that when creating base line projection collection 502, the X-ray utilized in step 904 is used
The identical power spectrum in source is decomposed to perform the basic material of step 916.
Two kinds of basic materials preferably include the height-Z elements such as golden (Au), and equivalent low-Z materials such as Si of sample 114.
We assume that all other material (in addition to main metal) can be by equivalent low-Z element representations in sample 114
Or represent.As a part for the process, in image processor 120, look-up table (LUT) is used in advance to determine two kinds of bases
The thickness of material (that is, height-Z metallic elements and equivalent low-Z elements), and their corresponding X-rays at the power spectrum of selection
Relation between decay.The explanation that the more information used and Fig. 4 A and 4B included below on LUT is associated.
In practice, since the resolution ratio of X-ray CT system 200 limits, some drifts can occur when using ideal LUT
Move.These drifts will cause unexpected phenomenon, such as spike in their edges in equivalent low-Z projections (P0) 510, and
By the abnormal negative value of the sample segment of height-Z metals masking.Influence of these phenomenons to equivalent low-Z projections 510 be included in from
New artifact is introduced in the image of backprojection reconstruction.
In step 917, image processor 120 is alternatively performed for filtering or smooth edges (that is, spike) and moved
Except the operation of the abnormal negative value (that is, nonnegativity restrictions) in equivalent low-Z elements set of projections 510, to create smoothly equivalent
Low-Z set of projections (P0).Reference numeral 510-1 represents the selectable smooth of the equivalent low-Z projections created in step 917
Version.
Then, for Program transformation to step 918, it receives the normalized height-Z set of projections 508-1 created in step 915,
510 or their the smoothed version 510-1 from step 917 is projected as defeated with reference to the equivalent low-Z created in step 916
Enter.
In step 918, normalized height-Z is projected 508-1 by the monochromatic x-rays energy based on selection, program, and
Low-Z projects 510 or smooth height-Z projection 510-1 fusions (such as mixing/combination/set).As a result, terminate in step 918
When create the monochromatic fusion set of projections 511 of sample 114, wherein virtually all of beam hardening artifact is thrown from monochrome fusion
Removed in shadow 511.
In step 922, the tomography volume data of program and then the correction from monochromatic 511 reconstruction sample of fusion projection
Collect 514-2.According to step 924, program determines whether the picture quality of the tomography volumetric data sets 514-2 of correction can change
Into.In many cases, it is not necessary to extra processing.If improvement is unnecessary, program is terminated or stopped in step 926
Processing.Otherwise, according to the iterative processing circulation 950 of the tomography volumetric data sets 514-2 for improving correction, program is gone to
Step 928.
Step 928 is the image for being used to improve the tomography volumetric data sets 514-2 of correction in iterative processing circulation 950
The first step of quality.Processing cycle further includes step 930,932,918,922 and 924.In step 928, program is from correction
Tomography volumetric data sets 514-2 in split equivalent low-Z tomographies volumetric data sets 512.In step 930, journey
Sequence performs the forward projection of the equivalent low-Z tomographies volumetric data sets 512 provided from step 928, to generate newly equivalent
Low-Z set of projections Pi, wherein i=1,2 ... N, and equivalent low-Z set of projections is normalized.New equivalent low-Z projections
Collection is represented by reference numeral 510-2.
In step 932, program performs integration to the part of the sample 114 by the masking of height-Z metals from Pi and P0,
To create the low-Z elements set of projections Pi ' of integration.Low-Z elements set of projections the Pi ' of integration is represented by reference numeral 510-3.
In step 918, the identical monochromatic x-rays energy based on selection, by (integration) low-Z set of projections 510-3
Combined with normalized height-Z projections 508-1, to create new monochromatic fusion projection 511.Then, from new monochromatic fusion projection
The tomography volumetric data sets 514-2 of 511 correction versions generation/new correction of reconstruction.
Finally, in step 924, program determines the picture quality of the tomography volumetric data sets 514-2 of correction again
Whether can improve.If experiment is not usually required to be more than it has been shown that initially determine that the improvement to picture quality is possible
The iteration of the step associated with processing cycle 950 twice, to realize the image of the tomography volumetric data sets 514-2 of correction
The optimal improvement of quality,.
Fig. 4 A and 4B illustrate the look-up table (LUT) utilized for removing metal artifacts.Use the elder generation of the element in sample
Knowledge is tested to build LUT.For given power spectrum, LUT provides the X-ray pad value of the element of a function as element thickness.
For example, it is assumed that main metal is Au and equivalent low-Z elements are Si.It can calculate, wrap under given spectrum D (E) in theory
Include Au and Si, t with two kinds of different-thicknessAuAnd tSiSample X-ray decay (that is, transmissivity),
According to above-mentioned formula, Fig. 4 A illustrate the initial LUT that can be built.Y-axis represents tSi, x-axis expression tAu, and in table
Value representThen, willIt is reversed toAnd anti-phase LUT can be built from initial LUT,
As shown in Figure 4 B.
In figure 4b, y-axis representsX-axis represents tAu, and the value in table represents tSi.In fact, throw in practical situations
Shadow is considered being equivalent toThen with known projection valuesCalculate the thickness of equivalent low-Z elements, tSi, and by making
The thickness of metal, t are calculated with anti-phase LUTAu.Image processor 120 is based on height-Z elements projection 508 and base line projection 502 creates
Equivalent low-Z elements set of projections 510.Each projection is provided and in X-ray beam 103 in equivalent low-Z set of projections 510
Rotate the information that the thickness of the equivalent low-Z elements in each projection angle formed during sample 114 is associated.Fig. 5 E are shown
The schematic diagram of equivalent low-Z set of projections 510.
Although the preferred embodiment of reference specifically illustrates and the invention has been described, those skilled in the art will manage
Solution, in the case where not departing from the scope of the present invention that appended claims are covered, can carry out in form and details
Various changes.
Claims (6)
1. a kind of X-ray CT system, including：
X-ray imaging system, the X-ray imaging system include：
X-ray source system, the X-ray source system generate X-ray beam,
Turntable, the turntable have the sample retainer for being used for keeping sample, and
Detector system, the detector system are rotated against in the X-ray beam in the sample by the turntable
Shi Shengcheng base line projection collection；And
Computer system, the computer system include controller and image processor, and described image processor is used for from described
Base line projection collection generates the baseline tomography volumetric data sets of the sample；The baseline tomography volume number will be come from
According to the height-Z segmentation of structures of collection to create the height-Z volumetric data sets of segmentation；Thickness based on the metal in each projection angle and
Decay in the X-ray of each projection angle, generation height-Z set of projections is concentrated from the height-Z volume datas of the segmentation；Consider X-
The power spectrum of beam, equivalent low-Z set of projections is generated using one or more height-Z set of projections；It is described equivalent with using
Low-Z elements projection generates the tomography volumetric data sets of correction with the height-Z set of projections.
2. system according to claim 1, it is characterised in that the computer system will be by that will be based in each projected angle
Height-the Z of the X-ray attenuation projection collection of the X-ray decay of degree and the thickness based on the metal in each projection angle is thick
Degree set of projections is normalized, and creates normalized height-Z set of projections.
3. system according to claim 2, it is characterised in that the monochromatic X- of the selection of the power spectrum based on the X-ray beam
Ray energy, the computer system merges the equivalent low-Z projections and the normalized height-Z projections, to create
In the monochromatic fusion set of projections of the X-ray energy of selection.
4. system according to claim 3, it is characterised in that the computer system is weighed from the monochromatic fusion projection
Build the tomography volumetric data sets of the correction.
5. system according to claim 1, it is characterised in that the X-ray source system generates pencil-beam.
6. system according to claim 1, it is characterised in that the X-ray beam is polychromatic beam.
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