CN105469366A - Analytic method for eliminating metal artifact of CT image - Google Patents
Analytic method for eliminating metal artifact of CT image Download PDFInfo
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- CN105469366A CN105469366A CN201510808114.3A CN201510808114A CN105469366A CN 105469366 A CN105469366 A CN 105469366A CN 201510808114 A CN201510808114 A CN 201510808114A CN 105469366 A CN105469366 A CN 105469366A
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 78
- 239000002184 metal Substances 0.000 title claims abstract description 78
- 238000004458 analytical method Methods 0.000 title claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 37
- 238000001228 spectrum Methods 0.000 claims abstract description 18
- 229910052704 radon Inorganic materials 0.000 claims description 6
- 238000013461 design Methods 0.000 claims description 4
- 239000011159 matrix material Substances 0.000 claims description 4
- 238000012545 processing Methods 0.000 claims description 3
- 230000010354 integration Effects 0.000 claims description 2
- 230000009466 transformation Effects 0.000 claims description 2
- 238000012937 correction Methods 0.000 abstract description 7
- 238000002591 computed tomography Methods 0.000 description 10
- 230000011218 segmentation Effects 0.000 description 5
- SYUHGPGVQRZVTB-UHFFFAOYSA-N radon atom Chemical compound [Rn] SYUHGPGVQRZVTB-UHFFFAOYSA-N 0.000 description 4
- 238000003759 clinical diagnosis Methods 0.000 description 3
- 238000001883 metal evaporation Methods 0.000 description 3
- 238000003745 diagnosis Methods 0.000 description 2
- 230000008030 elimination Effects 0.000 description 2
- 238000003379 elimination reaction Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000007943 implant Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 210000000214 mouth Anatomy 0.000 description 2
- 229910000645 Hg alloy Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 238000003709 image segmentation Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000010606 normalization Methods 0.000 description 1
- 150000003257 radon Chemical class 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 108010048734 sclerotin Proteins 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 210000004872 soft tissue Anatomy 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 210000000115 thoracic cavity Anatomy 0.000 description 1
- 238000003325 tomography Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10072—Tomographic images
- G06T2207/10081—Computed x-ray tomography [CT]
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Abstract
The invention provides an analytic method for eliminating a metal artifact of a CT image. With the method, the iterative operation can be avoided. The method comprises: a metal image is segmented from an image reconstructed based on projection data on the multi-energy-spectrum-ray condition; a projection image is solved; an approximate value of an energy spectrum function is searched; an expression of an artifact function is obtained and an artifact image is obtained; the artifact image is subtracted from an original image to obtain a corrected image as shown in an attached drawing. The method is characterized in that the band shaped artifact can be eliminated and the structural feature of original information can be kept; and no priori knowledge of the energy spectrum and original projection data are needed according to the correction method and the reconstruction speed is fast.
Description
Technical field
The present invention relates generally to medical X-ray Computed tomography (ComputedTomography, be called for short CT) field, specifically, relating to medicine CT is detected as in picture, when detected human body a part (such as oral cavity, thoracic cavity etc.) implanted metal thing, there is metal artifacts situation in the CT image of reconstruction.
Background technology
CT detects the acquisition object faultage image that imaging technique can can't harm, irreplaceable vital role is played in medical science auxiliary diagnosis. in the ideal case, the data for projection that the scanning system of CT equipment records is the line integral of material linear attenuation coefficient, the reconstructing system of CT equipment carries out image reconstruction by these line integral data, obtain the CT image that may be used for clinical diagnosis and use. but in actual CT scan, the data for projection that system obtains comprises various error usually, the error that such as metal object causes, this can cause occurring artifact in reconstruction image, reduce picture quality, having a strong impact on diagnostic result. the metal implant in human body has intraoral tooth filling usually, surgical clips and joint prosthesis etc. in body, these metal objects have high Decay Rate, when CT image reconstruction direct by data for projection, rebuild in image and there will be radial or banding artifact etc., generally be called metal artifacts.
The situation comprising metal object is often run in actual CT scan, such as oral cavity CT scan. because the complex genesis of metal artifacts, and the material of metal and geomery can directly cause the power of metal artifacts in image different with distribution, although therefore have some data about metal artifacts school removing method and patent at present, even if but still there is no a kind of method of more common elimination or abatement metal artifacts. for the metal artifacts reduction software for orthopaedics that Philip is released, also gratifying correction result cannot be provided for multiple situation. therefore, the method researching and developing some blanket metal artifacts abatements has very important significance for Medical CT system.
Metal artifacts reduction (Metalartifactreduction, MAR) algorithm is mainly divided into method of interpolation, projection correction, iterative approximation, the method such as bearing calibration and composed correction based on prior image. also there is the patent of a lot of metal artifacts reduction aspect in recent years, such as:
A kind of method for reducing metal artifacts in CT image data set is disclosed by the Chinese patent CN103190928A of Siemens application. the method by rebuilding the CT image data set through metal artifacts reduction and the 2nd CT image data set without metal artifacts reduction, and make use of data weighting method etc.
The Chinese patent CN103186889A applied for by GE company of the U.S. discloses a kind of method and apparatus for reducing the metal artifacts in medical image. and the method considers the artifact that same tomography comprises large metal object and the little metal object generation with different size simultaneously, processes the artifact that in same faultage image, large metal object and little metal object produce in a different manner.
Chinese patent CN103679642A discloses the bearing calibration of a kind of CT image metal artifact, device and CT equipment, metal shadowing's scope that the method original image determination objects interfered corresponding according to Raw projection data causes, then removes the diagnosis object data for projection after objects interfered and Modling model image based on the metal shadowing's data acquisition within the scope of metal shadowing successively; According to the data for projection of model image, secondary correction, reconstruction are carried out to described Raw projection data again, obtain the target image not having metal artifacts.
Chinese patent CN103745440A discloses a kind of CT system metal artifact correction method, create the matrix of coefficients of described CT system according to initiation parameter in the method, based on the object attenuation coefficient f in the process of described system matrix computation CT image reconstruction, optimize described object attenuation coefficient f again, realize the metal artifacts reduction to CT system.
Chinese patent CN103440636A discloses a kind of metal artifacts removing method of CT system, the method obtains new CT scan data through a series of data processing operation, and then rebuild image. high pressure and low pressure CT scan are converted simultaneously, thus realize the minimizing of calculated amount.
Above-mentioned technology has related to various metals artifact correction method, but all do not have method and algorithm to relate to the Analytical Expression of metal artifacts. The present invention gives a kind of analytic method of effective removal CT image metal artifact, avoid iterative computation, save reconstruction time.
Summary of the invention
The present invention, mainly for metal artifacts problem common in Medical CT, proposes a kind of analytic method of effective removal metal artifacts.
The present invention is achieved through the following technical solutions:
The analytic method of abatement CT image metal artifact, mainly comprise: first CT scan system obtains the data for projection of detected object f (x), then image reconstruction is carried out by CT reconstructing system, metal object is partitioned into from reconstruction image, again reprojection is carried out to metal objects, this data for projection is processed, carry out reconstruction again and obtain artifacts, finally from original image, deduct artifacts, obtain target image, namely the image after correcting. it is characterized in that, while eliminating banding artifact, remain the architectural feature of original information; The priori of X-ray energy spectrum and original data for projection is not needed in bearing calibration.
The data for projection P of the detected object described in acquisition, these data obtain in multi-power spectrum ray situation;
CT image P described in acquisition, from reconstructs projection data CT image f
e, E is the energy parameter of ray;
Metal object image described in acquisition, goes out the image of metal object by Threshold segmentation (general adopt threshold value be 3000HU) or Level Set Method from the CT Iamge Segmentation rebuild;
The data for projection of the image of the metal object described in acquisition, utilizes projection matrix to obtain its data for projection, and namely its Radon converts R Ψ
metal;
Metal artifacts image described in acquisition, the approximate function Asin (ω (E+)) of design power spectrum, the artifact expression formula K=R of proposition
-1(P-Rf
e0)=-R
-1(ln (π
2cosh (ρ R Ψ
metal)/(π
2+ 4 ρ
2(R Ψ
metal)
2))) to process data R Ψ
metal, then rebuild, obtain the approximate image K of artifact, f
e0that hypothesis is in certain ENERGY E
0under objective function, ρ is parameter, Ψ
metalit is the fundamental function of metallic region;
Image f after namely target image described in acquisition corrects
e0, original weight builds image f
ededuct artifacts K (x) and obtain f
e0.
The present invention relates to a kind of method of abatement CT image metal artifact newly, the method directly obtains the image of image artifacts, very effective. compared with metal artifacts reduction method in the past, beneficial effect of the present invention has: (1) remains the architectural feature of original information while eliminating banding artifact; (2) without the need to the priori of ray energy spectrum; (3) in bearing calibration without the need to original data for projection; (4) adopt analytic reconstruction method, speed of rebuilding is fast.
Accompanying drawing explanation
The two-dimentional lower jaw Voxel Phantom of improvement of Fig. 1 for using in embodiment;
Fig. 2 is the original image rebuild;
Fig. 3 is the artifacts rebuild;
Fig. 4 is the CT image after correcting.
Embodiment
Invention broadly provides a kind of method of cutting down CT image metal artifact, comprising and obtain data for projection, image reconstruction, segmentation metal objects, reprojection, data processing, artifacts reconstruction and obtain the image after correcting. target is the architectural feature that elimination banding artifact retains original information, obtain high-resolution CT image, for clinical diagnosis provides information more accurately. embodiments of the present invention: first obtain the data for projection under multi-power spectrum and carry out image reconstruction; Then carry out the image that Iamge Segmentation obtains metal objects, and ask its Radon to convert; By the analytic method proposed, this Radon transform data is processed, and the data after reconstruction process, obtain artifacts; Deduct artifacts by original image and obtain the CT image after correcting; Finally providing embodiment. concrete steps are as follows:
(1) original CT image is obtained
Carry out detected object scanning the data for projection obtained under multi-power spectrum X ray, by FBP algorithm or BPF algorithm reconstructed projection data, obtain original CT image, containing metal artifacts in this image.
(2) data for projection of metal image is obtained
Usually utilize threshold method to carry out Iamge Segmentation to original image, obtain metal image, the general threshold value adopted is 3000HU herein; And then obtain the data for projection of metal image.
(3) artifacts is obtained
First the approximate of energy spectrum function is found, provide the approximate expression of artifact function, obtain the artifact function determined. because in actual CT scan system, energy spectrogram be unknown, therefore approximate function can only be found according to its common characteristic, the function of this approximate power spectrum should meet: in energy range, integration is 1. such as: approximate function can select rectangular function, sine function, cosine function or other approximate function. according to can the feature of spectrogram, sine function is close to energy spectrum function. through being designed with related parameter, the approximate expression K=R of artifact function can be obtained
-1(P-Rf
e0). by this expression formula, the data for projection in step 2 is processed; Then ask Radon inverse transformation, utilize FBP or BPF algorithm realization herein, thus obtain artifacts. wherein relevant parameters can utilize some regularization method to ask its optimum solution.
(4) the CT image after correcting is obtained
Deduct artifacts in step 3 by the original image in step 1 and obtain the CT image after correcting.
(5) embodiment
It is the two-dimentional lower jaw Voxel Phantom improved that the present embodiment is chosen, comprise 512 × 512 pixels, the size of each pixel is 0.5mm × 0.5mm, as shown in Figure 1. the sclerotin composition in this body mould and soft tissue etc. are all arranged according to ICRU44 Report Parameters, their X-ray attenuation coefficient is obtained by XCOM software, and implants 3 mercury alloy objects.
This example adopts this body mould to produce artificial projections data. we used multi-power spectrum X ray in emulation. and regarding system parameter is as follows: x-ray source and rotation center distance are 1100mm, x-ray source and detector distance are 1600mm, the length of detector cells is that 0.87. uses the equidistant fan beam CT scan pattern of Circular test to produce the data for projection of this die body, wherein detector cells number is 512, and 360 degree of full scan projection angle numbers are 660.
Directly rebuild image according to step 1 in embodiment by data for projection, there is the artifacts such as obvious band shape in figure, have a strong impact on clinical diagnosis, as shown in Figure 2.
According to step 2 in embodiment above, selected threshold is 3000HU, to the Image Segmentation Using in Fig. 2, and its data for projection of recycling Radon conversion acquisition.
According to step 3 in embodiment above, choosing voltage range in this example is 0.01-1.2Kev, simulation process uses normalization energy spectrogram. power spectrum approximate function π sin (π (E-E0+h)/(2h))/(4h) chosen, wherein E0 is some energy, and h is an adjustable parameter; In this example, E0=0.65Kev, h=0.55Kev. are according to artifact expression formula-R
-1(ln (π
2cosh (ρ R Ψ
metal)/(π
2+ 4 ρ
2(R Ψ
metal)
2))) obtain artifacts as shown in Figure 3, can see that this figure is the presenting of banding artifact in Fig. 2, the parameter choose ρ=2.31. wherein optimized
According to step 4 in above-mentioned embodiment, original reconstruction figure image subtraction artifacts obtains the image after correcting, as shown in Figure 4.
Claims (7)
1. cut down an analytic method for CT image metal artifact, mainly comprise: from reconstruction image, be partitioned into metal object, reprojection is carried out to metal object; The approximate function of design X-ray energy spectrum; By processing the data for projection of metal object, carrying out reconstruction and obtaining artifacts; Finally from original image, deducting artifacts, obtain target image. the feature of described bearing calibration is: (1) employs the analytical expression of artifacts; (2) while eliminating banding artifact, remain the architectural feature of original information; (3) without the need to the priori of X-ray energy spectrum; (4) original data for projection is not used.
2. the analytic method of abatement CT image metal artifact according to claim 1, it is characterized in that: the data for projection obtained from multi-power spectrum ray, rebuild image by FBP algorithm or BPF algorithm, this image contains metal artifacts.
3. the analytic method of abatement CT image metal artifact according to claim 1, is characterized in that: utilize threshold method to be partitioned into metal image from reconstruction image, and utilize projection matrix to obtain the data for projection of metal image.
4. the analytic method of abatement CT image metal artifact according to claim 1, it is characterized in that: design a function be similar to X-ray energy spectrum, it is 1. can select rectangular function or sine function that this function meets integration in energy range. according to can the feature of spectrogram, use sine function Asin (ω (E+)) herein, it is closer to X-ray energy spectrum function.
5. the analytic method of abatement CT image metal artifact according to claim 1, is characterized in that: the approximate function utilizing design, processes the data for projection of metal image, obtain expression formula K (x)=-R of artifact function
-1(ln (π
2cosh (ρ R Ψ
metal)/(π
2+ 4 ρ
2(R Ψ
metal)
2))), i.e. artifacts, wherein ρ is a parameter, is R
-1radon inverse transformation,
Ψ
metalrepresent the fundamental function (be 1 in region, other are 0) of metallic region.
6. the analytic method of abatement CT image metal artifact according to claim 1, is characterized in that: parameter ρ can utilize regularization method to ask its optimum solution.
7. the analytic method of abatement CT image metal artifact according to claim 1, is characterized in that: build figure from original weight and deduct artifacts, obtains the target image after correcting.
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| JP2017221339A (en) * | 2016-06-14 | 2017-12-21 | 国立大学法人信州大学 | X-ray CT image reconstruction method and computer program |
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| CN110599559A (en) * | 2018-06-13 | 2019-12-20 | 西门子医疗有限公司 | Multi-energy metal artifact reduction |
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