CN104574416A - Low-dose energy spectrum CT image denoising method - Google Patents
Low-dose energy spectrum CT image denoising method Download PDFInfo
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- 238000000354 decomposition reaction Methods 0.000 claims abstract description 25
- 239000000463 material Substances 0.000 claims abstract description 25
- 238000013178 mathematical model Methods 0.000 claims abstract description 10
- 239000000758 substrate Substances 0.000 claims description 43
- 238000010521 absorption reaction Methods 0.000 claims description 28
- 239000011159 matrix material Substances 0.000 claims description 27
- 238000003384 imaging method Methods 0.000 claims description 8
- 230000009977 dual effect Effects 0.000 claims description 5
- 238000012804 iterative process Methods 0.000 claims description 4
- 238000010586 diagram Methods 0.000 description 16
- 210000000988 bone and bone Anatomy 0.000 description 13
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- 238000003745 diagnosis Methods 0.000 description 3
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- 230000002238 attenuated effect Effects 0.000 description 1
- 238000002591 computed tomography Methods 0.000 description 1
- 238000005094 computer simulation Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000011551 log transformation method Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
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- 238000003672 processing method Methods 0.000 description 1
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- 238000004088 simulation Methods 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
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Abstract
The invention discloses a low-dose energy spectrum CT image denoising method. The low-dose energy spectrum CT image denoising method includes the steps of (1) obtaining low-energy CT projection data and high-energy CT projection data of an imaged object under low-dose rays, carrying out CT image reconstruction on the low-energy CT projection data and the high-energy CT projection data to obtain a low-energy CT image (please see the specification) and a high-energy CT image (please see the specification), wherein H represents high energy, and L represents low energy; (2) building a mathematical model used for energy spectrum CT image denoising according to a base material decomposition model met by the reconstructed data in the step (1); (3) using generalized total variation as regularization prior, and building an objective function used for image denoising in cooperation with the mathematical model obtained in the step (2); (4) solving the objective function which is built in the step (3) and used for energy spectrum CT image denoising with a splitting Bregman algorithm, and completing energy spectrum CT image denoising. According to the low-dose energy spectrum CT image denoising method, the base material decomposition model met by the high-energy image and the low-energy image in an energy spectrum CT is used, energy spectrum CT image information and base material image information are combined, and energy spectrum CT image denoising is achieved.
Description
Technical field
The present invention relates to a kind of image processing method of medical image, particularly a kind of low dosage power spectrum CT image de-noising method.
Background technology
Along with the develop rapidly of CT technology, the dual intensity CT scan technology based on power spectrum integrating detector and the photon counting Detection Techniques based on energy-resolved detector make power spectrum CT imaging obtain realization.Power spectrum CT is one of developing direction of following CT imaging technique, because power spectrum CT can not only obtain the information of material attenuated inside coefficient, and also can with crossing the information of rebuilding and obtaining material composition.Power spectrum CT can forward to function assessment diagnosis from traditional form diagnosis, and such as, it can find the focus that conventional CT can't find, and the extreme early that can realize tumour is detected, and can accomplish etiologic diagnosis and the quantitative test of tumour.In addition, power spectrum CT can solve many defects that conventional CT imaging exists, as removed beam hardening and metal artifacts etc.
Power spectrum CT imaging under low dosage condition just may realize application clinically, so need to find efficient low dose imaging method.The existing method realizing the imaging of low dosage power spectrum CT image mainly contains two classes.Wherein in data acquisition, reduce tube current (mA) as much as possible and tube voltage (kV) is the simplest method of one.Photon noise intensity in power spectrum data for projection can be caused to increase considerably for the reduction of tube current and the impact of electronic noise is more outstanding; Change tube voltage and can affect the penetrability of X ray to tissue, thus affect the picture quality of various tissue.Another is Using statistics method for reconstructing, utilizes its physical model accurately, to advantages such as insensitive for noise, can reconstruct image, improve the noise of final image under irregular sampling and shortage of data situation, improves the spatial resolution of rebuilding image.Because power spectrum CT data for projection amount is huge, it is too large to there is calculated amount in this method, and reconstruction time is very long, is difficult to the requirement meeting clinical middle real-time, interactive.
Therefore, not enough for prior art, a kind of low dosage power spectrum CT image de-noising method is provided, the density measure accuracy of substrate matter can be improved, the photo-quality imaging of power spectrum CT image under low-dose scanning agreement can be realized.
Summary of the invention
The object of the invention is to avoid the deficiencies in the prior art part and a kind of low dosage power spectrum CT image de-noising method is provided, the picture quality of substrate matter density image can be improved, the photo-quality imaging of power spectrum CT image under low-dose scanning agreement can be realized.
Above-mentioned purpose of the present invention is realized by following technological means.
A kind of low dosage power spectrum CT image de-noising method is provided, comprises the steps,
(1) obtain the low-yield CT data for projection of imaging object under low dosage ray and high-energy CT data for projection, and respectively CT image reconstruction is carried out to low-yield CT data for projection and high-energy CT data for projection, obtain low-yield CT image
with high-energy CT image
, wherein
hrepresent high energy,
lrepresent low energy;
(2) according to the data reconstruction in step (1) the substrate matter decomposition model that meets, build the mathematical model being used for power spectrum CT image denoising;
(3) utilize the full variation of broad sense as regularization priori, the mathematical model that integrating step (2) obtains builds the objective function for image denoising;
(4) division Bregman Algorithm for Solving is adopted to the objective function for power spectrum CT image denoising built in step (3), complete power spectrum CT image denoising.
Preferably, the substrate matter decomposition model in above-mentioned steps (2) is:
Material is to the mass absorption function of X-ray
the mass absorption function of being verified by any two materials and substrate is represented:
, wherein
with
the mass absorption function of two materials respectively,
the density of required substrate matter respectively, and
value and X-ray energy have nothing to do;
According to substrate matter decomposition model, for high-energy CT data for projection and the low-yield CT data for projection of step (1) power spectrum CT, the expression formula of the mass absorption function of corresponding material is:
,
Definition material mass absorption function matrix
, substrate matter mass absorption Jacobian matrix
, substrate matter density matrix
;
ccalculated by inverse matrix and directly obtain, formula is
, definition substrate matter mass absorption matrix
ainverse matrix form
.
Preferably, in above-mentioned steps (3), concrete employing uses the full variation of second order broad sense as priori, and the full variation definition of second order broad sense is:
；
Wherein
for non-negative weighting coefficient;
for the auxiliary parameter that the full variation of broad sense is introduced, and get
represent symmetric gradient operator, wherein
represent gradient operator,
representing matrix transpose operation;
The objective function for image denoising built in described step (3)
be specially:
, the wherein power spectrum CT image that obtains after representing denoising of X, Y measures the power spectrum CT view data obtained,
with
regularization parameter, for portraying the full variational regularization intensity of broad sense.
Preferably, in above-mentioned steps (4), the concrete computation process of division Bregman algorithm is:
Introducing formula A, formula B and formula C carry out iterative,
, wherein
a vector value introduced,
represent residual error,
nrepresent iterative steps;
Concrete iterative process is carried out in accordance with the following steps:
(4.1) make
n=0,
(4.2) according to formula
awith
b ,solved by primal dual algorithm
;
(4.3) step (4.1) is obtained
substitute into formula
csolve
;
(4.4) iteration ends is judged whether
Judge whether n equals N, if n equals N, then iteration ends, the power spectrum CT image after using current results as denoising;
If n is less than N, then enter step (4.5);
(4.5) make
n=
n+ 1, return step (4.2).
Preferably, above-mentioned steps (1) is also provided with registration process step, specifically:
Whether location offsets for the low-yield CT data for projection that judgement obtains and high-energy CT data for projection, adopts the method for Registration of Measuring Data that low-yield CT data for projection and high-energy CT data for projection are carried out registration process when location offsets.
Low dosage power spectrum CT image de-noising method of the present invention, comprise the steps, (1) the low-yield CT data for projection of imaging object under low dosage ray and high-energy CT data for projection is obtained, and respectively CT image reconstruction is carried out to low-yield CT data for projection and high-energy CT data for projection, obtain low-yield CT image
with high-energy CT image
, wherein
hrepresent high energy,
lrepresent low energy; (2) according to the data reconstruction in step (1) the substrate matter decomposition model that meets, build the mathematical model being used for power spectrum CT image denoising; (3) utilize the full variation of broad sense as regularization priori, the mathematical model that integrating step (2) obtains builds the objective function for image denoising; (4) division Bregman Algorithm for Solving is adopted to the objective function for power spectrum CT image denoising built in step (3), complete power spectrum CT image denoising.The present invention utilizes the substrate matter decomposition model that in power spectrum CT, high low energy image meets, and Momentum profiles CT image information and substrate matter image information, achieve power spectrum CT image denoising.While the present invention can use low dosage to launch, still can ensure to produce high-quality power spectrum CT denoising image, the inventive method has good robustness, suppresses all there is good effect in two in noise elimination and artifact.
Accompanying drawing explanation
The present invention is further illustrated to utilize accompanying drawing, but the content in accompanying drawing does not form any limitation of the invention.
Fig. 1 is the schematic flow sheet of low dosage power spectrum CT image de-noising method of the present invention.
Fig. 2 is the image schematic diagram that ideal body mould does not contain artifact and noise; Wherein, Fig. 2 (a) is the image schematic diagram not containing any artifact and noise under desirable Clock body mould 80kVp; Fig. 2 (b) is the image schematic diagram that desirable Clock body mould does not contain any artifact and noise under 140kVp.
Fig. 3 is the image schematic diagram after the low dosage data acquisition FBP algorithm of Clock body mould is directly rebuild; Wherein, Fig. 3 (a) is the image schematic diagram after the low dosage data acquisition FBP algorithm of Clock body mould under 80kVp is directly rebuild; Fig. 3 (b) is the image schematic diagram of Clock body mould after 140kVp low dosage data acquisition FBP algorithm is directly rebuild respectively.
Fig. 4 is the image schematic diagram that desirable Clock body mould low dosage data acquisition denoising method of the present invention obtains; Wherein, Fig. 4 (a) is the image that the low dosage data acquisition of Clock body mould under 80kVp obtains by denoising method of the present invention, and Fig. 4 (b) is the image that the low dosage data acquisition of Clock body mould under 140kVp obtains by denoising method of the present invention.
Fig. 5 water base figure that to be desirable Clock body mould obtain based on image area decomposition method decomposition method and bone base figure schematic diagram; Wherein, Fig. 5 (a) is water base figure schematic diagram, and Fig. 5 (b) is bone base figure schematic diagram.
Fig. 6 water base figure that to be low dosage Clock body mould obtain based on image area decomposition method decomposition method and bone base figure schematic diagram; Wherein, Fig. 6 (a) is water base figure schematic diagram, and Fig. 6 (b) is bone base figure schematic diagram.
Fig. 7 is the water base figure and bone base figure schematic diagram that obtain based on image area decomposition method after adopting denoising method of the present invention to obtain result; Wherein, Fig. 7 (a) is water base figure schematic diagram, and Fig. 7 (b) is bone base figure schematic diagram.
Fig. 8 is image section horizontal central line sectional view, and wherein Fig. 8 (a) is 80kVp image section horizontal central line sectional view, and Fig. 8 (b) is 140kVp image section horizontal central line sectional view.
Fig. 9 is water base figure and bone base figure part of horizontal center line sectional view, and wherein Fig. 9 (a) is water base figure part of horizontal center line sectional view, and Fig. 9 (b) is bone base figure part of horizontal center line sectional view.
Embodiment
The invention will be further described with the following Examples.
embodiment
1
.
A kind of low dosage power spectrum CT image de-noising method, as shown in Figure 1, comprises the steps,
(1) obtain the low-yield CT data for projection of imaging object under low dosage ray and high-energy CT data for projection, and respectively CT image reconstruction is carried out to low-yield CT data for projection and high-energy CT data for projection, obtain low-yield CT image
with high-energy CT image
, wherein
hrepresent high energy,
lrepresent low energy;
(2) according to the data reconstruction in step (1) the substrate matter decomposition model that meets, build the mathematical model being used for power spectrum CT image denoising;
(3) utilize the full variation of broad sense as regularization priori, the mathematical model that integrating step (2) obtains builds the objective function for image denoising;
(4) division Bregman Algorithm for Solving is adopted to the objective function for power spectrum CT image denoising built in step (3), complete power spectrum CT image denoising.
Preferably, above-mentioned steps (1) is also provided with registration process step, specifically: whether location offsets for the low-yield CT data for projection that judgement obtains and high-energy CT data for projection, adopts the method for Registration of Measuring Data that low-yield CT data for projection and high-energy CT data for projection are carried out registration process when location offsets.
Wherein, the substrate matter decomposition model in step (2) is:
Material is to the mass absorption function of X-ray
the mass absorption function of being verified by any two materials and substrate is represented:
, wherein
with
the mass absorption function of two materials respectively,
the density of required substrate matter respectively, and
value and X-ray energy have nothing to do;
According to substrate matter decomposition model, for high-energy CT data for projection and the low-yield CT data for projection of step (1) power spectrum CT, the expression formula of the mass absorption function of corresponding material is:
,
Definition material mass absorption function matrix
, substrate matter mass absorption Jacobian matrix
, substrate matter density matrix
;
ccalculated by inverse matrix and directly obtain, formula is
, definition substrate matter mass absorption matrix
ainverse matrix form
.
Wherein, in step (3), concrete employing uses the full variation of second order broad sense as priori, and the full variation definition of second order broad sense is:
；
Wherein
for non-negative weighting coefficient;
for the auxiliary parameter that the full variation of broad sense is introduced, and get
represent symmetric gradient operator, wherein
represent gradient operator,
representing matrix transpose operation.
The objective function for image denoising built in step (3)
be specially:
, the wherein power spectrum CT image that obtains after representing denoising of X, Y measures the power spectrum CT view data obtained,
with
regularization parameter, for portraying the full variational regularization intensity of broad sense.
In step (4), the concrete computation process of division Bregman algorithm is:
Introducing formula A, formula B and formula C carry out iterative,
, wherein
a vector value introduced,
represent residual error,
nrepresent iterative steps.
Concrete iterative process is carried out in accordance with the following steps:
(4.1) make
n=0,
(4.2) according to formula
awith
b ,solved by primal dual algorithm
;
(4.3) step (4.1) is obtained
substitute into formula
csolve
;
(4.4) iteration ends is judged whether
Judge whether n equals N, if n equals N, then iteration ends, the power spectrum CT image after using current results as denoising;
If n is less than N, then enter step (4.5);
(4.5) make
n=
n+ 1, return step (4.2).
The present invention utilizes the substrate matter decomposition model that in power spectrum CT, high low energy image meets, and Momentum profiles CT image information and substrate matter image information, achieve power spectrum CT image denoising.While the present invention can use low dosage to launch, still can ensure to produce high-quality power spectrum CT denoising image, the inventive method has good robustness, suppresses all there is good effect in two in noise elimination and artifact.
embodiment
2
.
Describe the specific implementation process of the method for the invention with the Voxel Phantom data instance of Computer Simulation, as shown in Fig. 1, the implementation process of the present embodiment is as follows.
(1) utilize Clock Voxel Phantom to simulate and generate the checking assessment that low dosage power spectrum CT data for projection carries out algorithm of the present invention.In the present embodiment, simulation CT machine x-ray source is respectively to the distance of rotation center and detector: 570.00mm and 1040.00mm, the number of detection unit is 672, and size is 1.407mm, and the search angle rotated a circle is 1160 to number of samples.Clock phantom image size is 512 × 512.80kVp and the 140kVp data for projection that size is 1160 × 672 is generated respectively by CT system emulation.The variance of system electronic noise is 10.0.
(2) data reconstruction: utilize the systematic parameter obtained to carry out detection data correction, carry out log-transformation, and carry out filtered back projection's reconstruction.
(3) design of graphics is as denoising model: the substrate matter decomposition model that the power spectrum CT view data after the reconstruction obtain step (2) meets carries out mathematical modeling, complete the design of the priori item of the full variation of broad sense, construct the objective function of the belt restraining for power spectrum CT image denoising
,
, the wherein power spectrum CT image that obtains after representing denoising of X, Y measures the power spectrum CT view data obtained,
with
regularization parameter, in embodiments of the present invention,
,
, for portraying the full variational regularization intensity of broad sense.
Substrate matter decomposition model concrete form is:
Material is to the mass absorption function of X-ray
the mass absorption function of being verified by any two materials and substrate is represented:
, wherein
with
the mass absorption function of two materials respectively,
the density of required substrate matter respectively, and
value and X-ray energy have nothing to do;
According to substrate matter decomposition model, for high-energy CT data for projection and the low-yield CT data for projection of step (1) power spectrum CT, the expression formula of the mass absorption function of corresponding material is:
,
Definition material mass absorption function matrix
, substrate matter mass absorption Jacobian matrix
, substrate matter density matrix
;
ccalculated by inverse matrix and directly obtain, formula is
, definition substrate matter mass absorption matrix
ainverse matrix form
.
The detailed process that above-mentioned broad sense full variational regularization priori builds is: use the full variation of second order broad sense as priori, its definition is:
; Wherein
,
for non-negative weighting coefficient; The full variation of broad sense introduces auxiliary parameter
, and get
.
(3) complete denoising: on the correlation model basis that step (3) builds, adopt division Bregman algorithm to carry out image denoising process, concrete computation process is:
Introducing formula A, formula B and formula C carry out iterative,
, wherein
a vector value introduced,
represent residual error,
nrepresent iterative steps.
Concrete iterative process is carried out in accordance with the following steps:
(4.1) make
n=0,
(4.2) according to formula
awith
b ,solved by primal dual algorithm
;
(4.3) step (4.1) is obtained
substitute into formula
csolve
;
(4.4) iteration ends is judged whether
Judge whether n equals N, if n equals N, then iteration ends, the power spectrum CT image after using current results as denoising;
If n is less than N, then enter step (4.5);
(4.5) make
n=
n+ 1, return step (4.2).
In order to verify the effect of method for reconstructing of the present invention, the result of the present embodiment is shown as shown in Fig. 2-Fig. 7, wherein: Fig. 2 (a) and Fig. 2 (b) is the image that desirable Clock body mould does not contain any artifact and noise under 80kVp and 140kVp respectively.Fig. 3 (a) and Fig. 3 (b) is the image that Clock body mould obtains after 80kVp and 140kVp low dosage data acquisition FBP algorithm is directly rebuild respectively, can see that the reduction due to dosage causes reconstruction image to occur serious statistical noise.Fig. 4 (a) and Fig. 4 (b) is that desirable Clock body mould rebuilds the water base figure and bone base figure that obtain based on projection domain decomposition method respectively.Fig. 5 (a) and Fig. 5 (b) is that low dosage Clock body mould rebuilds the water base figure and bone base figure that obtain based on projection domain decomposition method respectively; equally, the noise existed in original high low energy image result in the density image of substrate matter and is also present in serious noise.Fig. 6 (a) and Fig. 6 (b) is the water base figure and bone base figure that adopt method for reconstructing of the present invention to obtain respectively, rebuild image as can be seen from two width of Fig. 6, the result effect in restraint speckle and artifact utilizing the inventive method reconstruction to obtain is obvious.
Fig. 7 (a) and 7(b) in depict and rebuild image level center line sectional view corresponding to substrate matter in Fig. 4, Fig. 5 and Fig. 6,512 pixels are contained in view of in the entire profile figure, whole display is then difficult to distinguish each method, therefore when only showing, only intercept wherein one section, for water base figure, its interval is [189,320].For bone base figure, its interval is [147,189].As seen from Figure 7, at water base figure with in bone base figure, no matter background area or target area, the inventive method reconstructed value is closer to ideal value.
The present invention utilizes the substrate matter decomposition model that in power spectrum CT, high low energy image meets, and Momentum profiles CT image information and substrate matter image information, achieve power spectrum CT image denoising.While the present invention can use low dosage to launch, still can ensure to produce high-quality power spectrum CT denoising image, the inventive method has good robustness, suppresses all there is excellent performance in two in noise elimination and artifact.
Finally should be noted that; above embodiment is only in order to illustrate technical scheme of the present invention but not limiting the scope of the invention; although be explained in detail the present invention with reference to preferred embodiment; those of ordinary skill in the art is to be understood that; can modify to technical scheme of the present invention or equivalent replacement, and not depart from essence and the scope of technical solution of the present invention.
Claims (5)
1. a low dosage power spectrum CT image de-noising method, is characterized in that: comprise the steps,
(1) obtain the low-yield CT data for projection of imaging object under low dosage ray and high-energy CT data for projection, and respectively CT image reconstruction is carried out to low-yield CT data for projection and high-energy CT data for projection, obtain low-yield CT image
with high-energy CT image
, wherein
hrepresent high energy,
lrepresent low energy;
(2) according to the data reconstruction in step (1) the substrate matter decomposition model that meets, build the mathematical model being used for power spectrum CT image denoising;
(3) utilize the full variation of broad sense as regularization priori, the mathematical model that integrating step (2) obtains builds the objective function for image denoising;
(4) division Bregman Algorithm for Solving is adopted to the objective function for power spectrum CT image denoising built in step (3), complete power spectrum CT image denoising.
2. low dosage power spectrum CT image de-noising method according to claim 1, is characterized in that:
Substrate matter decomposition model in described step (2) is:
Material is to the mass absorption function of X-ray
the mass absorption function of being verified by any two materials and substrate is represented:
, wherein
with
the mass absorption function of two materials respectively,
the density of required substrate matter respectively, and
value and X-ray energy have nothing to do;
According to substrate matter decomposition model, for high-energy CT data for projection and the low-yield CT data for projection of step (1) power spectrum CT, the expression formula of the mass absorption function of corresponding material is:
,
Definition material mass absorption function matrix
, substrate matter mass absorption Jacobian matrix
, substrate matter density matrix
;
ccalculated by inverse matrix and directly obtain, formula is
, definition substrate matter mass absorption matrix
ainverse matrix form
.
3. low dosage power spectrum CT image de-noising method according to claim 2, is characterized in that:
In described step (3), concrete employing uses the full variation of second order broad sense as priori, and the full variation definition of second order broad sense is:
；
Wherein
for non-negative weighting coefficient;
for the auxiliary parameter that the full variation of broad sense is introduced, and get
represent symmetric gradient operator, wherein
represent gradient operator,
representing matrix transpose operation;
The objective function for image denoising built in described step (3)
be specially:
, the wherein power spectrum CT image that obtains after representing denoising of X, Y measures the power spectrum CT view data obtained,
with
regularization parameter, for portraying the full variational regularization intensity of broad sense.
4., according to low dosage power spectrum CT image de-noising method according to claim 3, it is characterized in that:
In described step (4), the concrete computation process of division Bregman algorithm is:
Introducing formula A, formula B and formula C carry out iterative,
, wherein
a vector value introduced,
represent residual error,
nrepresent iterative steps;
Concrete iterative process is carried out in accordance with the following steps:
(4.1) make
n=0,
(4.2) according to formula
awith
b ,solved by primal dual algorithm
;
(4.3) step (4.1) is obtained
substitute into formula
csolve
;
(4.4) iteration ends is judged whether
Judge whether n equals N, if n equals N, then iteration ends, the power spectrum CT image after using current results as denoising;
If n is less than N, then enter step (4.5);
(4.5) make
n=
n+ 1, return step (4.2).
5. low dosage power spectrum CT image de-noising method according to claim 1, is characterized in that:
Described step (1) is also provided with registration process step, specifically:
Whether location offsets for the low-yield CT data for projection that judgement obtains and high-energy CT data for projection, adopts the method for Registration of Measuring Data that low-yield CT data for projection and high-energy CT data for projection are carried out registration process when location offsets.
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| CN106815813A (en) * | 2015-11-27 | 2017-06-09 | 西门子医疗有限公司 | Method and image-data processing apparatus for processing multi-energy computed tomography images data set |
| CN107356615A (en) * | 2016-05-10 | 2017-11-17 | 清华大学 | A kind of method and system for dual-energy x-ray CT |
| CN108475419A (en) * | 2015-12-15 | 2018-08-31 | 皇家飞利浦有限公司 | The method of data processing for computer tomography |
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