CN106618619B - Computed tomography apparatus - Google Patents
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Abstract
The invention discloses a computer tomography imaging device, which comprises a frame, an X-ray source and an X-ray detector which are arranged oppositely, a control unit and an image reconstruction unit, and is characterized in that the control unit is configured to: performing phantom scanning by using the computed tomography imaging equipment; setting that bone tissue consists of a first substance and a second substance, and acquiring theoretical projection values and ideal projection values of the first substance and the second substance with different thicknesses combined in a tomography system; obtaining a bone hardening artifact correction coefficient according to the thickness of the second substance, the ideal projection values of the first and second substances and the projection value after the hardening correction of the first substance, and storing the bone hardening artifact correction coefficient into an image reconstruction unit; the image reconstruction unit is configured to: and reading the stored bone hardening artifact correction coefficient and correcting the bone hardening artifact. The scheme of the invention can efficiently remove the bone hardening artifact on the premise of good universality.
Description
The present application is a divisional application of an invention patent application having an application date of 2016, 1 and 30, an application number of "201610069409.8", entitled "method and apparatus for correcting artifact in computed tomography".
[ technical field ] A method for producing a semiconductor device
The invention relates to the technical field of computed tomography, in particular to a method and a device for correcting computed tomography artifacts.
[ background of the invention ]
The computerized tomography is a technology of scanning specific parts of human body with rays according to a certain thickness of a layer and reconstructing a tomographic image by a computer according to different absorption capacities of different human tissues to the rays.
In the process of carrying out computed tomography and reconstruction by using X-rays, because the X-rays generated by the bulb tube have a certain frequency spectrum width, the absorption coefficient of substances to the X-rays is reduced along with the increase of the energy of the X-rays, after the X-rays with continuous energy spectrums pass through a scanned object such as a human body, low-energy rays are easy to absorb, high-energy rays are easy to pass, the average energy of beams can be increased, and the rays are gradually hardened. This effect is called the beam hardening effect. The existence of the beam hardening effect can cause artifacts in image reconstruction, and the reconstruction quality of the image is affected. Therefore, the prior art performs ray hardening correction based on water model on projection data before reconstructing an image, and the correction can eliminate the X-ray hardening phenomenon of soft tissue but cannot eliminate ray hardening artifact caused by human bones, namely bone hardening artifact.
Various correction methods for bone hardening artifacts are known: one is based on image post-processing technology, eliminating bone hardening artifacts (such as Jiang Hsieh et al, "An iterative approach to the beam hardening correction in the beam CT", Med. Phys.271, January 2000) by empirical parameters, and has the disadvantages that the source of the correction coefficient lacks theoretical basis, and the correction accuracy and efficiency are poor; another method is to generate correction factors by pre-scanning a specially made bone tissue phantom (for example, patent CN 01124649.9-computer tomography device), which has the disadvantage that the coefficients obtained by scanning the bone tissue phantom are often lack of universality (the bone tissue components of people of different ages are very different and the same correction factor cannot be used). Therefore, none of the above solutions can solve the problem of bone hardening artifacts well.
Therefore, there is a need to provide a new method for correcting bone hardening artifact in computed tomography and an apparatus for implementing the method, which can remove bone hardening artifact efficiently with good universality.
[ summary of the invention ]
The invention solves the problem of bone hardening artifacts in computed tomography images.
In order to solve the above problems, the present invention provides a method for correcting bone hardening artifact in computed tomography, comprising: performing phantom scanning using a computed tomography device; setting that bone tissue consists of a first substance and a second substance, and acquiring theoretical projection values of combinations of the first substance and the second substance with different thicknesses in a tomography system; performing first substance hardening correction on the theoretical projection value to obtain a projection value after the first substance hardening correction; calculating ideal projection values of the combination of the first substance and the second substance with different thicknesses in the tomography system; obtaining a bone hardening correction coefficient according to the thickness of the second substance, the ideal projection values of the first and second substances and the projection value after hardening correction of the first substance; artifact correction is performed using the bone-hardening correction coefficients.
Optionally, the method further comprises: and acquiring the equivalent filtering thickness corresponding to each detection unit when the measured projection value of the phantom is equal to the theoretical projection value.
Optionally, the mold body is a uniform mold body of known thickness and material.
Optionally, the mold body is made of water or organic glass.
Optionally, the first substance hardening correction comprises: calculating theoretical projection values and ideal projection values of first substances with different thicknesses in the tomography system; performing polynomial fitting on the theoretical projection value and the ideal projection value to obtain a first substance hardening correction coefficient; the first material hardening correction coefficient is used for correction.
Optionally, the obtaining a bone hardening correction coefficient according to the second material thickness, the ideal projection value, and the first material hardening corrected projection value includes: and performing polynomial fitting by using the thickness of the second substance as an independent variable and using the difference between the ideal projection value and the projection value after the hardening correction of the first substance as a dependent variable to obtain a bone hardening correction coefficient.
Optionally, the obtaining a bone hardening correction coefficient according to the second material thickness, the ideal projection value, and the first material hardening corrected projection value includes: and performing surface fitting by using the first material thickness and the second material thickness as independent variables and using the difference between the ideal projection value and the projection value after the first material hardening correction as a dependent variable to obtain a bone hardening correction coefficient.
Optionally, the first substance is water and the second substance is a calcium-containing substance.
Optionally, the second substance is calcium phosphate.
The invention also provides a computer tomography bone hardening artifact correction device, which comprises: a storage unit for storing the bone hardening artifact correction coefficient obtained by the method; and the correction unit selects the correction coefficient according to the scanning data to correct the bone hardening artifact.
Compared with the prior art, the invention has the following beneficial effects:
the scheme is based on a base material theory, the bone tissue is considered to be composed of two base material substances, a correction coefficient with universality can be generated through one-time die body scanning, and a good bone hardening artifact correction effect can be obtained only by applying a proper tissue model in the reconstruction process.
[ description of the drawings ]
FIG. 1 is a schematic block diagram of a computed tomography imaging system of the present invention;
FIG. 2 is a flowchart illustrating a method for correcting bone hardening artifacts according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart illustrating the calibration process using water hardness calibration coefficients according to one embodiment of the present invention;
fig. 4 is an example of a correction coefficient table in an embodiment of the present invention.
[ detailed description ] embodiments
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Fig. 1 is a schematic structural view of a computed tomography system, as shown in fig. 1, a computed tomography system 100 includes a gantry 110, the gantry 110 having a rotatable portion 130 that rotates about a system axis. The rotatable part 130 has an X-ray system of oppositely arranged X-ray source 131 and X-ray detector 132.
The computed tomography system 100 also has a table 120 on which the patient can be pushed into the scanning volume in the Z-axis direction during the examination. The X-ray source 131 rotates about the S-axis and the detector 132 moves together with respect to the X-ray source 131 to acquire projection measurement data, which are then used to reconstruct an image. A helical scan may also be performed during which the X-ray source 131 produces a helical trajectory relative to the patient by continuous motion of the patient along the S-axis and simultaneous rotation of the X-ray source 131.
The computed tomography system 100 may further comprise a control unit for controlling the components of the computed tomography system 100 during a scan according to a specific scan protocol and an image reconstruction unit. The image reconstruction unit is configured to reconstruct an image from the data to be corrected sampled by the detector 132.
While the computer Tomography apparatus using the bone hardening artifact correction method provided by the present invention has been illustrated by way of example, those skilled in the art will appreciate that other apparatuses such as a C-arm system using X-rays, or a combined medical imaging system (e.g., a combined Positron Emission Tomography-computer Tomography, PET-CT), or a Tomography apparatus using other types of rays, may be used with the correction method and apparatus of the present invention, and the type and structure of the computer Tomography apparatus are not limited in any way.
When the object to be examined is scanned and imaged in any kind of computer tomography imaging device, the existence of the beam hardening effect can cause the existence of bone hardening artifacts, influence the image imaging quality and cause reading inconvenience, so that the artifacts need to be corrected. The following are specific examples of embodiments for correcting bone hardening artifacts according to the disclosed embodiments of the present invention:
fig. 2 is a schematic flow chart of a bone hardening artifact correction method according to an embodiment of the present invention:
step S1 is performed to perform phantom scanning using the computed tomography device. The mold body can be selected to be uniform in thickness and material, and preferably the mold body is selected from a material similar to the chemical composition of human soft tissue, such as water or plexiglass.
Step S2 is executed to obtain theoretical projection values of the combination of the first substance and the second substance with different thicknesses in the tomography system. In an X-ray scan, the linear attenuation coefficient of any tissue can be expressed as a linear combination of the mass attenuation coefficients of the two basis materials, according to the basis material decomposition theory. In this embodiment, the bone tissue is composed of two different substances (base materials), for example, a substance in which the bone tissue is considered to be a mixture of water and another component in a certain ratio. The other component may preferably be a substance having a high calcium content (in this example, calcium phosphate is selected).
In the computed tomography of an object, the measured projection values represent the projection values of the scanned object actually measured by the detector, the theoretical projection values represent the projection values of the scanned object calculated by considering the energy distribution of X-ray photons, and the ideal projection values represent the projection values of X-rays passing through the object when the photon energies are all E0 (E0 is a configurable parameter representing the specific value when the photon energy is single). For example, the measured projection value projMeas may be expressed as follows:
in the formula (1), I0And I represent the intensity of X-rays incident on and transmitted through the scanned object, respectively.
The theoretical projection value ProjCal calculation formula of the phantom in step S1 can be expressed as follows:
in formula (2), E represents the photon energy of X-ray, S (E) is the X-ray spectrum emitted by the bulb, D (E) is the detector response of the tomography system, mufilter(E) And muphan(E) Linear attenuation coefficient, L, of equivalent filter material and die body material, respectivelyfilterEquivalent filtering thickness, L, corresponding to each detection unitphanIs the thickness of the phantom scanned in step S1.
Further, in this embodiment, LfilterAnd (3) equivalent filtering thickness corresponding to each detection unit for making the measured projection value of the phantom equal to the theoretical projection value (which can be within an allowable error range). This can be determined by iterative methods, for example, iteratively modifying the thickness values and calculating theoretical projection values for the phantom according to equation (2) until the theoretical projection values are equal to the measured projection values (within an allowable error range).
In step S2, ProjCal is definedi,jFor the theoretical projection values of the combination of the first substance and the second substance with different thicknesses in the tomography system, the theoretical projection values of the combination of different thicknesses for the combination of water and calcium phosphate in the embodiment can be obtained by the following formula：
Wherein, muH2O(E) Represents the linear attenuation coefficient, L, of waterH2O,i(i-0, 1,2, …) indicates different water thicknesses, μphospca(E) Represents the linear attenuation coefficient, L, of calcium phosphatephospca,j(j ═ 0,1,2, …) indicates different calcium phosphate thicknesses (in the formula of the present specification, the same symbols and variables are as defined in the other formulae unless otherwise specified).
Step S3 is executed to perform first material hardening correction on the theoretical projection value, and obtain a first material hardening corrected projection value. For the water and calcium phosphate combination of this example, a water hardness correction is made, which can be done by a method that produces a water hardness correction factor.
Fig. 3 shows a flow of water hardening correction using the water hardening correction coefficient in the present embodiment:
first, step S301 is executed to determine theoretical projected values of water with different thicknesses. The value ProjCalH2O,iCan be obtained by the following formula:
wherein, muH2O(E) Represents the linear attenuation coefficient, L, of waterH2O,i(i-0, 1,2, …) indicates different water thicknesses.
Step S302 is executed to determine ideal projection values of water with different thicknesses. The ideal projection value ProjidealH2O,iCan be obtained by the following formula:
ProjIdealH2O,i＝μH2O(E0)LH2O,i (5)
in the formula (5), muH2O(E0) Represents the linear attenuation coefficient, L, of water for an X-photon of energy E0H2O,i(i-0, 1,2, …) indicates different water thicknesses.
Step S303 is executed to obtain ideal projection values and theoretical projection values of water with different thicknessesAnd performing polynomial fitting to obtain a water hardening correction coefficient. The water hardening correction coefficient alphakCan be obtained by the following formula:
in the formula (6), N1 represents the polynomial order, αk(k＝0,1,…)。
Finally, step S304 is performed to perform correction using the water hardening correction coefficient. ProjCal theoretical projection values for different combinations of water and calcium phosphate obtained in step S2i,jCorrected projection value proj corrected thereofi,jCan be obtained by the following formula:
wherein alpha iskThe water hardness correction coefficient obtained in step S303 is k 0,1, ….
After the first material hardening correction is completed, as shown in fig. 2, step S4 is executed to calculate the ideal projection values of the combination of the first material and the second material with different thicknesses in the tomography system. In this embodiment, the ideal projection value ProjIdeali,jCan be obtained by the following formula:
ProjIdeali,j＝μH2O(E0)LH2O,i+μphospca(E0)Lphospca,j (8)
wherein, muH2O(E0) Represents the linear attenuation coefficient, μ, of water for an X-photon of energy E0phospca(E0) Represents the linear attenuation coefficient, L, of calcium phosphate for the energy E0X photonH2O,i(i-0, 1,2, …) indicates different water thicknesses, Lphospca,j(j-0, 1,2, …) indicates different calcium phosphate thicknesses.
Step S5 is executed to obtain a bone hardening correction coefficient according to the thickness of the second substance, the ideal projection values of the first and second substances, and the projection value after the hardening correction of the first substance. In this example, the combination of water and calcium phosphate is divided intoThickness L of waterH2O,i(i-0, 1,2, …) thickness L of calcium phosphatephospca,j(j ═ 0,1,2, …) as an independent variable, and a surface fitting is performed using as a dependent variable the difference between the ideal projected values of the combination of water and calcium phosphate of different thicknesses obtained in step S4 and the projected values after water hardening correction obtained in step S3, and fitting parameters are obtained as bone hardening correction coefficients, and this process can be implemented according to the following equation:
ProjErrori,j＝ProjIdeali,j-ProjCorrectedi,j＝f(LH2O,i,Lphospca,j) (9)
in formula (9), f (L)H2O,i,Lphospca,j) Is represented by LH2O,i(i ═ 0,1,2, …) and Lphospca,j(j ═ 0,1,2, …) is the surface function of the argument.
According to a variant of this embodiment, the calcium phosphate thickness L can also bephospca,j(j ═ 0,1,2, …) as an independent variable, and polynomial fitting was performed using as a dependent variable the difference between the ideal projected values of the combination of water and calcium phosphate of different thicknesses obtained in step S4 and the projected value after water hardening correction obtained in step S3, to generate a bone hardening correction coefficient, and this example process was carried out according to the following equation:
in the formula (10), the subscript i0 indicates that the thickness of water is a fixed value LH2O,i0N2 is a polynomial order, betak(k-0, 1, …, N2) is a polynomial coefficient.
Step S6 is executed to perform artifact correction using the bone hardening artifact correction coefficient. The correction coefficients obtained according to step S5 may be stored in the reconstruction unit of the computed tomography apparatus in the form shown in fig. 4, and during scanning reconstruction, corresponding bone tissue models (basis material models combined in different component proportions) are selected according to the scanning object, and then the equivalent thickness of the basis material through which X-rays pass in the original image is extracted according to the bone tissue models to select the corresponding bone artifact correction coefficients for correction, so as to obtain a better bone hardening artifact removal effect.
For example, one embodiment of the correction using the artifact correction coefficient may be: receiving scanning data, and reconstructing an image to be corrected and a reference image of the image to be corrected based on the scanning data; giving a first substance proportion to the pixel points of the reference image, and acquiring a first substance base map of the reference image based on the first substance proportion; projecting the first material base map and the reference image to obtain a first material equivalent length corresponding to each projection ray of the projection operation; determining an artifact correction coefficient in an artifact correction coefficient table according to the first material equivalent length corresponding to each projection ray; and performing artifact correction on the image to be corrected by using the artifact correction coefficient.
Accordingly, the present invention also proposes a bone-hardening artifact correction device, comprising: a storage unit for storing the bone hardening artifact correction coefficient obtained by the method; and the correction unit selects the correction coefficient according to the scanning data to correct the bone hardening artifact.
Those skilled in the art will appreciate that all or part of the steps in the various methods of the above embodiments may be implemented by associated hardware as instructed by a program, which may be stored in a computer-readable storage medium, which may include, but is not limited to: floppy disks, optical disks, CD-ROMs, magnetic-optical disks, ROMs (read-only memories), RAMs (random access memories), EPROMs (erasable programmable read-only memories), EEPROMs (electrically erasable programmable read-only memories), magnetic or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing machine-executable instructions.
In the present invention, each embodiment is written progressively, and the differences from the previous embodiments are emphasized, and the same methods or structures in each embodiment refer to the same parts in the previous embodiments.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (2)
1. A bone-hardening artifact correction device comprises a storage unit and a correction unit, and is characterized in that,
the storage unit is configured to: the method for acquiring the bone hardening artifact correction coefficient comprises the following steps: performing phantom scanning using a computed tomography device;
setting that bone tissue consists of a first substance and a second substance, and acquiring theoretical projection values of combinations of the first substance and the second substance with different thicknesses in a tomography system;
performing first substance hardening correction on the theoretical projection value to obtain a projection value after the first substance hardening correction;
calculating ideal projection values of the combination of the first substance and the second substance with different thicknesses in the tomography system;
obtaining a bone hardening artifact correction coefficient according to the thickness of the second substance, the ideal projection values of the first and second substances and the projection value after the hardening correction of the first substance;
the correction unit is configured to: and selecting the bone hardening artifact correction coefficient according to the scanning data to correct the bone hardening artifact.
2. The bone sclerosis artifact correction device of claim 1, wherein said performing bone sclerosis artifact correction comprises:
receiving scanning data obtained by the computer tomography equipment, reconstructing an image to be corrected and a reference image of the image to be corrected based on the scanning data, giving a first substance proportion to pixel points of the reference image, obtaining a first substance base map of the reference image based on the first substance proportion, projecting the first substance base map and the reference image, obtaining a first substance equivalent length corresponding to each projection ray of the projection operation, and selecting a bone hardening artifact correction coefficient to perform artifact correction on the image to be corrected according to the first substance equivalent length corresponding to each projection ray.
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| CN201611247279.9A Active CN106725569B (en) | 2016-01-30 | 2016-01-30 | Method and device for correcting bone sclerosis artifact |
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| WO2017128892A1 (en) * | 2016-01-30 | 2017-08-03 | 上海联影医疗科技有限公司 | Computed tomography artifact correction method and system |
| CN108109183B (en) * | 2016-11-25 | 2021-06-11 | 上海东软医疗科技有限公司 | Beam hardening correction method and device |
| CN106683144B (en) * | 2016-12-30 | 2020-07-14 | 上海联影医疗科技有限公司 | Image iterative reconstruction method and device |
| CN107330949B (en) * | 2017-06-28 | 2020-11-03 | 上海联影医疗科技有限公司 | Artifact correction method and system |
| US10977843B2 (en) | 2017-06-28 | 2021-04-13 | Shanghai United Imaging Healthcare Co., Ltd. | Systems and methods for determining parameters for medical image processing |
| CN108109185B (en) * | 2017-12-18 | 2021-07-20 | 上海联影医疗科技股份有限公司 | Method for generating correction coefficient for eliminating CT artifact and method for eliminating CT artifact based on correction coefficient |
| CN107730569B (en) * | 2017-11-30 | 2021-01-01 | 上海联影医疗科技股份有限公司 | Medical image artifact correction method and device |
| US10922855B2 (en) | 2017-11-30 | 2021-02-16 | Shanghai United Imaging Healthcare Co., Ltd. | Systems and methods for determining at least one artifact calibration coefficient |
| CN108670282B (en) * | 2018-03-28 | 2021-12-17 | 上海联影医疗科技股份有限公司 | Method for correcting bone hardening artifact |
| CN108918559B (en) * | 2018-07-28 | 2021-08-17 | 北京纳米维景科技有限公司 | X-ray image detector for realizing image self-correction and method thereof |
| WO2020077592A1 (en) * | 2018-10-18 | 2020-04-23 | 清华大学 | Ct system energy spectrum inconsistency correction method |
| CN110097517B (en) * | 2019-04-28 | 2022-12-27 | 东软医疗系统股份有限公司 | Method and device for removing image artifacts |
| CN111053566B (en) * | 2019-12-30 | 2021-09-07 | 上海联影医疗科技股份有限公司 | X-ray image reconstruction method and device, X-ray imaging system and medium |
| CN110811660B (en) * | 2019-10-25 | 2023-05-12 | 赛诺威盛科技(北京)股份有限公司 | Method for correcting CT ray beam hardening artifact |
| CN110840479B (en) * | 2019-12-03 | 2023-05-26 | 上海联影医疗科技股份有限公司 | Bone component determination method, device, equipment and storage medium |
| CN111080740B (en) * | 2019-12-27 | 2023-06-16 | 上海联影医疗科技股份有限公司 | Image correction method, device, equipment and medium |
| CN111627083B (en) * | 2020-05-26 | 2023-11-21 | 上海联影医疗科技股份有限公司 | Bone hardening artifact correction method, device, computer equipment and readable storage medium |
| CN112053329B (en) * | 2020-08-21 | 2023-04-14 | 东软医疗系统股份有限公司 | Method and device for acquiring bone hardening coefficient, storage medium and electronic equipment |
| CN113989400B (en) * | 2021-09-26 | 2024-08-30 | 清华大学 | CT image generation method and device, electronic equipment and computer storage medium |
| CN113961124B (en) * | 2021-09-27 | 2024-02-27 | 上海联影医疗科技股份有限公司 | Medical image display method, medical image display device, computer equipment and storage medium |
| CN114041811A (en) * | 2021-11-03 | 2022-02-15 | 海南大学 | Die body and application method of die body in scanning equipment |
| CN117796827A (en) * | 2022-09-26 | 2024-04-02 | 同方威视技术股份有限公司 | Calibration method and device for imaging equipment and imaging equipment |
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