A method and system for correcting CT ray hardening artifacts based on energy spectrum analysis

Abstract

The present invention relates to a CT ray hardening artifact correction method and system based on energy spectrum analysis, including: using an energy-resolving detector to obtain energy spectrum distribution data of different penetration thicknesses when X-rays penetrate a sample; determining the number of photons corresponding to different penetration thicknesses according to the energy spectrum distribution data and intercepting photons within a preset energy range; determining the penetration coefficient and hardening coefficient corresponding to different penetration thicknesses according to the number of photons corresponding to different penetration thicknesses and the number of intercepted photons, and obtaining a fitting relationship between the penetration coefficient and the hardening coefficient; using the fitting relationship between the penetration coefficient and the hardening coefficient to perform hardening correction on the cone beam projection image of the sample to obtain hardening-corrected projection data; performing image reconstruction on the hardening-corrected projection data to obtain a ray hardening correction image. By analyzing the energy spectrum when the X-ray scans the sample, a hardening correction relationship function is obtained, thereby performing hardening correction on the sample projection data to obtain a projection image with higher accuracy.

Description

Technical Field

[0001] The present invention relates to the field of computer tomography, and in particular to a method and system for correcting CT ray hardening artifacts based on energy spectrum analysis. Background Art

[0002] Radiation hardening artifact correction is a hot topic in the field of computed tomography application research. At present, a variety of correction methods have been developed, among which the more practical correction methods are hardware methods and software methods. The hardware method mainly includes the filter correction method, which is to place a filter at the exit of the radiation source to filter out the low-energy X-rays in the beam. This method is simple and easy to implement, but it will cause the number of photons in the imaging to decrease, thereby reducing the signal-to-noise ratio. Therefore, this method is usually not used alone. The more practical software methods include polynomial fitting method, Monte Carlo correction method, dual energy method and iterative correction method. In practical applications, it is necessary to reasonably select the corresponding hardening artifact correction method according to different system environments and experimental conditions. Therefore, there is currently no universal correction method that can solve all radiation hardening problems. Summary of the invention

[0003] The purpose of the present invention is to provide a CT ray hardening artifact correction method and system based on energy spectrum analysis. Based on the analysis of the energy spectrum of the X-ray transmission sample, the hardening correction relationship function of the CT projection data is obtained, thereby improving the accuracy of the CT projection image. This method can solve all ray hardening problems and is a universal correction method.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] The present invention provides a CT ray hardening artifact correction method based on energy spectrum analysis, the method comprising:

[0006] Use energy-resolving detectors to obtain energy spectrum distribution data of different penetration thicknesses when X-rays penetrate the sample;

[0007] Determine the number of photons corresponding to different penetration thicknesses according to the energy spectrum distribution data;

[0008] For the number of photons corresponding to different penetration thicknesses, photons within a preset energy range are intercepted according to the photon energy distribution to obtain the number of intercepted photons corresponding to different penetration thicknesses;

[0009] Determine the penetration coefficient and the hardening coefficient corresponding to different penetration thicknesses according to the photon number and the intercepted photon number corresponding to different penetration thicknesses, and obtain a fitting relationship between the penetration coefficient and the hardening coefficient;

[0010] Using the fitting relationship between the penetration coefficient and the hardening coefficient, hardening correction is performed on the cone beam projection image of the sample after CT scanning to obtain projection data after hardening correction;

[0011] Image reconstruction is performed on the projection data after the hardening correction to obtain a ray hardening correction image.

[0012] Optionally, the preset energy range is an energy value corresponding to an energy spectrum peak in an energy spectrum distribution curve of maximum penetration thickness to a maximum ray energy value.

[0013] Optionally, the fitting relationship expression of the penetration coefficient and the hardening coefficient is:

[0014] I′ t / I t =a*I t / I0+b

[0015] Among them, I′ t / I t Indicates the hardening coefficient; I′ t It indicates the number of intercepted photons corresponding to the penetration thickness t; I t It indicates the number of photons corresponding to the penetration thickness t; I t / I0 represents the penetration coefficient; I0 ​​represents the number of photons corresponding to the minimum penetration thickness; a and b are proportional coefficients.

[0016] Optionally, the step of performing hardening correction on the cone beam projection image of the sample after CT scanning by using the fitting relationship between the penetration coefficient and the hardening coefficient to obtain the projection data after hardening correction includes: preprocessing the cone beam projection image:

[0017] Performing logarithmic processing on the cone beam projection image and determining the maximum energy value and the minimum energy value of the logarithmic projection data;

[0018] The energy maximum is made to correspond to the number of photons at the minimum penetration thickness, the energy maximum is made to correspond to the number of intercepted photons at the maximum penetration thickness, and the logarithmic projection data between the energy maximum and the energy minimum are uniformly interpolated to obtain preprocessed projection data.

[0019] The present invention also provides a CT ray hardening artifact correction system based on energy spectrum analysis, the system comprising:

[0020] An energy spectrum distribution data acquisition module is used to acquire energy spectrum distribution data of different penetration thicknesses when X-rays penetrate a sample using an energy-resolving detector;

[0021] A photon number acquisition module, used to determine the photon numbers corresponding to different penetration thicknesses according to the energy spectrum distribution data;

[0022] A photon interception module, for intercepting photons within a preset energy range according to the photon energy distribution for the photon numbers corresponding to different penetration thicknesses, to obtain the intercepted photon numbers corresponding to different penetration thicknesses;

[0023] A hardening correction relationship function determination module is used to determine the penetration coefficient and hardening coefficient corresponding to different penetration thicknesses according to the number of photons and the number of intercepted photons corresponding to different penetration thicknesses, and obtain a fitting relationship between the penetration coefficient and the hardening coefficient;

[0024] A hardening correction module, used for performing hardening correction on the cone beam projection image of the sample after CT scanning by using the fitting relationship between the penetration coefficient and the hardening coefficient, to obtain projection data after hardening correction;

[0025] The image reconstruction module is used to reconstruct the projection data after the hardening correction to obtain a ray hardening correction image.

[0026] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] The present invention relates to a CT ray hardening artifact correction method and system based on energy spectrum analysis, including: using an energy-resolving detector to obtain energy spectrum distribution data of different penetration thicknesses when X-rays penetrate a sample; determining the number of photons corresponding to different penetration thicknesses according to the energy spectrum distribution data and intercepting photons within a preset energy range; determining the penetration coefficient and hardening coefficient corresponding to different penetration thicknesses according to the number of photons corresponding to different penetration thicknesses and the number of intercepted photons, and obtaining a fitting relationship between the penetration coefficient and the hardening coefficient; using the fitting relationship between the penetration coefficient and the hardening coefficient to perform hardening correction on the cone beam projection image of the sample to obtain hardening-corrected projection data; performing image reconstruction on the hardening-corrected projection data to obtain a ray hardening correction image. By analyzing the energy spectrum when the X-ray scans the sample, a hardening correction relationship function is obtained, thereby performing hardening correction on the sample projection data to obtain a projection image with higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A flow chart of a CT ray hardening artifact correction method based on energy spectrum analysis provided in Example 1 of the present invention;

[0030] Figure 2 A structural diagram of an energy resolution detection device provided in Example 1 of the present invention;

[0031] Figure 3 A structural diagram of a CT detection device provided in Example 1 of the present invention;

[0032] Figure 4 The uncorrected CT projection image provided by Embodiment 1 of the present invention;

[0033] Figure 5 The CT projection image after hardening correction provided in Example 1 of the present invention;

[0034] Figure 6 A block diagram of a CT ray hardening artifact correction system based on energy spectrum analysis provided in Example 2 of the present invention.

[0035] Reference numerals:

[0036] 1-X-ray source; 2-incident X-ray; 3-front collimator; 4-sample stage; 5-sample; 6-outgoing X-ray; 7-rear collimator; 8-energy-resolving detector 8; 9-CT flat panel detector. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The purpose of the present invention is to provide a CT ray hardening artifact correction method and system based on energy spectrum analysis. By analyzing the energy spectrum distribution before and after the X-rays penetrate the sample, the intensity correction of the projection image obtained by CT scanning is performed, and the influence of low-energy X-rays is filtered out by data weighted processing, which not only improves the accuracy of the projection image, but also is a universal correction method.

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides a CT ray hardening artifact correction method based on energy spectrum analysis, the method comprising:

[0042] Energy spectrum analysis:

[0043] S1. Using the energy resolution detector 8, obtain the energy spectrum distribution data of different penetration thicknesses when the X-ray penetrates the sample 5. Figure 2As shown, the structure of the energy resolution detection device is shown, and the energy resolution detector 8 is used to obtain the energy spectrum distribution of the sample 5 at different thicknesses of the tomographic scanning parameters and when there is no sample 5 (at the minimum penetration thickness). The energy resolution detection device includes an X-ray source 1, an incident X-ray 2, a front collimator 3, a sample stage 4, a sample 5, an outgoing X-ray 6, a rear collimator 7, and an energy resolution detector 88, which are sequentially arranged along the ray emission direction.

[0044] When X-rays penetrate the maximum thickness of sample 5, the number of collected photons is the least and the absorption curve is relatively flat. When X-rays penetrate the edge of sample 5, the absorption curve is relatively steep. In order to obtain a better correction effect of radiation hardening artifacts, more data are selected at the position when X-rays penetrate the edge of sample 5.

[0045] S2. Determine the number of photons corresponding to different penetration thicknesses according to the energy spectrum distribution data. t I t The value range is from I0 to I max ; The number of photons is the intensity of the energy spectrum.

[0046] Count and collect the number of photons in all energy ranges I t and I0, the number of photons at the maximum thickness is recorded as I max The number of photons at the minimum penetration thickness is I0, and the number of photons at the maximum penetration thickness is I max least.

[0047] S3, for the number of photons corresponding to different penetration thicknesses, intercept photons within a preset energy range according to the photon energy distribution to obtain the number of intercepted photons I′ corresponding to different penetration thicknesses t .

[0048] The preset energy range is the energy value E corresponding to the energy spectrum peak in the energy spectrum distribution curve of the maximum penetration thickness. min To the maximum ray energy value E max It can also be understood as the range from the channel address corresponding to the peak value of the energy spectrum to the channel address of the maximum ray. The result of the energy spectrum scan is the number of photons counted at different channel addresses. Different channels represent different energy values. The energy value and channel address are linearly related. The larger the channel value, the larger the energy value.

[0049] S4, according to the number of photons corresponding to different penetration thicknesses t and the intercepted photon number I′ t Determine the penetration coefficient I corresponding to different penetration thicknesses t / I0 and hardening coefficient I′ t / I t , and the fitting relationship between penetration coefficient and hardening coefficient is obtained.

[0050] The fitting relationship expression of the penetration coefficient and the hardening coefficient is:

[0051] I′ t / I t =a*I t / I0+b

[0052] Among them, I′ t / I t Indicates the hardening coefficient; I′ t It indicates the number of intercepted photons corresponding to the penetration thickness t; I t It indicates the number of photons corresponding to the penetration thickness t; I t / I0 represents the penetration coefficient; I0 ​​represents the number of photons corresponding to the minimum penetration thickness; a and b are constant coefficients.

[0053] When fitting the relationship between the penetration coefficient and the hardening coefficient, the hardening coefficient is used as the ordinate, that is, the number of intercepted photons divided by the number of total range photons, and the penetration coefficient is used as the abscissa.

[0054] After spectrum analysis:

[0055] S5. Perform hardening correction on the cone beam projection image of the sample 5 after CT scanning using the fitting relationship between the penetration coefficient and the hardening coefficient to obtain projection data after hardening correction.

[0056] The sample 5 is CT scanned by using the CT flat panel detector 9 to obtain a cone beam projection image of the sample 5 .

[0057] like Figure 3 As shown, the structure of the CT detection device is shown, including an X-ray source 1, an incident X-ray 2, a front collimator 3, a sample table 4, a sample 5, an outgoing X-ray 6, a rear collimator 7, and a CT flat panel detector 9 which are arranged in sequence along the ray emission direction.

[0058] Before step S5, the method includes: preprocessing the cone beam projection image:

[0059] Performing logarithmic processing on the cone beam projection image and determining the maximum energy value and the minimum energy value of the logarithmic projection data;

[0060] The energy maximum value f max Corresponding to the photon number I0 at the minimum penetration thickness, the energy minimum f min and the photon number I at the maximum penetration thickness max Correspondingly, the logarithmic projection data between the energy maximum value and the energy minimum value are uniformly interpolated to obtain preprocessed projection data.

[0061] After the above preprocessing process, the projection data of the CT scan can be matched with the energy distribution data corresponding to different penetration thicknesses. After the data matching, the projection data can be directly multiplied by the corresponding proportional coefficient to obtain the projection data after filtering out low-energy X-rays (the unprocessed projection data is multiplied by (a*m_pdata / f max +b)).

[0062] The projection data after cone beam scanning is the matrix m_pdata. The matrix m_pdata is logarithmized to calculate the maximum value f of the projection data. max and the minimum value f min , and compare them with I0 and I max Correspondingly, the corrected projection data m_pdata*(a*m_pdata / f max +b).

[0063] S6. Reconstruct the projection data after the hardening correction to obtain a ray hardening correction image.

[0064] like Figure 4 and 5 These are the images before and after correction, respectively. It can be seen intuitively that the correction method of the present invention can filter out the influence of low-energy X-rays, and the obtained image is clearer with a high signal-to-noise ratio.

[0065] In this embodiment, by analyzing the energy spectrum of sample 5 with different penetration thicknesses, a hardening correction relationship function (a fitting relationship between the penetration coefficient and the hardening coefficient) is fitted, and low-energy X-rays are filtered out from the CT projection data based on the correction relationship, thereby improving the signal-to-noise ratio of the CT scan image, making the acquired image clearer and more accurate. In addition, the method of this embodiment is not limited by any experimental environment and conditions, and is a universal correction method.

[0066] Example 2

[0067] like Figure 6 As shown, this embodiment provides a CT ray hardening artifact correction system based on energy spectrum analysis, the system comprising:

[0068] The energy spectrum distribution data acquisition module M1 is used to acquire energy spectrum distribution data of different penetration thicknesses when X-rays penetrate the sample 5 using the energy resolution detector 8;

[0069] A photon number acquisition module M2 is used to determine the photon numbers corresponding to different penetration thicknesses according to the energy spectrum distribution data;

[0070] The photon interception module M3 is used to intercept photons within a preset energy range according to the photon energy distribution for the photon numbers corresponding to different penetration thicknesses, so as to obtain the intercepted photon numbers corresponding to different penetration thicknesses;

[0071] The preset energy range is from the energy value corresponding to the energy spectrum peak in the energy spectrum distribution curve of the maximum penetration thickness to the maximum ray energy value.

[0072] A hardening correction relationship function determination module M4 is used to determine the penetration coefficient and hardening coefficient corresponding to different penetration thicknesses according to the number of photons and the number of intercepted photons corresponding to different penetration thicknesses, and obtain a fitting relationship between the penetration coefficient and the hardening coefficient;

[0073] The fitting relationship expression of the penetration coefficient and the hardening coefficient is:

[0074] I′ t / I t =a*I t / I0+b

[0075] Among them, I′ t / I t Indicates the hardening coefficient; I′ t represents the number of intercepted photons corresponding to different penetration thicknesses t; I t Represents the number of photons corresponding to different penetration thicknesses t; I t / I0 represents the penetration coefficient; I0 ​​represents the number of photons corresponding to the minimum penetration thickness; a and b are proportional coefficients.

[0076] A hardening correction module M5 is used to perform hardening correction on the cone beam projection image of the sample 5 after CT scanning by using the fitting relationship between the penetration coefficient and the hardening coefficient to obtain projection data after hardening correction;

[0077] The image reconstruction module M7 is used to reconstruct the projection data after the hardening correction to obtain a ray hardening correction image.

[0078] The system also includes a pre-processing module M6;

[0079] The preprocessing module M6 is used to preprocess the cone beam projection image;

[0080] The pre-processing module M6 comprises:

[0081] A logarithmic processing submodule, used for performing logarithmic processing on the cone-beam projection image and determining the maximum energy value and the minimum energy value of the logarithmic projection data;

[0082] The data corresponding submodule is used to correspond the energy maximum value with the number of photons at the minimum penetration thickness, correspond the energy maximum value with the number of photons at the maximum penetration thickness, and uniformly interpolate the logarithmic projection data between the energy maximum value and the energy minimum value to obtain preprocessed projection data.

[0083] As for the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0084] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A CT ray hardening artifact correction method based on energy spectrum analysis, characterized in that: The method comprises: Use energy-resolving detectors to obtain energy spectrum distribution data of different penetration thicknesses when X-rays penetrate the sample; Determine the number of photons corresponding to different penetration thicknesses according to the energy spectrum distribution data; For the number of photons corresponding to different penetration thicknesses, photons within a preset energy range are intercepted according to the photon energy distribution to obtain the number of intercepted photons corresponding to different penetration thicknesses; Determine the penetration coefficient and the hardening coefficient corresponding to different penetration thicknesses according to the photon number and the intercepted photon number corresponding to different penetration thicknesses, and obtain a fitting relationship between the penetration coefficient and the hardening coefficient; Using the fitting relationship between the penetration coefficient and the hardening coefficient, hardening correction is performed on the cone beam projection image of the sample after CT scanning to obtain projection data after hardening correction; Performing image reconstruction on the hardening-corrected projection data to obtain a ray hardening-corrected image; The fitting relationship expression of the penetration coefficient and the hardening coefficient is: I' t / I t =a*I t / I0+b Among them, I′ t / I t Indicates the hardening coefficient; I′ t It indicates the number of intercepted photons corresponding to the penetration thickness t; I t I represents the number of photons corresponding to the penetration thickness t; t / I0 represents the penetration coefficient; I0 ​​represents the number of photons corresponding to the minimum penetration thickness; a and b are proportional coefficients.

2. The method according to claim 1, characterized in that The preset energy range is from the energy value corresponding to the energy spectrum peak in the energy spectrum distribution curve of the maximum penetration thickness to the maximum ray energy value.

3. The method according to claim 1, characterized in that The method of using the fitting relationship between the penetration coefficient and the hardening coefficient to perform hardening correction on the cone beam projection image of the sample after CT scanning to obtain the projection data after hardening correction includes: preprocessing the cone beam projection image: Performing logarithmic processing on the cone beam projection image and determining the maximum energy value and the minimum energy value of the logarithmic projection data; The energy maximum is made to correspond to the number of photons at the minimum penetration thickness, the energy maximum is made to correspond to the number of intercepted photons at the maximum penetration thickness, and the logarithmic projection data between the energy maximum and the energy minimum are uniformly interpolated to obtain preprocessed projection data.

4. A CT ray hardening artifact correction system based on energy spectrum analysis, which operates according to the CT ray hardening artifact correction method based on energy spectrum analysis according to any one of claims 1 to 3, characterized in that: The system comprises: An energy spectrum distribution data acquisition module is used to acquire energy spectrum distribution data of different penetration thicknesses when X-rays penetrate a sample using an energy-resolving detector; A photon number acquisition module, used to determine the photon numbers corresponding to different penetration thicknesses according to the energy spectrum distribution data; A photon interception module, for intercepting photons within a preset energy range according to the photon energy distribution for the photon numbers corresponding to different penetration thicknesses, to obtain the intercepted photon numbers corresponding to different penetration thicknesses; A hardening correction relationship function determination module is used to determine the penetration coefficient and hardening coefficient corresponding to different penetration thicknesses according to the number of photons and the number of intercepted photons corresponding to different penetration thicknesses, and obtain a fitting relationship between the penetration coefficient and the hardening coefficient; A hardening correction module, used for performing hardening correction on the cone beam projection image of the sample after CT scanning by using the fitting relationship between the penetration coefficient and the hardening coefficient, to obtain projection data after hardening correction; The image reconstruction module is used to reconstruct the projection data after the hardening correction to obtain a ray hardening correction image.

5. The system according to claim 4, characterized in that The system also includes a pre-processing module; The preprocessing module is used to preprocess the cone beam projection image; The preprocessing module comprises: A logarithmic processing submodule, used for performing logarithmic processing on the cone-beam projection image and determining the maximum energy value and the minimum energy value of the logarithmic projection data; The data corresponding submodule is used to correspond the energy maximum value with the number of photons at the minimum penetration thickness, correspond the energy maximum value with the number of intercepted photons at the maximum penetration thickness, and uniformly interpolate the logarithmic projection data between the energy maximum value and the energy minimum value to obtain preprocessed projection data.

6. The system according to claim 4, characterized in that The preset energy range is from the energy value corresponding to the energy spectrum peak in the energy spectrum distribution curve of the maximum penetration thickness to the maximum ray energy value.

7. The system according to claim 4, characterized in that The fitting relationship expression of the penetration coefficient and the hardening coefficient is: I' t / I t =a*I t / I0+b Among them, I′ t / I t Indicates the hardening coefficient; I′ t It indicates the number of intercepted photons corresponding to the penetration thickness t; I t It indicates the number of photons corresponding to the penetration thickness t; I t / I0 represents the penetration coefficient; I0 ​​represents the number of photons corresponding to the minimum penetration thickness; a and b are proportional coefficients.

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