CN115908200A - Hardening artifact correction method, system, device and medium for image - Google Patents
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Abstract
The invention discloses a method, a system, equipment and a medium for correcting hardening artifacts of images, wherein the method for correcting the hardening artifacts comprises the following steps: acquiring energy spectrum projection data to be corrected, and determining effective energy spectrum values of a detector channel of an energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model; calculating correction compensation amount according to the energy spectrum projection data to be corrected and the effective energy spectrum value; and correcting the energy spectrum projection data to be corrected based on the correction compensation amount. The method effectively removes the hardening artifact phenomenon caused by the high atomic number material in the scanned object when the CT equipment scans the object; the problems of large calculated amount and low accuracy caused by image segmentation and forward and backward projection which are required to be related by adopting a high-order hardening artifact correction method are solved; the calculation amount of the hardening artifact correction is reduced, and the accuracy of the hardening artifact correction is improved.
Description
Technical Field
The invention relates to the technical field of medical instruments, in particular to a hardening artifact correction method, a hardening artifact correction system, hardening artifact correction equipment and hardening artifact correction media for images.
Background
X-rays generated by a bulb tube in a clinical CT (Computed Tomography) imaging system have a wide energy spectrum, and the attenuation of low-energy photons is greater than that of high-energy photons when interacting with a substance. When polychromatic X-rays penetrate an object, low energy photons are more easily absorbed than high energy photons. The lower and lower energy photon share in the ray, the energy spectrum of the X-ray gradually shifts to the high energy end, the average energy of the ray becomes higher, the energy spectrum becomes 'hard', and the beam hardening phenomenon is generated. For CT imaging systems, the hardening artifact of non-uniform bands in soft tissue regions can occur if hardening correction is not performed. In order to obtain CT images that can be used for clinical diagnosis, beam hardening correction is required during image reconstruction, and in particular when scanning high atomic number substances contained in the object, such as bone tissue or contrast agent iodine, without hardening correction, significant hardening artifacts may result in soft tissue regions.
Conventional hardening correction includes a high-order hardening correction method, which performs beam hardening correction by using two substances of water-bone or water-iodine as reference substances. The image is divided to obtain a base material image, and the base material image is forward projected to calculate the deviation caused by hardening by projection of the base material, so that hardening correction is performed.
Disclosure of Invention
The invention aims to overcome the defects of large calculation amount and low accuracy of a method adopting high-order hardening correction in the prior art, and provides a method, a system, equipment and a medium for correcting hardening artifacts of an image.
The invention solves the technical problems through the following technical scheme:
in a first aspect, the present invention provides a method for correcting a hardening artifact of an image, the method comprising:
acquiring energy spectrum projection data to be corrected;
according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model, determining effective energy spectrum values of a detector channel of an energy spectrum CT system in different energy intervals;
calculating a correction compensation amount according to the energy spectrum projection data to be corrected and the effective spectrum value;
and correcting the energy spectrum projection data to be corrected based on the correction compensation amount.
Preferably, the step of calculating a correction compensation amount according to the energy spectrum projection data to be corrected and the effective spectrum value includes:
determining line integral data of the density of the base material according to the to-be-corrected energy spectrum projection data;
and calculating the correction compensation quantity according to the effective spectrum value, the line integral data and the linear attenuation coefficient of each base material.
Preferably, the step of determining line integral data of the density of the base material from the spectral projection data to be corrected comprises:
determining the number of base substances and the number of energy intervals; the number of energy intervals is greater than the number of base substances;
and calculating the line integral data according to the number of the base substances, the number of the energy intervals and the projection data to be corrected.
Preferably, the step of calculating the line integral data from the spectral projection data to be corrected and the effective attenuation coefficient comprises:
and calculating the line integral data by adopting a least square method or matrix inversion according to the energy spectrum projection data to be corrected and the effective attenuation coefficient.
Preferably, the step of determining effective spectral values of detector channels of the energy spectrum CT system in different energy intervals according to the original data of the energy spectrum projection obtained by scanning the eccentrically placed standard water model includes:
acquiring the corresponding relation between the energy spectrum projection data and the effective energy spectrum data;
and performing iterative computation based on the original energy spectrum projection data and the corresponding relation to obtain the effective spectrum value.
Preferably, the step of correcting the energy spectrum projection data to be corrected based on the correction compensation amount includes:
and performing iterative calculation on the energy spectrum projection data to be corrected according to the correction compensation amount.
In a second aspect, the present invention provides a hardening artifact correction system for an image, the hardening artifact correction system comprising:
the acquisition module is used for acquiring the energy spectrum projection data to be corrected;
the determination module is used for determining effective energy spectrum values of a detector channel of the energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model;
the calculation module is used for calculating correction compensation according to the energy spectrum projection data to be corrected and the effective spectrum value;
and the correction module is used for correcting the energy spectrum projection data to be corrected based on the correction compensation amount.
In a third aspect, the present invention provides an electronic device comprising a processor, a memory and a computer program stored on the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the method for hardening artifact correction of an image as described above.
In a fourth aspect, the present invention provides a computer readable storage medium, having a computer program stored thereon, which, when executed by a processor, implements a method of hardening artifact correction for images as described above.
The positive progress effects of the invention are as follows: acquiring energy spectrum projection data to be corrected; according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model, determining effective energy spectrum values of a detector channel of an energy spectrum CT system in different energy intervals; calculating correction compensation amount according to the energy spectrum projection data to be corrected and the effective energy spectrum value; and correcting the energy spectrum projection data to be corrected based on the correction compensation amount. The method effectively removes the hardening artifact phenomenon caused by the high atomic number material in the scanned object when the CT equipment scans the object; the problems of large calculated amount and low accuracy caused by image segmentation and forward and backward projection which are required to be related by adopting a high-order hardening artifact correction method are solved; the calculation amount of hardening artifact correction is reduced, and the accuracy of hardening artifact correction is improved.
Drawings
Fig. 1 is a flowchart of a method for correcting image hardening artifacts according to embodiment 1 of the present invention.
Fig. 2 is a flowchart of step S3 of the image hardening artifact correction method according to embodiment 1 of the present invention.
Fig. 3 is a flowchart of step S31 of the image hardening artifact correction method according to embodiment 1 of the present invention.
Fig. 4 is a flowchart of step S2 of the image hardening artifact correction method according to embodiment 1 of the present invention.
Fig. 5 is a diagram of a first application example of the method for correcting the image hardening artifact according to embodiment 1 of the present invention.
Fig. 6 is a diagram illustrating a second application of the hardening artifact correction method for images according to embodiment 1 of the present invention.
Fig. 7 is a schematic diagram of a first module of an image hardening artifact correction system according to embodiment 2 of the present invention.
Fig. 8 is a schematic diagram of a second module of the image hardening artifact correction system according to embodiment 2 of the present invention.
Fig. 9 is a schematic structural diagram of an electronic device for implementing a method for correcting an image hardening artifact according to embodiment 3 of the present invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
Example 1
As shown in fig. 1, the method for correcting a hardening artifact of an image according to this embodiment includes:
s1, acquiring energy spectrum projection data to be corrected.
S2, determining effective spectral values of a detector channel of the energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning the eccentrically placed standard water model.
And S3, calculating the correction compensation amount according to the energy spectrum projection data to be corrected and the effective energy spectrum value.
And S4, correcting the energy spectrum projection data to be corrected based on the correction compensation amount.
The hardening artifact correction method provided by the application is suitable for Cone beam CT (Cone beam Computed Tomography) equipment, namely CBCT (Cone beam Computed Tomography) equipment, and the CT equipment mainly comprises the following steps: an X-ray source, a detector, and a rotating device. When high atomic number substances such as bone tissues or contrast agent iodine and the like are scanned, X-rays emitted by an X-ray dome are in a wide energy band, and the X-ray attenuation coefficient of the substances with the same density is changed along with the intensity of the X-rays, so that the phenomenon of hardening artifacts generated in a soft tissue area or the phenomenon of uneven strip substances generated among dense substances is caused. In the CT imaging process, the X-ray source performs relative rotational motion around the object from the detector, so as to obtain CT projection data at different rotation angles, which are also called CT projection values.
In step S1, the target object is placed on a scanning bed of the cone beam CT apparatus, and the target object is scanned by using the multi-energy ray. In order to reduce the total scanning time, a "helical" scan may be performed on the target object such that the angle at which the radiation beam intersects the target object is constantly changed to obtain initial spectral projection data, and the initial spectral projection data is subjected to a water hardness correction process to obtain spectral projection data to be corrected, denoted as p b . The water hardening correction, which corrects the projected value of the X-ray having a specific energy spectrum to the projected value of the ideal monoenergetic X-ray, is known to those skilled in the art and will not be described herein.
In the step S2, considering that the cone beam CT apparatus is mainly used for scanning a human body part and the density of the soft tissue of the human body is close to the density of water, the material of the mold body may be selected to be a material close to the density of water, and the liquid with the preset density may be selected to be water or a liquid close to the density of water for performing a water model experiment. It should be noted that, in this embodiment, when designing a standard water phantom, the design is performed according to parameters such as the size of the flat panel detector of the cone beam CT apparatus and the actually required scan thickness, so as to ensure that all X-rays penetrating through the phantom can be received by the flat panel detector.
The method comprises the steps of eccentrically placing a standard uniform cylindrical mold body with a preset size on a scanning bed of a cone beam CT device, and performing rotary scanning on the standard mold body filled with liquid with a preset density by using a multi-energy ray to obtain original data of energy spectrum projection, wherein the original data of the energy spectrum projection is multi-energy projection data. And after scanning the eccentrically placed standard die body, reconstructing a water model image by using full-energy data. The water model image is divided into a water model wall and water by threshold segmentation, and the material of the water model wall refers to polymethyl methacrylate and a high molecular polymer, which is called PMMA for short. And respectively assigning the segmented images as the density values of PMMA and water, performing 3D cone beam forward projection on the eccentrically placed cylindrical water model by utilizing the system geometry of CT equipment during scanning to obtain the penetration thickness penetrating through the wall of the base material water model and the penetration thickness penetrating through the base material water, and determining the linear attenuation coefficients of the water model wall and the water. A linear attenuation coefficient of an object may represent a relationship between the intensity of X-rays incident on the object and the intensity of X-rays exiting the object, and a linear attenuation coefficient of an object may be related to the thickness, area, shape, etc. of the object. And determining the corresponding relation between the original data of the energy spectrum projection and the effective energy spectrum data according to the original data of the energy spectrum projection, the penetrating thickness of the water mold wall and the water penetrating through the base material and the linear attenuation coefficient. The method reduces the calculation amount of hardening artifact correction and improves the accuracy of hardening artifact correction.
The original data of the energy spectrum projection can be estimated by adopting an iterative algorithm, and the effective spectrum value of each energy interval of each detector unit of the cone beam CT equipment is obtained through calculation, but the effective spectrum value of the edge channel of the detector under different energy intervals needs to be obtained through effective spectrum expansion of the middle region. Since the effective energy spectrum value of each energy interval of the detector unit needs to be calibrated by using the eccentric water model, but the eccentric water model has certain limitation, and the edge channel can not be covered, the edge channel can not be calibrated, so that the effective energy spectrum of the edge channel can be transformed and expanded based on the middle area.
For the above step S3, when a plurality of base substances exist, the effective attenuation coefficient of each base substance is determined, and the spectral projection data p to be corrected is calculated from the effective attenuation coefficient of each base substance and the spectral projection data p to be corrected i And calculating the line integral data of each base substance by adopting a matrix inversion mode. From the spectral projection data p to be corrected b And subscript b is an energy interval index, the line integral data of each base material and the effective energy spectrum values of the detector channel in different energy intervals are subjected to iterative calculation to obtain correction compensation quantity, and the correction compensation quantity is obtained by subtracting the projection value of the previous step from the calculated projection value after water hardening correction.
Aiming at the step S4, the energy spectrum projection data p to be corrected is corrected according to the correction compensation amount by using the following formula b Performing multiple iterative calculations, and recording the value of the b-th energy interval as p b (0) A 1 is to p b (0) As an initial value for the spectral projection data to be corrected, R w (. Cndot.) represents the course of water hardness correction. The calculated projection values measured in different energy intervals are approximate to the calculated projection values of an ideal single chromatogram and iodine water, water hardening correction is the prior art known by the technical personnel in the field, the cupping artifact of the water model is corrected after the nonlinear relation of the projection values p along with the change of the thickness L of the passing water is corrected to be linear relation, the concrete water hardening correction process is not repeated here, and the iterative correction process is as follows:
in particular, when the above formula is used to treat the initial value of the corrected spectral projection data
On the first iteration of the calculation, it is up or down>
When the second iterative calculation is performed,
each time based on an initial value p of the spectral projection data to be corrected b (0) And performing iterative calculation, and performing multiple corrections on the energy spectrum projection data to be corrected by analogy. The method effectively removes the hardening artifact phenomenon caused by the high atomic number material in the scanned object when the CT equipment scans the object.
In an optional embodiment, as shown in fig. 2, step S3 specifically includes:
and S31, determining line integral data of the density of the base material according to the energy spectrum projection data to be corrected.
And S32, calculating a correction compensation amount according to the effective spectrum value, the line integral data and the linear attenuation coefficient of each base material.
In the above steps S31-S32, the lower limit value E in the selected X-ray energy interval is obtained by calculating the effective spectrum value, the linear integral data of the density of each base material, and the linear attenuation coefficient of each base material according to the following formula min And selecting the upper limit value E of the energy interval of the X-ray max The calculated projection value of the correction compensation amount of (2). The method avoids the problems of large calculation amount and low accuracy caused by the fact that a high-order hardening artifact correction method needs to involve image segmentation and front and back projection.
Wherein j represents an energy sampling point of an energy interval from Emin to Emax, S j Represents the effective spectral value, L, at the energy sample point j 1 (n) Line integral data, L, representing the first base material in the nth iteration 2 (n) Is shown inLine integral data of the second base substance in n iterative calculations, E j Indicates a set energy interval, μ 1 (E j ) Represents the linear attenuation coefficient of the first base material at the energy sampling point j, the linear attenuation coefficient is a function of the energy value of the energy sampling point j, mu 2 (E j ) Represents the linear attenuation coefficient, p, of the second base material at the energy sampling point j cal (n) Indicating the calculated projection values.
In an optional embodiment, as shown in fig. 3, step S31 specifically includes:
s311, determining the number of the base substances and the number of the energy intervals; the number of energy intervals is greater than the number of base species.
And S312, calculating line integral data according to the number of the base substances, the number of the energy intervals and the projection data to be corrected.
For steps S311 to S312 above, M represents the number of selected base substances, which may be a combination of water/iodine decomposition, water/bone decomposition, or water/calcium decomposition; after the upper limit value and the lower limit value of the energy range are determined, the energy range is divided into B energy intervals. In this embodiment, the data value of B is greater than the data value of M, and the model of the projection value of each energy bin and the basis material line integral is:
wherein p represents [ Bx 1 ]]Of vector matrix form of (1), component p thereof b Is the projected value of the b-th energy interval,
represents [ B.times.M ]]In matrix form of (1), L represents [ M × 1 ]]Of vector form (c), component L thereof m Represents the line integral of the m-th base material; />
Represents an effective attenuation factor, the component of which->
To representAnd the effective attenuation coefficient of the mth base material in the mth energy interval can be obtained by die body calibration. Illustratively, when the number of the base substance is two and there are two energy intervals, the above formula may be expressed as follows:
in an optional embodiment, step S312 specifically includes:
s3121, determining an effective attenuation coefficient according to the number of the base substances and the range of the energy interval;
and S3122, calculating line integral data according to the energy spectrum projection data to be corrected and the effective attenuation coefficient.
For the above steps S3121-S3122, n represents the number of iterations, and a matrix inversion method is used to obtain the effective attenuation coefficient of each base substance in each energy interval according to the spectral projection data to be corrected and each base substance
The line integral data for the density of each base material was calculated.
In an optional embodiment, the line integral data is calculated by using a least square method or matrix inversion according to the spectral projection data to be corrected and the effective attenuation coefficient, and other algorithms may also be used to calculate the line integral data, which is not limited in this embodiment.
In an optional embodiment, as shown in fig. 4, step S2 specifically includes:
and S21, acquiring the corresponding relation between the energy spectrum projection data and the effective energy spectrum data.
And S22, carrying out iterative calculation based on the original data of the energy spectrum projection and the corresponding relation to obtain an effective spectrum value.
For the above step S21, the eccentric placement is performed by scanningWhen the effective energy spectrum data is calibrated by the standard water model to establish the corresponding relation between the energy spectrum projection data and the effective energy spectrum data, aiming at a certain detector unit of the CT equipment, an incident ray can penetrate through water model walls and water with different thicknesses in the scanning process. After the base material water mold wall and water are projected at a plurality of visual angles, correspondingly sampling projection generation data at each visual angle, and p i Spectral projection data, S, representing an energy interval of the ith sample point j Represents the effective energy spectrum data of the CT device, j represents the energy spectrum index, and j can be reasonably sampled. For example, the energy interval may be 5keV or other values, based on the available spectral data S j And spectral projection data p i Establishing a corresponding relation as shown in the following formula:
wherein the content of the first and second substances,
E j denotes the energy interval, μ P Represents the linear attenuation coefficient, mu, of the water mold wall w Represents the linear attenuation coefficient, L, of water P Denotes the path integral value (through thickness value) of the water mold wall, L w The path integral value (through thickness value) of water is shown. A. The ji Is indicated in the selected energy interval E j The attenuation effect value of the combination of the inner base material water mold wall and the base material water. E min A lower limit value, E, representing the energy interval of the selected X-rays max An upper limit value representing the energy interval of the selected X-ray, denoted by E min And E max Forming a range of selected X-ray energy intervals, p in the above formula i 、L P And L w Representing a known quantity.
For the above step S22, projecting the energy spectrum to the original data and the attenuation effect value A ji Performing mathematical operation by the formula to obtain effective energy spectrum data S j Then, the EM algorithm is adopted to project the acquired energy spectrum to original data P i And effective energy spectrum data S j Performing iterative calculation, wherein k represents the iterative times, and the initial value is setHas a performance spectrum value of
And updating by using the following iteration formula until an iteration stop condition is reached, and obtaining an effective spectrum value according to a final iteration result. For example, after an integration calculation with an accuracy of every 1keV in an energy interval of 30keV-60keV, the current effective spectral value is obtained>
Has a result of->
And a previous step>
A function of the result. Effective energy spectrum data S is obtained by the following formula j After multiple iterations, more accurate energy spectrum data, namely effective spectrum values, are obtained. It is understood that the number of iterations can be set according to the actual situation, and preferably, the number of iterations is set for the effective energy spectrum data S j Correction is performed for an even number of iterations.
It should be noted that the EM algorithm is a prior art known to those skilled in the art, and X-ray attenuation data is obtained by measurement, and the energy spectrum value of incident X-ray is estimated by using the X-ray attenuation data, which is not described herein again. Other algorithms may also be used to project the raw data p onto the energy spectrum i The iterative calculation is performed, which is not particularly limited in this embodiment.
Wherein n represents a selected energy range S j The energy subscript of the effective energy spectrum value in represents the energy spectrum precision, and k represents the iteration number.
In an alternative embodiment, as shown in fig. 5, during the effective energy spectrum calibration process with the eccentric water model, CT energy spectrum scanning is performed on the eccentric water model to obtain the original energy spectrum projection data. And (4) after the water model image obtained after scanning is reconstructed by using the full Bin data, selecting a proper threshold value to divide the water model image. For example, when the CT value of the water model image is larger than a first threshold value, the water model wall image is obtained by segmentation, and when the CT value of the water model image is smaller than a second threshold value, the water model image is obtained by segmentation. And calculating line integral data of the density of the X-ray of each detector channel of the CT equipment passing through the water model wall and water, performing iterative calculation according to the line integral data and the energy spectrum projection original data by adopting an EM (effective electromagnetic radiation) algorithm, and outputting an effective spectrum value of each energy interval of each detector channel when an iterative condition is met.
In an alternative embodiment, as shown in fig. 6, during the multi-material artifact hardening correction, the preprocessed energy spectrum scanning data is obtained, after the line integral data of each base material is calculated by the least square method or the matrix inversion method, the line integral data of the density of the X-ray passing through the water mold wall and the water of each detector channel of the CT device is determined. Calculating to obtain a projection value by using the calibrated effective energy spectrum value and the line integral data of each base material, subtracting the hardening artifact error from the original energy spectrum projection data, performing iterative calculation for multiple times until the iterative condition is met, and outputting the corrected energy spectrum projection data. The method effectively removes the hardening artifact phenomenon caused by the existence of high atomic number materials in the scanned object when the CT equipment scans the object.
In the embodiment, a hardening artifact correction method for an image is provided, and energy spectrum projection data to be corrected are obtained; determining effective energy spectrum values of a detector channel of an energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model; calculating correction compensation according to the energy spectrum projection data to be corrected and the effective energy spectrum value; and correcting the energy spectrum projection data to be corrected based on the correction compensation amount. The method effectively removes the hardening artifact phenomenon caused by the high atomic number material in the scanned object when the CT equipment scans the object; the problems of large calculated amount and low accuracy caused by image segmentation and forward and backward projection which are required to be related by adopting a high-order hardening artifact correction method are solved; the calculation amount of the hardening artifact correction is reduced, and the accuracy of the hardening artifact correction is improved.
Example 2
As shown in fig. 7, the hardening artifact correction system for an image of the present embodiment includes: an acquisition module 110, a determination module 120, a calculation module 130, and a correction module 140.
The obtaining module 110 is configured to obtain spectral projection data to be corrected.
The determining module 120 is configured to determine effective spectral values of detector channels of the energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model.
And the calculating module 130 is configured to calculate a correction compensation amount according to the energy spectrum projection data to be corrected and the effective energy spectrum value.
And the correction module 140 is configured to correct the energy spectrum projection data to be corrected based on the correction compensation amount.
The hardening artifact correction system provided by the application is suitable for Cone beam CT (Cone beam Computed Tomography) equipment, namely CBCT equipment, wherein the CT equipment mainly comprises: an X-ray source, a detector, and a rotating device. When high atomic number substances such as bone tissues or contrast agent iodine and the like are scanned, X-rays emitted by an X-ray dome are in a wide energy band, and the X-ray attenuation coefficient of the substances with the same density is changed along with the intensity of the X-rays, so that the phenomenon of hardening artifacts generated in a soft tissue area or the phenomenon of uneven strip substances generated among dense substances is caused. In the CT imaging process, the X-ray source performs relative rotational motion around the object from the detector, so as to obtain CT projection data at different rotation angles, which are also called CT projection values.
The target object is placed on a scanning bed of the cone beam CT equipment, and the target object is scanned by using the multi-energy rays. To reduce the total scan time, a "helical" scan may be performed on the target object such that the angle at which the radiation beam intersects the target object is constantly changed to obtain initial data for a spectral projection that is projected by the acquisition module 110The initial data is subjected to water hardening correction processing to obtain spectral projection data to be corrected, and the spectral projection data is marked as p b . The water hardening correction, which corrects the projected value of the X-ray having a specific energy spectrum to the projected value of the ideal monoenergetic X-ray, is known to those skilled in the art and will not be described herein.
Considering that the cone beam CT equipment is mainly used for scanning human body parts, and the density of human soft tissues is close to that of water, the material of the die body can be selected to be close to that of the water density, and the liquid with the preset density can be selected to be water or the liquid with the water density close to that of the water density to carry out water model experiments. It should be noted that, in this embodiment, when designing a standard water phantom, the design is performed according to parameters such as the size of the flat panel detector of the cone beam CT apparatus and the actually required scan thickness, so as to ensure that all X-rays penetrating through the phantom can be received by the flat panel detector.
The method comprises the steps of eccentrically placing a standard uniform cylindrical mold body with a preset size on a scanning bed of a cone beam CT device, and performing rotary scanning on the standard mold body filled with liquid with a preset density by using a multi-energy ray to obtain original data of energy spectrum projection, wherein the original data of the energy spectrum projection is multi-energy projection data. And after scanning the eccentrically placed standard die body, reconstructing a water model image by using full-energy data. The water model image is divided into a water model wall and water by threshold segmentation, and the material of the water model wall refers to polymethyl methacrylate and a high molecular polymer, which is called PMMA for short. The segmented images are respectively assigned to density values of PMMA and water, then, after 3D cone beam forward projection is carried out on an eccentrically placed cylindrical water model by utilizing the system geometry of CT equipment during scanning, the penetrating thickness penetrating through the wall of the water model of the base material and the penetrating thickness penetrating through the water of the base material are obtained, and the linear attenuation coefficients of the wall of the water model and the water are determined. And determining the corresponding relation between the original data of the energy spectrum projection and the effective energy spectrum data according to the original data of the energy spectrum projection, the penetrating thickness of the water mold wall and the water penetrating through the base material and the linear attenuation coefficient. The method reduces the calculation amount of the hardening artifact correction and improves the accuracy of the hardening artifact correction.
The original data of the spectral projection may be estimated by using an iterative algorithm, and the determination module 120 calculates to obtain an effective spectrum value of each energy interval of each detector unit of the cone beam CT apparatus, but the effective spectrum value of the edge channel of the detector in different energy intervals needs to be obtained by expanding the effective spectrum of the middle region. The effective energy spectrum value of each energy interval of the detector unit needs to be calibrated by an eccentric water model, but the eccentric water model has certain limitation, and an edge channel can not be covered necessarily, so that the edge channel can not be calibrated, and the effective energy spectrum of the edge channel can be transformed and expanded based on the middle area.
When a plurality of base substances exist, determining an effective attenuation coefficient of each base substance, and correcting the energy spectrum projection data p according to the effective attenuation coefficient of each base substance and the energy spectrum projection data p to be corrected i And calculating the linear integral data of each base substance by adopting a matrix inversion mode. The calculation module 130 projects data p according to the energy spectrum to be corrected i And the line integral data of each base substance and the effective energy spectrum values of the detector channels in different energy intervals are subjected to iterative calculation to obtain a correction compensation quantity, and the correction compensation quantity comprises a first correction compensation parameter obtained after water hardening treatment.
The correction module 140 uses the following formula to correct the spectral projection data p to be corrected according to the correction compensation amount b Performing multiple iterative calculations, and recording the value of the b-th energy interval as p b (0) A 1 is to p b (0) As an initial value for the spectral projection data to be corrected, R w (. Cndot.) represents the course of water hardness correction. The water hardness correction is the prior art known to those skilled in the art by correcting the non-linear relationship of the projection value p with the change of the thickness L of the passing water into a linear relationship with the calculated projection value approaching to the ideal single chromatogram and the calculated projection value of the iodine water measured in different energy intervals, the cupping artifact of the water model is corrected, and the concrete water hardness correction process is not described again,the iterative correction process is as follows:
in particular, when the above formula is used to treat the initial value of the corrected spectral projection data
Upon a first iterative calculation, a decision is made as to whether or not a particular combination of a number of combinations of the preceding combinations is present>
When an initial value of the spectral projection data to be corrected is +>
Upon performing a second iterative calculation, a decision is made as to whether or not a particular combination of bin and bin is present>
Each time based on an initial value p of the spectral projection data to be corrected b (0) And performing iterative calculation, and performing multiple corrections on the energy spectrum projection data to be corrected by analogy. The method effectively removes the hardening artifact phenomenon caused by the existence of high atomic number materials in the scanned object when the CT equipment scans the object.
In an optional embodiment, as shown in fig. 8, the calculation module 130 specifically includes:
a determining unit 131 for determining line integral data of the density of the base substance from the spectral projection data to be corrected.
And a calculating unit 132 for calculating a correction compensation amount according to the effective spectrum value, the line integral data and the linear attenuation coefficient of each base material.
The calculation unit 132 calculates a lower limit E in the selected X-ray energy interval from the effective spectral value, the line integral data of the density of each base material, and the linear attenuation coefficient of each base material by using the following formula min And selecting the upper limit value E of the energy interval of the X-ray max The calculated projection value of the correction compensation amount of (2). The method avoids the need of adopting a high-order hardening artifact correction method to relate to the imageSegmentation and forward and backward projection cause the problems of large calculation amount and low accuracy.
Wherein j represents an energy sampling point of an energy interval from Emin to Emax, S j Representing the effective spectral value, L, at energy sample point j 1 (n) Line integral data, L, representing the first base material in the nth iteration 2 (n) Line integral data, E, representing the second base substance in the nth iteration j Indicates a set energy interval, μ 1 (E j ) Represents the linear attenuation coefficient of the first base material at the energy sampling point j, which is a function of the energy value of the energy sampling point j, mu 2 (E j ) Representing the linear attenuation coefficient of the second base substance at the energy sample point j as a function of the energy value of the energy sample point j, p cal (n) Indicating the calculated projection values.
In an optional embodiment, the determining unit 131 is specifically configured to:
determining the number of base substances and the number of energy intervals; the number of energy intervals is greater than the number of base species.
And calculating line integral data according to the quantity of the base substances, the quantity of the energy intervals and the projection data to be corrected.
M represents the amount of a selected base material which may be a combination of water/iodine decomposition, water/bone decomposition, or water/calcium decomposition; after the upper limit value and the lower limit value of the energy range are determined, the energy range is divided into B preset energy intervals. In this embodiment, the data value of B is greater than the data value of M, and the determining unit 131 calculates the line integral data of the density of each base material according to the following formula:
wherein p represents [ Bx 1 ]]Of vector matrix form of (1), component p thereof b Is the projected value of the b-th energy interval,
represents [ B.times.M ]]In matrix form of (1), L represents [ M × 1 ]]Of vector form (c), component L thereof m Represents the line integral of the m-th base material; />
Represents an effective attenuation factor, the component of which->
And (3) representing the effective attenuation coefficient of the mth base material in the mth energy interval, wherein the effective attenuation coefficient can be obtained by die body calibration. Illustratively, when the number of the base substance is two and there are two energy intervals, the above formula may be expressed as follows: />
In an optional embodiment, step S312 specifically includes:
s3121, determining an effective attenuation coefficient according to the number of the base substances and the range of the energy interval;
and S3122, calculating line integral data according to the energy spectrum projection data to be corrected and the effective attenuation coefficient.
For the above steps S3121-S3122, n represents the number of iterations, and a matrix inversion method is used to invert the effective attenuation coefficient of each base substance in each energy interval according to the spectral projection data to be corrected and the energy spectrum projection data to be corrected
The line integral data for the density of each base material was calculated.
In an optional embodiment, the line integral data is calculated by using a least square method or matrix inversion according to the spectral projection data to be corrected and the effective attenuation coefficient, and other algorithms may also be used to calculate the line integral data, which is not limited in this embodiment.
In an optional embodiment, as shown in fig. 8, the determining module 120 specifically includes:
the obtaining unit 121 is configured to obtain a corresponding relationship between the energy spectrum projection data and the effective energy spectrum data.
And the iterative calculation unit 122 is configured to perform iterative calculation based on the original data of the energy spectrum projection and the corresponding relationship, so as to obtain an effective spectrum value.
When effective energy spectrum data are calibrated by scanning an eccentrically placed standard water model to establish a corresponding relation between energy spectrum projection data and the effective energy spectrum data, for a certain detector unit of the CT equipment, an incident ray can penetrate through water model walls and water with different thicknesses in the scanning process. After the base material water mold wall and water are projected at a plurality of visual angles, correspondingly sampling projection raw data at each visual angle, and p i Spectral projection data, S, representing the ith sample point j Represents the effective energy spectrum data of the CT device, j represents the energy spectrum index, and j can be reasonably sampled. For example, the energy interval may be 5keV or other values, and the obtaining unit 121 obtains the effective energy spectrum data S according to j And spectral projection data p i Establishing a corresponding relation shown as the following formula:
wherein, the first and the second end of the pipe are connected with each other,
E j denotes the energy interval, μ P Represents the linear attenuation coefficient, mu, of the water mold wall w Represents the linear attenuation coefficient, L, of water P Represents the path integral value (through thickness value), L, of the water mold wall w The path integral value (through thickness value) of water is shown. A. The ji Is represented in a selected energy interval E j The attenuation effect value of the combination of the inner base material water mold wall and the base material water. E min Representing the energy interval of selected X-raysLower limit value of, E max An upper limit value representing the energy interval of the selected X-ray, denoted by E min And E max Forming a range of selected X-ray energy intervals, p in the above formula i 、L P And L w Representing a known quantity.
The iterative computation unit 122 projects the energy spectrum onto the original data and the attenuation effect value A ji Performing mathematical operation by the formula to obtain effective energy spectrum data S j Then, the EM algorithm is adopted to project the acquired energy spectrum to original data P i And effective energy spectrum data S j Performing iterative calculation, wherein k represents the iteration times, and setting the initial effective spectrum value as
And updating by using the following iteration formula until an iteration stop condition is reached, and obtaining an effective spectrum value according to a final iteration result. For example, after an integration calculation with an accuracy of every 1keV in an energy interval of 30keV-60keV, the current effective spectral value is obtained>
Has a result of->
And the last step->
A function of the result. Effective energy spectrum data S is obtained by the following formula j After multiple iterations, more accurate energy spectrum data, namely effective spectrum values, are obtained. It is understood that the number of iterations can be set according to the actual situation, and preferably, the number of iterations is set for the effective energy spectrum data S j Corrections are made for an even number of iterations.
It should be noted that the EM algorithm is a prior art known to those skilled in the art, and X-ray attenuation data is obtained by measurement, and the energy spectrum value of incident X-ray is estimated by using the X-ray attenuation data, which is not described herein again. Other iterative algorithms can also be adopted to project the original data P to the energy spectrum i The iterative calculation is performed, which is not limited in this embodiment.
Wherein n represents a selected energy range S j The energy subscript of the effective energy spectrum value in represents the energy spectrum precision, and k represents the iteration number.
In the embodiment, a hardening artifact correction system for an image is provided, in which an obtaining module obtains energy spectrum projection data to be corrected; the determining module determines effective energy spectrum values of a detector channel of the energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model; the calculation module calculates the correction compensation amount according to the energy spectrum projection data to be corrected and the effective energy spectrum value; the correction module corrects the energy spectrum projection data to be corrected based on the correction compensation amount. The method effectively removes the hardening artifact phenomenon caused by the high atomic number material in the scanned object when the CT equipment scans the object; the problems of large calculated amount and low accuracy caused by image segmentation and forward and backward projection which are required to be related by adopting a high-order hardening artifact correction method are solved; the calculation amount of the hardening artifact correction is reduced, and the accuracy of the hardening artifact correction is improved.
Example 3
Fig. 9 is a schematic structural diagram of an electronic device provided in this embodiment. The electronic device comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, and the processor executes the program to realize the hardening artifact correction method of the image in embodiment 1. The electronic device 90 shown in fig. 9 is only an example, and should not bring any limitation to the functions and the scope of use of the embodiment of the present invention.
As shown in fig. 9, the electronic device 90 may take the form of a general purpose computing device, which may be, for example, a server device. The components of the electronic device 90 may include, but are not limited to: the at least one processor 91, the at least one memory 92, and a bus 93 that connects the various system components (including the memory 92 and the processor 91).
The bus 93 includes a data bus, an address bus, and a control bus.
The processor 91 executes various functional applications and data processing, such as a hardening artifact correction method of an image according to embodiment 1 of the present invention, by running the computer program stored in the memory 92.
The electronic device 90 may also communicate with one or more external devices 94 (e.g., keyboard, pointing device, etc.). Such communication may be through an input/output (I/O) interface 95. Also, the model-generating device 90 may also communicate with one or more networks (e.g., a Local Area Network (LAN), a Wide Area Network (WAN), and/or a public network, such as the Internet) via a network adapter 96. As shown in FIG. 9, the network adapter 96 communicates with the other modules of the model-generating device 90 via a bus 93. It should be understood that although not shown in the figures, other hardware and/or software modules may be used in conjunction with the model-generating device 90, including but not limited to: microcode, device drivers, redundant processors, external disk drive arrays, RAID (disk array) systems, tape drives, and data backup storage systems, etc.
It should be noted that although in the above detailed description several units/modules or sub-units/modules of the electronic device are mentioned, such a division is merely exemplary and not mandatory. Indeed, the features and functionality of two or more of the units/modules described above may be embodied in one unit/module according to embodiments of the invention. Conversely, the features and functions of one unit/module described above may be further divided into embodiments by a plurality of units/modules.
Example 4
The present embodiment provides a computer-readable storage medium on which a computer program is stored, which when executed by a processor, implements the steps in the hardening artifact correction method of an image of embodiment 1.
More specific examples, among others, that the readable storage medium may employ may include, but are not limited to: a portable disk, a hard disk, random access memory, read only memory, erasable programmable read only memory, optical storage device, magnetic storage device, or any suitable combination of the foregoing.
In a possible implementation, the present invention can also be implemented in the form of a program product comprising program code for causing a terminal device to perform the steps of the method for hardening artifact correction of images implementing embodiment 1 when the program product is run on the terminal device.
Where program code for carrying out the invention is written in any combination of one or more programming languages, the program code may execute entirely on the user device, partly on the user device, as a stand-alone software package, partly on the user device and partly on a remote device or entirely on the remote device.
While specific embodiments of the invention have been described above, it will be understood by those skilled in the art that this is by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (10)
1. A method for correcting an image hardening artifact, the method comprising:
acquiring energy spectrum projection data to be corrected;
determining effective energy spectrum values of a detector channel of an energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model;
calculating a correction compensation amount according to the energy spectrum projection data to be corrected and the effective spectrum value;
and correcting the energy spectrum projection data to be corrected based on the correction compensation amount.
2. The method for correcting hard artifacts of images according to claim 1, wherein said step of calculating a correction compensation amount based on said spectral projection data to be corrected and said effective spectral values comprises:
determining line integral data of the density of the base material according to the to-be-corrected energy spectrum projection data;
calculating the correction compensation amount according to the effective spectrum value, the line integral data and the linear attenuation coefficient of each base material.
3. A method of image hardening artifact correction as claimed in claim 2, wherein said step of determining line integral data of density of base material from said spectral projection data to be corrected comprises:
determining the number of base substances and the number of energy intervals; the number of energy intervals is greater than the number of base substances;
and calculating the line integral data according to the number of the base substances, the number of the energy intervals and the projection data to be corrected.
4. The method of image hardening artifact correction according to claim 3, wherein said step of calculating said line integral data from said number of basis materials, said number of energy bins, and said projection data to be corrected comprises:
determining an effective attenuation coefficient according to the quantity of the base substances and the range of the energy interval;
and calculating the line integral data according to the energy spectrum projection data to be corrected and the effective attenuation coefficient.
5. The method of image hardening artifact correction according to claim 4, wherein said step of calculating said line integral data from said spectral projection data to be corrected and said effective attenuation coefficient comprises:
and calculating the line integral data by adopting a least square method or matrix inversion according to the energy spectrum projection data to be corrected and the effective attenuation coefficient.
6. The method for correcting hard artifacts of images according to claim 1, wherein the step of determining effective spectral values of detector channels of a spectral CT system at different energy intervals according to raw spectral projection data obtained by scanning an eccentrically placed standard water phantom comprises:
acquiring the corresponding relation between the energy spectrum projection data and the effective energy spectrum data;
and performing iterative computation based on the original energy spectrum projection data and the corresponding relation to obtain the effective spectrum value.
7. The method for hardening artifact correction of images as claimed in claim 1, wherein said step of correcting said spectral projection data to be corrected based on said correction compensation amount comprises:
and performing iterative calculation on the energy spectrum projection data to be corrected according to the correction compensation amount.
8. A hardening artifact correction system for an image, said hardening artifact correction system comprising:
the acquisition module is used for acquiring the energy spectrum projection data to be corrected;
the determination module is used for determining effective energy spectrum values of a detector channel of the energy spectrum CT system in different energy intervals according to energy spectrum projection original data obtained by scanning an eccentrically placed standard water model;
the calculation module is used for calculating correction compensation according to the energy spectrum projection data to be corrected and the effective spectrum value;
and the correction module is used for correcting the energy spectrum projection data to be corrected based on the correction compensation amount.
9. An electronic device comprising a processor, a memory, and a computer program stored on the memory and executable on the processor, the computer program when executed by the processor implementing a method of hardening artifact correction of an image as claimed in any one of claims 1 to 7.
10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out a method of hardening artifact correction of an image as claimed in any one of claims 1 to 7.
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| CN117372287B (en) * | 2023-12-06 | 2024-03-15 | 赛诺威盛科技(北京)股份有限公司 | Compensation correction of detector spectral response, apparatus, device and medium |
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