CN113362404A - Scatter correction method, device and storage medium for computer tomography - Google Patents
Scatter correction method, device and storage medium for computer tomography Download PDFInfo
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Abstract
The embodiment of the invention discloses a scattering correction method and device for computed tomography and a storage medium. The method comprises the following steps: determining the pixel density of the attenuation value after the X-ray passes through the scanning target in a single projection and the pixel area density of the attenuation value; determining a second order correction coefficient for the single projection based on the pixel density and the pixel area density; performing second-order correction on the scattering correction value of each pixel in the single projection based on the second-order correction coefficient; and respectively correcting the signal intensity value detected by each pixel in the single projection based on the second-order corrected scattering correction value of each pixel. Embodiments of the present invention may eliminate the need for an anti-scatter grid (ASG) and thereby save costs. Moreover, embodiments of the present invention may achieve good scatter correction when the scan target is off-center.
Description
Technical Field
The present invention relates to the technical field of medical equipment, and in particular, to a scatter correction method, apparatus, and storage medium for computed tomography.
Background
Computed Tomography (CT) uses a precisely collimated X-ray beam, gamma rays, ultrasonic waves, etc. to scan a cross section of a certain part of a human body one by one together with a detector having a very high sensitivity, has the characteristics of fast scanning time, clear images, etc., and can be used for the examination of various diseases. Depending on the radiation used, computed tomography scans can be classified as: x-ray computed tomography (X-CT), Ultrasound Computed Tomography (UCT), and gamma-ray computed tomography (gamma-CT), among others.
In X-ray computed tomography systems, scattered radiation is a major cause of image degradation and non-linearity. The distance between the scanned object and the detector has a significant effect on the total scatter intensity reaching the detector. If the scan target is placed off-center, the relative distance of the scan target to the detector changes as the system rotates, and the scatter intensity received by the detector changes throughout the scan, resulting in artifacts.
Currently, an Anti-Scatter-Grid (ASG) is generally used to ensure that the Scatter intensity received by the detector is negligibly small. However, the introduction of ASG causes a cost problem. In addition, if the height of the ASG is reduced, artifacts may also result from non-uniformly received scatter intensity.
Disclosure of Invention
The embodiment of the invention provides a scattering correction method and device for computed tomography and a storage medium.
The technical scheme of the embodiment of the invention is as follows:
a scatter correction method for computed tomography, comprising:
determining the pixel density of the attenuation value after the X-ray passes through the scanning target in a single projection and the pixel area density of the attenuation value;
determining a second order correction coefficient for the single projection based on the pixel density and the pixel area density;
performing second-order correction on the scattering correction value of each pixel in the single projection based on the second-order correction coefficient;
and respectively correcting the signal intensity value detected by each pixel in the single projection based on the second-order corrected scattering correction value of each pixel.
Therefore, in the embodiment of the invention, the scattering correction can be realized by an algorithm, so that the ASG can be omitted, and the cost is saved. In addition, the second-order correction coefficient of a single projection is determined based on the pixel density and the pixel area density, the scattering signals under different conditions can be accurately estimated by using the second-order correction coefficient, and the method and the device are particularly suitable for the situation that a scanning target is eccentrically arranged and the relative distance between the scanning target and a detector is changed in the scanning process.
In one embodiment, the determining the pixel density of the attenuation values and the pixel area density of the attenuation values after the X-ray passes through the scan target in a single projection comprises:
determining the pixel density p and the pixel area density τ, where p ═ Atotal/nsize，τ＝Atotal/nsize 2；
Wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
Therefore, the embodiment of the invention can quickly determine the pixel density and the pixel area density based on the total number of the pixels with the attenuation values larger than zero and the sum of the attenuation values detected by all the pixels, and the calculation process is simple and convenient.
In one embodiment, the second order correction coefficient includes: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering;
the determining a second order correction coefficient for the single projection based on pixel density and pixel area density comprises:
determining the scaling factor based on the pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1；
Determining the scattering intensity scaling factor based on a pixel density p, wherein: gamma-gamma0-c2·ρ2；
Wherein:
r0is a preset value of a scale factor;
τ0the pixel area density is a preset value;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
Therefore, the embodiment of the invention provides the scaling factor based on the pixel area density and the scattering intensity scaling factor based on the pixel density, wherein the scaling factor and the scattering intensity scaling factor can be regarded as containing the position information of the scanning target, and can accurately estimate the scattering signals under different conditions, so that the embodiment of the invention can be applied to various extreme conditions, and has wider applicability.
In one embodiment, the second-order correcting the scatter correction value of each pixel in the single projection based on the second-order correction coefficient includes:
determining a second order corrected scatter correction value delta for the kth pixel based on the scaling factor r and the scatter intensity scaling factor gammaCorrec(k)；
Wherein: deltaCorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
A(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
Therefore, the embodiment of the invention can conveniently determine the second-order corrected scattering correction value of each pixel based on the scale factor and the scattering intensity scaling factor.
In one embodiment, the performing the correction on the signal intensity values detected by each pixel in the single projection based on the second-order corrected scatter correction value for each pixel comprises:
calculating a correction value m (k) for the detected signal intensity value for the kth pixel; wherein M (k) ═ M0(k)-δCorrect(k)；
Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel.
Therefore, the embodiment of the invention can conveniently correct the signal intensity value detected by each pixel based on the second-order corrected scattering correction value of the pixel.
A scatter correction apparatus for computed tomography comprising:
the first determination module is used for determining the pixel density of the attenuation value and the pixel area density of the attenuation value after the X-ray passes through the scanning target in a single projection;
a second determining module for determining a second order correction coefficient for the single projection based on the pixel density and the pixel area density;
the correction value correction module is used for carrying out second-order correction on the scattering correction value of each pixel in the single projection based on the second-order correction coefficient;
and the intensity value correction module is used for respectively correcting the signal intensity value detected by each pixel in the single projection based on the second-order corrected scattering correction value of each pixel.
Therefore, in the embodiment of the invention, the scattering correction can be realized by an algorithm, so that the ASG can be omitted, and the cost is saved. In addition, the second-order correction coefficient of a single projection is determined based on the pixel density and the pixel area density, the scattering signals under different conditions can be accurately estimated by using the second-order correction coefficient, and the method and the device are particularly suitable for the situation that a scanning target is eccentrically arranged and the relative distance between the scanning target and a detector is changed in the scanning process.
In one embodiment, the first determining module is configured to determine the pixel density ρ and the pixel area density τ, wherein:
ρ＝Atotal/nsize，τ＝Atotal/nsize 2；
wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
Therefore, the embodiment of the invention can quickly determine the pixel density and the pixel area density based on the total number of the pixels with the attenuation values larger than zero and the sum of the attenuation values detected by all the pixels, and the calculation process is simple and convenient.
In one embodiment, the second order correction coefficient includes: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering;
the second determining module is configured to determine the scaling factor based on the pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1(ii) a Determining the scattering intensity scaling factor based on a pixel density ρ, wherein γ ═ γ0-c2·ρ2；
Wherein:
r0is a preset value of a scale factor;
τ0the pixel area density is a preset value;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
Therefore, the embodiment of the invention provides the scaling factor based on the pixel area density and the scattering intensity scaling factor based on the pixel density, wherein the scaling factor and the scattering intensity scaling factor can be regarded as containing the position information of the scanning target, and can accurately estimate the scattering signals under different conditions, so that the embodiment of the invention can be applied to various extreme conditions, and has wider applicability.
In one embodiment, the correction value correction module is configured to determine a second-order corrected scatter correction value δ for the kth pixel based on the scaling factor r and the scatter intensity scaling factor γCorrec(k)；
Wherein: deltacorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
Λ(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
Therefore, the embodiment of the invention can conveniently determine the second-order corrected scattering correction value of each pixel based on the scale factor and the scattering intensity scaling factor.
In one embodiment, the intensity value correction module is configured to calculate a correction value m (k) of the detected signal intensity value for the k-th pixel; wherein M (k) ═ M0(k)-δCorrect(k) (ii) a Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel.
Therefore, the embodiment of the invention can conveniently correct the signal intensity value detected by each pixel based on the second-order corrected scattering correction value of the pixel.
A scatter correction apparatus for a computed tomography scan, 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 scatter correction method for a computed tomography scan as defined in any one of the above.
Therefore, the embodiment of the invention also provides a scatter correction device with a memory-processor architecture.
A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out a scatter correction method of a computed tomography scan as set forth in any one of the preceding claims.
Therefore, an embodiment of the present invention further provides a computer-readable storage medium containing a computer program for implementing a scatter correction method for computed tomography.
Drawings
Fig. 1 is an exemplary flow chart of a scatter correction method of computed tomography according to the present invention.
Fig. 2 is an exemplary diagram of signal intensity values detected by each pixel in the detector of the present invention.
Fig. 3 is an exemplary diagram of the signal attenuation values detected by the individual pixels in the detector of the present invention.
Fig. 4 is a graph comparing the first effect of the prior art scatter correction method with the scatter correction method of the present invention using ASG.
FIG. 5 is a graph comparing a second effect of a prior art scatter correction method using an ASG and a scatter correction method according to the present invention.
Fig. 6 is an exemplary block diagram of a scatter correction apparatus for computed tomography according to the present invention.
Fig. 7 is an exemplary block diagram of a scatter correction apparatus for computed tomography having a memory-processor architecture in accordance with the present invention.
Wherein the reference numbers are as follows:
| 100 | scatter correction method for |
| 101～104 | Step (ii) of |
| 600 | Scatter correction device for computed |
| 601 | |
| 602 | |
| 603 | Correction |
| 604 | Intensity |
| 700 | Scatter correction device for computed |
| 701 | Processor with a memory having a plurality of |
| 702 | Memory device |
Detailed Description
In order to make the technical scheme and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the scope of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
For simplicity and clarity of description, the invention will be described below by describing several representative embodiments. Numerous details of the embodiments are set forth to provide an understanding of the principles of the invention. It will be apparent, however, that the invention may be practiced without these specific details. Some embodiments are not described in detail, but rather are merely provided as frameworks, in order to avoid unnecessarily obscuring aspects of the invention. Hereinafter, "including" means "including but not limited to", "according to … …" means "at least according to … …, but not limited to … … only". In view of the language convention of chinese, the following description, when it does not specifically state the number of a component, means that the component may be one or more, or may be understood as at least one.
The applicant found that: in an X-ray computed tomography system, the distance between the scan target (i.e., the object being scanned) and the detector has a significant effect on the total scatter intensity reaching the detector. If the scan target is placed off-center, the relative distance of the scan target to the detector changes as the system rotates, and the scatter intensity received by the detector changes throughout the scan, resulting in artifacts. Cost issues can result if ASGs are employed. In addition, if the height of the ASG is reduced, artifacts may result from non-uniformly received scatter intensity.
The applicant has also found that: if the position information of the scanned object is acquired from the raw data of the whole 360 degrees and then the accurate scattered radiation is predicted based on the position information, the image reconstruction performance may be significantly reduced. For example, one common existing processing method is: the initial image is reconstructed or the entire sinogram space is searched to obtain position information of the scanned object, and then this a priori knowledge is used as input for further scatter correction. However, this prior art processing method can only start to perform correction after the whole scan is completed, and belongs to iterative reconstruction, thereby significantly reducing the image reconstruction speed.
In the embodiment of the invention, a scatter correction algorithm based on single projection (projection) is provided, which can be independently processed inside each projection, can well predict scatter changes received at different positions without adopting ASG (automatic sampling group), and can well maintain the image reconstruction speed.
Fig. 1 is an exemplary flow chart of a scatter correction method of computed tomography according to the present invention.
As shown in fig. 1, the method includes:
step 101: the pixel density of the attenuation values and the pixel area density of the attenuation values after the X-ray has passed through the scan object in a single projection are determined.
In current scatter correction methods, after calculating the estimated scatter, triangular convolution may be used to model the scatter distribution received by the detector in space. However, this is a rough estimation process. Physically, the shape of the convolution kernel representing the scatter distribution received by the detector and the overall normalized scale factor can be adjusted when changing the distance between the scanned object and the detector. The total attenuation of the scan object over the scan plane should be constant regardless of where the scan object is placed and from which projection the scan is taken. Thus, the actual projection size of the scanned object onto the detector, and the cumulative total attenuation at that projection, may provide additional correction factors.
Here, embodiments of the invention may introduce two additional correction factors: (1) pixel density of attenuation values after the X-ray has passed through the scan target; (2) pixel area density of the attenuation values. Wherein: the pixel density of the attenuation values after the X-rays have passed through the scanned object has an increasing relationship (preferably linearly proportional) with the attenuation values and a decreasing relationship (preferably linearly inverse) with the number of pixels of the detector: the pixel area density of the attenuation values has an increasing relationship (preferably linearly proportional) with the attenuation values and a decreasing relationship (preferably linearly inversely proportional) with the square of the number of pixels of the detector.
In one embodiment, in step 101, determining the pixel density of the attenuation values and the pixel area density of the attenuation values after the X-ray has passed through the scan target in a single projection comprises:
determining a pixel density ρ and a pixel area density τ, where ρ ═ Atotal/nsize，τ＝Atotal/nsize 2；
Wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
While the above exemplary description describes a typical example of determining the pixel density of attenuation values and the pixel area density of attenuation values, those skilled in the art will appreciate that this description is merely exemplary and is not intended to limit the scope of embodiments of the present invention.
Fig. 2 is an exemplary diagram of signal intensity values detected by each pixel in the detector of the present invention. Fig. 3 is an exemplary diagram of the signal attenuation values detected by the individual pixels in the detector of the present invention.
In fig. 2, the horizontal axis represents the number of pixels included in the detector, and the vertical axis represents the normalized signal intensity value received by the pixels. In fig. 3, the horizontal axis represents the number of pixels included in the detector, and the vertical axis represents the attenuation value of the signal. Fig. 3 may be equivalently converted based on fig. 2, and fig. 2 may also be equivalently converted based on fig. 3.
AtotalThe sum of the detected attenuation values for all pixels. That is, AtotalThe sum of the attenuation values on the vertical axis corresponding to all the pixels on the horizontal axis in fig. 3. For example, assume there are 700 pixels, pixel 0, pixel 1, and pixel 2 …, respectively, 699, where pixel 0 detects an attenuation value of A0The attenuation value detected by the pixel 1 is A1The attenuation value detected by the pixel 2 is A2… Pixel 699 detects an attenuation value of A699Then A istotal＝A0+A1+A2…+A699。
nsizeThe total number of pixels for which an attenuation value greater than zero is detected. That is, AtotalThe total number of all pixels on the horizontal axis corresponding to the attenuation value on the vertical axis of fig. 3 being greater than zero. For example, assume there are 700 pixels, pixel 0, pixel 1, and pixel 2 …, respectively, 699, where pixel 1 detects an attenuation value of A0The attenuation value detected by the pixel 1 is A1The attenuation value detected by the pixel 2 is A2… Pixel 699 detects an attenuation value of A699. The attenuation values of the pixels 100 to 500 are all larger than zero, i.e. the total number of pixels with attenuation values larger than zero is 401, then nsizeIs 401.
Step 102: second order correction coefficients for the single projection are determined based on the pixel density and the pixel area density.
Here, a second-order correction coefficient of the single projection, which contains or is associated with positional information of the scanning object, may be determined based on the pixel density and the pixel area density, and thus the scatter signal in different cases may be estimated more accurately based on the second-order correction coefficient. In particular, it is suitable for use in situations where the scan target is placed off-center and its relative distance from the detector changes during the scan.
In one embodiment, the second order correction coefficients include: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering; determining the second-order correction coefficients for the single projection based on the pixel density and the pixel area density in step 102 includes:
determining the scaling factor based on the pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1；
Determining the scattering intensity scaling factor based on a pixel density ρ, wherein γ ═ γ0-c2·ρ2；
Wherein:
r0is a preset value of a scale factor;
τ0the pixel area density is a preset value;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
Here, r is0,τ0,γ0,c1,c2To values that can be set according to the properties and scanning parameters of the computer tomography system.
Preferably, r0,τ0,γ0,c1,c2And may also be adjusted by the user based on experience. r is0And gamma0For the original correction coefficient of the single projection, the invention is implemented by applying r0And gamma0And correcting to obtain a second-order correction coefficient of a single projection.
The above exemplary description describes a typical example of determining second-order correction coefficients for a single projection based on pixel density and pixel area density, and those skilled in the art will appreciate that this description is merely exemplary and is not intended to limit the scope of embodiments of the present invention.
Step 103: and performing second-order correction on the scattering correction value of each pixel in the single projection based on the second-order correction coefficient.
Here, the scaling factor r and the scattering intensity scaling factor y determined in step 102 are based onDetermining a second order corrected scatter correction value delta for a kth pixelCorrec(k) In that respect Wherein:
δCorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
wherein: deltacorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
A(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
For delta0(k)、Λ(n1) And Λ (n)2) For a detailed description, reference may be made to a conference paper of "medical image" published in 3 months in 2018. See: details of "Wang, Y., Stierstorfer, K., Petersiloka, M., Grasruck, M., Tian, Y.," Scatter correction for Multi-slice CT system, "Proc. Please refer to the related browsing website: https:// www.researchgate.net/publication/323678669_ Scatter _ correction _ for _ multi-slice _ CT _ system. The embodiment of the present invention will not be described in detail.
It can be seen that in step 103, for each pixel of the detector, a respective second-order corrected scatter correction value can be calculated.
Step 104: a correction is performed separately for the signal intensity values detected by each pixel in the single projection based on the second order corrected scatter correction values for each pixel.
Here, a correction value m (k) of the detected signal intensity value is calculated for the k-th pixel; wherein M (k) ═ M0(k)-δCorrect(k) (ii) a Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel. For example, for each pixel shown in FIG. 2And respectively subtracting the scattering correction value after the second-order correction of the pixel from the measured signal intensity to obtain the correction value of the signal intensity.
In the method flow shown in fig. 1, a method of correcting the detected signal intensity for each pixel in a single projection is described. During the complete course of a computer tomography, a plurality of single projections need to be performed. For example, for a 360 degree computed tomography scan, it is often necessary to perform thousands of single projections. The correction of the raw data for each projection may be achieved by performing a correction on the signal intensity values detected by each pixel in each projection according to the method shown in fig. 1. Then, an image is reconstructed based on all corrected raw data of all projections.
Therefore, the scatter correction method of the present invention is completely based on projection, and the correction is completed before the image is reconstructed, thereby avoiding using raw data or iterative computation in the whole sinogram domain, which means that the embodiment of the present invention can have higher computation performance and can be integrated into the current data preprocessing pipeline. Moreover, the embodiment of the present invention has a good effect in the original data domain, so that the embodiment of the present invention can be used as a preprocessing step in an image reconstruction pipeline, and an image can be reconstructed off-line from the original data collected by a computed tomography system without ASG.
In particular implementations, the method flow of fig. 1 may be performed by a probe that includes a processor, or the method flow of fig. 1 may be performed by a control host.
The reconstructed images of embodiments of the invention show better homogeneity (especially in the case of off-centre scans) compared to images reconstructed using prior art scatter correction methods.
Fig. 4 is a graph comparing the first effect of the prior art scatter correction method with the scatter correction method of the present invention using ASG. In fig. 4, the scan target is a water mold. Fig. 4 shows the contrast between the reconstructed images of the 20 centimeter (cm) and 30cm water modes at 100 millimeters (mm) eccentricity.
In fig. 4, the upper three subgraphs are the reconstructed images of the 20 cm water model, and the lower three subgraphs are the reconstructed images of the 30cm water model. Both the 20 cm water phantom and the 30cm water phantom were scanned at 100 mm from the ISO center. Wherein: the two sub-graphs on the left are reconstructed images from raw data obtained from a standard 16-layer computed tomography system based on an arrangement of ASGs; the two sub-images in the middle are based on images reconstructed by a scattering correction algorithm in the prior art without ASG; the two right subgraphs are based on images reconstructed without ASG by the scatter correction method of the invention.
As can be seen from fig. 4, the quality of the image obtained with the scatter correction method of the present invention is close to that of a standard 16-slice computed tomography with ASG arranged and is significantly better than the image reconstructed with the scatter correction algorithm of the prior art.
FIG. 5 is a graph comparing a second effect of a prior art scatter correction method using an ASG and a scatter correction method according to the present invention. In fig. 5, the scan target is an anthropomorphic model.
FIG. 5 shows a comparison of an anthropomorphic model at 100 millimeters (mm) eccentricity. Wherein the left sub-image is based on an image reconstructed without ASG using prior art scatter correction algorithms. The right subgraph is based on an image reconstructed without ASG by the scatter correction method of the invention. It can be seen that the left sub-image can see artifacts, while the right sub-image has better image quality.
Based on the above description, the embodiment of the present invention further provides a scatter correction apparatus for computed tomography.
Fig. 6 is an exemplary block diagram of a scatter correction apparatus for computed tomography according to the present invention.
As shown in fig. 6, the scatter correction apparatus 600 for computed tomography includes:
a first determining module 601, configured to determine pixel density of attenuation values and pixel area density of the attenuation values after the X-ray passes through the scan target in a single projection;
a second determining module 602, configured to determine a second-order correction coefficient for the single projection based on the pixel density and the pixel area density;
a correction value correction module 603, configured to perform second-order correction on the scattering correction value of each pixel in the single projection based on the second-order correction coefficient;
an intensity value correction module 604 for performing a correction on the signal intensity values detected by each pixel in the single projection based on the second order corrected scatter correction value for each pixel.
In one embodiment, the first determining module 601 is configured to determine the pixel density ρ and the pixel area density τ, where:
ρ＝Atotai/nsize，τ＝Atotal/nsize 2；
wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
In one embodiment, the second order correction coefficients include: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering;
a second determining module 602, configured to determine the scaling factor based on the pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1(ii) a Determining the scattering intensity scaling factor based on a pixel density ρ, wherein γ ═ γ0-c2·ρ2；
Wherein:
r0is a preset value of a scale factor;
τ0the pixel area density is a preset value;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
In one embodiment, the correction value correction module 603 is configured to determine a second-order corrected scatter correction value δ for the kth pixel based on the scaling factor r and the scatter intensity scaling factor γCorrec(k)；
Wherein: deltaCorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
Λ(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
In one embodiment, the intensity value correction module 604 is configured to calculate a correction value m (k) of the detected signal intensity value for the k-th pixel; wherein M (k) ═ M0(k)-δCorrect(k) (ii) a Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel.
Based on the above description, the embodiment of the present invention also provides a scatter correction apparatus for computed tomography having a memory-processor architecture.
FIG. 7 is an exemplary block diagram of a scatter correction apparatus for computed tomography having a memory-processor architecture in accordance with the present invention. The scatter correction device 700 may be integrated into the detector or into the control host.
As shown in fig. 7, the scatter correction apparatus 700 comprises a processor 701, a memory 702 and a computer program stored on the memory 702 and executable on the processor 701, the computer program, when executed by the processor 701, implementing the scatter correction method of computed tomography as described above.
The memory 702 may be embodied as various storage media such as an Electrically Erasable Programmable Read Only Memory (EEPROM), a Flash memory (Flash memory), and a Programmable Read Only Memory (PROM). The processor 701 may be implemented to include one or more central processors or one or more field programmable gate arrays, wherein the field programmable gate arrays integrate one or more central processor cores. In particular, the central processor or central processor core may be implemented as a CPU or MCU or DSP, etc.
It should be noted that not all steps and modules in the above flows and structures are necessary, and some steps or modules may be omitted according to actual needs. The execution order of the steps is not fixed and can be adjusted as required. The division of each module is only for convenience of describing adopted functional division, and in actual implementation, one module may be divided into multiple modules, and the functions of multiple modules may also be implemented by the same module, and these modules may be located in the same device or in different devices.
The hardware modules in the various embodiments may be implemented mechanically or electronically. For example, a hardware module may include a specially designed permanent circuit or logic device (e.g., a special purpose processor such as an FPGA or ASIC) for performing specific operations. A hardware module may also include programmable logic devices or circuits (e.g., including a general-purpose processor or other programmable processor) that are temporarily configured by software to perform certain operations. The implementation of the hardware module in a mechanical manner, or in a dedicated permanent circuit, or in a temporarily configured circuit (e.g., configured by software), may be determined based on cost and time considerations.
The present invention also provides a machine-readable storage medium storing instructions for causing a machine to perform a method as described herein. Specifically, a system or an apparatus equipped with a storage medium on which a software program code that realizes the functions of any of the embodiments described above is stored may be provided, and a computer (or a CPU or MPU) of the system or the apparatus is caused to read out and execute the program code stored in the storage medium. Further, part or all of the actual operations may be performed by an operating system or the like operating on the computer by instructions based on the program code. The functions of any of the above-described embodiments may also be implemented by writing the program code read out from the storage medium to a memory provided in an expansion board inserted into the computer or to a memory provided in an expansion unit connected to the computer, and then causing a CPU or the like mounted on the expansion board or the expansion unit to perform part or all of the actual operations based on the instructions of the program code.
Examples of the storage medium for supplying the program code include floppy disks, hard disks, magneto-optical disks, optical disks (e.g., CD-ROMs, CD-R, CD-RWs, DVD-ROMs, DVD-RAMs, DVD-RWs, DVD + RWs), magnetic tapes, nonvolatile memory cards, and ROMs. Alternatively, the program code may be downloaded from a server computer or the cloud by a communication network.
"exemplary" means "serving as an example, instance, or illustration" herein, and any illustration, embodiment, or steps described as "exemplary" herein should not be construed as a preferred or advantageous alternative. For the sake of simplicity, the drawings are only schematic representations of the parts relevant to the invention, and do not represent the actual structure of the product. In addition, in order to make the drawings concise and understandable, components having the same structure or function in some of the drawings are only schematically illustrated or only labeled. In this document, "a" does not mean that the number of the relevant portions of the present invention is limited to "only one", and "a" does not mean that the number of the relevant portions of the present invention "more than one" is excluded. In this document, "upper", "lower", "front", "rear", "left", "right", "inner", "outer", and the like are used only to indicate relative positional relationships between relevant portions, and do not limit absolute positions of the relevant portions.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (12)
1. A scatter correction method (100) for computed tomography, comprising:
determining the pixel density of the attenuation values and the pixel area density of the attenuation values after the X-ray passes through the scanning target in a single projection (101);
determining a second order correction coefficient (102) for the single projection based on the pixel density and the pixel area density;
second order correction (103) of the scatter correction value for each pixel in the single projection based on the second order correction coefficient;
a correction (104) is performed separately for the signal intensity values detected by each pixel in the single projection based on the second order corrected scatter correction value for each pixel.
2. The scatter correction method (100) of computed tomography according to claim 1, wherein said determining a pixel density of attenuation values and a pixel area density (101) of the attenuation values after the X-rays in a single projection have passed through the scan object comprises:
determining the pixel density p and the pixel area density τ, where p ═ Atotal/nsize，τ＝Atotal/nsize 2；
Wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
3. The scatter correction method (100) of computed tomography according to claim 2, wherein the second order correction coefficients comprise: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering;
said determining a second order correction coefficient (102) for the single projection based on pixel density and pixel area density comprises:
determining the scaling factor based on the pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1；
Determining the scattering intensity scaling factor based on a pixel density p, wherein: gamma-gamma0-c2·ρ2；
Wherein:
r0is a preset value of a scale factor;
τ0a preset value of the integral density for a pixel;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
4. Scatter correction method (100) of computed tomography according to claim 3,
said second order correcting (103) the scatter correction value for each pixel in the single projection based on the second order correction coefficient comprises:
determining a second order corrected scatter correction value delta for the kth pixel based on the scaling factor r and the scatter intensity scaling factor gammaCorrec(k)；
Wherein: deltaCorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
Λ(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
5. The scatter correction method (100) of computed tomography according to claim 4, wherein said individually performing a correction (104) of the detected signal intensity values of each pixel in the single projection based on the second order corrected scatter correction values of each pixel comprises:
calculating a correction value m (k) for the detected signal intensity value for the kth pixel; wherein M (k) ═ M0(k)-δCorrect(k)；
Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel.
6. A scatter correction apparatus (600) for computed tomography, comprising:
a first determining module (601) for determining the pixel density of the attenuation values and the pixel area density of the attenuation values after the X-ray passes through the scanning target in a single projection;
a second determination module (602) for determining a second order correction coefficient for the single projection based on the pixel density and the pixel area density;
a correction value correction module (603) for performing a second-order correction on the scatter correction value of each pixel in the single projection based on the second-order correction coefficient;
an intensity value correction module (604) for performing a correction on the signal intensity values detected by each pixel in the single projection based on the second order corrected scatter correction value for said each pixel.
7. Scatter correction device (600) for computed tomography according to claim 6,
the first determining module (601) for determining the pixel density p and the pixel area density τ, wherein:
ρ＝Atotal/nsize，τ＝Atotal/nsize 2；
wherein: n issizeA total number of pixels for which an attenuation value greater than zero is detected; a. thetotalThe sum of the detected attenuation values for all pixels.
8. Scatter correction device (600) for computed tomography according to claim 7, characterized in that the second order correction coefficients comprise: a scaling factor r and a scattering intensity scaling factor gamma between the wide scattering and the narrow scattering;
the second determining module (602) is configured to determine the scaling factor based on a pixel area density τ, wherein: r ═ r0+(τ-τ0)/c1(ii) a Determining the scattering intensity scaling factor based on a pixel density p, wherein: gamma-gamma0-c2·ρ2(ii) a Wherein:
r0is a preset value of a scale factor;
τ0the pixel area density is a preset value;
γ0a preset value of a scattering intensity scaling factor;
c1is a first preset coefficient;
c2is a second predetermined coefficient.
9. Scatter correction device (600) for computed tomography according to claim 8,
the correction value correction module (603) is used for determining a second-order corrected scattering correction value delta of the kth pixel based on the scaling factor r and the scattering intensity scaling factor gammaCorrec(k)；
Wherein: deltaCorrect(k)＝(δ0(k)*Λ(n1)+r·δ0(k)*Λ(n2))·γ；
Wherein:
δ0(k) calculating a scattering correction value for the kth pixel point theoretically;
Λ(n1) A first point spread function for computed tomography;
Λ(n2) A second point spread function for computed tomography;
k is the number of the pixel, wherein the value range of k is [0, N ], and N is the maximum number of the pixel.
10. Scatter correction device (600) for computed tomography according to claim 9,
the intensity value correction module (604) for calculating a correction value M (k) for the detected signal intensity value for the k-th pixel,
wherein M (k) ═ M0(k)-δCorrect(k) (ii) a Wherein M is0(k) The original value of the signal intensity value detected for the kth pixel.
11. A scatter correction apparatus (700) for computed tomography, comprising a processor (701), a memory (702) and a computer program stored on the memory (702) and executable on the processor (701), the computer program, when executed by the processor (701), implementing a scatter correction method (100) for computed tomography according to any of claims 1 to 6.
12. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out a scatter correction method (100) of a computed tomography scan as set forth in any one of claims 1 to 6.
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