WO2014122840A1

WO2014122840A1 - Ct image generation device and ct image generation method

Info

Publication number: WO2014122840A1
Application number: PCT/JP2013/082226
Authority: WO
Inventors: ▲興▼▲東▼ 盛
Original assignee: 株式会社日立メディコ
Priority date: 2013-02-08
Filing date: 2013-11-29
Publication date: 2014-08-14
Also published as: CN103976753A; JPWO2014122840A1; CN103976753B; JP6014174B2

Abstract

Through the present invention, an error between projection and back projection in CT image generation is reduced. The CT image generation device according to the present invention is provided with: an X-ray scanner provided with an X-ray source and a detector; a storage module including a detector data block, a weighting data block, and a parameter data block; and a processor module including a main processor, a weighting calculation unit, a weighting vector multiplication unit, and a separable footprint computation unit. A scanner stores scanned data as detector data in the detector data block, the weighting calculation unit acquires a geometry parameter from the parameter data block and calculates a weighting vector, and the main processor controls a projection/back projection angle loop using the geometry parameter. The weighting vector multiplication unit multiplies the detector data by a weighting vector and acquires a corrected detector value, and the separable footprint computation unit executes a separable footprint projection/back projection algorithm using the corrected detector value.

Description

CT image generation apparatus and CT image generation method

The present invention relates to a CT image generation apparatus and a CT image generation method, and more particularly to a CT image generation apparatus and a CT image generation method using an improved separable footprint method.

X-ray computed tomography (CT) technology is already widely used in human examinations, and CT images have a 30-year history as the basis for disease diagnosis. However, improving CT image quality and reducing image artifacts has been an important research and clinical challenge consistently.

In practice, the CT image reconstruction algorithm mainly includes a filter back projection method and an iterative reconstruction algorithm. Among these, the filter back projection method is a conventional method of CT image reconstruction, and is widely applied in conventional CT products. However, in the filtered backprojection method, it is assumed that there is no noise interference in the projection data that reconstructs the image. However, in reality, noise always exists with the projection data, especially in the case of low-dose scanning. Since it is remarkable, it becomes difficult to obtain a high-quality CT image. In addition, with the development of clinical practice, the scope and depth of CT clinical application has gradually reached a high level that has not existed in the past. Under these new circumstances, the industry considers the safety of CT use. In addition, new high demands for image quality have emerged. This makes the filter backprojection method difficult to meet new demands.

In response to the above-mentioned new demand, iterative reconstruction algorithms are emphasized and studied in high-level applications. The iterative reconstruction algorithm successfully processes image artifacts due to electronic noise and other physical elements, thereby reducing the X-ray dose during the examination while ensuring image quality. However, due to the enormous amount of calculation, the image formation speed was delayed, and actual clinical application was not possible. However, in recent years, with the rapid development of computer hardware and computational science, iterative reconstruction algorithms can be applied to actual products. In addition, as the emphasis on medical care / health in society increases, the influence of X-ray radiation on human health during CT diagnosis has become more and more attention, and the reduction of X-ray radiation has already become a trend of CT development. . Therefore, iterative reconstruction algorithms are increasingly widely watched and are the focus of current research. At the same time, new high-accuracy backprojection methods that reduce artifacts and improve image quality in the filter backprojection method are being studied for medium and low level applications.

The iterative reconstruction algorithm mainly includes a projection and backprojection process that are repeated many times, but the main procedure in the conventional filter backprojection algorithm is backprojection. Projection and backprojection methods mainly include conventional ray-driven (Pay-Driven) and pixel-driven (Pixel-Driven) methods, but because of large model errors, it is not suitable for applications in iterative reconstruction algorithms. , It becomes difficult to converge the iterative algorithm. Therefore, highly accurate projection and backprojection methods have been researched and proposed, and the most typical ones are the recently proposed distance-driven (Separable Footprint) methods (for example, patent literature) 1, Patent Document 2). Of these, the separable footprint method is currently the best projection and backprojection model in the academic world, but this method is also a kind of approximation method, and there is still a certain model error, which further improves model accuracy.・ Improvement is expected.

JP 2005-522304 Gazette JP 2012-220422 A

In light of the above-described background, the present invention provides a CT image generation apparatus and a CT image generation method capable of reducing artifacts and further reducing projection and backprojection errors based on the separable footprint method. And

The present invention proposes to reduce the error of the weighting factor (weighting factor) by further modifying the weighting factor of the separable footprint algorithm. Although the present invention can be applied mainly to an iterative reconstruction algorithm that requires very high accuracy in projection and backprojection, it can also be used in a filter backprojection algorithm.

That is, the CT image generation apparatus of the present invention includes an X-ray scanner that includes an X-ray source and a detector and detects an object disposed between the X-ray source and the detector, a main processor, a weighting calculation unit, A processor module including a weighted vector multiplication unit and a separable footprint calculation unit; and a storage module for storing parameters used in the processor module, wherein the weight calculation unit receives geometric parameters from the storage module. , And calculates a weighting vector based on the geometric parameter, the main processor controls a projection / backprojection angle loop using the geometric parameter, and the weight vector multiplication unit includes the X-ray scanner To multiply the scanned detector data by the weighting vector Ri, calculates a corrected detector value, the separable flask footprint calculation unit, by using the corrected detector value, and executes a separable footprint projection-back projection algorithm.

The CT image generation method of the present invention includes a step of storing data scanned by an X-ray scanner as detector data, a step of calculating a weighting vector using a geometric parameter stored in a storage module, Controlling a projection / backprojection angle loop using a geometric parameter; obtaining a corrected detector value by multiplying the detector data by the weighting vector; and correcting the corrected detector value And performing a separable footprint projection / backprojection algorithm.

According to the CT image generation apparatus and CT image generation method of the present invention, a detector value with improved accuracy is obtained by multiplying the detector data by the weight vector by the weight vector multiplication unit. By performing projection and backprojection using this detector value, the error of the projection and backprojection can be reduced and the modeling accuracy of the algorithm can be improved compared to a device using a general separable footprint method. Can do.
This can improve the efficiency of the iterative reconstruction algorithm and reduce CT image artifacts.

It is a module diagram of a CT image reconstruction algorithm. It is a module diagram of a CT image reconstruction algorithm. It is a figure explaining the principle of the projection and back projection weighting based on the length in a CT image reconstruction algorithm. It is the figure explaining the principle of the separable footprint projection and back projection method in a CT image reconstruction algorithm, and the figure which showed the model error. It is a figure explaining the weight calculation in the CT image generation apparatus regarding this invention. It is the schematic explaining the function and weighting vector for calculating the weight in the CT image generation apparatus regarding this invention. It is the schematic explaining the detector data weighting by weighting in the CT image generation apparatus regarding this invention. It is a structural module figure explaining CT image generation device concerning the present invention. It is the operation | movement flowchart explaining the projection and backprojection process in CT image generation apparatus regarding this invention. It is the operation | movement flowchart explaining the projection and backprojection process in CT image generation apparatus regarding this invention. It is an operation | movement flowchart when the relative position of the X-ray source and detector in the CT image generation apparatus concerning this invention changes. It is an operation | movement flowchart when the relative position of the X-ray source and detector in the CT image generation apparatus concerning this invention changes.

Hereinafter, an embodiment of a CT image generation apparatus of the present invention and a CT image generation method realized thereby will be described.

The CT image generation apparatus of the present embodiment includes an X-ray scanner (701) that includes an X-ray source (302) and a detector (303) and detects an object disposed between the X-ray source and the detector. A storage module (705) including a detector data block (708), a weighted data block (709), a parameter data block (710), and an input / output result image data block (711), a main processor (715), A processor module (707) including a weight calculation unit (712), a weight vector multiplication unit (713), and a separable footprint calculation unit (714), a data interface module (702), and a user interface module (704); Is provided. The detector data block captures data scanned by the X-ray scanner via the data interface module and stores it as detector data. The weight calculation unit (712) obtains a geometric parameter from the parameter data block and calculates a weight vector based on the geometric parameter. The main processor uses the geometric parameters to control the projection / backprojection angle loop, and the weighted vector multiplication unit (713) obtains the corrected detector value by multiplying the detector data by the weighted vector. . The separable footprint calculation unit (714) executes a separable footprint projection / backprojection algorithm using the corrected detector values.

The CT image generation method according to the present embodiment includes an X-ray scanner that includes an X-ray source and a detector and detects an object disposed between the X-ray source and the detector, a detector data block, and weighting data. A storage module including a block, a parameter data block, and an input / output result image data block; a processor module including a main processor, a weight calculation unit, a weight vector multiplication unit, and a separable footprint calculation unit; and a data interface module A CT image generation method of a CT image generation apparatus comprising: a user interface module, wherein data scanned by the X-ray scanner is stored as detector data in the detector data block via the data interface module Step to make The weight calculation unit obtains a geometric parameter from the parameter data block and calculates a weight vector based on the geometric parameter; and the main processor uses the geometric parameter to project / A step of controlling a backprojection angle loop; a step in which the weight vector multiplication unit multiplies the detector data by the weight vector to obtain a corrected detector value; and the separable footprint computation unit comprises: Performing a separable footprint projection / backprojection algorithm using the corrected detector values.

Further, in the CT image generation apparatus and CT image generation method of the present embodiment, when the distance between the X-ray source and the detector changes according to the angle of projection and backprojection, the weight calculation unit calculates the geometric data from the parameter data block. A parameter is obtained and a weighting vector associated with the distance for each angle in the projection / backprojection angle loop is calculated. With this structure, the application range of the CT image generation apparatus of the present invention can be further expanded. Moreover, since the amount of calculation added is very small, the speed performance of an iterative algorithm can be maintained.

Further, in the CT image generation apparatus and CT image generation method of the present embodiment, the weighting vector at each angle is calculated from 1 / sin θ (θ is the angle between the X-ray and the detector, that is, the X-ray and the X-ray source. The angle of the angle formed by the perpendicular line from the sensor to the detector. Thereby, the length when passing through each pixel of X-rays can be accurately calculated, and the accuracy of the weighting vector can be increased.

Furthermore, in the CT image generation apparatus and CT image generation method of this embodiment, in back projection, first, the detector data is weighted with a weight (weighting vector), and then a separable footprint back projection operation is performed. First, a separable footprint projection operation is performed, and then the detector data obtained by the projection is weighted with a weight (weighting vector). Thereby, it is possible to accurately perform projection and backprojection, reduce an error between the projection and backprojection, and increase the modeling accuracy of the algorithm.

Furthermore, in the CT image generation apparatus and CT image generation method of the present embodiment, the geometric parameters are the distance between the X-ray source and the detector, the detector element size, and the center position of the detector. By calculating weighting vectors using these as geometric parameters, high-precision projection / backprojection can be performed according to various detector types and detection conditions.

Hereinafter, the CT image generation apparatus of the present embodiment will be described in more detail with reference to the drawings.
In the description of the drawings, the same portions or corresponding portions are denoted by the same reference numerals, and overlapping descriptions are omitted.

1A and 1B show module diagrams of the entire image reconstruction algorithm. FIG. 1A shows a conventional filter backprojection reconstruction, and FIG. 1B shows an iterative reconstruction, and the present invention can be applied to both. In the filter backprojection reconstruction, as shown in FIG. 1A, the projection data obtained by the X-ray scan is weighted (weighted) by the weighting module 105, and then a separable footprint backprojection is performed to obtain a CT image. In iterative reconstruction, as shown in FIG. 1B, the weighting module 105 weights every iteration and operates the projection and backprojection processes. The operation procedure refers to the projection and backprojection flow in FIGS. In the figure, the iterative reconstruction algorithm mainly includes a projection module 101, a backprojection module 102, a comparison module 103, and an update module 104. Among these, the projection module 101 and the back projection module 102 perform projection / back projection operations based on the separable footprint method. The weighting module 105 corrects and improves the projection and backprojection model accuracy by weighting each iteration.

FIG. 2 is a diagram showing the principle of length-based projection / backprojection weighting. In the figure, the length when the projection line 201 passes through one of the pixels 202 is the correlation coefficient between the projection line 201 and the pixel, that is, the corresponding detector unit on which the projection line is projected. It is defined that the weighting coefficient is the projection and backprojection weighting 203 for the pixel unit. This basic model is the basis of the separable footprint projection / backprojection method and the present invention.

FIG. 3 is a diagram showing the principle of separable footprint projection / backprojection method and its model error. In the separable footprint projection / backprojection method, projection and backprojection on a predetermined pixel 301 start from the X-ray source 302, pass through four vertices of the pixel 301, respectively, and correspond to four corresponding on the detector 303. A projection or backprojection of radiation to a position. In the projection process, the pixel values are each weighted and integrated into detector units within the four position ranges 304. Here, as shown in FIG. 3, the weighting coefficient 305 has a different value depending on the position of the detector unit, and the weighting coefficient 305 of the separable footprint projection for the predetermined pixel 301 becomes an approximate trapezoid. Is determined by the projection positions of the four vertices. The height of the trapezoid is approximately determined by the distance that the projection line passes through the pixel. In the separable footprint method, the weighting factor is approximately linearly changed between the position ranges 304 determined by the projections of the four vertices. There is. However, in practice, as can be seen from the geometrical relationship in the figure and the weighting principle in FIG. 2, the ideal weighting factor 306 between the positions determined by the projections of the four vertices is not a linear change relationship. Therefore, there is a certain error in the weighting factor 305 of separable footprint projection. In the backprojection process, similarly to the projection process, the detector values in the position range 304 determined by the projection of the four vertices are weighted using the weighting factor 305 and accumulated in the backward direction to the pixel value. Exists.

FIG. 4 shows the principle of weighting (correction coefficient) calculation in this embodiment. According to FIG. 4, the weighting (correction coefficient) is determined based on the geometric relationship of lengths that are cut off when the X-ray 401 passes through different positions of the predetermined pixel 402. In the figure, the length of a line segment (a line 405 cut from the X-ray source to the X-ray detector cuts the pixel 402) 403 is a weighted value in the separable footprint method, but the ideal weighted value is the cutting line. (Line in which the X-ray 401 to be projected is cut by the pixel 402) 404. In other words, in the separable footprint method, the length value of the cutting line 404 is approximated and replaced with a line segment 403, and this weight value is corrected by the geometric relationship between the line segment 403 and the cutting line 404. Can do. That is, the weighting (correction coefficient) calculation function is expressed by the following equation (1).

In Expression (1), L ₄₀₃ and L ₄₀₄ represent the lengths of the cutting line 403 and the line segment 404, respectively, and θ represents the angle of the angle formed by the ray 401 and the perpendicular 405 from the radiation source to the detector.

FIG. 5 shows a diagram showing a function for calculating a weight (correction coefficient) and a diagram showing a weight vector. In projection, all pixel 502 values on the path of the X-ray 501 are weighted and accumulated in the projection correspondence detector 503. Therefore, the correction coefficients for these pixel values are all related only to the angle of the ray. And expressed by the following equation (2).

In Expression (2), P ₁ , P ₂ ..., P _k are pixel values of all the pixels 502 on the path of the X-ray 501 in the drawing, and W ₁ , W ₂ ..., W _k are separable footprint methods. 1 / sin θ is a correction coefficient, that is, weighting. Expression (2) is converted into the following expression (3).

As can be seen from the above equation (3), the integration after performing weighted correction on each pixel may be regarded as correcting after the weighted integration, that is, correcting the detector unit value obtained by projection, Even when the detector unit 503 value is reweighted by weighting (correction coefficient), the weighting coefficient corresponds to the position θ of the detector unit 503 and the angle θ determined by the perpendicular line 504 from the X-ray source to the detector. is doing. The angle can be calculated by the following equation (4).

In the above equation (4), L ₅₀₄ is the distance of a perpendicular line from the X-ray source of the detector to the detector, L ₅₀₃ is the size of the detector unit, and m is detected as a vertical line 504 from a predetermined detector unit. The number of detectors up to the intersection with the detector. Thus, a weighting vector as indicated by 505 in FIG. 5 is obtained.

FIG. 6 is a diagram showing detector data weighting by weighting vectors. After obtaining the weight vector 601, the projection and back projection processes were corrected by correspondingly multiplying the detector vector 602 composed of the detector values of the detector units in each column on the detector and the weight vector 601. A detector vector 603 is obtained.

The basic concept of the weighting vector used in the CT image generation apparatus of this embodiment has been described above. Next, the structure of the CT image generation apparatus using the weighting vector will be described.

FIG. 7 is a module diagram of the CT image generation apparatus 700 of the present embodiment.
The CT image generation apparatus 700 includes an X-ray scanner 701, a data interface module 702, an image forming apparatus 703, and a user interface module 704. The X-ray scanner 701 includes an X-ray source and a detector, scans a subject, for example, a human body, obtains projection data, and uses the data as detector data. The data interface module 702 is connected to an interface between the X-ray scanner 701 and the image forming apparatus 703. The user interface module 704 provides functions such as display, printing, and setting to the user. The image forming apparatus 703 reconstructs scan data obtained by the X-ray scanner 701 to form a CT image, and mainly includes a storage module 705, a data bus 706, and a processor module 707.

The storage module 705 stores parameters and data, and mainly includes a detector data block 708 for storing projection data scanned by a scanner and projection data generated in an algorithm process, an X-ray source and a detector. A weighting data block 709 for storing weighting vectors calculated based on the geometric relationship with the position of the unit, and the basic geometric parameters of the CT apparatus, for example the relative geometry of the X-ray source and detector A parameter data block 710 for storing the academic position, the size of the monitor unit, and the like, and an output image data block 711 for storing the result image generated by the algorithm are included.

The data bus 706 is a data transmission path between the processor module 707 and the storage module 705. The processor module 707 is used for calculation processing of an image reconstruction algorithm, and mainly a main processor 715 for controlling a processing module of an algorithm process for controlling a projection / backprojection angle loop using a geometric parameter; A weighting calculation unit 712 for calculating and generating a weighting vector, which is a feature of the present invention, and a weighting vector multiplication unit for performing a multiplication process of the weighting vector and detector data (detector vector) to obtain a corrected detector value 713 and a separable footprint computation unit 714 that executes a separable footprint projection / backprojection algorithm using the corrected detector values.

The CT image generation apparatus 700 can be used when the distance between the X-ray source and the detector does not change with the angle of projection and backprojection. In this case, the CT image generation apparatus 700 performs the test at each angle. An image is formed by irradiating a target, and images obtained at different angles are superimposed. The main processor 715 controls image formation at each angle by a projection / backprojection angle loop.

8A and 8B show the operation flow of the projection and backprojection process when the distance between the X-ray source and the detector does not change with the angle of projection and backprojection. In any process, first, a geometric parameter value of CT is acquired (801), and then a weighting vector is calculated (802). In the projection process, the original separable footprint projection operation is first performed for each projection and backprojection angle (803), and then the projection result vector obtained by the projection is weighted and corrected with a weighting vector (804). In the backprojection process, detector data is first weighted with a weighting vector (805), and a separable footprint backprojection operation is performed on the corrected detector data after weighting (806). Thus, errors in the projection and back projection can be reduced, the accuracy of projection and back projection can be improved, and artifacts in the CT image can be reduced.

The CT image generation apparatus 700 can also be used when the distance between the X-ray source and the detector changes according to the angle of projection and back projection. 9A and 9B show an operational flow diagram of the projection and backprojection process when the relative position of the X-ray source and detector changes. Again, first obtaining the CT geometric parameter value (901) is the same as the operation flow of FIGS. 8A and 8B. However, when the distance between the X-ray source and the detector can change according to the angle of projection and back projection, it is necessary to calculate the weighting vector at each angle based on the change in distance. In the projection process, first, a weighting vector is calculated based on the geometric parameters at the current projection angle (902), the original separable footprint projection operation is performed (903), and then the projection result vector obtained by the projection is obtained. Weight correction is performed with the weight vector (904), and the above steps 902 to 904 are repeated each time the angle changes. Similarly, in the backprojection process, the weighting vector is first calculated by the geometric parameter at the current projection angle (902), and then the detector data is weighted by the weighting vector (905), and the weighted correction is performed. A separable footprint backprojection operation is performed on the detector data (906). Also in this case, the

above steps

902, 905 and 906 are repeated every time the angle changes.

In each angle loop, the amount of calculation of the weight vector has a linear relationship only with the number of detector units, and the amount of calculation for projection and backprojection operations is very small, which affects the calculation speed of the entire image reconstruction process. Since the influence is extremely small and the influence on the speed performance can be ignored, the efficiency of the iterative reconstruction algorithm can be improved.

As described above, the embodiments of the present invention have been described with reference to the drawings, but it should be understood that the above description does not limit the present invention in any way. Those skilled in the art can modify and change the present invention as necessary without departing from the substantial spirit and scope of the present invention, and all such modifications and changes are within the scope of the present invention.

302 X-ray source 303 Detector 505 Weighted vector 601 Weighted vector 700 CT image generator 701 X-ray scanner 702 Data interface module 704 User interface module 705 Storage module 707 Processor module 708 Detector data block 709 Weighted data block 710 Parameter data block 711 Output image data block 712 Weight calculation unit 713 Weight vector multiplication unit 714 Separable footprint calculation unit 715 Main processor

Claims

An X-ray scanner comprising an X-ray source and a detector for detecting an object disposed between the X-ray source and the detector;
A storage module including a detector data block, a weighted data block, a parameter data block, and an input / output result image data block;
A processor module including a main processor, a weighted calculation unit, a weighted vector multiplication unit, and a separable footprint computing unit;
A data interface module;
A user interface module;
The data scanned by the X-ray scanner is stored as detector data in the detector data block via the data interface module,
The weight calculation unit obtains a geometric parameter from the parameter data block, calculates a weight vector based on the geometric parameter,
The main processor controls the projection / backprojection angle loop using the geometric parameters;
The weighted vector multiplicative unit obtains a corrected detector value by multiplying the detector data by the weighted vector;
The separable footprint calculation unit executes a separable footprint projection / backprojection algorithm using the corrected detector value.
When the distance between the X-ray source and the detector changes in accordance with the angle of projection and backprojection, the weight calculation unit calculates the geometric data from the parameter data block for each angle in the projection / backprojection angle loop. The CT image generation apparatus according to claim 1, wherein a CT parameter is acquired and a weighting vector related to the distance is calculated.
The weighting calculation unit calculates the weighting vector at each angle from 1 / sinθ, where θ is an angle between the detector and the X-ray. The CT image generation device described.
In the back projection, the main processor first weights the detector data with the weighting vector, and then performs a separable footprint back projection operation.
4. The CT image generation apparatus according to claim 1, wherein in the forward projection, a separable footprint projection operation is performed first, and then the detector data obtained by the projection is weighted with a weighting vector. 5. .
The geometric parameter is a distance between the X-ray source and the detector, a detector element size, and a center position of the detector. CT image generation device.
In the CT image generation method of the CT image generation apparatus,
The CT image generation device comprises:
An X-ray scanner comprising an X-ray source and a detector for detecting an object disposed between the X-ray source and the detector;
A storage module including a detector data block, a weighted data block, a parameter data block, and an input / output result image data block;
A processor module including a main processor, a weighted calculation unit, a weighted vector multiplication unit, and a separable footprint computing unit;
A data interface module;
A user interface module;
The CT image generation method includes:
Storing the data scanned by the X-ray scanner in the detector data block via the data interface module as detector data;
The weight calculation unit obtains a geometric parameter from the parameter data block, and calculates a weight vector based on the geometric parameter;
Said main processor controlling a projection / backprojection angle loop using said geometric parameters;
The weighted vector multiplicative unit obtains an improved detector value by multiplying the weighted vector by the detector data;
CT image generation of a CT image generation device, wherein the separable footprint calculation unit includes a step of executing a separable footprint projection / backprojection algorithm using the improved detector value. Method.
In the step of calculating the weighting vector,
When the distance between the X-ray source and the detector changes according to the angle of projection and back projection,
The CT image generation according to claim 6, wherein a geometric parameter is acquired from the parameter data block and a weighting vector related to the distance is calculated for each angle in a projection / backprojection angle loop. Method.
The CT image generation method according to claim 6 or 7, wherein when the angle between the detector and the X-ray is θ, the weighting vector at each angle is calculated from 1 / sin θ.
In backprojection, the detector data is first weighted with the weighting, then a separable footprint backprojection operation is performed,
9. The CT image generation method according to claim 6, wherein in the forward projection, a separable footprint projection operation is first performed, and then the detector data obtained by the projection is weighted by weighting.
10. The geometric parameter according to claim 6, wherein the geometric parameter is a distance between the X-ray source and the detector, a detector element size, and a center position of the detector. CT image generation method.
An X-ray scanner comprising an X-ray source and a detector for detecting an object disposed between the X-ray source and the detector;
A processor module including a main processor, a weighted calculation unit, a weighted vector multiplication unit, and a separable footprint computing unit;
A storage module for storing parameters used in the processor module;
The weight calculation unit reads a geometric parameter from the storage module, calculates a weight vector based on the geometric parameter,
The main processor uses the geometric parameters to control a projection / backprojection angle loop;
The weight vector multiplication unit multiplies the detector data scanned by the X-ray scanner by the weight vector to calculate a corrected detector value;
The separable footprint calculation unit executes a separable footprint projection / backprojection algorithm using the corrected detector value.
Storing the data scanned by the X-ray scanner as detector data;
Calculating a weighting vector using the geometric parameters stored in the storage module;
Controlling a projection / backprojection angle loop using said geometric parameters;
Obtaining a corrected detector value by multiplying the detector data by the weighting vector;
Performing a separable footprint projection / backprojection algorithm using the corrected detector value, and a CT image generation method for a CT image generation apparatus.