KR101284986B1 - Method and apparatus for reconstructing high-resolution tomosynthesis - Google Patents

Abstract

The present invention relates to a method and apparatus for reconstructing a tomosynthesis cross-sectional image, and more particularly, to high-resolution tomosinesis of a region of interest of a target object with a small amount of X-rays by radiating X-rays to a region of interest of the target object within a limited photographing angle range. The present invention relates to a method and apparatus for reconstructing a tomosynthesis cross-sectional image capable of obtaining a cross-sectional image.
The high resolution tomoxy synthsis image reconstructing apparatus according to the present invention can obtain a high resolution cross-sectional image of a region of interest of a target object by irradiating X-rays to a local region of interest of the target object within a limited photographing angle range. In addition, the high resolution toxin synthsis image reconstruction apparatus according to the present invention subtracts the projection data component of the external region from the toxin synthesis projection data of the local region of interest of the target object to generate a tomography image of a high resolution region of interest, thereby generating Contrast and image quality can be improved.

Description

Method and apparatus for reconstructing high-resolution tomosynthesis

The present invention relates to a method and apparatus for reconstructing a tomosynthesis cross-sectional image, and more particularly, to high-resolution tomosinesis of a region of interest of a target object with a small amount of X-rays by irradiating X-rays to a region of interest of the target object within a limited photographing angle range. The present invention relates to a method and apparatus for reconstructing a tomosynthesis cross-sectional image capable of obtaining a cross-sectional image.

X-ray radiography (projection data) of the target object using the characteristic that the intensity of the X-rays decreases depending on the physical properties and the distance of the target object through which the X-ray passes when the X-ray passes through any object ) Is a device for acquiring and imaging. For example, when X-rays are irradiated to humans, projection images of the inside of the body may be obtained by using different X-ray attenuation coefficients according to types and characteristics of biological tissues.

The law of changing the intensity of X-rays according to the physical properties and the transmission distance of the object is called Lambert-Beers law and is expressed by the following equation (1).

[Equation 1]

Where I ₀ is the intensity of the initial X-ray, μ is the inherent X-ray attenuation coefficient, and L is the length of the object through which the X-rays pass. Equation (1) shows the relationship that the attenuation coefficient of the object to be transmitted is attenuated with distance when the initial X-rays are irradiated with an intensity of I ₀ . Equation (1) is a case in which the object is made of the same material, and when the object is made of various materials, the intensity of X-rays passing through the object is expressed as in Equation (2) below.

&Quot; (2) "

Here, s represents a path through which the X-rays pass through the target object, and the X-ray attenuation coefficient μ (s) is a function of the path since the position of the target object varies for each position.

However, the projection image of the target object acquired by the X-ray imaging apparatus is calculated based on the final X-ray intensity accumulated as the X-ray passes through the inside of the target object, and includes the internal information of the target object, Projecting the information on a two-dimensional image, the internal components of the object overlap each other, and particularly similar materials have a problem in that it is difficult to accurately determine the inside of the object because of high contrast.

In order to solve the problem of the X-ray imaging apparatus, X-ray cross-sectional imaging techniques such as computed tomography (CT) or tomosynthesis have been developed. The city, which is generally known, is composed of hundreds of projection data of the target object obtained by rotating the 360-degree along the circular orbit by pairing the X-ray generator and the X-ray detector with the rotation target as the center of rotation. Reconstruct the cross-sectional image. Here, reconstructing the cross-sectional image means that the X-rays transmit the cross-section of the target object in a quantitative manner to calculate the unique attenuation rate according to the type of the object and show it as an image.

On the other hand, tomosynthesis is obtained by rotating the X-ray generator and the X-ray detector at a limited scan angle of typically 20 to 60 degrees in a parallel plane or in an arc orbit with the target object to be photographed therebetween. Dozens of projection data are reconstructed to reconstruct the cross-sectional image of the target object. Hereinafter, a limited shooting angle range of 20 to 60 degrees, which is a conventional shooting angle of Tomosynthesis, is referred to as a first shooting angle range, and a shooting angle range of 180 to 360 degrees, which is a typical shooting angle of a city, is referred to as a second shooting angle range. . In addition, hereinafter, projection data acquired by the city is referred to as city projection data, and projection data obtained by Tomosynthesis is referred to as tomosynthesis projection data.

Looking at the city in more detail with reference to Figure 1, while rotating the X-ray generator 10 and the X-ray detector 20 arranged to face at a predetermined distance from the target object 11 while rotating in a 360-degree angle range X-ray detectors irradiated by the X-ray generator 10 and passed through the target object 11 at regular angular intervals are detected by the X-ray detector to obtain city projection data of the target object 11, and reconstructed the city projection data. Obtain a city cross-sectional image of 11). The most common method of creating the city cross-sectional image of the target object using the city projection data is back projection, and the equations related to the image reconstruction method by the reverse projection are as shown in Equations (3) and (4) below. .

&Quot; (3) "

&Quot; (4) "

Here, θ and t represent the coordinates of the rotation angle and the longitudinal direction of the X-ray detector 20, respectively, under geometric conditions for obtaining the city projection data, and tm is the total length of the detector 20. P _θ (t) is city projection data obtained in the θ direction. The function h (xcosθ + ysinθ-t) represents a reverse projection filtering function. Ram-Lak and Shepp-Logan filters are commonly used. The function to be obtained through the calculation of the reverse projection process is to indicate how much the X-rays are attenuated when passing through the target object, which is the attenuation rate at each position (x, y) of the target object, and the city cross section of the target object to be obtained. It means video.

Tomosynthesis reconstructs the cross-sectional image of the target object from the projection data acquired within a limited shooting angle range of 20 degrees to 60 degrees, thus reconstructing the cross-sectional image of the target object from hundreds of projection data shot at the 360 degree shooting angle of the city. Accessibility is easier in hardware than that, and since the cross-sectional image of the target object is reconstructed from a small number of projection data, it has the advantages of reducing the amount of radiation applied to the target object and fast image reconstruction.

Meanwhile, when the distance between the X-ray generator and the target object is reduced relative to the distance between the X-ray detector and the target object, projection data is acquired and reconstructed from the local ROI of the target object to generate a cross-sectional image of the target object. It is possible to obtain a high resolution cross-sectional image for. Equation (5) below is an equation for explaining the resolution (R) of the cross-sectional image of the target object. Referring to FIG. 2, the cross-sectional image resolution of the target object 11 is X-ray from the X-ray generator 10. It is determined by the relative ratio of the distance SD between the detectors 20 and the distance SOD between the X-ray generator 10 and the target object 11. Here, DS is a pixel size of the X-ray detector 20. In order to obtain a high-resolution cross-sectional image of the target object 11 in the X-ray detector 20 having a constant pixel size, the object 11 is close to the X-ray generator 10. The projection data of the target object 11 is obtained.

[Equation 5]

In general, since the pixel size DS of the X-ray detector is physically fixed, the relative ratio of the distance SD between the X-ray generator and the X-ray detector and the distance SOD between the X-ray generator and the target object is expressed by Equation (5). A high resolution cross-sectional image can be realized by the moving means for adjusting, but has a problem described below.

As shown in FIG. 3A, when the entire object 11 is positioned to be within the x-ray beam angle, projection data of the entire object 11 may be acquired. Since the cross-sectional image can be reconstructed, artifacts that occur when the target object 11 exists not only inside or outside the X-ray irradiation angle range are generated. However, as shown in FIG. 3 (b), when the position of the target object 11 is located close to the X-ray generator 10, a high-resolution cross-sectional image of the local region of interest ▲ is obtained. Only the region of interest (▲), which is a part of (11), is located in the X-ray irradiation angle range and the remaining region except for the region of interest (▲) because the X-ray generator 10 and the X-ray detector 20 rotate about the rotation center O. That is, the external region Δ is unevenly projected onto the X-ray detector 20 to generate an artifact. Since the outer region △ other than the region of interest ▲ overlaps and is included in the projection data component, the cross-sectional image of only the region of interest ▲ cannot be reconstructed, and since the X-ray irradiation angle range includes only the region of interest ▲, the target object (11) There is a problem that causes serious distortion in reconstructing the entire cross-sectional image. Hereinafter, as shown in FIG. 3B, in order to obtain a high-resolution cross-sectional image, the target object 11 is approached to the X-ray generator 10 so that a part of the target object 11 is out of the X-ray irradiation angle range. ) Is referred to as a first position, and as shown in FIG. 3A, a position where the entire object 11 is included in the X-ray irradiation angle range is referred to as a second position.

In the high-resolution city cross-section image at the first position, a part of the target object does not appear in the city projection data outside the X-ray irradiation angle range, and in the high-resolution tom synthesis cross-sectional image of the region of interest at the first position, a region other than the region of interest is present. There is a problem in that the outer regions overlap and are included in the tomosynthesis projection data component and appear as unwanted artifacts.

In order to solve the problem of the high-resolution city cross-sectional image in the first position, Patent Registration No. 10-687846 (hereinafter referred to as the prior art 1) first 360-degree to shoot the entire object through the city at the second position A cross-sectional image is obtained by radiating X-rays in an angular range, and the X-rays are irradiated in a 360-degree angle range on a portion of the target object including the ROI by moving the target object to the first position. The high-resolution city projection data generated by irradiating X-rays to a part of the target object including the ROI located in the X-ray irradiation angle range and the city projection data generated by irradiating X-rays to the entire target object at the second position A method of combining and reconstructing to obtain a high resolution city cross-sectional image for a region of interest is disclosed.

However, in the case of the related art 1, since the X-rays must be irradiated from the close distance to the ROI in a 360 degree shooting angle range so that the X-rays can be irradiated only to the local ROI of the target object to obtain a high resolution city cross-sectional image, the target object Due to the large amount of X-rays irradiated on X-rays, the X-ray exposure is high, and since a cross-sectional image is generated using a large number of projection data, high-performance hardware is required, and it takes a long time to reconstruct the cross-sectional image. In addition, even if the prior art 1 is applied, an external region other than the region of interest generated when acquiring a high-resolution toxin synthesized cross-sectional image of the region of interest at the first position is superimposed on the tomosynthesis projection data and appears as an artifact in the cross-sectional image to deteriorate the image quality. There is still a problem.

  Summary of the Invention The present invention solves the problems of the above-mentioned prior arts, and an object of the present invention is to reconstruct a high resolution tomoxy synthesized cross-sectional image for obtaining a high-resolution cross-sectional image of a region of interest of a target object with a low X-ray dose. To provide.

Another object of the present invention is to provide a high-resolution toxin synthesis image reconstruction method that can improve the contrast and accuracy of the cross-sectional image of the region of interest by removing the projection data components of the external region other than the region of interest from the tomosynthesis projection data of the target object. It is.

It is still another object of the present invention to provide a method for reconstructing a tomosynthesis cross-sectional image, which can quickly obtain a high-resolution cross-sectional image of a region of interest in a target object with a small amount of calculation.

In order to achieve the object of the present invention, a method for reconstructing a tomosynthesis cross-sectional image according to an embodiment of the present invention includes tomosynthesis of a local ROI at a first position where a part of a target object including a local ROI belongs to an X-ray irradiation range. (tomosynthesis) acquiring projection data, and reconstructing and reconstructing a city cross-sectional image of the target object from the computed tomography (CT) projection data of the target object obtained at a second position where the entire object belongs to the X-ray irradiation range Assuming that the city cross-sectional image of the external region excluding the local ROI is changed to a first position in the city cross-sectional image, calculating virtual tomoxysynthesis projection data of the external region by irradiating a virtual X-ray; Virtual tomosinesis projection of the outer region Subtracting the emitter to reconstruct the phase and subtracting the generated projection data to generate subtracted projection data includes generating a high-resolution tomography image synthesis section of the local region of interest.

The calculating of the virtual tomoxy synthsis projection data may include reconstructing the city cross-sectional image of the target object from the city projection data of the target object obtained at a second position in which the entire object belongs to the X-ray irradiation range, and the reconstructed city cross-sectional image. Generating an outer region city sectional image including an outer region excluding a local ROI from the second position to the first position of the outer region city sectional image based on the first position coordinate and the second position coordinate of the object; And calculating virtual tomosynthesis projection data of the external region by assuming X-rays, assuming that the external region city cross-sectional image is moved to the first position based on the position change. .

Here, the tomosynthesis projection data of the local ROI is obtained by irradiating X-rays with a first photographing angle range from a first position in which a part of the target object including the local ROI belongs to the X-ray irradiation range, and the city projection data is obtained from the entire object. Is obtained by irradiating X-rays in a second photographing angle range at a second position belonging to the X-ray irradiation range.

Preferably, the first shooting angle range is smaller than the second shooting angle range, and more preferably, the first shooting angle range is 20 degrees to 60 degrees and the second shooting angle range is 180 degrees to 360 degrees.

According to an embodiment of the present invention, a reconstructing apparatus of a high resolution tomosynthesis cross-sectional image may include: a gantry unit, an X-ray generating unit installed in the gantry, and an X-ray radiating unit installed in the gantry unit and irradiated from the X-ray generating unit and passing through a target object to detect a city. (computed tomography, CT) X-ray detection unit for obtaining projection data or tomosynthesis projection data, and a cross-sectional image reconstruction unit for reconstructing a cross-sectional image of the target object from the obtained city projection data or tomosynthesis projection data The cross-sectional image reconstruction unit may include a virtual tomo of an external region excluding the local ROI in the tomosynthesis projection data of the local ROI obtained at a first position where a part of the target object including the local ROI belongs to the X-ray irradiation range. Subtract Synthesis Projection Data To reconstruct a projection data generation subtraction reconstructs a high-resolution tomography image synthesis of the local region of interest. Here, the cross-sectional image reconstruction unit reconstructs the city cross-sectional image of the target object from the computed tomography (CT) projection data of the target object obtained at the second position where the entire target object belongs to the X-ray irradiation range, Assuming that the city cross-sectional image of the external region except the local ROI is repositioned to the first position, virtual X-rays are irradiated to calculate virtual tomosynthesis projection data of the external region.

The image reconstruction unit according to an embodiment of the present invention reconstructs a city image reconstructing a city cross-sectional image from computed tomography (CT) projection data obtained by irradiating X-rays at a second position where the entire object is within the X-ray irradiation range. An external region city image generation unit for generating a city sectional image of an external region excluding the local ROI from the reconstructed city sectional image, and a city of the external region based on the first position coordinates and the second position coordinates of the target object; A position calculation unit that calculates a position change from the second position to the first position of the cross-sectional image, and assumes that the external region city cross-sectional image is moved to the first position based on the position change, and irradiates a virtual X-ray to the outer region A virtual tomosynthesis projection data calculation unit for calculating the virtual tomosynthesis projection data of the tomograph, And a subtraction unit for generating subtraction projection data by subtracting the virtual tomosinesis projection data of the external region from the cisis projection data, and a tomosynthesis image reconstruction unit for generating a cross-sectional image of the local ROI by reconstructing the generated subtraction projection data. It is characterized by.

Preferably, the apparatus for reconstructing a high resolution toxin synthesized sectional image according to the present invention further includes a moving rotation unit that adjusts a distance between the X-ray generating unit and the target object based on the calculated position change.

The reconstruction apparatus of the high resolution toxin synthesizing cross-sectional image according to the present invention has various effects as compared with the conventional X-ray cross-sectional image reconstructing apparatus.

First, the apparatus for reconstructing a high resolution toxin synthesized cross-sectional image according to the present invention obtains a high resolution toxin synthesized cross-sectional image of a region of interest of a target object by irradiating X-rays to a region of interest of the target object within a limited photographing angle range. can do

Second, according to the present invention, the reconstruction apparatus of a high resolution tomoxy synthesized cross section image generates a high resolution region of interest section by subtracting projection data components of an external region from the region of interest projection data of an object, thereby improving contrast and image quality of the region of interest. You can.

Third, the apparatus for reconstructing a high resolution toxin synthesized cross-sectional image according to the present invention obtains a high resolution cross-sectional image of a region of interest of an object of interest only by using tomography images obtained by capturing several to tens of images within a limited photographing angle range. Can be obtained.

1 is a view for explaining a cross-sectional image capturing method using a conventional city.
2 is a view for explaining the resolution of the cross-sectional image in the cross-sectional image capturing method using the city.
3 is a diagram illustrating a problem occurring when photographing a high resolution cross-sectional image.
4 is a block diagram of an apparatus for reconstructing a high-resolution toxin synthesizing cross section image according to an exemplary embodiment of the present invention.
5 is a functional block diagram for explaining the cross-sectional image reconstruction unit according to the present invention in more detail.
6 is a flowchart illustrating a method of reconstructing an X-ray cross-sectional image according to the present invention.
7 illustrates the shape of an alphabet phantom as an object for computer simulation of the X-ray cross-sectional image reconstruction apparatus according to the present invention.
Fig. 8 (a) shows a cross-sectional image of the letter H position surface.
9 shows a profile (a) of a tomoxy synthes sectional image according to the prior art and a profile (b) of a tomosynthesis sectional image according to the present invention.

Hereinafter, an X-ray cross-sectional image reconstruction method and apparatus thereof will be described in detail with reference to the accompanying drawings.

4 is a block diagram of an apparatus for reconstructing a high-resolution toxin synthesizing cross section image according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the X-ray generator 110 and the X-ray detector 120 are fixedly disposed to face one end and the other end of the gantry 130, respectively. The X-ray 111 generated by the X-ray generator 110 passes through a target object 140 located on a virtual connection line between the X-ray generator 110 and the X-ray detector 120 and is irradiated to the X-ray detector 120. The X-rays 111 passing through the target object 140 are attenuated according to the characteristics and the passing distance of the target object 140 to be incident to the X-ray detector 120, and the X-ray detector 120 passes through the target object 140. X-rays are detected at the final intensity. The X-ray generator 110 includes a collimator 114 for adjusting the irradiation width of X-rays, and controls X-rays to be irradiated with only a specific portion of the target object 140 to a region other than the specific portion of the target object 140. Intercept X-rays irradiated.

The X-ray detector 120 includes an image intensifier having a scintillator attached to an X-ray irradiation surface, an indirect flat panel x-ray detector having a scintillator attached thereto, or a direct type having a photoconductor attached thereto. A direct flat panel x-ray detector can be used. The image amplifier is a device that converts and amplifies the optical signal emitted by the scintillator during X-ray irradiation into a high voltage, and is used in a C-arm X-ray imaging apparatus used in an imaging environment with low X-ray dose, that is, an interventional study. Used. The indirect planar X-ray detector detects optical signals generated by scintillators during X-ray irradiation with an array of photodiodes, and because of the high resolution such as the number of elements of the planar detector reaching 4000 × 3000, digital radiography (DR) and It is widely used in Siam X-ray imaging. On the other hand, the direct planar X-ray detector detects the photoelectric signal generated in the photoconductor by capacitive sensor array during X-ray irradiation, and its resolution is similar to the indirect planar X-ray detector, which is used in digital X-ray imaging and Siam X-ray imaging apparatus.

The gantry 130 is disposed on the rotation movement means 150 and configured to be rotatable about the rotation axis 151 by the rotation means 151 and 153 and the movement means 155. The gantry 130 is preferably made of a strong material such as aluminum because the gantry 130 must perform a rotational movement while supporting the load of the X-ray generator 110 and the X-ray detector 120. The gantry 130 on which the X-ray generator 110 and the X-ray detector 120 are disposed is connected to the rotating motor 153 through the rotating shaft 151. The target object 140 is positioned below the rotation axis 151, and the point where the rotation axis 151 extends and the irradiation center line 112 of the X-ray meets the center of rotation 113 formed in the object 140. On the other hand, the gantry 130 is fixed to the moving means 155 to determine the relative distance ratio between the X-ray generator 110 and the target object 140 and between the target object 140 and the X-ray detector by the moving means 155. Adjust As the relative distance ratio between the X-ray generator 110 and the target object 140 and the target object 140 and the X-ray detector is lowered by the moving means 155, that is, between the X-ray generator 110 and the target object 140. As the distance between the target objects 140 and the X-ray detector becomes smaller than the distance between the projection data and the reconstructed cross-sectional image of the target object 140 is enlarged in high resolution. Meanwhile, as the ratio of the relative distance between the X-ray generator 110 and the target object 140 and the target object 140 and the X-ray detector increases, that is, the distance between the X-ray generator 110 and the target object 140 increases. As the distance between the 140 and the X-ray detector increases, the cross-sectional image of the projection data and the projection data of the target object 140 is reduced. Therefore, in order to take a high-resolution cross-sectional image, the ratio of the relative distance between the X-ray generator 110 and the target object 140 and between the target object 140 and the X-ray detector must be low.

According to the field to which the present invention is applied, the gantry 130 is fixedly disposed on the rotating body 160 without the rotating means and the moving means, and the target object through the rotating means 171. 173 and the moving means 175 of the object support. 140 may be configured to be rotatable. The target object 140 is disposed on the target object support body 177, and the target object support body 177 is fixedly connected to the rotary shaft 173 connected to the rotary motor 171. The point of extension of the rotation axis 173 and the irradiation center line 112 of the X-ray is the rotation center 113 formed in the object 140. The rotating means 171, 173 rotates the target object 140 to the rotation center 113 within the set photographing angle range, and the X-ray generator 110 and the X-ray detector 120 generate a plurality of target objects 140 at the set photographing angle. Take a picture of projection data. On the other hand, the object support body 177 is fixedly disposed on the moving means 175, the moving means 175 is the object support body 177 along a virtual connection line connecting the X-ray generator 110 and the X-ray detector 120. ) To adjust the resolution of the target image.

The control unit 200 synchronizes and controls the X-ray generator 110 and the X-ray detector 120 to obtain projection data through the X-ray detector 120 when the X-ray generator 110 irradiates the X-rays. It controls the rotational movement of the gantry 130 or the object support body 177 through. Meanwhile, the cross-sectional image reconstruction unit 300 sets and controls a shooting angle range for obtaining a high resolution cross-sectional image of the ROI of the target object and a location where the X-ray is irradiated to the ROI, and captures the image at the preset shooting angle range and position. The projection data of the region of interest is subtracted from the virtual projection data of the region other than the region of interest to generate a high resolution tomosynthesis image of the region of interest.

5 is a functional block diagram for explaining the cross-sectional image reconstruction unit according to the present invention in more detail.

Referring to FIG. 5, the city image reconstructing unit 310 is obtained by irradiating X-rays within a second photographing angle range with a rotation center around the center of the entire object at a second position where the entire object belongs to the X-ray irradiation angle range. The city sectional image is reconstructed from one city projection data. The outer region city image calculator 320 receives a region setting signal from the reconstructed city section image and calculates a city section image of an outer region including only the outer region except for the ROI. The area setting signal is a user command for setting a region of interest through a user interface in the city cross-sectional image of the target object.

The position calculator 330 calculates a first position in which a part of the target object including the ROI of the target object set according to the region setting signal or the resolution setting signal belongs to the X-ray irradiation range. The resolution setting signal is a user command for setting the resolution of the set ROI. The position calculator 330 generates a movement control signal for adjusting a relative distance between the X-ray generator and the target object and between the target object and the X-ray detector based on the calculated first position, and the movement means is connected to the movement control signal. The gantry is moved or controlled to move the object support body.

The virtual projection data calculator 340 irradiates a virtual X-ray to a first photographing angle range of the city cross-sectional image of the external region calculated by the external region city image calculator 320, and loads the X-ray attenuation coefficient to the external area. Compute virtual tomoxysynthesis projection data for the area. The distribution of the X-ray attenuation coefficient means that the X-ray attenuation rate, which depends on the physical characteristics of the object to which X-rays are irradiated and the distance through which the X-rays are irradiated, is accumulated until the X-ray detector is detected along the irradiated X-rays and finally accumulated. X-ray intensity is detected by the X-ray detector.

The subtraction unit 350 calculates subtraction projection data by subtracting virtual tomosinesis projection data of an external region from tomosynthesis projection data of a target object region of interest captured at a first photographing angle range at a first position, and reconstructing the tomosynthesis image. The unit 360 reconstructs the subtraction projection data to generate a cross-sectional image of the ROI of the object. Since the projection data components due to the external region are subtracted from the subtraction projection data, the tomosynthesis cross-sectional image of the ROI generated from the subtraction projection data is a high resolution tomo corrected for distortion caused by the external region appearing in the ROI. Synthesis cross section image.

6 is a flowchart illustrating a method of reconstructing an X-ray cross-sectional image according to the present invention.

Referring to FIG. 6, a user command for setting the ROI of the target object and a user command for setting the resolution of the ROI are received through the user interface in the city cross-sectional image of the entire target object (S10). The ROI of the target object is set as a 3D region by using a setting means such as a keyboard, and the resolution is set for a high resolution tomosynthesis image of the ROI.

According to the input resolution, the relative distance between the X-ray generator and the ROI of the object and between the ROI of the object and the X-ray detector may be calculated according to Equation (5) to obtain projection data of the ROI at the input resolution. The first position is calculated (S20). Here, the first position means information in which the object is located between the X-ray generator and the X-ray detector.

The tomosynthesis projection data P _▲ (t) of the ROI is acquired by irradiating X-rays within the first photographing angle range with the ROI of the ROI at the calculated first position (S30).

Virtual tomosynthesis projection data of the outer region is calculated in order to reduce artifacts in the outer region Δ other than the region of interest, which appears unnecessarily superimposed on the tomosynthesis image of the region of interest (S40). In detail, first, the city cross-sectional image is reconstructed from CT projection data obtained by irradiating X-rays within a second photographing angle range with respect to the rotation center around the center of the entire object at a second position where the entire object belongs to the X-ray irradiation angle range. In addition, by using the ROI information input by the user command in the reconstructed city cross-section image, a city cross-section image of an external area excluding the ROI is composed, and the resolution setting information received by the user command and the target object The city cross-sectional image of the external area is calculated from the second position to the first position based on the first position coordinate and the second position coordinate, and the city cross-sectional image of the external area is obtained from the first position based on the position change. The target is irradiated with virtual X-ray to the first shooting angle range, and the X-ray attenuation coefficient is shipped It calculates a virtual Tomo-synthesis projection data in the sub-region. Here, the virtual tomoxy synthsis projection data P (t) of the outer region △ excluding the region of interest is calculated as in Equation (6) below.

&Quot; (6) "

Μ _C is an X-ray attenuation coefficient that varies depending on the physical characteristics of the object to which X-rays are irradiated and the distance that X-rays pass through the object, and L is the length of the outer region of the object through which X-rays pass.

Calculates subtraction projection data by subtracting the virtual tomoxy synthsis projection data P _Δ (t) of the outer region from the projection data P _▲ (t) of the region of interest and removing the projection data components of the outer region superimposed on the region of interest In operation S50, the calculated subtraction projection data may be reconstructed to obtain a high-resolution toxin synthesized cross-sectional image of the ROI (S60).

According to the field to which the present invention is applied, a user command for setting a region of interest and a user command for setting a resolution of the region of interest are input as a movement command of a gantry or an object support body, and in this case, the first position information is a gantry or The movement position of the object support body is calculated and provided to the virtual projection data calculation unit, and the virtual projection data calculation unit calculates the virtual tomosinesis projection data based on the first position information.

7 illustrates the shape of an alphabet phantom as an object for computer simulation of the X-ray cross-sectional image reconstruction apparatus according to the present invention. Meanwhile, FIG. 8 (a) shows a city cross-sectional image of the letter H position surface, and FIG. 8 (b) shows a tomosynthesis cross-sectional image showing artifacts due to overlapping of an external region of the letter H position plane according to the prior art. FIG. 8 (c) shows a cross-sectional image of the letter H position plane obtained by the high resolution toxin synthsis image reconstruction apparatus according to the present invention.

As illustrated in FIG. 7, an alphabet phantom, which is an object, is placed between the X-ray generator S and the X-ray detector D. FIG. The alphabet phantom has a cuboid shape, and the X-ray attenuation coefficient is distributed in the form of three letters K, H, and U inside. Fig. 8 (a) shows a city sectional image of the alphabet phantom and shows a city sectional image of the letter H position surface having the letter H shape. The city cross section image is a case where the magnification of the projection data is set to 1.3. FIG. 8 (b) shows a tomosynthesis cross-sectional image of the alphabet phantom without removing artifacts on the outer region with respect to the alphabet H position plane at an enlargement ratio of 3.9 and a photographing angle range of 60 degrees. As shown in FIG. 8 (b), the tomoxy synthesized cross-sectional image is represented at a higher resolution than the city cross-sectional image shown in FIG. 8 (a) due to the high magnification of 3.9. Because of this, artifacts from external regions other than the H-position plane are also combined. As shown in (c) of FIG. 8, it is possible to observe that the cross-sectional image of the letter H position surface of the H-plane is reconstructed by the high resolution toxin synthsis image reconstructing apparatus according to the present invention, and thus the image quality of the image is improved by removing the external region components other than the ROI. have.

9 shows a profile (a) of a tomoxy synthes sectional image according to the prior art and a profile (b) of a tomosynthesis sectional image according to the present invention. The profile of the cross-sectional image is used to more accurately identify the degree of image quality improvement, and represents the pixel intensity of the image along the white dotted lines shown in FIGS. 8B and 8C, respectively. The profile (Fig. 9 (b)) of the cross-sectional image according to the present invention can be seen that the pixel intensity is clearly distinguished compared to the profile of the tomosynthesis cross-sectional image (Fig. 9 (a)), which is according to the present invention. It can be seen that the cross-sectional image is significantly improved contrast than the conventional tomosynthesis cross-sectional image.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

310: city image reconstruction unit 320: outer region city image calculation unit
310: position calculator 340: virtual projection data calculator
350: subtraction part 360: tomosynthesis image reconstruction part

Claims (10)

Obtaining high resolution tomosynthesis projection data of the local ROI at a first position where a portion of the target object including the local ROI belongs to an X-ray irradiation range;
The city cross-sectional image of an external region excluding the local ROI is moved to the first position from the computed tomography (CT) projection data of the target object obtained at a second position in which the entire target object is within the X-ray irradiation range. Calculating virtual tomoxy synthsis projection data for the outer region;
Generating subtraction projection data by subtracting the virtual toxin synthesis projection data of the external region from the toxin synthesis projection data of the local region of interest; And
Reconstructing the generated subtraction projection data to generate a high resolution tomoxysynthesis cross-sectional image of the local ROI that corrects the distortion of the external region,
Computing the virtual tomoxy synthsis projection data
Generating an external region city cross-sectional image including an external region excluding the local ROI from the low resolution city cross-sectional image of the target object obtained at a second position in which the entire object is in the X-ray irradiation range;
Calculating a position change of the outer area city cross-sectional image from the second position to the first position based on the first position and the second position of the object; And
And calculating virtual tomosynthesis projection data of the external region by irradiating a virtual X-ray assuming that the external region city cross-sectional image is moved to the first position based on the change of position. Reconstruction method of tomosynthesis cross section image. delete The method of claim 1,
Tomosynthesis projection data of the local ROI is obtained by irradiating X-rays with a first photographing angle range at the first position where a part of the target object including the local ROI belongs to an X-ray irradiation range,
The city projection data is obtained by irradiating X-rays with a second photographing angle range at the second position where the entire object is in the X-ray irradiation range,
Wherein the first photographing angle range is smaller than the second photographing angle range. 4. The method of claim 3, wherein the first photographing angle range is 20 degrees to 60 degrees, and the second photographing angle range is 180 degrees to 360 degrees. The method of claim 3, wherein the reconstruction method of the high resolution tomosynthesis cross-sectional image
Receiving a region setting signal for setting a local ROI of the target object;
Receiving a resolution setting signal for setting a resolution of the target region of interest; And
And calculating the first position and the first photographing angle range based on the area setting signal and the resolution setting signal. A gantry unit, an X-ray generating unit installed in the gantry, and X-rays installed in the gantry unit and irradiated from the X-ray generating unit and passing through a target object are detected to detect computed tomography (CT) projection data or tomosynthesis. An x-ray detection unit for obtaining projection data and a cross-sectional image reconstruction unit for reconstructing a cross-sectional image of the target object from the acquired city projection data or tomoxy synthsis projection data,
The cross-sectional image reconstruction unit may include an external region excluding the local region of interest from tomosynthesis projection data of the local region of interest obtained at a first position where a portion of the target object including the local region of interest belongs to an X-ray irradiation range. Reconstructing the high-definition toxin synthesis image of the local region of interest by reconstructing the subtraction projection data generated by subtracting the virtual toxin synthsis projection data of
The cross-sectional image reconstruction unit reconstructs the city cross-sectional image of the target object from the computed tomography (CT) projection data of the target object obtained at a second position where the entire target object belongs to an X-ray irradiation range, The virtual tomosynthesis projection data of the external region is calculated by irradiating a virtual X-ray on the assumption that the city cross-sectional image of the external region except the local ROI is changed to the first position in the city cross-sectional image. Reconstruction device of high resolution tomoxysynthesis section image. The method of claim 6, wherein the cross-sectional image reconstruction unit
A city image reconstructing unit configured to reconstruct a city cross-sectional image from the computed tomography (CT) projection data obtained by irradiating X-rays at a second position in which the entire target object belongs to an X-ray irradiation range;
An external region city image generation unit configured to generate a city sectional image of an external region excluding the local ROI from the reconstructed city sectional image;
A position calculator configured to calculate a position change from the second position to the first position of the city section image of the external region based on the first position coordinate and the second position coordinate of the target object;
A virtual projection data calculator configured to calculate virtual tomosynthesis projection data of the external area by irradiating a virtual X-ray assuming that the external area city cross-sectional image is moved to the first location based on the position change;
A subtraction unit generating subtraction projection data by subtracting the virtual toxin synthesis projection data of the external region from the tomosynthesis projection data of the local ROI; And
And a tomosynthesis image reconstruction unit configured to reconstruct the generated subtraction projection data to generate a cross-sectional image of the local ROI. The method of claim 7, wherein the tomoxy synthsis projection data of the local ROI is obtained by irradiating X-rays with a first photographing angle range at the first position where a portion of the target object including the local ROI belongs to an X-ray irradiation range. ,
The city projection data is obtained by irradiating X-rays with a second photographing angle range at the second position where the entire object is in the X-ray irradiation range,
Wherein the first photographing angle range is smaller than the second photographing angle range. The reconstructing apparatus of claim 8, wherein the first photographing angle range is 20 degrees to 60 degrees and the second photographing angle range is 180 degrees to 360 degrees. The apparatus of claim 7, wherein the reconstruction device of the high resolution tomosinesis cross section image comprises:
And a moving rotation unit that adjusts a distance between the X-ray generating unit and the target object based on the calculated position change.

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