KR101685005B1 - An apparatus for Cone-Beam Computed Tomogram and method of generating Cone-Beam Computed Tomogram using it - Google Patents

An apparatus for Cone-Beam Computed Tomogram and method of generating Cone-Beam Computed Tomogram using it Download PDF

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KR101685005B1
KR101685005B1 KR1020150079744A KR20150079744A KR101685005B1 KR 101685005 B1 KR101685005 B1 KR 101685005B1 KR 1020150079744 A KR1020150079744 A KR 1020150079744A KR 20150079744 A KR20150079744 A KR 20150079744A KR 101685005 B1 KR101685005 B1 KR 101685005B1
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조승룡
위선희
박미란
장지은
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한국과학기술원
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Abstract

The present invention relates to a low dose X-ray cone beam CT imaging apparatus capable of generating a cone beam computer tomography reconstruction image, a material decomposition reconstruction image, and a monochromatic X-ray energy image in a single scan, and an image generating method using the same.
The low dose X-ray cone beam CT imaging apparatus according to the present invention comprises:
An X-ray irradiating unit for irradiating an X-ray toward a subject; A collimator for selectively decelerating a dose of the X-rays irradiated from the X-ray irradiating unit; An X-ray detecting module disposed to face the X-ray irradiating part and detecting first transmission image data that is not decelerated, and a photon coefficient detecting module that detects second transmission image data decoded by the collimator, ; And a controller for generating a reconstructed image using the first and second transmitted image data.

Description

[0001] The present invention relates to a low-dose X-ray cone beam CT imaging apparatus and an imaging apparatus using the same,

The present invention relates to a low-dose X-ray cone-beam CT imaging apparatus and an image generating method using the same, and more particularly, to a low-dose X-ray CT beam imaging apparatus capable of generating a cone beam computer tomography reconstruction image, A CT imaging apparatus and a method for generating an image using the same.

The photon counting module at the current technology level can not control the X-ray flux used in conventional CBCT (Cone-Beam Computed Tomogram) imaging, which can degrade the quality of the projected image.

Specifically, the conventional photon coefficient detecting module converts a different number of electrons according to the energy of an incident photon, and the converted electrons produce a pulse signal. Therefore, if two photons are incident at a similar time, the electrons that are converted at the same time by the existing technique can not be classified into individual photons. Therefore, at the same time, the converted electrons produce larger pulses, resulting in pulse overlapping phenomena. When the pulse overlap phenomenon occurs, the energy of the photon is measured differently from the actual value. These errors degrade the quality of the projected image and degrade the accuracy of the material classification.

Therefore, much research has been conducted to solve the pulse overlapping while maintaining the existing X-ray flux conditions. It is common to not use overlapping pulses at all to overcome the pulse overlap phenomenon. In 2010, an analytical model was developed to simulate the energy spectrum with pulse overlap, and the utility of this analytical model was verified in 2011. However, no research has been done to compensate for the pulse superposition using this analytical model, and its effectiveness has not been verified.

The object of the present invention is to provide a low-dose X-ray cone beam CT imaging apparatus capable of generating a cone beam computer tomography reconstruction image, a material decomposition reconstruction image, and a monochromatic X-ray energy image in one scan, and an image generating method using the same. have.

In order to solve the above object,

The low dose X-ray cone beam CT imaging apparatus according to the present invention comprises:

An X-ray irradiating unit for irradiating an X-ray toward a subject; A collimator for selectively decelerating a dose of the X-rays irradiated from the X-ray irradiating unit; An X-ray detecting module disposed to face the X-ray irradiating part and detecting first transmission image data that is not decelerated, and a photon coefficient detecting module that detects second transmission image data decoded by the collimator, ; And a controller for generating a reconstructed image using the first and second transmitted image data.

According to another aspect of the present invention, there is provided a low-dose X-

Irradiating the subject with x-rays; Selectively reducing a dose of the irradiated X-rays; Detecting non-decelerated first transmission image data and selectively decelerated second transmission image data; And generating a reconstructed image using the detected first and second transmitted image data.

According to the low dose X-ray cone beam CT imaging apparatus and the image generating method using the same according to the present invention,

Two types of transmission image data having different doses are obtained by partially transmitting the dose of the X-ray irradiated by the X-ray irradiating part and selectively decelerating the part of the X-ray irradiated by the X-ray irradiating part, And reconstructing at least one of the images,

It is possible to fundamentally reduce the pulse superposition phenomenon which is a main cause of the deterioration of the image quality occurring in the CT imaging apparatus constituted only by the conventional photon coefficient detecting module. In addition, there is an effect that cone beam computer tomography reconstruction image, material decomposition reconstruction image and monochromatic X-ray energy image can be generated by one scan.

1 and 2 are sectional views schematically showing a low-dose X-ray cone-beam CT imaging apparatus according to an embodiment of the present invention.
3 and 4 are views showing a collimator applied to a low-dose X-ray cone-beam CT imaging apparatus according to an embodiment of the present invention.
5 and 6 are diagrams showing a transmission image data detection unit applied to a low-dose X-ray cone-beam CT imaging apparatus according to an embodiment of the present invention, wherein FIG. 5A shows a case where only a conventional X- 5 (b) shows a case where the X-ray detecting module and the photon coefficient detecting module according to the embodiment of the present invention are alternately formed adjacent to each other.
FIG. 7 is a view for explaining an operation process of a low-dose X-ray cone beam CT imaging apparatus according to an embodiment of the present invention.
8 and 9 are flowcharts illustrating a method of generating a low-dose X-ray cone beam CT image according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals as used in the appended drawings denote like elements, unless indicated otherwise. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather obvious or understandable to those skilled in the art.

1 and 2 are sectional views schematically showing a low-dose X-ray cone-beam CT imaging apparatus according to an embodiment of the present invention.

1 and 2, a low dose X-ray cone beam CT imaging apparatus 100 (100a, 100b) according to an embodiment of the present invention includes an X-ray irradiating unit 10, a collimator 20, (30), and a control unit (not shown).

The X-ray irradiating unit 10 rotates along a predetermined rotation path and performs a function of irradiating the X-ray toward the inspected object S (see FIG. 7). On the other hand, the X-ray irradiating unit 110 may be replaced with a particle source that generates other kinds of particle beams as necessary.

The collimator 20 selectively decelerates the dose of the X-rays irradiated from the X-ray irradiating unit 10. Here, the deceleration means that a part of the dose of the irradiated X-ray is blocked and a part thereof is transmitted.

For this, the collimator 20 according to the embodiment of the present invention includes a plurality of slits 21 and a plurality of strips 22 formed as empty spaces as shown in FIG. The shape of the collimator 20 is not limited to this, and may be formed in another shape. For example, as shown in Fig. 4, a lattice-shaped slit 21 and a lattice-shaped strip 22 may be alternately arranged.

The X-rays are transmitted through the slit 21 without being decelerated, and the X-rays are selectively decelerated and transmitted through the strip 22. At this time, the strip 22 is preferably made of a material having an X-ray transmittance of 0.1% to 10%. When the transmittance is less than 0.1%, the amount of the second transmission image data detected by the photon coefficient detecting module 32 to be described later is too small to obtain a desired material decomposed reconstruction image. If the transmission ratio exceeds 10% The frequency of the phenomenon increases and the accuracy of the projected image becomes very low, so that the desired material decomposition reconstruction image can not be obtained. Therefore, the X-ray transmittance of the strip 22 is preferably 0.1% to 10%.

The collimator 20 is formed between the X-ray irradiating unit 10 and the transmitted image data detecting unit 30, as shown in FIGS.

Although the collimator 20 is shown as being located outside the X-ray irradiating unit 10 in FIG. 1, it may be located inside the X-ray irradiating unit 10. In this case, the collimator may be formed on the beam exit side of the X-ray irradiating unit 10. On the other hand, FIG. 2 illustrates that the collimator 20 is formed on the beam receiving side of the transmitted image data detecting unit 30. FIG.

The differences between the X-ray cone beam CT imaging apparatuses 100a and 100b according to the embodiment of FIGS. 1 and 2 are as follows.

1, the collimator 20 is positioned between the subject (S, see FIG. 7) and the X-ray irradiating unit 10 to reduce the X-ray dose received by the subject, There is an advantage that the first transmission image data and the second transmission image data having different dose amounts of the X-rays can be obtained while reducing the dose.

In the case of FIG. 2, the collimator 20 is formed on the beam receiving side of the transmitted image data detector 30, which facilitates the implementation of the apparatus. In addition, the penumbra area, which is a shadow effect at the edge of the collimator, is greatly reduced, and the available area for data processing is increased. Since the Phenom Brage region is distorted and difficult to use for image reconstruction or material classification, the region is generally discarded and the image is processed through the remaining data.

The transmitted image data detecting unit 30 includes an X-ray detecting module 31 arranged to face the X-ray irradiating unit 10 and detecting the first transmitted image data that has not been decelerated, a second transmitted image data And a photon coefficient detecting module 32 for detecting the photon coefficient.

The X-ray detection module 31 can not distinguish between the number of incident photons and the energy, and outputs a predetermined pulse when the energy exceeds a specific energy.

The photon coefficient detecting module 32 converts the number of electrons to a different number of electrons according to the energy of each photon, and outputs a pulse signal having a different height. Therefore, the energy information of the incident photons can be additionally obtained.

5 (a) shows a conventional X-ray detecting module, and FIG. 5 (b) shows an X-ray detecting module 31 and a photon coefficient detecting module 32 according to an embodiment of the present invention. ) Are alternately formed adjacent to each other.

The conventional X-ray detecting module of FIG. 5 (a) detects all the transmitted image data transmitted through the body of the subject. According to the embodiment of the present invention shown in FIG. 5 (b) The first transmission image data is detected by the X-ray detecting module 31 and passes through the strip 22 of the collimator 20 to selectively decelerate the X-rays (i.e., the first transmission image data) Data) is detected by the photon coefficient detection module 32. [ That is, the transmitted image data detecting unit 30 of the present invention can simultaneously detect two kinds of X-rays having different ray velocities.

On the other hand, the shape of the transmitted image data detecting unit 30 is not limited to this, and may be formed in another shape. For example, as shown in Fig. 6, the lattice-shaped slits 21 and the lattice-shaped strips 22 of Fig. 4 are arranged in a shape corresponding to the collimator 20, The module 31 and the photon coefficient detecting module 32 may be alternately formed adjacent to each other.

Next, the operation of the low-dose X-ray cone beam CT imaging apparatus according to the embodiment of the present invention will be described with reference to FIG.

7, a low-dose X-ray cone-beam CT imaging apparatus 100 according to an embodiment of the present invention includes an X-ray irradiator 10 and a transmitted-image data detector (not shown) disposed opposite to each other with a body S interposed therebetween 30 scan the subject (S) while rotating around the subject (S). At this time, a part of the X-rays irradiated from the X-ray irradiating unit 10 is transmitted through the slit 21 of the collimator 20 without being decelerated, detected by the X-ray detecting module 31, Another part of the irradiated x-rays is transmitted through the strip 22 of the collimator 20 while the dose is selectively decelerated and detected by the photon coefficient detecting module 32. Here, the non-decelerated X-rays are the first transmission image data, and the decelerated X-rays are the second transmission image data.

In this manner, the detected transmitted image data is processed by a control unit (not shown) to generate a reconstructed image. More precisely, the control unit reconstructs and reconstructs the reconstructed image using the first transmission image data detected by the X-ray detection module 31 and the second transmission image data detected by the photon coefficient detection module 32 .

Here, the control unit may be embodied in the apparatus of the present invention or may be configured as separate hardware connected to the apparatus of the present invention, such as a computer configured to perform processing for performing image restoration.

The control unit (not shown) generates various reconstructed images using an algorithm for image reconstruction of the detected first transmission image data and second transmission image data.

More specifically, the control unit generates the cone beam computer tomography reconstructed image using the first transmission image data.

Reconstruction algorithms for obtaining cone beam computed tomography reconstructed images are divided into an analytical reconstruction algorithm and an iterative reconstruction algorithm. The following equation (1) represents POCS-TV (Projection-Onto-Convex-Sets based Total-Variation), which is an iterative reconstruction algorithm, and Equation (2) represents an equation of Back- Projection Filtration (BPF) .

Equation (1):

Figure 112015054362190-pat00001

Here, the expression (1)

Figure 112015054362190-pat00002
Of the limit.

Equation (2):

Figure 112015054362190-pat00003

here,

Figure 112015054362190-pat00004
The
Figure 112015054362190-pat00005
to be.

In equation (1), f denotes the image to be reconstructed, M denotes the system matrix, g denotes the projection image, and TV denotes the total variation.

The POCS-TV algorithm in Eq. (1) is an algorithm to find the image f that minimizes the total variation of the reconstructed image. It is subject to the restriction condition and it is possible to reconstruct the high-quality image with the truncated projection image.

In equation (2)

Figure 112015054362190-pat00006
Shows the reconstruction of the PI-line with the BPF algorithm for circular cone beam CT.
Figure 112015054362190-pat00007
Where λ 1 and λ 2 are the rotation angles of the X-ray irradiator, and z 0 is the vertical coordinate of the PI-line.
Figure 112015054362190-pat00008
,
Figure 112015054362190-pat00009
The two end points of the PI-line,
Figure 112015054362190-pat00010
,
Figure 112015054362190-pat00011
Is the two end points of the line between the PI-line and the object, the points x A and x B are
Figure 112015054362190-pat00012
.
Figure 112015054362190-pat00013
Is a PI-line-backed video,
Figure 112015054362190-pat00014
Represents the integral value of the object according to the PI-line.

The BPF algorithm in Eq. (2) reverses the differential value of the data received by the detector over the PI-line and then reconstructs the reconstructed image through 1D-filtering along the PI-line.

Equation (1) above improves the image quality in reconstructing a scene with a lean view scan. This iterative reconstruction algorithm can improve not only the lean view but also the quality of the reconstructed image even if a part of the transmitted image data is lost by the collimator like the scan structure proposed in the present invention.

Therefore, when the first transmission image data is applied to the iterative reconstruction algorithm performing Equation (1), the first transmission image data is compared with the transmission image data by the conventional X-ray detection module (that is, Despite data loss, images similar to existing reconstructed image quality can be obtained. For example, when the X-ray detection module 31 and the photon coefficient detection module 32 are formed at a ratio of 1: 1, an image similar to the existing reconstructed image quality can be obtained even though there is a data loss of 50%.

Meanwhile, the second transmission image data obtained by the embodiment of the present invention has data loss (X-ray detection module 31 and photon coefficient detection module 32) as compared with transmission image data by the existing photon coefficient detection module, (About 99%) and 1% of the loss of the amount of photons by the collimator, the quality of the material decomposition reconstruction image is relatively poor .

Therefore, in order to improve this, a GMI (Gradient Magnitude Information) algorithm that performs the following equation (3) is applied to generate a GMI-based reconstructed image with improved image quality.

Equation (3):

Figure 112015054362190-pat00015

Where k is the kth basis material, and equation (3)

Figure 112015054362190-pat00016
Of the limit.

here

Figure 112015054362190-pat00017
A matrix corresponding to the reconstructed image,
Figure 112015054362190-pat00018
The total amount of change of the image,
Figure 112015054362190-pat00019
Wow
Figure 112015054362190-pat00020
The gradient information of the image obtained from the X-ray detecting module and the photon coefficient detecting module,
Figure 112015054362190-pat00021
Represents the weighting factor. The above equation minimizes the difference between the total variation of the image and the slope information of the image obtained from the photodetector module and the X-ray detection module while following the above constraints.

The GMI algorithm is an algorithm that adds a gradient magnitude constraint to the POCS-TV (Equation 1), and improves the quality of the reconstructed image effectively by using a cone-beam computer tomography reconstructed image as a prior image.

That is, a cone-beam computer tomography reconstructed image generated by applying the first transmission image data to an iterative or an analytical reconstruction algorithm and a GMI-based reconstructed image having improved image quality by applying the second transmitted image data to a GMI (Gradient Magnitude Information) .

In addition, the controller can generate the material decomposition reconstructed image by applying the GMI-based reconstructed image with improved image quality to the material decomposition reconstruction algorithm. For example, a substance decomposition reconstruction algorithm that performs Equation (4) below can be applied to generate a material decomposition reconstruction image.

Equation (4):

Figure 112015054362190-pat00022

here

Figure 112015054362190-pat00023
Is the linear attenuation coefficient,
Figure 112015054362190-pat00024
Is the density of the material,
Figure 112015054362190-pat00025
Is the mass ratio spatial distribution of the material m,
Figure 112015054362190-pat00026
Is the mass attenuation coefficient,
Figure 112015054362190-pat00027
Represents the density ratio spatial distribution of the material m. The reconstructed linear attenuation coefficient can be expressed as a spatial distribution of the density ratio of the material attenuation coefficient and the material m. Therefore, knowing the material attenuation coefficient depending on each energy used in the photon coefficient detection module, the density ratio spatial distribution of the material m can be known and the material decomposition can be performed.

Also, reconstructed images are obtained assuming that the projected image of the energy bin in each of the second transmission image data is monochromatic X-ray energy. The CT reconstructed image obtained at this time can be converted into a HU having an absolute value from a relative pixel value, which is referred to as a quantitative CT reconstructed image.

Next, a method of generating a low-dose X-ray cone beam CT image according to an embodiment of the present invention will be described with reference to FIGS. 8 and 9 are flowcharts illustrating a method of generating a low-dose X-ray cone beam CT image according to an embodiment of the present invention. The low-dose X-ray cone-beam CT image generating method according to the embodiment of the present invention can be performed mainly by using the low-dose X-ray cone beam CT imaging apparatus described above, but is not limited thereto. In the following description, the overlapping description with the aforementioned low dose X-ray cone beam CT imaging apparatus is omitted.

First, the X-ray irradiating unit 10 irradiates an X-ray toward a subject. (S10)

Next, the dose of the irradiated X-rays is selectively decelerated. (S20) At this time, the dose of the X-ray can be selectively decelerated by using the collimator 20 including a plurality of slits 21 and a plurality of strips 22 formed as empty spaces. The X-rays are transmitted through the slit 21 without being decelerated, and the X-rays are selectively decelerated and transmitted through the strip 22. At this time, it is preferable that the decelerated x-ray is 0.1% to 10% of the x-ray dose not decelerated.

Next, the decoded transmission image data (first transmission image data) and the selectively decoded transmission image data (second transmission image data) are detected. (S30) The first transmission image data is detected by the X-ray detection module 31, and the second transmission image data is detected by the photon coefficient detection module 32. [

Next, a reconstructed image is generated using the detected first and second transmitted image data. (S40) At this time, the generated reconstructed image may be at least one of a cone beam computer tomography reconstruction image, a material decomposition reconstruction image, and a monochromatic X-ray energy image.

The cone beam computer tomography reconstructed image is obtained by applying the first transmission image data detected by the X-ray detection module 31 to an iterative reconstruction algorithm performing the equation (1) or an analytical reconstruction algorithm performing the equation (2) Lt; / RTI > (S41a, S42, S43)

The second transmission image data detected by the photon coefficient detecting module 32 and the generated cone-beam computerized tomography reconstructed image are applied to a Gradient Magnitude Information (GMI) algorithm for performing Equation (3) Reconstructed image is generated and the generated GMI - based reconstructed image is applied to the material decomposition reconstruction algorithm which performs Equation (4), so that the material decomposition reconstruction image with improved image quality can be generated. (S41b, S44, S45, S46)

The monochromatic X-ray energy image can generate a monochromatic X-ray energy image using the substance decomposition information obtained from the second transmission image data. (S47)

According to the low-dose X-ray cone-beam CT imaging apparatus and the image generating method using the same, the dose of the X-ray irradiated by the X-ray irradiating unit is partially transmitted as it is and some are selectively decelerated, And reconstructs at least one or more images from the cone beam computer tomography reconstruction image, the material decomposition reconstruction image, and the monochromatic X-ray energy image from the acquired image data, thereby reducing the image quality deterioration It is possible to fundamentally reduce the pulse overlap phenomenon which is a main cause of the pulse overlap phenomenon. In addition, there is an effect that cone beam computer tomography reconstruction image, material decomposition reconstruction image and monochromatic X-ray energy image can be generated by one scan.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the spirit and scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

100, 100a, 100b: Low dose X-ray cone beam CT imaging device
10: X-ray inspection part 20: Collimator
21: slit 22: strip
30: Transmitted image data detection unit
31: X-ray detection module 32: Photon coefficient detection module

Claims (15)

An X-ray irradiating unit for irradiating an X-ray toward a subject;
A collimator for selectively decelerating a part of the dose of the X-rays irradiated from the X-ray irradiating unit;
An X-ray detecting module disposed to face the X-ray irradiating part and detecting first transmission image data that is not decelerated, and a photon coefficient detecting module that detects second transmission image data decoded by the collimator, ; And
And generating a reconstructed image using the detected first and second transmitted image data,
Ray CT apparatus according to claim 1,
The method according to claim 1,
Wherein the collimator is formed on the beam exit side of the X-ray irradiating unit.
The method according to claim 1,
And the collimator is formed on a beam receiving side of the transmitted image data detecting unit.
The method according to claim 1,
Wherein the collimator includes a slit for passing an x-ray and a strip for decelerating the x-ray, wherein the strip has an x-ray transmittance of 0.1% to 10%.
The method according to claim 1,
Wherein the X-ray detecting module and the photon coefficient detecting module are alternately adjacent to each other.
The method according to claim 1,
Wherein the control unit applies the first transmission image data to an iterative reconstruction algorithm or an analytical reconstruction algorithm to generate a cone beam computer tomography reconstructed image.
The method of claim 6,
Wherein the controller generates the GMI-based reconstruction image by applying the generated cone-beam computer tomography reconstructed image and the second transmission image data to a GMI (Gradient Magnitude Information) algorithm.
The method of claim 7,
Wherein the controller applies the generated GMI-based reconstructed image to a material decomposition reconstruction algorithm to generate a material decomposition reconstructed image.
The method according to claim 1,
Wherein the control unit generates a monochromatic X-ray energy image using the substance decomposition information obtained from the second transmission image data.
Irradiating the subject with x-rays;
Selectively decelerating a part of the dose of the irradiated X-rays;
Detecting non-decelerated first transmission image data and selectively decelerated second transmission image data;
And generating a reconstructed image using the detected first and second transmitted image data.
The method of claim 10,
Wherein the X-ray dose of the second transmission image data is 0.1% to 10% of the X-ray dose of the first transmission image data.
The method of claim 10,
Wherein the generating the reconstructed image comprises:
Wherein the first transmission image data is applied to an iterative reconstruction algorithm or an analytical reconstruction algorithm to generate a cone beam computer tomography reconstructed image.
The method of claim 12,
Wherein the generating the reconstructed image comprises:
And generating a GMI-based reconstruction image by applying the generated cone-beam computer tomography reconstructed image and the second transmission image data to a GMI (Gradient Magnitude Information) algorithm.
14. The method of claim 13,
Wherein the generating the reconstructed image comprises:
Wherein the generated GMI-based reconstructed image is applied to a material decomposition reconstruction algorithm to generate a material decomposition reconstructed image.
The method of claim 10,
Wherein the generating the reconstructed image comprises:
And generating a monochromatic x-ray energy image using the substance decomposition information obtained from the second transmission image data.
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