KR101657870B1 - Method and apparatus for digital tomosynthesis using automatically controlled focus adjusted moving grid - Google Patents

Abstract

Disclosed is a digital tomographic image synthesizing apparatus and a method thereof using an autofocused movable grid. The apparatus includes a sensor for sensing the angle of the beam, a grid array controller for automatically changing the focus of the grid in consideration of the beam array based on the angle of the beam, and a detector for measuring the X-ray dose along the grid of the changed focus . According to the present invention, the scattering line which degrades the image quality is corrected in digital single-layer synthetic imaging for chest radiography. It is possible to cope with the generation of X-ray scattered rays irradiated from various angles and improve the quality of the reconstructed image.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for synthesizing a digital tomographic image using an autofocused movable grid,

Field of the Invention [0002] The present invention relates to a digital tomographic image synthesis method and apparatus, and more particularly to an autofocused movable grid.

Simple examination of the chest is a low-cost, high-efficiency test that obtains a lot of information in a short time. It is widely used for general diagnosis and follow-up observation. However, simple examination of the chest has a disadvantage in that it has a relatively low sensitivity and specificity. The sternum, the mediastinum, the bilateral hysterosal part where the blood vessels overlap, and the area where the stomach and the liver are obscured are difficult to diagnose as a rectangle of the image.

To overcome these drawbacks, there is a chest digital tomosynthesis system (CDT system). Computed tomography (CT) computed tomography (CT) is a diagnostic tool that reconstructs 3D images at a limited angle and provides depth information. The computed tomography (CT) Is a new diagnostic device that has recently attracted attention due to its remarkably low dose. In addition, reconstruction of the image is possible, and the rate of utilization for chest examination is increasing.

On the other hand, X-ray scattering easily occurs because chest has many organs with a relatively high cushioning coefficient. Scattering causes degradation of image quality and adversely affects the diagnosis of lesions in terms of diagnostic imaging. Therefore, a system for removing scatter is required.

However, since there is almost no way to control the scatter occurrence itself, a method is under development in which a signal is not detected in the detector after the scatter line is generated. At this time, the most important thing is the grid (Grid). In general, high kVp imaging, wide field of view, and thick areas tend to maximize scattering.

Since the CDT system is operated in a shooting environment in which a detector and an X-ray tube (or a tube) are moved in parallel, unlike a conventional digital tomosynthsis system (DBT system) for mammography, And the angle between the source to detector distance (SDD) and the angle of the X-ray entering the detector changes. The characteristics of such a CDT system serve as a decisive factor for the exposure dose.

In particular, the X-rays spread radially may be absorbed by the parallel patteren grid and disappear according to the incident angle of the X-ray generator. There is a need for a method and apparatus capable of maintaining a parallel pattern grid while moving the grid in the same direction as the tube when the X-ray generator is moving on top of the point where the primary beam itself as well as the scatter is absorbed.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for synthesizing a digital tomographic image using an autofocused movable grid.

Another object of the present invention is to automatically change the focus of the grid by angle so that the detector and the X-ray tube emitting the beam move in parallel.

Another object of the present invention is to provide an embedded system adapted to a change in angle of an X-ray tube.

A further technical object of the present invention is to provide a tube-detector linear movement and a tube-detector circular movement.

According to an aspect of the present invention, a digital tomographic image synthesizing apparatus using an autofocused movable grid includes a sensor for sensing an angle of a beam, a focus of the grid in consideration of a beam array based on the angle of the beam, and a detector for measuring an X-ray dose according to the grid of the changed focus.

According to the present invention, it is possible to correct a scattering line which degrades image quality in digital single-layer synthetic imaging for chest radiography.

According to the present invention, it is possible to cope with the generation of X-ray scattered rays irradiated at various angles and improve the quality of the reconstructed image.

According to the present invention, the improved image quality can contribute to the dose reduction effect by reducing the retraining rate in the clinic.

According to the present invention, scattering line removal effect at various angles can be applied unlike the existing grid.

According to the present invention, it is possible to prevent a grid cutoff phenomenon by compensating for misalignment between a radial X-ray and a grid, thereby increasing the efficiency of the effective X-ray, Image quality can be provided.

According to the present invention, it is possible to provide a grid which does not cause deterioration of the image quality and removes the scatter regardless of the photographing angle.

1 shows an example of a scattering line correction method using a computer.
2 shows an example of a scattering line correction method using a grid.
3 is a block diagram illustrating an example of a digital tomographic image synthesizer using an autofocused movable grid according to the present invention.
In FIG. 4, the grid array is changed according to the angle of the tube.
5, the rotation of the grid array due to the movement of the tube can be confirmed.
6 is a flowchart illustrating a digital tomography method using an autofocused movable grid according to the present invention.
FIG. 7 shows a simulation for obtaining CDT system dose characteristics using GATE simulation
8 (Figs. 8A and 8B) show an example of an actual experimental apparatus of the CDT system according to the present invention.
FIG. 9 is a view comparing the absorbed dose according to the GATE simulation and the absorbed dose according to the actual experiment.
10 is a diagram showing a linear movement of the detector along the direction of the X-ray.
Fig. 11 is a view showing the thickness and spacing of the soft spots. Fig.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Also, in order to clearly illustrate the present invention in the drawings, portions not related to the present invention are omitted, and the same or similar reference numerals denote the same or similar components.

The objects and effects of the present invention can be understood or clarified naturally by the following description, and the objects and effects of the present invention are not limited only by the following description.

The objects, features and advantages of the present invention will become more apparent from the following detailed description. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

When an X-ray is emitted and passes through an object, a secondary X-ray having a different direction from the incident X-ray is generated, which is referred to as a scattering line. Spawning line drops the quality of the image.

Methods for removing scatter lines include conventional methods (eg, grid, air-gap, collimation, etc.) and computer-assisted calibrations.

1 shows an example of a scattering line correction method using a computer.

Referring to FIG. 1, a computer-assisted scatterometry correction method is required to measure a scattering line for each pixel of an image.

A Beam-Stop Array or Beam-Hole Array is used as a scattering line measurement tool. At least two shots are required to obtain scattering lines per pixel. At this time, additional exposure to the patient may occur.

2 shows an example of a scattering line correction method using a grid.

Referring to FIG. 2, a grid (Grid) is a method using a point at which a primary X-ray is incident almost perpendicularly to a detector but a scattered ray is incident in a random direction. The X-ray passing through the subject is physically blocked so that the scattered ray component obliquely incident on the lead-through grid is prevented from reaching the detector.

A method and an apparatus for synthesizing a digital tomographic image using an autofocused movable grid according to the present invention will now be described.

This method and apparatus are characterized in that the focus of the grid automatically changes in consideration of a beam array in which the grid changes according to the CDT geometry. Because of the CDT geometry, the x-ray tube and the detector move in parallel, so the focus type of the grid varies by angle.

3 is a block diagram illustrating an example of a digital tomographic image synthesizer using an autofocused movable grid according to the present invention.

Referring to FIG. 3, a digital tomography apparatus 300 using an autofocused movable grid may include a sensor 310, a detector 340, and a controller 320. The control unit 320 may include a grid array control unit 325.

The grid array controller 325 changes the grid array according to the angle change of the tube. In FIG. 4, the grid array is changed according to the angle of the tube.

For example, the grid array controller 325 automatically changes the focus of the grid in consideration of a beam array that changes in accordance with the CDT geometry. That is, the focus of the grid is automatically changed in consideration of the beam array based on the detected angle of the beam

As another example, the grid array control 325 controls the focus type of the grid by angle so that the detector and the X-ray tube on the CDT geometry move in parallel.

The detector 340 measures the amount of radiation passing through the grid. The detector may be a display for viewing the natural color of the visible light from a different point of view. The X-ray detector is a sensor device that converts X-rays into visible light and then converts the X-rays into electrical signals. That is, it can serve as a sort of photoelectric sensor that generates an electrical signal through light (X-ray). Therefore, if you connect the monitor to the X-ray detector, you can see the recorded image.

For example, the embedded system may be implemented by introducing an embedded system corresponding to a change in the angle of the tube, and the sensor 310 and the grid array control unit 325 may be included in the embedded system 330.

When the sensor 310 mounted on the embedded system 330 detects the angle of the beam, the grid array controller 325 adjusts the rotation angle of the grid according to the angle of the beam (S320)

As another example, the control unit 320 may further include a calculation unit 327, and the calculation unit 327 may perform parallel-GPU-based accelerating calculation. There is an effect of reducing the error by the basic CPU calculation speed.

In particular, if the error of the grid angle calculated through the parallel-GPU-based acceleration calculation in the calculation unit 327 differs by more than 1% from the preset initial angle value, the control unit 320 displays a graphical user interface (GUI) It may be possible to control the warning lamp display unit 350 to display a warning lamp through interlocking with the software. That is, the digital tomographic image synthesizer 300 using the autofocused movable grid may further include a warning lamp display unit 350. [

As another example, the digital tomographic image synthesizer 300 using the autofocused movable grid may further include a driver 335, which may be motorized, or a timing belt system .

More specifically, the grid array controller 325 connects the driving unit 335 of the basic motor type when the detector moves in a linear direction to acquire a medical image, so that the grid array controller 325 rotates the grid array Can be controlled. Referring to FIG. 10, the black detector moves linearly leftward and rightward along the direction of the X-ray emitted from the tube.

The grid array controller 325 can move the grid using the presence of two moving devices, i.e., a tube and a detector 340, so that power consumption due to the additional detector is unnecessary.

The following equation is an example of determining the X-ray absorption efficiency (%) of the grid according to the present invention.

Here, the width of the grid strip is the thickness of the grid lead strip, and the width of interspace (= D) is the spacing of the stamen (ie, the width of the medium). Referring to Fig. 11, the thickness and spacing of the stamina can be seen. The grid ratio is h / D.

The grid array control unit 325 can return the grid to the first stored position after the shooting is finished. There is an effect that it can be used in dual mode of digital single layer synthesis device for basic chest radiography and general radiography device.

The present invention is applicable not only to tube-detector linear movement in simple geometry calculations, but also to other apparatuses such as tube-detector circular movement.

5, the rotation of the grid array due to the movement of the tube can be confirmed.

6 is a flowchart illustrating a digital tomography method using an autofocused movable grid according to the present invention.

Referring to FIG. 6, a patient is placed on a table for photographing and a posture is set (S600).

Subsequently, conditions for shooting are set (S605). Examples include angle range, tube voltage, tube current, and source to detector distance (SDD).

Subsequently, photographing is started (S615).

At this time, as the X-ray tube moves in the linear orbit, the X-ray angle changes in the set angle range (S620). Or when the X-ray tube moves, the position of the detector is calculated (S622) so that the center of the X-ray tube and the center of the detector coincide with each other. Or the movable grid attached to the detector moves at an angle calculated according to the set SDD and X-ray emission angle (S624).

Then, it is determined whether the combination of the X-ray tube, the detector, and the grid is properly aligned (S630). If so, the detector receives the signal and reconstructs the image (S635). If not, step S615 is taken again.

7 shows a simulation for obtaining CDT system dose characteristics using GATE simulation. Here we show a method for verifying the dose distribution that varies with the angle of the CDT system by comparing the resulting data with the actual data and demonstrating the need for a mobile grid that is tailored to the array of simulated beams that varies with the angle. For example, the tube voltage of the used x-ray tube may be set to 120 kVp, and the distance from the x-ray source to the detector may be set to 178 cm.

Referring to FIG. 7, a GATE (Geant4 Application for Tomographic Emission) simulation result is obtained to obtain a CDT system dose characteristic, and the dose evaluation ability is verified by comparing with the actual experiment.

Specifically, the dose is measured while acquiring the projection at intervals of 5 degrees.

In the simulation, the CDR system environment was modeled by GE 's volume rad. In the case of SDD, the maximum distance that can be realized when the tube angle is 0 degree in the actual laboratory environment was 178 cm.

The photon conditions used in the simulation were 120 kVp and 0.3 mAs, and the number of photons was calculated using the SRS78 program. The photon number at 1 mAs, incident area 1 mm2, and SDD 75 cm was calculated using the following equation Respectively.

Where F is the number of photons used in the simulation, A _n is the number of photons per energy obtained using SRS-78, M is a mAs correction factor, E is an area correction factor, and C is attenuated by collimation Photon correction factor.

8 (Figs. 8A and 8B) show an example of an actual experimental apparatus of the CDT system according to the present invention.

Referring to FIG. 8, the CDT system environment is simulated at intervals of 5 degrees using the X-ray generator (E7239X, Toshiba, Japan) of FIG. 8A and the ionization chamber (9095, RADCAL, USA) can do.

It is possible to perform real experimental measurement of the research for comparison evaluation between the actual experiment and the simulation result, and to compare the result of the actual experiment and the simulation at the time of the simulation in order to prove the scattering acid removal effect of the grid You can set the criteria.

FIG. 9 is a view comparing the absorbed dose according to the GATE simulation and the absorbed dose according to the actual experiment.

Referring to FIG. 9, it can be confirmed that the dose tendency of the simulation and the actual experiment are similar in the result of the dose verification experiment through the simulation and the actual experiment in the CDT geometry.

GATE's experimental results are lower than the actual results. In particular, as the angle increases, the error with the actual experiment increases.

The tendency of these graphs is judged to be due to the environmental error caused by the manual adjustment of the angle in the actual experiment and the physical reaction that can not be implemented completely in the simulation.

In actual experiments, the X-ray intensity of the cathode is stronger than that of the anode due to the inclination effect caused by the angle of the X-ray tube target. However, in the simulation used in this experiment, since the homogeneous X-ray is generated without inclination effect, it is considered that the error with the actual experiment is increased as the angle increases.

The following table shows the absorbed dose in the CDT system, the standard deviation of the scaling factor, which is the difference between the actual GATE simulation and the GATE simulation with less than 0.01%.

Angle  Actual experiment (mGy) GATE simulation (mGy) Scaling factor -15 1.407 (0.064) 1.656 0.176 -10 1.886 (+/- 0.184) 2.181 0.209 -5 1.898 (0.028) 2.178 0.198 0 2.126 (0.028) 2.176 0.035 5 2.064 (+ -0.057) 2.156 0.065 10 1.945 (+/- 0.071) 2.158 0.151 15 1.837 (+/- 0.051) 2.049 0.149

In conclusion, it can be seen that the CDT system reconstructs a three-dimensional image with less projection data than CT by acquiring an image at a limited angle in an imaging environment in which the X-ray tube and detector move in parallel.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. Should be regarded as belonging to the above-mentioned patent claims.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventive concept as defined by the appended claims. But is not limited thereto.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

Claims (10)

In a digital tomography (CDT) system using an autofocused mobile grid,
A sensor for detecting the angle of the beam;
An X-ray tube for radiating the beam;
A grid array controller for automatically changing a focus of the grid in consideration of a beam array based on the angle of the beam; And
A detector for measuring an X-ray dose according to the changed focus grid; And
A motor-driven driving unit,
The position of the detector moves in a linear direction so that the center of the X-ray tube and the center of the detector coincide with each other,
When the detector moves in a linear direction, the grid array controller connected to the driving unit controls the rotation of the grid array,
The grid array controller determines whether or not the combination of the X-ray tube, the detector, and the grid is properly aligned. If the alignment is properly performed, the grid array controller receives the signal from the detector and reconstructs the image. Wherein the digital tomographic image synthesizing apparatus comprises: The apparatus of claim 1, wherein the grid array controller
Wherein the X-ray tube that emits the beam and the focus of the grid by angle are automatically changed so that the detector moves in parallel. The method according to claim 1,
Wherein the angle of the beam is sensed based on an angle change of the X-ray tube. The method according to claim 1,
Further comprising an embedded system adapted to varying the angle of the X-ray tube,
Wherein the sensor and the grid array controller are included in the embedded system. The method according to claim 1,
GPU-based accelerating calculation based on the parallel-GPU-based accelerating calculation. 6. The method of claim 5,
The calculation unit calculates whether or not the error of the grid angle calculated through the parallel-GPU-based acceleration calculation differs by more than 1% from the preset initial angle value,
And a warning lamp display unit for displaying a warning lamp based on the calculation result. The method according to claim 6,
Wherein the display of the warning light is determined through interlocking with GUI (Graphic User Interface) software for tomosynthesis photographing. delete The method according to claim 1,
Wherein the grid array controller returns the grid to the first set position after the photographing is finished. The method according to claim 1,
Wherein the grid array controller performs any one of a tube-detector linear movement and a tube-detector circular movement.

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