KR101645346B1 - Tomography apparaus and method for geometric calibration thereof - Google Patents

Abstract

A geometric correction method of a tomographic device is disclosed. A geometric correction method of a tomographic apparatus according to an embodiment of the present invention includes a step of irradiating a wave to a rotating object, a step of calculating a sinogram based on the size of the beam reflected from the object by the rotation angle Calculating distance data to the object by the rotation angle in the sineogram, and determining a constant value included in the distance function as distance data to the calculated object.

Description

[0001] TOMOGRAPHY APPARATUS AND METHOD FOR GEOMETRIC CALIBRATION THEREOF [0002]

The present invention relates to a tomographic apparatus and a geometric correction method thereof, and more particularly to a tomographic apparatus that performs geometric correction by determining a constant value included in a distance function using distance data of a target object from a measurement apparatus, .

Tomography refers to a set of techniques for imaging invisible information. Tomography includes dashed tomography based on the theory of bankruptcy of an elastic wave or electromagnetic wave generated from a source, diffraction tomography using a wave scattering phenomenon, and reflection tomography for analyzing the waveform reflected from a target.

Among them, ISAR (Inverse Synthtic Aperture Radar) using the reflection tomography technique is one of powerful methods of obtaining a two-dimensional image of a moving object by using electromagnetic waves.

ISAR assumes that the radar is fixed and the object is rotating, but in order to obtain good images, accurate distance from the measuring equipment to the rotation axis of the rotating object is required. In addition, the distance from the measuring equipment to the rotating shaft of the rotating object can be varied and it is affected by temperature or humidity, so periodic measurement is required.

In this way, it is called geometric correction, for example, to correct the distance from the transceiver of a power source such as an electromagnetic wave to the rotational axis of the object. The geometric correction is not only periodically performed as described above, .

Therefore, a need has arisen for a method that can easily and accurately perform geometric correction when using a device such as a reflective tomography device, e.g. ISAR.

Korean Patent Publication No. 2001-0090113

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a tomographic apparatus and a geometric correction method thereof that can obtain an image with excellent contrast ratio.

It is still another object of the present invention to provide a tomographic apparatus and a geometric correction method thereof that can improve the accuracy of geometric correction while reducing cost and effort involved in performing geometric correction.

The technical objects of the present invention are not limited to the above-mentioned technical problems, and other technical subjects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a geometric correction method for a tomographic apparatus including: irradiating a wave on a rotating object; Calculating a sinogram by the magnitude of the wave reflected from the object by the rotation angle; Calculating distance data from the rotation angle to the object in the sinogram; And determining a constant value included in the distance function as the calculated distance data to the object.

According to an embodiment of the present invention, the distance function is a function representing the distance from the object to the measuring device for irradiating the wave with respect to the rotation angle, and is defined as f (?) = DR cos? D is the distance between the measuring device for irradiating the wave and the rotation axis of the object, and R is the distance from the rotation axis of the object to the point target.

According to an embodiment of the present invention, the step of calculating the distance data from the rotation angle to the object in the sineogram may include calculating a point at which the brightness of the sineogram on the rotation angle- To a distance between the first and second points.

According to an embodiment of the present invention, the geometric correction method of the tomographic apparatus further includes generating a two-dimensional image of the object by applying a backprojection algorithm to the distance function in which the constant value is determined .

According to another aspect of the present invention, there is provided a tomography apparatus including: a transceiver for irradiating a wave to a rotating object, receiving a wave reflected from the object for each rotation angle and returning; And a control unit for calculating a sinogram based on the magnitude of the wave reflected from the object by the rotation angle, wherein the control unit calculates distance data from the rotation angle to the object in the sineogram , And determines a constant value contained in the distance function as the distance data.

According to an embodiment of the present invention, the distance function is a function representing the distance from the object to the transmitting / receiving unit for irradiating the wave with respect to the rotation angle, and is defined as f (?) = DR? Cos? D is the distance from the transceiver to the rotation axis of the object, and R is the distance from the rotation axis of the object to the point target.

According to an embodiment of the present invention, the control unit may determine a point at which the brightness of the sineogram on the rotation angle is highest, as a distance from the measurement apparatus to the object.

According to an embodiment of the present invention, the tomography apparatus may further include an image acquisition unit for generating a two-dimensional image of the object by applying a backprojection algorithm to the distance function in which the constant value is determined.

A program for performing the above-described method may be recorded in the computer-readable recording medium according to another embodiment of the present invention.

According to the present invention as described above, accurate geometry correction can be performed using measured data.

In addition, it is possible to obtain an image with an excellent contrast ratio as the accurate geometric correction is performed.

1 is a block diagram for explaining a tomography apparatus according to an embodiment of the present invention.
2 is a view for explaining an image acquisition method using a tomography apparatus according to an embodiment of the present invention.
3 is a view for explaining a process of calculating distance data by measuring a distance from a transmitting / receiving device to a target by a rotation angle of a target according to an embodiment of the present invention.
4 is a view for explaining a magnitude of a wave reflected by a target object rotated at a specific rotation angle and reflected back according to an embodiment of the present invention.
FIG. 5 is a diagram for explaining a sinogram obtained by superimposing a magnitude graph of a wave reflected from a target by a rotation angle according to an embodiment of the present invention. FIG.
FIG. 6 is a view for explaining distances in the transmitting and receiving unit according to rotational angles of a target object calculated in a sinogram according to an exemplary embodiment of the present invention.
FIGS. 7 to 9 are diagrams for explaining the effect of the geometric correction method of the tomographic apparatus according to the embodiment of the present invention.
10 is a flowchart for explaining a geometric correction method of the tomographic apparatus according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

Also, the singular forms herein may include plural forms unless specifically stated in the text. It is noted that the terms "comprises" and / or "comprising" used in the specification are intended to be inclusive in a manner similar to the components, steps, operations, and / Or additions.

1 is a block diagram for explaining a tomography apparatus according to an embodiment of the present invention.

The tomography apparatus 100 shown in Fig. 1 shows only the components related to this embodiment. Therefore, those skilled in the art will recognize that other general-purpose components other than the components shown in FIG. 1 may be further included.

The tomography apparatus 100 according to an embodiment of the present invention includes a transceiver 110 and a controller 130. [

The transmission / reception unit 110 irradiates a wave to a rotating object, and receives waves reflected from the object by the rotation angle and returned.

The wave irradiated from the transceiver 110 may be electromagnetic waves or ultrasonic wave, but is not limited thereto. In addition, the shape of the wave irradiated by the transmission / reception unit 110 may be a fan beam or a conical file that is sharp in the horizontal direction and gentle in the vertical direction.

The wave irradiated from the transceiver 110 reaches the object and is reflected and received by the transceiver 110 again. Therefore, when the time from when the wave is output from the transmission / reception unit 110 to the time when the wave reaches the target and then is received by the transmission / reception unit 110 is measured, when the target is rotated at a certain angle in a certain reference state, 110) to the object can be calculated.

The control unit 130 calculates a sinogram according to the magnitude of the wave reflected from the object by the rotation angle to obtain distance data from the transmission / reception unit 110 to the object.

Here, the term "sinogram" means that the object is visualized by rotating the object at various angles and irradiating the wave. Specifically, when a wave is irradiated to a target object rotated at a specific angle, the wave is reflected at the position where the target object is present, and data having the maximum magnitude of the reflected wave can be obtained.

By rotating the object and acquiring the above data and combining it into a picture, a sinogram can be obtained. The bright part of the sinogram indicates a point where the wave irradiated from the transmission and reception unit 110 is returned to the object and the dark part is reflected and the reflected wave is weak in size.

The control unit 130 calculates distance data for each rotation angle in the sinogram, and determines a constant value included in the distance function using the distance data. Specifically, the control unit 130 can calculate the distance data by determining the point at which the brightness on the sinogram is the brightest as the distance from the transmitting / receiving unit 110 to the object.

Here, the distance function means a function indicating the distance from the transmission / reception unit 110 to the object by the rotation angle.

When expressed as an equation,

Can be defined as follows.

D is the distance from the transceiver to the rotation axis of the object, and R is the distance from the rotation axis of the object to the point target.

The point target means one point where a wave irradiated by the transmission / reception unit 110 reaches and reflects when the object rotates at a specific angle in an arbitrary reference state.

As described above, the distance function includes the distance from the transmission / reception unit 110 to the rotation axis of the object. Therefore, when the constant value of the distance function is determined using the distance data from the transmission / reception unit 110 to the object, .

In addition, since the constant value included in the distance function, that is, the distance from the transmission / reception unit 110 to the object rotation axis is determined based on the measured data, more accurate geometric correction can be performed.

Meanwhile, in the above-described embodiment, the case where the wave to be irradiated is a plane wave is described as an example, but the invention may be implemented using a spherical wave. Particularly, when the distance between the transmitting / receiving unit 110 and the object is close, the distance can be measured more accurately.

If the wave to be irradiated is a plane wave, the distance from the transmission / reception unit 110 to the object may be expressed as follows by the rotation angle.

2 is a view for explaining an image acquisition method using a tomography apparatus according to an embodiment of the present invention.

Only the components related to the present embodiment are shown in the tomography apparatus 110 shown in Fig. Accordingly, those skilled in the art will recognize that other general-purpose components other than the components shown in FIG. 2 may be further included.

The transmission unit included in the transmission / reception unit 110 irradiates the wave generated by the wave generation unit 150 to the object 210. [ According to one embodiment of the present invention, the object 210 may be positioned on the turntable and rotated about a rotational axis. Therefore, the distance between the transmission / reception unit 110 and the object 210 may vary as the object 210 is rotated at a certain angle in an arbitrary reference state.

On the other hand, a portion of the object 210 to which the wave irradiated by the transmission / reception unit 110 reaches and reflects when the object 210 rotates at a specific angle can be defined as one point. In Fig. 2, since the irradiated wave reaches the front part of the object 210, which is a needle model, it will be reflected, so that an arbitrary point of the forward part can be defined as a point target.

The control unit 130 calculates a sinogram by the magnitude of the wave reflected from the object 210 by the rotation angle, calculates distance data from the sineogram to the object 210 by the rotation angle, Lt; / RTI >

Since the distance function includes the constant value from the transmission / reception unit 110 to the object rotation axis, the geometric correction can be performed by determining the constant value with the measured data.

3 is a view for explaining a process of calculating distance data by measuring a distance from a transmitting / receiving device to a target by a rotation angle of a target according to an embodiment of the present invention.

3, the distance from the transmission / reception unit 110 to the object rotation axis is D, the distance from the arbitrary point target 310 reflected by the wave radiated from the transmission / reception unit 110 to the rotation axis is R The distance from the transceiver 110 to the object in accordance with the rotation angle [theta]

Can be defined as follows.

Here, the distance f from the transmitting / receiving unit 110 to the object is measured, and the constant values D and R can be determined by applying the least squares method. As described above, since the constant value D means the distance from the transmission / reception unit 110 to the object rotation axis, the geometric correction can be performed by determining the constant value of the distance function with the measured data.

4 is a view for explaining a magnitude of a wave reflected by a target object rotated at a specific rotation angle and reflected back according to an embodiment of the present invention.

4 is a diagram showing the magnitude of a wave that is irradiated by the transmitter of the transmitter-receiver unit 110 when the object is rotated by an arbitrary reference state, and the point target of the object is fitted back and returned to the receiver. The horizontal axis represents the distance from the transmission / reception unit 110 to the object point target, and the vertical axis represents the magnitude of the reflected waves reflected.

In FIG. 4, except for the noise, a point at which the reflected wave exhibits the maximum peak value is calculated as meaningful data, the object is rotated by a predetermined angle interval, and the same process is performed to calculate a sinogram of the object .

Here, the term "sinogram" means that a plurality of graphs as shown in FIG. 4 are obtained by irradiating a wave by rotating an object at various angles, and then superimposing and visualizing the graph.

FIG. 5 is a diagram for explaining a sinogram obtained by superimposing a magnitude graph of a wave reflected from a target by a rotation angle according to an embodiment of the present invention. FIG.

Fig. 5 shows a sino graph when the object is a needle. The axis of abscissa represents an angle obtained by rotating the needle in an arbitrary reference state, and the axis of ordinate represents the distance to the transmitting / receiving unit for irradiating the needle and the wave.

The more bright part in the sinogram, the greater the intensity of the returning waves that hit the target's chain. The darker the part, the less reflected waves are reflected.

In the case of an ideal shape needle, even if rotated in a certain reference state, the distance from the transmitting / receiving part as the measuring device will be kept constant, so that the position of the brightest part on the sinogram will not change even if the rotation angle changes .

5, the most bright portion appears at about 580 nm from the transmission / reception unit, so that it can be seen that the wave emitted from the transmission / reception unit is reflected back to the needle about 580 nm away from the transmission / reception unit.

Looking at the front and rear of 580nm, the sinogram appears very dark, meaning that there is no wave reflected back from that part. Therefore, it can be seen that no object exists in the corresponding section.

On the other hand, the portion with the highest brightness at a certain angle, which is the horizontal axis on the sinogram, means that the wave reflected from the object is the largest, so that the object exists at the distance of the vertical axis where the brightest portion appears.

Here, the data as shown in FIG. 6 can be calculated by calculating the position data of the portion with the highest brightness on the sinogram according to the rotation angle and plotting the graph.

FIG. 6 is a view for explaining distances in the transmitting and receiving unit according to rotational angles of a target object calculated in a sinogram according to an exemplary embodiment of the present invention.

5, the distance between the transmitting and receiving unit and the target object is determined as the distance at which the brightness of each rotation angle is the brightest at the corresponding rotation angle, and the data shown in FIG. 6 can be calculated by plotting the distance.

Subsequently, the calculated data values are substituted into Equation (1), and then the minimum square method is applied to determine the constant values D and R included in the distance function.

Here, the constant value D means the distance from the transmission / reception unit 110 to the object rotation axis, so that the geometric correction can be performed as the constant value of the distance function is determined.

FIGS. 7 to 9 are diagrams for explaining the effect of the geometric correction method of the tomographic apparatus according to the embodiment of the present invention.

The tomography apparatus according to an embodiment of the present invention may further include an image acquisition unit (not shown) capable of acquiring a two-dimensional image of a target by applying a backprojection algorithm to the calculated distance function. The image acquiring unit can generate a two-dimensional image of the object using the distance function of which the constant value is determined and the calculated sinogram as the input values.

In the present embodiment, a needle having a high reflectance is easy to construct as an ideal point target in all directions. The image shown in FIG. 7 can be obtained by performing the above-described geometric correction on the target chain needle and applying a backprojection algorithm to the calculated sinogram.

FIG. 8 is a diagram showing a two-dimensional tomographic image of a needle obtained when the geometry correction is performed erroneously and the axis of rotation is about 10 cells out of the order.

8, even if the distance from the measuring apparatus to the rotation axis of the object is slightly different, it does not appear that there is a large difference visually. However, when the entropy value of the tomography image is calculated, the distance from the measuring apparatus to the rotation axis of the object varies. The values are different.

9 is a diagram for explaining entropy values when geometric correction is performed incorrectly and geometric correction is performed correctly according to an embodiment of the present invention.

If the center of rotation axis is miscorrected by 1 cell from -10 to 10 around the rotation axis, the entropy value indicating the image quality index is changed. Referring to FIG. 9, it can be seen that the entropy value is largest when? N is 0 in the case where the geometric correction is performed correctly, that is, in the X axis.

As described above, since the entropy value indicates the index of the image quality, it can be confirmed that the quality of the two-dimensional tomographic image is most excellent when the geometric correction is performed correctly.

10 is a flowchart for explaining a geometric correction method of the tomographic apparatus according to an embodiment of the present invention.

The transceiving unit 110 irradiates a wave to a rotating object (S1010), and calculates a sinogram by the size of the beam reflected by the object at each rotation angle (S1020).

Thereafter, the distance data from the measuring apparatus to the object is calculated in the sinogram (S1030), and a constant value included in the distance function is determined using the calculated data (S1040).

Here, the distance function is a function indicating the distance from the object to the measuring device for irradiating the wave by the rotation angle. Since the distance function includes the distance between the measuring device and the rotation axis of the object as a constant value, geometric correction can be performed by determining a constant value with the measured data.

In addition, by performing the geometric correction based on the measured data as described above, it is possible to achieve an effect that the geometric correction can be performed more easily and accurately.

Meanwhile, the above-described method can be implemented in a general-purpose digital computer that can be created as a program that can be executed by a computer and operates the program using a computer-readable recording medium. In addition, the structure of the data used in the above-described method can be recorded on a computer-readable recording medium through various means. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical reading medium (e.g., CD ROM,

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed methods should be considered from an illustrative point of view, not from a restrictive point of view. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: Tomography apparatus 110: Transmitting /
130:

Claims (11)

Irradiating a rotating object with a wave;
Calculating a sinogram by the magnitude of the wave reflected from the object by the rotation angle;
Calculating distance data from the rotation angle to the object in the sinogram;
And determining a constant value included in the distance function as the calculated distance data to the object,
The distance function may include:
And a distance from the object to the measurement device for irradiating the wave with respect to the rotation angle. The method according to claim 1,
The distance function may include:
f (?) = DR? cos? (?),
D is the distance between the measuring device for irradiating the wave and the rotation axis of the object, and R is the distance from the rotation axis of the object to the point target. The method according to claim 1,
Calculating the distance data from the rotation angle to the object in the sinogram,
And determining a point at which the brightness on the sinogram of each rotation angle is most bright as a distance from the measurement apparatus to the object. The method according to claim 1,
And generating a two-dimensional image of the object by applying a backprojection algorithm to the distance function in which the constant value is determined. The method according to claim 1,
Wherein the wave is a plane wave or a spherical wave. A transmitting and receiving unit for irradiating a wave to a rotating object and receiving a wave reflected from the object for each rotation angle and returning; And
And a controller for calculating a sinogram based on the magnitude of the wave reflected from the object by the rotation angle,
Wherein,
Calculating distance data from the rotation angle to the object in the sinogram, and determining a constant value included in the distance function as the distance data,
The distance function may include:
And a distance from the object to the transmitting / receiving unit for irradiating the wave with respect to the rotation angle. The method according to claim 6,
The distance function may include:
f (?) = DR? cos (?),
D is the distance from the transceiver to the rotation axis of the object, and R is the distance from the rotation axis of the object to the point target. The method according to claim 6,
Wherein,
Wherein the distance from the transceiving unit to the object is determined as the point at which the brightness on the sinogram is the most bright by the rotation angle. The method according to claim 6,
And an image acquiring unit for generating a two-dimensional image of the object by applying a backprojection algorithm to the distance function in which the constant value is determined. The method according to claim 6,
Wherein the wave is a plane wave or a spherical wave. A computer-readable recording medium on which a program for performing the method according to any one of claims 1 to 5 is recorded.

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