KR20090041649A - Method for correcting central axis shift of x-ray computed tomography - Google Patents

Abstract

A method for correcting a central axis of an X-ray CT apparatus is provided to obtain a clear three-dimensional image in an X-ray CT(Computed Tomography) photography by removing a blurring phenomenon. A virtual model(230) is prepared. The center of the virtual model is matched with a center(255) of a central axis(250) of an X-ray CT apparatus(200). The virtual model is arranged on the X-ray CT apparatus. The virtual model is scanned by the X-ray CT apparatus. The detector plane data is obtained. The middle plan data of the virtual model is extracted from the detector plan data. The center of the middle plane data of the virtual model is compared with the center of the detector plane data. The movement value of the middle plane data of the virtual model is obtained. The center of the central axis of the X-ray CT apparatus is corrected by using a movement value of the middle plane data.

Description

Method for correcting central axis shift of X-ray computed tomography

The present invention relates to a method for correcting the movement of the central axis of the X-ray imaging apparatus. More particularly, the present invention relates to a Citi image of a virtual model, to obtain detector plan data, to extract middle plan data from the detector plan data, and to detect the detector. Comparing the plan data and the middle plan data to obtain a movement value, and then using the movement value to correct the central axis movement of the X-ray Citigraphic apparatus suggesting a method for correcting the center point movement of the central axis of the X-ray Citigraphy apparatus It is about a method.

Today, devices for acquiring medical images have been developed to more accurately diagnose a patient's condition.

Among them, three-dimensional tomographic systems such as X-ray computed tomography have an advantage of obtaining accurate three-dimensional images. For this reason, three-dimensional tomography systems, such as x-ray systems, have become one of the most widely used equipment for acquiring medical images.

In this case, in order to obtain a 3D image, the X-ray device first acquires a plurality of 2D images, and then reconstructs the 2D images through mathematical calculations to obtain a 3D image.

The 3D image reconstruction technique has been technically developed from the 2D image reconstruction technique.

Representative two-dimensional image reconstruction techniques include parallel-beam reconstruction, equal-angle fan-beam reconstruction, and equal-spaced fan-beam reconstruction.

The 3D projection reconstruction technique is a cone-beam reconstruction technique, also called a FDK (Feldkamp) technique, which extends the z-axis to enable 3D processing based on the 2D equal space fan beam reconstruction technique. It is a three-dimensional reconstruction technique.

In this case, the 3D projection reconstruction technique receives 2D projection data from an X-ray Citi apparatus and reconstructs it into a 3D image through mathematical calculation. The X-ray source and detector of the X-ray Citi apparatus are used. Problems such as blurring in a 3D image often occur because the center point of the central axis of the detector is not located at the correct position or moves.

Accordingly, the present invention is to solve the above-mentioned disadvantages and problems of the prior art, to obtain the detector plan data by Citi shooting a virtual model, to extract the middle plan data from the detector plan data, the detector plan data And comparing the middle plan data to obtain a moving value, and then using the shift value to correct the center point of the central axis of the X-ray imaging apparatus, thereby providing a center point of the X-ray source and the detector central axis. The present invention provides a method for correcting the movement of the central axis of the X-ray imaging apparatus that can eliminate the cause of not clearing the 3D image such as blurring due to movement or blurring. There is a purpose.

The object of the present invention is to prepare a virtual model; Positioning a center point of the virtual model on the X-ray city photographing device by matching the center point of the central axis of the X-ray city photographing device; Acquiring a plurality of detector plan data by scanning the virtual model with the X-ray imaging apparatus; Extracting middle plan data of the virtual model from the detector plan data; Comparing a center point of each of the middle plan data of the virtual model with a center point of each detector plan data to obtain a movement value of each of the middle plan data of the virtual model; And correcting the center point of the central axis of the X-ray city photographing apparatus by using the shift value.

In addition, the object of the present invention is the step of correcting the center point of the central axis of the X-ray Citigraphy apparatus using the movement value stores the obtained movement values, and then the detector plan data obtained by the X-ray Citigraphy apparatus They are also achieved by a method of correcting the central axis movement of the X-ray Citigraphic apparatus, characterized in that the step of correcting by using the stored movement value and reconstructing to obtain a three-dimensional image.

In addition, the object of the present invention is the step of correcting the center point of the central axis of the X-ray imaging apparatus using the movement value, the step of rearranging the position of the source and the detector of the X-ray imaging apparatus with the obtained movement values It is also achieved by the method of correcting the central axis movement of the X-ray Citigraphic apparatus characterized in that;

In addition, the object of the present invention is to extract the middle plan data of the virtual model from the detector plan data extracts the data of the row located in the middle of the entire row in each of the detector plan data, the extracted intermediate It is also achieved by a method of correcting the central axis movement of the X-ray Citigraphic apparatus, characterized in that by extracting the data of the virtual model of the data of the row.

In addition, the object of the present invention is also achieved by a method for correcting the center point of the central axis of the X-ray Citigraphic apparatus, characterized in that the virtual model is caused by the cross section.

In addition, the object of the present invention is also achieved by a method for correcting the movement of the central axis of the X-ray Citigraphic apparatus, characterized in that the virtual model is spherical or cylindrical.

The method of correcting the movement of the central axis of the X-ray imaging apparatus of the present invention occurs due to the fact that the center point of the central axis is not positioned or moved at the correct position, and thus removes blurring phenomenon in which the 3D image is not clear. There is an effect of providing a method for correcting the movement of the central axis of the X-ray Citigraphy apparatus that can obtain a clear three-dimensional image during Citi shooting.

Details of the above objects and technical configurations and the effects thereof according to the present invention will be more clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention. Like numbers refer to like elements throughout.

In the method for correcting the movement of the central axis of the X-ray imaging apparatus of the present invention, first, a virtual model having a cross section is prepared. In this case, the virtual model is preferably spherical or cylindrical so that the cross section is a circle. Of course, the virtual model is made of a material that increases the difference between the density and the portion other than the virtual model, it is preferable that the X-rays are made of a material having a low transmittance.

Subsequently, the virtual model is placed on the X-ray city photographing apparatus. In this case, the center point of the virtual model should be positioned to coincide with the center point of the central axis of the X-ray city photographing apparatus.

The method of confirming that the center of the virtual model is positioned to coincide with the center point of the central axis of the X-ray city photographing apparatus may be confirmed by scanning the virtual model with the X-ray city photographing apparatus and reconstructing it into a 3D image. have.

Subsequently, the virtual model is scanned by the X-ray imaging apparatus to obtain a plurality of detector plan data.

Then, middle plan data of the virtual model is extracted from the detector plan data.

In this case, middle plan data of the virtual model may be extracted by extracting data of a row located in the middle of all the rows from the detector plan data, and extracting data of the virtual model from the extracted intermediate rows of data. have.

Subsequently, a moving value of each of the middle plan data of the virtual model is obtained by comparing the center of each of the middle plan data of the virtual model and the center of each of the detector plan data.

Subsequently, the center point of the central axis of the X-ray imaging apparatus is corrected using the shift values.

In this case, there are two methods for correcting the movement of the central axis of the X-ray imaging apparatus. First, the acquired movement values are stored, and detector plan data obtained by the X-ray imaging apparatus, In detail, there is a method of correcting projection data of an object included in the detector plan data and reconstructing the corrected detector plan data to obtain a 3D image, and secondly, in consideration of the obtained movement values, There is a method of rearranging positions of sources and detectors of the X-ray Citigraphic apparatus so that the center point of the central axis of the X-ray Citigraphic apparatus does not move or move.

That is, in the first method, the center point of the central axis of the X-ray imaging apparatus does not coincide with the center of the object or is moved during scanning, and is corrected in software to obtain a clear 3D image by correcting the 3D image reconstruction. The second method is to align the X-ray source and the detector of the X-ray Citigraphy device, and to hardware-correct that the center point of the X-ray Citi-graphy device does not coincide with the center of the object or is moved during scanning. That's how.

1A and 1B are diagrams illustrating a method of obtaining detector plan data of an X-ray Citigraphy apparatus.

Referring to FIGS. 1A and 1B, the X-ray city photographing apparatus 100 includes an X-ray source 110 and a detector 120.

The X-ray imaging apparatus 100 irradiates the object 130 having the object point 135 with the X-ray generated by the X-ray source 110 and is received by the detector 120. In this case, the X-rays are irradiated with a cone beam.

An image 140 of the object 130 is formed in the detector 120. When the detector 120 reads the image 140, the object 120 becomes projection data of the object. In this case, the projection data of the object includes the object point data generated by the object point 135. In this case, the data read from the detector 120 is detector plan data.

Therefore, the data read from the detector 120 may be divided into detector plan data, which is data of the entire detector 120, and projection data, which is a part of the detector plan data.

In order to obtain the 3D image, the X-ray imaging apparatus 100 rotates the circular trajectory up to 360 degrees while the X-ray source 110 and the detector 120 move by the same angle about the central axis 150. A plurality of detector plan data, which is data that is a two-dimensional image, is acquired by a scan.

The plurality of detector plan data including the target point 135 data may be reconstructed into a 3D image.

The 3D image reconstruction has various techniques, but in the present invention, the filter back-projection algorithm proposed by Feldkamp, Davis, and Kress (FDK) was used.

First, preprocessing and filtering are performed. The detector plan data acquired by the X-ray imaging apparatus 100 are loaded one by one.

Then, Jacobian weighting processing is performed on the detector plan data.

In this case, the Jacobian weighting process is a process for correcting a change in a value between polar coordinates and rectangular coordinates during a mathematical process.

The detector plan data is filtered using a filter.

At this time, the filtering becomes the core of the filter bag-projection algorithm technique. When the filtering is not performed, the shape of the object part derived as a result of the reconstruction appears blurred and unclear. In order to solve this problem, each projection data is filtered so that the shape of the original object can be approximated. The filtering process is performed between the Jacobian weighting process and the back-projection process to be described later.

Then back-projection is performed. The weighting factor of the target point data of the detector plan data according to the distance is calculated.

Then, interpolation is performed using the detector plan data to determine the value of each target point of the three-dimensional volume. And the value of the target point is stored.

The reconstructed slice is then stored.

Each of the detector plan data is sequentially processed through the preprocessing, filtering, back-projection processing, and reconstruction section storage, and then the reconstruction result is stored in the section.

At this time, the X-ray source 110, the center point 155 of the central axis and the center point 125 of the detector are located on one center connecting line 160 to maintain a straight line to the X-ray around the center point 155 of the central axis The source 110 and the center point 125 of the detector are rotated.

As described with reference to FIGS. 1A and 1B, the X-ray source 110, the center point 155 of the central axis, and the center point 125 of the detector are used to acquire an accurate 3D image in the X-ray Citigraphy apparatus 100. The center connection line 160, which is a straight line, should be positioned. Due to a mechanical defect or vibration during driving of the X-ray imaging apparatus 100, the center point 155 of the central axis may not move while being scanned.

2 is a view showing that the center point of the central axis is moved.

Referring to FIG. 2, FIG. 2 illustrates a phenomenon in which the X-ray source 110 is not positioned on the above-described center point connecting line 160, that is, the center point 155 of the central axis is moved. In the detector plan data obtained in this state, the center point 125 of the detector plan data and the center point 127 of the projection data generated by the object 130 are located at different positions.

That is, it is measured that the projection data, which is the data of the object 130, is shifted sideways as a whole. When the above-described three-dimensional image reconstruction is performed with the detector plan data including the data, a three-dimensional image having a blurring phenomenon that appears to overlap the image is obtained.

3, 4A, 4B, and 5 are diagrams illustrating a method of correcting the movement of the central axis of the X-ray imaging apparatus according to an embodiment of the present invention.

Referring to FIG. 3, FIG. 3 illustrates an overall X-ray imaging apparatus for illustrating a method of correcting a central axis movement of an X-ray imaging apparatus according to an embodiment of the present invention.

As described above, the X-ray imaging apparatus 200 includes the X-ray source 210 and the detector 220. At this time, the virtual point of the sphere (sphere) or cylinder (cylinder) so that the cross section can be drawn to the circle (circle) in the center point 255 of the central axis 250 that the X-ray source 210 and the detector 220 rotates Model 230 is located.

At this time, the center point of the virtual model 230 is positioned to exactly match the center point 255 of the central axis. Whether the center point of the virtual model 230 coincides with the center point 255 of the central axis may be used as it is. That is, this may be confirmed by using a laser beam provided in the X-ray city photographing apparatus 200.

In the present invention, the virtual model 230 may use a virtual model having a cylindrical shape. The virtual model 230 may have a diameter of 10 mm or more, and a height of 50 mm or more. It is preferably made of aluminum or teflon.

The virtual model 230 is scanned by the X-ray Citigraphic apparatus equipped with the virtual model 230.

In this case, the X-ray source 210 and the detector 220 of the X-ray imaging apparatus are scanned at a predetermined angle to obtain a plurality of detector plan data.

After obtaining the plurality of detector plan data, the middle plan data 245 of the virtual model 230 is extracted from each detector plan data.

Referring to FIGS. 4A and 4B, a method of extracting middle plan data 245 of the virtual model 230 from the detector plan data is illustrated, and FIG. 4A illustrates one detector plan data. Assuming that the detector 220 is composed of 256 * 256 pixels and the detector plan data has obtained such data, the 128th pixel line, which is a line located in the middle of the rows and columns of the detector plan data, is the row. It becomes the centerline in overheating. In this case, the point where the center line of the row and the column meet is the center point 225 of the detector described above and the center point of the detector plan data. When the image generated by the virtual model 230 is read, the projection data 240 of the virtual model 230 is obtained.

At this time, the method of extracting the middle plan data 245 of the projection data 240 of the virtual model 230, as shown in Figure 4b is the pixel line of the 128th row of the middle of the row in the detector plan data Extracting and selecting only pixels having data of the virtual model 230 among the data may extract the middle plan data 245 of the virtual model 230.

In this case, the middle plan data of the virtual model 230 illustrated in FIG. 4B is located at the same position as the center point 225 of the detector, that is, the center point of the detector plan data. The center point 255 of the central axis of the ray-citigraphy apparatus is not moved, and the center point 225 of the X-ray source 210 and the detector and the center point 255 of the center axis are positioned on a straight line connecting line 260. It can be seen.

Referring to FIG. 5, FIG. 5 illustrates that the center point 229 of the middle plan data 245 of the virtual model 230 and the center point 225 of the detector, that is, the center points of the detector plan data do not coincide with each other. The center point 229 of the plan data 245 is moved to the left, which shows that the center point 255 of the central axis is caused by the movement.

In this case, the degree of movement of the middle plan data 245 of the virtual model 230 in the detector plan data may be mathematically calculated, and the center point 229 of the middle plan data is the center point 225 of the detector, that is, This can be known by calculating the number of pixels moved from the center point of the detector plan data 245.

That is, the center point 229 of the middle plan data 245 shown in FIG. 5 is located at (123,128) pixels, and the center point 225 of the detector, that is, the center point of the detector plan data is located at (128,128) pixels. The middle plan data 245 is shifted 5 pixels to the left.

In this case, other detector plan data are compared with the center point 229 of the middle plan data 245 and the center point 225 of the detector in the same manner as described above, and the projection data of the virtual model 230 is moved. If and are moved, the moved value can be calculated.

When reconstructing the detector plan data into a 3D image, the detector plan data may be corrected by moving the projection data 240 of the virtual model 230 to the right by 5 pixels.

In this case, the movement of the central axis of the X-ray imaging apparatus may be corrected using the obtained movement values. There are two methods.

First, a software method of correcting the detector plan data obtained by the X-ray imaging apparatus using the shift values.

That is, each movement value is calculated and stored from the detector plan data, the detector plan data are corrected using the movement values, and then reconstructed to obtain a 3D image.

In this case, the stored movement values may be used to continuously correct the detector plan data by using the hardware before or after the X-ray Citigraphic apparatus is corrected by a hardware correction method described below or once again by software. Can be.

Secondly, there is a hardware method of correcting the central axis movement of the X-ray imaging apparatus using the movement value.

That is, after calculating and obtaining the movement values from the detector plan data obtained by the X-ray Citigraphic apparatus, the X-ray source 210 and the detector 220 of the X-ray Citigraphic apparatus using the movement values themselves. By rearranging the positions of the center axis, the center point of the central axis and the center point 225 of the X-ray source 210 and the detector 220 are positioned on the center connection line 260 which is a straight line.

Accordingly, in the method for correcting the central axis movement of the X-ray Citigraphy apparatus of the present invention, the Citi image of the virtual model is acquired to obtain detector plan data and projection data, the middle plan data is extracted from the detector plan data, and the detector plan data. After obtaining the movement value by comparing the data and the middle plan data, we propose a method of correcting the movement of the central axis of the X-ray imaging apparatus by using the movement value. It is possible to eliminate the cause of not being able to sharpen the 3D image such as the blurring phenomenon caused by the movement or not being located at the correct position.

Although the present invention has been shown and described with reference to preferred embodiments as described above, it is not limited to the above-described embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

1A and 1B are diagrams illustrating a method of obtaining detector plan data of an X-ray Citigraphy apparatus.

2 is a view showing that the center point of the central axis is moved.

3, 4A, 4B, and 5 are diagrams illustrating a method of correcting the movement of the central axis of the X-ray imaging apparatus according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100,200: X-Ray Citigraphy Device 110,210: X-Ray Source

120,220 Detector 130 Object

230: virtual model

Claims (7)

Preparing a virtual model; Positioning a center of the virtual model on the X-ray Citigraphic apparatus by matching a center point of a central axis of the X-ray Citigraphic apparatus; Acquiring a plurality of detector plan data by scanning the virtual model with the X-ray imaging apparatus; Extracting middle plan data of the virtual model from the detector plan data; Comparing a center point of each of the middle plan data of the virtual model with a center point of each detector plan data to obtain a movement value of each of the middle plan data of the virtual model; And And correcting the center point of the central axis of the x-ray city photographing apparatus by using the shift value. The method of claim 1, Correcting the center point of the central axis of the X-ray Citigraphy apparatus using the shift value Storing the obtained movement values, and then correcting the detector plan data obtained by the X-ray Citigraphy apparatus using the stored movement values and reconstructing the obtained motion information to obtain a 3D image. How to compensate for the central axis movement of the Citi shooting device. The method of claim 1, Correcting the center point of the central axis of the X-ray Citigraphy apparatus using the shift value And rearranging positions of sources and detectors of the X-ray Citigraphy apparatus with the obtained movement values. The method according to any one of claims 1 to 3, Extracting middle plan data of the virtual model from the detector plan data extracts data of a row located in the middle of all rows from each of the detector plan data, and extracts the virtual model of the extracted intermediate row data. And extracting the data of the X-ray Citigraphic apparatus. The method of claim 4, wherein The virtual model is a method for correcting the movement of the central axis of the x-ray Citigraphic apparatus, characterized in that the cross section is caused. The method of claim 5, wherein And the virtual model is spherical or cylindrical. The method of claim 6, Aligning the center of the virtual model with the center point of the central axis of the X-ray Citigraphy apparatus and positioning on the X-ray Citi apparatus A method of correcting the movement of the central axis of the X-ray Citigraphy apparatus, wherein the center of the virtual model is matched to the center point of the central axis of the X-ray CIT imaging apparatus using the laser beam provided in the X-ray CIT imaging apparatus. .

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