JPH0746584A - X-ray radiographic equipment - Google Patents

Abstract

PURPOSE:To eliminate contrast caused by distortion by performing address translation for correcting the distortion of an image at an image intensifier. CONSTITUTION:First of all, an inputted video signal is converted to a digital signal by an A/D converter 21, stored in a memory 22 and passed through two conversion tables 23 and 24 later. The first conversion table 23 is provided for address translation, and the address of a new pixel is written in each address to be accessed by the address of a pixel. The next conversion table 24 is provided for gradation conversion, and a converted pixel value is written in an address to be accessed by a pixel value. Then, the digital signal passed through these conversion tables 23 and 24 is returned to an analog signal by a D/A converter 25 and outputted to a CRT display device 15 or an imager 16. At such a time, the distortion of the image is corrected by the conversion table 23 for address translation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray imaging apparatus which is used for general nondestructive inspection or is used for medical image diagnosis and which is a combination of an image intensifier and a TV camera.

[0002]

2. Description of the Related Art In an X-ray photographing apparatus in which an image intensifier and a TV camera are combined, an X-ray emitted from an X-ray tube and passing through a subject is made incident on an incident surface of the image intensifier. The optical image generated on the output surface of the fire is converted into a video signal by a TV camera, and this is sent to a CRT display device for display, or printed by an imager or the like.

In this case, conventionally, image processing such as a histogram flattening method or a histogram expansion method may be performed in order to make it easier to observe an image to be output (displayed or printed out). The histogram flattening method is
The frequency of pixel values is flattened to be the same for all pixel values, and the histogram expansion method expands the dynamic range of pixel values by performing gradation conversion.

[0004]

However, the histogram flattening method has a problem that it takes a long time to process and it is difficult when the matrix size is large when an image must be displayed in real time. According to the method, the contrast of the entire image is emphasized, but there is a problem that the contrast of the part of interest is not always sufficiently obtained. Furthermore, in these, since there is no consideration for the quality of the image obtained by the image intensifier / TV camera, the problem due to the distortion of the image intensifier cannot be solved. That is, due to the distortion of the image intensifier, the contrast is not uniform between the central portion and the peripheral portion of the image, and the information of the X-ray absorption distribution of the subject is not accurately reflected.

In view of the above, the present invention maximizes the information of the X-ray absorption distribution of the object at high speed by correcting the distortion of the image caused by the image receiving system and performing the appropriate gradation conversion. It is an object of the present invention to provide an X-ray imaging apparatus improved so that it can be expressed.

[0006]

In order to achieve the above object, in the X-ray imaging apparatus according to the present invention, the address conversion conversion table is used to perform address conversion for correcting image distortion in the image intensifier. The feature is that each pixel value of the image data is converted into a new pixel value by the gradation conversion conversion table in accordance with the gradation conversion characteristic determined according to the image data after the address conversion. There is.

[0007]

[Function] By performing address conversion for correcting image distortion in the image intensifier,
The contrast generated by this distortion can be eliminated. That is, the original information regarding the X-ray absorption of the subject can be retrieved. Next, in order to express this original X-ray absorption information in a form that can be most easily identified as the contrast of the image, the contrast is partially extended or partially compressed in the gradation conversion conversion table. Performs gradation conversion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. In FIG. 1, an X-ray tube 11 and an image intensifier 12 are arranged to face each other so as to sandwich a subject 10. X-ray tube 11
X-rays are radiated toward the subject 10 from the
The X-rays that have passed through enter the incident surface of the image intensifier 12. Image Intensifier 1
The X-ray image input to 2 is converted into an optical image and output, and the optical image is captured by the TV camera 13 and converted into a video signal. This video signal is passed through an image processing device 14 which performs digital image processing, and then a CRT display device 15
Or to the imager 16 and printed out on film.

The image processing device 14 includes an A / D converter 21.
Memory 22, two conversion tables 23 and 24,
It is composed of a D / A converter 25 and a CPU 26. The input video signal is first converted into a digital signal by the A / D converter 21 and stored in the memory 22.
It goes through two conversion tables 23, 24. These conversion tables 23 and 24 are composed of RAM or the like, and the first conversion table 23 is for address conversion, and a new pixel address is written in each address accessed by the pixel address. The next conversion table 24 is for gradation conversion, and the converted pixel value (density value) is written in the address accessed by the pixel value (density value). Then, the digital signal passed through the conversion tables 23 and 24 is converted back into an analog signal by the D / A converter 25 and output to the CRT display device 15 and the imager 16. The CPU 26 controls writing / reading of the memory 22, control of the conversion tables 23 and 24, and the like.

The image distortion is corrected by the conversion table 23 for address conversion. That is, the incident surface of the image intensifier 12 is a curved surface represented by the hyperbolic rotational symmetry, and is not flat. Therefore, if the image represented by the video signal (X-ray absorption distribution of the subject 10) is treated as represented by the flat XY plane, the image is distorted. That is, the position is extended when the incident surface is more inclined with respect to the direction of the X-ray beam. Therefore, even if X-rays are uniformly input,
The incident intensity per pixel becomes small at the position where the incident surface is inclined, and conversely, the incident intensity becomes maximum at the position where the incident surface is perpendicular to the X-ray beam, resulting in contrast. Therefore, the address is converted from the address on the curved surface to the address on the flat surface to correct this distortion, and the contrast based on this distortion is eliminated.

As shown in FIG. 2, assuming that the X-ray focal point 31 is on the angle θ in the −X direction with respect to the normal line of the incident surface (curved surface) 32 of the image intensifier 12, the following formula 1 is established. .

[Equation 1] Here, (x, y) is a coordinate on the curved surface 32 (that is, represented by a video signal), and (x ′, y ′) is a flat XY.
Represents the coordinates on the surface. Then, since the entrance surface 32 is represented by the rotational symmetry of the hyperbola as described above, the following mathematical formula 2 is provided between x and y.

[Equation 2] Is established. Therefore, it is possible to convert the coordinates from (x, y) to (x ', y') based on these Equations 1 and 2. The CPU 26 performs the calculation for that purpose and controls the conversion table 23 based on the result, so that the address conversion can be performed in the conversion table 23.

Next, the image data passed through the conversion table 23 is sent to the conversion table 24 and gradation conversion as shown in FIG. 3 is performed. Here, the histogram of the image data output from the conversion table 23 is as shown in FIG. 4, and it is assumed that the frequency is low in the areas of pixel values a and d and high in the areas of b and c. in this case,
Since the frequency is low in the areas a and d, it is not difficult to discriminate even if the contrast is compressed. Further, in the areas b and c, the frequency is high and the contrast is so close that it is difficult to discriminate when the state is left as it is. Therefore, the contrast should be extended. Therefore, in the areas b and c of the input data, the distribution is stretched in the contrast direction to reduce the frequency of each pixel value, and conversely, in the areas a and d, the distribution is compressed in the contrast direction to increase the frequency of each pixel value. As a result, the histogram is flattened. This can be realized by decreasing the gradient of the gradation conversion characteristic in the areas a and d and increasing it in the areas b and c. FIG. 3 shows one gradation conversion characteristic according to this, and it is a straight line having a large inclination in the regions b and c, and has a downward convex 2 in the region a.
In the area of the quadratic function, d, the quadratic function is convex upward.

By the gradation conversion by the conversion table 24 as described above, the density difference (difference in X-ray absorption) of the image is expressed to the maximum, and the image can be easily observed.
The CPU 26 sets and controls conversion characteristics in the conversion table 24. That is, the CPU 26 monitors the input data to the conversion table 24, creates a histogram thereof (as shown in FIG. 4), obtains the optimum conversion parameter from the histogram, and sets it in the conversion table 24. When creating the histogram, the noise removal processing may be performed in advance instead of using the input data as it is. As a noise removal processing method, a method in which the frequency is less than a predetermined ratio of the average frequency is determined as noise, or a discontinuous histogram is determined as noise.

[0014]

As described in the above embodiments, according to the X-ray imaging apparatus of the present invention, the image distortion in the image intensifier is corrected, and then the optimum gradation conversion is performed. , It is possible to display or print the information regarding the X-ray absorption of the subject with the contrast that is the most distinguishable. Therefore, for example, in the case of an X-ray medical image, an image with high diagnostic ability can be obtained. Moreover, since only input / output conversion is performed using the conversion table, the speed is high.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining address translation.

FIG. 3 is a graph showing gradation conversion characteristics.

FIG. 4 is a graph showing a histogram.

[Explanation of symbols]

 10 subject 11 X-ray tube 12 image intensifier 13 TV camera 14 image processing device 15 CRT display device 16 imager 21 A / D converter 22 memory 23 address conversion conversion table 24 gradation conversion conversion table 25 D / A conversion Vessel 26 CPU

Claims (1)

[Claims] 1. An X-ray generator, an image intensifier on which X-rays transmitted through an object are incident, a TV camera for converting an optical image output from the image intensifier into a video signal, and the video signal An A / D converter for converting into digital image data, an address conversion conversion table for performing address conversion for correcting image distortion in the image intensifier, and image data after passing through the address conversion conversion table. A gradation conversion conversion table for converting each pixel value into a new pixel value, and gradation conversion characteristics are obtained according to input image data of the gradation conversion conversion table to set the gradation conversion conversion table. X having control means for performing
X-ray equipment.