JP3248238B2 - X-ray imaging device - Google Patents

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, and more particularly to an X-ray imaging apparatus for obtaining an X-ray fluoroscopic image using an X-ray television system.

[0002]

2. Description of the Related Art In an X-ray imaging apparatus for obtaining an X-ray fluoroscopic image using an X-ray television system, a video signal of the X-ray fluoroscopic image is digitized, and image processing is performed to extract a blood vessel image or the like in which a contrast agent is present. Is displayed. A mode called a map mode is mainly performed in a cardiovascular examination in order to display an extracted blood vessel image on a fluoroscopic image so as to facilitate an operator's catheter insertion operation.

In order to extract a blood vessel image, a fluoroscopic image (background image) without a contrast agent is usually obtained in advance, and the background image is subtracted from the fluoroscopic image when the contrast agent is injected into a blood vessel. Perform processing.

Conventionally, in the map mode, an image after such subtraction processing is linearly emphasized, then superimposed on a perspective image, and displayed as a map image.

[0005]

However, there is a problem that the map image obtained by the conventional X-ray imaging apparatus has a poor S / N ratio and is difficult to see, and the catheter operation is difficult. That is, since a fluoroscopic image used for extracting a blood vessel image by the subtraction process uses an image obtained by low-dose X-ray fluoroscopy, the subtraction image has a poor S / N ratio. Conventionally, this subtraction image is emphasized and superimposed on the perspective image,
The noise is also emphasized by the emphasizing process, and the S / N ratio of the finally displayed map image is deteriorated.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to obtain a map image with a good S / N ratio and easy catheter operation by emphasizing only a blood vessel component without emphasizing a noise component when a subtraction image is emphasized. It is an object of the present invention to provide an X-ray imaging apparatus improved as much as possible.

[0007]

In order to achieve the above object, in an X-ray imaging apparatus according to the present invention, there are provided means for obtaining a video signal of an X-ray fluoroscopic image, means for digitizing the video signal, and Subtracting means for obtaining a subtraction image in which the contrast agent portion is displayed as a grayscale in one direction from the median grayscale grayscale by subtracting the digital data in And a gradation conversion unit that has a gradation conversion characteristic that enhances the gradation more than the gradations in the other direction, and that performs gradation conversion of the subtraction image with the gradation conversion characteristic, and a subtraction image that has passed through the gradation conversion unit. And a means for converting the image data after the superimposition into an analog signal.

[0008]

A video signal of an X-ray fluoroscopic image is digitized and a subtraction image is obtained by performing a subtraction between frames. In this subtraction image,
The contrast agent portion is displayed as a gradation on one side (for example, a black side) from the median gray scale gradation. This subtraction image is subjected to gradation conversion. The gradation conversion characteristic is such that the gradation on one side (for example, black side) from the median value is more than the gradation on the median value and the other side (white side). It has to be emphasized. Therefore, by this gradation conversion,
It is possible to emphasize only the blood vessel component without emphasizing the noise component. By superimposing the subtraction image after such gradation conversion and the perspective image, a map image with a good S / N ratio can be obtained.

[0009]

An embodiment of the present invention will be described below in detail with reference to the drawings. In FIG. 1, a high voltage is supplied from a high voltage generator 11 to an X-ray tube 12, and X-rays are emitted from the X-ray tube 12 toward a subject 13. The X-ray transmitted through the subject 13 is an image intensifier 14
And the X-ray image is converted into a visible light image, and the TV camera 15 and the camera control unit 16
A video signal of a fluoroscopic image is obtained. This video signal is sent to the digital image processing device 20 and subjected to image processing, and then sent to an image monitor (not shown) for display.

The digital image processing apparatus 20 includes an A / D converter 21, a switch 22, and arithmetic units 23, 24, 25, and 2.
8, frame memory 26, gradation converter 27, D /
An A converter 29 is controlled by a CPU 31 having an input device 32 such as a keyboard device.

When the operator operates the input device 32 to input the start of the map mode, the switch 22 is switched to the side a. At the same time, the operator steps on a foot switch (not shown), X-ray irradiation is started, X-ray fluoroscopy is started, and video signals are input to the digital image processing device 20. Thereafter, the operator injects a contrast agent into the subject 13.

A video signal is first converted into a digital signal by an A / D converter 21 and a switch 22 on the a side is provided.
Are sent to computing units 23 and 24 through The computing unit 23 performs a black peak hold operation by comparing the sent image data for each frame and selecting data indicating that the image is blacker. Also,
On the other hand, the computing unit 24 performs a white peak hold operation by comparing the transmitted image data for each frame and selecting data representing whiter.

The black peak hold image obtained by the arithmetic unit 23 and the white peak hold image obtained by the arithmetic unit 24 are sent to the arithmetic unit 25, where the two are subtracted. The black peak hold image is an image in which blood vessels appear because the image is a superimposed contrast agent portion, while the white peak hold image is an image in which the contrast agent portion is ignored, and represents only the background. It is an image. Therefore, when these are subtracted, an image of only the contrast agent portion from which the background image has been removed, that is, an image of only blood vessels is extracted. At this time, the most significant bit of the data representing the density (gray scale) of each pixel of the subtraction image is inverted, and the portion that becomes 0 by subtraction is set to be the median value (halftone) of the gray scale gradation. That is, at the stage where the white peak hold image is subtracted from the black peak hold image, some take a negative pixel value. Then, the negative pixel represents the contrast agent portion. Therefore, by setting the pixel value 0 of the image after the subtraction as the median value, the contrast agent portion (blood vessel portion) can be displayed as a black gradation from the median value.

This peak hold subtraction operation is repeated until the contrast agent flows away from the blood vessel at the site of interest, and the finally obtained peak hold subtraction image is stored in the frame memory 26. Then, at this time, the switch 22 is switched to the b side.

Then, a video signal (digital data of) an X-ray fluoroscopic image in the absence of a contrast agent is sent to one input of the arithmetic unit 28. The other input is
A peak hold subtraction image read from the frame memory 26 and passed through the gradation converter 27 is sent. This gradation converter 27 is a look-up table having an input / output conversion table as shown in FIG. 2. The peak hold subtraction image is subjected to gradation conversion in accordance with this table so that the blood vessel portion (input black side) is emphasized. At the same time, the blood vessel portion is inverted so that the blood vessel portion is displayed in white.

The vicinity of the halftone on the input side of the tone converter 27 is a place where the value becomes zero due to the subtraction as described above, and is a noise component. Therefore, if tone conversion is performed in accordance with a conversion characteristic curve that is convex downward on the black side from halftone, only the blood vessel portion can be enhanced without enhancing the noise component. In this embodiment, by operating the input device 32, the conversion characteristic curve shown in FIG. 2 is changed as shown by a dotted line so that the degree of emphasis can be adjusted.

The peak hold subtraction image that has passed through the gradation converter 27 is returned to the original state by the arithmetic unit 28 even after the most significant bit of the data representing the density of each pixel is inverted again, and then X-ray fluoroscopy is performed. Added to the image. Therefore, an image is obtained in which the image in which the blood vessel portion is emphasized white is superimposed on the background image, which is converted back to an analog signal by the D / A converter 29 and output to an image monitor (not shown) to display a map image. Is made.

In this embodiment, the most significant bit of the data representing the density of each pixel of the peak hold subtraction image is inverted and then subjected to gradation conversion. After the gradation conversion, the most significant bit is again inverted. The difference between the black peak hold image and the white peak hold image causes discontinuity of the data in the background, but avoids the problem of data discontinuity due to the subtraction. To do that.

In the above embodiment, the subtraction is performed between the black peak hold image and the white peak hold image. However, it is sufficient that the image of the contrast agent portion can be extracted. Subtraction with an image when it does not exist may be performed.

[0020]

As described above, according to the X-ray imaging apparatus of the present invention, when the subtraction image from which the contrast agent image (blood vessel image) is extracted is emphasized, the contrast agent image is gray scale in the subtraction image. Paying attention to the fact that the gradation is displayed as a gradation in one direction from the median of the gradation, the gradation in one direction from the median is emphasized more than the gradation in the median and the other direction. Therefore, it is possible to enhance only the contrast agent image (blood vessel image) without enhancing the noise component,
By superimposing this on a perspective image, a map image with a good S / N ratio can be obtained. Therefore, by observing the map image, the operator can easily perform the operation of inserting the catheter into the blood vessel.

[Brief description of the drawings]

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

FIG. 2 is a graph showing characteristics of the gradation converter according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 High voltage generator 12 X-ray tube 13 Subject 14 Image intensifier 15 TV camera 16 Camera control unit 20 Digital image processing device 21 A / D converter 22 Switching device 23-25, 28 Arithmetic unit 26 Frame memory 27 Gradation Converter 29 D / A converter 31 CPU 32 Input device

Claims (1)

(57) [Claims] 1. A means for obtaining a video signal of a fluoroscopic image,
Means for digitizing the video signal, and subtraction means for subtracting digital data between frames to obtain a subtraction image in which the contrast agent portion is displayed as a grayscale in one direction from the median of grayscale grayscales, A gradation conversion characteristic for enhancing the gradation in the one direction compared to the median value and the gradation in the other direction, and performing gradation conversion of the subtraction image with the gradation conversion characteristic. An X-ray imaging apparatus comprising: means, means for superimposing a subtraction image having passed through the gradation conversion means on a perspective image, and means for converting the superimposed image data into an analog signal.