JP3360440B2 - Digital X-ray equipment - 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 for obtaining a video signal of an X-ray transmission image, and more particularly to a digital X-ray imaging apparatus for digitizing a video signal and performing various processes.

[0002]

2. Description of the Related Art Conventionally, X-rays have been projected from an X-ray tube toward a subject.
The X-ray transmitted through the subject is incident on an X-ray image intensifier, and an X-ray TV camera is coupled to the X-ray image intensifier to obtain a video signal of an X-ray transmission image. 2. Description of the Related Art A fluoroscopic image is displayed on a TV monitor or the like to be used for medical diagnosis. In a digital X-ray imaging apparatus, this video signal is digitized and recorded, and various processes are performed, or the video signal is converted back to an analog video signal and displayed on a TV monitor or the like.

Normally, this digital X-ray apparatus has an automatic gradation processing function, and detects the maximum value and the minimum value of one digitized image data (pixel value data). Then, gradation conversion is performed so that pixel values within the range between the maximum value and the minimum value are developed from 0% to 100% (from black level to white level) of the display gradation.

[0004]

However, in the conventional digital X-ray imaging apparatus, there is a problem that the display image may be difficult to see depending on the observation site due to the automatic gradation processing function. That is, since the gradation conversion characteristic changes in accordance with the maximum value and the minimum value of the image data for each of a large number of images sequentially obtained for each frame, the display gradation changes for each frame, This makes the screen flicker, making it hard to see.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a digital X-ray imaging apparatus in which the flickering of a displayed image is eliminated and the automatic gradation processing function is improved so that the displayed image can be easily viewed. I do.

[0006]

In order to achieve the above object, in a digital X-ray imaging apparatus according to the present invention,
X-ray generation means for irradiating the subject with X-rays, X-ray imaging means for receiving X-rays transmitted through the subject to obtain a video signal of an X-ray transmission image, and X-rays incident on the X-ray imaging means
X-ray control means for controlling the X-ray conditions in the X-ray generation means in accordance with the intensity of the rays, A / D conversion means for converting the video signal into a digital signal, and conversion of the gradation of the digital video signal Means for detecting the maximum value and the minimum value of each of the digital video signals in each image, means for detecting a temporal change in the X-ray condition, A gradation conversion control unit for controlling a gradation conversion characteristic of the gradation conversion unit according to the detected maximum value and minimum value when a change in the condition is larger than a predetermined change width. It has become.

In the above-mentioned gradation conversion control means, it is possible to arbitrarily set the detection value of the change width of the X-ray condition.

[0008] Further, a time interval for detecting a change in X-ray conditions can be varied.

Further, the detection of the maximum value and the minimum value of the digital video signal may be performed in an arbitrary area within one image.

[0010]

In a digital X-ray imaging apparatus, the X-ray conditions in the X-ray generation means are usually changed according to the intensity of the X-rays incident on the X-ray imaging means, whereby the luminance of the video signal is kept constant. Automatic brightness adjustment function is provided.
If the X-ray condition does not change much, it is a result of the fact that the luminance of the video signal has not changed much, and in such a case, it is meaningless to change the gradation conversion characteristic. Therefore, if the change in the X-ray condition is smaller than the predetermined change width, the change in the gradation conversion characteristic according to the detected maximum value and the minimum value is substantially stopped, so that the unnecessary gradation conversion characteristic is not used. Can be avoided, and flickering of the displayed image can be eliminated.

If it is possible to arbitrarily set the detection value of the change width of the X-ray condition, the gradation conversion characteristic is changed only when there is a change of a desired size arbitrarily determined according to the imaging region and the situation. Can be changed.

Further, by making the time interval for detecting a change in the X-ray condition variable, the gradation conversion characteristic can be changed only when the changed state continues for a certain period of time.

Further, if the detection of the maximum value and the minimum value of the digital video signal is performed in an arbitrary area within one image, the change following only the change in the desired area of interest is followed, and other unnecessary areas can be detected. The gradation conversion characteristic can be changed without following the change in the area. Therefore, although there is no change in the region of interest, there is a problem that the entire gradation conversion characteristic changes according to the change in the other region and the display image of the region of interest flickers. Disappears.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, an X-ray tube 11 irradiates an X-ray to a subject 10 so that the X-rays passing through the subject 10 enter an X-ray image intensifier 12. An optical image corresponding to the X-ray transmission image is output from the X-ray image intensifier 12, and the optical image is sent to an X-ray TV camera 14 via an optical system 13, and the X-ray TV camera 14
Thus, a video signal representing an X-ray transmission image is obtained.

The X-ray tube 11 generates X-rays by electric power (X-ray high voltage or filament current) supplied from the X-ray controller 16. X-ray conditions such as the X-ray high voltage and the filament current (tube voltage and tube current) are controlled by the X-ray controller 16. By controlling these X-ray conditions (specifically, usually a tube voltage) according to the output of the photomultiplier 15 inserted into the optical system 13, the brightness of the video signal from the X-ray TV camera 14 is reduced. Be kept constant. That is, since the output of the X-ray image intensifier 12 corresponds to the input (the intensity of the X-ray transmitted through the subject 10 and incident on the X-ray image intensifier 12), the output of the photomultiplier 15 is output. By controlling the X-ray conditions accordingly, the intensity of the X-rays that pass through the subject 10 and enter the X-ray image intensifier 12 is kept constant, thereby reducing the luminance of the video signal from the X-ray TV camera 14. Can be kept constant.

Note that such an automatic brightness adjustment function is provided by X
It can also be realized by a configuration in which a video signal from the line TV camera 14 is taken into the X-ray controller 16 and fed back to the X-ray conditions. In that case, the photomultiplier 15 becomes unnecessary. In these automatic brightness adjustment functions, the X-ray image intensifier 12 is transmitted through the subject 10.
The signal detected as corresponding to the intensity of the X-ray incident on the screen may be an average value of the entire screen, or may be an average value of a predetermined central area of the screen.

A video signal obtained from the X-ray TV camera 14 is converted by an A / D converter 21 into digital image data. This image data passes through a look-up table 22, is further sent to a D / A converter 23, is returned to an analog video signal, and is sent to a TV monitor device 24 for display. The look-up table 22 functions as a tone converter composed of a kind of input / output converter, which functions as a tone converter that converts input image data (pixel values) into values suitable for display and outputs the converted values. . Its conversion characteristics (input / output characteristics)
As shown in FIG. 2, a width (window) W of an input is developed from 0% to 100% of an output (from a black level to a white level of a display image). The gradation conversion characteristic is represented by a window W and its center C. The look-up table 22 is a kind of input / output converter, and is usually constituted by a RAM or the like. An address of the RAM is designated by an input value, and an output value corresponding to the input value is written to each address. An arbitrary conversion characteristic can be obtained by changing the value written to each address.

The digital image data output from the A / D converter 21 is divided into a maximum value detection circuit 31 and a minimum value detection circuit 3.
2 and the maximum value and the minimum value in one image are detected and sent to the control circuit 33.

On the other hand, a signal representing an X-ray condition (for example, a tube voltage) is taken out from the X-ray controller 16, converted into a digital signal by an A / D converter 35, and input to a change width detection circuit 36. . The variation width detection circuit 36 detects the variation width (deviation) of the X-ray condition over time, and data representing the variation width is sent to the control circuit 33.

When the change width of the X-ray condition is larger than a predetermined value, the control circuit 33 calculates the window W and the center C from the maximum value and the minimum value input at that time, and calculates those values. The value is set in the look-up table 22 (a value is written to each address of the RAM configuring the look-up table 22). When the change width of the X-ray condition is smaller than a predetermined value, the value of the previous window W and the center C or a value close thereto is output to the lookup table 22.

An input device 34 such as a keyboard is connected to the control circuit 33. The input device 34 allows input of a detection value of a change width of X-ray conditions, a detection time interval, and the like. . Regarding the control of the detection time interval of the change width of the X-ray condition, for example, the change width detection circuit 36 always captures the change at a fixed time interval (for example, 1/30 second interval), and the control circuit 33 controls the change at the set time interval. , Or the control circuit 33 controls the sampling timing itself in the change width detection circuit 36 in accordance with the input time interval.

The X-ray conditions (for example, the tube voltage) change as shown in FIG. 3 by the above-described automatic brightness adjustment function. That is, when the power is turned on, the X-ray condition quickly rises with time and converges to condition A after hunting several times. In the case where the imaging region is changed or the subject 10 moves greatly, the hunting is performed in the same manner, and the other conditions B
Converges to. If the detected value of the change width of the X-ray condition is set to P in FIG. 3, the gradation conversion characteristic does not substantially change due to the fluctuation due to the transient hunting or the like. Therefore, it is possible to prevent the screen from flickering due to the unnecessary and frequently changing gradation conversion characteristics.

FIG. 4 shows an example of a display image seen in the positioning performed in abdominal angiography in actual clinical practice. The display image includes a blood vessel image 41 and a spine image 4
2. The lung field image 43 and the like appear. The portion of the lung field image 43 has a high X-ray intensity and a considerably high luminance of the video signal. The part of the lung field image 43 may or may not enter the screen due to the respiration of the subject (patient). Therefore, if the gradation conversion characteristic is changed according to the detected maximum value and minimum value, the gradation conversion characteristic will change according to the respiratory movement. However, even in such a case, the X-ray condition hardly changes depending on the above-described automatic brightness adjustment function, and the change width of the X-ray condition falls within the detection value P. Therefore, since the control circuit 33 does not change the gradation conversion characteristic according to the maximum value and the minimum value detected at that time, the gradation conversion characteristic does not substantially change.
It is possible to display a stable contrast image without flickering on the screen.

Since the input device 34 can arbitrarily set the detection value of the change width of the X-ray condition, it is possible to suppress the change in the gradation conversion characteristic according to the preference of the observer, the imaging region, and the like. In addition, since the time interval for capturing the change width of the X-ray condition can be arbitrarily input by the input device 34, the desired time response of the automatic gradation processing can be obtained. That is, when the change in the X-ray condition does not continue for a desired time or longer, the flicker on the screen is suppressed by not changing the gradation conversion characteristic.

The detection of the maximum value and the minimum value may be performed not for the whole area of one screen but for a specific area of one screen. In that case, an area detection circuit 37 is inserted before the maximum value detection circuit 31 and the minimum value detection circuit 32 as shown by a dotted line. Then, the gradation conversion characteristic can be changed only when the maximum value and the minimum value of the image data change within the desired region of interest. That is, even if the maximum value or the minimum value changes in a region other than the region of interest, if they do not change in the region of interest, the gradation conversion characteristics do not change. be able to. That is, although there is no change in the region of interest, there is no inconvenience that the entire gradation conversion characteristic changes according to the change in the other region and the display image of the region of interest flickers. .

[0026]

As described above, according to the digital X-ray imaging apparatus of the present invention, it is possible to suppress the flickering of the screen due to the unnecessary change of the gradation conversion characteristic by the automatic gradation processing. Thus, an image which is easy to see for a doctor or the like can always be obtained.

[Brief description of the drawings]

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

FIG. 2 is a graph showing gradation conversion characteristics.

FIG. 3 is a time chart showing a temporal change in X-ray conditions (X-ray tube voltage).

FIG. 4 is a diagram showing an example of a display image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Subject 11 X-ray tube 12 X-ray image intensifier 13 Optical system 14 X-ray TV camera 15 Photomultiplier 16 X-ray controller 21, 35 A / D converter 22 Look-up table 23 D / A converter 24 TV Monitor device 31 Maximum value detection circuit 32 Minimum value detection circuit 33 Control circuit 34 Input device 36 Change width detection circuit 37 Area detection circuit 41 Blood vessel image 42 Spine image 43 Lung field image

Claims (1)

(57) [Claims] An X-ray generating means for irradiating an X-ray toward a subject, an X-ray imaging means for receiving an X-ray transmitted through the subject to obtain a video signal of an X-ray transmission image, and the X-ray imaging X-ray control means for controlling X-ray conditions in the X-ray generation means according to the intensity of X-rays incident on the means, A / D conversion means for converting the video signal into a digital signal, and the digital video signal Means for converting the gradation of the digital video signal, means for detecting the maximum value and the minimum value of the digital video signal in each image, and means for detecting the temporal change in the X-ray condition And gradation conversion control means for controlling the gradation conversion characteristics of the gradation conversion means according to the detected maximum value and minimum value when the change in the X-ray condition is larger than a predetermined change width. Digital X characterized by having
X-ray equipment.