JP3326885B2 - X-ray television equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical X-ray television apparatus.

[0002]

2. Description of the Related Art An X-ray television apparatus converts an X-ray transmission image into an image signal using an image intensifier and a television camera, sends the image signal to a television monitor, and displays an X-ray fluoroscopic image. However, in order to make the displayed image easy to see, a recursive filter circuit is often provided.

This recursive filter circuit reduces noise by adding a kind of afterimage effect by adding image signals in the time direction, and converts image data input as that of the current frame (m-th frame) to Am. Bm-1 is the image data output as one frame before (m-1 th frame), and k is the recursive filter coefficient.
By calculating Bm = (1 / k) Am + {1- (1 / k)} Bm-1, image data Bm output as that of the current frame is obtained. As a specific circuit, an LUT (lookup table; a kind of input / output conversion) represented by a linear function (of an input signal) having a slope of 1 / k (where k ≧ 1) is used to convert the image data of the current frame. LUT represented by a linear function having a gradient of {1- (1 / k)}, holding only one frame of image data output as a result of passing the image data and that of the immediately preceding frame. Are added.

In this recursive filter circuit, as can be seen from the above equation, when the coefficient k is increased, the ratio of the image data of the past frame is increased as compared with the image data of the current frame. Although the effect is enhanced, blurring and blurring of the image become noticeable when the image has motion. Therefore, conventionally, image data between frames is compared, a portion having a large difference is determined to be a moving portion, and an image signal of a current frame that does not pass through a recursive filter circuit is used as a pixel signal of the portion, The pixel signal of the part where the difference is small and it is determined that there is no motion is configured to pass through a recursive filter circuit.

[0005]

However, the conventional recursive filter circuit causes a problem particularly in an area where the input image signal is small. That is, there is a difference in the X-ray quantum density between the low-brightness region and the high-brightness region of the image. As a result, even in a stationary portion, the amplitude of the noise constantly changes. This noise is caught and determined to be a portion having a large motion, and an image signal that does not pass through the recursive filter circuit is output. Therefore, in the low-luminance region, even if the portion is a static portion, an image signal that does not pass through the recursive filter circuit is displayed, so that only a rough and hard-to-view image is displayed.

It seems that this inconvenience can be solved by increasing the recursive filter coefficient or increasing the threshold value of the motion detection. However, in this case, even in the case of a moving object, the time direction of the image signal is reduced. Since the afterimage effect due to the integration is added, a problem occurs that the image is blurred and displayed. For this reason, for example, only images that are not useful for actual clinical image diagnosis, such as not being able to capture the movement of the catheter, can be obtained.

SUMMARY OF THE INVENTION In view of the above, the present invention makes it possible to correctly recognize a low-luminance area of an image as a stationary part if it is stationary while avoiding a moving object from being blurred. It is an object of the present invention to provide an X-ray television device in which an image can be displayed with an improved N ratio.

[0008]

In order to achieve the above object, in an X-ray television apparatus according to the present invention, a coefficient of a recursive filter circuit for processing an X-ray image signal is changed according to an input value thereof. The coefficient increases as the input value decreases, and the recursive filter effect increases, and the output of the recursive filter circuit is compared with the image signal of the current frame. When the difference is greater than a predetermined value, an image signal of the current frame is output, and display is performed using this image signal.

[0009]

When the signal value is small in the low luminance area, the recursive filter effect increases, the noise amplitude is compressed, and the S / N ratio increases. Therefore, it is possible to avoid that this area is recognized as a moving part due to the noise. Therefore, a stationary low-luminance area is correctly recognized as a part having no motion, and the area is displayed as a smooth image with an increased S / N ratio by a recursive filter circuit.

[0010]

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, X
X-rays are radiated from the X-ray tube 1 toward the subject 2, and the X-rays transmitted through the subject 2 are transmitted through an image intensifier 3.
Incident on. In the image intensifier 3, the X-ray image is converted into a visible light image and output while being multiplied. This visible image enters the television camera 5 via the optical system 4, and a video signal is obtained via the camera control unit 6. The video signal is sent to the television monitor 8 via the digital image processing device 7, and an X-ray transmission image is displayed on the screen of the television monitor 8.

The digital image processing device 7 includes an A / D converter 71 and a recursive filter circuit 72.
The recursive filter circuit 72 includes LUTs 73 and 74, an adder 75, and a frame memory 76.

When a video signal from the camera control unit 6 is sent to the digital image processing device 7 one screen at a time (one frame at a time), the video signal is first converted into a digital signal by an A / D converter 71 and then recursively filtered. Circuit 7
Sent to 2. In the recursive filter circuit 72, A /
The digital image signal of the current frame sent from the D converter 71 is input / output converted by the LUT 73 and
5 is input. The digital image signal output from the adder 75 one frame before is stored in the frame memory 76. The digital image signal is input / output converted by the LUT 74 and sent to the adder 75. The digital image signal for the current frame output from the adder 75 is stored in the frame memory 76.

When the digital image signal is output from the A / D converter 71 one frame at a time, the frame memory 7
6 is the 1 frame output from the adder 75 one frame before.
Since the digital image signal of the frame is stored, the digital image signal of this frame and the digital image signal of the current frame are input / output converted by the LUTs 74 and 73 as described above.
The sum is added by the adder 75 and stored in the frame memory 76 again. Since this operation is repeated for each frame, the adder 75 outputs a digital image signal obtained by adding the image components of the past several frames immediately before stored in the memory 76 to the image signal of the current frame. ,
An afterimage effect is provided.

Here, the input / output conversion characteristics of the LUT 73 are as follows:
1 for input (i) with constant slope (1 / k)
Instead of the following function, the function includes a function f (i) having a higher order, i.e., the smaller the value of i is, the smaller the value of i is, and the larger the value of i is, the larger the value becomes. It is as shown in FIG. Conversely, the input / output conversion characteristics of the LUT 74 are shown in FIG.
The larger the input (i), the larger the
The larger the value of i, the smaller the value. That is, i is simply a constant gradient {1- (1 / k)}.
Is not a linear function, but a function g (i) of a high order having the above characteristics. However, since the signals passed through the LUTs 73 and 74 are added by the adder 75, the output after the addition needs to be "1". In other words, in other words, instead of using the coefficient k as a constant, it can be said that k may be a function for i, which changes in accordance with i, such that i becomes larger as i becomes smaller and becomes smaller as i becomes larger.

Therefore, in a region where the image signal is small, the degree of the inclusion of the signal of the past frame becomes larger than the signal of the current frame, and the afterimage effect becomes large.
In a region where the image signal is large, the degree of inclusion of the signal of the past frame is smaller than the signal of the current frame, and the afterimage effect is further reduced. As a result, the lower the luminance of the image, the lower the S / N ratio, that is, the larger the noise, the more the afterimage effect is given and the noise is reduced.

The output of the adder 75 is sent to a subtractor 77, which subtracts it from the signal of the current frame, which is the output of the A / D converter 71, and then passes through the LUT 78. The LUT 78 has an input / output conversion characteristic as shown in FIG. 2C. No input is passed below a certain threshold, and an input above a second threshold higher than that is output as it is. As a result, the continuity of the output is obtained for an input between the two threshold values. The output of the LUT 78 is added to the adder 7
9 and is added to the output from the adder 75.

Therefore, when the output of the subtractor 77 is large,
Since this is output from the LUT 78 as it is, the output of the adder 75 is canceled by the subtraction in the subtractor 77 and the addition in the adder 79. That is,
The image signal of the current frame is output from the adder 79 as it is, not the output through the recursive filter circuit 72.

On the other hand, when the output of the subtracter 77 is small, the output of the LUT 78 is 0, and the output of the recursive filter circuit 72 is output from the adder 79 as it is.

If the image signal input to the digital image processing apparatus 7 does not change over several frames, the signal passed through the recursive filter circuit 72 and the signal of the current frame are almost the same. When the image signal changes, the difference between the signal that has passed through the recursive filter circuit 72 and the signal of the current frame occurs, so that the output of the subtracter 77 becomes large. That is, the output of the subtractor 77 indicates whether the motion is large, and the subtracter 77 functions as a motion detector. The LUT 78 determines whether the movement is large. When the motion is small, only the signal that has passed through the recursive filter circuit 72 is used to increase the afterimage effect and improve the S / N ratio of the image. In this case, since the motion is small, no image blur occurs even if the afterimage effect increases. When the movement is large, the signal passing through the recursive filter circuit 72 is added to the adder 7.
9, the adder 79 outputs the image signal of the current frame as it is, thereby preventing image blurring. Since the operation according to the motion detection is performed for each pixel, an afterimage effect is applied to a still portion in an image, and no afterimage effect is applied to a moving portion.

The recursive filter circuit 72
Gives a more afterimage effect in the low-luminance region as described above,
Since the / N ratio is improved, it is possible to avoid the disadvantage that the output of the subtractor 77 becomes large due to noise in the low luminance region, and that there is motion in the low luminance region. That is, the stationary part is detected as a stationary part even if the part is a low luminance area, and the part is detected as a recursive filter circuit 7.
After passing through 2, the adder 79 outputs an image signal with an improved S / N ratio.

The digital image signal output from the adder 79 is converted into an analog signal by the D / A converter 80 and then sent to the television monitor 8 for display.

Therefore, for example, as shown in FIG.
A line image is displayed. In FIG. 3, 31 is a spinal cord,
32 indicates a myocardium, 33 indicates a diaphragm, and 34 indicates an inserted catheter. The myocardium 32 and catheter 34 are assumed to be moving. Normally, the X-ray apparatus has an automatic brightness adjustment function, and is controlled so that the brightness at the center of an image is constant. Therefore, the periphery of the spinal cord 31 and the diaphragm 33 are in a low-luminance area, but the recursive filter circuit 72 acts to add a residual image effect and compress the noise amplitude. Therefore, this part is not detected as a part moving due to noise, and is displayed as an image whose S / N ratio has been improved by the recursive filter circuit 72. On the other hand, the moving diaphragm 33 or the catheter 34
Since the motion is detected, an image that does not pass through the recursive filter circuit 72 is displayed, and the image clearly shows the motion.

The above-mentioned input / output conversion characteristics of the LUTs 73, 74, 78 are merely examples, and can be freely changed as long as the above basic conditions are satisfied.

[0024]

As described above, according to the X-ray television apparatus of the present invention, a stationary low-luminance area is correctly recognized as a part having no motion, and the area is subjected to S / N by a recursive filter circuit. It is displayed as a smooth image with an increased ratio. Therefore, the S / N of the entire image
The ratio becomes uniform. The moving part is clearly displayed as the moving part.

[Brief description of the drawings]

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

FIG. 2 is a graph showing input / output conversion characteristics of an LUT.

FIG. 3 is a diagram showing a displayed image.

[Explanation of symbols]

 Reference Signs List 1 X-ray tube 2 Subject 3 Image intensifier 4 Optical system 5 TV camera 6 Camera control unit 7 Digital image processing device 71 A / D converter 72 Recursive filter circuit 73, 74, 78 LUT 75, 79 Adder 76 Frame memory 77 subtractor 80 D / A converter 8 television monitor

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/321 A61B 6/00

Claims (1)

(57) [Claims] 1. An X-ray irradiating means for irradiating an X-ray to a subject, an imaging means for obtaining an image signal representing an image of the X-ray transmitted through the subject, and a recursive filter coefficient to which the image signal is inputted is inputted. The recursive filter means, which changes according to the input value and the coefficient increases as the input value decreases, compares the output of the recursive filter means with the image signal of the current frame. Means for outputting an output of the filter means and outputting an image signal of the current frame when the difference is larger than a predetermined value, and image display means to which the output image signal is sent. X-ray television device.