JPH0787394A - X-ray television apparatus - Google Patents

Abstract

PURPOSE:To display a moving object while preventing the object from being displayed as being shaked and improving the S/N of a low luminance area standing still. CONSTITUTION:A recursive filter circuit 72 is constituted of LUTs 73, 71, an adder 75, and a frame memory 76. The input/output conversion characteristic of the LUT 73 is made a value obtained by adding a function f(i) suppressed in an area where input (i) is small to (i/k). Then, the input/output conversion characteristic of the LUT 74 is made the value obtained by adding the function g(i) suppressed in the area where the input (i) is large to (1-(1/k)).

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 by using an image intensifier and a television camera and sends it to a television monitor apparatus to display an X-ray fluoroscopic image. However, a recursive filter circuit is often provided in order to make the displayed image easy to see.

The recursive filter circuit adds a kind of afterimage effect by time-wise addition of image signals to reduce noise. The image data input as the current frame (m-th frame) is Am. The image data output as one frame before (m-1th frame) is Bm-1, and the recursive filter coefficient is k.
Then, Bm = (1 / k) Am + {1- (1 / k)} Bm-1 is calculated to obtain the image data Bm output as that of the current frame. As a concrete circuit, the image data of the current frame is represented by a LUT (look-up table; a kind of input / output conversion) represented by a linear function (of the input signal) having a slope of 1 / k (where k ≧ 1). LUT represented by a linear function having a slope of {1- (1 / k)}, which holds only one frame of image data output as one of the previous frame Is added to the one passed.

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 to the image data of the current frame is increased, and the noise removal by the time direction integration is performed. Although the effect is enhanced, the blurring / blurring of the image becomes noticeable when the image has movement. Therefore, conventionally, image data between frames is compared, a part where the difference is large is determined to be a moving part, and the image signal of the current frame that does not pass through the recursive filter circuit is used as the pixel signal of that part. The signal of the pixel in the portion where the difference is small and there is no movement is configured to pass through the recursive filter circuit.

[0005]

However, the conventional recursive filter circuit has a problem especially in a region where the input image signal is small. That is, there is a difference in the X-ray quantum density between the low-brightness area and the high-brightness area of the image, and therefore the S / N ratio is inevitably worse in the low-brightness area. As a result, the amplitude of noise constantly changes even in a stationary portion, and this noise is captured, it is determined that the portion has a large movement, and an image signal that does not pass through the recursive filter circuit is output. Therefore, in the low-brightness 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-see image is displayed.

This inconvenience seems to be solved by increasing the recursive filter coefficient or increasing the threshold value for motion detection. Then, even in the case of a moving object, the time direction of the image signal will be corrected. Since the afterimage effect due to the integration is added, the problem that the image is blurred is displayed. Therefore, for example, only an image that is not useful for actual image diagnosis such as the movement of the catheter cannot be obtained can be obtained.

In view of the above, the present invention makes it possible to correctly recognize a low-luminance area of an image as a stationary portion if it is stationary, while avoiding a moving object being displayed in a blurred manner, and S / It is an object of the present invention to provide an X-ray television device improved so that the N ratio can be improved for display.

[0008]

To achieve the above object, in an X-ray television apparatus according to the present invention, the coefficient of a recursive filter circuit for processing an X-ray image signal is changed according to its input value. The smaller the input value, the larger the coefficient and the greater the recursive filter effect.The output of this recursive filter circuit is compared with the image signal of the current frame, and when the difference is less than a predetermined value, the recursive filter circuit It is characterized in that an output is output, and when the difference is larger than a predetermined value, the image signal of the current frame is output and the display is performed by this image signal.

[0009]

When the signal value is small in the low luminance region, the recursive filter effect is increased, the noise amplitude is compressed, and the S / N ratio is increased. Therefore, it is possible to avoid recognizing this region as a moving part due to the noise. Therefore, the static low-luminance region is correctly recognized as a non-moving portion, and the region is displayed as a smooth image with a high S / N ratio by the recursive filter circuit.

[0010]

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, X
X-rays are irradiated from the radiation tube 1 toward the subject 2, and the X-rays transmitted through the subject 2 are image intensifiers 3.
Incident on. In the image intensifier 3, the X-ray image is converted into a visible light image and outputted 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. This video signal is sent to the television monitor device 8 via the digital image processing device 7, and an X-ray transmission image is displayed on the screen of the television monitor device 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 the video signal from the camera control unit 6 is sent to the digital image processing device 7 screen by screen (frame by frame), it is first converted into a digital signal by the A / D converter 71 and then a recursive filter. 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 added by the adder 7.
Input to 5. The frame memory 76 stores the digital image signal output from the adder 75 one frame before, and this digital image signal is input / output converted by the LUT 74 and then 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 digital image signals are sequentially output from the A / D converter 71 frame by frame, the frame memory 7
1 is output from the adder 75 one frame before 6
Since the digital image signal of the frame is stored, this and the digital image signal of this one frame are input / output converted by the LUTs 74 and 73 as described above, and then,
The sum is added by the adder 75 and the result is stored again in the frame memory 76. Since this operation is repeated for each frame, the adder 75 outputs a digital image signal obtained by adding the image components of the previous several frames stored in the memory 76 to the image signal of the current frame. ,
Afterimage effect will be added.

The input / output conversion characteristics of the LUT 73 are as follows.
1 for input (i) with constant slope (1 / k)
It is not a quadratic function, but includes a function f (i) having a high degree that it becomes smaller as i becomes smaller and becomes larger than i as it becomes larger. It is as shown in A of FIG. On the contrary, the input / output conversion characteristic of the LUT 74 is B in FIG.
The smaller the input (i), the larger
The larger i is, the smaller it is. That is, simply, a constant slope {1- (1 / k)} i
The function g (i) having a high degree having the above-described characteristics is included instead of the linear function with respect to. 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, a function with respect to i that changes depending on i such that the smaller i is and the larger i is, may be used.

Therefore, in the area where the image signal is small, the degree of inclusion of the signal of the past frame is larger than that of the signal of the current frame, and the afterimage effect is increased, and conversely,
In the area where the image signal is large, the degree of inclusion of the signal of the past frame is smaller than that of the signal of the current frame, and the afterimage effect is reduced. As a result, the lower the luminance region of the image, which has a low S / N ratio, that is, the noise is relatively large, the more the afterimage effect is imparted and the noise is reduced.

The output of the adder 75 is sent to the 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 it through the LUT 78. This LUT 78 has an input / output conversion characteristic as shown in C of FIG. 2, and does not pass an input at a certain threshold value or less, and outputs an input above a second threshold value higher than that as it is. The output has continuity with respect to the input between the two threshold values. The output of this LUT 78 is 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 it 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 directly output from the adder 79 instead of being output through the recursive filter circuit 72.

On the other hand, when the output of the subtractor 77 is small, the output of the LUT 78 is 0. Therefore, the output of the recursive filter circuit 72 is directly output from the adder 79.

If the image signal input to the digital image processing device 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, so the output of the subtractor 77 is When the image signal is changed, on the contrary, when the image signal is changed, there is a difference between the signal passed through the recursive filter circuit 72 and the signal of the current frame, so that the output of the subtractor 77 is increased. That is, the output of the subtractor 77 indicates whether or not the motion is large, and the subtractor 77 functions as a motion detector. Then, the LUT 78 determines whether or not this movement is large. When the movement 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, the image blur does not occur even if the afterimage effect becomes large. When the movement is large, the signal passed through the recursive filter circuit 72 is added by the adder 7
9, the image signal of the current frame is output from the adder 79 as it is, so that the blurring of the image is prevented. Since the operation according to such motion detection is performed for each pixel, the afterimage effect is applied to the static part of the image and the afterimage effect is not applied to the moving part.

The recursive filter circuit 72
As described above, the image sticking effect is further imparted in the low luminance region and S
Since the / N ratio is improved, it is possible to avoid the inconvenience that the output of the subtractor 77 becomes large due to the noise in the low luminance region and the movement is made in the low luminance region. That is, the stationary portion is detected as a stationary portion even if the portion is a low-luminance area, and the recursive filter circuit 7 detects the stationary portion.
An image signal with an improved S / N ratio is output from the adder 79 after passing 2.

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 device 8 for display.

Therefore, for example, X as shown in FIG.
A line image is displayed. In FIG. 3, 31 is the spinal cord,
Reference numeral 32 is a myocardium, 33 is a diaphragm, and 34 is an inserted catheter. The myocardium 32 and the catheter 34 are assumed to be in motion. Usually, the X-ray apparatus has an automatic brightness adjustment function and is controlled so that the brightness of the central portion of the image becomes constant. Therefore, although the peripheral edge of the spinal cord 31 and the diaphragm 33 are in the low brightness region, the afterimage effect is further imparted by the action of the recursive filter circuit 72 and the amplitude of noise is compressed. Therefore, this portion is not detected as a moving portion due to noise, and is displayed as an image with an improved S / N ratio by the recursive filter circuit 72. On the other hand, the moving diaphragm 33 and catheter 34
Since the movement is detected, an image that does not pass through the recursive filter circuit 72 is displayed, and the image clearly shows the movement.

The above-mentioned input / output conversion characteristics of the LUTs 73, 74 and 78 are 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 non-moving area, and the area is S / N-ized by the recursive filter circuit. It is displayed as a smooth image with a high ratio. Therefore, the S / N of the entire image
The ratio will be uniform. Also, the moving part is clearly displayed as the moving part.

[Brief description of drawings]

FIG. 1 is a block diagram of an 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]

 1 X-ray tube 2 Subject 3 Image intensifier 4 Optical system 5 Television 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 device

Claims (1)

[Claims] 1. An X-ray irradiating means for irradiating an object with X-rays, an imaging means for obtaining an image signal representing an image of the X-rays transmitted through the object, and a recursive filter coefficient for inputting the image signal. The recursive filter means that changes according to the value and the coefficient becomes larger as the input value becomes smaller, and the output of the recursive filter means and the image signal of the current frame are compared. The present invention is characterized by having a means for outputting the output of the filter means and for outputting the image signal of the current frame when the difference is larger than a predetermined value, and an image display means for transmitting the image signal output by the current frame. X-ray television device.