JP3334321B2 - 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 an X-ray television device that obtains an image signal by a line.

[0002]

2. Description of the Related Art In an X-ray television apparatus, when so-called X-ray fluoroscopy is performed by obtaining a video signal of an X-ray transmission image of a subject and sending it to a monitor device to display the transmission image in real time. The display image is represented as a moving image that changes every moment, and the contrast of the display image greatly fluctuates due to movement such as framing, heartbeat, and breathing. Therefore, an AGC (auto gain control) circuit is used in order to always display an easy-to-view image suitable for the state of a subject on a monitor screen regardless of these. The AGC circuit automatically adjusts the gain of the video signal in accordance with the luminance of the display image, and keeps the luminance of the display image constant. In recent years, a method of digitally realizing the function of the AGC circuit by converting a video signal into a digital signal and then adjusting a display window (a window that defines a display range of pixel data) has been used. I have.

[0003]

However, in any of the circuits and methods described above, fine adjustment cannot be made for various changes in contrast of the subject, and the optimum contrast is instantaneously obtained during framing. There is a problem that an image cannot be obtained, or conversely, it is too sensitive to a periodic change in the contrast of the image such as a heartbeat exercise, and only an image that is difficult to see is obtained. Also, when the collimator is inserted, the collimator portion is determined to be the thickest portion of the subject, and the brightness of the display image is excessively increased in accordance with this, or the portion where the X-rays are directly incident (halation portion) is determined as the subject. In some cases, the brightness of the display image may be lowered unnecessarily, and the contrast of the part to be observed may be reduced, which may hinder the observation.

[0004] In view of the above, the present invention can display an image having an optimum contrast with respect to any image fluctuation, and can optimize the contrast after eliminating the effects of halation and collimator. It is an object of the present invention to provide an X-ray television device improved so as to be able to perform the following.

[0005]

To achieve the above object, an X-ray television apparatus according to the present invention comprises:
X-ray generation means for irradiating the subject with X-rays, X-ray imaging means for receiving an X-ray transmitted through the subject and generating an image signal of an X-ray transmission image, and converting the image signal into a digital signal A / D conversion means, peak value detection means for detecting a larger or smaller peak value in one frame of the digital image signal, smoothing means for smoothing the peak value in a time direction over many frames, Means for obtaining the display window of the digital image signal from the peak value after smoothing, and obtaining the smoothing coefficient from the obtained display window and the temporal change of the peak value, and controlling the smoothing means by the coefficient. Means for displaying the determined gradation in the display window among the digital image signals from the A / D conversion means. It is the distinctive feature and a tone conversion means for converting the gray level.

The smoothing means for smoothing the peak value in the time direction over a large number of frames can be constituted by a recursive filter means. In this case, the smoothing coefficient is a recursive filter coefficient. Means for obtaining the coefficient of the recursive filter from the display window and the temporal change of the peak value, and controls the recursive filter means with this coefficient.

Further, a variation in the magnitude of the digital image signal from the A / D conversion means is detected, an area where the maximum value continues in a certain range is determined as a halation area, and an area where the minimum value continues in a certain range is determined. Judge as the collimator area,
A peak value detection control means for performing peak value detection by the above-described peak value detection means only in an area excluding these areas may be provided.

[0008]

The display window of the digital image signal is obtained from the peak value after smoothing. The peak values are detected as the larger and smaller peak values in one frame of the digital image signal, respectively. The peak value after smoothing is obtained by dividing these peak values into a large number of frames. Over time. Further, the smoothing is controlled by a temporal change of the obtained display window and the peak value. Therefore, in the end, the display window of the current frame is determined based on the display window in the previous frame and the temporal change of the peak value. Therefore, the display window is not affected by a relatively gradual change in contrast due to a periodic motion such as a heartbeat. To obtain an image with stable contrast, and when the contrast of the image greatly changes due to framing or the like, the response sensitivity can be increased to quickly shift to the optimum contrast. Also, if the display window is narrow,
The response sensitivity to the change of the display window can be reduced so that an image can be easily viewed when displayed.

If the smoothing means for smoothing the peak value in the time direction over many frames is constituted by the recursive filter means, practically,
It can be easily realized with a simple configuration.

Further, a peak value detection control means is provided, and if a change in the magnitude of the digital image signal from the A / D conversion means is detected, an area where the maximum value continues in a certain range is determined as a halation area. In addition, since the area where the minimum value continues in a certain range can be determined as the collimator area, the peak value detection can be performed by the above-described peak value detection means only in the area excluding each of these areas. it can. That is, in the halation area where the X-rays are directly incident and the area where the X-rays are shielded by the collimator, the above-described peak value detection can be prevented from being performed. The window can be controlled.

[0011]

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 the embodiment shown in FIG. 1, X-rays are emitted from the X-ray tube 21 toward the subject 10, and the X-rays transmitted through the subject 10 enter the image intensifier 22. I have. The transmitted image of the subject 10 represented by the transmitted X-ray is converted into an optical image by the image intensifier 22. The optical image output from the image intensifier 22 is made incident on a TV camera 23 through an appropriate optical system.
, An image signal of an X-ray transmission image is obtained. This image signal is converted into a digital image signal by an A / D converter 24, sent to a gradation conversion circuit 26 via a digital image processing circuit 25 and the like, subjected to gradation conversion, and then analog-converted by a D / A converter 27. The image signal is returned to the image monitor 28, and an X-ray transmission image is displayed on the image monitor 28.

The conversion characteristic of the gradation conversion circuit 26 is determined by a signal sent from the display window determination circuit 39. In order to determine the display window, a direct line detection circuit 31, a collimator detection circuit 32, a white peak detection circuit 33, a black peak detection circuit 34, smoothing circuits 35 and 36, control circuits 37 and 38, and the like are provided.

The direct ray detection circuit 31 detects that the X-rays
The portion which directly enters the image intensifier 22 without being attenuated by transmitting 0 is detected. Further, the collimator detection circuit 32 is a circuit that detects a portion where X-rays are shielded by a collimator (not shown). In a region where these are detected, a gate is applied so that a white peak detection circuit 33 and a black peak detection circuit 34 described below do not operate.

The white peak detection circuit 33 and the black peak detection circuit 34 provide a white peak (maximum value) WP and a black peak (minimum value) BP of a digital image signal for one frame in an area where such a gate is not applied. And are respectively detected. WP, B detected
P is smoothed in the time direction in smoothing circuits 35 and 36, respectively. That is, these WP, B
P is obtained sequentially in time for each frame, but is smoothed between the values obtained sequentially in time, and the white peak WP ′ and the black peak B after smoothing are obtained.
P ′ is obtained. Control circuit 3 for the degree of smoothing
7 and 38 respectively. The smoothed WP 'and BP' are input to the display window determination circuit 39, and the value W of the display window is obtained as the difference between WP 'and BP'.

The control circuits 37 and 38 output the W
Control is performed such that the greater the difference between P ′, BP ′ and WP, BP of the current frame and the larger the display window W, the less the degree of time direction smoothing is. Smoothing circuits 35 and 36
Performs the time-direction smoothing of the value obtained for each frame, and therefore can be configured by an integrating circuit or the like, but is configured by a recursive filter circuit as shown in FIG.

That is, the smoothing circuit 35 will be described. First, the input WP is multiplied by (1 / K) times by the multiplication circuit 41, and the delay circuit 4
Send to 4. The delay circuit 44 delays the input signal by one frame, and sends a signal delayed by one frame to the multiplication circuit 42. The multiplication circuit 42 multiplies the input signal by {1- (1 / K)} times, and sends the output signal to the addition circuit 43. Therefore, in the adder circuit 43, the signal obtained through the WP multiplication circuit 41 of the current frame and the signal obtained through the WP ′ multiplication circuit 42 obtained up to the previous frame and delayed by the delay circuit 44 are added. The value after the addition is output as WP ′ via the delay circuit 44. In other words, the output WP ′ is obtained by adding the WP of the previous frame to the WP of the current frame at a predetermined ratio, and thus smoothing in the time direction is performed. The coefficient that determines the ratio is the recursive filter coefficient K
(K ≧ 1).

The recursive filter coefficient K is given by the control circuit 37. The control circuit 37 includes a subtraction circuit 51 for obtaining a difference Δ between WP of the current frame and WP ′ of the previous frame, this Δ, and the display window determination circuit 3
And a K calculation circuit 52 for calculating the value of K based on the display window value W sent from the control unit 9. It should be noted that the smoothing circuit 36 and the control circuit 38 have an input BP instead of WP and an output BP 'instead of WP'.
Since they are the same as the smoothing circuit 35 and the control circuit 37 except for the following, the description is omitted.

In the display window determining circuit 39, the value of W is obtained from the difference between WP 'and BP' after smoothing as described above, and further, as shown in FIG.
W 'is obtained by adding certain set-up values a and b. The thus obtained W ′ is sent to the gradation conversion circuit 26 (along with W′U and W′L representing the upper and lower limits of W ′). The gradation conversion circuit 26 converts only the window portion indicated by W 'among the input gradations into the entire display gradation. That is, as shown in FIG. 3, if the display is performed in 256 gradations from pure black to pure white, only the size of the input signal that falls within the display window W ′ is 2
The gradation is converted into 56 levels.

In the control circuit 37, the K calculation circuit 52 calculates the value of K based on the characteristics as shown in FIG. That is, the WP of the current frame and the W
When the difference Δ from P ′ is small, the value of K is large, and when Δ is large, K is determined according to a curve in which the value of K is reduced.
The value is changed so as to be small when W is large and large when W is small. Thus, when the temporal variation of the WP is small, K is increased and the smoothing degree in the time direction is increased to reduce the response sensitivity. Conversely, when the temporal variation of the WP is large, K is decreased and the temporal sensitivity is reduced. The degree of smoothing is reduced, and the response sensitivity is increased. As a result, when the WP fluctuates as shown by a solid line in FIG. 5, for example, a relatively smooth WP fluctuation due to a periodic motion such as a heartbeat is subjected to strong smoothing so as to suppress the fluctuation, and framing or the like is performed. It is possible to reduce the smoothing effect and respond immediately to a sudden change in WP, and obtain a changing WP 'as shown by the dotted line.

Since the degree of smoothing is controlled in the same manner for the BP, the display window W 'is not affected by relatively slow fluctuations of the heartbeat or the like. A sudden change due to framing or the like can be immediately made to respond. Further, when the display window W 'is small, K is increased to increase the smoothing effect of WP and BP, so that the display window W' does not largely move with respect to fluctuations of WP and BP. Since the display window W 'is small as described above, the contrast of the input image is small and the small contrast range (W') is enlarged to all display gradations and displayed.
Since the contrast of the original image is emphasized, and if W ′ is greatly changed in such a case, it becomes rather difficult to see, so that such practical difficulty in viewing can be avoided. . On the other hand, when the display window W 'is large, even if the response of W' is improved, the display image does not become difficult to see. Therefore, the smoothing effect of WP and BP is reduced and the display for the fluctuation of WP and BP is performed. By making the response of the window W 'quick,
It is possible to immediately follow a change in the contrast of an image.

In the display window determination circuit 39, W is obtained from the difference between WP 'and BP' after smoothing as described above.
Set-up values a and b at the lower and upper limits of the value of
Is added to obtain W ′. However, depending on the actual image monitor device 28, all values larger than WP ′ become pure white and B ′
Since values smaller than P 'may be difficult to see if they are all displayed in black, this is taken into account.

By the way, if an image as shown in FIG. 6 is obtained, a portion of the subject 10 and a portion where the X-rays are directly incident without causing the subject 10 to generate halation (directly) are included in the image. A line portion 11 and a collimator portion (a portion where X-rays are shielded by the collimator) 12 are present. In this case, looking at the signal on one scanning line 13, it is as shown in FIG. 7. In the area A corresponding to the direct line portion 11, the input value is the maximum value (the maximum value of the A / D converter 24). Bit) and the collimator part 1
In the area B corresponding to 2, the input value becomes the minimum value (the minimum bit of the A / D converter 24). Therefore, in the case of an input image having the direct line portion 11 and the collimator portion 12 as described above, if the white peak detection circuit 33 and the black peak detection circuit 34 are operated as they are, the optimum display contrast for the subject 10 is obtained. Cannot be obtained.

To prevent this inconvenience, the direct line detection circuit 3
1 and a collimator detection circuit 32. The direct line detection circuit 31 determines that the region A corresponds to the direct line portion 11 when the maximum value of the input signal continues for a certain number of pixels or more. The collimator detection circuit 32 determines that the input signal has the minimum value in the area B corresponding to the collimator portion 12 when the number of pixels continues for a certain number or more. The white peak detection circuit 33 and the black peak detection circuit 34 are gated so that the white peak detection circuit 33 and the black peak detection circuit 34 operate only in a region excluding a region obtained by adding a fixed width C to the detected regions A and B.
Therefore, when a signal as shown in FIG. 7 is input, peak detection is performed only in a region corresponding to the portion of the subject 10, and the peak value WP of the pixel value of the image portion of the subject 10 is detected.
And BP can be obtained.

[0024]

As described above, according to the X-ray television apparatus of the present invention, when the contrast of the X-ray transmission image of the subject fluctuates, no matter what it is, It can always be displayed as an image having the optimum contrast. That is, the display contrast is not fluctuated so much as to relatively periodic contrast fluctuation such as heartbeat and breathing, and is displayed as a stable contrast image. In this case, the display contrast is made to correspond immediately, and in any case, the actual visibility can be improved. When the contrast of the original image is small and the small contrast is emphasized and displayed, the follow-up of the contrast of the display image with respect to the contrast variation of the original image is weakened. An easily viewable display image can be obtained without being too large.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a part of the circuit of the embodiment of FIG. 1 in detail;

FIG. 3 is a diagram showing gradation conversion characteristics.

FIG. 4 is a characteristic diagram of a recursive coefficient K.

FIG. 5 is a graph showing a temporal change of a peak value.

FIG. 6 is a diagram showing an example of an X-ray image.

FIG. 7 is a graph showing signal intensity on a scanning line 13 in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Subject 11 Direct line part 12 Collimator part 13 Scanning line 21 X-ray tube 22 Image intensifier 23 TV camera 24 A / D converter 25 Digital image processing circuit 26 Gradation conversion circuit 27 D / A converter 28 Image monitor 31 Direct Line detection circuit 32 Collimator detection circuit 33 White peak detection circuit 34 Black peak detection circuit 35, 36 Smoothing circuit 37, 38 Control circuit 39 Display window determination circuit 41, 42 Multiplication circuit 43 Addition circuit 44 Delay circuit 51 Subtraction circuit 52 K calculation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/50-5/63 H04N 5/14-5/217 H04N 5/30-5/335 A61B 6 / 00-6/14

Claims (1)

(57) [Claims] An X-ray generating means for irradiating a subject with X-rays, an X-ray imaging means for receiving an X-ray transmitted through the subject and generating an image signal of an X-ray transmission image, and A / D conversion means for converting into a digital signal, peak value detection means for detecting a larger or smaller peak value in one frame of the digital image signal, and smoothing of the peak value in a time direction over many frames. Smoothing means, means for calculating the display window of the digital image signal from the smoothed peak value, and calculating the smoothing coefficient from the temporal change of the calculated display window and the peak value. Means for controlling the smoothing means, and, among the digital image signals from the A / D conversion means, the gradation in the display window determined above. X-ray television apparatus comprising: a gray scale conversion unit for converting the image into all gray levels to be displayed.