JPH07105354A - Medical picture processor - Google Patents

Abstract

PURPOSE:To automatically implement optimum picture filtering processing depending on picture quality changing timewise and on picture quality of each part in one picture. CONSTITUTION:A filter characteristic of a filtering processing circuit 28 is controlled by a filter characteristic calculation circuit 27. A recursive filter 21, a subtractor circuit 22, an absolute value integration circuit 23 and an area setting circuit 24 obtain a signal representing noise in each area, a mean value calculation 25 and an area setting circuit 26 detect a luminance for each area and outputs of the circuits 23, 25 are fed to the filter characteristic calculation circuit 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for digitally processing medical images such as X-ray images.

[0002]

2. Description of the Related Art Medical images such as X-ray images are digitized and subjected to processing such as edge enhancement so as to be suitable for observation for diagnosis. Among various medical images, especially X-ray images obtained by using an X-ray TV system are sequentially obtained for each frame, but the S / N ratio of the image changes in real time depending on the X-ray condition and subject condition. To do. Therefore,
Conventionally, an operator manually sees an X-ray image displayed on the screen of a monitor device and manually operates several types of edge enhancement filters having a constant frequency characteristic according to a change in the S / N ratio. I am trying to choose.

[0003]

However, it is impossible to adjust the degree of edge enhancement to the optimum one for the ever-changing image quality by the manual method as in the past, and as a result, As a result, there is a problem in that, with insufficient adjustment, only an image with noticeable noise or an image that is not very sharp can be obtained. In addition, although there is a bright portion and a dark portion in one image, and the S / N ratios are different in those portions, conventionally, the edge enhancement processing is adjusted for each portion in this one image. I can't do it either.

In view of the above, the present invention makes it possible to automatically perform an optimum filtering process according to the image quality that changes every moment and according to the image quality of each part in one image. An object is to provide an image processing device.

[0005]

In order to achieve the above object, in the medical image processing apparatus according to the present invention, means for integrating sequentially input digital images in the time direction, and the integrated digital image A means for obtaining a difference from a sequentially input digital image for each of a plurality of set small areas, and a luminance for each of a plurality of small areas of the sequentially input digital image set as the same as or different from the above. Means, filtering processing means for performing edge enhancement processing on the sequentially input digital images, and control means for determining the frequency characteristic of the filtering means for each region according to the obtained difference and brightness. It is characterized by being equipped.

[0006]

When the digital images sequentially input are integrated in the time direction, the noise component is relatively suppressed. Therefore,
If the difference between this integrated digital image and the sequentially input digital image is calculated, it will be in accordance with the amount of noise. Since this difference is obtained for each area, the noise situation for each area is detected.
The brightness for each area is also calculated separately, and the filter characteristics are determined according to the noise condition and the brightness for each area, so that optimum edge enhancement processing can be performed for each area.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to an X-ray TV system. In this figure, X-rays are emitted from an X-ray tube 11 toward a subject 10. The X-rays that have passed through the subject 10 enter an image intensifier (II) 12, and the transmitted image by the X-rays is converted into an optical image. This optical image is converted into a video signal by the TV camera 13, and this video signal is digitized by the A / D converter 14. This digital image signal is sent to the real-time edge enhancement circuit 16 through the noise reduction filter 15,
Receive edge enhancement processing in real time. After that, the gradation conversion circuit (window circuit) 17 converts the gradation, the D / A converter 18 restores the analog video signal, and the analog video signal is sent to the monitor device 19 for display.

Real-time edge enhancement circuit 16
Includes a filtering processing circuit 28 that performs edge enhancement processing on an input digital image signal in real time. Further, in order to control the filtering processing circuit 28 in real time, a recursive filter 21, a subtraction circuit 22, and an absolute value integration. Circuit 23, area setting circuit 24,
26, an average value calculation circuit 25, and a filter characteristic calculation circuit 27.

The input digital image signal is first integrated in the time direction by the recursive filter 21, and becomes an image with a kind of afterimage added, and the noise is suppressed. The output image of the recursive filter 21 and the original input image are input to the subtraction circuit 22, and the difference between them is obtained. Since the output image of the recursive filter 21 is the noise-removed image as described above, the difference becomes smaller if the input image has less noise, and this difference corresponds to the magnitude of the noise of the input image.

Therefore, the output of the subtraction circuit 22 is input to the absolute value integration circuit 23, and the size of the noise of the input image is calculated for each of a plurality of small areas set by the area setting circuit 24. The area setting circuit 24 arbitrarily divides one image, and here, for example, N × N as shown in FIG.
It is supposed to be divided into individual areas. Then, the absolute value integration circuit 23 integrates the absolute value of the difference for each of the N × N areas. As a result, the magnitude of noise, that is, the S / N value is obtained for each area.

On the other hand, the input digital image is sent to the average value calculating circuit 25, and the average value of the brightness of each area set by the area setting circuit 26 is obtained. This area setting circuit 2
6 is the same as the above-mentioned area setting circuit 24 and can be divided into areas separately from the area setting circuit 24, but may be divided into the same area.

Then, the S / N value for each area from the absolute value integrating circuit 23 and the average brightness for each area from the average value calculating circuit 25 are input to the filter characteristic calculating circuit 27, and these inputs are made. Optimal filter characteristics are calculated for each area according to the data. Here, the filtering processing circuit 28 performs the edge enhancement processing of the image by a bandpass filter having a frequency fo as the center frequency as shown in FIG. 4, and noise reduction is achieved by changing the gain at that fo. The degree of edge enhancement can be adjusted. The filter characteristic is controlled according to the filter characteristic obtained by the filter characteristic calculation circuit 27.

For example, fo of the filter characteristic shown in FIG.
Assuming that the gain at K is K, this K is determined by the filter characteristic calculation circuit 27 as shown in FIG. That is, based on the curve using K in FIG. 3 as a parameter, S
/ K is small when the N value is large (there is a lot of noise),
When the S / N value is small (there is little noise), K is increased, and the value of K is decreased as the average brightness is smaller and in the darker part. Note that fo is determined from the frequency band Fs of the image signal and the frequency band Fn of noise.

Thus, the X-ray image signals sequentially output from the TV camera 13 are filtered by the filtering processing circuit 28 having optimum filter characteristics corresponding to the image quality of each area of each image in real time. The optimum edge enhancement processing for each area is performed in real time.

Although noise has been described above,
Since the difference output from the subtraction circuit 22 corresponds not only to noise but also to image movement, the output of the absolute value integration circuit 23 also represents image movement for each area. Therefore, the filter characteristic calculation circuit 27
Also means that the optimum filter characteristic according to the magnitude of motion is calculated for each area.

Further, since the value of K is roughly determined depending on the photographed part of the subject and the photographing mode, FIG.
The value of K is not calculated by a complicated calculation such as the graph in FIG. 1, but some K values are selected in advance when the region to be imaged and the imaging mode are determined, and the filter characteristic calculation circuit 27 selects the optimum value from them. You may make it possible to sort out such items. Contrary to such simple control, more complicated control can be performed so that the center frequency fo of the filter characteristic is also changed. Further, the brightness of each area may be calculated so as to represent the brightness of each area, rather than the average brightness of that area as described above.

[0017]

As described in the above embodiments, according to the medical image processing apparatus of the present invention, noise is suppressed in a portion having a poor S / N ratio, and edges are made sharper in a portion having a good S / N ratio. In addition to being able to emphasize, noise is noticeable in visually dark areas, so the noise removal effect can be increased in dark areas compared to bright areas, thereby suppressing annoying noise in dark areas. You can In this way, the filtering process can be dynamically controlled according to the noise condition of each part of the image, and it becomes possible to obtain a sharp image with no noticeable noise in the entire image.

[Brief description of drawings]

FIG. 1 is a block diagram of a medical image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of screen division according to the embodiment.

FIG. 3 is a graph showing the value of K with respect to the S / N value and the average luminance in the example.

FIG. 4 is a graph showing a filter characteristic in the example.

[Explanation of symbols]

 10 subject 11 X-ray tube 12 image intensifier 13 TV camera 14 A / D converter 15 noise reduction filter 16 real-time edge enhancement circuit 17 gradation conversion circuit 18 D / A converter 19 monitoring device 21 recursive filter 22 subtraction circuit 23 absolute value Integration circuit 24, 26 Region setting circuit 25 Average value calculation circuit 27 Filter characteristic calculation circuit 28 Filtering processing circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9191-5L G06F 15/68 400 A

Claims (1)

[Claims] 1. A means for integrating sequentially input digital images in a time direction, and a means for obtaining a difference between the integrated digital image and the sequentially input digital images for each of a plurality of set small areas. A means for obtaining brightness for each of a plurality of small areas of the sequentially input digital images which are set to be the same as or different from the above, and a filtering processing means for performing edge enhancement processing on the sequentially input digital images. A medical image processing apparatus comprising: a control unit that determines the frequency characteristic of the filtering unit for each area according to the obtained difference and brightness.