JPH0549631A - X-ray imager - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a sharp image even when shooting a moving subject. [Structure] After the start of photographing, images of a plurality of subjects are photographed close to each other in time, and two images consecutive in time are compared to measure the amount of movement of the subject. Then, when the amount of movement of the subject becomes equal to or greater than a predetermined value, the exposure of the X-ray is terminated and the photographing of the subject is stopped. Finally, one static X-ray image is created from the images of a plurality of subjects photographed from the start to the end of photographing by averaging processing or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image capturing apparatus such as digital radiography (DR).

[0002]

2. Description of the Related Art An apparatus for taking an X-ray still image is usually
X-rays that have passed through the X-ray generator and subject (human body, industrial products, etc.)
An image tube (Image Intensifie) that converts lines into visible images.
r = II), an image capturing device (an ordinary camera or an image sensor such as CCD) for capturing an image formed on the projection surface of the image tube.

In order to obtain a proper image that is neither too dark nor too bright, whichever image capturing device is used, the amount of X-rays incident on the image capturing device must be kept within a certain range. I won't. Therefore, in the conventional X-ray image capturing apparatus, a light amount detector is provided behind the image tube, and the image capturing is terminated when the total amount of light incident on the image tube reaches a predetermined value. It was set to end) (photo timer method). In some cases, the measurement range of the light quantity detector is set not to the entire projection surface of the image tube but to a preset partial area.

[0004]

When photographing a human body with X-rays, the exposure X-rays cannot be made very strong. Therefore, the time required to capture one image (that is,
The time until the total amount of light reaches a certain value) is inevitably long, but there is a problem that the image of the subject is blurred when photographing a moving subject such as the stomach.

The present invention has been made in order to solve such a problem, and an object thereof is to obtain an X-ray image capable of obtaining a sharp image even when a moving subject is imaged. To provide a device.

[0006]

The X-ray image capturing apparatus according to the present invention, which has been made to solve the above-mentioned problems, comprises: a) capturing a plurality of images of subjects in close proximity in time after the start of capturing. And b) means for measuring the amount of movement of the subject by comparing two images that are temporally consecutive, and c) when the amount of movement of the subject is greater than or equal to a predetermined value. And an image creating means for creating one image from the images of the plurality of objects photographed by the photographing means between the start of photographing and the stop of photographing. Is characterized by.

[0007]

By comparing two temporally consecutive images photographed by the photographing means, the magnitude of the movement of the subject can be measured. In the X-ray image radiographing apparatus of the present invention, the amount of movement of the subject from the start of photography to the stop (end) of photography is stopped because the photography by the photographing means is stopped when the magnitude of the movement exceeds a predetermined value. Can be suppressed below a predetermined value. Therefore, a sharp X-ray image without blur can be obtained by creating one image by averaging processing from a plurality of images photographed between them.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a medical X-ray imaging apparatus according to an embodiment of the present invention is shown in FIG. 2, and its basic function will be described first.

X supplied with a tube current from the X-ray generator 16.
The ray tube 10 emits X-rays having a predetermined intensity toward the subject 11. The X-rays that have passed through the subject 11 form a perspective image of the subject on the projection surface of the image tube 12. This image is taken by the TV camera 13 and displayed on the monitor 21 by the digital radiography control device (DR) 15 which functions as a control device for the entire device. The present X-ray image capturing apparatus can capture a still image in which the state of the subject is fixed at any time in addition to the moving image.

When taking a still picture, the image tube 1
The photomultiplier 14 arranged behind the second projection surface detects the brightness of the projection surface, and when the integrated value reaches a predetermined value, the X-ray generation is stopped, and the brightness of the image has a proper value. I am trying to be.

Further, in the X-ray imaging apparatus of the present embodiment, in order to obtain a sharp image with little blurring even for a moving subject, i) a function of quantitatively detecting the movement of the subject, ii. ) A function of generating a signal for ending the generation of X-rays when the detected amount of movement reaches a predetermined value, and iii) averaging the images taken from the start to the end of the shooting It has a function to create a still image of. Hereinafter, the operation of each unit when shooting one still image will be described based on the flowchart of FIG.

The X-ray generator 16 is started when the photographing of a still image is started.
Then, the tube current is started to be supplied to the X-ray tube 10 and the subject 11 is irradiated with the X-ray (step S1). Then TV
The camera 13 has an X rate of 1 for every 1/30 second, and the X of the subject 11 is X.
Take line images continuously. Of these, the step S2 is to photograph the first one image. The image data of the X-ray image photographed in this way is A / D in DR15.
Converted to digital data by converter 18 and DR15
It is stored in the internal memory (not shown) (step S
3). Next, in step S4, the second X-ray image is photographed, and in step S5 this image data is stored in another location of the memory.

In this way, after the data of two temporally consecutive images are stored in the memory, in step S6, the amount of movement of the object 11 is measured from the two image data stored in the memory. And that value is the predetermined threshold THmov
Is greater than.

In this embodiment, the motion detector 20 in the DR 15
Performs this movement amount measurement and determination, but employs the following method as a method for measuring the movement amount from the images of two subjects. First, one image is divided into small areas of 4 × 6 pixels (pixels), and a parameter called the similarity s of two images is calculated for each small area by the following formula.
The reason why the difference between the two images is not taken for each pixel here is to avoid that noise, which tends to occur on a pixel-by-pixel basis, greatly affects the similarity.

S = [{(S _n + S _n-1 ) / 2} + {(m _n −m _n-1 ) / 2} ² ] ² / (S _n · S _n-1 ) This similarity s calculation In the formula, S _n is a variance of luminance values of 4 × 6 = 24 pixels included in a certain small area of the n-th image data (n = 2, n−1 = 1 in this case), m _n Is the average value of the brightness values of those pixels. One image is 1152
If it is composed of × 1024 pixels, the number of such small areas is (1152/6) × (1024/4) = 49152, but the value of the parameter s is set for all these small areas. It is calculated and it is determined whether or not the value s is larger than a predetermined threshold THpv. Then, the number N _{n of} small areas with s> THpv is sequentially added to the value stored in the memory. Since the integrated value ΣN _n increases as the amount of movement of the subject increases, the integrated value ΣN _n is used as a parameter representing the amount of movement.

Therefore, in step S6, it is determined whether or not the integrated value ΣN _n in the memory is larger than a predetermined integrated threshold THmov, and if the motion amount is still less than the threshold THmov, the process proceeds to step S7. In step S7, the total amount of light detected by the photomultiplier 14 is the predetermined threshold THph.
o Determine if it is greater than or equal to. If the total amount of light is still below the threshold THpho, the process returns to step S4.

In this way, while the integrated value of ΣN _n , which is the parameter representing the amount of movement of the subject 11, is equal to or less than the integrated threshold THmov, the processes of steps S4 to S7 are repeated, and the TV camera 13 continuously and successively. X taken in
The above calculation and determination are performed between the line images.

During this period, when the amount of movement of the subject becomes a predetermined value or more (that is, when ΣN _n > THmov)
Goes from step S6 to step S8, and the determination signal is sent from the motion detector 20 of the DR 15 to the comparator 19. As a result, the comparator 19 sends an X-ray cutoff signal to the X-ray generator 16 and terminates X-ray exposure. Also, when the total amount of light detected by the photomultiplier 14 becomes equal to or more than the threshold value THpho during the repetition of the processing of steps S4 to S7, the processing proceeds from step S7 to S8 and the integrator 17 to the comparator 1
The determination signal is sent to 9, and the X-ray exposure is similarly ended.

There are various other known methods for measuring the amount of motion from two pieces of image data, but the present invention may use them.

An example of taking an X-ray image of the stomach as a moving subject is shown in FIG. As shown in FIG. 3A, when the stomach wall moves from the position of the dotted line to the position of the solid line while capturing two images (in the contrast examination, the inside of the stomach is dark and the outside is bright). Are those 2
Taking the difference between the images (subtracting the image data of the position of the solid line after the movement from the image data of the position of the dotted line before the movement), as shown in FIG. 3 (b), it becomes bright at the location where the stomach wall has moved. There is a part that becomes dark or dark (the rest is zero deduction). Since the similarity s is equal to or larger than the threshold value THpho in both small areas of these brightened or darkened portions (the portions shaded with both diagonal lines in FIG. 3B), the example of FIG. The N _n is approximately equal to a value obtained by dividing the areas of the one-sided diagonal line and the two-sided diagonal line by the area of the small region. As described above, in the X-ray image capturing apparatus according to the present exemplary embodiment, the X-ray exposure is terminated when the total amount of movement of the subject reaches the predetermined value, and the X-ray capturing of the subject is terminated. The amount of movement of the subject in the k x-ray images can be suppressed to an arbitrary value.

The X-ray image data of the k objects photographed in this way are added for each pixel by the averaging unit 22 of the DR 15 to obtain the average value. In one X-ray image obtained by averaging in this way, the influence of noise generated for each pixel is also reduced to 1 / k ^1/2 , so both sharpness and sharpness are suppressed. Becomes In addition to the simple averaging as in the present embodiment, various methods such as averaging for weighting a preset attention portion can be used for the averaging process.

[0022]

According to the X-ray image capturing apparatus of the present invention, the magnitude of the movement of the subject is measured while capturing one still image,
The shooting time is controlled so that the size is equal to or smaller than a predetermined value. Therefore, by setting this predetermined value to the maximum allowable blur amount or less for performing effective X-ray image diagnosis, the X-ray image obtained by the X-ray image radiographing apparatus always provides an effective diagnosis. It will be sharp enough to do. Further, since images taken during that time are averaged to obtain one image, it is possible to obtain a beautiful image in which noise for each pixel is suppressed.

[Brief description of drawings]

FIG. 1 is a flowchart showing the procedure of processing from the start to the end of X-ray exposure in an X-ray imaging apparatus that is an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an X-ray image capturing apparatus according to an embodiment.

FIG. 3 is an explanatory diagram showing an example of movement of a subject during shooting.

[Explanation of symbols]

10 ... X-ray tube 11 ... Subject 12 ... Image tube 13 ... TV camera 14 ... Photomal 16 ... X-ray generator 17 ... Integrator 19 ... Comparator 21 ... Monitor 15 ... Digital radiography controller (DR) 18 ... A / D converter 20 ... Motion detection unit 22 ... Addition averaging unit

Claims (1)

[Claims] 1. A movement of a subject by comparing a) a photographing means for photographing images of a plurality of subjects in close proximity to each other after the start of photographing, and b) two images consecutive in time. A means for measuring the amount, c) a photographing stopping means for stopping the photographing of the subject in the photographing means when the amount of movement of the subject exceeds a predetermined value, and d) a photographing means for the period from the start of photographing to the stop of photographing. An X-ray imaging apparatus, comprising: an image creating unit that creates one image from a plurality of captured images of a subject.