JP2715212B2 - Radiation image superposition processing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for superimposing radiographic images for adding two image signals carrying radiographic image information of the same subject.

[0002]

2. Description of the Related Art A recorded radiographic image is read to obtain an image signal, and the image signal is subjected to appropriate image processing.
2. Description of the Related Art Reproduction and recording of images are performed in various fields.
For example, recording an x-ray image using a low gamma x-ray film designed to be compatible with subsequent image processing;
The X-ray image is read from the film on which the X-ray image is recorded, converted into an electric signal, the electric signal (image signal) is subjected to image processing, and then reproduced as a visible image in a copy photograph or the like, thereby obtaining a contrast. A system capable of obtaining a reproduced image with good image quality such as image quality, sharpness, and graininess has been developed (see Japanese Patent Publication No. Sho 61-5193).

[0003] Further, according to the present applicant, radiation (X-ray, α
Radiation, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated, and then, when irradiated with excitation light such as visible light, the amount of stimulated emission light corresponding to the accumulated energy is increased. Phosphor that emits light (stimulable phosphor)
Utilizing, a radiographic image of a subject such as a human body is once photographed and recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light,
A radiation recording / reproducing system that photoelectrically reads the obtained stimulated emission light to obtain an image signal, and outputs a radiation image of a subject as a visible image to a recording material such as a photographic photosensitive material or a CRT based on the image signal. Have already been proposed (JP-A-55-12429, JP-A-56-11395, JP-A-55-0163472,
Nos. 56-164645 and 55-116340).

This system has the practical advantage of being able to record images over a very wide radiation exposure area as compared to conventional radiographic systems using silver halide photography. That is, it has been recognized that the amount of stimulating light emitted by excitation after accumulation with respect to the amount of radiation exposure is proportional over a very wide range, and thus the amount of radiation exposure varies considerably depending on various imaging conditions. Also, the stimulable light emitted from the stimulable phosphor sheet is read, the gain is set to an appropriate value, read by photoelectric conversion means, converted into an electric signal (image signal), and a photograph is taken using this image signal. By outputting a radiation image as a visible image to a display device such as a photosensitive material or a CRT, a radiation image which is not affected by a change in radiation exposure amount can be obtained.

[0005] On the other hand, a superposition process of radiographic images has been conventionally known (for example, see Japanese Patent Application Laid-Open No. 56-11399).
Generally, a radiographic image is used for diagnosis and other purposes, and in using the radiographic image, it is required to detect a minute radiation absorption difference of a subject satisfactorily. The degree of this detection in a radiographic image is referred to as contrast detectability or simply detectability, and the higher the detectability, the higher the diagnostic performance,
It can be said that the radiation image has a high practical value. Therefore, in order to enhance the diagnostic performance, it is desired to increase the detectability, but the biggest obstacle is various noises.

For example, in the above-described radiation image recording system using the stimulable phosphor sheet, the following noise is recognized in the step of storing, reading, and reading out the radiation image on the stimulable phosphor sheet. .

(1) Quantum noise of radiation (2) Noise due to non-uniform distribution of phosphor coating or phosphor particle distribution on stimulable phosphor sheet (3) Image stored and recorded on stimulable phosphor sheet is stimulated Noise of excitation light to be emitted (4) Noise of stimulated emission light emitted, collected and detected from the stimulable phosphor sheet (5) Electrical noise in a system that amplifies and processes electrical signals This is a method for greatly reducing these noises and making it possible to clearly observe even a slight difference in radiation absorption of the subject in the final image, that is, to greatly improve the detectability. The general method and operation of the superposition process are as follows.

A radiation image is photographed (recorded) on a plurality of recording media, and a plurality of image signals obtained by subjecting the plurality of recording media to a reading process are superimposed. This allows
The various noises described above can be reduced. That is, since the above-described noise (1) to (5) of the stimulable phosphor sheet often shows a different distribution for each sheet image,
By superimposing the images of these sheets, each noise is averaged, and the noise becomes less noticeable in the superimposed image. That is, an image signal with a good S / N is obtained. The same applies to the case where a radiation image recorded on an X-ray film is read. More specifically, among the noises (1) to (5), there are many noises that can be approximated by Poisson statistics, and in particular, one of the dominant factors in the noise of radiation images is (1) Radiation noise is an example. It is. Here, assuming that the noise can be approximated by Poisson statistics,
The two radiation images are signals S ₁ of the same magnitude,
When it is considered that the image has S ₂ and noises N ₁ and N ₂ , the magnitude of the signal and noise when two images are superimposed is S ₁ + S ₂ and the noise is

[0009]

(Equation 1)

## EQU1 ## On the other hand, when considering S / N, which is one index representing the detectability of a radiation image, the S / N of each image before superimposition is S ₁ / N ₁ and S ₂ / N _{2, respectively.}
However, by performing the superposition processing, the S / N becomes

[0011]

(Equation 2)

Thus, the S / N is improved. In addition, when performing the superposition process, by weighting each signal, it is possible to optimize the S / N improvement.

Conventionally, in order to actually perform the superposition process, for example, when a stimulable phosphor sheet is used, two stimulable phosphor sheets are stacked on a cassette and an object is photographed. A reading process similar to a normal reading process is sequentially performed on the two stimulable phosphor sheets,
A method of obtaining two sets of image signals is used.

[0014]

In the above-described radiographic image superimposition processing, each of two sets of image signals carrying radiographic image information of the same subject is weighted with an appropriate value, and the corresponding image data is processed between corresponding pixels. The addition is performed to obtain an addition signal.

However, since an appropriate value for weighting the image signal is a value appropriately set manually for each image signal or a predetermined constant value, it is necessary to perform appropriate weighting for a radiation image to be superimposed. And it was difficult to improve the image quality of the obtained superimposed image.

The present invention has been made in view of the above circumstances, and provides a radiographic image superposition processing method and apparatus capable of obtaining optimum weighting coefficients of two sets of image signals and improving the quality of superimposed images. It is the purpose.

[0017]

SUMMARY OF THE INVENTION A first radiographic image superposition processing method according to the present invention is directed to a method for superposing a pixel corresponding to a first and a second image signal carrying radiographic image information of the same subject. In the radiographic image superposition processing method of obtaining an addition signal by performing addition between signals,
Is the image signal of S ₁ , the noise of the first image signal is N ₁ ,
When the second image signal is S ₂ , the noise of the second image signal is N _2, and the added signal is S, S = (N ₂ ² / (N ₁ ² + N ₂ ² )) × S ₁ + (N ₁ ²
/ (N ₁ ² + N ₂ ² )) × S ₂ , and the added signal S is obtained by weighted addition.

A first radiographic image superposition processing apparatus according to the present invention is an apparatus for performing the above-described first radiographic image superposition processing method according to the present invention. In a radiographic image superposition processing apparatus comprising an adding means for performing addition between signals of corresponding pixels with respect to the carried first and second image signals to obtain an added signal, the adding means includes S ₁ , the noise of the first image signal is N ₁ , the second image signal is S ₂ , the noise of the second image signal is N _2, and the addition signal is S , S = (N ₂ ² / (N ₁ ² + N ₂ ² )) × S ₁ + (N ₁ ²
/ (N ₁ ² + N ₂ ² )) × S ₂ .

According to a second radiographic image superposition processing method according to the present invention, addition is performed between signals of corresponding pixels with respect to first and second image signals carrying radiographic image information of the same subject. In the method of superimposing radiographic images to obtain an addition signal, the first image signal is S ₁ , the sensitivity of the first image signal is Sk1, the second image signal is S2, and the second image signal is S2. the sensitivity Sk2, the sum signal when the S, S = (Sk2 / ( Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S ₂ , and the added signal S is obtained by weighted addition.

Here, the sensitivity of the image signal means the sensitivity of the image signal in the case of an image signal read from a stimulable phosphor sheet, for example, and the X-ray image is recorded. An image signal read from an X-ray film or the like means the sensitivity of the X-ray film.

Further, a second radiographic image superposition processing apparatus according to the present invention is an apparatus for performing the above-described second radiographic image superposition processing method according to the present invention, and is a radiographic image of the same subject. In a radiographic image superposition processing apparatus comprising an addition unit that performs addition between signals of corresponding pixels with respect to first and second image signals carrying information to obtain an addition signal, The first image signal is S ₁ , and the sensitivity of the first image signal is S
k1, wherein the second image signal S _2, the sensitivity of the second image signal Sk2 and the added signal is taken as S, S = (Sk2 / ( Sk1 + Sk2)) × S 1 + (Sk1 / ( Sk1
+ Sk2)) × S ₂ .

[0022] In the first superposition processing method and apparatus according to the present ^{_{invention, S = (N 2 2 /}} (N 1 2 + N 2 2)) × S 1 + (N 1 2 / (N 1 2 + N ₂ ² )) × S ₂ (1) The added signal S is obtained by weighted addition as follows.
Weighting in the equation (1) factor _{^{N 2 2 / (N 1 2}} + N
₂ ²⁾ and _{^{N 1 2 / (N 1 2}} + N 2 2) are those determined as follows.

That is, S = a × S₁+ (1-a) × S_Two .. (2) where a is an arbitrary constant.
Image signal S₁Noise of N ₁, Image signal S_TwoNoise of N
_TwoThen, the noise of the addition signal S becomes

[0024]

(Equation 3)

## EQU2 ##

Therefore, a constant a that minimizes the noise N is determined, and this constant a is used as a weighting coefficient in the equation (2).
, The radiation image obtained from the addition signal S is optimal.

Here, since the noise N can be minimized by minimizing N ² , the equation (3) is modified to obtain N ² = (a × N ₁ ) ² + ((1−a) × N ₂ ) ² ... (4) and partial differential of equation (4) with a constant a gives

[0028]

(Equation 4)

At the point where the value obtained by partially differentiating the square of the noise N with the constant a becomes 0, the noise N ² is minimized.
(5) ^{_{from, 2a × N 1 2 -2 (}} 1-a) × N 2 2 = 0 ... When determining the value of the constant a as the _{(6), a = N 2} 2 / (N 1 2 + N 2 2 ), (1-a) = N 1 2 / (N 1 2 + N 2 2) ...
(7)

By substituting the value of the constant a into equation (2), equation (1) is obtained. Therefore, if the addition signal S is obtained by the weighted addition shown in Expression (1), the noise of the addition signal S is minimized.

[0031] In the second superposition processing method and apparatus according to the present invention, by S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1 + Sk2)) × S 2 ... (8) comprising a weighted addition , The sum signal S is obtained,
In Equation (8), the sensitivities Sk1 and Sk2, which are parameters for performing image processing and the like on an image signal, are used for the following reasons.

That is, in a region where the level of the image signal is the most dominant, the square value of the noise has a substantially linear relationship with the radiation dose irradiated to the recording medium, and the sensitivity is further reduced when the recording medium is irradiated. It has a strong correlation with the radiation dose. Therefore, by replacing the N ₁ ² and N ₂ ² in the first superposition processing method and apparatus according to the present invention in sensitivity Sk1 and Sk2, is the noise of the addition signal S than is set to be minimum.

The sensitivity in a linear relationship with the square value of the noise is a logarithm of the sensitivity obtained from the image signal as shown in a graph 30 in FIG. The sensitivity in equation (8) represents the logarithmic value of the sensitivity. Therefore, when weighted addition is performed using the sensitivity before taking the logarithmic value, assuming that the sensitivities before taking the logarithmic value are Sk1 ′ and Sk2 ′, the equation (8) becomes as follows: S = (log Sk2 ′ / ( (log Sk1 ′ + log Sk2 ′)) × S ₁ + (log Sk1 ′ / (log Sk1 ′ + log Sk2 ′)) × S ₂ (8 ′).

Further, in the third radiographic image superposition processing method according to the present invention, the first and second image signals carrying the radiographic image information of the same object are added between signals of corresponding pixels. In the radiographic image superimposition processing method for obtaining an addition signal S, the sensitivity of the first image signal for each pixel is determined based on the first image signal S ₁ and the second image signal S _2. Sk1 and the second
Calculated image signals of sensitivity Sk2 respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S _{2 is} obtained for each corresponding pixel to obtain the added signal S.

Further, the third radiographic image superposition processing apparatus according to the present invention adds the first and second image signals carrying the radiographic image information of the same subject between signals of corresponding pixels. In the radiographic image superimposition processing apparatus comprising an adding means for obtaining an addition signal S by performing the above-mentioned processing, wherein the adding means determines whether each of the pixels has been detected based on the first image signal S ₁ and the second image signal S _2. The sensitivity Sk1 of the first image signal and the second image signal Sk2
And an arithmetic unit for obtaining respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S _2, and an adder that performs weighted addition for each of the corresponding pixels.

Further, in the fourth radiographic image superposition processing method according to the present invention, the first and second image signals carrying radiographic image information of the same subject are added between signals of corresponding pixels. Is performed to obtain an addition signal S, a blur signal of the first image signal S ₁ and the blur signal of the second image signal S ₂ are obtained, and the blur signal of the first image signal S ₁ is obtained. based on the blur signal and the second image signal S ₂ of the unsharp signal, the sensitivity of the first image signal for each pixel Sk1 and the second
Calculated image signals of sensitivity Sk2 respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S _{2 is} obtained for each corresponding pixel to obtain the added signal S.

Further, the fourth radiographic image superposition processing apparatus according to the present invention adds the first and second image signals carrying the radiographic image information of the same subject between signals of corresponding pixels. In a radiation image superimposition processing apparatus comprising an adding means for obtaining an addition signal S by performing
The adding means determines a blur signal of the first image signal S ₁ and the second image signal S ₂ , and calculates a blur signal of the first image signal S _{1 and} a blur signal of the second image signal S ₂ . based on the signal, a calculation unit for obtaining said first image signal sensitivity Sk1 and the second image signal Sk2 respectively for each of the pixels, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / ( Sk1
+ Sk2)) × S _2, and an adder that performs weighted addition for each of the corresponding pixels.

[0038]

In the radiographic image superposition processing method and apparatus according to the present invention, a weighting coefficient that minimizes noise of the addition signal S is used as a weighting coefficient of the image signal when obtaining the addition signal. For this reason, noise of an image obtained by reproducing the addition signal is minimized, and an image with good image quality can be obtained.

If the sensitivity for calculating the weighting coefficient that minimizes the noise of the addition signal S is determined for each pixel, the difference in the dose of radiation that has passed through the subject and reached the recording sheet or the like for each location can be determined. And the noise can be minimized for each pixel, so that the image quality can be further improved.

Further, if the blur signal of the image signal is obtained and the sensitivity of each pixel is obtained based on the blur signal, the weighting coefficient is determined by obtaining the global sensitivity of each pixel which is not affected by noise. Can be.

[0041]

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, a stimulable phosphor sheet is used as a recording medium.

FIG. 1 shows two stimulable phosphor sheets 4A and 4A.
FIG. 4B is a diagram showing a state in which the radiation 2 transmitted through the same subject 1 is applied to B.

That is, the first stimulable phosphor sheet 4A
And the second stimulable phosphor sheet 4B is superposed and arranged to drive the radiation source 3 to emit the radiation 2, and the radiation 2 transmitted through the subject 1 is transmitted to the first and second stimulable phosphor sheets. 4A and 4B, the radiation image information of the subject 1 is accumulated and recorded on the stimulable phosphor sheets 4A and 4B.

Next, these two stimulable phosphor sheets 4
From A and 4B, a radiation image is read by an image reading means as shown in FIG. 2, and an image signal representing the radiation image is obtained. First, the laser light (excitation light) 11 from the laser light source 10 is deflected by the scanning mirror 12 while the stimulable phosphor sheet 4A is moved in the direction of the arrow Y by the sub-scanning means 9 such as an endless belt. The main scanning is performed in the X direction. By the excitation light scanning, the stimulated emission light 13 of a light amount corresponding to the accumulated and recorded radiation image information is emitted from the stimulable phosphor sheet 4A. The stimulating light 13
A light guide 14 made by molding a transparent acrylic plate enters the inside of the light guide 14 from one end face, and travels through the light guide 14 while repeating total internal reflection, thereby forming a photomultiplier (photomultiplier tube) 15. Received. The photomultiplier 15 outputs an output signal S _A corresponding to the light emission amount of the stimulating light 13, that is, indicating the image information.

The output signal S _A is logarithmically amplified by a logarithmic amplifier 16 and then passed through an A / D converter 17 to be converted into a digital image signal S ₁ . The image signals S ₁ are stored in the storage medium 18 such as a magnetic disk, for example. Next, in the same manner as above, another stimulable phosphor sheet 4
Recording image information B is read, the image signal S ₂ of the digital indicating the image information is stored similarly in the storage medium 18.

Next, a superposition process is performed using the image signals S ₁ and S ₂ obtained as described above. FIG. 3 shows an apparatus for performing this superposition processing. First storage medium
The image signals S ₁ and S ₂ are read out from the image file 18A and the image file 18B in the image processing unit 18, and a superposition calculation circuit
Entered in 19. The superposition operation circuit 19 outputs the input 2
One of the image signals S _1, S ₂ each sensitivity Sk1, Sk2 is required. Here, the sensitivity refers to a photoelectric conversion rate that determines a level of an image signal of a predetermined amount of stimulated emission light. This sensitivity depends on reading conditions when reading an image signal,
These are parameters for determining image processing conditions when performing image processing on an image signal, and an algorithm for calculating the parameters is determined in advance from a result of statistically processing a large number of radiation images. As one of the algorithms, there are known a number of methods of obtaining a histogram of an image signal and obtaining reading conditions and / or image processing conditions based on the histogram (for example, see Japanese Patent Application Laid-Open No. 60-1).
85944, JP-A-61-280163, etc.). Therefore, a detailed description for determining the sensitivity is omitted here. Further, the sensitivities Sk1 and Sk2 obtained here are obtained by taking the logarithms of the sensitivities Sk1 'and Sk2' obtained from the image signal as shown in the graph 30 of FIG. That is, Sk1 = log Sk1 'and Sk2 = log Sk2'.

[0048] Sensitivity Sk1, Sk2 by weighting in sensitivity Sk1, Sk2 respect are the two image signals S _1, S ₂ required, the formula S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1 + Sk2)) × S ₂ ... (8) to determine the addition signal S. Which in formula (1) described above, the N ₁ ² sensitivity Sk1, because it is obtained by replacing the N ₂ ² Sensitivity Sk2, the addition signal S noise has become smallest.

Meanwhile, the sensitivity Sk1 sensitivity before taking logarithm as Sk2 Sk1 ', Sk2' When using the, S = (log Sk2 '/ (log Sk1' + log Sk2 ')) × S 1 + (log Sk1 '/ (log Sk1' + log Sk2 ')) × S 2 ... (8') by may be obtained addition signal S.

Further, when a scale for convenience is used for the sensitivity Sk in FIG. 4 (for example, when a scale is used like the horizontal axis Sk "in FIG. 4), the relationship between Sk" and Sk 'is determined. Is

[0051]

(Equation 5)

S = (4-Sk2 ″) / ((4-Sk1 ″) + (4-Sk2 ″)) × S ₁ + (4-Sk1 ″) / ((4-Sk1 ″) + (4−Sk2 ″)) × S ₂ (8 ″) to determine the addition signal S.

When the addition signal S is obtained as described above, the addition signal S is subjected to image processing such as gradation processing and frequency processing in the image processing circuit 20 and then sent to the image reproducing device 21 to be subjected to radiation image processing. To be played. If a radiation image is reproduced based on the addition signal S, a radiation image with a minimum noise and a good image quality can be obtained.

On the other hand, the above-described sensitivities Sk1 and Sk2 may be obtained for each pixel from which an image signal is obtained. Less than,
The image signals S ₁ describes a method of determining the sensitivity of each pixel.

Firstly, JP from the image signals S ₁ described above the sensitivity Sk1 and latitude Gp1 image signals S ₁ 60-185
Determined by the method disclosed in JP-A-944. Here, the latitude corresponds to the light amount ratio of the strongest stimulated emission light to the weakest stimulated emission light. For example, the sensitivity Sk1 is 2, when the latitude Gp1 has been determined as of 2, the relationship between the sensitivity Sk1 and the image signals S ₁ is as shown in FIG. Here, when the pixel value is 10 bits, Smin = 0 and Smax = 11023. Assuming that the xy coordinates as shown in FIG. 6 are determined for the stimulable phosphor sheet 4A and the sensitivity at an arbitrary point (x, y) on the stimulable phosphor sheet 4A is Sk1 (x, y),

[0056]

(Equation 6)

S ₁ (x, y): It can be obtained from the value of the image signal S ₁ at an arbitrary point (x, y) on the stimulable phosphor sheet 4A.

From equation (9), the sensitivity Sk1 (x,
When y) is obtained, the sensitivity of each pixel on the stimulable phosphor sheet 4B also similarly image signals S ₁ Sk2 (x,
y) is determined, the formula S (x, y) = Sk2 (x, y) / (Sk1 (x, y) + Sk2 (x, y)) × S 1 + Sk1 (x, y) / (Sk1 (x, y) + Sk2 (x, y )) addition signal S is obtained by × S ₂ ... (10).

As described above, if the weighting coefficient is obtained for each pixel, the weight of the radiation dose transmitted through the subject and reaching the stimulable phosphor sheet is not affected by the difference in each location.
Noise can be minimized for each pixel.

If the sensitivity for each pixel is determined based on the blur signal of each image signal, global sensitivity can be determined without being affected by fine changes or noise of the image signal. More preferred. Here, the blur signal is
Method using blur mask signal, median filter, FF
It is obtained by using various smoothing processes such as a method using a T filter and a V-filter.

[0061] In the embodiment described above, two image signals S _1, S ₂ but defines a weighting coefficient used for weighting based on their sensitivity Sk1, Sk2, two image signals S _1, S ₂ of detecting the respective noise N _1, N _2, described above on the basis of the noise N _1, N ₂ formula (1)
May be used to perform weighted addition.

Further, in the above-described embodiment,
Japanese Patent Application Laid-Open No. 60-185944, Japanese Patent Application Laid-Open No. 61-280163, etc. are used to determine the sensitivity.However, the present invention is not limited to this, and any method such as a method using a neural network may be used. You may do so.

In the above embodiment, the superimposition processing using the image signal read from the stimulable phosphor sheet has been described. However, the two image signals of the same subject which are the object of the present invention are not limited to this. Instead, an image signal obtained from another recording medium such as an image signal read from an X-ray film or an image signal obtained from an image intensifier may be used.

[0064]

As described above in detail, the radiographic image superposition processing method and apparatus according to the present invention can minimize the noise of the added signal obtained by the weighted addition processing. Therefore, by reproducing this addition signal, it is possible to obtain a radiation image with improved graininess and good image quality.

If the sensitivity used for the weighting coefficient in the weighting addition process is determined for each pixel, a radiation image with better image quality can be obtained without being affected by a change in dose at each location of the subject. It becomes possible.

Further, if the blur signal of the image signal is obtained and the sensitivity of each pixel is obtained based on the blur signal, it is possible to obtain a global sensitivity which is not affected by fine changes in the image signal and noise. Is more preferable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a radiographic image accumulation recording step in a radiographic image superposition processing method of the present invention.

FIG. 2 is a schematic diagram illustrating reading of radiation image information from a stimulable phosphor sheet on which accumulation recording has been performed.

FIG. 3 is a block diagram showing an outline of an apparatus for performing a superposition process;

FIG. 4 is a graph showing a relationship between sensitivity and noise.

FIG. 5 is a graph showing a relationship between sensitivity and an image signal.

FIG. 6 is a diagram showing a stimulable phosphor sheet as x and y coordinates.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Subject 2 Radiation 3 Radiation source 4A, 4B Storage phosphor sheet 10 Laser light source 11 Laser light 12 Scanning mirror 13 Stimulated emission light 14 Light guide 15 Photomultiplier 16 Logarithmic amplifier 17 A / D converter 19 Superposition operation circuit 20 Image processing circuit 21 Image reproduction device S ₁ , S ₂ Digital image signal S Addition signal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication H04N 5/325 A61B 6/00 350M

Claims (8)

(57) [Claims] 1. A radiographic image superposition processing method in which first and second image signals carrying radiation image information of the same subject are added between signals of corresponding pixels to obtain an addition signal. The first image signal is S ₁ , the noise of the first image signal is N ₁ , the second image signal is S ₂ , the noise of the second image signal is N _2, and the sum signal is S 1 S = (N ₂ ² / (N ₁ ² + N ₂ ² )) × S ₁ + (N ₁ ²
/ (N ₁ ² + N ₂ ² )) × S ₂ , wherein the addition signal S is obtained by weighted addition. 2. A radiation image superimposing means comprising an adding means for performing addition between signals of corresponding pixels with respect to first and second image signals carrying radiation image information of the same subject to obtain an addition signal. In the matching processing apparatus, the adding means may be arranged such that the first image signal is S ₁ , the noise of the first image signal is N ₁ , the second image signal is S ₂ , and the noise of the second image signal is S ₁ . N ₂ and the sum signal S
S = (N ₂ ² / (N ₁ ² + N ₂ ² )) × S ₁ + (N ₁ ²
/ (N ₁ ² + N ₂ ² )) × S _2, which is an addition means for performing weighted addition. 3. A radiographic image superposition processing method in which first and second image signals carrying radiographic image information of the same subject are added between signals of corresponding pixels to obtain an added signal. When the first image signal is S ₁ , the sensitivity of the first image signal is Sk1, the second image signal is S2, the sensitivity of the second image signal is Sk2, and the addition signal is S. a, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1 + S
k2)) A method of superimposing radiographic images, wherein the addition signal S is obtained by weighted addition of × S ₂ . 4. A superposition of radiation images, comprising an adding means for performing addition between signals of corresponding pixels with respect to first and second image signals carrying radiation image information of the same subject to obtain an addition signal. In the matching processing device, the adding means may be arranged such that the first image signal is S ₁ , the sensitivity of the first image signal is Sk1, the second image signal is S ₂ , and the sensitivity of the second image signal is Sk2. and the added signal is taken as S, S = (Sk2 / ( Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × superposition processing apparatus for radiation images, which is a summing means for performing S ₂ becomes weighted addition. 5. A method of superimposing radiographic images in which first and second image signals carrying radiation image information of the same subject are added between signals of corresponding pixels to obtain an addition signal S In the above, the first image signal S ₁ and the second image signal S ₂
Based on, obtains the sensitivity Sk2 of the first image signal sensitivity Sk1 and the second image signal for each pixel, respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S ₂ , wherein the weighted addition is performed for each of the corresponding pixels to obtain the addition signal S. 6. A radiographic image forming apparatus comprising: an adding unit for obtaining an addition signal S by adding between signals of corresponding pixels to first and second image signals carrying radiation image information of the same subject. in superimposing processing apparatus, the adding means, the first image signal S ₁ and on the basis of the second image signal S _2, the said each pixel first image signal sensitivity Sk1 and the second a calculation unit for obtaining an image signal Sk2 respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S ₂ , wherein the weighted addition is performed for each of the corresponding pixels. 7. A method of superimposing radiographic images in which first and second image signals carrying radiation image information of the same subject are added between signals of corresponding pixels to obtain an addition signal S In the above, the first image signal S ₁ and the second image signal S ₂
Respectively, based on the blur signal of the first image signal S _{1 and} the blur signal of the second image signal S ₂ , the sensitivity Sk1 of the first image signal for each pixel and the determined the sensitivity Sk2 of the second image signals, respectively, S = (Sk2 / (Sk1 + Sk2)) × S 1 + (Sk1 / (Sk1
+ Sk2)) × S ₂ , wherein the weighted addition is performed for each of the corresponding pixels to obtain the addition signal S. 8. A radiographic image forming apparatus comprising: an adding means for obtaining an addition signal S by adding between signals of corresponding pixels to first and second image signals carrying radiation image information of the same subject. In the superposition processing device, the adding means obtains a blur signal of the first image signal S ₁ and the second image signal S ₂ , and calculates a blur signal of the first image signal S ₁ and the second signal. based on the unsharp signal of the image signal S _2, a calculation unit for determining the sensitivity Sk1 and the second image signal Sk2 each of said for each of the pixel first image signal, S = (Sk2 / (Sk1 + Sk2)) × S ₁ + (Sk1 / (Sk1
+ Sk2)) × S ₂ , wherein the weighted addition is performed for each of the corresponding pixels.