JPH0415639A - Radiation image read condition and/or image processing condition determination device - Google Patents

Abstract

PURPOSE:To accurately find read conditions, etc., by finding plural candidates for the read conditions, etc., by mutually different arithmetic processes according to an image signal (including a 1st image signal) and finding the read conditions, etc., according to those candidates. CONSTITUTION:Position where the frequency on a histogram 70 are T is searched for in the increasing order of the value of a preread image signal Sp to find preread image signals Sp1 and Sp2 corresponding to the 1st position (a) and next position (b) where the frequency becomes T. Thus, it is judged that the range between the two found preread image signals Sp1 and Sp2 corresponds to a subject image 3 on an X-ray image. Then the read conditions are so determined that stimulated luminescent light emitted at positions on an X-ray image corresponding to the preread image signals Sp1 and Sp2 is converted into the minimum value SQ1 and maximum value SQ2 of an image signal SQ, that is, into a straight line G1; and a primary read is made under the read conditions. Consequently, the accurate read conditions, etc., are found.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is based on an image signal representing a radiographic image, reading conditions for obtaining an image signal, image processing conditions for performing image processing on an image signal, etc. The present invention relates to a device for determining desired radiation image reading conditions and/or image processing conditions.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. By performing image processing on this electrical signal (image signal) and then reproducing it as a visible image in a photocopy, etc., a reproduced image with good image quality performance such as contrast sharpness and graininess can be obtained. (Tokuko Showa 6)
1-5193).

The applicant has also discovered that when radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, a portion of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, the energy is accumulated. Using a stimulable phosphor that exhibits stimulable luminescence in response to energy, radiographic image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor. A stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, and the resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image data, the radiation of the subject is determined. Images can be transferred to recording materials such as photosensitive materials,
A radiation image recording and reproducing system that outputs a visible image on a CRT, etc. has already been proposed (Japanese Patent Laid-Open No. 55-124
No. 29, No. 56-11395, No. 55-183472, No. 56-104645, No. 55-116340, etc.).

This system has the practical advantage of recording images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. It is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over a very wide range, and therefore even if the amount of radiation exposure varies considerably depending on various imaging conditions, The amount of stimulated luminescence light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means and converted to electricity (No. 8), and this electrical signal is used to convert the photosensitive material into By outputting a radiographic image as a visible image on a recording material such as a CRT or a display device such as a CRT, a radiographic image that is not affected by fluctuations in radiation exposure can be obtained.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining an image signal by reading it under optimal reading conditions depending on the dose of radiation applied to the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image signal obtained by this pre-reading is analyzed, and then the sheet is irradiated with a high-level light beam and scanned, and this radiation image is There is also a system configured to perform actual reading in which image signals are obtained by reading under optimal reading conditions.

Kokoro reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as the reading cane that determines the relationship between human output and the scale factor. Alternatively, it refers to the power of excitation light during reading.

Also, the high level/low level of the destination beam is, respectively.
If the energy of the light beam irradiated per unit area of the sheet or the energy of stimulated luminescence light emitted from the sheet depends on the wavelength of the light beam (has a wavelength sensitivity distribution), The energy of the light beam irradiated per unit area of the sheet is the weighted energy after weighting with the wavelength sensitivity.As a method of changing the level of the light beam, light of different wavelengths is used. A method using a beam, a method of changing the intensity of the light beam itself emitted from a laser light source, a method of changing the intensity of the light beam by inserting or removing an N or D filter, etc. on the optical path of the light beam, a method of changing the intensity of the light beam, a method of changing the intensity of the light beam emitted from a laser light source, etc. Various known methods can be used, such as changing the scanning density by changing the diameter or changing the scanning speed.

In addition, regardless of whether the system performs this pre-reading or the system that does not, the obtained image signal (including the pre-read image signal) is analyzed and the optimal image processing conditions are determined when applying image processing to the image signal. Some systems let you decide. The term "image processing conditions" as used herein is a general term for various conditions when performing processing on an image signal that affects the gradation, sensitivity, etc. of a reproduced image based on the image signal. The method of determining the optimal image processing conditions based on this image signal is not limited to systems using stimulable phosphor sheets, and for example, image signals are obtained from radiation images recorded on recording sheets such as conventional X-ray films. It is also applied to the system.

The calculation to obtain reading conditions and/or image processing conditions (hereinafter referred to as reading conditions, etc.) based on the above image signals (including pre-read image signals) is the result of statistically processing a large number of radiation images in advance. (See, for example, Japanese Patent Laid-Open No. 60-1115944 and Japanese Patent Laid-Open No. 61-280163).

One of the conventionally used algorithms is
A method is known in which a histogram of an image signal is obtained and reading conditions etc. are determined based on this histogram. Regarding the method of determining reading conditions etc. based on this histogram,
By subdividing this, both the maximum and minimum values of the range required as image information are found from the histogram of the image signal, and the image information within the range between the maximum and minimum values is read accurately, for example, in main reading. (Refer to Japanese Patent Application Laid-Open No. 156055), find only the maximum value from the above histogram, set the value obtained by subtracting a predetermined value from the maximum value as the minimum value, and compare this maximum value with the minimum value. A method of determining the range between the values and the range of necessary image information (see Japanese Patent Application Laid-open No. 185944/1983), find only the minimum value from the histogram, and add a predetermined value to the minimum value by 1.
．． A method of setting the value as the maximum value and setting the range between the minimum value and the maximum value as the range of necessary image information (Japanese Patent Application Laid-Open No. 1983-1999)
280163), other methods using differential histograms (see Japanese Patent Application No. 62-67302), methods using cumulative histograms (see Japanese Patent Application Laid-Open No. 61-170730), and dividing histograms into multiple small regions based on discrimination criteria. There are known methods for determining the range of necessary image information using a number of methods, such as a dividing method (see Japanese Patent Application No. 82-98716), and thereby determining reading conditions, etc.

In addition to the various methods described above to obtain a histogram of an image signal and determine reading conditions based on this histogram, in recent years, a concept called neural networks, which is completely different from the algorithms described above, has emerged and has been applied to various fields. It is being done.

This neural network is able to communicate between each unit within the neural network by inputting information (teacher signal) on whether the output signal output when a certain input signal is given is a correct signal or an incorrect signal. It is equipped with a hack propagation function that modifies connection weights (synaptic connection weights), and by repeatedly ``learning,'' when a new signal is input, This can increase the probability of outputting a correct answer. (For example, rD, E,
Rumelhart, G. E., Hinton and
R, J, WilliamsLearning rep
residences by baCk-pr
opagatingerrors, Nature, 32
3-9.533-356.1986aJ, r Hideki Aso; Backpropagation Computer No.
, 2453-60J, ``Neural Computer, Tokyo Denki University Press,'' written by Yuki Kinzoku (author).

It is possible to apply this neural network to determining reading conditions, etc., and by inputting an image signal etc. to the neural network, reading conditions etc. can be outputted.

On the other hand, when photographing and recording radiation images on a recording sheet, it is important to avoid irradiating radiation to parts of the subject that are not necessary for observation, or to prevent radiation from being irradiated to parts unnecessary for observation. Scattered rays may appear in some areas, reducing image quality, so use an irradiation field diaphragm to limit the irradiation area so that only the necessary areas of the subject and part of the recording sheet are irradiated with radiation. Often. When analyzing image signals to determine reading conditions, etc. as described above, if the image signal used for analysis is an image signal obtained from a recording sheet photographed using an irradiation field aperture, this irradiation field Even if the image signal is analyzed while ignoring its existence, the radiographic image that has been photographed and recorded will not be grasped correctly, incorrect reading conditions, etc. will be required, and a radiographic image with excellent observation suitability may not be reproduced and recorded. In order to solve this problem, before determining the reading conditions, etc., it is necessary to recognize the irradiation field and determine the reading conditions, etc. based on the image signal within the irradiation field. This irradiation field recognition method includes, for example, differences in the average value of image signals inside and outside the irradiation field, differences in the degree of dispersion of image signals inside and outside the irradiation field, changes in image signals near the contour of the irradiation field, etc. The irradiation field can be recognized based on either one or a combination thereof (for example, Japanese Patent Application Laid-Open No. 61-39039, Japanese Patent Application Laid-Open No. 6:259538, Japanese Patent Application Laid-open No. 1-42436, (Refer to Kaihei 2-67690).

In addition, different radiation images may be photographed and recorded in a plurality of divided regions of -2 recording sheets. According to this divisional shooting, for example, when shooting a subject that is small compared to the area of the recording sheet, it is possible to record the shooting of multiple subjects on one recording sheet, which is economical. When reading a recording sheet to obtain an image signal, it is possible to read a plurality of images at once, and the reading processing speed is also improved.

In this case, as in the case of the above-mentioned irradiation field, if the reading conditions, etc. are determined using the image signal corresponding to the entire surface of one recording sheet, there is a possibility that incorrect reading conditions, etc. will be determined. The area is divided as shown in the image above, and the division pattern is recognized, which indicates which area of the divided areas the radiographic image is recorded in. Based on this, the image signal corresponding to the radiographic image is extracted and the reading conditions are determined. etc. is required. Various methods for recognizing this division pattern are also known (for example, Japanese Patent Laid-Open No. 1-2120fiS).

(Patent Application No. 1983-253062). By combining the various irradiation field recognition methods and the two-division pattern recognition method described above with the various methods for determining the reading conditions, etc., a very wide variety of methods for determining the reading conditions, etc. can be realized.

(Problems to be Solved by the Invention) In various systems that have been considered so far, among the above-mentioned numerous methods for determining reading conditions, etc., for example, imaging conditions (normal imaging, enlarged imaging, tomography, etc.) The optimal method is selected for each classification according to the head (1 neck, 1 chest, 1 abdomen, etc.), etc.

However, none of the above methods is perfect, and in cases where a radiographic image with a pattern that is significantly different from the expected standard pattern is read,
In some cases, reading conditions or the like that are significantly different from each other may result in meaningless signals being obtained and the need for re-imaging.

In view of the above circumstances, it is an object of the present invention to provide a radiation image reading condition and/or image processing condition determination device that can more accurately determine the reading condition 1 image processing condition.

(Means for Solving the Problems) One of the present inventions uses the above-mentioned stimulable phosphor sheet,
This is used in systems that read ahead. That is, the radiation image reading condition and/or image processing condition determining device of the present invention irradiates excitation light onto a stimulable phosphor sheet on which a radiation image is recorded and stimulates the stimulated luminescence light emitted from the stimulable phosphor sheet. Based on the first image signal representing the radiation image obtained by reading, the stimulable phosphor sheet is irradiated with excitation light again and the stimulated luminescence light emitted from the stimulable phosphor sheet is read. Determination of radiation image reading conditions and/or image processing conditions for obtaining reading conditions for obtaining a second image signal representing a radiation image and/or image processing conditions for performing image processing on the obtained second image signal. In the apparatus, a plurality of condition calculation means for calculating candidates for the reading condition and/or the image processing condition based on the first image signal and by mutually different calculations; The apparatus is characterized by comprising a condition determining means for determining the reading condition and/or the image processing condition based on the candidate.

Another aspect of the present invention is to determine image processing conditions not limited to stimulable phosphor sheets.

That is, the radiographic image processing condition determining device of the present invention is a radiographic image processing condition determining device that determines image processing conditions for performing image processing on an image signal based on an image signal representing a radiographic image. , and a plurality of condition calculating means for calculating candidates for the image processing condition by mutually different calculations, and a condition determining means for calculating the image processing condition based on the plurality of candidates calculated by the plurality of condition calculating means. It is characterized by:

Here, the calculation method for determining the candidates in the plurality of condition calculation means is not limited to a specific method, and the various methods described above or other known methods may be used.

Further, the method of determining the reading condition 1 image processing condition based on the plurality of candidates in the condition determining means is not limited to a specific method, and for example, selecting any one of the plurality of candidates, Alternatively, various methods can be employed, such as calculating the average value of these multiple candidates.

(Function) The present invention obtains candidates for a plurality of reading conditions and one image processing condition using mutually different calculations for two radiation images, and obtains reading conditions, etc. based on these plural candidates. Reading conditions etc. are required.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 8 is a perspective view showing an example of a computer system including an example of an X-ray image reading device and an example of the radiation image reading condition and/or image processing condition determining device of the present invention. This system uses the aforementioned stimulable phosphor sheet and performs pre-reading.

In an X-ray imaging device (not shown), an X-ray image of a subject is accumulated and recorded on a stimulable phosphor sheet.

The stimulable phosphor sheet 11 on which this X-ray image is recorded is
First, the sheet 11 is set at a predetermined position in a pre-reading means 100 which performs pre-reading by scanning with a weak light beam and emitting only a portion of the radiation energy accumulated in the sheet 11 . The stimulable phosphor sheet 11 set at a predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveying means 13 such as an endless belt driven by a motor 12. On the other hand, a weak light beam 15 emitted from a laser light source 14 is reflected and deflected by a rotating polygon mirror IB that is driven by a motor 23 and rotates at high speed in the direction of the arrow, passes through a focusing lens 17 such as an fθ lens, and then passes through a mirror 18 to is incident on the sheet 11 in the sub-scanning direction (arrow Y
Main scanning is performed in the direction of arrow X, which is substantially perpendicular to the main direction. From the point on the sheet 11 that has been irradiated with the beam 15, stimulated luminescence light 1 is emitted with an amount of light corresponding to the radiographic image information that has been stored and recorded.
9 is emitted, and this stimulated luminescence light 19 is guided by a light guide 20 and passed through a photomultiplier (photomultiplier tube).
21 in a charging manner. The light guide 20 is made by molding a light-guiding material such as an acrylic plate, and is arranged so as to extend along the linear entrance end surface 20a or the main scanning line on the stimulable phosphor sheet 11. The light receiving surface of the photomultiplier 21 is coupled to the annularly formed output end surface 20b. The above-mentioned entrance end surface 20a
The stimulated luminescent light 19 that has entered the light guide 20 from above travels inside the light guide 20 through total internal reflection, exits from the output end face 20b, is received by the photomultiplier 21, and represents a radiation image. The amount of stimulated luminescent light 19 is converted into an electrical signal by a photomultiplier 21.

The analog output signal S output from the photomultiplier 21 is logarithmically amplified by a logarithmic amplifier 26 and digitized by an A/D converter 27 to obtain a pre-read image signal Sp. The signal level of this pre-read image signal Sp is
It is proportional to the logarithm of the amount of stimulated luminescence light emitted from each pixel of 1.

In the above-mentioned pre-reading, reading conditions, such as the voltage value applied to the photomultiplier 21 and the amplification factor of the logarithmic amplifier 26, are determined so that the radiation energy accumulated in the stimulable phosphor sheet 11 can be read over a wide range. It is being

The obtained pre-read image signal Sp is sent to the computer system 4
It is input to 0. This computer system 40 includes an example of the radiation image reading condition and/or image processing condition determination device of the present invention, and includes a main body 41 in which a CPU and internal memory are built-in, and a floppy disk inserted as an auxiliary memory. Drive unit 4 that is driven
2. A keyboard 43 for the operator to input necessary instructions to the computer system 40. and a CRT display 44 for displaying necessary information.

In this computer system 4o, the division pattern and the irradiation field are recognized as described later based on the input pre-read image signal Sp, and then the reading conditions for the main reading, that is, the sensitivity Sk and the latitude for the main reading are determined. Gp is calculated, and the calculated sensitivity Sk and latitude G are
For example, the voltage value applied to the photomultiplier 21', the amplification factor of the logarithmic amplifier 26', etc. are controlled according to p.

Here, the latitude Gp corresponds to the light intensity ratio of the most intense stimulated luminescence light to the weakest stimulated luminescence light that is converted into an image signal during main reading, and the sensitivity Sk corresponds to the ratio of the light amount of the most intense stimulated luminescence light to the weakest stimulated luminescence light that is converted into an image signal during main reading. This refers to the photoelectric conversion rate that determines the level of image signal generated from stimulated luminescence light.

The stimulable phosphor sheet 11' for which pre-reading has been completed is set at a predetermined position in the main reading means 100', and the sheet 11' is scanned by a light beam 15' which is stronger than the light beam used for the above-mentioned pre-reading. An image signal can be obtained according to the reading conditions determined by the actual reading means 100'.
Since the configuration of the pre-reading means 100 is different from that of the above-mentioned pre-reading means 100, components corresponding to those of the pre-reading means 100 are shown with a dash attached to the number used, and explanations will be given. is omitted.

The image signal S0 obtained by being digitally converted into I/O by the A/D converter 27' is inputted to the computer system 40 again. Appropriate image processing is performed on the image signal SQ within the computer system 40, and the image signal subjected to this image processing is sent to a reproduction device (not shown), and an X-ray image based on this image signal is reproduced and displayed in the reproduction device. Ru.

Next, a method will be described in which the computer system 4o first recognizes the division pattern and the irradiation field based on the pre-read image signal Sp, and then determines the reading conditions for actual reading. In this embodiment, each means is considered to be a combination of hardware and software of the computer system 40 that realizes the functions corresponding to each means of the present invention.

FIG. 1 is a diagram showing an example of an X-ray image.

Here, the stimulable phosphor sheet 11 is divided into two parts vertically and horizontally (four parts in total) among the partial areas 11a to 11d, except for the partial area 11d, and the other three partial areas 11a to J
, Lc, and in each of the irradiation fields 2, a subject image 3 with a human head as the subject and a direct X-ray section 6 are formed.
It is formed.

First, in order to recognize the division pattern, the pre-read image signal Sp corresponding to each of the partial areas 11a to lid is
The average value of is determined for each of the partial regions 11a to lid,
This average value is compared with a predetermined threshold, and if the average value is higher than the predetermined threshold, an X-ray image has been formed in that partial area, and if the average value is lower than the predetermined threshold. It is determined that no X-ray image is formed in that partial area.

That is, here, it is determined that X-ray images are formed in three partial areas 11a-lie among the partial areas 11a-1bj, and no X-ray image is formed in partial area 11d.

Next, the following calculations are performed for each of the partial areas 11a-J, lc in which the X-ray images determined in this manner are recorded, and the irradiation field 2 is recognized.

An example of a method for recognizing the irradiation field 2 of the partial area ILa will be described below.

FIG. 2 shows an X-ray image recorded in the partial area 11a.
FIG. 3 is a diagram showing a graph of a pre-read image signal obtained from a line image and its differential value.

Here, the center C of the partial area 11a is selected, and along each of the plurality of line segments 5 extending radially from the center C, a differential operation is performed on the pre-read image signal Sp corresponding to each pixel of each line segment. This is determined as a point where the value of the pre-read image signal Sp suddenly drops or as a contour point located on the contour of the irradiation field.

Hereinafter, a case will be described in which contour points on a line segment along the ξ axis among the plurality of line segments 5 are found.

Graph A is a graph representing the value of the pre-read image signal Sp obtained from each pixel along the ξ axis.

The value of the pre-read image signal Sp of the direct X-ray unit 6 where X-rays are directly irradiated onto the stimulable phosphor sheet 11 other than the subject image 3 in the irradiation field 2 is the highest, and the value of the pre-read image signal Sp is the highest at the contour of the irradiation field 2. The value of the pre-read image signal Sp is decreasing.

Graph B is a graph obtained by differentiating the pre-read image signal Sp shown in graph A from the center C in the negative direction of ξ (leftward in the figure) and in the positive direction of ξ (rightward in the figure).

In graph B, on the line segment going from center C to the negative direction of the ξ axis, the main peak that protrudes downward is al, and therefore the position of this beak al is the contour point and 1. It is determined by

In the graph B, there is a peak a2 projecting downward on a line segment extending from the center C in the positive direction of the ξ axis, and the position of this beak a2 is determined as a contour point.

As described above, contour points 7 are determined for each of the plurality of line segments 5 connecting the center C and the end of the partial region 11a. After these contour points 7 are determined, if a line along these contour points 7 is determined, that line becomes the contour of the irradiation field. The line along this contour point 7 can be created by, for example, connecting the remaining points after smoothing the points, or by locally applying the least squares method to find a plurality of straight lines and connecting them.
Although it can be determined by a method such as fitting a spline curve, in this embodiment, a plurality of straight lines along the contour point 7 are determined using Hough transformation.

The process of finding this straight line will be explained below.

When one end of the partial area 11a shown in FIG. 2 (lower left end in the figure) is set as the origin and the X-axis and y-axis are determined as shown in the figure,
The coordinates of each contour point (Xi, yl) (xz, yz
), ..., (Xn, yn), or in this case, by representing these coordinates, the coordinates (Xo, Yo
). Here, the coordinates of the above contour point are (Xo,)'o
) then these X. .

A curve expressed by p-xo eos θ+y (, sin θ =il) with Yo as a constant is defined by all contour point coordinates (X.

yo). This curve is as shown in FIG. 3, and there are as many curves as there are contour point coordinates (Xo, yo).

Next, an intersection point (ρ., θ.) where a predetermined number of zero or more of the above-mentioned plurality of curves intersect with each other is determined. Note that due to errors in the contour point coordinates (Xo, Yo), it is rare for many curves to intersect exactly at one point, so in reality, for example, the intersections of two curves exist at intervals of less than a very small predetermined value. Then, the center of the group of intersection points is the above intersection point (ρ., θ
. ). Next, from the intersection (ρ0.θ0), a straight line defined by the following formula (2) is determined in the xy orthogonal coordinate system. When the contour points 7 are lined up as shown in FIG. 2, this straight line is a straight line Ll-L which is an extension of each line segment forming the contour of the irradiation field 2 as shown in FIG.

It is required as. Next, the multiple straight lines I obtained in this way
, 1. L2. L3. ...L, is found, and this region is recognized as the irradiation field 2. This area is recognized in detail as follows, for example. Computer system 40-former line segments MIMz, M3, . . . M, connecting the corners of the partial area 11a and the center C,
(Four lines in the case of the partial area 11a or rectangle) are stored, and the presence or absence of an intersection between each of these line segments M1 to M□ and each of the above-mentioned straight lines L1-La is checked. If this intersection exists,
Partial area 11 of the plane bisected by the straight line
The plane containing the corner of a is truncated. By performing this operation on all the straight lines, -L, and the line segments M1 to M, a region surrounded by the straight lines, ~L, is left. This remaining area is the irradiation field 2 (see FIG. 2).

When the irradiation fields 2 are determined for each partial region 11a to 11lie (see Fig. 1) in this way, the reading conditions for main reading are determined based on the pre-read image signals sp corresponding to these three irradiation fields 2. It will be done.

FIG. 5 is a diagram showing a histogram of the pre-read image signal Sp corresponding to the entire area of the three irradiation fields 2. The horizontal axis of the figure represents the value of the pre-read image signal Sp, and the vertical axis (upper) represents the frequency of appearance of the pre-read image signal Sp with each position (each pre-read image signal Sp corresponding to each pixel of the X-ray image is (count as one)
It represents. Moreover, the vertical axis (lower part) of the figure shows the value of the image signal SQ obtained by the main reading.

This histogram 70 has a thick (divided into the subject image 3)
1), and a peak B, which corresponds to the direct X-ray section 6 and is located at a position where the value of the pre-read image signal Sp is larger than that of the peak A. Here, the position where the frequency is T on the histogram 70 is searched from the smaller value of the pre-read image signal Sp to the larger value, and the first position a where the frequency is T is searched.
and the pre-read image signal 5l) 1, 5l) corresponding to the next position.
Z is required. It is determined that the range sandwiched between the two pre-read image signals 5l)1 and 5l)Z thus obtained corresponds to the subject image 3 on the X-ray image. If you try to perform actual reading, the pre-read image signals Spt, ! so that the stimulated luminescence light emitted from the location on the X-ray image corresponding to lz is converted into the minimum value SQL+maximum value SQ2 of the image signal SQ, that is, the straight line G1 shown in FIG. Reading conditions are determined, and the main reading is performed according to these reading conditions. Here, the reading conditions are determined by the horizontal position of the straight line G1 in FIG. 5 (sensitivity Sk) and the slope of the straight line G1 (latitude Gp).

However, if the histogram 70 has irregularities that cross the threshold value T, as in the histogram 70' shown in FIG. When the actual reading is performed based on the conditions, the image signal SQ carries only the area (corresponding to the area A' on the histogram) sandwiched by the pre-read image signal 5l) ISp2' of the subject image 3 (see Fig. 1). In this case, there is a drawback that, for example, it becomes necessary to perform re-imaging.

Next, another example of determining reading conditions for main reading will be described.

FIG. 6 is a diagram showing an example of a neural network equipped with an error backpropagation learning (pack propagation) function. Error backpropagation learning (pack propagation) is, as mentioned above, by comparing the output of the neural network with the correct answer (teacher signal), and sequentially calculating connection weights (synaptic connection weights) from the output side to the input side. It is a “learning” algorithm that corrects the

As shown in the figure, the first layer (input layer), second layer (intermediate layer), and third layer (output layer) of this neural network are composed of n1 units, n2 units, and 2 units, respectively. Each signal F1+FZ input to the first layer (input layer)
,...+Fnl is a pre-read image signal Sp corresponding to each pixel in the irradiation field 2 of the X-ray image, which is appropriately spaced, and is the third layer (output layer). The two outputs V from
? , ``ll'2 are signals corresponding to the sensitivity Sk and latitude Gp, respectively, during main reading.

The i-th unit of the layer is k. Each input to the unit 7 is X7, and each output is Y:su:
Assume that the weight of the connection from to 7+i is Wi:1, and that each unit u7 has the same characteristic function. At this time, the input X' and output y of each unit 7 are as follows: Each unit I (i=
1.2. ---, nl) F1, F
Z + "Fnl is input as is to each unit u: (i-i, 2..., nl) without being weighted.

01 input signals F1. F2. −． Fat is transmitted to the final output ()'++Yz while being weighted by the weight Wii''1 of each connection, thereby determining the reading conditions (sensitivity Sk and latitude Gp) for the actual reading.

Here, a method for determining the weight w k k+ l of each of the above-mentioned connections will be explained. First, the weight w of each connection is determined by a random number.
An initial value of 77” is given. At this time, the input Fl
-F. Even if 1 fluctuates to the maximum, the output V: +Y
2 is a value within a predetermined range or a value close to this,
It is preferable to limit the range of the random numbers.

A number of stimulable phosphor sheets on which X-ray images with known optimal reading conditions have been recorded are read in the manner described above to obtain a pre-read image signal sp, and this pre-read image signal Sp is thinned out to produce the 01 The inputs F1°Fz, . . . , Fyu, are determined. This 01 inputs F1. F2. ..., Fゎ, are input to the neural network shown in Figure 6, and the output of each unit 7 is ? is monitored.

Once each output y: is determined, the final output V? J
y2 and the teacher signal (sensitivity 5k-yI and latitude 1) as the correct reading condition for this image.
, 1 El-(yI yx)2 ... (01~ EZ""(3'2 Fz)2 ・
...(7) is required. These squared errors E1. E2
The weight W''+'r'' of each connection is modified as follows so that each of the values is minimized. The output of y1 will be described below, and since V2 is the same as y:,
It is omitted here.

To minimize the squared error E1, this El should be w::”l
The weight of each connection W7: ``'' is modified as it is a function of .

Here, η is a coefficient called a learning coefficient.

Here, and from equation (4), x: °1-Σw,," y ... (4)' Therefore, equation (9) can be expressed as (11) using equation (5). Transforming the equation, here, from equation (3), f' (x) = f (x) (1-f (
x)), so...(13) r'(X?) -y: (I Y?) = l
t4).

In equation (10), set -2 to (12), (14)
Substituting the formula into formula (10) yields.

Here, from equation (6), ``(3'? Y?) ・yl (1yI) ・yI ... (15) Substituting this equation (15) into equation B), Wl, mW, - η・(y+d)・V?(
1-y? )・y2...(16) According to this equation (16), Wl l (i-1
, 2, . . . nx) are modified.

Next, ・Y? (1y?)・W? ?・-・(20)(
Put -1 in equation 10), and change equation (20) to (10)
Substituting into the equation gives, So, by substituting equation (4) and (51) into equation (17), from equation (13), f' (x? ) = V: (I V? )
= 419), so this equation (19) and (12)
, Substituting equation (:4) into equation (18), = (y:y'\')・yl・(1y:)・y?・(I
Y+')・w'::my'...(21) Substituting this equation (21) into equation (8), replacing k-1, w: ? -W Explosion-η・(y? y?)°y:(l
Y? ) ・y ・ (I Y?) ・y；ew
J.

...(22), and Wll(i-1, 2,
... nx) is substituted into this equation (22), and W: child (
j-1,2゜-z nl; j-1,2,-, nz)
will be corrected.

Theoretically, by using equations 1B) and (22) and setting the learning coefficient η sufficiently small and increasing the number of learnings sufficiently, the weight w k k+ l of each connection can be focused to a predetermined value. However, making the learning coefficient η too small is not realistic because it slows down the progress of learning. On the other hand, if the learning coefficient η is set to a large value, the learning may oscillate (the weights of the connections described above may not converge to a predetermined value). Therefore, in practice, an inertia term as shown in the following equation is added to the connection weight correction amount to suppress vibration, and the learning coefficient η is set to a somewhat large value.

(e.g., D.E., Rumelhart, G.E., Hi
ton and R.J., Williams: Lea.
rning 1internal representative
trons byerror propagation
In Parallel Distributed
Processing, VoluIle l, J, L,
McClelland, D. E., Ruelhart.
and The PDP Re5earch Group
p, HIT Press, 198 [see 3bJ) ΔW: :” (t+1)−α・6w77” (t
) 6 w k k '' l (t) represents the amount of correction obtained by subtracting the weight w k k '' of the connection before correction from the connection weight W k k +l after correction in the .sup.th learning. Further, α is a coefficient called an inertia term.

As the inertia term α and the learning coefficient η, for example, α−o9η−0.
25 to modify the weight w k k + l of each connection (
For example, 200,000 times, the weight W77'' of each connection is fixed to the final value. At the end of this learning, the two outputs y:, yz are the sensitivity Sk and latitude during the main reading, respectively. This becomes a signal that correctly represents Gp.

After completing the learning, a pre-read image signal Sp representing an X-ray image whose reading conditions are unknown during actual reading is determined, and the irradiation field of the X-ray image is recognized based on this pre-read image signal Sp. Then, the pre-read image signal Sp of the irradiation field is manually input to the neural network shown in Fig. 6, and the output 3': +Yz obtained thereby determines the reading conditions (sensitivity Sk and latitude Gp) for the actual reading for that X-ray image. This is the signal that represents the signal. Since this signal is obtained after the learning has been performed as described above, it represents the reading conditions for actual reading with a fairly high degree of accuracy.

It should be noted that the neural network described above is not limited to a three-layer structure, and it goes without saying that it may have even more layers. It goes without saying that each layer can be configured with any number of units depending on the number of pixels of the input pre-read image signal Sp, the accuracy of the required reading conditions, etc.

If the reading conditions are determined using this neural network, the accuracy of the reading conditions will be determined depending on the number of units that make up the neural network, the number of layers, the number of learning times, etc. Even if the pre-read image signal Sp is input, unlike in the case of the histogram analysis described above, the reading conditions may not be completely optimal. Even when the read image signal Sp is input, unlike the case of the histogram analysis described above, it has the property that it is unlikely that the reading conditions will be completely different.

In addition, here, based on the two reading conditions obtained using two mutually different algorithms as described above, in order to further obtain the reading conditions for main reading, two reading conditions obtained using the above mutually different algorithms will be used. The conditions,
Here, they are referred to as "reading condition candidates."

In the present invention, the algorithm for determining the reading condition based on the above two reading condition candidates is not limited to a specific algorithm (for example, each of the above two candidates for both sensitivity Sk and latitude Gp) is not limited to a specific algorithm. For safety reasons, use this average value as the reading condition for the main reading, or use the average value for sensitivity Sk, and use the larger value for latitude Gp (the straight line in Figure 6) for safety. This corresponds to the fact that the slopes of Gl and Gl' are flat.In other words, straight line G1 is straighter than straight 19G1.
'The value of latitude Gp is larger than .

FIG. 7 shows the reading conditions (sensitivity S
FIG. 3 is a diagram for explaining an example of an algorithm for determining latitude Gp). The horizontal axis of this figure represents the reading conditions (sensitivity Sk and latitude Gp), and the vertical axis represents the confidence level P that the reading condition candidate is the correct reading condition.

A function of the certainty factor P for each algorithm for determining reading condition candidates is determined and stored in the computer system 40 (see FIG. 9). Here, the function 71 is a function of certainty P corresponding to the histogram analysis described above, and the function 72 is a function corresponding to the neural network described above. As mentioned above, when employing histogram analysis, correct reading conditions may be determined with high precision, but there are also cases where extremely deviant reading conditions are required. On the other hand, when a neural network is used, there is little expectation that completely optimal reading conditions will be required, but extremely deviant reading conditions are also rarely required.

Therefore, the confidence level P is determined for each of the two reading condition candidates found above, and for each of the sensitivity Sk and latitude Gp, and the one with the higher confidence level P for each of the sensitivity Sk and latitude Gp is read. Adopted as a condition.

According to the reading conditions (sensitivity Sk and latitude Gp) obtained in this way, the voltage applied to the photomultiplier 21' of the main reading means 100', the amplification factor of the amplifier 26', etc. are controlled, and according to the controlled conditions, A reading will be held.

In addition, in the above embodiment, when finding candidates for reading conditions,
Have we explained an example of finding the candidate using histogram analysis and an example of finding the candidate using a neural network?For example, the various algorithms mentioned above are known for histogram analysis, and which algorithm is used? However, in the present invention, the algorithm for finding candidate reading conditions is not particularly limited. Further, the number of candidates for reading conditions is not limited to two, and a larger number of candidates may be found.

In the above embodiment, the pre-reading means 100 and the main reading means 100'
However, as mentioned above, the pre-reading means 100 and the main reading means 100' are structured separately, so
The pre-reading means 100 and the main reading means 100' may be used as a single unit. In this case, after pre-reading, the stimulable phosphor sheet 11 may be further moved back, and the main reading may be performed by scanning again.

When the pre-reading means and the main reading means are used, it is necessary to switch the intensity of the light beam between the pre-reading and the main reading. Various methods can be used, such as a method of switching the intensity itself.

Further, in the above embodiment, a device for determining reading conditions for reading a book using the computer system 40 was explained.
During actual reading, reading is performed under predetermined reading conditions regardless of the pre-read image signal Sp, and the computer system 40 determines the image processing conditions when performing image processing on the image signal S0 based on the pre-read image signal Sp. Alternatively, the computer system 40 may obtain both the reading conditions and the image processing conditions.

Furthermore, although the above embodiment has been described with respect to a radiation image reading device that performs pre-reading, the present invention can also be applied to a radiation image reading device that immediately performs reading equivalent to the above-mentioned main reading without performing pre-reading. In this case, when reading, an image signal is obtained by reading under predetermined reading conditions, and based on this image signal, the convertan stem 4
Image processing conditions are determined within 0, and image processing is performed on the image signal according to the determined image processing conditions.

Further, the present invention can be used not only for systems using stimulable phosphor sheets, but also for devices using conventional X-ray films.

(Effects of the Invention) As explained in detail above, the radiation image reading condition and/or image processing condition determining device of the present invention can perform reading based on image signals (including the first image signal) and using mutually different calculations. Since a plurality of candidates for conditions, etc. are determined, and reading conditions, etc. are determined based on the plurality of candidates, reading conditions, etc. can be determined more accurately than in the past.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of an X-ray image, and Figure 2 is a partial X-ray image of the X-ray image shown in Figure 1 and a pre-read image signal obtained from this X-ray image. Figure 3 is a graph to explain how to find a straight line along contour points. Figure 4 is a graph showing how to find a straight line along contour points. Figure 4 is a graph for extracting the area surrounded by straight lines along contour points. An explanatory diagram for explaining the method, FIG. 5 is a diagram showing a histogram of a pre-read image signal corresponding to an irradiation field, FIG. 6 is a diagram showing an example of a neural network, and FIG. 7 is a diagram showing an example of a neural network. FIG. 8 is a perspective view showing an example of a radiation image reading device and an example of a computer system incorporating an example of the present invention; FIG. FIG. 1 is a perspective view showing an example of a computer system including an example of a processing condition determination device. 2...Irradiation field 3...Subject image 6...
Direct X-ray section 11, 11'... stimulable phosphor sheet 19, 19'
... Stimulated luminescent light 21, 21'... Photo multiplier 26, 26'
... Logarithmic amplifier 27゜27' ... A/D converter 40 ... Computer system 100 ... Pre-reading means 100' ... Main reading means Fig. Fig. Fig. Fig. Fig.

Claims (2)

[Claims] (1) A first image signal representing the radiation image obtained by irradiating the stimulable phosphor sheet on which the radiation image is recorded with excitation light and reading the stimulated luminescence light emitted from the stimulable phosphor sheet. based on the reading conditions for obtaining a second image signal representing the radiation image by irradiating the stimulable phosphor sheet with excitation light again and reading the stimulated luminescence light emitted from the stimulable phosphor sheet. and/or in a radiation image reading condition and/or image processing condition determination device for determining image processing conditions for performing image processing on the obtained second image signal, based on the first image signal and different from each other. a plurality of condition calculation means for calculating candidates for the reading condition and/or the image processing condition; and a plurality of condition calculation means for calculating the reading condition and/or the image processing condition based on the plurality of candidates obtained by the plurality of condition calculation means. 1. A radiographic image reading condition and/or image processing condition determining device, comprising: condition determining means for determining the condition. (2) In a radiation image processing condition determination device that determines image processing conditions for performing image processing on an image signal based on an image signal representing a radiation image, the image processing is performed based on the image signal and by mutually different calculations. a plurality of condition calculation means for finding candidate conditions;
A radiation image processing condition determining device comprising: condition determining means for determining the image processing condition based on the plurality of candidates determined by the plurality of condition calculating means.