JPH0266682A - Correct/error deciding method for outline candidate point in radiation field - Google Patents

Abstract

PURPOSE:To exactly recognize the radiation field by deriving an outline candidate point and a variation point which is generated characteristically only in the radiation field, and deciding that the outline candidate point is an erroneously detected point which does not exist on the outline of the radiation field, when the outline candidate point exists on a prescribed point side from the variation point. CONSTITUTION:On a cumulative phosphor sheet 11, an object image 3 in which a head part of the human body is an object is photographed and recorded in a radiation field 2. Also, in the radiation field 2, a foreign matter 4 is also photographed and recorded. The foreign matter 4 is a character, etc., which are imprinted together with the object in the radiation field 2 by using, for instance, a lead plate. In this case, the center C of a cumulative phosphor sheet is selected as a prescribed point in the radiation field 2, a differential operation is performed to pre-read image data Sp corresponding to each picture element on each segment along each of plural segments 5 extended radially from this center C, and a point where a value of the pre-read data Sp drops suddenly is derived as an outline candidate point.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to reading a recording sheet on which a radiation image of a subject is recorded to obtain a large number of image data corresponding to each pixel on the recording sheet. Based on these image data, a contour candidate point that is considered to be a point on the contour of the radiation irradiation field formed on the recording sheet is determined, and whether or not this contour candidate point is an erroneously detected point that is not on the contour. The present invention relates to a method for determining whether an irradiation field contour candidate point is correct or incorrect.

(Prior Art) Reading a recorded radiation image to obtain image data, performing appropriate image processing on this image data, and then reproducing and recording the image is performed in various fields. An X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with the image processing of A system has been developed that can obtain reproduced images with good image quality performance such as contrast sharpness and graininess by performing image processing on this electrical signal (image data) and then reproducing it as a visible image in a copy photograph, etc. (Refer to Japanese Patent Publication No. 61-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with 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, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain image data, and based on this image data, a radiation image of the subject can be recorded on a recording material such as a photographic light-sensitive material, a CRT, etc. Radiation image recording and reproducing systems that output visual images have already been proposed (Japanese Patent Application Laid-Open No. 12429/1983, No. 5B-11395, Japanese Patent Application Laid-open No. 55-1139).
No. 183472, No. 5B-104645, No. 55-1
No. 16340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining image data by reading it under optimal reading conditions depending on the dose of radiation irradiated on the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image data obtained by this pre-reading is analyzed, and then the above sheet is irradiated with a light beam of a higher level than the light beam used during the above-mentioned pre-reading. There is also a system configured to perform main reading to obtain image data by scanning the radiation image and reading it under the optimum reading conditions for this radiation image (Japanese Patent Laid-Open No. 58-67240).
No. 58-87241, No. 58-87242, etc.)
.

Here, 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 reading gain, scale factor, or , the power of excitation light during reading, etc.

Also, the high level and low level of the light beam are, respectively.
If the intensity of the light beam irradiated per unit area of the sheet or the intensity of stimulated luminescence light emitted from the sheet depends on the wavelength of the light beam (has a wavelength sensitivity distribution), It refers to the weighted intensity after weighting the intensity of the light beam irradiated per unit area of the sheet by the wavelength sensitivity, and the method of changing the level of the light beam is to use light beams of different wavelengths. methods to use, methods to change the intensity of the light beam itself emitted from a laser light source, methods to change the intensity of the light beam by inserting or removing an ND filter, etc. on the optical path of the light beam, methods to change the beam diameter of the light beam. How to change the scanning density,
Various known methods can be used, such as a method of changing the scanning speed.

In addition, regardless of whether the system performs this prefetching or the system that does not, the obtained image data (including prefetched image data) is analyzed to determine the optimal image processing conditions when performing image processing on the image data. Some systems let you decide. The method for determining the optimal image processing conditions based on this image data is not limited to systems using stimulable phosphor sheets, but for example, image data is obtained from a radiation image recorded on a recording sheet such as a conventional X-ray film. It is also applied to the system.

Various methods have been proposed to determine the optimal reading conditions and image processing conditions by analyzing the above image data (including pre-read image data), but one method is to create a histogram of the image data. known (for example,
(Japanese Patent Application No. 12658/1982).

By calculating the histogram of image data, it is possible to know, for example, the maximum value, minimum value, and value of the image data at the point where the frequency is maximum, and from these six values, the stimulable phosphor sheet, It is possible to grasp the characteristics of a radiation image recorded on a recording sheet such as a line film.

Therefore, by determining the optimal reading condition 1 image processing condition based on this histogram, it becomes possible to reproduce and output a radiation image that is highly suitable for observation.

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 enter some areas, reducing image quality. Therefore, use an irradiation field diaphragm to limit the radiation irradiation area so that only the necessary parts of the subject and part of the recording sheet are irradiated with radiation. Often.

However, when analyzing image data to determine reading condition 1 image processing conditions as described above, if the image data used for analysis is image data obtained from a recording sheet photographed using an irradiation field aperture. Even if you analyze the image data while ignoring the existence of this irradiation field, the radiographic image taken and recorded will not be understood correctly, and incorrect reading conditions and image processing conditions will be required, resulting in a radiographic image that is suitable for observation being reproduced and recorded. There may be cases where this is not done.

In order to solve this problem, before determining the reading condition 1 image processing conditions, it is necessary to recognize the irradiation field and determine the reading condition 1 image processing conditions based on the image data within the irradiation field.

Among the methods for recognizing the irradiation field, a versatile method that can accurately recognize the irradiation field even if the irradiation field has an irregular shape is, for example, a method that uses a predetermined point within the irradiation field. Based on the image data corresponding to each pixel along multiple radial line segments connecting to the edge of the sheet, contour points that are considered to be on the contour of the irradiation field are determined for each of the above line segments, and these contour points are calculated. The present applicant has already proposed a method for recognizing an area surrounded by a line along the line as an irradiation field (Japanese Patent Application No. 82-93633).

(Problem to be solved by the invention) By first determining the irradiation field as described above and then analyzing the image data corresponding to the determined irradiation field,
Appropriate reading conditions 2 and image processing conditions are required.

However, if a foreign object other than the subject (for example, a lead protector for radiation protection or a fixture to fix the subject) is photographed together with the subject, calculations to determine the irradiation field may not be performed effectively. In this case, the reading conditions are determined based on the image data corresponding to the erroneously recognized irradiation field.

There is a problem in that even though image processing conditions have been determined and calculations have been made to recognize the irradiation field, a radiation image that is suitable for observation may not be reproduced and recorded.

In view of the above problems, the present invention calculates some contour candidate points that are considered to be on the contour of the irradiation field, and then determines whether or not the obtained contour candidate points are on the contour of the irradiation field. The purpose of this invention is to provide a method for determining whether a candidate point of an irradiation field outline is correct or incorrect.

(Means for Solving the Problems) The method of determining whether the irradiation field contour candidate points are correct or incorrect according to the present invention is based on reading a recording sheet such as a stimulable phosphor sheet or photographic film on which a radiation image of a subject is recorded. After obtaining a large number of image data corresponding to each pixel, an image corresponding to each pixel on a line connecting a predetermined point included in the radiation irradiation field formed on the recording sheet and the end of the recording sheet is generated. Based on the data, a contour candidate point that is considered to be the intersection point between the contour of the irradiation field and the above line segment is determined, and a change point in the image data along the above line segment that occurs characteristically only within the irradiation field is determined. The present invention is characterized in that when a change point is found, it is determined that a contour candidate point on the predetermined point side of the change point is an erroneously detected point that is not on the contour.

In a preferred embodiment of the present invention, the recording sheet on which the radiation image of the subject is recorded is read by photoelectric reading of light representing the radiation image obtained from each pixel on the recording sheet. "Light representing the radiation image obtained from each pixel on the recording sheet" includes stimulated luminescence light emitted from the stimulable phosphor sheet,
This includes light transmitted through or reflected from photographic film.

(Function) Since the outside of the irradiation field of the recording sheet is a part that is irradiated with only scattered radiation, the image data obtained from this area is, for example, image data that is proportional to the radiation dose. In this case, the value of the image data is small, and the image data of each adjacent pixel does not change significantly (approximately -like). Furthermore, since the irradiation field is an area to which radiation has been actively irradiated, the value of the image signal is large and has the characteristic of rapidly changing at the boundary of the irradiation field. Therefore, if the contour candidate point obtained once is on the contour of the irradiation field, the above image data will not exceed the predetermined value outside that point, and the image data of each adjacent pixel will not be higher than the predetermined value. No major changes will occur.

The present invention has been made from the above-mentioned point of view, and calculates contour candidate points and changing points that characteristically occur only within the irradiation field. If there is a contour candidate point on the inside of the irradiation field, the irradiation field can be recognized more accurately by determining that this contour candidate point is an erroneously detected point that is not on the contour of the irradiation field.

- If the first contour candidate point is determined to be a falsely detected point, other contour candidate points may be found outside the above change point, and the contour candidate determined to be a falsely detected point The irradiation field may be determined based on a large number of contour candidate points on many other line segments, ignoring the line segment corresponding to the point.

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

FIG. 4 is a perspective view showing an embodiment of a radiation image reading device using an example of the method for determining whether a candidate point of an irradiation field contour is correct or incorrect according to the present invention. This example uses a stimulable phosphor sheet,
This is a system that reads ahead.

The stimulable phosphor sheet (11) on which a radiation image has been recorded is first scanned with a weak light beam to emit only a part of the radiation energy stored in this sheet (11), and is scanned by a predetermined pre-reading means 100 for pre-reading. set in position. 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 1 emitted from a laser light source 14
5 is reflected and deflected by a rotating polygon mirror I6 that is driven by a motor 23 and rotates at high speed in the direction of the arrow, and after passing through a focusing lens 17 such as an fθ lens, the optical path is changed by a mirror 18 and the light beam enters the sheet 11 for sub-scanning. Main scanning is performed in the direction of arrow X, which is substantially perpendicular to the direction (direction of arrow Y). From the part of the sheet 11 irradiated with this light beam 15, stimulated luminescence light I9 of a light amount corresponding to the radiographic image information stored and recorded is emitted.
is emitted, and this stimulated luminescence light 19 is guided by a light guide 20 and photoelectrically detected by a photomultiplier (photomultiplier tube) 21 as a photodetector. The light guide 20 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that the linear entrance end surface 20a extends along the main scanning line on the stimulable phosphor sheet ll. The light receiving surface of the photomultiplier 21 is coupled to the annularly formed output end surface 20b. The stimulated luminescence light 19 entering the light guide 20 from the input end face 20a travels through the light guide 20 through repeated total reflection, exits from the output end face 20b, and is received by the photomultiplier 21, resulting in a radiographic image. The photomultiplier 21 converts the amount of stimulated luminescent light 19 representing .

The analog output signal S output from the photomultiplier 21 is amplified by the amplifier 2G, and digitized by the A/D converter 27 to obtain pre-read image data Sp.

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

The obtained pre-read image data Sp is manually input to the recording means 28 and is stored for a while. Thereafter, the pre-read image data Sp stored in the storage means 28 is read out and inputted to the calculation means 29, and the calculation means 29 prints the data on the stimulable phosphor sheet 11 based on the input pre-read image data Sp. The formed radiation irradiation field is determined, and based on the preread image data Sp corresponding to this irradiation field, the reading conditions Gl for main reading, such as the voltage applied to the photomultiplier 21' and the amplification factor of the amplifier 26', are determined. etc. are required.

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' that is stronger than the light beam used for the above-mentioned pre-reading. Image data is obtained according to the reading condition G1 determined by the main reading means 100.
Since the configuration of ' is different from the configuration of the above-mentioned pre-reading means 100, components corresponding to the respective components of the pre-reading means 100 are indicated by adding a dash to the number used in the pre-reading means 100, Explanation will be omitted.

The image data SO obtained by being digitized by the A/D converter 27' is sent to the image processing means 5°. The image processing means 50 performs appropriate image processing on the image data S0. The image data subjected to this image processing is sent to the reproduction device 60, and a radiation image based on this image data is reproduced and displayed.

Here, a method for determining the irradiation field based on the pre-read image data Sp by the calculating means 29 will be explained in detail.

FIG. 1 shows an example of a radiographic image, pre-read image data Sp obtained from this radiographic image, and its differential value Δ, in order to explain an embodiment of the method for determining whether the irradiation field contour candidate point is correct or incorrect according to the present invention.
It is a figure showing Sp.

On the stimulable phosphor sheet 11, a subject image 3 whose subject is a human head is photographed and recorded within an irradiation field 2. Further, a foreign object 4 is also photographed and recorded within the irradiation field 2. Foreign object 4
is, for example, a character or the like imprinted along with the subject within the irradiation field 2 using a lead plate.

Here, the center C of the stimulable phosphor sheet is selected as a predetermined point in the irradiation field 2, and along each of a plurality of line segments 5 extending radially from the center C, a point corresponding to each pixel on each line segment is selected. A differential eL calculation is performed on the pre-read image data Sp, and points where the value of the pre-read image data Sp suddenly drops are determined as contour candidate points.

Hereinafter, a case will be described in which contour candidate 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 pre-read image data Sp obtained from each pixel along the ξ axis.

The value of the pre-read image data Sp of the direct radiation section 6 where radiation is directly irradiated onto the stimulable phosphor sheet 11 other than the subject image 3 and foreign object 4 in the irradiation field 2 is the highest, and the value of the pre-read image data Sp is the highest at the contour of the irradiation field 2. The pre-read image data SpO value is decreasing. Furthermore, the value of the pre-read image data Sp changes rapidly at the boundary between the foreign object 4 and the direct radiation area 6 around it.

Graph B is a graph obtained by differentiating the pre-read image data 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 only al, and outside of peak a1 (area D) there is a large peak that protrudes upward. There is no peak.

Therefore, the position of this peak a1 is determined as the contour candidate point.

In graph B, there are two downwardly protruding peaks a2+ a3 on the line segment going from the center C to the positive direction of the ξ axis.
There are (two contour candidate points). However, peak al
and a peak b protruding upward between the peak aZ and the peak aZ.
exists. Peak b is a change point that characteristically occurs only within the irradiation field 2, and such a large upwardly protruding peak does not occur outside the irradiation field 2. Therefore, due to the presence of peak b, peak a2 is removed from the contour candidate points, and peak a3 is adopted as the contour candidate point.

Note that the calculation for finding contour candidate points along each line segment is performed after finding a plurality of contour candidate points (for example, peaks a2 and a3 in the above example) in one search. The plurality of contour candidate points are selected based on the presence or absence of points, and the point most suitable as a contour candidate point among the remaining contour candidate points (for example, among the peaks that protrude downward outside the above-mentioned change point, the peak An algorithm may be used to set the final outline candidate point (the point with the largest size, etc.) as the final contour candidate point, or, for example, a differential operation may be performed sequentially from the center C toward the outside of the image, and the outline candidate point (the point with the largest size, etc.) In the example, az) is calculated, and then differential operation is performed toward the outside to determine the outline candidate point (peak a2) due to the presence of a change point (peak b in the above example) that characteristically occurs only within irradiation field 2.
It is an operation that has an algorithm that calculates only one contour candidate point at the same time, such as canceling the , and then performing differential operation toward the outside to find the contour candidate point (peak a3 in the above example). Good too.

As described above, the center C and the stimulable phosphor sheet 1
Contour candidate points 7 (the contour candidate points finally determined as described above will be referred to as contour points 7 hereinafter) are obtained for each of the plurality of line segments 5 connecting the ends of the contour lines 1 and 1. 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. It can be determined by applying a spline curve, etc.
The calculation means 29 in this embodiment is configured to obtain a plurality of straight lines along the contour points 7 using Hough transformation. The process of finding this straight line will be explained in detail below.

The X-axis as shown in the figure, with one end of the stimulable phosphor sheet 11 shown in FIG. 1 (lower left end in the figure) as the origin.

When the y-axis is determined, the coordinates of each contour point are (xl).

Ys), (Xz, Yz),...
..., Cxn, yn), but here these coordinates are represented by coordinates (Xo, Yo). The calculation means 29 (see FIG. 4) calculates the coordinates of the contour points (x□).

yo), then the curve expressed by ρ=XQ eO8θ+y□ sinθ with these Xo and Yo as constants is defined as the coordinates of all contour points (xO.

yo). This curve becomes as shown in FIG. 2, and there are the same number of contour point coordinates (x□, yo).

Next, the calculating means 29 calculates the intersection point (ρ., θ.) where a predetermined number of zero or more of the above-mentioned plurality of curves intersect with each other. Note that the contour point coordinates (x,).

yo), it is rare for many curves to intersect exactly at one point, so in reality, for example, when the intersection points of two curves exist at an interval of less than a predetermined minute value, the Let the center be the above-mentioned intersection (ρ0.θ0). Next, from the intersection (ρ0.θ0), a straight line defined by the following equation 1 is found in the x-y orthogonal coordinate system. This straight line is a straight line extending along a plurality of contour point coordinates (Xo, yo). When the contour points 7 are lined up as shown in Fig. 1, this straight line is a straight line t, l-L, which is an extension of each line segment forming the outline of the irradiation field 2 (see Fig. 1), as shown in Fig. 3. , is obtained as . Next, the multiple straight lines Ll + L2 obtained in this way
, L3, . . . Ln is determined, and this region is recognized as the irradiation field 2. In detail, this area is recognized as follows, for example. The calculating means 29 (see FIG. 4) calculates line segments M1, M2, M3, connecting the corners of the stimulable phosphor sheet 11 and the center C.
...M.

(4 stimulable phosphor sheets [if 1 is rectangular) are stored, and each of these line segments M1 to M and each of the above straight lines L1 to Lo
The presence or absence of an intersection with is checked. If this intersection exists, of the plane bisected by the straight line, the plane on the side including the sheet corner is truncated. By performing this operation on all the straight lines L1 to L0 and the line segment Ml-Mffi, a region surrounded by the straight lines L1-Lfl is left.

This remaining area is irradiation field 2 (see Figure 1).
It is.

When irradiation field 2 is obtained in this way, this irradiation field 2
Based on the pre-read image data Sp corresponding to , reading conditions are determined so that image data within this irradiation field 2 is read under appropriate reading conditions during actual reading.

In the embodiment described above, the point in the irradiation field that is the starting point in the direction of differential processing is set as the center C of the stimulable phosphor sheet, but this point is not limited to the center point of the sheet;
Any point that exists within may be used. For example, if the irradiation field 2 is narrowed down to an extremely small size, the center point C of the sheet may be located outside the irradiation field.
In that case, the point where the value of the pre-read image data is maximum, the center of gravity when each pixel is weighted with the corresponding each pre-read image data, and the pre-read image when the pre-read image data is binarized. The center of gravity of many pixels corresponding to the larger data value side, etc.
It is desirable to use a point that will always be within the irradiation field.

In the above embodiment, the pre-reading means 100 and the main reading means 100
' are constructed separately, but as mentioned above, the structure of the pre-reading means 100 and the main reading means 100' is between the two, so the pre-reading means 100 and the main reading means 100' can be integrated. May be used for both purposes. In this case, after performing pre-reading by scanning with a weak light beam, the stimulable phosphor sheet 11 may be moved back once, and then main reading may be performed by scanning again with a strong light beam.

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 the reading conditions for main reading by the calculation means 29 has been described, but during main reading, reading is performed under predetermined reading conditions regardless of the pre-read image data Sp, and the calculation means 29 Now, the pre-read image data Sp
Based on this, the image processing means 50 generates the image data S.

It is also possible to obtain the image processing conditions G2 when performing image processing on the image, and manually input the image processing conditions obtained by the calculation means 29 to the image processing means 50 as shown by the broken line in FIG. 29, both the above-mentioned reading conditions and image processing conditions may be obtained.

Furthermore, although the above embodiment describes 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 reading of the Joki book without performing pre-reading. can. In this case, when reading, image data is obtained by reading under predetermined reading conditions, and based on this image data, image processing conditions are determined by the calculation means, and the determined image processing conditions are applied to the image data. Considered when applying processing.

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

FIG. 5 is a perspective view of an embodiment of an X-ray image reading device that reads an X-ray image recorded on an X-ray film.

An X-ray film 30 on which an X-ray image has been recorded, which has been set at a predetermined position, is conveyed by a film conveyance means 31 in the direction of arrow Y' shown in the figure.

Further, the reading light 33 emitted from the light source 32 elongated in the -dimensional direction is converged by the cylindrical lens 34 and irradiates the X-ray film linearly in the X' force direction substantially perpendicular to the arrow Y' direction. Below the X-ray film 30 irradiated with the reading light 33, the above-mentioned light beam is placed at a position where the reading light 33 transmitted through the X-ray film 30 and whose intensity is modulated by the X-ray image recorded on the X-ray film 30 is received. A MOS sensor 35 is provided in which a large number of solid-state photoelectric conversion elements are arranged in a straight line corresponding to the pixel spacing in the X' force direction of the X-ray image. In this MOS sensor 35, the X-ray film 30 is connected to the reading light 33.
While being transported in the direction of arrow Y' while being irradiated by
The reading light transmitted through the line film 30 is received at predetermined time intervals corresponding to each pixel interval in the Y' direction of the X-ray image.

FIG. 6 is a circuit diagram showing an equivalent circuit of the MOS sensor 35.

Signals from photocarriers generated when the reading light 33 hits a large number of solid-state photoelectric conversion elements 36 are transferred to capacitors Ci (i-1, 2°...) within the solid-state photoelectric conversion elements 36.
, n). The accumulated photocarrier signals are sequentially read out by sequentially opening and closing the switch section 38 controlled by the shift register 37, thereby obtaining a time-series image signal. This image signal is then amplified by the amplifier 39 and output from its output terminal 40.

The output analog image signal is sampled and converted into a digital image signal. Then, based on the image signal, candidate points for the contour of the X-ray irradiation field are determined in the same manner as in the above-mentioned embodiment. It is determined whether the candidate points are correct or incorrect, and the irradiation field is recognized.

Note that in this embodiment, instead of the MOS sensor 35, a C
CD, CP D (Charge Prlmlng
Needless to say, it is possible to use a device such as Device). Furthermore, in reading the X-ray film, it is of course possible to scan the film two-dimensionally with a light beam in the same way as reading the stimulable phosphor sheet described above. Further, in the above embodiment, the light transmitted through the X-ray film 40 is received, but it is of course possible to be configured so that the light reflected from the X-ray film 40 is received.

As described above, the irradiation field contour candidate point correctness determination method of the present invention uses a radiation image reading device that obtains a large number of image data corresponding to each pixel on the recording sheet by reading a recording sheet on which a radiation image of a subject is recorded. Can be generally applied.

(Effects of the Invention) As explained in detail above, the method for determining whether the irradiation field contour candidate point is correct or incorrect according to the present invention determines the contour candidate point and a change point that occurs characteristically only within the irradiation field. At this time, the contour candidate point on the inside of the recording sheet is determined to be an erroneously detected point that is not on the contour of the irradiation field based on this change point, so the irradiation field can be recognized accurately and proper reading can be performed. Condition 1 Image processing conditions can be determined.

[Brief explanation of the drawing]

Figure 1 shows an example of a radiographic image, the pre-read image data obtained from this radiographic image, and a graph of its differential value. Figure 2 explains a method for finding straight lines along contour points. FIG. 3 is an explanatory diagram for explaining a method for extracting an area surrounded by a straight line along a contour point, and FIG. 4 is an example of a method for determining whether the irradiation field contour candidate point is correct or incorrect according to the present invention. FIG. 5 is a perspective view of an embodiment of the X-ray image reading device used, and FIG. 6 is a perspective view of an embodiment of the X-ray image reading device that reads X-ray images recorded on X-ray film. M
FIG. 2 is a circuit diagram showing an equivalent circuit of an OS sensor. 2...Irradiation field 3...Subject image 4...
Foreign matter 5... Line segment 6... Direct radiation part 7... Contour candidate point 11.11'... Stimulable phosphor sheet 19.19'... Stimulated luminescence light 21.21'...・Photo multiplier 26.28
'...Amplifier 27.27'...A/D converter 28...-Storage means 30...X-ray film 50...Image processing means 100...Pre-reading means 29...Calculating means 35...MOS sensor 60...Reproducing device 100'...Reading means Fig. Fig. Fig.

Claims (1)

[Scope of Claims] After obtaining a large number of image data corresponding to each pixel on the recording sheet by reading a recording sheet on which a radiation image of the subject is recorded, the radiation field formed on the recording sheet is Based on the image data corresponding to each pixel on the line segment connecting the predetermined point included in the recording sheet and the edge of the recording sheet,
A contour candidate point that is considered to be an intersection point between the contour of the irradiation field and the line segment is determined, and a change point of the image data along the line segment that characteristically occurs only within the irradiation field is determined, and this change point is determined. is determined, the contour candidate point on the predetermined point side of the change point is determined to be an erroneously detected point that is not on the contour.