JPS6248866A - Read condition deciding method for radiographic information - Google Patents

Abstract

PURPOSE:To set properly the read conditions of a book by deciding the read conditions based on picture information of advanced read with respect to a region where a difference between an estimated picture density by an approximate expression and an actual sample picture density exceeds a prescribed value. CONSTITUTION:An irradiation visual field recognition circuit expresses the density change between N picture elements near a sheet edge by an approximate expression of a linear expression, obtains an estimated picture density d' with respect to each picture element based on the expression and obtains a difference d-d' from the actual density (d) with respect to each picture element. Then the difference d-d' and a prescribed density delta are compared sequentially from a picture element at the sheet edge to obtain a coordinate X0, Y0 where the difference d-d' exceeds the density delta, the outside from the coordinate X0, Y0 is recognized as an out-visual field region and the inner part is recognized as an in-visual field 103B and irradiated visual field information St representing the field 103B is sent to a control circuit. The control circuit decides a read gain set value and a recorded scale factor set value based only on the advanced read picture signal in the field 103B shown in the information St. Thus, the optimum condition is set without being affected by stored recording information at the outside of the irradiation field.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention is directed to irradiating excitation light to a stimulable phosphor sheet on which radiographic image information is accumulated and recorded, thereby excitation light emitted from the stimulable phosphor sheet. The present invention relates to a method for determining optimal reading conditions in a radiation image information reading method for reading the radiation image information by photoelectrically detecting stimulated luminescence light.

(Technical Background and Prior Art of the Invention) When radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated onto a certain type of phosphor, part of this radiation energy is released into the fluorophore. It is known that the phosphor is accumulated in a phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy. The fluorophore shown is called a storage fluorophore (Rurinary fluorophore).

Using this stimulable phosphor, radiographic image information of the human body, etc. is once recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to stimulate it. Generate luminescent light, read the resulting stimulated luminescent light in a charging manner to obtain an image signal, and based on this image signal, display a radiation image on a recording material such as a photographic light-sensitive material or a display device such as a CRT as a visible image. The applicant has already proposed a radiation image information recording and reproducing system for outputting radiation image information. (Unexamined Japanese Patent Publication No. 55i249
No. 2, No. 56-11395, etc. ) This method has the practical advantage of recording 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 by excitation after accumulation is proportional to radiation exposure (2) over an extremely wide range. Even if the exposure amount varies considerably, the photoelectric charge of the stimulated luminescence light emitted from the stimulable phosphor sheet is read by the charging conversion means with the reading gain set to an appropriate value and converted into an electrical signal. By using this electrical signal to output a 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 transmittance can be obtained.

Furthermore, according to this system, radiation image information accumulated and recorded on a stimulable phosphor sheet is converted into an electrical signal, then subjected to appropriate signal processing, and this electrical signal is used to produce recording materials such as photographic light-sensitive materials, CRTs, etc. By outputting a radiation image as a visible image on a display device such as the above, it is possible to obtain a very large effect that a radiation image with excellent observation and interpretation suitability (diagnosis suitability) can be obtained.

In this way, in a radiation imaging system using a stimulable phosphor sheet, the reading gain can be set to an appropriate value to photoelectrically convert the exhaust light emitted and output as a visible image. fluctuations in the radiation exposure ω due to fluctuations in the tube voltage or MAS value, fluctuations in the sensitivity of the stimulable phosphor sheet, fluctuations in the sensitivity of the photodetector, changes in the exposure amount due to subject conditions, or changes in radiation transmittance depending on the subject. Even if the accumulated energy stored in the stimulable phosphor varies due to various factors, or even if the radiation exposure port is reduced, it will not be affected by fluctuations in these factors1.
It becomes possible to reduce the 11fJ4-line image by 1q.

However, in order to eliminate the influence of fluctuations in fan-shaped conditions or to obtain radiographic images that are highly suitable for observation and interpretation, it is necessary to change the recording state of the radiographic image information accumulated and recorded on the stimulable phosphor sheet, or the chest, Recording patterns (hereinafter collectively referred to as ``accumulated recorded information'') determined by the part of the subject such as the abdomen, masonry methods such as plain radiography and contrast radiography, etc., are used for I2 interpretation. The recording scale factor is determined prior to the output of a visible image, and the reading gain is adjusted to an appropriate value based on the acquired accumulated recording information, and the recording scale factor is adjusted to optimize the resolution according to the contrast of the recording pattern. It is necessary to determine the

As a method for grasping the accumulated record information of radiographic images before outputting visible images, Japanese Patent Laid-Open No. 58-67240
The method disclosed in No. This method uses excitation light of a lower level than the excitation light that is irradiated during the reading operation (hereinafter referred to as "main reading") to obtain a visible image for observation and interpretation. Perform the reading operation (hereinafter referred to as "read ahead") to understand the accumulated record information of the radiographic image stored on the stimulable phosphor sheet, grasp the outline of the accumulated record of the radiographic image, and read the main reading. When performing this, reading conditions such as the reading gain and recording scale factor are optimally determined based on this pre-read information.

Note that the excitation light used for pre-reading is at a lower level than the excitation light used for main reading because the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is lower than the excitation light used for main reading. This means that it is smaller than the actual value. Methods for making the pre-reading excitation light lower than the main reading excitation light include reducing the output of the excitation light source such as a laser light source, and using an ND filter, AOM, etc. in the optical path of the excitation light emitted from the light source. A method of attenuation, a method of providing a light source for pre-reading and a light source for main reading separately, and making the output of the former smaller than the output of the latter, and a method of reducing the beam diameter of the excitation light,
Examples include a method of increasing the scanning speed of excitation light and a method of increasing the transport speed of the stimulable phosphor sheet.

According to the above method, the recording state and recording pattern of the radiographic image information accumulated and recorded on the stimulable phosphor sheet can be known in advance before the actual reading, so the reading system has an exceptionally wide dynamic range. By appropriately adjusting the reading gain and appropriately determining the recording scale factor based on this recorded information, it is possible to obtain a radiographic image that is highly suitable for observation and interpretation, even without using it.

On the other hand, when recording radiation image information (Ia shadow), in order to avoid irradiating radiation to areas that are not necessary for diagnosis,
Alternatively, if radiation is applied to an area unnecessary for diagnosis, scattered radiation will enter the area necessary for diagnosis from that area, reducing contrast resolution. Photography is often performed by narrowing down the irradiation field.

However, when the radiation irradiation field is narrowed down in this way, the scattered radiation generated from the subject in the irradiation field usually enters the irradiation field on the stimulable phosphor sheet, and the highly sensitive stimulable phosphor sheet The sheet also accumulates and records this scattered radiation. Therefore, in the image information obtained by pre-reading,
This includes radiation caused by scattered radiation, so
Even if the above-mentioned reading conditions are determined based on such pre-read image information, the optimum reading conditions cannot be determined, and as a result, it becomes impossible to obtain a reproduced radiation image with excellent observation and interpretation aptitude.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to read radiation image information from a stimulable phosphor sheet that has been photographed with an irradiation field aperture. It is possible to eliminate the influence of accumulated information outside the radiation irradiation field and find the optimal reading conditions for image information within the irradiation field.
The purpose of this invention is to provide a method for determining reading conditions for radiation image information.

(Structure of the Invention) The method for determining reading conditions for radiation Q11m image information of the present invention is to pre-read a stimulable phosphor sheet on which radiation image information has been recorded (photographed) by applying field aperture as described above. In the radiation image information reading method in which the reading conditions for main reading are determined based on the information 1q obtained by this pre-reading, from the pre-read image signal obtained by the pre-reading, the information from the edge of the recording area of the sheet to the center side is determined. A sample image signal related to an arbitrary pixel column extending toward the end is extracted, and the image density change between a predetermined number of pixels near the end indicated by this sample image signal is expressed by an approximate equation substantially consisting of a linear culm equation. Find the difference between the assumed density based on this approximation formula and the actual image density indicated by the sample image signal, and calculate the area from the edge to the center until the difference reaches a predetermined value. rJJ51 The outside irradiation area and the area inside it are recognized as the radiation irradiation field, and the reading conditions for main reading are determined based on the pre-read image information regarding the area thus recognized as the radiation irradiation field. It is characterized by:

(Actual 1M Embodiment) The present invention will be described in detail below based on the embodiment shown in the drawings.

FIG. 1 shows a radiation image information recording and reproducing system in which reading conditions for main reading are determined by a method according to an embodiment of the present invention. This radiation image information recording and reproducing system basically includes a radiation image capturing section 20, a pre-reading reading section 30, a main reading reading section 40, and an image reproducing section 50.
It consists of

In the radiation image capturing unit 20, for example, xI+! Radiation 1; 1102 is emitted from a radiation source 100 such as a tube toward a subject (subject) 101. This subject 101
As described above, a stimulable phosphor sheet 103 that accumulates radiation energy is placed at a position where the radiation 102 that has passed through the stimulable phosphor sheet 103 is irradiated.
The transmitted radiation image information of the subject 101 is accumulated and recorded. Note that an aperture 104 that narrows down the irradiation field of the radiation 102 is arranged between the radiation source 100 and the subject 101.

The stimulable phosphor sheet 103 on which the radiation image information of the subject 101 has been recorded in this manner is sent to the pre-reading reading section 30 by sheet transport means 110 such as a transport roller. In the pre-reading reading section 30, the pre-reading laser light source 2
The laser beam 202 emitted from the laser beam 2
A filter 2 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by excitation of 02
03, the light is linearly deflected by a light deflector 204 such as a galvanometer mirror, and is incident on the stimulable phosphor sheet 103 via a plane reflecting mirror 205. Here, the laser light source 201 is selected so that the wavelength range of the laser light 202 as excitation light does not overlap with the wavelength range of the stimulated luminescence light emitted by the stimulable phosphor sheet 103. On the other hand, the phosphor sheet 103 is transferred to a sheet transport means 21 such as a transport roller.
0 to perform sub-scanning in the direction of arrow 206, and as a result, the entire surface of phosphor sheet 103 is irradiated with laser light 202. Here, the emission intensity of the laser light source 201, the beam diameter of the laser light 202, the laser light 202
The scanning speed of the stimulable phosphor sheet 103 and the transport speed of the stimulable phosphor sheet 103 are as follows.
The energy of the excitation light (laser light 202) for pre-reading is selected to be smaller than that for main reading performed in the main reading reading unit 40, which will be described later.

When the laser beam 202 is irradiated as described above, the stimulable phosphor sheet 103 emits stimulated luminescent light with an amount of light corresponding to the radiation energy stored therein, and this emitted light is transmitted to the pre-reading light guide. 201. The stimulated luminescence light is guided through the light guide 207, exits from the exit surface, and is received by a photodetector 208 such as a photomultiplier. A filter is attached to the light receiving surface of the photodetector 208, which transmits only light in the wavelength range of stimulated luminescence light and cuts light in the wavelength range of excitation light, and detects only stimulated luminescence light. It is now possible to do so. The detected stimulated luminescence light is converted into an electrical signal carrying accumulated recording information, and is sent to an amplifier 2.
09. The signal output from the amplifier 209 is digitized by the A/D converter 211, and is input to the main reading control circuit 314 of the main reading reading section 40 as a pre-reading image signal @Sp.

This main reading control circuit 314 determines the reading gain setting @a, the recording scale factor setting value b, and the reproduction image processing condition setting value C based on the accumulated recording information indicated by the pre-reading image signal Sp. The pre-read image signal Sp is also input to an irradiation field recognition circuit 220, which will be described in detail later.

The stimulable phosphor sheet 103 that has undergone pre-reading as described above is transferred to the main reading reading section 40.

The laser light 302 emitted from the main reading laser light source 3°1 in the main reading reading section 40 is
A filter 30 that cuts the wavelength range of stimulated luminescent light emitted from the stimulable phosphor sheet 103 by the excitation of the stimulable phosphor sheet 103
3, the beam diameter is strictly adjusted by a beam expander 304, linearly deflected by an optical deflector 305 such as a galvanometer mirror, and then passed through a plane reflector 306 to a stimulable phosphor. The light is incident on the sheet 103. An fθ lens 307 is arranged between the optical deflector 305 and the plane reflection v1306, and the stimulable phosphor sheet 10
The beam diameter of the laser beam 302 that scans the area 3 is made uniform. On the other hand, the stimulable phosphor sheet 103 is moved by the arrow 30 by a sheet transport means 320 such as a transport roller.
The stimulable phosphor sheet 103 is transported in the direction 8 for sub-scanning, and as a result, the entire surface of the stimulable phosphor sheet 103 is irradiated with laser light. When the laser beam 302 is irradiated in this way, the stimulable phosphor sheet 103 emits stimulated luminescent light of light m corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the main reading light guide 309. incident on . Stimulated luminescent light guided through the main reading light guide 309 while undergoing repeated total reflection is emitted from its exit surface and is received by a photodetector 310 such as a photomultiplier. A filter that selectively transmits only the wavelength range of the stimulated luminescent light is attached to the light receiving surface of the photodetector 310, so that the photodetector 310 detects only the stimulated luminescent light.

The output of the photodetector 310 that photoelectrically detects the stimulated luminescent light representing the radiation image recorded on the stimulable phosphor sheet 103 is read based on the read gain setting value a determined by the control circuit 314. An amplifier 311 with a set gain amplifies the electrical signal to an appropriate level. The amplified electrical signal is input to the A/D converter 312, and based on the recording scale factor setting value, it is converted into a digital signal with a recording scale factor suitable for the signal fluctuation range, and is input to the signal processing circuit 313. . The digital signal is subjected to signal processing (image processing) such as gradation processing in the signal processing circuit 313 based on the reproduction image processing condition setting value C so as to obtain a radiographic image with excellent suitability for visual X-ray interpretation. receive.

The read image signal (main reading image signal @) SO output from the signal processing circuit 313 is transmitted to the optical modulator 401 of the image reproducing unit 50.
is input. In this image reproducing unit 50, a laser beam 403 from a recording laser beam fl 402 is modulated by an optical modulator 401 based on the main reading image signal SO input from the signal processing circuit 313, and the scanning mirror
A photosensitive material 40 such as a photographic film is deflected by
5. Scan above. The photosensitive material 405 is transported in a direction perpendicular to the scanning direction (direction of arrow 406) in synchronization with the scanning, and the book reading image signal S is transferred onto the photosensitive material 405.
A radiation image based on O is output. In addition to this method, the above-mentioned CR method can be used to reproduce radiographic images.
Various methods such as display by T can be adopted.

In order to accumulate and record radiation image information (WI shadow) on the stimulable phosphor sheet 103, for the reason mentioned above, the aperture 104 is operated and, for example, as shown in FIG.
As shown in >, irradiation field diaphragm may be applied. That is, in this case, a radiation irradiation field (image recording part) is formed in a part of the recording area 103A of the stimulable phosphor sheet 103.
103B will be formed. Based on the pre-read image signal Sp from the recording area 103A of the stimulable phosphor sheet 103, the reading gain and recording scale factor as the main reading conditions are determined, and as described above, those reading conditions are , the accumulated recorded image within the irradiation field 103B becomes inappropriate.

Therefore, the irradiation field recognition circuit 220 uses the pre-read image signal Sp.
The radiation field 103B is recognized based on the radiation field 1.
The information St indicating 03B is sent to the control circuit 314, and the control circuit 314 sends the information St indicating the irradiation field 103B indicated by the irradiation field information St.
The reading gain setting value a1 recording scale factor setting (lb) is determined only from the pre-read image signal Sp for the inside.

Irradiation field recognition by the irradiation field recognition circuit 220 will be described in detail below. This irradiation field recognition circuit 220 is
From the entire pre-read image signal sp input from the D converter 211, an arbitrary signal extending from the edge of the recording area of the stimulable phosphor sheet 103 toward the center, as shown by Xl-X11it in FIG. An image signal for a pixel row (for example, a pixel row in the main scanning direction) is extracted. Generally, the change in the image 1tid indicated by the sample image signal extracted in this way is
The result will be as shown in (b) of the figure. That is, irradiation field 1
The area within 03B has a relatively high concentration and changes according to the image@information, and the area outside the edge of this irradiation field 103B, that is, the outside area of irradiation field, has a relatively high concentration.
The concentration will be lower than inside. Here, the scattered radiation from the subject is also irradiated to the outdoor irradiation area, and this scattered radiation ω gradually decreases as it moves away from the irradiation field 103B, so the image density d in the outdoor irradiation area changes as shown in the figure. show. FIG. 3 shows an enlarged view of the density change in this part, and as shown in the figure, the image@density d changes relatively slowly and linearly near the edge of the sheet, and approaches the irradiation field 103B. It increases rapidly as the temperature increases.

As shown in FIG. 3, the irradiation field recognition circuit 220 detects linear density changes between a predetermined number N of pixels near the edge of the sheet.
It is expressed by a known method, for example, as an approximate expression consisting of a linear equation: y=ax+b.

Note that this approximation formula is a formula that substantially represents a straight line,
Other higher order equations may also be employed.

Next, the irradiation field recognition circuit 220 calculates the assumed image density d' for each pixel in the pixel column based on the above approximate expression, and calculates the difference 1d-d'l from the actual density d for each pixel. Next, the irradiation field recognition circuit 220 detects the concentration difference 1d-
d' 1 and the predetermined density δ are sequentially compared starting from the pixels on the sheet edge side. When J5 is near the edge of the sheet, the above concentration difference 1d-d'l is naturally small, but the irradiation field 1033
The predetermined density δ is exceeded for the first time in the pixel Xo of the edge portion J'-3. Therefore, the irradiation field recognition circuit 22
0 recognizes the pixel Xo whose CJ degree difference 1d-d'l exceeds the predetermined density δ for the first time as an irradiation field edge point pixel. Note that the preferable value of the predetermined concentration δ can be determined experimentally or empirically. The above analysis is performed on Sheet 10
3 for the opposite end of field edge point pixel X for pixel column XI. Two can be detected (see Fig. 2(a)).

The irradiation field recognition circuit 220 performs the above-mentioned analysis, for example, on the pixel row X2 X2 parallel to the pixel row Xs Xt, and the pixel rows YI Yl, Y2 Y2 perpendicular to the pixel row Xs Xt (see FIG. 2(a)). The irradiation field edge point pixels Xo and Yo are determined. Then, the area outside these edge point pixels Xo and Yo is recognized as the outside irradiation area, and the area inside is recognized as the irradiation field 103B, and this recognized irradiation field 1
The irradiation field information St indicating 03B is transmitted to the control circuit 31 as described above.
Send to 4. If the control circuit 314 determines the reading gain setting value a and the recording scale factor setting value S based only on the pre-read image signal Sp in the irradiation field 103B indicated by the information 3t, these conditions will be determined based on the accumulated record of the outside irradiation area. It is not affected by information and can be optimal for the radiation image information actually recorded within the irradiation field 103B.

In this embodiment, the image processing condition setting value C is also determined based only on the pre-read image signal So for the irradiation field 103B, and is made to be optimal for the radiation image information within the irradiation field 103B. There is.

The pixel row from which the sample image signal is extracted is the example shown in FIG.
It is not limited to J (Xi Xi to Xz X2) and two vertical rows (Yr-Yt and Y2Y2). The method of extracting the sample image signal shown in Fig. 2 is as follows.
For example, this is effective when it is determined that the irradiation field 103B is narrowed down to a rectangular shape on the stimulable phosphor sheet 103, and the irradiation field recognition circuit 220 is also configured to recognize the irradiation field based on this premise. It is. If the shape of the irradiation field is not determined, sample image signals are extracted from a large number of relatively dense pixel columns, and the obtained irradiation field edge point pixels are extracted. A bound! The area inside the IfiI line may be recognized as the irradiation field.

The apparatus roughly shown in FIG. 1 has a reading system for main reading and a reading system for pre-reading separately.
As shown in No. 67242, the reading system for main reading and the reading system for pre-reading are used together, and when the pre-reading is completed, the stimulable phosphor sheet is returned to the reading system by the sheet transport means and the main reading is performed. The excitation light energy adjusting means may be used to adjust the excitation light energy to be smaller than that during main reading, and the method of the present invention is also applicable when reading radiation image information using such an apparatus.

(Effects of the Invention) As explained in detail above, according to the method for determining reading conditions for radiation image information of the present invention, in pre-reading, the influence of the portion outside the radiation irradiation area is eliminated, and accumulated records recorded in the radiation irradiation field are It is possible to understand information correctly and appropriately set reading conditions for book reading.

Therefore, according to the method of the present invention, it is possible to always reproduce a radiographic image with excellent observation and interpretation aptitude even from an accumulative sheet or a light sheet that has been photographed using a radiation aperture.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a radiation image information recording and reproducing system that determines reading conditions according to an embodiment method of the present invention. FIG. FIG. 3 is an explanatory diagram illustrating an example of a radiation field narrowing state on a type I phosphor sheet and a change in image density of one pixel row of the sheet. FIG. 3 is an explanatory diagram illustrating the method of the present invention. 30...Reading unit for pre-reading 40...Reading unit for main reading 50...Image reproduction unit 100...Radiation source 101...Subject 102...Radiation rays 103...Storage phosphor sheet 104... Aperture 201... Laser light source for pre-reading 202... Laser light for pre-reading 204... Optical deflector for pre-reading 208... Photodetector for pre-reading 210... Sheet transport means for pre-reading 220. ... Irradiation field recognition circuit 301 ... Laser light source for main reading 302 ... Laser light for main reading 305 ... Optical deflector for main reading 310 ... Photodetector for main reading 311 ... Amplifier 3
12... A/D converter 314... Control circuit 3
20...Actual reading sheet transporting means a...Reading gain setting value b...Recording scale factor setting value Sp...Pre-reading image signal So...Actual reading Im image signal St...
Irradiation field information i1@Shige・-

Claims (1)

[Claims] (1) Excitation light is irradiated onto a stimulable phosphor sheet on which radiographic image information is accumulated and recorded by applying an irradiation field aperture, and the stimulated luminescence light emitted from the sheet by the irradiation with this excitation light is detected by a photodetector. Prior to reading photoelectrically to obtain an image signal for visible image reproduction, the sheet is irradiated with excitation light at a lower level than the excitation light used for this reading, and the information is stored and recorded on this sheet. Performing pre-reading to read an outline of image information, and determining reading conditions for performing the main reading based on the information obtained by this pre-reading;
In the radiation image information reading method in which the main reading is performed according to the reading conditions, a sample regarding an arbitrary pixel column extending from the edge of the recording area of the sheet toward the center from the pre-read image signal obtained by the pre-reading is provided. An image signal is extracted, and the image density change between a predetermined number of pixels near the edge indicated by this sample image signal is expressed by an approximate equation consisting essentially of a linear equation, and the assumed image density according to this approximate equation and the sample The difference between the image density and the actual image density indicated by the image signal is determined, and the area from the edge to the center until the difference reaches a predetermined value is defined as the radiation exposure area, and the area inside of that area is defined as the radiation exposure area. A method for determining reading conditions for radiation image information, characterized in that the reading conditions are determined based on pre-read information regarding the area recognized as the radiation irradiation field.