JPH0532740B2 - - Google Patents

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 radiation image information is stored and recorded, thereby causing radiation image information to be emitted from the stimulable phosphor sheet. A radiation image information reading method of photoelectrically detecting stimulated luminescence light to read the radiation image information, in particular, prior to main reading for visible image reproduction, an outline of accumulated recorded information is grasped in advance. This invention relates to a method for reading radiographic image information, in which optimal reading conditions are set for each divided imaging area when reading radiographic image information from a stimulable phosphor sheet on which divided imaging has been performed. It is.

(Technical Background and Prior Art of the Invention) Certain phosphors are exposed to radiation (X-rays, α-rays, β-rays,
When irradiated with γ-rays, electron beams, ultraviolet rays, etc., a portion of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, it It is known that phosphors exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors.

This stimulable phosphor is used to temporarily record radiation image information of a subject such as a human body on a stimulable phosphor sheet, and then scan this stimulable phosphor sheet with excitation light such as a laser beam. Generate stimulated luminescence light, photoelectrically read the resulting stimulated luminescence light to obtain an image signal, and based on this image signal, a radiation image of the subject is displayed on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs a visible image.

(JP-A-55-12429, JP-A No. 56-11395, etc.) This system is said to be able to record images over an extremely wide radiation exposure range compared to conventional radiographic systems that use silver halide photography. It has practical advantages. In other words, in stimulable phosphors, 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 an extremely wide range. Even if the amount of radiation exposure varies considerably depending on the imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value and converted into an electrical signal. This electrical signal is used to output the radiographic image as a visible light image to a recording material such as a photographic material or a display device such as a CRT, thereby obtaining a radiographic image that is not affected by fluctuations in radiation exposure. be able to.

In addition, 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 radiographic image as a visible image on a display device such as the above, it is possible to obtain a very large effect that a radiographic image with excellent observation and interpretation suitability (diagnosis suitability) can be obtained.

In this way, in a radiation imaging system that uses a stimulable phosphor sheet, the reading gain can be set to an appropriate value to photoelectrically convert the stimulated luminescence light and output it as a visible image. Fluctuations in radiation exposure due to fluctuations in tube voltage or MAS values,
Accumulation occurs in the stimulable phosphor due to factors such as variations in the sensitivity of the stimulable phosphor sheet, variations in the sensitivity of the photodetector, changes in exposure due to subject conditions, or differences in radiation transmittance depending on the subject. Even if the stored energy differs, and even if the amount of radiation exposure is reduced, it is possible to obtain a radiation image that is not affected by fluctuations in these factors.

However, in order to eliminate the effects of fluctuations in imaging conditions or to obtain radiographic images that are 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, The recording pattern (hereinafter collectively referred to as "accumulated recorded information") determined by the part of the subject such as the abdomen and the imaging method such as plain radiography or contrast radiography is used for observation and interpretation. This information is determined prior to the output of a visible image, and the reading gain is adjusted to an appropriate value based on the acquired recorded information, and the recording scale is adjusted to optimize the resolution according to the contrast of the recorded pattern. When an actor is determined and further image processing such as gradation processing is performed on the read image signal, it is necessary to optimally set image processing conditions.

In this way, Japanese Patent Laid-Open No. 58
The method disclosed in No.-67240 is known. This method uses excitation light of a lower level than the excitation light that is to be irradiated during the reading operation (hereinafter referred to as "main reading") to obtain a visible image for observation and interpretation, and accumulates the excitation light in advance before the main reading. A reading operation (hereinafter referred to as "pre-reading") for grasping the accumulated record information of radiographic images accumulated and recorded on the phosphor sheet.
A system that determines the recording scale factor or image processing conditions by appropriately adjusting the reading gain based on this read-ahead information when performing actual reading by grasping the outline of the accumulated record of radiological images. It is.

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-read excitation light lower than the main-read 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 increasing 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 reading with an exceptionally wide dynamic range is possible. By appropriately adjusting the reading gain based on this recorded information, determining the recording scale factor, and applying signal processing according to this recording pattern to the electrical signal after reading, even without using It becomes possible to obtain radiographic images with excellent suitability for observation and interpretation.

By the way, when radiographic image information is stored and recorded (photographed) on the stimulable phosphor sheet described above, so-called divided photographing is often performed. This divided imaging is an imaging method in which the recording area of the stimulable phosphor sheet is divided into a plurality of sections and radiation for the storage recording is irradiated to each section. According to this divided imaging, for example, when photographing a small part on a large stimulable phosphor sheet, it is possible to record multiple parts on one stimulable phosphor sheet, which is economical. Furthermore, the processing speed for recording and reading radiation image information is also improved.

However, when reading radiation image information from a stimulable phosphor sheet that has been photographed in sections as described above, if the reading conditions are determined based on the above-mentioned pre-reading, the reading conditions may become inappropriate. be. That is, conventionally, the above-mentioned pre-reading has been performed on the entire recording area of the stimulable phosphor sheet or a partial area close to it, and therefore, the pre-reading is determined based on the pre-reading image signal obtained by this pre-reading. The reading conditions are determined to be appropriate for the entire radiographic image information that has been stored and recorded. However, in the case of segmented imaging, the radiation dose irradiated to each segment may differ greatly from each other, and in such a case, the reading conditions determined as described above may affect the radiation image of some of the segments. It happens that the information becomes inappropriate. In an extreme example, for example, if a stimulable phosphor sheet is divided into two sections and each section is irradiated with a particularly high dose of radiation and a particularly low dose of radiation to accumulate and record radiographic image information, the above-mentioned look-ahead method will not work. The reading conditions determined based on this will be optimal for image information that is intermediate between the two pieces of radiation image information that have actually been stored and recorded, and will be inappropriate for either of the two pieces of radiation image information. Sometimes I get used to it. Such problems arise not only due to differences in the irradiated radiation dose, but also due to differences in the imaging site, imaging method, etc. in each divided section.

(Objective of the Invention) Therefore, an object of the present invention is to provide a radiation image information reading method that can eliminate the above-mentioned problems.

(Structure of the Invention) The radiation image information reading method of the present invention performs the above-mentioned main reading, and determines the reading conditions for performing the main reading based on the information obtained by this pre-reading. In the radiation image information reading method, when reading radiation image information from a stimulable phosphor sheet on which segmented imaging has been performed as described above, the area of each segmented section is identified based on the information regarding segmented imaging, and these The above-mentioned reading conditions are obtained for each of the identified regions, and when performing the main reading, the corresponding reading conditions are set for each of the above-mentioned regions.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a radiation image information recording and reproducing system for reading radiation image information using a method according to one 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 reproduction section 50. In the radiographic image capturing unit 20, radiation 102 is emitted from a radiation source 100 such as an X-ray tube toward a subject (subject) 101, for example. The stimulable phosphor sheet 103 that accumulates radiation energy is placed at the position where the radiation 102 that has passed through the subject 101 is irradiated, as described above. Transmission radiation image information is accumulated and recorded.

The storage phosphor sheet 103 on which the radiation image information of the subject 101 is recorded in this manner is sent to the pre-reading reading section 30 by a sheet transport means 110 such as a transport roller. The laser beam 202 emitted from the pre-reading laser light source 201 in the pre-reading reading section 30 cuts the wave area of the stimulated luminescent light emitted from the stimulable phosphor sheet 103 by the excitation of the laser beam 202. filter 203
After passing through, it is linearly deflected by a light deflector 204 such as a galvanometer mirror, and then reflected by a plane reflecting mirror 2.
05 onto the stimulable phosphor sheet 103. 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 1
03 is transported in the direction of an arrow 206 by a sheet transport means 210 such as a transport roller to perform sub-scanning, and as a result, the entire surface of the 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 scanning speed of the laser light 202, and the transport speed of the stimulable phosphor sheet 103 are determined by the energy of the pre-read excitation light (laser light 202), which will be described later. It is selected to be smaller than that of the book reading performed in the book reading reading section 40.

When the laser beam 202 is irradiated as described above,
The stimulable phosphor sheet 103 emits stimulated luminescent light in an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light is transmitted to the pre-reading light guide 2.
It is incident on 07. This light guide 20 is the stimulable luminescent light.
7, 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 the stimulated luminescence light and cuts out light in the wavelength range of the excitation light, so that only the stimulated luminescence light can be detected. It's summery. The detected stimulated luminescence light is converted into an electrical signal carrying accumulated recording information and amplified by an amplifier 209. The signal output from the amplifier 209 is sent to the A/D converter 21
1, the pre-read image signal Sp
The book reading control circuit 31 of the book reading reading section 40
4 is input. This book reading control circuit 314 is
When only one radiation image information is accumulated and recorded on the stimulable phosphor sheet 103a (that is, other than when the divisional imaging described above is performed), the accumulated record indicated by the pre-read image signal Sp from the entire area of the sheet 103 Based on the information, for example, through histogram analysis, the reading gain setting value a, the recording scale factor setting value b, and the playback image processing condition setting value c are determined.
Determine.

The stimulable phosphor sheet 103 that has undergone pre-reading as described above is transferred to the main reading reading section 40. In the reading unit 40 for main reading, a laser beam 302 emitted from a laser light source 301 for main reading is passed through a filter that cuts out the wavelength range of stimulated luminescence light emitted from a stimulable phosphor sheet 103 by excitation of this laser light 302. After passing through 303, the beam diameter is strictly adjusted by a beam expander 304, linearly deflected by an optical deflector 305 such as a galvanometer mirror, and accumulated fluorescence is transmitted through a plane reflection area 306. body sheet 103
enter the top. Optical deflector 305 and plane reflector 306
An fθ lens 307 is disposed between the stimulable phosphor sheet 103 and the laser beam 302 to have a uniform beam diameter. On the other hand, the stimulable phosphor sheet 103 is transported in the direction of the arrow 308 by a sheet transport means 320 such as a transport roller, and is sub-scanned, so that the laser beam is emitted over the entire surface of the stimulable phosphor sheet 103. irradiated. When irradiated with the laser beam 302 in this manner, the stimulable phosphor sheet 103 emits stimulated luminescence light with an amount corresponding to the radiation energy stored and recorded therein, and this luminescent light enters the main reading light guide 309. do. 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 b, it is converted into a digital signal by a recording scale factor suitable for the signal fluctuation range, and is input to the signal processing circuit 313. be done. The digital signal is subjected to signal processing (image processing) in the signal processing circuit 313 based on the reproduction image processing condition setting value c so as to obtain a radiation image with excellent observation and interpretation suitability, and is output.

The read image signal (main read image signal) So output from the signal processing circuit 313 is output to the optical modulator 401 of the image reproduction section 50. This image reproduction section 5
0, the laser beam 403 from the recording laser light source 402 is transmitted by the optical modulator 401 to the actual reading image signal input from the signal processing circuit 313.
The light-sensitive material 405, such as a photographic film, is modulated based on So and deflected by a scanning mirror 404.
Scan above. The photosensitive material 405 is then transported in a direction perpendicular to the scanning direction (arrow 406 direction) in synchronization with the scanning, and a radiation image based on the actual reading image signal So is output onto the photosensitive material 405. In addition to this method, there are other ways to reproduce radiographic images, such as displaying on a CRT as described above.
Various methods can be adopted.

Here, in the radiographic image capturing section 20, the stimulable phosphor sheet 103 may be imaged in segments as shown in FIG. 2, for example. The following is the stimulable phosphor sheet 1 that was photographed in such a divided manner.
The reading conditions when reading radiographic image information from 03, that is, the determination of the reading gain setting value a and the recording scale factor setting value b will be described in detail.

The control circuit 314 is configured to receive divided imaging information Sd from, for example, a terminal device installed near the radiation image capturing section 20.
This divided photography information Sd is information indicating a division format in divided photography. For example, the example shown in FIG. 2 is 4-division photography, and when such photography is performed, division photography information Sd indicating the 4-division format is input to the control circuit 314. Split shooting is now performed according to a predetermined format (for example, in the case of 4 splits, the second
The control circuit 314 stores the area of each section for each format, and based on the input divided shooting information Sd, Look-ahead image signal
Extract Sp for each area of each partition. Then, the optimal reading gain setting value a and recording scale factor setting value b are determined for each extracted set of pre-read image signals Sp. For example, when reading ahead the stimulable phosphor sheet 103 shown in FIG.
For each reading gain setting value a ₁ , a ₂ , a ₃ , a ₄ and recording scale factor setting value b ₁ , b ₂ , b ₃ ,
b ₄ is required.

The control circuit 314 applies the set values a ₁ , a ₂ , a ₃ , a ₄ and b ₁ , b ₂ , b ₃ , b ₄ obtained as described above to each section "1", "2", "3". ” and “4” and are stored in the storage means. When the main reading is performed in the main reading reading section 30, the control circuit 314
For example, by receiving a synchronization signal synchronized with the operation of the optical deflector 305 and the sheet transport means 320, it is possible to recognize which section includes the area where the book reading is being performed, and to recognize that section (the section "1", " 2”, “3”,
4)) and _{the recording scale factor setting value b 1 , b 2 , b 3 or b 4 are} stored as described above. selectively reading out the means from the respective amplifiers 31;
1 and the A/D converter 312. Therefore, the reading gain and recording scale factor as reading conditions in the main reading should be set optimally for each divided section's accumulated recorded information, even if the accumulated recorded information is different for each divided section. Become.

Here, the radiographic image capturing section 20 and the prefetching reading section 30 are connected via the sheet transport means 110 and the like, and each stimulable phosphor sheet 10
3 are transferred to the prefetch reading unit 30 in the order of imaging, the divided imaging information Sd may simply be input to the control circuit 314 in the order of imaging. That is, for example, the control circuit 314 is provided with a storage means for sequentially storing the divided photographing information Sd regarding each sheet 103, and the reading of the information Sd from the storage means is performed as follows.
By synchronizing with pre-reading and performing the reading in the order in which they are stored, each piece of divided photographic information Sd will be used for the signal extraction in correct correspondence with each stimulable phosphor sheet 103.

On the other hand, the radiation image capturing section 20 and the pre-reading section 3
0 are independent from each other and the stimulable phosphor sheets 103 are not always read in advance in the order of imaging, the identification code (for example, barcode, etc.) unique to each stimulable phosphor sheet 103 is used as divided imaging information.
The information Sd is input to the control circuit 314 together with Sd.
is stored in the storage means in association with the above identification code, and when pre-reading, the stimulable phosphor sheet 103
The above-mentioned identification code may be read from the above-described code, and the divided photographing information Sd corresponding to the code may be read out from the above-mentioned storage means and used for signal extraction.

Of course, the storage phosphor sheet 10 has one radiation image information stored and recorded over the entire recording area.
Regarding No. 3, the above-mentioned signal extraction is not performed in the control circuit 314. To do this, for example, for such a sheet 103, the divided photographing information sd should not be input to the control circuit 314, and in such a case, the control circuit 314 may be configured to What is necessary is to determine the gain setting value a and the recording scale factor setting value b.

As described above, the read gain of the amplifier 311 and the A/
Although we have described an embodiment in which the recording scale factor of the D converter 312 is optimally set for each divided section, for example, when a photomultiplier or the like is used as the photodetector 310, its high voltage also affects the reading sensitivity. The method of the present invention can be similarly applied to optimally set other reading conditions such as the high voltage of the photomultiplier for each divided section.

In addition, in the example of divided photography shown in Fig. 2,
Radiographic image information is accumulated and recorded (photographed) in each divided section, but as shown in FIG. 3, for example, some of the plurality of divided sections may not be photographed. Therefore, as the divided shooting information Sd, in addition to the above divided format,
Information indicating the partitions that have actually been affected is also input to the control circuit 314, and at the same time, this control circuit 314 is configured to determine the partitions that have not been affected from the above two pieces of information, and No particular reading conditions may be set for the divided sections. In such a case, it is meaningless to send the main reading image signal So regarding that section to the image reproducing unit 50, so for the section for which reading conditions have not been set, for example, the A/D converter 312 automatically Alternatively, a signal indicating the lowest concentration may be output. This is preferable because in the radiographic image reproduced by the image reproduction unit 50, black spots and the like due to noise components are prevented from occurring in areas where no imaging has been performed.
Further, in the above case, the actual reading may not be performed for the sections for which reading conditions have not been set. By doing so, no time is wasted in reading the book, and the processing time for reading the book is shortened.

Furthermore, when the radiation irradiation field is narrowed down in each division, this irradiation field is recognized when determining the reading conditions for each division, and the reading conditions are determined based on the pre-read image signal Sp only within the recognized area. It is preferable to decide. In this way, the determined reading conditions will be based on the pre-read image signal from the field of irradiation.
It is no longer affected by Sp, and becomes more appropriate for the accumulated recorded information regarding the subject. Note that in order to recognize the radiation irradiation field, a method such as that proposed by the present applicant in Japanese Patent Application No. 160355/1980 may be used.Furthermore, the apparatus shown in Fig. 1 has a reading system for main reading and a reading system for pre-reading. For example, as shown in Japanese Patent Application Laid-open No. 58-67242, the reading system for main reading and the reading system for pre-reading are used together, and when the pre-reading is completed, the sheet is stored by the sheet transport means. The phosphor sheet is returned to the reading system for main reading, and during pre-reading, the excitation light energy may be adjusted to be smaller than that during main reading using the excitation light energy adjustment means. The present invention is also applicable to the case where radiographic image information is read by a similar device.

(Effects of the Invention) As explained in detail above, according to the radiation image information reading method of the present invention, when determining the reading conditions for main reading based on pre-reading, each accumulation of divided imaging areas of the stimulable phosphor sheet is Even if the recorded information differs greatly from each other, it is possible to set the optimum reading conditions for each piece of accumulated recorded information. Therefore, according to the method of the present invention, it is possible to always reproduce radiographic images with excellent suitability for observation and interpretation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a radiation image information recording and reproducing system for reading radiation image information according to an embodiment method of the present invention, and FIGS. 2 and 3 are
FIG. 2 is a schematic diagram showing a state of recording radiation image information on a stimulable phosphor sheet according to the present invention. 20... Radiation image capturing unit, 30... Reading unit for pre-reading, 40... Reading unit for main reading, 100... Radiation source, 101... Subject, 102... Radiation,
103...Storage phosphor sheet, 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, 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, 312... A/D converter, 313... signal processing circuit, 314... control circuit, 320... Main reading sheet transport means, a... Reading gain setting value,
b... Recording scale factor setting value, Sp...
Pre-reading image signal, So... Actual reading image signal, Sd...
...Divided shooting information.

Claims (1)

[Scope of Claims] 1. Excitation light is irradiated onto a stimulable phosphor sheet on which radiation image information of a subject is accumulated and recorded, and stimulated luminescence light emitted from the sheet by the irradiation with 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. A radiation image information reading method that performs pre-reading to read an outline of image information, determines reading conditions for performing the main reading based on the information obtained by this pre-reading, and performs the main reading according to these conditions. In the method, when the radiation image information is read from a stimulable phosphor sheet on which divided imaging has been performed by irradiating radiation to each of a plurality of sections when storing and recording the radiation image information, based on the information regarding the divided imaging. each area of the plurality of sections is identified, the reading condition is determined for each of the identified areas, and when performing the main reading, the corresponding reading condition is set for each area. A radiation image information reading method characterized by: