JPH0448022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a reading device for radiographic image information stored and recorded on a stimulable phosphor sheet, and more particularly, The present invention relates to a radiation image information reading device that can accurately read stimulated luminescence light emitted from the sheet in accordance with radiation image information.

(Technical Background of the Invention and Prior Art) Certain phosphors have a tendency to accumulate (X-rays, α-rays, β-rays,
When irradiated with γ-rays, ultraviolet rays, etc., a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor increases depending on the accumulated energy. is known to exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors.

Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily stored in a sheet having a layer made of a stimulable phosphor (hereinafter referred to as a ``stimulable phosphor sheet'').
Or just say "sheet". ), this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, and the stimulated luminescent light is read photoelectrically to obtain an image signal. A method for recording and reproducing radiation image information has been proposed, which processes radiation images to obtain radiation images of a subject with good diagnostic suitability. (For example, JP-A-55-12429, JP-A No. 56-11395)
No. 55-163472, No. 56-104645, No. 55-
116340, etc.) A radiation image information reading device used in the radiation image information recording and reproducing method proposed as described above is shown in FIG. 5, and its mechanism will be explained with reference to FIG.

A laser beam 101a of a constant intensity is emitted from a laser light source 101 as excitation light to a galvanometer mirror 1.
02, and this galvanometer mirror 10
2, the laser beam is deflected and irradiated onto the sheet 103 so that the laser beam performs main scanning (scanning in the direction of arrow A) in the width direction of the sheet 103 placed below the galvanometer mirror 102. Furthermore, the seat 103 is, for example, an endless belt device 109
Because it is attracted to and transported in the direction of arrow B,
The main scan is repeated at an angle substantially perpendicular to the sub-scan, and the laser beam 101 covers the entire surface of the sheet 103.
Two-dimensional scanning is performed using b. For this reason,
According to the scanning by the laser beam 101b, the laser beam 1
The irradiated portion of the sheet 01b emits stimulated light with an intensity corresponding to the accumulated and recorded image information, and this emitted light is transmitted to a transparent condenser with an incident end surface 104a formed parallel to the main scanning line near the sheet. The light enters the light condenser 104 from the incident end face 104a of the light body 104. This light condenser 104 has a front end surface 1 located near the sheet 103.
04b is formed into a planar shape and gradually becomes cylindrical toward the rear end side, and becomes almost cylindrical at the rear end portion 104c and is connected to the photomalle 105, so that the incident end surface The stimulated luminescent light entering from 104a is transferred to the rear end 10.
Gather them at 4c and tell them to Fotomal 105. In the photoprinter 105, the stimulated luminescent light is converted into an electrical signal and then sent to the image information reading circuit 106. The electrical signal is processed by the image information reading circuit 106, and is output as a visible image to the CRT 107, recorded on a magnetic tape 108, or directly recorded as a hard copy on a photosensitive material, etc. Can be done.

During the above-mentioned reading, since the incident end surface 104a of the light condenser 104 is parallel to the main scanning line and has a width covering almost the entire width of the sheet 103, the incident end surface 104a
All the light from the point where the laser beam 101b can be seen is read, and not only the stimulated luminescence light from the point where the laser beam 101b is incident, but also the light from the incident end face 10.
All the light from other places on the sheet 103 that can see 4a is also read. The afterglow emitted by the sheet 103 poses a problem as light other than the stimulated luminescence light that enters the incident end surface 104a and is read. This afterglow includes instantaneous luminescence afterglow and stimulated luminescence afterglow.

Instantaneous afterglow is a phenomenon in which the instantaneous light emitted from a sheet when radiation is irradiated to record image information on the sheet does not disappear and continues to emit light while attenuating even after the radiation irradiation is cut off. To tell. The characteristics of this instantaneous light emission afterglow vary depending on the type of stimulable phosphor used in the sheet, but are generally as shown in FIG. 6. Figure 6 is a graph showing luminescence intensity on the vertical axis and time (t) on the horizontal axis. After radiation irradiation was performed for △t ₂ hours from time t ₁ to t ₂ , when the irradiation was cut off, the luminescence An instantaneous afterglow is shown in which the intensity of the instantaneous emitted light of intensity "A" does not immediately become zero, but decreases along an exponential function with a gradually increasing time constant.

Specifically, the decay of the luminescence intensity of this instantaneous luminescence afterglow is, for example, about 180 seconds after radiation irradiation (i.e.,
The luminescence intensity "B" of the instantaneous luminescence afterglow at time "t ₃ " (t ₃ - t ₂ ) = 180 seconds) is approximately 10 ^- of the intensity of the stimulated luminescence light emitted by excitation light scanning. It will be about ⁴ times as much.

For this reason, after recording image information by irradiating radiation through a subject onto a sheet, if a predetermined amount of time elapses before this image information is read, the intensity of the instantaneous light emission afterglow will decrease enough to the point where the afterglow can be ignored. Become. However, when reading radiation image information immediately after recording it, the image information recording section is integrated into a radiation image information reading device, such as the one disclosed in Japanese Patent Application No. 1983-66730, which was previously filed by the present applicant. When recording and reading are carried out continuously, at high speed, and in large quantities using a device built into a radiographic image information recording/reading device (i.e., a radiographic image information recording/reading device), the luminescence intensity of instantaneous afterglow as well as stimulated luminescence is Since the light is read before it has sufficiently attenuated, the influence of the instantaneous light emission afterglow on the read image information increases.

In addition, stimulated luminescence light is emitted from a very small area where the excitation light is incident, whereas instantaneous luminescence afterglow is emitted from the entire surface irradiated with radiation. From the incident end surface 104a of the body 104, the stimulated luminescent light and the incident end surface 10
The instantaneous light emission afterglow from all the locations where 4a can be expected are captured simultaneously to create a photo of 10.
Sent to 5. In this case, compared to the area of the sheet 103 where the laser beam is irradiated, the light condenser 10
Since the area of the part where the incident end surface 104a of No. 4 can be seen is extremely large, as mentioned above, after a predetermined period of time has elapsed after radiation irradiation, the intensity of the instantaneous afterglow is compared to the intensity of the stimulated emitted light. Even if it becomes negligibly small, the amount of instantaneous light emission afterglow cannot be ignored as the amount of light transmitted to the photoprint 105.

On the other hand, instantaneous luminescence afterglow refers to the phenomenon that even after excitation light (e.g., laser light) is irradiated to produce stimulated luminescence in order to read the radiographic image stored and recorded on the sheet, even if the excitation light is cut off, the stimulated luminescence still remains. This refers to a phenomenon in which light does not disappear at the same time as it is blocked, but continues to emit light even though it is attenuated. The characteristics of this stimulated luminescence afterglow vary depending on the type of stimulable phosphor used in the sheet, but are generally as shown in FIG. 7. Figure 7 is a graph showing the luminescence intensity on the vertical axis and the time (t) on the horizontal axis. When excitation light is irradiated for △t ₅ hours from time t ₄ to t ₅ and then cut off, the luminescence intensity The intensity of the stimulated luminescent light of "C" does not immediately become zero, but decreases along an exponential function with a gradually increasing time constant. (In other words, the intensity decreases rapidly at first, and then the rate of decrease gradually decreases.) Specifically, the attenuation of the luminescence intensity of this stimulated luminescence afterglow occurs when the initial time constant is about 1 microsecond. be. That is, the emission intensity is 1/e (D/C=
1/e) (t ₆ -t ₅ ) is about 1 microsecond. By the way, the speed at which the excitation light is scanned (main scan) on the stimulable phosphor sheet by a galvanometer mirror is generally about 50 hertz, so one scan takes about 20,000 microseconds. Therefore, the intensity of the stimulated luminescence afterglow, which decays along an exponential function with an initial time constant of 1 microsecond, is an order of magnitude smaller than the intensity of the stimulated luminescence light, and the stimulated luminescence afterglow at each point is The strength is almost negligible.

However, stimulated luminescence light is emitted from a very small area where the excitation light is incident, whereas stimulated luminescence afterglow is emitted from all the surfaces scanned by the excitation light. light body 10
4, the stimulated luminescence light and the stimulated luminescence afterglow from all the places where the incidence end face 104a can be seen are taken in at the same time and sent to the photoprint 105. In this case sheet 103
Compared to the area of the area where the excitation light is incident and stimulated luminescence occurs, the area of the area where the stimulated luminescence afterglow occurs due to the scanning of the excitation light is extremely large, as in the case of instantaneous luminescence afterglow. Even if the intensity of the stimulated luminescence afterglow is negligibly small compared to the intensity of the stimulated luminescent light, the amount of the stimulated luminescent afterglow cannot be ignored as the amount of light transmitted to the photoprint 105. The afterglow that is read at the same time as the stimulated luminescence light becomes a noise component in the image signal of the radiographic image, making it difficult to read accurate radiation image information.

In particular, instantaneous luminescence afterglow is a problem when reading the radiation image information immediately after recording it on a stimulable phosphor sheet. This becomes a particular problem as the scanning speed increases.

Next, the influence of afterglow on image information will be specifically explained using FIGS. 8A and 8B. FIG. 8A shows radiation image information of, for example, a human head recorded on a sheet 103a, and FIG. 8B shows the information recorded on a sheet 103a through a condenser when scanning with excitation light (laser light) along line a. The amount of light transmitted to the photographic image is shown with the horizontal axis representing the position corresponding to the scanning of line a. In Figure 8B, the amount of light actually transmitted to the photomal is shown by the broken line _l1 , and the amount of afterglow (the sum of the instantaneous afterglow and the stimulated afterglow) out of the amount of light shown by the broken line _l1 is shown by the dashed line. l ₃ and the amount of stimulated luminescence is shown by the solid line l ₂ . In other words, the amount of afterglow l ₃ and the amount of stimulated luminescence
The sum of l ₂ is the amount of light transmitted to the photoprint, l ₁ . This amount of light _l1 is converted into an electrical signal in the form of a photo signal and then subjected to logarithmic conversion (LOG conversion), and a reproduced image is obtained from this logarithmically converted signal. In this case, the value is different when the amount of light l ₁ transmitted to the photomal is converted into an electrical signal and logarithmically converted, and when only the stimulated luminescence amount l ₂ is converted to an electrical signal and this is logarithmically converted. If an image is reproduced using the value of l ₁ , the reproduced image will be a different image from the actual image. That is, the reproduced image becomes inaccurate or unclear, which poses a serious problem in diagnostic suitability.

In addition to the afterglow problem mentioned above, the laser beam 101
A part of the light b is reflected by the surface of the sheet 103, and this reflected light is further reflected by the incident end surface 104a of the condenser 104 and returns to an unspecified surface of the sheet 103.
The phosphor in that area may be excited and stimulated luminescence may occur. When such stimulated luminescence light generated from outside the scanned area is read, it becomes a noise component of the image signal and reduces the sharpness of the image.

Therefore, it is desired to develop a timer that is equipped with a means to prevent afterglow other than stimulated luminescence light from the scanning location of the excitation light from entering the incident end face of the light collector, as described above. The present applicant has already filed an application for an invention proposing a method for solving this problem (Japanese Patent Application No. 153691/1982).

In the reading device according to the above invention, in order to prevent afterglow from reaching the light condenser, the slit is wide enough to only allow excitation light to irradiate the sheet and stimulated luminescence light from the sheet to enter the condenser. The invention is characterized in that a light shielding member is provided between the incident end surface of the light condenser and the sheet, and covers a portion of the sheet along the scanning line before and after scanning. However, since the light collector is placed close to the sheet in order to increase the efficiency of collecting stimulated luminescence light, it is spatially difficult to actually provide a light shielding member between the sheet and the light collector. Furthermore, in order to reduce the range of the sheet picked up by the light collector without cutting off the necessary stimulated luminescence light by the light shielding member, the slit of the light shielding member should be made as small as the range of the sheet, and the light shielding member should be made as small as the range of the sheet. The members had to be arranged so as to be almost in contact with the sheet, which caused problems such as difficulty in arrangement and difficulty in manufacturing light shielding members with minute slit widths.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and it is possible to eliminate instantaneous luminescence afterglow, stimulated luminescence afterglow, and from outside the scanned part by means that can be easily designed and manufactured. The object of the present invention is to provide a radiation image information reading device that can perform highly accurate reading by preventing the generated stimulated luminescence light from entering a condenser and reducing its influence on reading. be.

(Structure of the Invention) The radiation image information reading device of the present invention has a slit extending in the main scanning direction between the sheet and the incident end surface of the condenser, so that light other than stimulated luminescence light can reach the incident end surface. The light-shielding member is further provided with a light shielding member for preventing the stimulated luminescence light emitted from the scanning point of the sheet, and focuses the stimulated luminescence light emitted from the scanning point of the sheet into the slit only in the sub-scanning direction, so that the stimulated luminescence light is transmitted through the slit to the incident end surface of the light condenser. The device is characterized in that it includes an optical system through which emitted light is incident. The above optical system makes the stimulated luminescence light from the scanning point enter the cylindrical lens and focuses it only in the sub-scanning direction within the slit, and reflects the stimulated luminescence light that has passed through the cylindrical lens by a mirror. Similarly, the stimulable luminescent light can be designed to pass through any optical path before converging within the slit.

Therefore, the reading device of the present invention prevents afterglow and the like from reaching the condenser, and also makes the design of the reading device easier and more versatile.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure around the scanning section of a reading device according to an embodiment of the present invention.

The stimulable phosphor sheet 3 is moved in the direction of arrow B for sub-scanning. Laser scanning light 1b as excitation light main scans the sheet 3 along scanning line 3a, and stimulated luminescence light 1c is emitted from the scanning position on sheet 3 irradiated with laser scanning light 1b.
Moreover, above the sheet 3, this stimulated luminescent light 1c
A cylindrical lens 5 is provided which allows the cylindrical lens 5 to enter the light within a field angle range of θ and focuses it only in the sub-scanning direction. The light enters the incident end face 4a of the light condenser 4 provided immediately above.

The sheet 3 emits an instantaneous afterglow 1A during accumulation recording from a portion 3A before scanning, and from a portion 3B immediately after scanning.
It emits an afterglow 1B of stimulated luminescence. In order to prevent these afterglow lights from entering the light collector 4, a light shielding member 6 is provided below the light collector 4.
This light shielding member 6 has a slit 6a extending in the main scanning direction and having a length equal to or longer than the main scanning width in the center thereof, and the focal position of the stimulated luminescent light 1c by the cylindrical lens 5 is within the slit 6a. It is arranged so that it comes to The width W of this slit 6a is defined as b/a, where a is the distance from the scanning position to the cylindrical lens 5, and b is the distance from the cylindrical lens 5 to the focusing position of the stimulated luminescence light.
The imaging magnification of the cylindrical lens expressed as M
Further, it is defined by S×M, where S is the width of the sheet 3 on which the emitted light is to be collected. Therefore, if the imaging magnification M is increased, the width W of the slit 6a can be made sufficiently large even if the width S of the condensing range is decreased, and the slit can be easily formed. The cylindrical lens 5 needs to be placed as close to the sheet 3 as possible (increasing the angle of view θ) in order to make all of the stimulated luminescence light from the condensing range incident, so it is recommended to use one with a small focal length. It is preferable to use a round bar lens or a semi-round bar lens which can provide a relatively short focal length. Further, in the present embodiment described above, the laser scanning light 1b is reflected by a reflecting mirror 7 disposed below the light shielding member 6, and then passes through the cylindrical lens 5 to scan the sheet 3, as shown in the figure. However, since the cylindrical lens 5 does not need to act as a lens for the laser scanning light 1b, the portion of the cylindrical lens 5 on which the laser scanning light 1b is incident may be made flat, as shown in FIG.

Next, with reference to FIG. 3, an optical system for collecting stimulated luminescence light on a condenser according to another embodiment of the present invention will be described.

In the embodiment shown in FIG. 3a, two cylindrical lenses 5A and 5B having the same focal length are used.
are arranged continuously in the sub-scanning direction. This is 1
When using two cylindrical lenses, the angle of view θ is
This is effective when it is not possible to make a sufficiently large cylindrical lens.
It is reflected by A and 8B and guided to be focused at the same position within the slit 6a of the light shielding member 6.
In addition, another embodiment shown in FIG. 3b is also effective for increasing the angle of view θ, and three cylindrical lenses 5C, 5D, and 5E having the same axis are successively disposed in the slit 6a. It focuses the stimulated luminescence light that has passed through three lenses.

Furthermore, in the first embodiment of the present invention shown in FIG. 1, the laser scanning light 1b was irradiated onto the sheet 3 from below the light shielding member 6, but the laser scanning light 1b is as shown in FIG. Alternatively, it is also possible to irradiate from above the light shielding member 6. That is, the light-shielding portion 6A of the light-shielding member 6 is made of a dichroic film that transmits light with the wavelength of the laser scanning light 1b and cuts out the stimulated emission light and the light with the wavelength of afterglow, and the slit portion 6B of the light-shielding member 6 is made of a transparent film. By using a film or a dichroic film that passes light with the wavelength of stimulated luminescence light and cuts out light with the wavelength of laser scanning light, it is possible to irradiate laser scanning light from above the light shielding member while blocking afterglow. This is what I did. The embodiments of the present invention have been described above, but in addition to the above-described embodiments, it is possible to design devices of various embodiments by changing the arrangement and combination of optical systems, etc.
It has an extremely wide range of applications.

Note that the shape of the condenser constituting the radiation image information reading device of the present invention is not limited to the shape shown in FIG. As described in , the exit end face may be divided into a plurality of sections, and each section may be connected to a photodetector such as a photodetector.

(Effects of the Invention) As described above in detail, according to the radiation image information reading device of the present invention, the light shielding member prevents afterglow from reaching the incident end surface of the light collector, and only stimulated luminescence light is transmitted. Since it is guided to the condenser through a slit, the influence of afterglow on reading can be greatly reduced, and a part of the laser scan can be prevented from being reflected on the surface of the sheet and reaching the incident end face of the condenser. Since the reflected light is prevented from returning to the sheet from the incident end surface, stimulated luminescence does not occur outside the scanned area, and an image with high sharpness can be obtained. In addition, by disposing the light shielding member of the optical system including the cylindrical lens between the sheet and the light shielding member, there is no need to arrange the light shielding member and the light condenser close to the sheet, which simplifies the design and improves the image formation of the cylindrical lens. When the magnification is increased, a sufficient afterglow light-shielding effect can be obtained even if the slit width is large, and the practical value of this is extremely large, as it facilitates the production of light-shielding members.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure near the scanning section of a reading device according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG. 1 showing the shape of the cylindrical lens in the embodiment shown in FIG. , FIG. 3 is a cross-sectional view showing the optical system of the scanning section according to another embodiment of the present invention, FIG. 4 is a cross-sectional view showing the structure near the scanning section according to another embodiment of the present invention, and FIG. 5 is a conventional one. 6 is a graph showing the temporal characteristics of instantaneous luminescence afterglow, FIG. 7 is a graph showing the temporal characteristics of stimulated luminescence afterglow, and FIG. 8A is a graph showing the temporal characteristics of stimulated luminescence afterglow. Fig. 8B shows the intensity of the emitted light transmitted through the light condenser when the excitation light scans the sheet on which the radiographic image information of Fig. 8A is recorded. It is a graph. 1b... Laser scanning light, 1c... Stimulated luminescence light,
4... Light collector, 5, 5A, 5B, 5C, 5D, 5
E... Cylindrical lens, 6... Light shielding member,
6a...Slit.

Claims (1)

[Claims] 1 Main scanning means for generating stimulated luminescence light by main scanning a stimulable phosphor sheet on which radiographic image information is stored and recorded using excitation light; the sheet and excitation light are relatively perpendicular to the main scanning direction; sub-scanning means that performs sub-scanning by moving in the main scanning direction; a light condenser that has an entrance end face extending parallel to the main scanning line in the main scanning direction and guides light incident from the entrance end face to an exit end face; , a photodetector connected to the exit end surface of the light condenser, a light shielding member having a slit extending in the main scanning direction and disposed between the surface of the sheet and the entrance end surface of the light condenser; an optical system that focuses the stimulated luminescent light emitted from the scanning point of the sheet only in the sub-scanning direction by a cylindrical lens provided above the sheet, and makes it enter the incident end surface of the light condenser through the slit. A radiation image information reading device characterized by: