JPH0551219B2 - - Google Patents

Description

Detailed Description of the Invention (Field of the Invention) The present invention involves accumulating and recording radiation image information on a stimulable phosphor sheet that is circulated and then irradiating it with excitation light. Regarding a radiation image information recording/reading device that detects stimulated light emitted in response to excitation light, reads image information, and converts it into an electrical signal, in particular, it uses a multilayer film filter to improve the utilization efficiency of the excitation light. The present invention relates to an image information reading device.

(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.

Using this stimulable phosphor, radiographic image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is then exposed to two-dimensional data using excitation light such as a laser beam. The stimulated luminescent light is scanned to generate stimulated luminescent light, and the resulting stimulated luminescent light is photoelectrically read by a photodetector to obtain an image signal. Based on this image signal, recording materials such as photographic light-sensitive materials, CRTs, etc. The present applicant has already proposed a radiation image information recording and reproducing system that causes a display device to output a radiation image of a subject as a visible image. (Unexamined Japanese Patent Publication No. 55-12429
No. 56-11395, 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 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 radiation image as a visible image to a recording material such as a photographic material or a display device such as a CRT, thereby obtaining a radiation image that is not affected by fluctuations in radiation exposure. be able to.

In the radiation image information recording and reproducing system described above, the storage phosphor sheet does not ultimately record image information, but temporarily carries image information in order to provide the image to the final recording medium as described above. Therefore, this stimulable phosphor sheet may be used repeatedly, and such repeated use is extremely economical.

Also, for example, when a mobile station such as an X-ray imaging vehicle is equipped with a radiation image information recording/reading device that uses a stimulable phosphor sheet and travels to various locations for group examinations to take X-rays. It is inconvenient to load a large number of stimulable phosphor sheets into a vehicle, and there is a limit to the number of sheets that can be loaded onto a moving vehicle. Therefore, a storage phosphor sheet is made to be reusable and loaded onto a moving vehicle, radiographic image information for each subject is recorded on it, and the image signal obtained by reading it is stored on a magnetic tape, etc. whose storage capacity is limited. If the radiation images are copied onto a large recording medium and the stimulable phosphor sheet or the like is reused, radiographic images of a large number of objects can be taken using a mobile vehicle, which is extremely useful in practice. Furthermore, if continuous imaging is performed through this cyclical reuse, the imaging speed can be increased in mass medical examinations, which has an extremely large practical effect.

In order to reuse the stimulable phosphor sheet as described above, the radiation energy remaining in the stimulable phosphor sheet after the stimulated luminescence light has been read can be absorbed by, for example, As shown in No. 56-12599, the remaining radiation image can be erased by irradiating the sheet with light or heat, and the stimulable phosphor sheet can be used again for recording radiation images.

Therefore, the present applicant has proposed a circulating conveyance means for conveying a stimulable phosphor sheet capable of accumulating and recording radiation images along a predetermined circulation path, and a means for irradiating radiation through the sheet through a subject in the circulation path. Thereby, an image recording section that accumulates and records radiographic image information of the subject on this sheet, and an excitation light that emits excitation light that scans the sheet on which radiographic image information is accumulated and recorded in the image recording section, which is located in the circulation path. an image reading section comprising a light source and a photoelectric reading means for reading stimulated luminescence light emitted from a sheet scanned by the excitation light to obtain an image signal; and an image reading section in the circulation passageway. and an erasing section that releases radiation energy remaining on the sheet prior to image recording on the sheet after image recording, and the stimulable phosphor sheet is circulated between the respective sections. We previously proposed a radiographic image information recording/reading device that can be used repeatedly (Japanese Patent Application Laid-open No. 192240/1983). According to the radiographic image information recording/reading device having such a structure, radiographic image information can be recorded and read continuously and efficiently.

By the way, in the above-mentioned radiation image information recording and reproducing system, a problem has conventionally been recognized that the utilization efficiency of excitation light is low. That is, most of the excitation light such as laser light is reflected on the surface of the stimulable phosphor sheet and cannot be effectively used for excitation of the stimulable phosphor. Therefore,
Particularly when reading with high sensitivity is desired, a high-output excitation light source is required, and its power consumption is also disadvantageous. This problem naturally occurs in the radiation image information recording/reading apparatus in which the stimulable phosphor sheet is recycled as described above.

(Objective of the Invention) The present invention has been made in view of the above-mentioned circumstances, and provides an accumulation property that sufficiently increases the utilization efficiency of excitation light and thus enables high-sensitivity reading with a low-output excitation light source. The object of the present invention is to provide a radiation image information recording/reading device that uses a circulating fluorescent sheet.

(Structure of the Invention) The irradiation image information recording/reading device of the present invention includes a circulation conveying means for conveying a stimulable phosphor sheet along a circulation path, an image recording section, an image reading section, and an erasing section as described above. In the radiation image information recording/reading apparatus, the stimulable phosphor sheet has a reflectance of stimulated luminescence light on the surface of the phosphor layer, which increases in accordance with an increase in the angle of incidence of the excitation light. Using a sheet formed with a multilayer film filter that allows light to pass through regardless of the angle of incidence, this stimulable phosphor sheet is placed in the image reading section with the multilayer film filter facing the excitation light irradiation side. It is characterized by the following.

The above-mentioned multilayer film filter is made by sequentially stacking several to several dozen layers of two or more types of materials with different optical refractive indexes on a substrate with a thickness of about 1/4 of the wavelength of light by vacuum evaporation or other methods. It is what it is. In this case, by appropriately setting the optical refractive index and film thickness of each substance,
Various properties can be obtained. Note that as the low refractive index material, for example, SiO ₂ , MgF ₂ , etc. are used, while as the high refractive index material, for example, TiO ₂ , ZrO ₂ , ZnS, etc. are used.

(Function) When a stimulable phosphor sheet having a multilayer filter as described above is arranged in the image reading section with the filter facing the excitation light irradiation side, the incident angle is made sufficiently small (normally as much as possible
The excitation light incident on the stimulable phosphor sheet (approximately 0°) passes through the multilayer filter well and reaches the phosphor layer. The excitation light that reaches this phosphor layer and is diffusely reflected there returns to the multilayer filter at various angles, but at this time, a large amount of the excitation light that enters the multilayer filter at a large angle of incidence is reflected by the filter. , it is folded back to the phosphor layer side again. In other words, the excitation light reflected on the stimulable phosphor layer is trapped between the phosphor layer and the multilayer filter, so that the excitation light is effectively used to excite the stimulable phosphor. Become so.

On the other hand, the stimulated luminescent light emitted from the stimulable phosphor layer by the irradiation with the excitation light is also emitted at different angles, but this stimulated luminescent light is not suitable for the multilayer film filter having the above-mentioned characteristics. It can be efficiently detected by a photodetector.

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

1 and 2 show an apparatus according to one embodiment of the present invention. As shown in FIG. 1, endless belts 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
and guide rollers 11, 12, 13, 1 that rotate following the endless belts 1, 6, 7, 10, respectively.
4, and guide plates 15, 16, 17, 18, 19,
20, 21, and Nitsu rollers 22, 23, 24,
A circulation path 26 for sheet conveyance is configured, which includes a plurality of stimulable phosphor sheets 3 (in this example, five sheets).
0 are arranged at appropriate intervals from each other, and these stimulable phosphor sheets 30 are transported by the endless belts 1 to 10 as sheet circulation conveyance means and the nip rollers 22, 23, 24, 25 in the direction indicated by the arrow A in the figure. It is designed to be conveyed in a circular manner.

The endless belts 2 and 3 are configured to vertically hold the stimulable phosphor sheet 30 between them, and a photographing stand is provided on the side of the endless belts 2 and 3 (left side in the figure). A radiation source 42 such as an X-ray source is provided at a position facing the endless belts 2 and 3 with the imaging table 41 in between. A recording section 40 is configured. During radiography of the subject (subject) 43,
The sheet 30 used for imaging is held between the endless belts 2 and 3 as shown in the figure, and the sheet 30 is held between the endless belts 2 and 3,
The radiation source 4 is placed in front of the imaging table 41.
2 is activated. As a result, the transmitted radiation image of the subject 43 is projected onto the sheet 30, and the radiation image information of the subject 43 is stored and recorded on the sheet 30.

An image reading section 50 is provided at the lower right end position of the circulation passage 26 in the figure. This image reading section 50
A laser light source 51 is installed above the endless belt 8 that constitutes a part of the reading section 50, and a laser light source 51 is installed to scan the sheet 30 on the endless belt 8 with its output laser light 52 in the width direction of the sheet 30 on the endless belt 8. Mirror 53 and galvanometer mirror 5
4 is provided. By this reciprocating movement of the galvanometer mirror 54, the laser beam 52 is main-scanned over the sheet 30 on which the radiation image has been accumulated and recorded. Note that this sheet 30 is used in the image recording section 40.
After the radiation image is recorded in , the sheet is conveyed to the image reading section 50 by driving the sheet circulating conveyance means. At the scanning position of the laser beam 52 on the sheet 30, there is a condensing reflective mirror 5 along the main scanning line.
5 and a condensing optical element 56 are arranged. Stimulated luminescence light emitted from the sheet 30 irradiated with the laser beam 52 and directly traveling to the condensing optical element 56 and stimulated luminescence light also emitted from the sheet 30 and reflected by the condensing reflective mirror 55 are collected. The light enters the condensing optical element 56 from the incident end surface 56A of the light optical element 56, and is guided through the condensing optical element 56 by total reflection.
The stimulated luminescence light is received by a photomultiplier (photomultiplier tube) 57 connected to the emission end surface 56B of the photoelectronic light, and the stimulated luminescence light is read out photoelectrically. At the same time as the main scanning of the laser beam 52 is performed as described above, the sheet 30 is moved by the endless belt 8 in the direction of arrow A in the figure (that is, in the direction substantially perpendicular to the main scanning direction).
The sheet 30 is conveyed to perform sub-scanning, and the stored radiation image information is read over the entire surface of the sheet 30. The image signal S1 read by the photo multiplier 57 is transmitted to an image processing circuit 60, subjected to necessary image processing, and then sent to a necessary image reproduction device 61. As mentioned above, this reproducing device may be a display such as a CRT, a recording device that performs optical scanning recording on a photosensitive film, or a device that temporarily records on a recording device such as a magnetic tape for that purpose.

The sheet 30 whose image has been read is conveyed along the guide plate 18 by the endless belts 9 and 10, and sent to the erasing section 70 through the nip roller 22, the guide plate 19, and the nip roller 23.
The erasing unit 70 consists of a box 71 and a large number of erasing light sources 72 such as fluorescent lights arranged inside the box 71. After the shutter 73 is opened, the sheet 30 is removed by the nip roller 23. Box 71
transported inside. When the sheet 30 is sent into the box 71, the shutter 73 is closed. Box 7
The erasing light source 72 in 1 mainly emits light in the excitation wavelength range of the stimulable phosphor of the sheet 30,
The radiation energy remaining in the sheet 30 after the image reading is emitted from the sheet 30 by irradiating the sheet 30 with such light. Note that since the shutter 73 is closed at this time, the erasing light does not leak and enter the image reading section 50 and generate noise in the read signal.

The sheet 30 in which the image (afterimage) has been erased to such an extent that radiation image information can be recorded again is
The nip roller 24 is rotated and the data is discharged to the outside of the erasing section 70. The discharged sheet 30 is placed on the guide plate 20
The image is then sent to the nip roller 25 through the nip roller 25, and then sent to the endless belt 1 along the guide plate 21 by the nip roller 25, and then sent to the image recording section 40 in the same manner as described above to be used for radiography.

Next, image reading will be described in more detail with reference to FIG. 2, which shows an enlarged view of the main parts of the image reading section 50. As shown in the figure, the stimulable phosphor sheet 30 is made of a flexible support 30A made of carbon-containing PET (polyethylene terephthalate), for example.
A stimulable phosphor layer 30B is formed thereon, and a filter 30 made of a multilayer film as described above is further formed thereon.
It is formed by laminating C. The stimulable phosphor sheet 30 is placed in the device in such a direction that radiation is irradiated from the multilayer filter 30C side. Therefore, in the image reading section 50, the multilayer filter 30C of the stimulable phosphor sheet 30 faces the laser light irradiation side, so the laser light 52 passes through the filter 30C and reaches the phosphor layer 30B. irradiated.

The multilayer filter 30C is, for example, a short pass filter having spectral transmittance characteristics as shown in FIG. Note that this multilayer film filter 30C absorbs almost no light, so the reflectance is obtained by subtracting the transmittance shown in FIG. 3 from 1 (100%). In this embodiment, a beam with a wavelength of 633 nm emitted from a He--Ne laser is used as the excitation light 52. As shown in FIG.
The light transmittance of the multilayer filter 30C for
Approximately 90 when the above incident angles are 0°, 30°, and 45°, respectively.
%, 20%, and 5%, which rapidly decreases (that is, the reflectance increases) as the incident angle increases. On the other hand, the stimulable phosphor layer 30B has a wavelength of 360 to 420 nm (mainly 390 nm) due to the excitation of the laser beam 52.
It emits stimulated luminescence light 15 having a wavelength of m). As shown in FIG. 3, the multilayer filter 3
0C means light in this wavelength range is 90
Transmits well with a transmittance of around %. Furthermore, the above
The incidence angle dependence of the transmittance of 390nm and 633nm light is
This is shown in Figure 5 for easy understanding.

As shown in FIG.
It is made to be incident on the top. Therefore, this laser beam 52 passes through the multilayer filter 30 with a transmittance of about 90%.
C is transmitted well, reaches the stimulable phosphor layer 30B, and excites the stimulable phosphor as described above. This laser light 52 is reflected to some extent on the surface of the stimulable phosphor layer 30B and returns to the multilayer filter 30C side. This reflection is diffuse reflection, and the reflected light 52a enters the multilayer filter 30C at various angles of incidence. Of the reflected light 52a, the light that enters the multilayer filter 30C at a large angle of incidence is reflected at a high reflectance by the filter 30C having the above-mentioned characteristics, and is again reflected in the stimulable phosphor layer. Returning to the 30B side, the stimulable phosphor is excited. That is, in this device, the laser beam 52, which is excitation light, is confined between the multilayer filter 30C and the stimulable phosphor layer 30B, and is effectively used for excitation of the stimulable phosphor. It becomes like this. According to experiments conducted by the present inventors, by increasing the utilization efficiency of excitation light as described above, the reading sensitivity can be doubled compared to the case of using a conventional stimulable phosphor sheet without the multilayer filter 30C. It turns out that it can be increased to a certain degree.

Incidentally, the stimulated luminescent light 59 also enters the multilayer filter 30C at different angles, but the multilayer filter 30C is capable of absorbing the stimulated luminescent light 5 as described above.
9 is transmitted well regardless of the angle of incidence,
The stimulated luminescent light 59 efficiently enters the condensing optical element 56.

As mentioned above, if the stimulable phosphor sheet 30 with the multilayer filter 30C is used, the reading sensitivity can be improved, but on the other hand, compared to the case where a stimulable phosphor sheet without the multilayer filter 30C is used. The sharpness of the read image decreases. This is thought to be because the excitation light once scattered on the stimulable phosphor layer 30B is used to excite the stimulable phosphor, so that the excitation is performed by partially blurred excitation light. This sharpness can be increased by, for example, making the phosphor layer 30B of the stimulable phosphor sheet 30 thinner, or when a particularly high sharpness is not required but high sensitivity is required instead. teeth,
In particular, the above-mentioned measures for improving sharpness may not be performed.

In the embodiment described above, a short pass filter having the spectral transmittance characteristics shown in FIG. 3 is used as the multilayer filter.
In the device of the present invention, it is also possible to use a stimulable phosphor sheet in which a multilayer film filter (the spectral transmittance characteristics of which are schematically shown in FIG. 4) as a so-called bandpass filter is formed on a phosphor layer. .
In other words, such a band-pass filter type multilayer filter has spectral transmittance characteristics in which the reflectance for excitation light increases as the angle of incidence increases, while the stimulated luminescence light is transmitted satisfactorily regardless of the angle of incidence. The same effect as described above can be obtained by using a material having . FIG. 6 shows an example of the dependence of the light transmittance of the multilayer filter, which is a bandpass filter, on the angle of incidence.

In addition, in the device of the present invention, the multilayer film filter formed on the stimulable phosphor sheet is
Excitation light transmittance is 70% or more, preferably 80% or more (that is, excitation light reflectance is 30% or less, more preferably 20% or less) within 5 degrees, and excitation light reflectance is 60% at an incident angle of 30 degrees or more. It is more preferable to use one having a stimulated luminescence light transmittance of 60% or more and more preferably 80% or more at an incident angle of 0 to 40°.

(Effects of the Invention) As explained in detail above, in the radiation image information recording/reading device of the present invention, the use efficiency of excitation light is improved by the action of the multilayer film filter formed on the phosphor layer of the stimulable phosphor sheet. It has become possible to sufficiently increase the Therefore, according to the device of the present invention,
By using a low-output excitation light source and reducing power consumption, the sensitivity of reading radiation image information can be sufficiently increased. In addition, in the device of the present invention, since a multilayer film filter that produces the above-mentioned effects is provided on each of the stimulable phosphor sheets, compared to the case where the multilayer film filter is provided on the reading system side in close contact with the sheet, This is advantageous in that it is possible to prevent the conveyed sheet from rubbing against the multilayer filter and causing both to wear out.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing a device according to an embodiment of the present invention, FIG. 2 is a side view showing an enlarged main part of the device according to the embodiment, and FIG. 3 is a diagram showing a multilayer filter used in the device according to the present invention. A graph showing examples of spectral transmittance characteristics for each light incident angle, FIG. 4 is a graph showing spectral transmittance characteristics of another multilayer filter that can be used in the device of the present invention, and FIGS. 2 is a graph showing an example of the dependence of the transmittance of a multilayer film filter used in the device on the angle of incidence for excitation light and stimulated emission light. 1~10... Endless belt, 11~14...
...Guide roller, 15~21...Guide plate, 22~
25...Nitsupurora, 26...Circulation passage, 30
...Stormable phosphor sheet, 30B...Stormable phosphor layer, 30C...Multilayer film filter, 40... Image recording section, 50... Image reading section, 70... Erasing section.

Claims (1)

[Scope of Claims] 1. Circulating conveyance means for conveying a stimulable phosphor sheet capable of accumulating and recording radiation image information along a predetermined circulation path, the sheet having image information in the circulation path; an image recording section that accumulates and records the radiographic image information on the sheet by irradiating it with radiation; and an excitation light that scans the sheet on which the radiographic image information is accumulated and recorded in the image recording section in the circulation path. an image reading unit having an excitation light source that emits light, and a photoelectric reading unit that reads stimulated luminescence light emitted from a sheet scanned by the excitation light to obtain an image signal; and in the circulation path, the image reading unit A radiation image information recording/reading device comprising: an erasing unit that releases radiation energy remaining on the sheet prior to recording an image on the sheet after image reading is performed, As a body sheet, a multilayer film filter is provided on the surface of the phosphor layer, the reflectance of the excitation light increases as the angle of incidence increases, while the stimulated luminescence light is transmitted satisfactorily regardless of the angle of incidence. A radiographic image information recording/reading apparatus, characterized in that the stimulable phosphor sheet is disposed in the image reading section with the multilayer filter facing the excitation light irradiation side. 2. The radiation image information recording/reading apparatus according to claim 1, wherein the multilayer film filter is a short pass filter. 3. Claim 1, wherein the multilayer filter is a bandpass filter.
The radiation image information recording/reading device described in Section 1.