JP4173871B2 - Photodetector for radiation image reader - Google Patents

Description

  The present invention relates to a photodetector in a radiation image reading apparatus, and more particularly to a photodetector provided with an excitation light separation filter.

  Conventionally, when irradiated with radiation, a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, a stimulable phosphor (stimulable phosphor) that exhibits stimulated emission according to the accumulated energy. ) Is used to record radiation image information of a subject such as a human body on a sheet-like storage phosphor, and the storage phosphor sheet is scanned with excitation light such as a laser beam to generate photostimulated light. Radiation image recording that reads the obtained stimulated emission light photoelectrically to obtain an image signal and outputs a radiographic image of the subject as a visible image on a recording material such as a photographic photosensitive material or a CRT based on this image data Reproduction systems have already been put into practical use (Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, etc.). This system is composed of a radiation image recording device, a radiation image reading device, and a radiation gland image reproducing device.

  Among these systems, the photodetector for photoelectrically reading the above-mentioned stimulated emission light used in the radiation image reading apparatus is a photomultiplier tube (photomultiplier) which is a photoelectric conversion means, and a storage phosphor. It consists of a light guide that guides the stimulated emission light from the sheet to the photomultiplier, but because the stimulated emission light is faint light, light other than the stimulated emission light will enter the photomultiplier as noise. It is necessary to prevent the incident.

  A typical light other than the stimulated emission light is excitation light for scanning the stimulable phosphor sheet.

  The excitation light scans the stimulable phosphor sheet. At this time, the light incident end face of the light guide is arranged in the immediate vicinity of the excitation light being scanned in order to efficiently collect the excitation light. As a result, not only the stimulated emission light but also the excitation light may enter the incident end face of the light guide.

However, since the excitation light and the stimulated emission light have different wavelength bands, both light can be easily separated. That is, an excitation light cut filter having a characteristic that allows transmission of stimulated emission light while preventing transmission of light in the wavelength band of excitation light is disposed between the light guide and the photomultiplier. ing.
JP-A-55-12429 JP-A-56-11395 JP 55-163472 A Japanese Patent Laid-Open No. 56-10645 JP 55-116340 A

  By the way, the excitation light separation filter (hereinafter abbreviated as a filter) cannot completely block the excitation light from entering the photomultiplier. Therefore, the excitation light that has passed through this filter and reached the photomultiplier is superimposed on the image signal as a noise component, and the image reading performance reproduced based on this image signal is degraded. In particular, when this image is a medical radiation image, there is a possibility that the diagnosis may be affected by a noise component.

  Therefore, it is conceivable to increase the thickness of the filter to lengthen the process of blocking the passage of excitation light and to prevent the excitation light from entering the photomultiplier as much as possible. When the thickness is increased, the stimulated emission light propagating in the filter is reflected also on the surface other than the entrance surface and the exit surface of the filter, for example, the side surface in the longitudinal direction of the photodetector (the direction parallel to the main scanning direction of the excitation light). Opportunities arise and the probability of reflection on this surface increases.

  By the way, the outer surface of such a filter is generally coated with a light-shielding paint or the like in order to prevent natural light or the like from entering the inside of the filter from the outside.

  When such a paint is applied, light from the outside becomes difficult to enter the inside, but conversely, the light transmitted through the inside is easily released to the outside because the total reflection condition is relaxed. Conventionally, however, the thickness of this filter is about 2 mm at the most, so that the emission of such photostimulable light from the outer surface to the outside has not reached a problem level.

  In the case of using a filter having a relatively small photocathode width and a thickness close to the photocathode width, there is a problem that the propagation efficiency of the stimulated emission light is lowered.

  The present invention has been made in view of the above circumstances, and even when the filter is thick, the stimulated emission light propagating through the inside is prevented from being incident while the excitation light or the like is not incident from the outside. It is an object of the present invention to provide a photodetector with improved S / N by preventing leakage.

  The photodetector of the radiation image reading apparatus according to the present invention prevents excitation light from entering by covering the outer surface of the filter with a light shielding member, and an excitation light separation filter between the light shielding member and the outer surface of the filter. By interposing a medium such as air with a refractive index lower than that of the light guide, it is possible to maintain the total reflection of the stimulated emission light propagating through the light guide and prevent leakage of the stimulated emission light to the outside. The S / N in the photomultiplier tube is improved.

That is, the photodetector of the radiation image reading apparatus of the present invention irradiates the stimulable phosphor sheet on which the radiation image is recorded with excitation light, and is excited by the excitation light and emitted from the stimulable phosphor sheet. Stimulated luminescent light corresponding to the radiographic image is made incident from the incident end face thereof, and is provided in optical contact with the exit end face of the light guide, and a light guide that repeats total internal reflection and leads to the exit end face. A radiation image reading apparatus comprising: an excitation light separating filter that selectively transmits the stimulated emission light; and a photomultiplier tube that photoelectrically detects the stimulated emission light transmitted through the excitation light separation filter. In the photodetector
Light is incident on the entire outer surface of the excitation light separation filter from the outside of the excitation light separation filter through a medium having a refractive index lower than that of the excitation light separation filter. A light blocking member for blocking is provided.

  Here, various members such as a light shielding film and a light shielding cloth can be applied as the light shielding member. As the light-shielding film, a film formed of a material such as carbon kneaded polyethylene, carbon kneaded polypropylene, or carbon kneaded PET (polyethylene terephthalate) can be used.

  The light shielding film does not necessarily cover the entire outer surface of the filter, and covers only the entire outer surface in the longitudinal direction of the filter, which is the direction along the main scanning direction of the excitation light that is likely to be incident on the excitation light. The light guide paint may be applied to the outer surface corresponding to the short side direction (thickness direction) of the light guide. This is because the probability that the stimulated emission light leaks to the outside from the outer surface in the short side direction is extremely low.

  Further, as the medium having a lower refractive index than the excitation light separation filter, for example, a substance such as air can be used.

  In addition, when the photodetector has a configuration having an adapter for connecting these between the excitation light cut filter and the photomultiplier tube, the excitation light cut filter is also applied to the outer surface of the adapter. It is desirable to provide a light shielding member through a medium having a low refractive index in the same manner as the outer surface.

  Further, a light-shielding paint is applied to the outer surface of the photomultiplier tube, particularly when the photomultiplier tube is elongated (so-called long photomultiplier) along the main scanning direction of the excitation light. It is desirable to perform shading.

  According to the photodetector of the radiation image reading apparatus of the present invention, the entire outer surface of the excitation light separation filter, particularly the entire outer surface in the longitudinal direction of the filter, which is the direction along the scanning direction of the excitation light, is covered with the light shielding member. Therefore, it is possible to prevent noise light such as excitation light that scans the stimulable phosphor sheet from entering from the outer surface of the filter, and to prevent a decrease in S / N due to light incident from the outer surface. On the other hand, by interposing a medium having a lower refractive index than that of the excitation light separation filter between the outer surface of the filter and the light shielding member, the total reflection of the stimulated emission light propagating through the light guide is reflected. Thus, the S / N in the photomultiplier tube can be improved by preventing leakage of the stimulated emission light to the outside.

  Hereinafter, embodiments of the photodetector of the radiation image reading apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a specific first embodiment of a photodetector of a radiation image reading apparatus according to the present invention, and FIG. 2 is a diagram showing a radiation image reading apparatus using the photodetector shown in FIG. It is.

  The illustrated radiographic image reading apparatus scans the stimulable phosphor sheet 1 on which radiographic image information is accumulated and recorded and scans the excitation light L to emit stimulated emission light M corresponding to the radiographic information stored and recorded. A scanning system 20, a photodetector 10 for photoelectrically detecting the stimulated emission light M emitted from the sheet 1, and a logarithmic amplifier for logarithmically amplifying the image signal S obtained by photoelectrically converting the stimulated emission light M 30 and an A / D converter 40 for A / D conversion.

  More specifically, the excitation light scanning system 20 is described in detail below. The conveying device 25 that conveys the stored stimulable phosphor sheet 1 in the arrow Y direction at a predetermined speed, and excitation light such as laser light and visible light with a predetermined light amount. A light source 21 that emits L, a polygon mirror 23 that reflects and deflects the excitation light L and is rotated by a motor 22, and the reflected and deflected excitation light L is converged on the sheet 1 placed on the transport device 25. The sheet 1 has substantially the entire surface by main scanning in the direction of arrow X of the excitation light L to the sheet 1 by rotation of the polygon mirror 23 and sub-scanning by conveyance of the conveyance device 25. The excitation light L is irradiated.

  More specifically, as shown in the side view of FIG. 1, the photodetector 10 causes the stimulated emission light M emitted from the sheet 1 to enter from the incident end face 15a and repeats total internal reflection to guide to the output end face 15b. Light guide 15, the excitation light separation filter 14 that is provided in contact with the emission end face 15 b of the light guide 15 and selectively transmits the stimulated emission light M, and the stimulated emission that is transmitted through the excitation light separation filter 14. A long photomultiplier tube (hereinafter referred to as a long photomultiplier) 11 that extends in the direction of the arrow X, which is the main scanning direction of the excitation light, is provided for photoelectrically detecting the light M.

  Furthermore, this long photomultiplier 11 is provided with an adapter 13 for facilitating connection with the excitation light separation filter 14, and the long photomultiplier 11 and the excitation light separation filter 14 are connected via the adapter 13. Has been.

  On the outer peripheral surface of the long photomultiplier 11, a light shielding material 12 such as a light shielding paint for preventing a part of the excitation light L irradiating the sheet 1 from entering from the peripheral surface and blocking the transmission of the excitation light L is applied. Has been.

  In addition, the adapter 13 and the excitation light separation filter 14 are provided with a flexible structure that blocks transmission of excitation light L such as a light shielding film and natural light through an air layer 16 having a refractive index lower than the refractive index of the filter 14. A light-shielding member 17 is provided. As the light-shielding film, a film formed of a material such as carbon kneaded polyethylene, carbon kneaded polypropylene, or carbon kneaded PET (polyethylene terephthalate) can be used.

  The light shielding member 17 only needs to be provided at least in the entire periphery of the adapter 13 and the excitation light separation filter 14 in the longitudinal direction (arrow X direction), and is not necessarily provided over the entire circumference. Therefore, it is sufficient to apply a light-shielding paint or the like to the adapter 13, the filter 14, and the end surfaces along the arrow Y direction which is the short side direction.

  Hereinafter, the operation of the photodetector 10 of the present embodiment will be described.

  The stimulated emission light M emitted from the sheet 1 enters the light guide 15 from the incident end face 15a of the light guide 15, and this stimulated emission light M repeats total reflection inside the light guide 15 and exits the end face 15b. Proceed to

  Here, not only the stimulated emission light M but also a part of the excitation light L that is scanned by the sheet 1 and reflected by the sheet 1 enters the inside of the light guide 15, but the emission end face 15 b of the light guide 15. The excitation light L does not pass through the filter 14 due to the action of the excitation light separation filter 14 provided in contact with the filter 14 and does not reach the photomultiplier 11.

  On the other hand, the stimulated emission light M passes through the filter 14 and reaches the photomultiplier 11.

  The stimulated emission light M repeats total reflection even inside the filter 14, but the peripheral surface of the filter 14 is in optical contact with the air layer 16 having a refractive index smaller than that of the filter 14. The total reflection condition is also maintained inside the filter 14, and the stimulated emission light M reaches the photomultiplier 11 without leaking outside the filter 14.

  By the way, a part of the excitation light L reflected by the sheet 1 and the natural light may be incident on the light guide 15, the filter 14, and the outer peripheral surface of the adapter 13. Of these, the light incident on the light guide 15 is attenuated while passing through the filter 14 and does not reach the photomultiplier 11, but the light incident on the outer peripheral surface of the adapter 13 enters the photomultiplier 11. Also, the light that has arrived and entered from the outer peripheral surface of the filter 14 reaches the photomultiplier 11 without being sufficiently attenuated by the filter 14, and the S / N of the image signal is reduced.

  However, according to the photodetector 10 of the present embodiment, the outer peripheral surfaces of the filter 14 and the adapter 13, particularly the portion (longitudinal direction) along the main scanning direction of the excitation light L in which the excitation light L or the like is likely to enter, Since the light shielding member 17 for blocking the transmission of the excitation light L or the like is provided, the excitation light L or the like does not enter from these portions, and therefore it is possible to prevent the S / N of the image signal from being lowered. it can.

  In particular, a photodetector with a longer excitation light separation filter 14 in order to improve the attenuation performance of the excitation light L incident from the incident end face 15a of the light guide 15, and the excitation light L of the excitation light separation filter 14 and the adapter 13 This is more effective in the photodetector having the long photomultiplier 11 having a long length along the main scanning direction.

  In other words, since the length of the filter 14 and the adapter 13 in the scanning direction of the excitation light L is long in these photodetectors, the excitation light L or the like enters the filter 14 or the adapter 13 from the outer surface in that direction. This is because it is easy.

  In the photodetector of the present embodiment, the air layer 16 is applied as a low refractive index medium for maintaining the stimulated emission light M to be totally reflected inside the filter 14. The vessel is not limited to this, and any medium other than air can be applied as long as it is a medium having a lower refractive index than that of the excitation light separation filter 14.

  FIG. 3 is a side view similar to FIG. 1, showing a second embodiment of the photodetector of the present invention. The light detector 10 'shown in the figure is made of a hard material such as metal or glass with light-shielding paint, with respect to the light detector 10 shown in FIG. The operational effects are the same as those of the photodetector 10 shown in FIG.

  In each of the embodiments described above, the present invention is applied to the photodetector provided with the long photomultiplier, but each photodetector of the present invention is not limited to the application to such a long photomultiplier.

The side view which shows 1st Embodiment of the 1st photodetector of this invention The figure which shows the radiographic image reading apparatus using the photodetector shown in FIG. The side view which shows 2nd Embodiment of the 1st photodetector of this invention

Explanation of symbols

10 photodetector
11 Long photomaru
12 Shading material
13 Adapter
14 Excitation light cut filter
15 Light guide
16 air
17 Light-shielding member L Excitation light M Photoluminescence light

Claims (4)

The stimulable phosphor sheet on which the radiation image is recorded is irradiated with excitation light, and the stimulated emission light emitted from the stimulable phosphor sheet and excited by the excitation light is incident on the stimulable phosphor sheet. A light guide that is incident from the end face and repeats total internal reflection and leads to the exit end face, and excitation light that is provided in optical contact with the exit end face of the light guide and selectively transmits the stimulated emission light In a photodetector of a radiation image reading apparatus comprising a separation filter and a photomultiplier tube that photoelectrically detects the stimulated emission light transmitted through the excitation light separation filter,
Light is incident on the entire outer surface of the excitation light separation filter from the outside of the excitation light separation filter through a medium having a refractive index lower than that of the excitation light separation filter. A photodetector for a radiation image reading apparatus, comprising a light blocking member for blocking.   The photodetector of the radiographic image reading apparatus according to claim 1, wherein the medium is air.   3. The photodetector of a radiation image reading apparatus according to claim 1, wherein the light shielding member is a light shielding film or a light shielding cloth.   4. The radiation image reading apparatus according to claim 1, wherein the photomultiplier tube is a long photomultiplier tube extending in a longitudinal direction of the excitation light separation filter. 5. Photo detector.

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