JPH0711678B2 - Radiation image information reader - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention irradiates excitation light to a stimulable phosphor sheet on which radiation image information is stored and recorded, and thereby stimulates emission from the stimulable phosphor sheet. The present invention relates to a radiation image information reading device that photoelectrically detects emitted light to read the radiation image information, and more particularly relates to a radiation image information reading device that improves the utilization efficiency of the excitation light by using a multilayer filter. is there.

(Technical background and prior art of the invention) When a certain kind of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is in the phosphor. It is known that when the phosphor is irradiated with excitation light such as visible light, the phosphor emits stimulated luminescence according to the accumulated energy. It is called a luminescent phosphor (stimulable phosphor).

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on the stimulable phosphor sheet, and this stimulable phosphor sheet is irradiated with excitation light to generate stimulated emission light. , Photoelectrically reading the obtained stimulated emission light with a photodetector to obtain an image signal, and based on this image signal, a radiation image of the subject is visible on a recording material such as a photographic light-sensitive material or a display device such as a CRT. The present applicant has already proposed a radiation image information recording / reproducing system for outputting as. (JP-A-55-12429, JP-A-56-11395, etc.) This system is practical because it can record an image over an extremely wide radiation exposure area as compared with a conventional radiographic system using silver salt photography. Have advantages. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the radiation exposure amount over a very wide range,
Therefore, even if the radiation exposure amount fluctuates considerably due to various photographing conditions, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value. A radiation image that is not affected by fluctuations in radiation exposure is obtained by converting it into an electrical signal and using this electrical signal to output a radiation image as a visible image on a recording material such as a photographic photosensitive material or a display device such as a CRT. be able to.

By the way, in the above-mentioned radiation image information recording / reproducing system, reading of stimulated emission light is roughly performed by two methods. That is, one of them is to perform pixel division by scanning excitation light, and the photostimulable emitted light is detected by a light receiving element (for example, a photomultiplier tube) having a wide light receiving surface, and the other is to divide the pixel into light receiving elements. (For example, a two-dimensional solid-state image sensor or a semiconductor line sensor),
The electric circuit forms a time-series image signal.

However, in the former method, an optical deflector is required to perform the excitation light scanning, and the device becomes complicated and large in size, and since the processing is performed pixel by pixel in order by the excitation light scanning, the entire processing time becomes long and high speed is achieved. There is a problem that it is difficult to read. When the photomultiplier tube is used, there is a drawback that the device is apt to become large in size due to the main body of the multiplier tube and the condensing optical system thereof.

The latter method has the advantage that high-speed reading is possible and the reading device can be formed in a small size, but it has a drawback that the sensitivity and S / N of the two-dimensional solid-state imaging device and the semiconductor line sensor are not good.

(Object of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a radiation image information reading apparatus which can be formed in a small size, has a high reading processing speed, and is excellent in sensitivity. It is intended.

(Structure of the Invention) In the radiation image information reading apparatus of the present invention, basically, the photodetector composed of the above-described pixel-divided photoelectric conversion element is used to detect stimulated emission light, and the photodetector is accumulated. The fluorescent phosphor sheet is arranged so as to face the sheet on the side opposite to the excitation light irradiation surface, and is made substantially parallel to the sheet between the sheet and the photodetector, and the excitation light is excellent. It is characterized in that a multi-layer film filter that reflects light to the above and transmits the stimulated emission light well is arranged.

Since the above-mentioned detector is provided on the opposite side of the excitation light source via the sheet, it is not necessary to consider its arrangement in relation to the optical path of the excitation light. Therefore, the photodetector can be arranged at any position where the stimulated emission light can be efficiently incident. Further, as the detector in the device of the present invention, a general photodetector which does not allow excitation light to pass therethrough even in its structure can be used.
For example, as shown in JP-A-60-111568, it is possible to use one formed by laminating an electrode layer, a photoconductor layer and a divided transparent electrode layer on a light-shielding substrate.

In addition, the above-mentioned multilayer filter has a different optical refractive index.
It is formed by sequentially depositing several to several tens layers of a substance of at least one kind on a substrate with a thickness of about 1/4 of the wavelength of light by vacuum deposition or the like. In this case, various characteristics can be obtained by appropriately setting the photorefractive index and the film thickness of each substance. Note that, as the low refractive index substance, for example, SiO ₂ , MgF ₂ or the like is used, while as the high refractive index substance, for example, TiO ₂ , ZrO ₂ , ZnS or the like is used. Further, examples of the multilayer filter having the above-mentioned transmission and reflection characteristics include a dichroic filter.

It should be noted that disposing the multilayer filter between the stimulable phosphor sheet and the photodetector means that the filter is attached so as to be in contact with the surface of the photodetector and the stimulable phosphor sheet is in contact with the surface on the contrary. It may be attached, or may be separated by a minute distance from both the stimulable phosphor sheet and the photodetector.

(Operation) When the multilayer filter as described above is provided between the stimulable phosphor sheet and the photodetector, a part of the excitation light that has passed through the sheet without exciting the stimulated emission light from the sheet. Will be reflected in a large amount on the filter and will be folded back toward the stimulable phosphor sheet. That is, the excitation light that has passed through the stimulable phosphor sheet is, so to speak, trapped between the sheet and the multilayer filter, so that the excitation light is effectively used for exciting the stimulable phosphor.

On the other hand, the stimulated emission light emitted from the stimulable phosphor sheet by the irradiation of the excitation light is also emitted from the sheet, but this stimulated emission light is well transmitted through the multilayer film filter having the above-mentioned characteristics. , Can be efficiently detected by the photodetector.

(Embodiment) Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

Figures 1, 2 and 3 show a first embodiment device of the invention. In this embodiment, the reading unit is formed as a line sensor, for example. For example, as shown in FIG. 1, the stimulable phosphor sheet 10 in which transmission radiation image information of the subject is accumulated and recorded by irradiating radiation such as X-rays through a subject such as a human body, has two pairs of nip rollers. The sheet is conveyed in the arrow Y direction for sub scanning by the sheet conveying means 11 such as the above. The line sensor 3 is arranged close to the stimulable phosphor sheet 10 from below. The line sensor 3 is arranged so as to extend over the entire width of the recording area of the sheet 10 in a direction substantially perpendicular to the sub-scanning direction Y. A linear excitation light source 2 is disposed above the sheet 10 so as to face the line sensor 3 with the sheet 10 interposed therebetween. The linear excitation light source 2 is, for example, an array in which LEDs or semiconductor lasers are connected in a row and emits light at the same time, or an omnidirectional light source, for example, a fluorescent lamp, an Xe lamp, or an aperture having a row of slits or small holes. A combination or the like can be used.

FIG. 2 and FIG. 3 respectively show the normal cross-sectional shape and the side cross-sectional shape of the line sensor 3, and the line sensor 3 will be described in detail below with reference to these FIGS. The line sensor 3 is formed by laminating a transparent electrode layer 7, a thin photoconductor layer 8 and a transparent electrode layer 9 on a light shielding substrate 6. Here, by dividing either or both of the transparent electrode layers 7 and 9 for each pixel, this laminated body forms a series of a large number of solid-state photoelectric conversion elements corresponding to the pixels. This device is an example of the transparent electrode layer 9
Is divided for each pixel. On the surface of the transparent electrode layer 9 facing the stimulable phosphor sheet 10, a multilayer film filter 30 described in detail later is provided.

When reading the radiation image information from the stimulable phosphor sheet 10, the excitation light source 2 linearly irradiates the sheet with the excitation light 14. The stimulated emission light 15 carrying the image information generated from the sheet 1 by the irradiation of the excitation light passes through the transparent electrode layer 9 and is received by the photoconductor layer 8. As the photoconductor layer 8, one having an energy gap Eg smaller than the energy hc / λ ₂ (= hν ₂ ) of the stimulated emission light 15 is used.

Further, the transparent electrode layer 9 (formed of, for example, ITO) is divided into minute units in the longitudinal direction of the line sensor 3, and it is generated between the divided one transparent electrode layer 9 and the transparent electrode layer 7. A potential difference (a potential difference generated by accumulating a signal by a photo carrier generated by receiving the stimulated emission light 15 in the photoconductor layer 8 between the two electrode layers 7 and 9) becomes an image signal for one pixel. Equivalent to. The signals by the photocarriers taken out for each of the electrodes thus divided are sequentially read out in time series by using a shift register described later. This is 1
An image signal of a scanning line segment can be obtained. Thereafter, the above operation is repeated each time the stimulable phosphor sheet 10 is moved in the direction of arrow Y by one scanning line pitch with respect to the light source 2 and the line sensor 3, and the image information over the entire surface of the sheet 10 is time-sequentially displayed. Image signal can be read.

Next, the scanning circuit following the line sensor 3 will be described.
FIG. 4 is an equivalent circuit of a line sensor and a scanning circuit using a photoconductor. Solid-state photoelectric conversion device using photoconductor
Signals due to photocarriers generated when the stimulated emission light (hν ₂ ) hits 8a, 8b, and 8c are accumulated in the capacitor C ₁ in the photoconductors 8a, 8b, and 8c. The accumulated photocarrier signals are sequentially read by the sequential opening and closing of the switch unit 17 performed by the shift register 16, whereby a time-series image signal can be obtained. The image signal is then amplified by the amplifier 12 and output from the output terminal 13.

It should be noted that the MO composed of the switch unit 17 and the shift register 16
The S section may be replaced with a CCD. Line sensor 3
In addition to those in the above-mentioned embodiments, for example, an array of photodiodes as shown in JP-A-60-111568 may be used.

In the above example, the photodetector includes a large number of solid-state photoelectric conversion elements.
Although the line sensors are arranged in rows, the photodetector according to the present invention is not limited to this, and may be a point sensor having one solid-state photoelectric conversion element, or the solid-state photoelectric conversion element may be two-dimensional. It may be a planar sensor arranged in a physical array.

Next, the operation of the above-described multilayer filter 30 will be described in detail. The multilayer filter 30 is, for example,
A dichroic filter having a spectral transmittance characteristic as shown in FIG. 5, a glass substrate 30A and a multilayer film 30B formed on the surface thereof as shown in FIGS. 2 and 3.
Consists of. Further, in this embodiment, the filter 30
Is arranged such that the transparent electrode layer 9 of the line sensor 3 and the substrate 30A are brought into close contact with each other, and the multilayer film 30B is separated from the stimulable phosphor sheet 10 by a minute distance.

The multilayer filter 30 hardly absorbs light, and therefore the reflectance obtained by subtracting the transmittance shown in FIG. 5 from 1 (100%). In this embodiment, as the laser beam 14 which is the excitation light, a beam having a wavelength of 633 nm emitted from a He—Ne laser is used. As shown in FIG. 5, a multilayer filter 30 for a beam with a wavelength of 633 nm is used.
Has a light reflectance of about 90%.

On the other hand, in the apparatus of the present embodiment, the stimulable phosphor sheet 10 that is subjected to the radiation image information reading is the laser beam 14 described above.
The excitation light of 15 emits stimulated emission light 15 having a wavelength of 360 to 420 nm (mainly 390 nm). Wavelength as shown in Fig. 5
The light transmittance of the multilayer filter 30 for a 390 nm beam is about 80%.

The light beam 14 as the excitation light is made incident on the stimulable phosphor sheet 10 as described above, and excites the stimulable phosphor sheet 10. A part of the laser beam 14 passes through the sheet 10 without exciting the stimulable phosphor sheet 10 and is emitted to the lower side of the sheet 10. The transmitted light 14a of the excitation light is reflected at a high reflectance by the filter 30 having the above-described characteristics, returns to the stimulable phosphor sheet 10 side again, and excites the stimulable phosphor sheet 10. That is, in this device, the laser beam 14 as the excitation light is in the form of being confined between the multilayer filter 30 and the stimulable phosphor sheet 10, and is effectively used for exciting the stimulable phosphor sheet 10. Like

Further, the stimulated emission light 15 also enters the multilayer filter 30, but since the multilayer filter 30 transmits the stimulated emission light well as shown in FIG. 5, the stimulated emission light is a line. It is efficiently detected by the sensor 3. By using the multilayer filter as described above, according to the apparatus of the present embodiment, the stimulated emission light is effectively utilized by effectively utilizing the laser beam which is the excitation light without affecting the detection of the stimulated emission light. It is possible to increase the amount of light of the device and to remarkably increase the sensitivity of the device. Further, by providing this multilayer film filter 30, since excitation light does not pass through the filter and only stimulated emission light is transmitted and is detected, when the stimulated emission light is detected by the line sensor, It is not necessary to provide a special means such as a cut filter that selectively allows only the exhaust light to enter the line sensor and cuts the excitation light.

Incidentally, the multilayer filter in the above embodiment has a very preferable characteristic of transmitting incident photostimulable emission light by about 80% and reflecting excitation light by about 90%, but generally it reflects excitation light. If the transmittance is 60% or more and the transmittance of stimulated emission light is 60% or more, a preferable effect of increasing sensitivity can be achieved. In addition to the glass substrate, a transparent plastic sheet made of polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide or the like may be used as the substrate for supporting the multilayer film.

By the way, the laser beam 14 passes through the sheet without exciting a part of the sheet as described above, and another part is reflected on the surface of the sheet 10 to excite the sheet. Not known to be. The stimulated emission light 15 is emitted from the sheet 10 to the line sensor 3
It is emitted not only to the side (the lower side of the seat) but also to the upper side of the seat 10. Therefore, in the optical path of the laser beam 14, which is close to the sheet 10 together with the multilayer filter 30, the reflectance of the laser beam increases in accordance with the increase of the incident angle, while the stimulated emission light has its incident angle. If a multi-layer film filter that reflects well regardless of the laser beam is provided, the laser beam can be used more effectively and the stimulated emission light can be collected efficiently. An embodiment in which a multilayer filter is provided on each of the upper and lower sides of the sheet will be described below with reference to FIGS. The same parts as those in the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted.

A multilayer filter (hereinafter referred to as a first multilayer filter) 30 arranged so as to be in contact with the line sensor 3 as described above is provided on the lower side of the sheet 10, and a second multilayer filter 40 is provided on the upper side. It is arranged respectively. The second filter 40 is, for example, a bandpass filter having a spectral transmittance characteristic as shown in FIG. 7 when the incident angle to the filter is 0 °. As shown in FIG.
It is composed of 40A and multiple films 40B formed on the surface thereof. The second multi-membrane filter 40 can be manufactured by using the same material as the above-mentioned first multilayer membrane filter 30 and by the same method. Also, the laser beam 14 is usually the sheet 10,
That is, the light is incident on the second multilayer filter 40 from a direction substantially perpendicular to the second multilayer filter 40 (direction in which the incident angle is approximately 0 °).

The second multilayer filter 40 hardly absorbs light, so the transmittance shown in FIG. 7 is 1 (100%).
The value subtracted from is the reflectance. In this embodiment,
Since the wavelength of the laser beam 14 is 633 nm as described above, the light transmittance of the second multilayer filter 40 with respect to the laser beam 14 is at the incident angle of 0 °, that is, the sheet 10
It is about 90% when it is incident for excitation of.
On the other hand, the incident angle dependence of the transmittance of the second multilayer filter 40 for the laser beam 14 as the excitation light and the stimulated emission light 15 (wavelength 390 nm) is as shown in FIG.

The laser beam 14 is incident on the stimulable phosphor sheet 10 at an incident angle close to 0 ° as described above. Therefore, the laser beam 14 satisfactorily transmits the second multilayer filter 40 with a transmittance of about 90%, reaches the stimulable phosphor sheet 10, and excites the stimulable phosphor sheet 10. The laser beam 14 is reflected on the surface of the stimulable phosphor sheet 10 to some extent and returns to the second multilayer filter 40 side. This reflection is irregular reflection, and the reflected light 14b is the second multilayer filter 40.
Will be incident at various incident angles. Of the reflected light 14b, the light that enters the second multilayer filter 40 at a large incident angle is the second light having the characteristics described above.
Is reflected with high reflectance by the multilayer filter 40 of
The stimulable phosphor sheet 10 is excited again by returning to the stimulable phosphor sheet 10 side. That is, in this device, the laser beam 14 as the excitation light is confined between the second multilayer filter 40 and the stimulable phosphor sheet 10,
The stimulable phosphor sheet 10 is more effectively used for excitation.

The stimulated emission light 15 is also incident on the second multilayer filter 40 at various angles.
As shown in the figure, the stimulated emission light 15 always reflects nearly 100% regardless of its incident angle. Therefore stimulated emission light 1
As shown in FIG. 6, most of the light diverging to the second multilayer filter 40 side out of 5 is the second multilayer filter 40.
The light is reflected by the line sensor 3 disposed on the lower side of the stimulable phosphor sheet 10. As described above, when the second multilayer filter 40 is used together with the first multilayer filter 30, the laser beam as the excitation light is more effectively used to increase the light amount of the stimulated emission light, Emitted light is detected efficiently, and the sensitivity and
The S / N can be remarkably increased compared to the conventional one.

The multilayer filter in the above embodiment has extremely preferable characteristics such that nearly 100% of incident photostimulated luminescence light is reflected and excitation light is transmitted by about 90% when the incident angle is 0 °. However, in general, the light transmittance of excitation light is 70% or more when the incident angle is 0 to 5 °, and the reflectance of excitation light is 60% or more when the incident angle is 30 ° or more.
When the reflectance of stimulated emission light is 60% or more, a preferable effect of increasing sensitivity can be achieved. In addition to the glass substrate, a transparent plastic sheet made of polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide or the like may be used as the substrate for supporting the multilayer film.

According to the experiments conducted by the present inventors, by providing the first multilayer filter as described above to enhance the utilization efficiency of the excitation light, the reading sensitivity is increased by about 1.5 times as compared with the case where the multilayer filter is not provided. It was found that the reading sensitivity can be further increased, and the reading sensitivity can be further increased when the second multilayer filter is provided together with the first multilayer filter.

A lens optical system (for example, a rod lens array) for collecting stimulated emission light may be arranged between the multilayer filter 30 attached to the line sensor 3 and the stimulable phosphor sheet 10. . In this case, the excitation light (transmitted light) 14a that has passed through the stimulable phosphor sheet 10 and passed through the lens optical system and is incident on the multilayer filter 30 is reflected by the multilayer filter 30 and again within the lens optical system. Since it returns to the stimulable phosphor sheet 10 through almost the same optical path, it is folded back to almost the same position on the sheet 10 and the excitation efficiency is improved.

Further, in the example described above, the multilayer filter 30 is arranged so as to contact the line sensor 3, but the multilayer filter 30 may be arranged so as to contact the stimulable phosphor sheet 10. Further, as shown in FIG. 9, the multilayer film filter 30 is used for the line sensor 3 and the stimulable phosphor sheet.
It may be separated from both sides of 10 and placed close to both sides.

In addition to the above-described multilayer film filter that moves relative to the sheet as described above, for example, the multilayer film filter is temporarily brought into close contact with the entire scanning region of the sheet, and the filter feeding unit together with the sub-scanning unit of the sheet. May be provided to send the multilayer filter together with the sheet in the sub-scanning direction. In this case, by returning the multilayer filter to the reading start position from the accumulative phosphor sheet on which the image information has been read, and repeating the operation of stacking it on the sheet to be read next, one multilayer filter is obtained. Only need to be provided.

(Effects of the Invention) As described in detail above, in the radiation image information reading apparatus of the present invention, a photodetector including a photoelectric conversion element that time-serializes the signal of each pixel by an electric circuit, not by scanning a light spot. Therefore, the radiation image information reading speed can be sufficiently increased, and an optical deflector for light spot scanning and a condensing optical system are not required, so that the apparatus can be downsized. Further, in the device of the present invention, the use efficiency of the excitation light can be sufficiently increased by the action of the multilayer filter arranged between the stimulable phosphor sheet and the photodetector. Therefore, according to the device of the present invention, it is possible to use a small-output excitation light source, reduce power consumption, and sufficiently increase the sensitivity of reading radiation image information. Furthermore, since the device of the present invention is one in which a multilayer filter having the above-described effects is arranged in the excitation light optical path, according to the device, all the stimulable phosphor sheets are covered with an expensive multilayer filter. The radiation image information reading system can be formed at a lower cost than the case of wearing the radiation image information.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an apparatus according to one embodiment of the present invention, FIGS. 2 and 3 are a front sectional view and a side sectional view showing an essential part of the apparatus according to the above embodiment, and FIG. FIG. 5 is a circuit diagram showing a scanning circuit used in the embodiment device, FIG. 5 is a graph showing the spectral transmittance characteristics of the multilayer filter used in the device of the present invention, and FIG. 6 is a device of another embodiment of the present invention. FIG. 7 is a side view, FIG. 7 is a graph showing the spectral transmittance characteristics of the second multilayer filter used in the device shown in FIG. 6, and FIG. 8 is excitation light and stimulated emission of the second multilayer filter. FIG. 9 is a side view showing a device showing another embodiment of the present invention. 2 ... Excitation light source, 3 ... Line sensor 6 ... Light-shielding substrate, 7 ... Transparent electrode layer 8 ... Photoconductor layer 9 ... Pixel-divided transparent electrode layer 10 ... Storage phosphor sheet, 11 …… Sheet conveying means 14 …… Excitation light, 15 …… Stimulated emission light 30 …… Multilayer film filter, 30A …… Substrate 30B …… Multilayer film

Claims (2)

[Claims] 1. A surface side of the sheet opposite to the excitation light irradiation surface, which comprises an excitation light source for irradiating excitation light to a stimulable phosphor sheet on which radiation image information is stored and recorded, and a photoelectric conversion element divided into pixels. A photodetector disposed opposite to the sheet, which reflects the excitation light well and transmits the stimulated emission light well, and is substantially parallel to the sheet between the sheet and the photodetector. Radiation image information reading device comprising a multilayer film filter arranged as described above. 2. The multilayer filter has a light reflectance of the excitation light of 60% or more and a transmittance of the stimulated emission light of 60.
% Or more, The radiation image information reading device according to claim 1, wherein