JPH0787322A - Image signal reading method - Google Patents

Abstract

PURPOSE:To acquire an image of high S/N which is free from the noise compo nent caused by the excited light with no use of a filter when the image signals are read out of a radiation detector consisting of a scintillator made of a stimulable phosphor and a solid-state photodetector. CONSTITUTION:A radiation detector 1 consists of a scintillator 3 made of a stimulable phosphor and a solid-state photodetector 2 including many solid-state photodetecting elements which detect the stimulated luminescence emitted from the scintillator 3 and transmit the stimulated luminescence after converting it into the image signals. Then the detector 1 is irradiated by an X-ray 5 transmitted through an object 6. The radiation image information on the object 6 is stored in the scintillator 3. Then plural image signals Sti are continuously read out at each prescribed time interval ti and until the signals Sti are equal to the fixed value Stn while the scintillator 3 is irradiated by the excited light 8A. Then, a fixed image signal Stn is subtracted from each signal Sti, and these subtraction results are added together for each solid-state photodetecting element and transmitted. An image signal S' from which the signal Stn is subtracted is reproduced by a reproducing means 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal reading method, and more particularly to a method for reading an image signal from a radiation detector using a combination of a scintillator made of a stimulable phosphor and a solid-state photodetector. is there.

[0002]

2. Description of the Related Art Conventionally, in radiography in various fields such as medical radiography for radiography for the purpose of medical diagnosis and industrial radiography for the purpose of destructive inspection of substances, etc. A so-called radiographic method combined with a radiographic film is used. According to this method, when radiation such as X-rays transmitted through the subject enters the intensifying screen, the phosphor contained in the intensifying screen absorbs the energy of this radiation and emits fluorescence (instantaneous emission). Due to this light emission, the radiographic films superposed so as to be in close contact with the intensifying screen are exposed to light, and a radiographic image is formed on the radiographic film. In this way, the radiation image can be directly obtained as an image visualized on the radiation film.

On the other hand, in various fields, a radiographic image recorded on a radiographic film is photoelectrically read to obtain an image signal, the image signal is subjected to appropriate image processing, and then the image is reproduced and recorded. It is being appreciated. For example, an X-ray image is recorded using a film having a low gamma value designed to be suitable for later image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By performing image processing on this electric signal (image signal) and reproducing it as a visible image on a copy photograph or the like, a reproduced image with good image quality performance such as contrast, sharpness, and graininess is obtained. (See Japanese Patent Publication No. 61-5193).

In addition, the applicant of the present invention has conducted radiation (X-ray, α
Radiation, β rays, γ rays, electron rays, ultraviolet rays, etc.), some of this radiation energy is accumulated, and when excitation light such as visible light is subsequently irradiated, accumulation that shows stimulated emission according to the accumulated energy Using fluorescent phosphor (stimulable phosphor),
Radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light, and the obtained luminescence is obtained. A radiation image recording / reproducing system has already been proposed which photoelectrically reads out the emitted light to obtain an image signal and outputs a radiation image of a subject as a visible image on a recording material such as a photographic photosensitive material or a CRT based on the image data. (Japanese Patent Laid-Open Nos. 55-12429, 56-11395, 55-163472, and 56-1)
04645, 55-116340, etc.).

This system has the practical advantage of being able to record images over a very wide radiation exposure area as compared to conventional radiographic systems using silver halide photography. 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 dose over a very wide range, and therefore the radiation exposure dose varies depending on various imaging conditions. Even if it fluctuates significantly, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and converted into an electric signal. Recording material such as photographic light-sensitive material,
By outputting a radiation image as a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by variations in radiation exposure dose.

However, in order to obtain a radiographic image with such a radiographic system, when the above-mentioned radiographic image is directly visualized, the radiographic film used for radiography and the intensifying screen are made to coincide in sensitivity region. Need to do.

In the system for photoelectrically reading a radiation image using the above-mentioned radiographic film and stimulable phosphor sheet, the radiation image is subjected to image processing as described above to obtain the density and contrast according to the purpose. It is necessary to adjust to have, or to convert the radiation image into an electric signal once, and it is necessary to perform reading scanning using an image reading device therefor, which makes the operation for obtaining the radiation image complicated. It takes time to obtain a radiation image.

Therefore, in order to solve the above-mentioned problems in the conventional system, a radiation detector has been proposed (for example, JP-A-59-211262 and JP-A-59-211).
No. 263, JP-A 2-164067, PCT International Publication No. WO92 / 06501, Signal, noise, and read out consid
erations in the development of amorphous silicon p
hotodiode arrays for radiotherapy and diagnostic x
-ray imaging, LE Antonuk et.al, University of Mi
chigan, RAStreet Xerox, PARC, SPIEVol.1443 Medic
al Imaging V; Image Physics (1991), p.108-119).

This radiation detector is composed of a plurality of solid-state photodetector elements arranged in a matrix of transparent conductive films and conductive films sandwiching an amorphous semiconductor film on a substrate made of quartz glass having a thickness of 3 mm and orthogonal to each other. As described above, a scintillator that converts radiation into visible light is laminated on a solid-state photodetector that includes a plurality of signal lines and scanning lines that are patterned in a matrix.

By arranging this radiation detector so that the scintillator faces the surface on the radiation incident side, and irradiating the radiation detector with the radiation transmitted through the subject, the radiation is directly incident on the scintillator and converted into visible light. , Or when the scintillator is a stimulable phosphor, the radiation image information accumulated and recorded in the scintillator is excited by excitation light to be emitted as stimulated emission light, and the converted visible light or emitted light is emitted. The stimulated emission light is detected by the photoelectric conversion unit of the solid-state light detection element and photoelectrically converted into an image signal carrying radiation image information. This image signal is read by a predetermined reading means from a transfer section provided in each solid-state photodetection element of the radiation detector, and after being subjected to predetermined image processing, reproduced by a reproducing means such as a CRT. By using such a radiation detector, the radiation image of the subject can be immediately reproduced without performing a complicated operation, so that the radiation image can be immediately obtained in real time, and the drawbacks of the conventional system described above It can be resolved.

[0011]

In the above radiation detector, when the scintillator is a stimulable phosphor, the scintillator must be irradiated with the excitation light when the image signal is read out. The image signal detected by the solid-state photodetector and read from the solid-state photodetector is included as a noise component. For this reason, it is necessary to provide a filter between the scintillator and the solid-state photodetector that transmits only the stimulated emission light and does not transmit the excitation light so that the irradiated excitation light is not detected by the solid-state photodetector.

However, since the wavelength of the stimulated emission light differs depending on the type of the stimulable phosphor, when different types of the stimulable phosphor forming the scintillator are used, the luminescent Since it is necessary to provide a filter according to the wavelength of the stimulated emission light emitted by the exhaustive phosphor,
Radiation detector design becomes extremely cumbersome.

In view of the above circumstances, it is an object of the present invention to provide an image signal reading method capable of removing a noise component due to excitation light from an image signal read by a radiation detector without providing a filter. It is a thing.

[0014]

In a first image signal reading method according to the present invention, the image information is accumulated and recorded by irradiation with radiation carrying image information, and the image information is carried by irradiation of excitation light. It has a scintillator made of a stimulable phosphor that emits stimulated emission light, and a number of two-dimensionally arranged solid-state photodetectors that convert the stimulated emission light emitted from the scintillator into an image signal and output it. An image signal reading method for reading the image signal from a radiation detector formed by stacking a solid-state photodetector, wherein the image is read in all the solid-state photodetectors while irradiating the scintillator with the excitation light. The image signal is read from the solid-state photodetector a plurality of times until the signal converges to a constant value image signal, and the constant value of the constant value is read from each of the plurality of read image signals. Subtracting the image signal, it is characterized in that the image signal of the predetermined value is output by adding the plurality of image signals are subtracted.

In the second image signal reading method according to the present invention, the image information is accumulated and recorded by being irradiated with the radiation carrying the image information, and the stimulated emission light which carries the image information by the irradiation of the excitation light. A solid-state photodetector having a scintillator made of a stimulable phosphor that emits light, and a number of two-dimensionally arranged solid-state photodetectors for converting the photostimulated luminescence emitted from the scintillator into an image signal and outputting the image signal. An image signal reading method for reading the image signal from a radiation detector, which is formed by stacking a plurality of layers with each other, wherein a first image signal immediately after the scintillator is irradiated with the excitation light is read from the solid-state photodetector. Reading the second image signal when the image signal converges to an image signal of a constant value in all the solid-state photodetectors while irradiating the scintillator with the excitation light Performed, wherein the first and the second image signal from an image signal of subtracting, is characterized in that outputs an image signal which is the subtraction.

[0016]

According to the image signal reading method of the present invention, when the scintillator is a stimulable phosphor, the solid-state light is irradiated on all the solid-state photodetectors while irradiating the scintillator with excitation light until the image signal converges to a constant value. The image signal is read out from the detector a plurality of times, the image signal having a constant value is subtracted from each of the read out image signals, and the subtracted image signals are added and output. It is the one. That is, since the readout of the image information accumulated and recorded in the scintillator is destructive readout, if the excitation light is not emitted when the image information is read out, the image signal read out after that should be 0. However, if irradiation of the excitation light is continued, the image signal becomes a constant value, and the image signal having the constant value carries a noise component due to the excitation light applied to the scintillator. Therefore, by subtracting the image signal having a constant value from the image signals read out multiple times while the excitation light is being radiated, and adding the subtracted image signals and outputting the result, the scintillator and solid-state light detection are performed. It is possible to remove the noise component due to the excitation light from the read image signal without providing a filter between the device and the device.

Further, even if the image signal immediately after the scintillator is irradiated with the excitation light is read out and the image signal converged to a constant value is subtracted from the image signal to be output, the scintillator and the solid-state photodetector are combined. The noise component due to the excitation light can be removed from the read image signal without providing a filter between them.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an image signal reading device using a radiation detector for carrying out an embodiment of an image signal reading method according to the present invention, and FIG. 2 is a diagram showing a radiation detector used in the image signal reading device. It is a figure showing the detail of the solid-state photodetector. As shown in FIGS. 1 and 2, an apparatus for carrying out the image signal reading method according to the present invention is, for example, BaF.
(BrI): a planar scintillator 3 made of a stimulable phosphor such as Eu ^2+, and stimulated emission light converted by the scintillator 3 are detected, and this visible light carries a radiation image of a subject. Photoelectric conversion unit for photoelectric conversion into image signals
The radiation detector 1 is formed by stacking a solid-state photodetector 2 in which a plurality of solid-state photodetection elements 23, each of which includes a transfer unit 19 for reading out an image signal accumulated in the photoelectric conversion unit 18, in a two-dimensional array. It is what constitutes. As shown in FIG. 2, each solid-state photodetector 23 is connected by a scanning line 20a and a signal line 20b. The scanning line 20a extends in the horizontal direction of FIG. It is connected to the gate of the transfer unit 19 (transistor) of the photodetection element 23. On the other hand, the signal line 20b extends in the vertical direction in FIG. 2 and is connected to the transfer register 22 and the drains of the transfer units 19.

Here, the details of the solid-state light detecting element 23 will be described. FIG. 3 is a diagram showing details of the solid-state photodetector 23. As shown in FIG. 3, the solid-state photodetector 23 has signal lines 12A and 12B made of a patterned conductive film on a substrate 11 made of a resin sheet, and a photoelectric conversion portion made of amorphous silicon 13 and a transparent electrode 14. The thin film transistor 17 is composed of a photodiode 15 as an amorphous silicon 16, a transfer electrode 16A (gate) provided in the amorphous silicon 16 and the amorphous silicon 16, and a transfer section 19 as a transfer section 19. Here, the signal line 12B is a drain, is connected to the signal line 20b described above, and is connected to the transfer electrode 16B.
A is connected to the scan line 20a. The solid-state photodetector 2 is constructed by arranging a plurality of the solid-state photodetection elements 23 thus configured in a two-dimensional manner.

Next, the operation of the image signal reading device according to the present invention will be described.

As shown in FIG. 1, the X-rays 5 emitted from the X-ray source 4 are applied to the subject 6 and transmitted through the subject 6.
The X-ray 5 transmitted through the subject 6 is applied to the radiation detector 1. The X-rays 5 applied to the radiation detector 1 are applied to the scintillator 3, whereby the radiation image information of the subject 6 is accumulated and recorded in the scintillator 3.

Then, excitation light 8A is emitted from the excitation light source 8. The excitation light 8A is continuously applied to the scintillator 3. As a result, stimulated emission light is emitted from the scintillator 3. Here, since the radiation energy accumulated and recorded in the scintillator 3 is reduced by the irradiation of the excitation light 8A,
The amount of stimulated emission light emitted from the scintillator 3 decreases with the passage of time, and as shown in FIG. 4, the image signal obtained by photoelectrically converting the stimulated emission light decreases. Then, the image signal is read out a plurality of times during the irradiation of the excitation light 8A until the value of the image signal read out at a predetermined time interval becomes a constant value. That is, as shown in FIG. 4, the image signal St _i is generated every time t _i at a predetermined time interval.
Is read out, and this image signal St _i has a constant value,
That is, the process is repeated until the difference value between the image signal St _{i + 1} and the image signal St _i becomes 0 at a certain time t _i .
The details of reading the image signal will be described below.

By irradiating the excitation light 8A from the excitation light source 8,
The scintillator 3 emits stimulated emission light. The emitted stimulated emission light is received by the photodiode 15 as the photoelectric conversion unit 18 of each solid-state photodetector 23 constituting the solid-state photodetector 2, and a signal charge is generated in the photodiode 15. In this way, in each solid-state light detection element 23, a signal charge proportional to the emission brightness of the stimulated emission light, that is, the intensity of the incident radiation is generated.

Next, at every time t _i , the scanning pulse generator 21
From the top row to the transfer section 19 of each solid-state photodetection element 23, the switch of the transfer section 19 of each top-row solid-state photodetection element 23 is in the "ON" state (transfer electrodes of the solid-state photodetection elements 23). 16
A voltage is applied to A and a current flows between the signal lines 12A and 12B). That is, the signal charge generated in the photodiode 15 is transferred through the thin film transistor 17.
As a result, the signal charge of each solid-state photodetecting element 23 in the top row is sent to the transfer register 22 at the same time. From the output terminal 22a of the transfer register 22, the electric signal (image signal) S accumulated for each solid-state photodetection element 23 from time t _i to t _{i + 1.}
t _i are extracted in time series.

In this way, the transfer pulse is sent from the scanning pulse generator 21 to each row in order from the top row to the bottom row, and the image signal St _i from each solid-state photodetecting element 23 in each row is output terminal. It is output from 22a in time series. Then, such processing for outputting the image signal St _i by sending a pulse from the scanning pulse generator 21 is performed a plurality of times while the scintillator 3 is being irradiated with the excitation light 8A.

Here, the time interval for reading the image signal St _i a plurality of times is the time until the transfer section 19 becomes saturated, and is set to an interval of several ms to several tens of ms.

When the image signal St _i is read out as shown in FIG.
performed until t _n, the image signal St _i obtained for each emission of the excitation light 8A is input to the image processing unit 30, an image processing unit
Once stored in 30 memories. Next, the image signal St _n having the above-described constant value is subtracted from the image signal St _i read out at each time t _i , and the subtracted image signal becomes the processed image signal S ′. That is,

[0029]

[Equation 1]

The following calculation is performed for each solid-state light detecting element 23. The processed image signal S'represents the shaded area A in FIG. Thus, the processed image signal S'is input to the reproducing means 31 and reproduced as a visible image.

Here, the image signal St having a constant value
_n carries a noise component due to the excitation light 8A with which the scintillator 3 is irradiated. Therefore, each solid-state photodetector element 23 that constitutes the solid-state photodetector 2 as described above.
From the image signal St _i until the image signal St _i becomes the image signal St _n having a constant value, the solid-state photodetector elements 23 are read.
By subtracting the image signal St _n from each image signal St _i and adding them to obtain the processed image signal S ′, the noise component due to the excitation light 8A can be removed from the image signal St _i without providing a filter, It is possible to obtain a high-quality reproduced image with less noise.

As the reproducing means 31, various means such as electronically displaying a CRT or the like and recording a radiation image displayed on the CRT or the like on a video printer or the like can be adopted. Further, the radiation image of the subject 6 may be recorded and stored on a magnetic tape, an optical disc, or the like.

In the above-described embodiment, the image signal St _i is read out every predetermined time t _i , and the image signal St
_The constant image signal value St _n is subtracted from _i , and the subtracted image signal St _i is added and output as an image signal S ′. For example, as shown in FIG.
There reads the image signal St ₁ at time t ₁ immediately after being irradiated to the scintillator 3, the image signal St _n became a constant value after a predetermined time, the image signal obtained by subtracting from an image signal St ₁ (St ₁ -St _n ) may be output.

That is, the image signal St at time t _{1
Since 1} is obtained by the maximum value of the stimulated emission light emitted from the scintillator 3, the value of the image signal obtained from each solid-state photodetector is the excitation light 8A to the scintillator 3.
It is roughly determined by the amount of stimulated emission light immediately after being irradiated with. Therefore, the image signal St ₁ obtained from the stimulated emission light at time t ₁ immediately after the excitation light 8A is irradiated is obtained for each solid-state photodetecting element 23, and then converges to a constant value at time t _n . The image signal St _n is subtracted from the image signal S ₁ and the subtracted image signal is reproduced.
By reproducing at 31, it is possible to obtain a high-quality reproduced image with reduced noise due to the excitation light 8A.

Further, in the above-mentioned embodiments, the resin sheet is used as the substrate of the solid-state photodetector, but the present invention is not limited to this, and it may be a thickness of about several hundreds of microns that does not absorb a radiation image. For example, an inorganic material such as quartz glass may be used.

Furthermore, although the amorphous silicon layer is used as the semiconductor layer in the above-mentioned embodiments, the present invention is not limited to this, and any semiconductor layer may be used.

[0037]

As described in detail above, in the image signal reading method according to the present invention, the image signal is read a plurality of times while the scintillator is a stimulable phosphor and the radiation detector is irradiated with the excitation light. Read out or read out the image signal immediately after the excitation light is irradiated, and then read out the multiple image signals or the image signal immediately after the excitation light is irradiated to a constant value by the irradiation of the excitation light. Since the converged image signal is subtracted and output, the noise component generated by the excitation light included in the image signal having a constant value can be removed from the image signal and output. Thereby, the excitation light and the stimulated emission light can be separated without providing a filter between the scintillator and the solid-state photodetector. Therefore, the noise component due to the excitation light is removed without changing the design or exchanging the filter caused by the difference in the stimulable phosphor contained in the scintillator.
Highly reproduced images can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an image signal reading device for carrying out an image signal reading method according to the present invention.

FIG. 2 is a diagram showing details of a solid-state photodetector used in an image signal reading apparatus for carrying out an image signal reading method according to the present invention.

FIG. 3 is a sectional view showing details of a solid-state photodetector.

FIG. 4 is a diagram showing an image signal read by an embodiment of an image signal reading method according to the present invention.

FIG. 5 is a diagram showing an image signal read by an embodiment of an image signal reading method according to the present invention.

[Explanation of symbols]

1 radiation detector 2 solid-state photodetector 3 scintillator 4 X-ray source 5 X-ray 6 subject 8 excitation light source 8A excitation light 23 solid-state light detection element 30 information processing means 31 reproduction means St _i image signal St _n constant value image signal

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 31/09 7630-4M H01L 31/00 A

Claims (2)

[Claims] 1. A scintillator composed of a stimulable phosphor that emits stimulable luminescent light that carries the image information when the image information is stored and recorded by being irradiated with radiation that carries the image information. A radiation detector formed by stacking a solid-state photodetector having a large number of two-dimensionally arranged solid-state photodetectors for converting stimulated emission light emitted from the scintillator into an image signal and outputting the image signal. An image signal reading method for reading a signal, wherein the solid-state photodetector is irradiated with the excitation light onto the scintillator until all of the solid-state photodetection elements converge to an image signal having a constant value. Before the image signal of the constant value is subtracted from each of the image signals read out a plurality of times. Image signal readout method characterized by adding and outputting the plurality of image signals. 2. A scintillator composed of a stimulable phosphor that emits stimulable luminescent light that carries the image information when the image information is accumulated and recorded by being irradiated with radiation that carries the image information. A radiation detector formed by stacking a solid-state photodetector having a large number of two-dimensionally arranged solid-state photodetectors for converting stimulated emission light emitted from the scintillator into an image signal and outputting the image signal. An image signal reading method for reading a signal, comprising: a first method immediately after irradiating the scintillator with the excitation light.
Of the image signal is read from the solid-state photodetector, while irradiating the scintillator with the excitation light, a second image signal when the image signal converges to an image signal of a constant value in all the solid-state photodetectors Is read out, the second image signal is subtracted from the first image signal, and the subtracted image signal is output.