JPS595773A - Image detector - Google Patents

Abstract

PURPOSE:To carry out image detection and charging automatically and successively through a beam scan by forming a detection plate in the double-layer structure of the 1st photoconductor layer which operates as a charging and discharging circuit and the 2nd photoconductor layer which operates an optical switch. CONSTITUTION:The detection plate 31 is irradiated with X rays from an X-ray source 51 through a subject 52 and the X rays is absorbed by the 1st photoconductor layer 2. The 2nd photoconductor layer 3 operates as the optical switch which turns on and off by being irradiated with a laser beam 56 from a laser light scanning mechanism 53. The conductor layer 2 consists of electrostatic capacitance 21 to be charged and a resistance 22 which varies in value with the quantity of the X rays, and the photoconductor layer 3 consists of a switch 24, conductive resistance 25, capacitor 23, and dark resistance 26. The switch 24 when irradiated with the laser beam turns on to output the charging current of the electrostatic capacitance 21 through an amplifier 32 and the switch 24 turns off until it is irradiated with the laser beam for the next time, discharging the capacitance 21 through the resistance 22.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image detection device, and more particularly to an image detection device that exposes a subject to image light, forms a latent image on a detection plate, and detects an image in time series by scanning the detection plate with a beam. The present invention relates to a device that shortens detection time without requiring complicated processes.

Generally, when trying to form an image of a subject by exposure from an irradiation source, the reflected light or transmitted light from the subject is transmitted to the image plane, but it is better in various respects to maintain a small amount of irradiation on the subject. few.

In particular, in medical X-ray photography, the human body is irradiated with XM and the X-rays that pass through the X-rays are detected, and if the exposure dose is high, leukemia, sensitive tumors, etc. will occur.

Conventionally, in medical X-ray photography, in order to reduce the radiation dose to the examinee and to improve diagnostic performance through various image processing, the latent image created on the photoconductor by X-ray irradiation has been converted into electrical signals. It is considered to be extracted as This Makumoto process is known from Japanese Patent Application Laid-Open No. 54-31219, etc., and the detection plate is insulated except for the conductive layer at both ends.
It has two layers: a body layer and a photoconductor layer.

This method is compared with other well-known imaging methods, indirect methods using image intensifiers and TV image pickup tubes, and xeroradiography (electron X-ray photography). Moreover, it is superior to the latter in that the amount of X-rays required for imaging is small.

However, the above method uses sequential primary charging and charge distribution.

It requires a complicated process of image exposure and beam scanning, and requires time for image detection, and is not suitable for continuous fluoroscopy in real time or continuous pulse imaging in angiography.

Further, in the above method, the wavelength of the scanning beam is limited by the photoconductive material, and only a specific one such as a He-Cd laser can be used.

In view of the above points, the present invention shortens the detection time without requiring complicated processes, expands the permissible wavelength range of the scanning beam, enables the use of )le-Ne laser, etc., and improves the efficiency of the device. The object of the present invention is to provide a new image detection device that can be made smaller and lower in cost.

A feature of the present invention is that the detection plate has two layers, a first photoconductor layer and a second photoconductor layer, excluding the conductor layers at both ends, and the second photoconductor layer is scanned by a scanning beam. By acting as a light switch, the first photoconductor layer acts as a charge discharge circuit during image exposure (when the light switch is off) and as a charge charging circuit (when the light switch is on).

Thereby, a change in the amount of charge after a certain period of time (for example, after one frame time in two-dimensional scanning) is detected as a signal as a current output during charging according to the image exposure amount.

According to the present invention, image detection and charging are performed automatically and sequentially by beam scanning, eliminating the need for primary charging and associated processes. As a beam source, a commonly used, highly reliable, and low-cost He--Ne laser or the like may be used.

The present invention will be described in detail below.

First, in order to facilitate understanding, the principle of image detection according to the present invention will be explained with reference to FIGS. 1 to 3.

Figure 1 shows the first part of the image that corresponds to one pixel. A simplified equivalent circuit diagram of each sub-region of the second optical conductor layer is shown.

For the sake of simplicity, the second photoconductor layer is not originally intended as a complete optical switch, but rather as a capacitor.

It means that it has a resistor as a component (K will be explained later) or that it functions only as a complete optical switch for ease of understanding. This simplified equivalent circuit is for TV
This is similar to the case where a vidicon tube, which is an image pickup tube, accumulates a light image formed on its photocathode, and the latent image is read out by lightning or laser beam scanning.

Note that each of the above-mentioned small areas refers to a spot area of a scanning laser beam that moves moment by moment. In Figure 1, tl is the first photoconductor layer, t is the second photoconductor layer, and t+ is the image exposure layer. O is sensitive only to the initial light (in this case, X-rays), and t is sensitive to only the initial light (in this case, a laser beam) for image reading.
t is a capacitor that charges a constant amount of charge Q0.

A variable resistor R having a variable resistance value depending on the X-ray scene is arranged in parallel. This resistance depends on the generation of electron-hole pairs by X-ray irradiation, and exhibits a large resistance value when the amount of exposure is small.

Also, at t, an optical switch S using a scanning laser beam is activated.
arranged in series with l. Note that the constant voltage E is applied when the optical switch S is turned on. It shows the charge state up to the moment t=T when the beam crosses the small area. Strictly speaking, there is a slight time Δt from when the beam starts irradiating the small area until it finishes, and during this Lt, Q
. Charging is performed.

That is, both t=0 and t=T are completely Q. means the moment when the laser beam is charged, but for ease of understanding, the moment when the laser beam crosses is assumed to be 1=0.

First, in FIG. 1 (4), when 1=0, the optical switch S
is turned on, and the capacitor t is charged with a constant amount of charge Q0.

Then, when the scanning beam leaves the small area, the optical switch S
is turned off (Fig. 1@), and the charges stored in the capacitor begin to self-discharge within a closed loop via the resistor R during image exposure. The correlation between charge reduction and elapsed time is shown in Figure 2. If the resistance value of R is small, that is, in the case of a bright area, the amount of discharge is large and the amount of charge reduction is large;
If the resistance value of is large, that is, in the case of a dark area, the amount of discharge is small and the amount of charge reduction is small.

Generally, when discharging in a parallel circuit of a capacitor and a resistor, the amount of charge decreases exponentially over time.

FIG. 1(C) again shows the situation just before the laser beam reaches the small area. The amount of charge remaining in the capacitor is Qo-ΔQ1 when the resistance value is small (bright part) in Figure 2.
If the resistance value is large, the dark area), Qo - ΔQ.

FIG. 10 again shows the moment t=% when the laser beam reaches the small area. At this time, the lower light switch S is turned on again, and the charge decrease amount ΔQ from 1=0 to t=%
will charge the capacitor. In other words, in the bright area mentioned above, △QI + in the dark area, △Q! The external capacitor is charged.

In FIG. 1C), the amount of charge decrease -ΔQ cannot be detected externally, but in FIG.

FIG. 3 is an overall equivalent circuit diagram of two photoconductor layers L+ t Lt . In other words, this is equivalent to arranging a plurality of tll At in parallel in each small area shown in FIG.

Next, an overall explanation of the image detecting device of the present invention will be given with reference to FIG. 51 is an X-ray generation source, and 52 is an object. Here, X-rays are continuously irradiated. The portion of the X-ray 54 that does not pass through the object is slightly attenuated and is detected by the detection plate 3.
1 conductor layer 1 and is absorbed by the first photoconductor layer 2 . The X-rays passing through the object 52 undergo a large attenuation and a small dose passes through the conductor 1 and is absorbed by the first photoconductor layer 2, producing a photoconductive effect. 55 is a dark box, in which a laser beam 56 from a laser beam scanning mechanism 53 scans the transparent conductor layer 4 of the detection plate 31. Laser scanning can be thought of as two-dimensional X and Y scanning, similar to a TV camera. The laser beam 56 passes through the transparent conductor layer 4 and irradiates the second photoconductor 3, as shown in FIG.
Move dimensionally. Note that two-dimensional scanning is also possible by scanning the laser one-dimensionally and moving the detection plate orthogonally to the scanning direction. In Figure 5, the time T until the laser beam crosses the same small area again is 1
Equivalent to one frame. In other words, as shown in FIG. 5, for an arbitrary point P, the time required for the scanning beam to travel by PQ + RP from when it reaches that point to when it reaches that point again is a constant time T. . In other words, the scanning beam crosses any point on the detection plate at a constant period.

In FIG. 4, the image exposure light (X-rays) and the image detection light (laser beam) are irradiated from opposite directions, but they can also be irradiated from the same direction. That is, it is sufficient if the X-ray source is set on the laser light source side, the X-rays pass through the second photoconductor layer 3 without being absorbed, and are absorbed by the first photoconductor layer 2.

In any case, the conductor layer on the side irradiated with the scanning beam is transparent to the scanning beam, and the metal thin film, for example, when the second photoconductor layer is made of amorphous silicon, the conductor layer on the side irradiated with the scanning beam is visibly transparent Nesa Glass SnO, , Au thin film, etc. are selected.

By the way, in the equivalent circuit diagram of FIG. 1 described above, for ease of understanding, each small region that corresponds to the second photoconductor layer is connected in series with the optical switch 24 as shown in FIG. A conduction resistor 25 is also connected in parallel with a capacitor 23 . This is a circuit in which a dark resistor 26 is arranged. Here, the dark resistance 26 refers to the resistance when the second photoconductor is not irradiated with laser light. Note that 27128 is an electrode, 33 is an output terminal of the amplifier 32, and 34 is a ground.

By the way, the conduction resistance 25 is required to be sufficiently low due to a sufficient amount of beam light.

The first reason for this is to avoid large changes in the charge and voltage of the capacitor 21 due to changes in the resistance 22 due to changes in the X-ray dose. This is because the voltage when charging of the capacitor 21 is completed is given by the voltage division between the resistor 22 and the conduction resistor 26. The second reason is to reduce the time constant of the conduction resistance 25 and the capacitances 21 and 23. This means that the capacitance 21 is completely filled as much as possible within the time that the scanning beam scans this one pixel.
It is impossible to complete the charging and discharging of the capacitance [23].

This issue is important regarding the scanning speed and afterimage of this method. The other side of capacitance 21 is connected through electrode 27 to the input of amplifier 32. Therefore s? Ix capacity 21
Full 1! The current flows into the input of the dJ amplifier 32. It is desirable that the input impedance of the amplifier 32 is sufficiently low.

This is in series with the conduction resistance 25, and is for the same reason that the conduction resistance 25 described above is required to be low.

When the scanning beam leaves the purple part of the picture, the light switch 25
is turned off. The first photoconductor layer is irradiated with X-rays and has a reduced resistance 22 due to the photoconductive effect of X-rays.
begins to discharge the charged capacitance 21. At the same time, charging of the capacitance 23 begins. If the X-ray irradiation continues until the next beam scan, the capacitor -i:21 continues to discharge during that time. If the X-ray irradiation is stopped before the next beam scan, the discharge is stopped at that point. This means that the resistance 22 has become very large as a dark resistance.

The surface potential of the capacitor 21 decreases in proportion to the discharge of its charge. If the X-ray irradiation dose is constant with no change over time during one frame scanning period of the beam, this surface potential will decrease exponentially with time.

The internal charge decreases as well. This amount of discharged charge is replenished by the same amount again when the next beam is scanned. That is, the total amount of discharged charges is equal to the total amount of charged charges during the next scan.

This charging current flows into the amplifier 32 as an input current for each scan, and is taken out as a voltage at its output.

FIG. 7 shows another embodiment in which the transparent conductive layer is grounded. The capacitance of the first photoconductive layer is controlled by the optical switch 2 during beam scanning.
This charging current is supplied from the amplifier input. Since this supplied current becomes a signal current, the operation is exactly the same in principle as described above. However, the direction of the signal current is reversed.

FIG. 8 shows an embodiment in which a blocking contact 5 is provided between the first photoconductor layer 2 and the second photoconductor layer 3. In FIG. The blocking contact is a barite such as a PN junction and has a barrier potential.

FIG. 9 shows an equivalent circuit in this case. The blocking contact is represented by a diode 30 as a PN junction and a battery 29 as a barrier potential. The barrier potential exhibited by this cell 29 is for radiation or light to which the first photoconductor layer is sensitive, and the barrier potential is negligible for light beams to which the second photoconductor layer is sensitive. It is so small that it is only shown as a diode 30 in series with the optical switch 24 which is turned on by some light beam passing through the second photoconductor layer.

The detection plate in Figure 8.9 is
This will be explained using figures.

When the second photoconductor layer is irradiated with a light beam, the two optical switches 24 and 24' are turned on, the electrostatic field 4123 is discharged, and the first capacitance 21 is connected to the first capacitor 21 through the diode 30'. A voltage is applied and the capacitor 21 is charged. When the light beam irradiation ends, the conductivity of the first photoconductor increases due to the effect of the X-ray irradiation, the charge in the capacitor 21 begins to discharge through the isolateral internal resistance 22, and the surface potential of the first photoconductor decreases. Start. If this voltage drop exceeds the barrier potential exhibited by battery 29, diode 30 will become conductive. However, if this decrease in surface potential is within a range smaller than the barrier potential, the internal resistance of the first photoconductor layer will be reduced by the charging current of the electrostatic field t23 and the dark resistance 26 as described above in discharging this capacitor 21.
The current also flows through the internal resistance of the first photoconductor layer, but
If this value is too large, it will result in a large energy loss.
This results in a decrease in photoelectric conversion efficiency. In other words, the charge that has been charged in the capacitance of the second photoconductor layer until the next scan is discharged during the next scan and is lost as heat, and this is due to the radiant energy received by the first photoconductor. It can be considered as a part of

Therefore, if this blocking contact is provided and the device is operated so as not to exceed the barrier potential, this loss will not occur, so that the signal current can be increased, that is, the shear ratio and sensitivity can be improved. By reducing the leakage current, it becomes possible to easily hold charge for at least one scanning period, so when reading one screen, shading and fluctuations in the output signal are reduced, and accuracy is improved. Furthermore, since no charge current flows into the electrostatic field t23, the discharge current during beam irradiation becomes small, and therefore the scanning time within one pixel can be shortened, which has the effect of enabling high-speed scanning of the reading beam. Note that the same effect can be obtained even if this blocking contact is provided between the second photoconductor layer and the transparent conductor layer.

FIG. 10 shows an antireflection film 6 provided by coating or other means on the outside of the transparent conductor layer 4 fixed to the second photoconductor layer of the detection plate.

FIG. 11 is a partially enlarged view of FIG. 1θ. The beam from the laser is prevented from being lost due to reflection on the surface of the transparent conductor layer 4, increasing the transmittance and improving the output efficiency of the laser beam. In addition, even if the beam that reaches the surface of the second photoconductor layer 3 is reflected, it is efficiently transmitted through the anti-reflection film on the surface of the transparent conductor layer, so there is little re-reflection at this part and the beam is This has the effect of reducing the spot diameter and improving resolution.

FIG. 12 shows an embodiment in which the conductor layer 1 on the image projection side is replaced with a transparent conductor layer. If the projected image is visible light, it is sufficient to simply replace the conductive layer 1 with a transparent conductive layer 1, such as a Nesa film, but if the projected image is X-rays or other radiation, it emits fluorescent light upon receiving this radiation. The first photoconductor 2 can be acted upon by pasting the silicon base plate 7. Naturally, in this case, the effect is obtained when the first photoconductor is sensitive to the wavelength of fluorescent light, but it also holds true when the first photoconductor is not sensitive to the radiation of the projected image. If it is sensitive to radiation, it will be used as a sensitizing agent.

FIG. 13 is a partially enlarged view of FIG. 12, showing that the large arrow 56 is fluorescent.

Incidentally, in the above embodiment, a continuous reading system has been described, but it is also possible to perform image recognition light and reading by primary charging the first photoconductor and the second photoconductor. In this case, the second photoconductor layer can also simply act as an insulator.
Alternatively, when charging only the first photoconductor, it can be irradiated with light to function as a light switch.

In addition, when the latent image is to be completely eliminated, the light can be opened and used as a switch.

PB instead of an amorphous selenium plate as the '1st photoconductor layer.
O, etc. may be used, and CdSe, CdTe, etc. may be used instead of amorphous silicon as the second photoconductor.

As described above, according to the present invention, the following effects are obvious.

1. By performing continuous X-ray irradiation and repeated scanning, display on a monitor such as a TV becomes possible, and a device with fluoroscopy and imaging functions can be constructed.

2 A large field of view and high-quality X-rays that cannot be obtained using an image intensifier and TV system
This has the effect that a line image can be obtained as a video signal.

3. Continuous high-speed imaging allows video signals to be converted, and when used in combination with image processing, it has the effect of providing X-ray images that are easy to diagnose even in cardiovascular diagnostic methods.

4 Image signals can also be supplied to copying devices made of materials other than copper salt film.

By the way, although the image exposure light has been described above as X-rays, it is not limited to this, and can be applied to visible light, infrared light, ultraviolet light, and other electromagnetic waves in general.

Furthermore, the scanning beam is not limited to the laser beam, and can be selected as appropriate without departing from the scope of the present invention.

[Brief explanation of drawings]

Figures 1 to 3 are detailed explanatory diagrams of the present invention, with Figure 1 being a simplified equivalent circuit diagram of each small region of the detection plate, and Figure 2 showing changes over time in the amount of accumulated charge. Figure 3 is
4 is an explanatory diagram of the entire image detector according to the present invention; FIG. 5 is an explanatory diagram of two-dimensional scanning readout using a laser beam; and FIG. 6 is an illustration of each of the detection plates. Actual equivalent circuit diagram of a small area; Figure 7 is an explanatory diagram with modified electrical connections in Figure 6; Figures 8 and 9 are configuration diagrams of a detection plate with blocking contacts; Figure 1 is an equivalent circuit diagram; Figures 11 and 11 are configuration diagrams and characteristics explanatory diagrams of a detection plate provided with an antireflection film. Figures 12 and 13 are configuration diagrams and characteristic diagrams of a detection plate provided with a fluorescent film. , , L is the first photoconductor layer. t21 L! is the second photoconductor layer. 1 is a conductor layer, 2 is a first photoconductor layer, 3 is a second photoconductor layer, 4 is a transparent conductor layer, 5 is a blocking contact layer, 6 is an antireflection film, and 7 is a fluorescent layer. , 21 is the capacitance of the first photoconductor, 22 is the isolateral internal resistance, 23 is the capacitance of the photoconductor of the umbrella 2, 24 is the optical switch of the second photoconductor, and 25 is the second photoconductor. 2 is the conduction resistance of the photoconductor when the optical switch is ON, 26 is the dark resistance of the second photoconductor, 27 is the electrode of the conductor, 28 is the electrode of the transparent conductor, and 29 is the equivalent barrier potential of the blocking contact. , 3° is a diode with a blocking contact, 31 is a detection plate, 32 is a current amplifier, 33 is an output terminal of the amplifier, 34 is ground, 5
1 is an X-ray generation source, 52 is an X-ray object, 53 is a laser scanning mechanism, 54 is an X-ray, '55 is a dark box, and 56 is a laser beam.

Claims (1)

[Claims] 1. Imagewise exposing a subject to form a latent image on a detection plate; 1.
- In a device that detects images in time series by scanning the detection plate with a beam, the detection plate is provided on a first conductive layer and on one side of the conductive layer, and forms a latent image by image exposure. a first photoconductor layer provided on the other side of the first photoconductor layer and receiving the scanning beam; 2. The image detecting device according to claim 1, wherein the image detecting device has a second conductive layer provided on the surface side, and the image exposing light is X-rays. 3. The image detection device according to claim 1, wherein the image exposure and scanning beams are irradiated from different directions. 4. The image detection device according to claim 1, wherein the image exposure and the scanning beam are irradiated from the same direction. 5. The image detection device according to claim 3 or 4, wherein the conductive layer on the side to which the scanning beam is irradiated is transparent to the scanning beam. 6. Reflection on the surface of the transparent conductive layer. The image detection device according to claim 5, which has a protective film. 7. A phosphor layer is provided on the surface of the conductor layer, and the first photoconductor layer receives light of a wavelength different from the image exposure light. Image detection device according to claim 1. 8. A blocking layer between the first photoconductor layer and the second photoconductor layer that acts as a blocking contact only for the latent image after image exposure. The image detection device according to claim 1, having a contact layer. 9. The first photoconductor layer is a thin film of amorphous selenium, and the second photoconductor layer is a thin film of amorphous silicon. 10. An image detection device according to claim 1. 10. An image detection device according to claim 1, in which the scanning beam crosses any point on the detection plate at a constant period.