JP2000235075A - Charge reading-out method and device for radiation solid detector, and radiation solid detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a range of an image signal get to a full range of an A/D converting range irrespective of a radiation dose getting incident into a detector, in a radiation solid detector. SOLUTION: This detector is provided a reading time controlling means 40 for controlling a reading time. The means 40 reads out a part of signal charges by carrying out previous reading using a reading circuit 30 prior to main reading for reading the signal charges accumulated in a condensing part 21b, gets from an output amplifier 32 an image signal S2 based on an electric charge quantity read out therein to analyze a histogram of the image signal S2, and controls the reading time to make the maximum image signal value S2max in a desirable range of radiation information constitute the maximum value Dmax of an A/D converting range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for reading out electric charges of a solid-state radiation detector for reading out electric charges carrying radiation information stored in a solid-state detecting element to obtain an electric signal representing the radiation information, and to use the method. The present invention relates to a solid-state radiation detector.

[0002]

2. Description of the Related Art Today, in radiography for medical diagnosis and the like, electric charges obtained by detecting radiation are temporarily stored in a power storage unit of a solid-state detection element, and the stored electric charges are converted into electric signals representing radiation information. Various radiation image recording / reading apparatuses using a solid-state radiation detector that converts and outputs a radiation have been proposed and put into practical use. Various types of solid-state radiation detectors used in this device have been proposed, but from the viewpoint of the charge generation process of converting radiation into electric charge, the solid-state radiation detector and the direct conversion type solid-state radiation detector are used. The solid-state radiation detectors are divided into two types, and from the viewpoint of a charge readout process of reading out accumulated charges to the outside, they are classified into two types, a TFT (thin film transistor) readout type and an optical readout type.

Here, a radiation solid-state detector of the light conversion type is a solid-state detection unit (image reading unit) having a large number of photoelectric conversion elements formed on an insulating substrate, and a phosphor formed on the solid-state detection unit. The signal charge obtained by detecting the fluorescence emitted from the phosphor by the irradiation of the radiation with the photoelectric conversion element is temporarily stored in the power storage unit of the photoelectric conversion element, and the stored charge is converted into an electric signal. (For example, JP-A-59-211263, JP-A-2-64067, PC
T International Publication No. WO92 / 06501, SPIE Vol.1443Medical
Imaging V; Image Physics (1991), pp. 108-119).

A direct conversion type solid-state radiation detector is composed of a large number of charge collecting electrodes formed on an insulating substrate, and a charge carrying radiation information when the radiation formed on the charge collecting electrodes is irradiated. It has a solid-state detection unit formed by laminating a radiation conductor that generates a signal, the signal charges generated in the radiation conductor by being irradiated with radiation are collected by the charge collection electrode and temporarily stored in the power storage unit, It converts stored charges into electrical signals and outputs them (MATERIAL P
ARAMETERS IN THICK HYDROGENATED AMORPHOUS SILICON
RADIATION DETECTORS, Lawrence Berkeley Laboratory.U
niversity of California, Berkeley.CA 94720 Xerox Pa
rc.Palo Alto.CA 94304, Metal / AmorphousSilicon Mult
ilayer Radiation Detectors, IEE TRANSACTIONS ON NUC
LEAR SCIENCE.VOL.36.NO.2.APRIL 1989, Japanese Unexamined Patent Publication No. 1-26292
No. 0). The solid-state detection element in this method has a charge collection electrode and a radiation conductor as main components.

[0005] The TFT readout method refers to a method in which a signal charge stored in a power storage unit of a solid state detection element is converted to a TF connected to the power storage unit.
This is a method of scanning and reading T, and the optical reading method is a method of irradiating a solid state detection element with reading light (electromagnetic wave for reading) to read out.

The applicant of the present application has proposed an improved direct conversion type solid-state radiation detector in Japanese Patent Application Nos. 10-232824 and 10-271374. The improved direct conversion type solid-state radiation detector is a combination of the direct conversion type and the optical readout type, and includes a first conductive layer having transparency to recording radiation, the first conductive layer, A recording photoconductive layer that exhibits photoconductivity (accurately, radiation conductivity) when irradiated with recording radiation that has passed through the body layer, and a charge having the same polarity as the charge charged on the first conductor layer. A charge transporting layer that acts as a substantially insulator and acts as a substantially conductor with respect to the charge of the opposite polarity to the charge. Is formed by laminating a reading photoconductive layer exhibiting electromagnetic wave conductivity) and a second conductor layer having transparency to reading electromagnetic wave in this order, and the recording photoconductive layer and the charge transport At the interface with the layer (power storage unit), a signal charge carrying image information ( It is intended for storing an image charge). A first conductor layer and a second conductor layer;
The conductive layer functions as an electrode. In addition, the solid-state detection element in this system has a recording photoconductive layer, a charge transport layer, and a read photoconductive layer as main components.

In the improved direct conversion type solid-state radiation detector, a signal charge is read out, for example, by forming a second conductive layer (hereinafter referred to as a reading electrode) in a plate shape, and placing the second conductive layer on the reading electrode side. A method of detecting signal charges by scanning a spot-like reading light (an electromagnetic wave for reading) such as a laser, and a method in which a reading electrode is a comb-like stripe-like electrode and is substantially perpendicular to the longitudinal direction of the stripe-like electrode. There is a method of detecting signal charges by scanning a line light source extending in a desired direction in the longitudinal direction of the stripe-shaped electrode.

[0008] Regardless of the readout method, the solid-state radiation detector is a two-dimensional radiation detector in which a plurality of solid-state detection elements each corresponding to a pixel are arranged substantially in a matrix. It is a solid state detector. Where "substantial"
Although the detector itself cannot be said to consist of individual solid-state detection elements arranged in a matrix, in the process of processing an image signal obtained by reading out latent image charges, for example, a signal at a sampling point is used. Can be considered as a signal of a predetermined pixel, and is thus referred to. When the reading electrode is a stripe electrode, the stripe electrode itself corresponds to a pixel in the arrangement direction.

[0009]

However, the solid-state radiation detectors of any of the above-mentioned methods have a limited dynamic range because the maximum charge amount (saturated charge amount) that can be accumulated or read out is limited, and the readout is not possible. A / D conversion range when digitizing the image signal is forced to be narrow.

In reading out signal charges stored in the power storage unit to the outside and converting them into electric signals,
Since the reading time of the signal charge is fixed, the range of the electric signal varies depending on the range of the dose of the radiation incident on the detector. For example, when comparing a high-dose imaging in which the same subject is irradiated with a relatively high-dose radiation and a low-dose imaging in which a low-dose radiation is irradiated, the signal range becomes large in the high-dose imaging and the A / D While the maximum input range of the converter may be exceeded, the signal range becomes narrow at the time of low-dose imaging, and the A / D conversion cannot be used to the fullest. Therefore, the bit resolution is reduced and quantization noise is noticeable. In addition, there is a problem that the detector is susceptible to the fixed noise of the detector or the recording / reading device and the S / N is reduced.

The present invention has been made in view of the above circumstances, and is capable of setting the maximum value of an output electric signal to a desired value irrespective of the dose of radiation incident on the solid-state detection element. It is an object of the present invention to provide a charge reading method and device for a detector and a solid-state radiation detector used for the same.

[0012]

According to the present invention, there is provided a charge reading method for a solid-state radiation detector, which reads a charge carrying radiation information stored in a solid-state detection element to obtain an electric signal representing the radiation information. Wherein the readout time of the electric charge accumulated in each of the solid-state detection elements is controlled in accordance with the dose of radiation incident on the radiation solid-state detector.

[0013] Here, "control according to the dose" means that the A / D at the time of high-dose imaging is smaller than when the readout time is fixed.
This means that the readout time is changed so as not to exceed the maximum input range of the D converter, and to output an electric signal at a level that can use a wider A / D conversion range during low-dose imaging.

The "dose of the incident radiation" is not limited to the dose of the incident radiation itself, and is not limited to the dose of the incident radiation as long as the reading time can be changed so that the electric signal in the appropriate range is output. Including those in For example, the radiation dose in the vicinity of the detector (beside the detector or the back of the detection surface, etc.), the radiation dose generated from the radiation source, the luminescence amount of the fluorescent light emitted from the phosphor upon receiving the radiation, and the like are used. You may.

As the dose used for the control, it is preferable to use a maximum dose corresponding to a desired range of radiation information obtained by the entire detector, that is, a maximum value corresponding to a maximum value of the desired range of the electric signal. The maximum dose may be obtained by grasping the doses of all the detection elements constituting the detector, or a specific detection element that will be the maximum dose if the pattern of the radiation information is known in advance, for example. May be used only. Not limited to the maximum dose, various values such as an average value, an intermediate value between the maximum value and the minimum value, and a median value can also be used.

In the charge readout method according to the present invention, it is desirable to perform the above control so that the maximum value of the electric signal is constant regardless of the dose.

"The maximum value of the electric signal is constant" means that the maximum value of the electric signal is made constant so that a wider A / D conversion range can be used as compared with the case where the reading time is made constant. I just need. Most preferably, the maximum value is the same as the maximum input range of the A / D converter.

In the charge readout method according to the present invention, it is preferable that the control is performed by detecting a dose by a dose detecting means provided separately from a solid-state detecting element for obtaining an electric signal.

The dose detecting means is separate from the solid-state detecting element, and can detect a dose of radiation incident on the solid-state detecting element or a dose corresponding to the dose. Any type may be used as long as it includes, for example, a phototimer for detecting an irradiation radiation dose near the solid-state detection element or a generated radiation dose emitted from a radiation source, or a photodiode for detecting a fluorescence emission amount. Can be used.

Further, in the charge reading method according to the present invention, prior to reading for obtaining an electric signal, a part of the electric charge accumulated in the solid state detecting element is read for obtaining the electric signal. It is desirable to read the data in a shorter time, and to perform the control according to the amount of the read charges.

In the charge readout method according to the present invention, when the solid-state radiation detector is an optical readout type detector that performs charge readout by irradiating readout light, it is necessary to obtain an electric signal. Prior to reading, the radiation solid state detector is irradiated with a smaller amount of preread light than the amount of read light for acquiring an electric signal, and a part of the electric charge stored in the solid state detection element is read out. It is desirable that the control be performed according to the amount of the read charges.

The “reading light” is applied to any solid-state detecting element constituting the detector, so that the electric charge stored in the power storage unit of the solid-state detecting element can be output to the outside. It may be an electromagnetic wave in a narrow sense, for example, not limited to visible light.

Further, in the charge reading method according to the present invention, a part of the charges stored in the solid-state detecting element is read, and an electric signal corresponding to the part is obtained, and the maximum of the obtained electric signals is obtained. It is desirable to perform the control according to the value.

In the above description, "a part of the electric charge stored in the solid-state detection element" does not necessarily have to mean all the solid-state detection elements constituting the detector. For example,
When the pattern of the radiation information is known in advance, for example, one of the electric charges stored in one or more elements in a specific region on the detector which is convenient to perform the control according to the pattern. The unit may be read.

A read circuit for reading a part of the electric charge is
It may be shared with a readout circuit for acquiring an image signal, or may be separate from it.

In order to obtain the “maximum value of the electric signals”, it is preferable to perform an analysis (for example, a histogram analysis) based on the electric signals of a plurality of solid state detection elements.

The charge reading device of the solid-state radiation detector according to the present invention realizes the above-described reading method, that is, reads out the charge carrying the radiation information accumulated in the solid-state detection element to obtain an electric signal representing the radiation information. A charge readout device for a solid-state radiation detector, comprising: readout time control means for controlling a readout time of charges accumulated in each of the solid-state detection elements in accordance with a dose of radiation incident on the solid-state radiation detector. It is characterized by the following.

In this charge reading device, any device may be used as long as it has means for realizing the various reading methods described above, and each means may be integrated with the detector or may be provided separately. May be used. For example, a dose detecting means for detecting a dose may be arranged on the radiation source side to detect the generated radiation dose. In the case of using an optical readout detector, a light source that emits read-ahead light may be provided outside the detector.

The solid-state radiation detector according to the present invention has a function of realizing the above-mentioned reading method, that is, a solid-state detection element which receives radiation and accumulates a charge carrying radiation information, and a solid-state detection element which accumulates the electric charge. A solid-state radiation detector comprising: a readout unit that reads out an electric charge and obtains an electric signal representing radiation information, the readout time of the electric charge accumulated in each of the solid-state detection elements, A reading time control means for controlling according to the dose of the incident radiation is provided.

The read-out time control means may have a function of detecting a dose, or may perform the above-mentioned control by obtaining information on the dose from another dose detection means.

It is desirable that the read-out time control means of the solid-state radiation detector performs the control so that the maximum value of the electric signal becomes constant regardless of the dose.

Further, the solid-state radiation detector of the present invention is characterized in that a dose detecting means for detecting a dose of radiation incident on the solid-state radiation detector is provided separately from a solid-state detecting element for acquiring an electric signal. It can be.

Further, the reading time control means of the radiation solid state detector according to the present invention obtains a part of the electric charge accumulated in the solid state detecting element before obtaining the electric signal. It is preferable that the control is performed in a shorter time than the read time of the above, and the control is performed according to the charge amount of the read charges.

In the case where the solid-state radiation detector of the present invention is an optical reading type detector for reading out electric charges by irradiating a reading light, the reading time control means includes a reading time controlling means for obtaining an electric signal. Prior to reading, one of the electric charges accumulated in the solid-state detection element obtained by irradiating the radiation solid-state detector with a pre-read light having a lower amount than the light amount of the read light for acquiring the electric signal. It is desirable that the control be performed in accordance with the amount of charge of the portion.

Further, the readout time control means of the solid-state radiation detector of the present invention reads out a part of the electric charge stored in the solid-state detection element to obtain an electric signal corresponding thereto,
It is desirable that the control be performed in accordance with the maximum value of the obtained electric signals.

[0036]

According to the charge readout method and apparatus and the solid-state radiation detector of the present invention, the charge readout time is controlled in accordance with the incident radiation dose and the like. Since the maximum value can be set to a desired value, for example, the electric signal can be prevented from exceeding the maximum input range of the A / D converter at the time of high-dose imaging, and the reading time can be reduced at the time of low-dose imaging. It is possible to increase the bit resolution of the A / D conversion and to improve the S / N as compared with the case where it is fixed.

The incident radiation dose can be obtained by various methods, for example, by a dedicated detecting means or by pre-reading, and a suitable method can be used according to the mode of the apparatus, so that the application range is wide. The detection means such as a photo timer generally has a narrow detection area and a limited measurement area. However, if pre-reading is performed, the incident radiation dose for all elements or a desired number can be obtained using the solid-state detection element itself constituting the detector. Can be obtained, and the amount of incident radiation can be obtained more accurately, so that accurate control can be performed.

If the maximum value of the acquired electric signals is obtained by histogram analysis or the like and the control is performed according to the maximum value, the maximum value of the electric signal representing the radiation information in the desired range is always obtained. It is possible to output a desired value. For example, the maximum value of the electric signal can always be the same as the maximum input range of the A / D converter regardless of the radiation dose.

[0039]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a solid-state radiation detector 10 according to the embodiment. The radiation solid state detector 10 is a radiation solid state detector of a light conversion type and a TFT readout type,
FIG. 2 shows a circuit block diagram of one pixel of the photoelectric conversion element and the readout circuit which constitute the detector 10.

As shown in the figure, the detector 10 includes a solid state detector 20 for detecting radiation carrying image information, a readout circuit 30 as readout means for reading out charges from the solid state detector 20 and outputting an image signal. Having. Solid detector 20
Is a photoelectric conversion element (photoelectric conversion unit 2) as a solid state detection element.
1a and power storage unit 21b) 21 and power storage unit 21b
Transfer section 2 composed of a TFT for transferring the signal charge stored in the memory
2 are formed by arranging many two-dimensionally. The readout circuit 30 includes a gate of each TFT and a scanning line 27 for each row.
b, a scanning pulse generator 31 commonly connected to the solid-state detector 20, an output amplifier 32 for reading out signal charges transferred from the solid-state detector 20 for each column via the signal line 27a to the outside, a capacitor 33, and both of them. SW (switch)
34. The output amplifier 32, the capacitor 33, etc.
The photoelectric conversion elements 21 are provided in columns.

As shown in FIG. 2, a fluorescent substance 29 is provided on the detection surface side of the solid-state detection section 20, and emits radiation from the radiation source 1 with the transfer section 22 turned off and the SW 34 turned on. The radiation R transmitted through the subject 9 is
Irradiates the phosphor 2 with light P corresponding to the dose of the radiation R.
9, charges corresponding to the dose of the radiation R are generated in the photoelectric conversion unit 21a and stored in the power storage unit 21b. Next, when the transfer unit 22 is turned on and the SW 34 is turned off, the power storage unit 21 is turned on.
The charge stored in b is transferred to the output amplifier 32 side, integrated by the output amplifier 32 and the capacitor 33, converted into an image signal S1 having a voltage value, and output to the outside. As can be seen from this, the read time is determined by the ON time of the transfer unit 22 under the SW 34 OFF state.

By the way, as shown in FIG.
At 0, a read time control means 40 is provided, which is connected to the transfer section 22 via the scanning pulse generator 31 and also to the SW 34. Read time control means 40
Prior to the main reading for reading out the signal charges representing the image information stored in the power storage unit 21b, a part of the signal charges is read out by performing a short-time pre-reading using the readout circuit 30, and the read-out charge amount The output image signal S2 is obtained from the output amplifier 32, the histogram analysis of the image signal S2 is performed, and the maximum image signal value S2ma in the desired range of the radiation information is obtained.
The read time is controlled so that x becomes the maximum input value of the A / D conversion range. Note that the signal level of the image signal S2 is smaller than the signal level of the image signal S1, but is in a proportional relationship, and the content analysis of the image information represented by the image signal S1 can be performed by using the image signal S2.

FIG. 3 shows an example of histogram analysis of the image signal S2 and the image signal S1 by changing the readout time.
FIG. 6 is a diagram for explaining a method of changing the maximum value of. 3A shows a histogram analysis result X1 at the time of high-dose imaging and a histogram analysis result X2 at the time of low-dose imaging.
The middle (B) portion shows a change in the image signal S1 output from the output amplifier 32 according to the readout time t at each shooting.
Hereinafter, the operation of the read time control unit 40 will be described in detail with reference to FIG.

When an image of the subject 9 is taken, there may be a radiographic part in which the radiation source directly enters the detector from the radiation source without transmitting through the subject 9. When a histogram analysis of the image signal S2 having the blank portion is performed, FIG.
As shown in part (A), a relatively low-dose component A representing subject information and a relatively high-dose component B representing a blank portion can be separated and extracted. The transparent portion is a meaningless portion as image information, and it is not efficient to match the A / D conversion range including this portion. Therefore, the range A on the relatively low dose side becomes the full A / D conversion range. Image signal S
It is desirable to adjust the range of 1. That is, the maximum value S2max of the range A should be the maximum value Dmax of the A / D conversion range.

In analyzing the histogram, the image signals S2 from all the detection elements constituting the detector may be used, but not all of them need be used. For example, when the image pattern is known in advance, necessary data can be specified, so that the number of data used for analysis can be reduced and the processing time can be reduced.

The read time control means 40 controls the maximum value of the image signal S1 by changing the read time.

The image signal S output from the output amplifier 32
The level of 1 gradually increases with a different slope according to the amount of charge stored in the power storage unit 21b. Power storage unit 21b
Assuming that a sufficient reading time is taken for reading out all the electric charges accumulated in the capacitor 33, the saturation voltage of the capacitor 33 after the lapse of the reading time (t0) becomes the value of the image signal S1.

Since the amount of charge stored in the power storage unit 21b is in accordance with the dose of the radiation incident on the detector 21, the saturation voltage is high during high-dose imaging and low during low-dose imaging. If a sufficient readout time is taken, the range up to the saturation voltage becomes the maximum value of the image signal S1 in each state, and as shown in FIG. 3B, a high value corresponds to the maximum value S2max. The range is Y1 during dose imaging and Y2 during low dose imaging.

On the other hand, if the reading time is shortened,
b, a voltage corresponding to the amount of charge transferred, that is, a voltage corresponding to the read charge is generated in the output amplifier 32,
The signal value decreases. The signal value at this time is Y1 or Y2
Since the proportional relationship is maintained, appropriate information is obtained as image information.

Therefore, for example, assuming that the reading time at the time of high-dose imaging is t1 and the reading time at the time of low-dose imaging is t2, in any case, the maximum value of the image signal S1 is fixed and the image signal S1 is obtained. The range that can be taken can be the range indicated by Z in the figure. That is, by controlling the readout time according to the dose of the radiation R, the image signal S1 can be obtained regardless of the dose.
Can be set to a desired value.

As can be seen from FIG. 3, the maximum value S2max of the component A representing the subject information at the time of low dose imaging is
The maximum read time tmax is set so as to be the maximum allowable input value of the A / D converter, that is, the maximum value Dmax of the A / D conversion range. When the read time is shortened at a high dose, the maximum value of the image signal is reduced to the dose. Regardless of the dose, control can be performed so that the maximum input value of the A / D converter is always the same, regardless of the dose.
The full / D conversion range can be achieved.

If the read time is shortened and the charge transfer is interrupted halfway, the charge is left unread in the power storage unit 21b.
When the next photographing is performed with the residual charges left unread, the residual charges appear as noise in the next image. Therefore, the residual charges are discharged by the next photographing. Preferably, means are provided.

In this embodiment, the output amplifier 32
Since the integration amplifier circuit is constituted by the capacitor 33 and the capacitor 33, the rising curve of the image signal S1 shown in the right half of FIG. 3 is substantially linear. Gradually increases according to “1-EXP (−t / RC)”. Also in this case, the image signal S is changed by changing the readout time in the same manner as described above.
It is the same that the range of 1 can be changed.

In the above description, the present invention is applied to a radiation solid-state detector of a light conversion type and a TFT readout type. However, the above-described embodiment is not limited as long as it is a TFT readout type detector. The same method can be applied to, for example, the above-described direct conversion type detector that employs the TFT readout method.

Next, an embodiment in which the present invention is applied to an optical readout type solid-state radiation detector will be described. Fig. 4 shows Japanese Patent Application No.
FIG. 4A is a perspective view showing an example of a configuration in which the present invention is applied to an improved direct conversion type solid-state radiation detector (electrostatic recording medium) described in JP-A-232824 and JP-A-10-271374. , FIG.
4B is an XZ sectional view, and FIG. 4C is an XY sectional view. The detector 50 has an integrated EL luminous body 60 as a light source for reading light and pre-reading light, a reading circuit 70, and a reading time control means 45. Needless to say, a dedicated light source may be provided for each, and the light source is not limited to the integral type and may be provided separately from the detector.

The solid-state detecting section 56 of the detector 50 includes a first conductive layer 51, a recording photoconductive layer 52, a charge transport layer 53, a reading photoconductive layer 54, and a second conductive layer 55. They are laminated in order. The conductor layer 55 is formed in a comb-tooth shape (hereinafter, the comb-tooth portion (the hatched portion in the drawing) is a comb electrode 55).
a)). The recording photoconductive layer 52, the charge transport layer 53, and the reading photoconductive layer 54 constitute a main part of the solid-state detection element.

The EL luminous body 60 includes the conductive layer 61 and the EL layer 6.
2, a conductive layer 63 and an insulating layer 64;
4 is laminated on the second conductor layer 55 side. The conductive layer 61 is formed in a comb-like shape so as to intersect (substantially perpendicular in this example) with the comb electrode 55a of the detector 50, and thereby, a linear light source is formed by the comb-like teeth 61a (hatched portion in the figure). Are arranged in a large number in a plane.

The readout circuit 70 is connected to each of the comb teeth 5 of the conductor layer 55.
A plurality of current detection amplifiers 71 are connected to each of the comb teeth 5a, and the current flowing through each comb tooth 55a is detected in parallel for each comb tooth 55a by scanning exposure of read light or read-ahead light. Things. The conductor layer 51 of the detector 50 is connected to one input of the connection means 72 and the negative electrode of the power supply 73, and the positive electrode of the power supply 73 is connected to the other input of the connection means 72. The current detection amplifier 71 may have an integration amplifier configuration including the above-described output amplifier and capacitor, but is not limited thereto. Any configuration may be adopted as long as the current flowing out can be detected (for example, Japanese Patent Application No.
No. 232824).

When reading out the signal charge (negative charge) stored in the power storage unit 57 at the interface between the recording photoconductive layer 52 and the charge transport layer 53 of the detector 50, first, the connecting means 52 is connected to the detector 50. And a predetermined DC voltage is applied between each of the comb teeth 61a and the conductive layer 63 while the comb teeth 61a are sequentially switched by the EL luminous body 60 to read the linear read light. Are sequentially emitted, and the conductive layer 55 is scanned with the reading light.

The scanning generates positive and negative charge pairs in the photoconductive layer 54, and the positive charges in the photoconductive layer 54 rapidly move in the charge transport layer 53 so as to be attracted to the signal charges stored in the power storage unit 57. Then, the electric charge is recombined with the signal charge in the power storage unit 57 and disappears. A current due to the movement of the electric charges in this process is generated in the solid detection section 56, and the current is detected in parallel for each comb tooth 55a by the current detection amplifier 71 connected to each comb tooth 55a. Solid-state detector 5 by reading light scanning
Since the current flowing through 6 depends on the signal charge, detecting this current corresponds to reading the signal charge.

Incidentally, also in the present embodiment, the detector 50 is provided with the read time control means 45.
The read time control means 45 performs read-ahead using the read circuit 70 in the same manner as the read time control means 40 before the main read for reading the signal charges stored in the power storage unit 57.
Here, in the case of using the optical reading type detector, the pre-reading is performed by irradiating the solid-state detecting unit 56 of the detector 50 with a pre-reading light having an amount smaller than the amount of the reading light for the main reading, and This is performed by reading out a part of the electric charge stored in the memory. For example, the comb teeth 61 a and the conductive layer 63 are formed by the EL luminous body 60.
During this process, a direct current voltage lower than that at the time of main reading is applied, or the switching speed of the comb teeth 61a is increased to increase the scanning speed, thereby causing the line-shaped pre-read light to sequentially emit light. The current output from the detection unit 56 is detected by the current detection amplifier 71. Instead of sequential light emission, a DC voltage lower than that at the time of main reading may be applied to perform the entire surface exposure. Note that the light amount of the pre-read light is smaller than the light amount of the read light for main reading, and a part of the signal charge carrying the radiation information stored in the power storage unit 57 can be output to the outside. The amount may be sufficient, and is not limited to these examples, and various known methods can be used.

A histogram analysis is performed based on the image signal obtained by the current detection amplifier 71 by the pre-reading,
The reason for adjusting the signal range by controlling the read time is
This is the same as the above-mentioned light conversion method.

In controlling the read time, it goes without saying that the control method is changed according to the configuration of the current detection amplifier 71. For example, in the case of the above-described integrating amplifier configuration including the output amplifier and the capacitor, as shown in FIG.
May be controlled. In the case of a configuration including an output amplifier and a resistor, the scanning speed of the reading light may be controlled.

In the above description, the pre-reading is performed using the solid-state detecting element itself constituting the detector, and the desired range of the radiation image information is set to the appropriate range of the A / D conversion range (preferably, regardless of the dose). Although the method of controlling the read time so that the signal has the full range has been described, the present invention is not necessarily limited to this.

For example, it is possible to detect not only the dose of the radiation incident on the solid-state detection element itself but also the radiation corresponding to the dose. Specifically, as shown in FIG. 5, a phototimer 80 for detecting the dose of the radiation R is provided, and the readout time control means 40 ′ controls the readout time in accordance with the detection result of the phototimer 80, so that Irrespective of the detection level of the timer 80, the range of the image signal S1 can be set to an appropriate range of the A / D conversion range.

The phototimer 80 may be provided integrally with the detector 10 or may be provided separately. Further, the radiation R transmitted through the subject may be detected on the detector 10 side, or the radiation dose generated on the radiation source side may be detected. In any case, a value (preferably a value corresponding to the maximum value of the desired range of the radiation image information) corresponding to the dose of the radiation incident on the solid-state detection element may be obtained, and the reading time may be controlled accordingly. .

In the light conversion type detector, not only the radiation but also the amount of fluorescence emitted from the phosphor upon receiving the radiation may be detected by a photodiode or the like.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the present invention. . In short, the present invention
Equipped with a means capable of controlling the read time, the read time of the charge stored in the power storage unit, for example, by controlling according to the dose of radiation incident on the solid-state detection element, regardless of the dose, etc. What is necessary is that the range of the electric signal (image signal) output from the detector always be a desired range. In order to realize this, it does not matter whether the dose detection means, the readout time control means, and the like are provided integrally with the detector or provided separately. It goes without saying that the integrated type is easier to handle and more convenient.

Further, it does not matter whether the detector is a one-dimensional line sensor or a two-dimensional area sensor.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a solid-state radiation detector (light conversion system) according to an embodiment of the present invention;

FIG. 2 is a circuit block diagram of one pixel of a photoelectric conversion element and a readout circuit constituting the detector.

FIG. 3 is a diagram illustrating an example of histogram analysis of an image signal and a method of changing a signal range of an image signal by changing a readout time.

FIG. 4 is a block diagram showing a schematic configuration of a solid-state radiation detector (optical readout system) according to an embodiment of the present invention; a perspective view (A), an XZ sectional view (B), and an XY sectional view (C). )

FIG. 5 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 10,50 radiation solid state detector 20,56 solid state detector 30,70 readout circuit 40,45 readout time control means 80 photo timer (dose detection means)

Continued on the front page F-term (reference) 2G088 EE01 FF02 GG09 GG20 GG21 JJ05 KK11 KK18 KK32 LL11 LL15 4M118 AA10 AB10 BA05 CA02 CB11 DD02 DD09 FB09 FB13 FB16 FC02 GA10 5C024 AA12 BA00 CA15 EA04 GA01 JA04

Claims (13)

[Claims] 1. A charge reading method for a solid-state radiation detector for reading electric charges carrying radiation information stored in a large number of solid-state detection elements and acquiring an electric signal representing the radiation information, wherein: A charge reading method, wherein a reading time of accumulated charges is controlled according to a dose of radiation incident on the solid-state radiation detector. 2. The charge reading method according to claim 1, wherein the control is performed such that the maximum value of the electric signal is constant regardless of the dose. 3. The charge readout method according to claim 1, wherein the dose is detected by a dose detection unit provided separately from the solid-state detection element for acquiring the electric signal. 4. A method according to claim 1, wherein a part of the electric charge stored in said solid state detection element is read out in a time shorter than a reading time for obtaining said electric signal, prior to reading out for obtaining said electric signal. 3. The charge reading method according to claim 1, wherein the control is performed according to a charge amount of the read charge. 5. In the case where the radiation solid state detector is an optical readout type detector that performs charge readout by irradiating readout light, the electric signal is read before the electric signal is obtained. By irradiating the solid-state radiation detector with pre-read light having a smaller amount than the amount of read light for acquiring, a part of the electric charge accumulated in the solid-state detection element is read, and the electric charge amount of the read electric charge is read. 3. The charge readout method according to claim 1, wherein the control is performed according to the following. 6. A method according to claim 1, wherein a part of the electric charge stored in said solid-state detection element is read, an electric signal corresponding to the electric charge is obtained, and said control is performed according to a maximum value of the obtained electric signals. 6. The charge readout method according to claim 4, wherein: 7. A charge reading device for a solid-state radiation detector for reading electric charges carrying radiation information accumulated in a solid-state detection element and acquiring an electric signal representing the radiation information, wherein the electric charge is stored in each of the solid-state detection elements. A charge readout device comprising readout time control means for controlling a readout time of the charged electric charge according to a dose of radiation incident on the radiation solid state detector. 8. A solid-state detecting element for receiving radiation and accumulating electric charges carrying radiation information, and reading means for reading out the electric charges accumulated in the solid-state detecting element and acquiring an electric signal representing the radiation information. A solid-state radiation detector comprising read-out time control means for controlling a read-out time of electric charges stored in each of the solid-state detection elements according to a dose of radiation incident on the solid-state radiation detector. Radiation solid state detector. 9. The radiation solid-state detection device according to claim 8, wherein the read-out time control means performs the control so that the maximum value of the electric signal is constant regardless of the dose. vessel. 10. A radiation detecting means for detecting a radiation dose incident on said radiation solid state detector is provided separately from said solid state detecting element for acquiring said electric signal. The solid-state radiation detector according to the above. 11. The read time control means according to claim 1, wherein a part of the electric charge stored in said solid state detection element is read out from said read time for obtaining said electric signal before said read for obtaining said electric signal. 10. The solid-state radiation detector according to claim 9, wherein the readout is performed in a short time, and the control is performed in accordance with the amount of the read-out charges. 12. An optical readout type detector in which the solid-state radiation detector performs charge readout by irradiating readout light, wherein the readout time control means performs reading for obtaining the electric signal. Previously, one of the charges accumulated in the solid-state detection element obtained by irradiating the radiation solid-state detector with a pre-read light having a lower amount than the light amount of the read light for acquiring the electric signal. The solid-state radiation detector according to claim 9, wherein the control is performed in accordance with the amount of charge of the unit. 13. The read-out time control means reads out a part of the electric charge stored in the solid-state detection element, acquires an electric signal corresponding thereto, and responds to a maximum value of the acquired electric signal. The radiation solid state detector according to claim 11, wherein the control is performed by using the radiation solid state detector.