JP3707924B2 - X-ray imaging device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an X-ray imaging apparatus. In particular, the present invention relates to an X-ray imaging apparatus that is used in an X-ray diagnostic apparatus for reducing the amount of X-ray irradiation to a subject, and also used in an industrial nondestructive inspection apparatus for the same kind of purpose.
[0002]
[Prior art]
As shown in FIG. 7, a conventional sensor for sensing light / X-rays is provided with an electrode 72 divided into each element constituting a matrix, a semiconductor layer 73 common to the elements, and a common electrode 74. The light / X-rays incident on the light are converted into electric charges, stored in the storage capacitor 75, and read out by driving the switching element 76. The single radiation sensor is also similar to the above sensor in that the charge generated in the semiconductor layer is read out in a matrix.
[0003]
On the other hand, in a so-called X-ray imaging apparatus for X-ray diagnosis, a minute X-ray sensor is provided on the front, rear, or vicinity of the X-ray film, and X-rays are generated by signals from the X-ray sensor. The X-ray generator is controlled to stop generating X-rays when a dose is detected. This is generally called a phototimer.
[0004]
[Problems to be solved by the invention]
However, these detectors only try to obtain images of X-rays that have been irradiated and transmitted through the subject, and there is no viewpoint of irradiating the minimum necessary X-ray dose. That is, the image quality of an X-ray image is affected by the incident X-ray dose. Generally, when the X-ray dose decreases, the fluctuation of the X-ray appears as photon noise, which affects the image quality. Although irradiation with a sufficient X-ray dose reduces photon noise, there is a problem that the exposure of the subject increases. In particular, an apparatus used for diagnostic purposes needs to minimize exposure to a subject.
[0005]
The present invention was devised to solve the above-described problems, and provides an X-ray imaging apparatus capable of obtaining an X-ray image with good image quality and minimizing exposure to a subject. There is.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray imaging apparatus of the present invention converts a semiconductor layer that converts X-ray energy into electric charge, or a scintillator that converts X-ray energy into light and light from the scintillator into electric charge. A semiconductor layer; a first electrode provided on one side of the semiconductor layer; a matrix-like second electrode provided on a surface opposite to the first electrode; and the second electrode; and A switching element provided in a matrix on a substrate, a charge storage capacitor connected to the second electrode and storing charges converted by the semiconductor layer, and a current flowing through the first electrode are integrated and integrated. Control means for emitting a signal when the amount (charge amount) reaches a specified value is provided.
[0007]
X-rays emitted by the X-ray generator pass through the subject and enter the imaging apparatus. X-rays pass through the first electrode, most of which is absorbed by the semiconductor layer, and the X-ray energy creates charges (electron-hole pairs).
[0008]
Alternatively, the X-rays are absorbed by the scintillator and emit fluorescence, and electric charges are generated by the semiconductor layer such as a photodiode by the fluorescence.
[0009]
X-ray two-dimensional image is obtained by sequentially scanning and reading out this charge with the second electrode and switching element, and when the amount of charge flowing through the first electrode reaches a specified value, a signal is output to generate X-rays. Transmission to the device or the like stops the generation of X-rays.
[0010]
【Example】
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram of an X-ray imaging apparatus according to the present invention, but the semiconductor layer 2 and the first electrode 1 which are layers common to the matrix are not shown. FIG. 2 is an explanatory view seen from a cross section. In FIG. 2, X-rays incident from the top pass through the first electrode 1 and are absorbed by the semiconductor layer 2 to form electron-hole pairs and generate charges. The generated charges are attracted to the opposite electrodes by the voltage applied to the semiconductor layer 2, and the charges are accumulated in each capacitor 4. As shown in the figure, there are a case where a positive voltage is applied to the first electrode 1 by the DC voltage source 12 and a case where a negative voltage is applied to the first electrode 1 as shown in FIG. Determined by lifetime and mobility.
[0011]
Signal readout is performed by sequentially driving the switching elements 5 connected to the second electrode 3 and the capacitor 4 and arranged in a matrix, so that the accumulated charge for each line enters the amplifier 9 through the readout line. A / D converter 11 passes through multiplexer 10 and is A / D converted.
[0012]
By the way, a detecting means 6 for measuring and integrating the current flowing through the first electrode and detecting the amount of charge is provided. This detection means is well known in the measurement field, and in particular, a measurement operational amplifier is generally used, but is not limited thereto. This output is input to the comparator circuit 8 and is compared with a signal from the circuit 7 for setting a specified value (threshold value), so that a signal is output when the amount of charge flowing through the first electrode reaches a specified value. Is output from the comparator circuit 8.
[0013]
The production method of the present invention will be described.
[0014]
A switching element and a second electrode provided in a matrix on a substrate are manufactured by a thin film technology used for home appliances such as a liquid crystal display. With this technology, a switching element having a TFT or MIM structure divided for each element, a second electrode connected to the switching element (which is also divided for each element), and a drive line for driving the switching element (For example, in the column direction) and data lines (for example, in the row direction) in which charges flow through the switching elements are formed. In general, the switching element is made of amorphous silicon or polysilicon, chemical materials such as nitride film, oxide film, and polyimide are used as insulators, and various materials such as chromium, tantalum, aluminum, and copper are already used as metal materials. Has been.
[0015]
A semiconductor layer is provided over the entire sensor on the second electrode. This layer may be a single continuous layer, or may be divided into several layers such as a matrix or a plurality of divided layers obtained by combining several matrices. As this material, a chalcogenide-based material such as selenium can be formed by vapor deposition, or silicon or a cadmium telluride alloy can be formed by CVD. In order to sufficiently absorb X-rays, the thickness of these semiconductor layers is preferably as thick as possible. The thickness is as low as 1 to 5 mm for silicon, 300 to 1000 μm for selenium, and 100 to 300 μm for cadmium telluride alloys.
[0016]
When X-rays are converted to fluorescence after being converted to fluorescence by a scintillator, most of the X-rays are absorbed by the scintillator. For example, the thickness of a cesium iodide scintillator doped with thallium or sodium is preferably 300 to 700 μm, and that of cadmium tungstate is preferably 200 to 500 μm. Various other materials are known for the scintillator.
[0017]
Further, a first electrode is provided over the semiconductor layer. In this material, ITO (Indium / Tin / Oxide) is most famous when the incident ray is light, but X-ray has high X-ray transmission power, so various thin film metal layers and alloys. It may be a layer.
[0018]
The first electrode 1 is divided into several parts, examples of which are shown in FIGS. FIG. 3 is an example in which the first electrode is not divided, and FIGS. 4 and 5 are examples in which the first electrode 1 is divided into appropriate shapes.
[0019]
FIG. 6 is a configuration example of the X-ray imaging apparatus when the first electrode is divided as shown in FIGS. 4 and 5, and the first electrode is divided into a desired shape, and the charge amount of each electrode Thus, a signal is output from the comparator circuit 21. For this purpose, a detection means 22 for detecting the charge amount is provided for each divided electrode to detect the charge amount and input it to the comparator circuit 21 or to collect a plurality of divided electrodes. There is a way to detect.
[0020]
In addition, a plurality of set values are set to a prescribed value (threshold value) setting circuit 23 corresponding to the number of detection means for detecting the charge amount, and each of them is compared and a signal is converted into a digital signal by an A / D conversion circuit. It can also be handled.
[0021]
This signal is transmitted as a signal for stopping the operation of the X-ray generator to an X-ray generator composed of an X-ray tube, a high voltage generator, etc., and if the generation of X-rays is stopped, exposure is reduced. A good X-ray image can be obtained.
[0022]
Since an ordinary X-ray generator has an X-ray on / off signal therein, the X-ray can be easily stopped by a simple logic circuit that superimposes this signal and the above signal.
[0023]
【The invention's effect】
According to the X-ray imaging apparatus of the present invention, since the generation of X-rays can be controlled while measuring the X-ray intensity transmitted through the subject, the X-ray generation can be stopped when an appropriate X-ray dose is reached. Further, exposure to the subject can be minimized, and an X-ray image with good image quality can be obtained. In addition, the operator of the apparatus can easily set the conditions of the X-ray generator.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an X-ray imaging apparatus according to the present invention.
FIG. 2 is a cross-sectional view of an X-ray imaging apparatus according to the present invention.
FIG. 3 is a diagram showing an example of the first electrode of the X-ray imaging apparatus of the present invention.
FIG. 4 is a diagram showing an example of the first electrode of the X-ray imaging apparatus of the present invention.
FIG. 5 is a diagram showing an example of the first electrode of the X-ray imaging apparatus of the present invention.
FIG. 6 is a diagram showing a modified embodiment of the X-ray imaging apparatus of the present invention.
FIG. 7 is a diagram illustrating a configuration of a conventional X-ray imaging apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st electrode 2 Semiconductor layer 3 2nd electrode 4 Capacitor 5 Switching element 6 Detection means 7 which detects electric charge amount Circuit 8 which sets a defined value (threshold) Comparator circuit 9 Amplifier 10 Multiplexer 11 A / D converter 12 DC voltage source 21 Comparator circuit 22 Circuit for setting a prescribed value (threshold value) 23 Detection means 72 for detecting charge amount Electrode 73 Semiconductor layer 74 Common electrode 75 Storage capacitor 76 Switching element

Claims (1)

A semiconductor layer that converts X-ray energy into electric charge, a scintillator that converts X-ray energy into light, a semiconductor layer that converts light from the scintillator into electric charge, and a first electrode provided on one surface of the semiconductor layer When the matrix of the second electrode provided on the opposite side to the first electrode leads and the second electrode, and a switching element provided in a matrix on a substrate, the second A charge storage capacitor connected to the electrode for storing the charge converted by the semiconductor layer; and a control means for generating a signal when the current flowing through the first electrode reaches a specified value. X-ray imaging apparatus characterized by

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