RADIATION IMAGE DETECTING APPARATUS

Abstract: The apparatus has X-ray sensors 1 each associated with an analogue amplifier 22, a pulse discriminator 23 and a picture element signal-forming circuit 24. The amplifier 22 is kept free of temperature variation by means of a heater 21 which is energized through switch 9 from source 7a except when an X-ray image is detected and the circuits 23 and 24 are switched on. The heat from 21 is equivalent to the heat dissipation of circuits 23 and 24 while they are in use. Alternative arrangements for maintaining a stable temperature in apparatus which has a linear array of sensors movable to scan a plane comprise a cooling means such as a heat sink or air blower at a rest position at one or both ends of the scanning path.

Description: Background of the Invention The present invention relates to a radiation image detecting apparatus having its radiation receiving section made up of arrayed radiation sensors. In a method of electronically detecting a radiation image, the radiation receiving portion consists either of one-dimensionally arrayed radiation sensors devised as to scan an image plane or of two-dimensionally arrayed sensors fixed at an image plane. Each of the radiation sensors is either a single semiconductor sensor or a radiation scintillator combined with a photosensor. In any case each sensor, which converts the radiations incident thereon to electric pulse signals, is followed by an amplifier, a signal discriminator and a counter. The counter counts the number of the pulse signals (pulses) outputted from the counter in the form of a digital signal. Similar radiation intensity signals from all of the counters belonging the arrayed radiation sensors are purposefully treated by a common picture-signal forming circuit, which provides a picture signal to a CRT to make it display a radiation image. Radiation image detecting apparatus based on such a method as mentioned above are disclosed, for example, in the Japanese Laid-open Patent Application No. 59-94046 and European Patent Publication EP-0-137-487-A2. The apparatus devised as mentioned above have an important problem to be solved in regard of protecting the constituent circuits from being unfavorably affected by the heat dissipated by the circuits themselves. Suppose that the power comsumption per sensor consists of 140 mW at the amplifier, 100 mW at the signal discriminator and 10 mW at the counter, making a total of 250 mW. A one-dimensional array of 1000 sensors, for example, causes an overall heat dissipation of 250 W. This value estimated with 1000 sensors supposed may further increase by several times to some hundred times or more, if the sensors are increased in number for making the image resolving power higher or for constituting the arrayed sensors in two-dimension. In case the radiation image to be detected is, for instance, an X-ray image for diagnosis, one shot of the detection takes only one second or less, and therefore, if a very small number of images are enough for the diagnosis, there is no problem in substance. It is, however, not rare that several tens of images are needed for the diagnosis of one desease. In such a case, if competent measures are not provided to protect the circuits from the heat effect, a series of the X-ray image detection work must be interrupted frequently for cooling the circuits. This not only lowers the efficiency of the image detection work but also keeps the patient under an unpleasant condition for a long time. Objects and Summary of the Invention The present invention aims at solving such a disadvantageous problem as mentioned above with respect to the known radiation image detecting apparatus having its radiation receiving section made up of arrayed radiation sensors, and makes it an object to provide such an apparatus improved in protecting the constituent circuit from the unfavorable heat effect. Another object of the present invention is to constitute such an improved apparatus so that the same may be operated continuously for a long time. A further object of the present invention is to make it possible to apply the merits of the invention both to the apparatus in which said arrayed radiation sensors form a two-dimensional matrix-shaped radiation receiving plane and to the apparatus in which said arrayed radiation sensors form a one-dimensional (linear) radiation receiving element made to sweep an image plane on which a radiation image to be detected is formed. To achieve the above objects, a radiation image detecting apparatus according to one of the claims 1 to 3 is provided. Brief Explanation of the Drawings The present invention is further desscribed in detail in the following on reference to the accompanying drawings, in which: Fig. 1 shows a block diagrammatic construction of the unit circuit per sensor used in an embodiment of the present invention; Fig. 2 shows a block diagrammatic construction of the unit circuit per sensor used in another embodiment of the present invention; Fig. 3 shows a block diagrammatic construction of the unit circuit used in a further embodiment of the present invention; Detailed Description of the Invention Referring to Fig. 1, which shows one X-ray detecting unit, an X-ray sensor 1 (corresponding to one picture element a pixel) composed of a single X-ray sensing device is accompanied by an analog amplifier 2, a pulse discriminator 3 (analog circuit) and a picture (element) signal forming circuit 4, which is a digital circuit with a counter included therein. Many such X-ray detecting units as shown in Fig. 1 are assembled with the X-ray sensors 1 arranged in the form of a matrix, on which an X-ray image to be detected is projected. In the above constitution of the X-ray detecting unit (Fig. 1) the X-ray sensor 1, biased with a negative voltage of several tens to hundreds of volts through a bias terminal 1a, outputs an electric pulse signal consisting of pulses whose number is equal or proportional to the X-ray photons incident on the sensor 1. The pulse signal outputted from the X-ray sensor 1 is amplified by the amplifier 2 and then inputted to the pulse discriminator 3, which trims the height and ground level of the pulses and then outputs them toward the picture element signal forming circuit 4. This circuit 4 makes a picture element signal in the form of a digital signal from the pulse signal originally outputted from the X-ray sensor 1. Such picture element signals from all of the X-ray detecting units assembled with their X-ray sensors constituting the X-ray image receiving plane are used to display a detected X-ray image on a CRT (not shown). The circuit leading the picture element signals to the CRT from the picture element signal forming circuit 4 is not shown in Fig. 1, because it has no relation to the description of the features of the present invention. In the above-described process of signal treatment, the performance of the analog amplifier 2 is expected to be very stable because, for instance, a small zero-level drift due to temberature variations may cause the amplifier 2 to misdetect the pulse signal from the X-ray sensor 1. On the other hand, the pulse discriminator 3 and the picture element signal forming circuit 4 are not so sensitive to temperature. Therefore, it is very important for a reliable operation of the apparatus to keep the amplifier 2 as free as possible from temperature variations. Since such temperature variations are caused mainly by intermittent switching the power to the circuit, namely, to the amplifier 2 in the present case, the embodiment shown in Fig. 1 is devised so that the amplifier 2 and the group of other circuits 3 and 4 may be separately supplied with power. For the purpose, power supply lines 2a and 2b to the amplifier 2 are connected to a power source 7 only through a main switch 6, whereas the pulse pulse discriminator 3 and picture element signal forming circuit 4 are power-supplied through both the main switch 6 and another switch 5 located inside the main switch 6. In such a wiring constitution of the power supply, it is possible to keep only the amplifier 2 always at a substantially constant temperature, though higher than an ambient temperature, by keeping the switch 6 turned on even while the apparatus is standing by for detecting one image in a series of many X-ray images to be detected. On the other hand, the pulse discriminator 3 and the picture element signal forming circuit 4 are power-supplied through the switch 5 only when an X-ray image is practically detected. The amplifier 2 is thus protected from the adverse effect of temperature variations, assuring the apparatus to function properly and reliably. Fig. 2 shows a modification of the embodiment shown in Fig. 1 In this modified embodiment, the amplifier 2 has its bias controlled by a bias control circuit 2c, which, devised to operate synchronously with the operation of the switch 5, lowers the bias current of the amplifier 2 while the apparatus is standing-by for image detection. The lowering of the bias current saves energy consumption and decreases the temperature rise in average. A reference sign 2d represents a terminal for receiving a bias control instruction signal. Another embodiment, which is suitable for constituting the electronic circuit portion of the X-ray detecting unit in the form of a monolithic integrated circuit, is described in the following on reference to Fig. 3. Blocks 22, 23 and 24 represent integrated circuits corresponding respectively to the amplifier 2, pulse discriminator 3 and picture element signal forming circuit 4 of Fig.1, and constitute the electronic circuit portion 8 of an X-ray detecting unit. An enclosure-shaped element 21 is a heating element characteristic of this embodiment. The heating element 21 is made of a resistive or semiconductive material deposited around the amplifier portion 22 so as to enclose the same. In such constitution of the whole circuit, the amplifier 22 is kept always power-supplied directly from a power source 7a, while the other circuit portions 23 and 24 are energized with a switch 9 turned to a contact 9a only when an X-ray image is detected. The heating element 21 is kept switched off during the detection of an X-ray image. On the other hand, while the aparatus is standing for the next detection of X-ray images, the switch 9 is turned to a contact 9b to supply power to the heating element 21, making the same generate a heat necessary to keep the amplifier 22 at a constant tremperature substantially equal to the temperature when the amplifier 22 was warmed also by the heat dissipation from the circuit portions 23 and 24. In the present embodiment, the heating element 21 can be constituted in the form of a power transistor. In the descriptions regarding to the above embodiments, the temperature-sensitive circuit portion which is to be kept at a constant temperature has been restricted to an amplifier. It goes without saying, however, that the above-described measures for keeping a circuit at a constant temperature may be applied to any other circuits. As is easily understood from the above descriptions, the present invention improves the X-ray image detecting apparatus with arrayed X-ray sensors so as to function stably without intermission during a substantially continuous operation for detecting a series of many X-ray images.

Claims: A radiation image detecting apparatus comprising radiation sensors (1) arrayed so as to form a radiation image receiving plane, and signal-treating circuits (22, 23, 24) for converting signals outputted from said radiation sensors (1) to an image signal to be displayed on a CRT, each of said signal treating circuits (22, 23, 24) being divided into a temperature-sensitive circuit portion (22) and a temperature-insensitive circuit portion (23, 24) CHARACTERIZED in that said temperature-sensitive circuit portion (22) is provided with a heating element (21) for keeping said temperature-sensitive circuit portion (22) at a temperature substantially equal to an operating temperature even when said apparatus is kept on standby as a whole with said temperature-insensitive circuit portion (23, 24) switched off, said heating element (21), energized only when said temperature-insensitive circuit portion (23, 24) is kept switched off, generating a heat having on said temperature-sensitive circuit portion (21) the same thermal effect as said temperature-insensitive circuit portion (23, 24) in operation has on said temperature-sensitive circuit portion (21). An apparatus as defined in claim 1, wherein said heating element (21) is made of an electrically resistive material. An apparatus as defined in claim 1, wherein said heating element (21) is made of an electrically semiconductive material.

Inventors: KIRI, MOTOSADA, MATSUOKA, TAKESHI
Applicants: SHIMADZU CORPORATION
Application year: 1987
Main classification: G03B42
IPC codes: A61B6, H04N1, G01T1, H04N5, G21K5