JP2014166578A - Radiation imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation imaging system which uses a communication channel having the possibility of data disappearance and delay for synchronous signal communication between an X-ray generator and an imaging apparatus.SOLUTION: An X-ray generator 3 dispatches a radiation permission demand signal, and an imaging apparatus 1 performs preparatory operation on receiving it, and returns a permission signal simultaneously with the start of image receiving operation. The X-ray generator 3 starts irradiation on receiving the permission signal, but a time limit is set for a time difference from the generation of the permission demand signal to receipt of the permission signal, and the permission signal delayed over the time limit is invalidated. The X-ray generator 3 is limited not to irradiate radiation ray exceeding the predetermined maximum time, and the imaging apparatus 1 has capability of storing received image at least during the time "time-out period+the maximum irradiation time-the preparatory operation time".

Description

  The present invention relates to a radiographic imaging system that acquires an intensity distribution of radiation that has passed through an object as an image.

  Conventionally, a method of irradiating an object with radiation, detecting an intensity distribution of the radiation transmitted through the object, and obtaining a radiation image of the object is widely used in industrial nondestructive inspection and medical diagnosis. The most common method for obtaining a radiographic image of an object is to combine a so-called fluorescent screen (or intensifying screen) that emits fluorescence with a radiation and a silver salt film, and to transmit the radiation through the object. This is a method for obtaining a visible image by irradiating and converting radiation to visible light with a fluorescent plate to form a latent image on the silver salt film and then chemically treating the silver salt film. The radiographic image obtained by this imaging method is a so-called analog photograph, and is used for diagnosis, examination and the like.

  In addition, a computed radiography apparatus (CR apparatus) using an imaging plate (IP) coated with a stimulable phosphor as a phosphor has begun to be used. When IP is primarily excited by radiation irradiation and is subjected to secondary excitation by visible light such as red laser light, light emission called stimulable fluorescence occurs. The CR device acquires a radiation image by detecting this light emission with an optical sensor such as a photomultiplier tube, and outputs a visible light image to a photographic material or a CRT based on this image data. Although the CR device is a digital device, it is an indirect digital radiography device that requires an image forming process of readout by secondary excitation.

Recently, a technique for acquiring a digital image by using a photoelectric conversion device in which pixels including minute photoelectric conversion elements, switching elements, and the like are arranged in a lattice form as an image receiving means has been developed.
Patent Documents 1 to 5 disclose radiation imaging apparatuses in which phosphors are stacked on a two-dimensional imaging element made of CCD or amorphous silicon. These photographing devices can display the acquired image data immediately, and are called direct digital photographing devices.

  Advantages of the digital photographing device over the analog photographic technology include filmlessness, expansion of acquired information by image processing, creation of a database, etc., and advantages of the direct digital photographing device over the indirect digital photographing device include immediacy. As described above, the ability to display a photographed image on the spot is extremely useful in a medical site that requires urgent action.

  However, since there is a dark current that contributes to noise in the two-dimensional solid-state imaging device, the imaging time cannot be increased unnecessarily. For this reason, signals are exchanged between the X-ray generator and the digital imaging apparatus directly, and the X-ray irradiation and the imaging timing of the solid-state imaging device are synchronized. Specifically, in response to the imaging request signal from the X-ray generator, the imaging apparatus initializes the solid-state imaging device, and after this is completed, the imaging preparation completion signal is transmitted to the X-ray generator. Starts X-ray irradiation. When the X-ray irradiation is completed after the irradiation time set in the X-ray generation apparatus has elapsed in advance, an irradiation end signal is transmitted from the X-ray generation apparatus to the imaging apparatus. In the photographing apparatus, the accumulation operation of the solid-state imaging device is ended, and the operation mode is shifted to the image data output operation.

  If an error occurs in the signal path and an erroneous imaging preparation completion signal arrives at the X-ray generator, the result of X-ray irradiation before initialization of the solid-state imaging device of the imaging apparatus is completed. Become. If an erroneous irradiation end signal reaches the imaging apparatus, the solid-state imaging device starts an image data output operation even though X-ray irradiation continues. In any case, the X-rays irradiated during the period when the accumulation operation is not performed are not reflected in the image data, and thus the subject has received unnecessary exposure.

  As described above, since the synchronization signal between the X-ray generation apparatus and the imaging apparatus is an important signal, there is a need for a device that minimizes errors and timing shifts. Specifically, an independent signal line is provided for each meaning of the signal, a differential signal line is used, a shield wire is added to the cable, an input circuit with hysteresis is used, and spike noise is not misidentified. Band filters and an increase in the number of samplings.

  If an independent signal line is provided or a shield is added, the thickness of the cable will increase, and the thick cable will make it difficult to lay in the building, making installation and maintenance difficult. To do.

  By the way, a signal transmission line having characteristics completely opposite to those of the dedicated signal line, that is, a signal having various meanings is carried on one signal line, and a shield is not usually used, and it is easy to lay with a thin cable. Many signal transmission paths are used. A typical example is the transmission standard defined in the IEEE 802.3 standard of Non-Patent Document 1. In particular, variations using UTP (Unshielded Twist Pair) cables are purchased by individuals and installed in the home by themselves. It is showing widespread use.

  In this transmission standard, a plurality of terminals are connected to the same signal transmission path to form a network. The same transmission line may be a virtual identical transmission line that is DC-electrically separated and bridged by semiconductor switch means, and transmits and receives a serial signal with an error detection code. Each terminal can start outputting at an arbitrary timing as long as other terminals are not outputting. If a plurality of terminals output simultaneously, an error occurs in the signal and the signal is discarded. Similarly, when an error occurs in a signal due to an external factor, the signal is similarly discarded.

  Because of these characteristics, this transmission standard does not guarantee that the signal will reach the other party reliably, and recognizes the possibility of the signal disappearing without being noticed by either the sending side or the receiving side. I do not have. However, when the transmission side notices the loss of a signal, it has a mechanism for trying to retransmit and a mechanism for preventing an erroneous signal from reaching. Further, only one signal can exist on a transmission line at a certain moment, and even if a plurality of requests for transmitting signals are generated at the same time, it is necessary to send them sequentially on the transmission line. However, the transmission standard itself does not define anything about signal ordering and multiplexing.

  As described above, IEEE 802.3 does not guarantee the reliable transmission of signals, so that it is necessary to devise another way to exchange signals with certainty using this. Also for multiplexing, a mechanism is required in which a plurality of independent signals are sequentially sent out to one transmission line and reproduced as independent signals without being mixed on the receiving side. Non-Patent Document 2 TCP (Transmission Control Protocol), Non-Patent Document 3 UDP (User Datagram Protocol) are indispensable technologies as solutions including these problems and some functions. Protocol. These protocols are widely used as basic technologies for the Internet.

  A solution to the reliable transmission problem described above is provided by TCP. TCP is a protocol for delivering a series of data streams to the other party in order so as not to cause a missing part in the middle. Since this protocol requires a response for confirming that data has arrived at the other party, even if the transmission direction of the data itself is one direction, physically two-way signal transmission is performed.

  If a packet containing data does not reach the other party, or if the packet sent back by the receiver does not return correctly to the sender, the sender will resend the previous packet with a response timeout. . Thus, in TCP, when a communication error occurs, it takes time for an actual signal to arrive at the receiving side.

  On the other hand, in UDP, a mechanism for packet retransmission based on a response or timeout such as TCP is not defined, and reliable signal transmission is not guaranteed. Instead, the signal is transmitted in the shortest time except for the delay time occurring in the lower layers. Note that a mechanism for setting a plurality of virtual communication paths between transmission and reception ends includes both TCP and UDP, and this mechanism is called a port number.

  As is clear from the above example comparing TCP and UDP, in general, serial communication paths can be used practically by accepting an unexpected increase in transmission delay time when an error occurs and ensuring the content transmission. It is necessary to select one of the means for ensuring the immediacy of transmission by accepting the loss of the signal due to the occurrence of an error according to the nature of the application. In addition, between the two may be adopted by adjusting parameters such as limiting the maximum number of retransmissions.

US Pat. No. 5,418,377 US Pat. No. 5,396,076 US Pat. No. 5,381,014 US Pat. No. 5,132,539 U.S. Pat. No. 4,810,881 Japanese Patent No. 3413084

802.3TM IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements Part 3: Carriersense multiple access with collision detection (CSMA / CD) access method and physical layer specifications RFC 793-Transmission Control Protocol RFC 768-User Datagram Protocol

  As described above, the conventional digital radiography system has problems of space saving and easy installation of wiring between devices. This is an issue that means that the wireless connection is completely abolished ultimately.

  On the other hand, cheap and easy laying connection means for communication between electronic devices already exist in general, but these technologies have not been linked to date. The reason for this is that while the radiography system requirements have a very low error transmission rate and stable propagation delay time, wireless communication technology does not increase the error rate. This is because it is covered by error detection and retransmission, and as a result, the propagation delay time changes dynamically. This has the same technical idea even in a wireless LAN communication standard using a digital wireless device that has become popular in recent years.

  When the operation of a transmission standard such as IEEE 802.3 is actually confirmed, it is designed to reduce the load in advance, and a large number of retransmissions and delays hardly occur in the connected network. In many cases, the propagation time in one network is limited to a range that can be assumed to be almost immediate.

  Also, in digital imaging devices, efforts are constantly made to improve and stabilize detector performance, and although it is not always possible to receive images, it is possible to maintain the image reception state sufficiently longer than the irradiation time of general imaging methods. It has become. This means that the timing synchronization between the X-ray generator and the imaging apparatus is practical even if there is a certain amount of error.

  Therefore, it can be seen that even when these two technologies are combined, a good operation is exhibited without problems in many situations. In other words, even if a signal propagation delay occurs and there is a difference between the image reception start time and the irradiation start time, the performance of the X-ray detector has been improved. There is no problem even if the image receiving state is extended in advance.

  However, in extremely limited scenes, for example, when disturbances such as noise are applied to the transmission line, it is inevitable that retransmission due to an error will occur and suddenly a large delay time will occur. In such a case, since synchronization is not correctly performed, there is a possibility that X-rays may be irradiated beyond the receivable time unless any countermeasure is taken. When it is detected that the synchronization is not correctly performed, the X-ray generator needs to be controlled so as not to start the irradiation operation.

  An object of the present invention is to solve the above-mentioned problems and to capture an X-ray irradiation period while performing timing synchronization between the X-ray generation apparatus and the imaging apparatus using a communication path whose transmission delay time changes dynamically. An object of the present invention is to provide a radiographic imaging system that operates so as to be within an image receivable period of the apparatus and restricts the X-ray irradiation not to be performed when the operation cannot be guaranteed.

  In order to achieve the above object, a technical feature of the radiographic imaging system according to the present invention is a radiographic imaging system including an X-ray generation device, an imaging device including a radiation detector, and a communication path therebetween. A trigger input means for inputting a trigger by an operator in real time at the moment when radiation is to be irradiated is connected to the X-ray generator, and the X-ray generator outputs an irradiation permission request signal when the trigger is input; The image is transmitted to the imaging apparatus through a communication path, and the imaging apparatus returns an irradiation permission signal through the communication path when the image receiving operation of the radiation detector is enabled after receiving the irradiation permission request signal. The generator is to start X-ray irradiation upon receipt of the irradiation permission signal.

  According to the radiographic imaging system of the present invention, apparatuses are connected using a communication path that may cause errors, signal loss, and signal propagation delay, and the X-ray generator and imaging apparatus are synchronized through the communication path. Even when signals are transmitted and received, the X-ray irradiation period is set within the image receivable period. Further, if the propagation delay becomes large and the irradiation period may not fit within the image receivable period, the irradiation itself is not permitted.

  For this reason, it is possible to eliminate the possibility of excessive exposure while improving the ease of handling of the device by means of wired connection means that can be easily installed and routed and wireless communication.

It is a block diagram of a radiography system. It is an operation | movement flowchart figure. It is a timing chart figure at the normal time. It is a timing chart figure at the time of permission request signal delay. It is a timing chart figure at the time of permission signal delay. It is a timing chart figure at the time of timeout. It is a timing chart figure at the time of trigger re-input.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 shows a configuration diagram of a radiation imaging system according to the present invention. An X-ray tube 2 is arranged above an imaging device 1 incorporating a radio, and this X-ray tube 2 is connected to an X-ray generator 3. Further, it is connected to the network connection box 5 and the network device 6 via the UTP cable 4. A wireless access point 7 is connected to the network device 6 and performs wireless communication with the photographing apparatus 1. The network connection box 5 and the X-ray generator 3 are connected in the same manner as in the past, but since the network connection box 5 is installed adjacent to the X-ray generator 3, the range of the conventional connection is as follows. Most of the connections are made with the UTP cable 4. In this network, a network device 6 and a UTP cable 4 corresponding to the 100BASE-TX standard are used.

  The imaging apparatus 1 includes a flat panel X-ray detector (FPD) inside. The X-ray detector is configured to perform a preparatory operation before X-ray irradiation, and then shift to an accumulation mode to accumulate image data in the sensor, and then read the accumulated image charges to form image data. Has been. The preparatory operation is performed in order to discharge dark current charges accumulated in the sensor in advance, and is necessary for improving the image quality and ensuring the dynamic range. Further, it is required to improve the image quality by reading out the image data after the accumulation is completed and before the excessive dark current charge is accumulated.

  FIG. 2 is an operation flowchart, and an irradiation switch is attached to the X-ray generator 3. In step S1, the operator presses the irradiation switch in accordance with the timing to be imaged. Even if this irradiation switch is pressed, X-rays are not immediately emitted from the X-ray tube 2, and the network connection box 5 of the X-ray generator 3 is notified that the irradiation switch has been pressed.

  In step S2, the X-ray generator 3 and the network connection box 5 newly generate a request signal ID, and transmit an irradiation permission request signal including the request signal ID to the imaging apparatus 1. As the request signal ID, for example, the current time of a clock in the network connection box 5 is used.

  The irradiation permission request signal reaches the photographing apparatus 1 wirelessly via the network device 6 and the wireless access point 7. At this time, depending on the frequency of other signals relayed by the network device 6 or the wireless access point 7, a delay may occur because the signals are temporarily stored and then relayed. In addition, sudden external noise may cause an error in the signal and be discarded on the receiving side.

  When the imaging apparatus 1 receives the irradiation permission request signal in step S3, the imaging apparatus 1 performs a preparation operation for the internal X-ray detector. Send to. At this time, the ID included in the irradiation permission request signal is copied and included in the permission signal. The irradiation permission signal is delivered to the network connection box 5 via the wireless access point 7 and the network device 6, and the occurrence of delay at this time is the same as described above.

  When the network connection box 5 receives the irradiation permission signal, the network connection box 5 gives the irradiation permission to the X-ray generator 3 through the conventionally connected UTP cable 4. In step S5, the X-ray generator 3 measures time starting from the time when the irradiation permission request signal is transmitted. If the irradiation permission signal can be received within the time-out period, X-ray irradiation is started from that time. At this time, it is not valid as a permission signal unless it is an irradiation permission signal including the same ID as the transmitted one. If the permission signal cannot be received within the time-out period, irradiation is not started even if the permission signal is subsequently received.

  The X-ray generator 3 has a time-out time so that the irradiation does not continue beyond a predetermined maximum irradiation time after starting the irradiation of radiation. The photographing apparatus 1 knows the timeout time and the maximum irradiation time in advance, and after starting the image receiving operation, the time after “timeout time + maximum irradiation time” starts from the time when the irradiation permission request signal is received. Up to this time, at least the image receiving operation is continued, and thereafter the X-ray detector reading operation is started.

  When the operator re-inputs the trigger, another irradiation permission request signal is sent, but the ID at this time is generated to be different from the previous ID. The ID is not reused until a sufficient time has passed. Thereby, even if the permission signal corresponding to the previous permission request signal arrives after the trigger is re-input, irradiation is not started.

  The time adjustment may be predetermined as a constant, or may be dynamically adjusted by a dosimeter attached to the X-ray tube 2, a phototimer detector sandwiched between the imaging apparatus 1 and the subject, or the like. However, in any case, the maximum time is not exceeded.

  When the photographing apparatus 1 shifts to the image accumulation mode, it continues this for a predetermined time. This connection time is determined by “timeout time + maximum irradiation time−preparation operation time”. When the period of the accumulation mode expires, the imaging apparatus 1 reads image data from the internal X-ray detector.

  FIG. 3 shows the exchange of the irradiation permission request signal and the irradiation permission signal, and the respective operations of the X-ray generation device 3 and the imaging device 1 arranged along the time axis. This is when the irradiation permission signal returns with a margin for the timeout time of the X-ray generator 3. The accumulation operation time on the photographing apparatus 1 side lasts for “timeout time + maximum irradiation time−preparation operation time”. It can be seen that the X-ray irradiation period of the X-ray generator 3 in FIG. 3 is completely within the accumulation operation period.

  FIG. 4 and FIG. 5 also show similar time charts, and illustrate two types when the irradiation permission signal is returned just before the timeout time. FIG. 4 shows a case where there is a delay in the transmission of the irradiation permission request signal and the transmission of the irradiation permission signal is instantaneous. In this case as well, the X-ray irradiation period is within the accumulation operation period.

  On the contrary, FIG. 5 shows the case where the transmission of the irradiation permission request signal is instantaneous, but there is a delay in the transmission of the irradiation permission signal. In this case as well, the X-ray irradiation period is within the accumulation operation period. .

  FIG. 6 is a time chart when the irradiation permission signal does not reach within the timeout time. At this time, even if the operator keeps pressing the irradiation switch, the network connection box 5 does not give the permission signal to the X-ray generator 3, so X-rays are not irradiated. In order for the operator to attempt X-ray irradiation again, it is necessary to release the irradiation switch and then press the irradiation switch again. Although not specifically described with reference to the drawings, even when one of the two signals disappears, irradiation is not performed due to a timeout.

  FIG. 7 shows a time chart when a time-out occurs due to a significant delay in the signal and the operator re-inputs the irradiation switch. By re-input, an irradiation permission request is made using an ID different from the previous one. A signal is generated and transmitted. The previous permission signal that has been delayed significantly arrives later, but is ignored because the ID is different, and irradiation is not started at this point.

  On the other hand, in response to the new arrival of the irradiation permission request signal, the imaging apparatus 1 cancels the accumulation operation and performs a re-preparation operation, and returns the irradiation permission signal. The ID at this time is the received new request The signal ID is attached. Irradiation is started from the X-ray tube 2 only after this ID arrives at the X-ray generator 3.

  As described above, some examples of cases where irradiation is performed and cases where it is prohibited are given. In any case, after X-ray irradiation is completed in the case where irradiation is performed, from the X-ray generation device 3 An irradiation end signal is generated and transmitted to the photographing apparatus 1. When the imaging apparatus 1 receives this signal during the accumulation time, the imaging apparatus 1 may shorten the planned accumulation period and end at that point.

  In addition, image data is read from the X-ray detector after the accumulation time is completed regardless of whether irradiation has been performed. This indicates that it is possible to read image data from the X-ray detector even though X-rays were not actually irradiated, but this does not compromise the safety of the subject. There is no adverse effect on the device.

  The present invention is not limited to this embodiment, and various applications are conceivable. For example, the maximum irradiation time and the time-out time are not described as being changeable in the present embodiment, but it is only necessary to share numerical values between the imaging apparatus 1 and the X-ray generation apparatus 3 prior to imaging. There is no hindrance if possible.

  Further, although the present embodiment has been described with respect to the still image shooting system, it may be used with respect to a moving image shooting apparatus. In this case, the preparation operation period is replaced with the preparation period of the moving image photographing apparatus, and the accumulation time is replaced with, for example, repeated reading of frame data from the moving image sensor and capture into the memory.

DESCRIPTION OF SYMBOLS 1 Imaging device 2 X-ray tube 3 X-ray generator 4 UTP cable 5 Network connection box 6 Network equipment 7 Wireless access point

Claims (8)

  A radiographic imaging system including an X-ray generation apparatus, an imaging apparatus including a radiation detector, and a communication path between them, and trigger input means for inputting a trigger by an operator in real time at the moment when radiation should be irradiated Is connected to the X-ray generator, and when the trigger is input, the X-ray generator transmits an irradiation permission request signal to the imaging apparatus through the communication path, and the imaging apparatus transmits the irradiation permission request signal. When the image receiving operation of the radiation detector becomes possible after receiving the radiation, an irradiation permission signal is returned through the communication path, and the X-ray generator starts X-ray irradiation upon reception of the irradiation permission signal. Radiation imaging system.   In the X-ray generator, an irradiation permission time-out time is set, and after the irradiation permission time-out time has elapsed since the irradiation permission request signal is issued, the irradiation permission signal is received so that irradiation is not started. The X-ray generation device determines the maximum irradiation time, limits the maximum length of irradiation, and notifies the imaging device in advance of the irradiation permission timeout time and the maximum irradiation time. The radiographic image capturing system according to claim 1.   The imaging apparatus sets at least the image receivable period of the radiation detector (irradiation permission timeout time + maximum irradiation), where t is the time from when the irradiation permission request signal is received until the irradiation permission signal is returned. The radiographic imaging system according to claim 1, wherein the radiographic imaging system has a capability of lasting only for time-t).   The irradiation permission request signal includes an ID whose content changes each time a signal is transmitted, and is included in the irradiation permission request signal when the imaging apparatus returns the irradiation permission signal to the irradiation permission request signal. The radiographic imaging system according to any one of claims 1 to 3, wherein a copy of the ID that is included is returned in the irradiation permission signal.   The X-ray generator stores the ID when transmitting the irradiation permission request signal by the trigger input means, and within the irradiation permission timeout time when receiving the irradiation permission signal not including the ID. Even if irradiation is not started, the radiographic imaging system of Claim 4 characterized by the above-mentioned.   When the time during which a signal may stay on the communication path is Tr, and the minimum trigger interval that can be input from the trigger input means is Tc, the bit width representing the ID is a variation of the ID. It has a width that is sufficiently larger than the number represented by (Tr / Tc), and the X-ray generator generates the ID so that the same ID is not repeatedly used during the time Tr. The radiographic imaging system according to claim 4 or 5, characterized in that   The radiographic imaging system according to claim 1, wherein CSMA multiple access is performed on the communication path.   When the irradiation of radiation is finished, the X-ray generator transmits the irradiation end notification signal, and when the imaging apparatus receives the irradiation end notification signal, the image receiving operation is ended even within the image receivable period. The radiation image capturing system according to claim 1, wherein reading of the radiation detector is started.

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