Abstract:
In a monitoring method and image processing apparatus for monitoring electronic transmission of an image, an image detector supplies an input image to a processing circuit that caches it in an image storage. The cached image, or an image derived therefrom, is forwarded as an output image to a viewing device, which outputs the image to a viewer. To monitor the image transfer, an insertion circuit upstream from the processing circuit inserts a dynamic input test signal into the input image. A test circuit downstream from the processing circuit tests whether the output image contains a dynamic output test signal corresponding with the input test signal. Given the absence of the dynamic output test signal, alarm notification is provided to the viewer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention concerns a method for monitoring electronic transmission of an image, of the type wherein an input image is supplied from an image detector to a processing circuit, the input image is cached (buffered) in an image storage within the processing circuit, and the cached image, or an image derived by the processing circuit using the cached image, is conveyed as an output image to a viewing device at which it is displayed. The present invention furthermore concerns an image processing apparatus to implement such a method, with a processing circuit with an image memory, an image detector upstream from the processing circuit, and a viewing device downstream from the processing circuit.  
         [0003]     2. Description of the Prior Art  
         [0004]     Monitoring methods and image processing apparatuses of the above type are generally known. They are used, for example, in medical image processing in the framework of a technique known as the road map method.  
         [0005]     In the road map method, the input image is generated in the image detector, normally from x-ray radiation. Suitable synchronization signals (hsync and vsync) are then added to the input image, and a video signal this is generated. The video signal is supplied to the image processing circuit and cached there in an input image memory.  
         [0006]     In the processing circuit, a reference image can be subtracted from the input image. The reference image normally is an image of the presently imaged subject notification, different from the output test signal is output to the viewer by the test circuit if the dynamic output test signal.  
         [0007]     Testing whether the dynamic output test signal differs from the dynamic input test signal encompasses testing whether the dynamic output test signal is present at all, i.e., whether it is absent from the output image.  
         [0008]     The object also is achieved by an insertion circuit that implements such a monitoring method that is fashioned as an assembly module for an image processing apparatus, in particular as a plug-in card.  
         [0009]     The above object also is achieved by an image processing apparatus to implement such a method, in which an insertion circuit is connected between the image detector and the processing circuit and a test circuit is connected between the processing circuit and the viewing device.  
         [0010]     The monitoring method operates particularly reliably when the input test signal is generated by the insertion circuit, but it is also possible for the input test signal to be supplied to the insertion circuit from the outside.  
         [0011]     The input test signal itself can be of an arbitrary nature as long as the actual input image is not, or is at least only insignificantly, affected, and the absence of the dynamic output test signal is can be recognized in good time. A simple possibility to insert an input test signal (which does not or only insignificantly affects the input image) I to insert the input test signal into the area of the image edge in the input image.  
         [0012]     In one embodiment the alarm notification is that the viewing device discontinues display of the output image, this prevents the viewer from ignoring the alarm notification. The alarm notification can further involve a direct through-switching of the input image supplied by the image detector to the viewing device, so that an unprocessed, but at least current, image is supplied to the viewer, as a replacement.  
         [0013]     As an alternative or in addition to the output image, or the use of the input image supplied by the image detector, a predetermined, in particular static alarm notice also can be output. For example, a notification having the content “Warning—no current image” can be output continuously or blinking at the viewing device.  
         [0014]     In an embodiment wherein the insertion circuit and the test circuit mutually monitor each other, and given detection of an error function of one of these circuits by the other circuit, a warning notification is output to the viewer by the other circuit, so the monitoring method operates even more securely. In particular in this case a relatively uncritical error can be detected in the insertion or test circuit before it can lead to a critical non-detection of the absence of the dynamic output test signal.  
         [0015]     In a further embodiment in the event of error, the function of the circuit that is detected as malfunctioning is taken over by the other circuit. This allows the monitoring method to be continued for a limited time—for example, until the end of an already running examination—since the probability of a second error in the remaining examination time is relatively low. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is an overview of an x-ray system and an image processing apparatus, constructed and operating in accordance with the invention.  
         [0017]      FIG. 2  is a block diagram of the image processing apparatus from  FIG. 1 .  
         [0018]      FIG. 3  is a flow chart of the inventive method.  
         [0019]      FIG. 4  is an example of an image presented at the display in accordance with the invention.  
         [0020]      FIG. 5  is a flow chart for the insertion of the input test signal in accordance with the invention,  
         [0021]      FIG. 6  illustrates an alternative embodiment of the image processing apparatus from  FIG. 2 .  
         [0022]      FIG. 7  shows an embodiment of the image processing apparatus from  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     According to  FIGS. 1 and 2 , an image processing apparatus has an image detector  1 , a processing circuit  2  and a viewing device  3 . The viewing device  3 , for example, can be a standard monitor or a flat-panel display (TFT display).  
         [0024]     In the image detector  1 , an image of a subject is obtained by x-ray irradiation with an x-ray system R. The input image is supplied from the image detector  1  to the processing circuit  2 . There—see in particular  FIG. 2  the input image is cached in an input image memory  5 . Processing of the input image (described in more detail below) ensues within the processing circuit  2 . As a result of this processing, in the output image memory  6  an output image is stored that corresponds with the cached image, or that has been generated using the cached image. The output image is conveyed to the viewing device  3  and presented thereat to a viewer  7 .  
         [0025]     Control commands can be emptied by the user  7  into the x-ray system R and into the processing circuit  2 . Corresponding to the control commands, for example, the x-ray system R is rotated around the subject  4 , or it is determined whether the image stored in the input image memory  5  is or is not directly connected through to the output image memory  6 .  
         [0026]     As shown in  FIG. 2 , in addition to the image detector  1 , the processing circuit  2  and the viewing device  3 , the image processing apparatus has an input-side synchronization signal generator  8  and an output-side synchronization signal generator  9 .  
         [0027]     The input-side synchronization signal generator  8  provides horizontal and vertical synchronization signals to the image detector  1 , possibly also to the input image memory  5 . The read-in of the input image supplied by the image detector  1  into the input image memory  5  is controlled using the synchronization signals of the input-side synchronization signal generator  8 .  
         [0028]     In an analogous manner, the output-side synchronization signal generator  9  provides horizontal and vertical synchronization signals to the output image memory  6 , possibly also to the viewing device  3 . The readout of the output image from the output image memory  6  is controlled using these synchronization signals.  
         [0029]     As already mentioned, upon entry of appropriate control signals by the viewer  7 , it is possible to accept the input image stored in the input image memory  5  directly into the output image memory  6 , but processing of the input image in advance normally ensues. Generally, as a rule the input image and a reference image stored in a reference image memory  10  are supplied within the processing circuit  2  to a subtractor  11 . The subtractor  11  subtracts the reference image from the input image and thus generates a difference image. The difference image is then written into the output image memory  6  via a characteristic line adapter  12 . In this case, the output image is thus not directly determined from the input image by itself, but rather using the difference image.  
         [0030]     The reference image is normally an image of the same subject that is also currently acquired by the image detector  1 , but acquired at an earlier point in time—for example before the beginning of a medical intervention—and written into the reference image memory  10 . The difference image therefore shows very clearly the changes that have taken place in the intervening time.  
         [0031]     The read-in of the input image into the input image storage  5  and the readout of the output image from the output image storage  6  ensue independent of one another. It is therefore possible that—for example due to interferences in the synchronization signals emitted by the input-side synchronization signal generator  8 —the input image is no longer present in the input image memory  5 . This cannot be detected without assistance by the viewer  7  of the output image. It also is possible that the input image has not actually changed.  
         [0032]     In order to be able to detect a such a falsely static output image, i.e., the presentation of an output image that is no longer current, the image processing apparatus has an insertion circuit  13 , a test circuit  14  and a changeover switch  15 . These components  13 ,  14  and  15  accomplish the inventive monitoring method by means of which it can be detected whether the output image is still dynamic, i.e., whether the current input image or an output image derived therefrom has been transmitted to the viewing device  3 .  
         [0033]     The insertion circuit  13  is connected between the image detector I and the processing circuit  2 , and includes a test signal generator  16  and a mixer  17 .  
         [0034]     The input image is first supplied to a mixer  17  and the input test signal synchronization signals are supplied from the input-side synchronization signal generator  8 . Alternatively, the synchronization signals can be added to the input image, in which case a new feed is not necessary.  
         [0035]     A dynamic input test signal also is supplied to the mixer  17  by the test signal generator. The input test signal is inserted by the mixer  17  into the input image at a predetermined location of the input image. This is explained in detail below in connection with  FIGS. 3 and 4 .  
         [0036]     As shown in  FIG. 3 , the input test signal is inserted into the input image in step S 1 . In step S 2 , it is tested whether an elapsed time δt has exceeded a time limit T. If the time limit T has not yet been exceeded, the process jumps back to step S 1 . If the time limit T has been exceeded, in steps S 3  and S 4  the input test signal is changed and the elapsed time δt is reset.  
         [0037]     The input test signal can be of an arbitrary nature as long as it is sufficiently dynamic. For example, a counter reading of a counter that counts up each second can be inserted into the input image in digital form. Alternatively or additionally, an intrinsically constant marking can also, for example, be displaced within a predetermined line of the input image. Another alternative is for intrinsically constant marking to be alternately inserted and not inserted in the input image.  
         [0038]     The generation and insertion of the input test signal in the input image can ensue via the test signal generator  16  and the mixer  17  in the same manner that is generally known for the generation and mixing of an on-screen display for computer and television devices. Detailed explanations to assemble and to fashion the test signal generator  16  and the mixer  17  therefore are not necessary.  
         [0039]     According to the exemplary embodiment of  FIG. 2 , the input test signal is itself generated by the insertion circuit  13 . This is preferable but not necessary. Alternatively, it is possible (as indicated dashed in  FIG. 2 ) to supply the input test signal to the insertion circuit  13  from outside.  
         [0040]     The insertion of the input test signal must ensue in such a way that the actual input image—and thus the output image—is not disturbed. The input test signal is therefore preferably is inserted—see  FIG. 4 —into the input image by the insertion circuit  13  in the area of the image edge. For example, the input test signal can be inserted into the input image in the area of the upper 5% or in the area of the lower 5% of the image. Such an insertion does not normally interfere. Generally, all lines of the input image or of the corresponding output image are not shown on the viewing device  3 . The input test signal thus can be inserted into the input image in the region border or known as the frame. In this case, is not perceived at all by the viewer  7 . The input test signal alternatively can be located in the visible region of the input image. Generally, however, the information content of the input image at the edges is uninteresting for the viewer  7 . Also in this case, the input test signal thus does not interfere with the detection of the relevant information content of the input image or of the output image determined therefrom.  
         [0041]     The inventive (forced-dynamic) input image is output from the insertion circuit  13  to the input image memory  5  and stored therein. The output image is then determined using the stored input image and is stored in the output image memory  6 . The input test signal possibly may be changed, but it is neither shifted nor deleted. A corresponding output test signal is thus attained in the output image.  
         [0042]     The test circuit  14  is connected between the processing circuit  2  and the viewing device  3 . It has an extractor  18  and a dynamics detector  19 . The changeover switch  15  is downstream from the test circuit  14 , fashioned as an error-protection changeover switch.  
         [0043]     The output image is supplied to the extractor  18  from the output memory storage  6  and its is supplied from the output-side synchronization signal generator  9 . Here as well a new feed of the synchronization signals is not necessary if they have already been added to the output image. The extractor  18  first outputs the output image—with or without the output test signal—to the changeover switch  15 . It is output from this to the viewing device  3 .  
         [0044]     The extractor  19  also extracts the output test signal from the output image. This is possible because the input test signal possibly may be changed but is neither shifted nor deleted. When, for example, the input test signal was thus inserted by the insertion circuit  13  into the third or tenth image line of the input image, the third or tenth image line of the output image can be detected by the extractor  18  using the synchronization signals and supplied to the dynamics detector  19 . The supplied signal then can be evaluated by this. This is explained in detail below in connection with  FIG. 5 .  
         [0045]     As shown in  FIG. 5 , within the test circuit  14  an elapsed time δt′ is first reset in step S 5 . The output test signal is then extracted from the output image in step  86 . In step S 7  it is checked whether the output test signal has remained unchanged. If this is not the case, the output test signal is dynamic: the image transmission is thus current. In this case, the elapsed time δt′ is reset in step S 8  and the process jumps back to step S 6 .  
         [0046]     If the extracted output test signal has remained unchanged, it is tested in a step S 9  whether the elapsed time δt′ has exceeded the time limit T. As long as this is not the case, the process jumps back to step S 6 . In any other case an alarm reaction is executed in a step S 10 .  
         [0047]     The test circuit  14  thus tests whether a dynamic output test signal corresponding with the input test signal has been added to the output image. It is tested whether an output test signal is present at all, as well as whether the output test signal, if present, is of a dynamic nature. When the output test signal is completely absent or is not dynamic, the alarm reaction (step S 10 ) is executed by the test circuit  14 .  
         [0048]     In the simplest case, the alarm reaction of step S 10  is the output of a predetermined acoustic and/or optical alarm signal. For example, an alarm bell can be triggered, or an alarm light can be illuminated (continuously or blinking). It is also possible to output an alarm message, as shown in  FIG. 4 .  
         [0049]     Preferably, however, the changeover switch  15  is triggered by the test circuit  14 . For this, the input image itself and the input-side synchronization signals are also supplied from the image detector  1  to the changeover switch  15 . It is then possible for the test circuit  14  to trigger the changeover switch  15  upon the absence of the dynamic output test signal. Display of the output image is thereby disconnected by the viewing device  3 . Furthermore, the input image supplied by the image detector  1  is sent directly through to the viewing device  3 . The viewer  7  thus receives a significantly worse but current image of the subject  4 .  
         [0050]     As shown in  FIG. 2 , the insertion circuit  13  and the test circuit  14  are operated independent of one another. In a preferred embodiment explained below in connection with  FIG. 6 , this is not the case.  
         [0051]     According to  FIG. 6 , the insertion circuit  13  transmits a signal S to the test circuit  14  at regular time intervals indicating the insertion circuit  13  is operational. For example, the insertion circuit  13  can have a watchdog circuit, by means of which the insertion circuit  13  first monitors itself. The state of the watchdog circuit is then transmitted to the test circuit  14  as the signal S.  
         [0052]     In an analogous manner, a signal S′ of the test circuit  14 , indicating that it is operational, also can be transmitted to the insertion circuit  13 .  
         [0053]     The insertion circuit  13  and the test circuit  14  thus are able to monitor each other. If, for example, the insertion circuit  13  detects a malfunction of the test circuit  14 , it can—for example via a warning light  20 —output a warning notification to the viewer  7 . Vice versa, the test circuit  14  can detect a malfunction of the insertion circuit  13  and output a corresponding warning notification to the viewer  7  by triggering a warning light  21 .  
         [0054]     As shown in  FIG. 6 , it is possible for a back-up test circuit  14 ′ to be associated with the insertion circuit  13  and a back-up insertion circuit  13 ′ to be associated with the test circuit  14 . These back-up circuits  13 ′,  14 ′ normally are inactive. They can be activated as needed by appropriate control signals. It is therefore possible that, in the event of failure, the function of the circuit  14 ,  13  detected as malfunctioning is taken over by the respective other circuit  13 ,  14 .  
         [0055]     As an alternative or in addition to reciprocal monitoring, the insertion circuit  13  and the test circuit  14  can be fashioned as inherently fail-safe circuits.  
         [0056]     As can be seen from  FIG. 7 , the image processing apparatus can be a modularly designed apparatus. The insertion circuit  13  and the test circuit  14  are fashioned as assembly modules  22  for the image processing apparatus, in particular as plug-in cards  22 .  
         [0057]     According to  FIG. 7 , each plug-in card  22  has a video input  23 , a video output  24  and a synchronization signal input  25 . The video input  23 , the video output  24  and the synchronization signal input  25  can be, for example, connections for coaxial cables. Each plug-in card  22  also can have—for example at the rear—connections  26  via which the changeover signal to change over the changeover switch  15  is emitted,  
         [0058]     According to  FIG. 7 , each plug-in card  22  has a data medium  27 , for example an EEPROM  27 , in particular in the form of a flash EPROM. A computer program  28  that determines the functioning of the respective plug-In card  22  is stored in the data medium  27 . Based on the computer program  28 , it can be determined, for example, whether the plug-in card  22  acts as an insertion circuit  13  or as a test circuit  14 . Since the data carrier  27  preferably is electronically erasable and writable, updates of the computer program  28  are thus possible at any time.  
         [0059]     Each plug-in card  22  may further have a switch  29  at the front side. With appropriate programming of the plug-in cards  22  by means of a suitable computer program  28 , it can first be determined by the switch setting of the switch  29  whether the plug-in card  22  acts as an insertion circuit  13  or as a test circuit  14 .  
         [0060]     By means of the inventive monitoring method and the insertion circuit  13  and the test circuit  14 , a test is thus possible in a simple manner as to whether the output image always actually reflects the current state of the input image detected by the image detector  1 .  
         [0061]     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art,