Patent Document

FIELD OF THE INVENTION 
     The present invention relates to an arrangement for image data receiving means, such as a film cassette or equivalent for use in mammography and to a method for image data receiving means used in mammography and to a mammography apparatus in which the image data receiving means can be used. In particular, the invention concerns solutions regarding the loading, removal and movement of the image data receiving means in the cassette tunnel or similar space of mammography apparatus. 
     BACKGROUND OF THE INVENTION 
     The image data receiving means generally used in mammography are x-ray films placed in cassettes. Such cassettes are available in several different types, depending e.g. on the manufacturer of the cassette and the type of imaging the cassette is designed for. Often there are also differences between cassettes according to whether the film used in them is intended to be developed in a darkroom or e.g. in a special film development device. These so-called daylight cassettes are gradually replacing darkroom cassettes. In this field, many kinds of devices for the loading of cassettes with a film and for the removal of the film from cassettes have been developed, and likewise different labeling devices, i.e. devices e.g. for printing or exposing patient information and imaging parameters on the film in a cassette. 
     The imaging apparatus used in mammography generally have in their imaging area a space with at least one feed/eject opening, a cassette tunnel or equivalent, into which a cassette loaded with a film is entered and where it is positioned at a desired imaging position and from where it is removed and taken to a separate labeling stage. In many imaging apparatus, the cassette tunnel is so implemented that its open end or ends form a cassette feed/eject opening. When both ends of the tunnel are open, the cassette can be moved in the tunnel by pushing it from one end of the tunnel and pulling from the other. Moreover, in some devices the tunnel wall is provided with additional holes to make it easier to move the cassette. 
     However, handling the cassette in such a cramped tunnel, besides being difficult and awkward, is also time-consuming. Especially in mammographic screening studies, in which the cassette may have to be changed as many as 50 times an hour, cassette handling alone takes up a considerable amount of time, and for an individual patient this means that the imaging operation, which many patients find unpleasant, takes an annoyingly long time. 
     Traditionally, mammography apparatus have been used to take various individual transillumination radiographs. However, the information given by a transillumination radiograph is not always sufficient in a diagnostic sense. For this reason, there has been a trend in recent times towards discovering new imaging methods e.g. to make different layers in the tissue under imaging more clearly visible in the images. A contribution to this development has been the progress in the technology and prices of digital sensors toward a level that is beginning to enable their use in mammography apparatus, too, both in an economic sense and in respect of image quality and authority approval. 
     In many imaging modes that are more complex than transillumination imaging, a requirement is that it should be possible to change in some way the position of the object to be imaged with respect to the imaging means during the imaging process. Such a change can be implemented either as a stepwise action or as a continuous movement during imaging. When controlled movement of the object to be imaged is difficult to achieve, as is the case in mammography, one can naturally seek for means for moving the imaging means. 
     Prior-art mammography apparatus have means for moving the imaging means in relation to the object to be imaged e.g. to change the height position of the imaging means in relation to the object to be imaged, means for interdependently revolving the imaging means around the object to be imaged, and means for inclining the radiation source in relation to the object to be imaged and the image data receiving means. As for other movements, certain apparatus also have means for moving e.g. a screen placed near the radiation source to define the radiation beam in a desired manner, and even means for moving the object to be imaged during the imaging process. However, independent movements of image data receiving means that may be needed during imaging have been difficult to implement in a desired manner because, if the structure of the apparatus has permitted such movements at all, they have had to be carried out manually. 
     In some mammography apparatus, difficulties have been encountered in getting the cassette correctly positioned in the imaging area. If the cassette is in the wrong position, this may result in leaving part of the tissue to be imaged outside the area of which an image is formed on the film or other receiving medium, which may necessitate renewal imaging. This creates extra work and an unnecessary additional exposure of the tissue to radiation. 
     Often the actions requiring handling of the cassette in the cassette tunnel have to be performed in ergonomically difficult working positions. This is the case especially when more than one image is taken of the same object, possibly even on the same film, in which case the cassette has to be changed or moved to a new position in the cramped cassette tunnel while the object to be imaged may remain positioned during all this time, in mammography in practice generally compressed between the compression plates of the imaging apparatus. 
     Recording patient information, dates, imaging parameters and projections etc. on the film or equivalent is an essential part of the imaging process. Especially in mammographic screening studies referred to above, there is a great risk of labeling errors occurring due to human factors. When the actions related to labeling are carried out as an operation physically separate from the actual imaging process, the cassettes may be interchanged when being taken from the imaging apparatus to the labeling station. Thus, information of a wrong patient and/or wrong imaging parameters may be entered on the film. And when human activities are concerned, it may even happen that some or even all of the data is not recorded at all when the labeling of an individual cassette or a whole batch of cassettes is accidentally neglected e.g. as a result of a lapse of memory. On the whole, labeling the films is an operation that requires accurate management and contributes for its part to the total duration of the imaging process. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object of the invention is to eliminate above-mentioned drawbacks in a profitable way that improves working comfort and ergonomics in the imaging process, which involves no need to enter or remove the film cassette through narrow holes or to move it in the cramped cassette tunnel of the mammography apparatus. 
     One of the objects of the invention is to enable a more efficient utilization of time especially in conjunction with mammographic screening studies by reducing the time spent between exposures. 
     A further object of the invention is to achieve an arrangement in which, when a cassette is being loaded into the mammography apparatus, an automatic system according to preferred embodiments of the invention seizes the cassette and drives it to the correct imaging position in the cassette tunnel, thus allowing the operator of the apparatus to proceed sooner to other actions in preparation for imaging. 
     A further object of the invention is to enable accurately correct positioning of the image data receiving means in the imaging area so as to minimize the need for taking renewed images in consequence of inaccurate positioning of the tissue to be imaged. 
     Another object of the invention is to achieve an arrangement in which an exposed cassette can be automatically driven out of the cassette tunnel when desired, so that the operator of the apparatus could easily change/remove the cassette without having to dig it out from the opening of the cassette tunnel. 
     In certain preferred embodiments of the invention, the object is to achieve an arrangement in which the recording of patient information and imaging parameters on the film, which constitutes an essential part of the imaging process, can be performed automatically in the imaging apparatus in connection with the imaging process. 
     An object of preferred embodiments of the invention is also to achieve an arrangement that can be used for moving image data receiving means of different types and sizes in the imaging area of the imaging apparatus. 
     A further object of the invention and some of its embodiments is to provide possibilities to use a mammography apparatus even in imaging processes requiring complex movements of the imaging means and their accurate control, and in general to provide better possibilities to accurately and with ease move the imaging means in mammographic imaging processes. 
     The problems described above are solved and the objects stated are achieved by a solution according to the fundamental idea of the invention disclosed in the present application, in which the mammography apparatus is provided with devices by means of which the image data receiving means can be easily and accurately moved in the cassette tunnel or a corresponding space in the mammography apparatus, using control means and/or automatically. 
     In the following, some of the preferred embodiments of the invention will be described in greater detail with reference to the attached drawings. However, the invention is not intended to be exclusively limited to these embodiments; instead, its exact essential features are presented in the claims below. In the attached drawings, 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, some of the preferred embodiments of the invention will be described in greater detail with reference to the attached drawings. However, the invention is not intended to be exclusively limited to these embodiments; instead, its exact essential features are presented in the claims below. In the attached drawings, 
         FIG. 1  presents a typical mammography x-ray apparatus. 
         FIG. 2  presents a typical C-arm structure of the mammography apparatus, 
         FIG. 3  presents an arrangement according to the invention for moving the image data receiving means that are used in mammography, and 
         FIG. 4  presents means according to a preferred embodiment of the invention for labeling of the image data receiving means in the cassette tunnel of a mammography apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The mammography x-ray apparatus  1  presented in  FIG. 1  consists of a frame part  11  and a C-arm  12  connected to it. Typically, placed at opposite ends of the C-arm  12  are a radiation source  13  and an image data receiving means  14 ′, which is located e.g. inside a so-called bottom shelf structure  14 . These imaging means  13 ,  14 ′, being placed inside the casing of the apparatus, are not actually visible in  FIG. 1 . In addition, placed in the area between these imaging means  13 ,  14 ′, typically near the image data receiving means  14 ′, are means  15 ,  16  for positioning the object to be imaged in the imaging area. Typically, the C-arm  12  can be both moved vertically and horizontally in relation to the means  15 ,  16  for positioning the object to be imaged and rotated in relation to the frame part  11 . The positioning means  15 ,  16  typically consist of an upper compression plate  15  and a lower compression plate  16 , and the lower compression plate  16  may also be arranged to function as a so-called bucky. “Bucky” means a grid structure placed between the tissue to be imaged and the image data receiving means to prevent radiation scattered from the tissue from reaching the image data receiving means. 
       FIG. 2  presents one C-arm structure  12  used in mammography apparatus. The C-arm  12  in  FIG. 2  differs from the structure in  FIG. 1  especially in respect of the way in which the cassette tunnel or similar space  17  has been arranged in the imaging area of the apparatus. The solution illustrated in  FIG. 1 , in which both ends of the cassette tunnel  17  are closed and a cassette  14 ′ is entered into the cassette tunnel  17  by driving the bottom shelf structure  14  downwards so that a space is formed between it and the lower compression plate  16 , allowing the cassette  14 ′ to be inserted into the cassette tunnel  17  via this space from above, is fairly seldom used in mammography apparatus.  FIG. 2  presents perhaps a more typical solution, in which at least one end of the cassette tunnel  17  is open, allowing the cassette  14 ′ to be inserted directly into the tunnel  17  from the side of the structure, without requiring operation of the means for driving the C-arm  12 . 
     Generally speaking, in mammography systems there are used more or less integrated structures of several different types for forming the assembly consisting of the bottom shelf, lower compression plate and bucky/grid  14 ,  16  and the associated cassette tunnel or similar space  17 . For example, in the solution illustrated in  FIG. 2 , the cassette tunnel  17  has been integrated as a part of the lower compression plate/bucky/grid structure  16  of the apparatus. Anyway, all cassette tunnel solutions have the common aim of bringing one edge of the cassette tunnel  17  as close as possible to that wall  18  of the bottom shelf or similar structure  14 ,  16  which comes into contact with the chest during imaging, because the image data receiving means must be so placed in the imaging area as to allow a maximal amount of tissue even in the region of the sternum and armpit to be imaged. 
     When the cassette tunnel  17  has been arranged to be loaded in a horizontal plane—while the C-arm  12  of the mammography apparatus is in a vertical position as shown in  FIG. 2 , its feed/eject opening is generally disposed in a lateral location as seen from the direction  18  from which the tissue to be imaged is entered. This obviates the need for re-positioning the object to be imaged, which is an awkward operation that may be unpleasant to the person being imaged, only because a change of cassette  14 ′ is needed. 
       FIG. 3  illustrates an arrangement according to the invention which allows the entry, the ejection and if so desired, even other kinds of movements of a film cassette  14 ′ in the cassette tunnel  17 . In the embodiment illustrated in  FIG. 3 , the arrangement for moving the cassette  14 ′ in the cassette tunnel  17  comprises a bottom shelf  14 , depicted in a sectioned view in the figure, means  19  for moving the cassette  14 ′, a button  20  for starting the ejection of the cassette  14 ′, and a bucky  16 . The means  19  for moving the cassette  14 ′ comprise a driving roller  21 , a driving roller motor not visible in the figure, being placed below the bottom shelf  14 , and a turning shaft  22  functionally connecting the roller  21  and its motor and provided with a gearing  22 ′. In the arrangement in  FIG. 3 , the cassette tunnel  17  is so implemented that it forms a part of the bucky  16 , with an opening/openings  17 ′ at its sides serving as cassette  14 ′ feed/eject openings. The means  19  for moving the cassette  14 ′ are mounted on a carriage  23  which can be moved along guide rails  24  and which is connected to a spring  25  continuously tending to draw it by means of a drawing band  26  toward that end  18  of the bucky  16  which comes into contact with the chest. The bottom of the bottom shelf  14  is also provided with an elongated aperture  29 , shown in  FIG. 3 , laid in a direction parallel to the guide rails  24 , the shaft  22  of the driving roller  21  going through this aperture. Thus, the means  19  for moving the cassette  14 ′ can move in the direction of this aperture and the guide rails  24 . The cassette tunnel  17 , e.g. its bottom, may additionally be provided with one or more sensors  27  which are connected to the control means  30  of the apparatus to probe the position of the cassette  14 ′ in the cassette tunnel  17 . 
     Disposed on the side opposite to that wall  18  of the bucky  16  that comes into contact with the chest of the object to be imaged is arranged an elongated cut-out or groove  28  substantially parallel to the guide rails  24 , into which the shaft of the driving roller  21  is directed when the bucky  16  is being mounted on the bottom shelf  14  from the direction of the wall  18  placed against the chest. The length of this cut-out  28  is so designed that it will position the driving roller  21  in relation to the cassette tunnel  17  so that the circumference of the roller  21  will come into contact with the side wall of the cassette  14 ′ as it is fed in the cassette tunnel  17 . A spring  25  continuously draws the means  19  for moving the cassette  14 ′ toward the cassette  14 ′, ensuring that a frictional force sufficient for converting the rotational motion of the roller  21  into a linear movement of the cassette  14 ′ exists between the sidewall of the cassette  14 ′ and the driving roller  21 . In the solution illustrated in  FIG. 3 , the guide slot  28  and guide rails  24  for guiding the bucky  16  are disposed at an angle substantially perpendicular to the feed direction of the cassette  14 ′ in the cassette tunnel  17 , but naturally they may also be arranged at a different angle. 
     In mammography, cassettes  14 ′ of different sizes are commonly used to meet different imaging needs. The arrangement presented in  FIG. 3  is modified so as to allow the use of another cassette size, by replacing the bucky  16  on the bottom shelf  14  with one having a cassette tunnel  17  dimensioned for the other cassette size and a cut-out or recess  28  coming into contact with the driving roller  21  that has a length corresponding to this arrangement, by means of which cut-out or recess the means  19  for moving the cassette  14 ′ are moved along the guide rails  24  to correct position for moving this different-sized cassette  14 ′. 
     The arrangement illustrated in  FIG. 3  may function e.g. as follows. When a cassette  14 ′ is fed through the feed opening  17 ′ into the cassette tunnel  17 , the control system  30  of the apparatus detects by means of a sensor  27  placed in the tunnel  17  that a cassette  14 ′ has been entered in the tunnel  17  and starts the drive motor of the driving roller  21 . As the cassette  14 ′ is pushed further in, its rear edge meets the driving roller  21 , which begins to draw the cassette  14 ′ into the tunnel  17 , whereupon the person inserting the cassette  14 ′ can release his/her grip of it. Preferably, into the cassette tunnel  17  open at both of its ends a sensor  27  is provided in the area of both of the feed openings, in which case the control system  30  will control the drive motor of the driving roller  21  to rotate in the appropriate direction to draw the cassette  14 ′ into the tunnel. 
     Disposed at a suitable location at the other end relative to the feed opening  17 ′ of the tunnel  17 , there may be another sensor (not shown in the figure) to detect the edge of the cassette  14 ′, allowing the control system either to stop the motor or to drive the cassette  14 ′ from this detection point to a given other imaging position as required in each case. In most cases, this position is the location where the midpoint of the cassette  14 ′ lies on the center axis of the field of rays used for imaging. According to the invention, the control system of the apparatus may be so implemented that it also includes an ability to measure and learn the correct position of the cassette  14 ′ in the tunnel  17 . After the cassette  14 ′ has been correctly positioned, the control system gives a permission for starting the actual imaging process. 
     Upon completion of the imaging process, the means  19  for moving the cassette  14 ′ drive the cassette  14 ′ out of the cassette tunnel  17  either on the basis of a signal obtained from a cassette eject button  20  or automatically e.g. via a predetermined eject opening. The arrangement preferably comprises two or an even number of cassette eject buttons  20 ,  20 ′, which are disposed substantially near each end opening of the cassette tunnel  17 . The control system identifies which one of the buttons  20 ,  20 ′ has been pressed and drives the cassette  14 ′ out of the tunnel  17  via the eject opening corresponding to this button  20 ,  20 ′. In the embodiment illustrated in  FIG. 3 , the means  19  for moving the cassette  14 ′ do not automatically drive the cassette  14 ′ far enough out of the eject opening to allow it to fall but only far enough to make it easy for the operator of the apparatus to get hold of the cassette  14 ′ in order to remove it from the tunnel  17 . 
     Among the advantages of the embodiment of the invention as presented in  FIG. 3  are the profitableness resulting from its structural simplicity, and especially its small space requirement. In a mammography apparatus, it is not recommendable to fit any complex arrangements in the regions below the lower compression plate because any large structures in these areas are a significant obstruction to patient positioning for different projections. 
     In the embodiment presented in  FIG. 3 , the means for moving the cassette in the cassette tunnel comprise only one roller, but naturally more rollers can be used without departing from the basic idea of the invention. 
     An alternative solution for providing the apparatus with means for moving the cassette according to the invention is to use two driving rollers immovable in the plane of the cassette feed direction, at least one of which is provided with means for implementing an axial motion of the roller. By placing such cassette moving means at suitable locations in the cassette tunnel or its immediate vicinity, it will be possible to use one driving roller for moving a cassette of one size and another roller for moving a cassette of another size, and this axial movement permits a roller which is used for moving a cassette of a given size but which would prevent some other bucky, cassette and so on from being fed into the cassette tunnel  17  to be drawn out of the cassette tunnel when necessary. 
     Another alternative way of providing the apparatus with means for moving cassettes of different sizes is to use a single driving roller having an increased length in the direction of its rotation axis, which is brought into the cassette tunnel or to a substantially close vicinity to it in a horizontal position, i.e. in an orientation parallel to the bottom/top of the cassette tunnel, and positioned there in a fixed location. When the length of the roller is suitably selected, it will be long enough to move cassettes of different sizes. 
     Naturally, a roller is not the only driving means applicable for moving a cassette in the cassette tunnel as provided by the invention; instead, in principle, any known/applicable power transmission solution can be used. However, according to the fundamental idea of the invention, it is preferable to use means that require only little space and that can simply be placed in the cassette tunnel or in its immediate vicinity in a mammography apparatus. Such solutions typically include, however, rollers or other drive wheels or equivalent coming into a direct or indirect contact with the cassette like those described above, from which it is possible to construct simple overall solutions that enable cassettes of different sizes to be moved in the cassette tunnel. Corresponding means can advantageously even be used to provide the cassette tunnel or similar space with a drive system by means of which the cassette can be moved in the tunnel both in its feed direction and in a direction substantially perpendicular to the feed direction. In this way, conditions are created for the use of the imaging apparatus in so-called spiral or complex motion tomographic imaging, or conditions for solutions that can be utilized in one preferred embodiment of the invention, the use of means for moving the cassette in co-action with means for labeling of films, also disposed in the cassette tunnel. In the following, these embodiments of the invention will be described in some more detail, but as for bidirectional cassette movement mentioned above, we can already state at this point that, by suitably arranging the cassette tunnel and the means for moving the cassettes, it will be possible to use in the imaging apparatus even cassettes of different types and sizes whose so-called labeling window may be located at different positions, because, using cassette moving means like this, the cassettes can be correctly positioned in the cassette tunnel in alignment with the labeling device even if the latter are stationarily mounted in the apparatus. 
     An additional feature of the invention is a possibility to use the cassette moving means even for other purposes besides cassette feed and eject functions and positioning of the cassette in the cassette tunnel. One embodiment of this type relates to the labeling of films, i.e. to the recording of imaging parameters, patient information etc. on the film. FI patent application 19992537 filed simultaneously with the present application contains a more detailed discussion of the problems associated with prior-art labeling arrangements and the special features of an invention concerning a labeling arrangement, presented in the application in question. In this context, we shall only describe an embodiment in which a labeling device as presented in  FIG. 4  is so arranged in conjunction with the cassette tunnel as to allow the labeling of the film to be performed directly in the cassette tunnel. 
     The means  3  for the labeling of films presented in  FIG. 4  comprises a frame part  31 , a carriage  33  functionally connected to the frame part  31  via guide rails  32 , a screw conveyor  35  for moving the carriage and a motor  36  driving the screw conveyor. Mounted on the carriage is a display or other recording element  37  and a contact means  38 , such as a pin or equivalent. A labeling device  4  like this can be arranged in conjunction with the cassette tunnel either so that the desired markings can be recorded on the film while the cassette is in a typical imaging position or so that the cassette is driven to a given labeling position (LP) for labeling, as shown in  FIG. 3 . In both cases, the means of the invention for moving the cassette can be utilized for opening and closing the shutter of the labeling window of the cassette so that when the cassette is in its labeling position, its labeling window is located in a position where, as the carriage  33  is being raised, the contact means  38  meets a counterpart provided in the shutter structure of the labeling window of the cassette. Thus, the labeling window of the cassette can be opened and closed by moving the cassette itself by the arrangement of the invention. 
     The recording means  37  may be e.g. a liquid crystal display, from which the desired data can be projected onto the film in a known manner by using a lamp placed behind the display. When a liquid crystal display is used, it is preferably so disposed in the labeling means structure that the display  37  can be moved as close to the film as possible for the time required for labeling, e.g. by using a vertical motion of the carriage as in the solution presented in  FIG. 4 . In this case, it may be unnecessary to provide any separate optical devices between the display and the film to ensure a successful labeling exposure, although a suitable lens is generally required. If a film marking technique is used that requires no movement of the display  37  or equivalent element, then the solution presented in  FIG. 4  can naturally be further considerably simplified. In this case, an arrangement in which the display  37  or equivalent element is immovably mounted directly on the frame part  31  and in which the contact element  38  used is e.g. a solenoid will be sufficient. 
     The labeling function can naturally also be made by using previously known solutions based on a scanning technique, in which case the labeling window structure of the cassette does not necessarily comprise an actual shutter that can be opened/closed. In a scanning technique, the essential feature is that a printing or exposure head is moved over the labeling area of the film. When the labeling is implemented utilizing cassette moving means according to the present application, a recording head of this type can be immovably mounted in the cassette tunnel or in its immediate vicinity and the scanning movement can be implemented as a movement of the cassette. Devices based on scanning technique generally use recording heads that expose the film in only one dimension, while another dimension of the marking is accomplished by the scanning movement itself. For example, a single-row LED display is considerably cheaper than a corresponding matrix display. 
     This naturally also applies to many other techniques, such as optical fibers. 
     The above-described opening/closing movements of the labeling window will be unnecessary and can be omitted in solutions where a labeling window substantially impermeable to wavelengths of visible light, and a recording element producing information that is capable of penetrating the cassette&#39;s labeling window impermeable to visible light, or that can otherwise, e.g. in a converted form, be conveyed through it, are used. 
     The advantages of the arrangement of the invention are clearly visible in screening studies as mentioned above, in which it can be utilized e.g. as follows: After taking the first image, the operator of the imaging apparatus emerges from behind the radiation shield and steps in front of the apparatus, holding the next cassette ready in his hand, presses the cassette eject switch on that side where he wants the cassette to come out of the cassette tunnel, or removes the cassette automatically ejected by the apparatus and inserts the new cassette via the opening of the cassette tunnel, whereupon the automatic system of the apparatus positions the cassette in the correct position. Next, the C-arm of the device is turned into the next projection angle and, if necessary, the position of the object to be imaged is corrected, and thus the apparatus is ready to take the next image. If the apparatus is additionally provided with means for automatic labeling of the cassette according to a preferred embodiment of the invention before it is driven out of the cassette tunnel, then the imaging work can be carried out considerably more effectively than before as the time spent on supplementary work associated with the imaging process is substantially reduced. 
     The amount of manual work to be done in connection with the arrangement of the invention can be further reduced by adding to the cassette tunnel feed opening a cassette feed magazine operated by any known technique. The arrangement of the invention can even be thought of as being developed as far as creating a mammography imaging line that is completely automated except for the positioning of the object to be imaged. The first part of such a line could consist of a station for loading cassettes with film, said station either simultaneously functioning as the cassette feed magazine of the mammography apparatus or being connected to a cassette feed magazine via a cassette conveyor line, from which magazine the cassette is fed into the cassette tunnel of the mammography apparatus, where the cassette moving means provided in the tunnel take care of the cassette movements needed for its positioning in connection with imaging, possible cassette motion and labeling during imaging and finally driving the cassette out of the cassette tunnel, either from the same side as or from a different side than where the cassette was inserted into the tunnel, in which case, depending on the solution, the cassette is conveyed either via the same aforementioned cassette conveyor line or via a separate line to a film development unit containing means known in themselves for automatic removal of the film from the cassette and for its development. 
     Besides facilitating the supplementary functions to be performed in connection with the imaging process, the arrangement of the invention can also be utilized e.g. in so-called stereotactic imaging, which involves taking at least two pictures of the same object on the same film or e.g. on a digital cassette, typically requiring the cassette to be moved to a new position between the exposures. In the arrangement of the invention, the cassette motion can be controlled e.g. by means of pre-input operation parameters or by operating the motor of the driving roller via control buttons on the imaging apparatus. 
     Furthermore, the arrangement of the invention provides possibilities e.g. for taking film-based narrow-beam tomograms with a mammography apparatus. In this type of imaging, the object to be imaged is scanned with a radiation beam that is narrower than the object to be imaged while the position of the radiation source and film cassette in relation to the stationary tissue layer or area to be imaged is changed during the imaging process, e.g. by revolving the imaging means around the object to be imaged, the film cassette being simultaneously moved in a manner required by the imaging condition known in itself so that the radiation beam also sweeps over the film during the imaging cycle. 
     Although the prices of digital sensors are continuously falling, especially sensors having a large surface area are still very expensive. The arrangement of the invention makes it possible to use a digital sensor for taking mammographic radiographs e.g. by using a narrow sensor attached to a suitable cassette or plate, moving the sensor in synchronism with the scanning movement of a narrow radiation beam implemented by keeping the radiation source stationary while moving a screen placed near the radiation source to define the radiation beam. 
     The examples presented above are not meant to be an exhaustive list of concrete and preferred ways of applying the invention; instead, its embodiments may vary within the scope of the inventive idea defined in the following claims.

Technology Category: 1