Abstract:
A system for reading out X-ray information stored in a phosphor layer, includes: a read-out unit having components for irradiating the phosphor layer with stimulation radiation which can stimulate the phosphor layer to emit emission radiation dependent upon the X-ray information contained in the phosphor layer, and for collecting the emission radiation stimulated in the phosphor layer; and a carrier onto which the read-out unit is mounted. At least one of the components of the read-out unit is mounted onto the carrier over at least one first bearing which has a translatory degree of freedom in a first direction. The first bearing enables movement of the at least one component in relation to the carrier in the first direction.

Description:
The invention relates to a system for reading out X-ray information stored in a phosphor layer of a medium. 
   BACKGROUND OF THE INVENTION 
   X-ray information can be stored in so-called storage phosphors, whereby X-ray radiation passing through an object, for example a patient, is stored as a latent picture in a phosphor layer of a medium. In order to read out the latent picture, the phosphor layer is irradiated with stimulation radiation, and so stimulated into emitting emission radiation. The emission radiation, the intensity of which corresponds to the stored picture, is collected by an optical detector and converted into electric signals. The electric signals are further processed, as required, and finally made available for examination, in particular for medical/diagnostic purposes, whereby they are displayed in corresponding display equipment, eg. a monitor or a printer. 
   European Patent Application EP 1 378 766 A1, herein incorporated by reference in its entirety for background information only, made known a system, whereby a read-out unit is mounted onto a carrier by means of tapered screws, and this carrier together with the read-out unit is moved over the phosphor layer during read-out. In specific situations, for example where there is jolting, temperature fluctuation or tilting of the carrier while being moved, this can lead to reduction of the quality of the X-ray information read out from the phosphor layer. 
   SUMMARY OF THE INVENTION 
   It is the aim of the invention to provide a system of the type mentioned at the outset, which guarantees the highest quality possible of X-ray information read out from the phosphor layer. This problem is solved when at least one component of a read-out unit is mounted on a carrier over at least one first bearing which has a translatory degree of freedom in a first direction, by means of which a movement of the component of the read-out unit in relation to the carrier is made possible in the first direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side view of the system in accordance with the invention; 
       FIG. 2  shows a front view of a first embodiment of the system in accordance with the invention; 
       FIG. 3  shows a front view of a second embodiment of the system in accordance with the invention; 
       FIG. 4  shows a view of one of the components shown in  FIGS. 2 and 3  in viewing direction B; 
       FIG. 5  shows both ends of the component shown in  FIG. 4 , enlarged; 
       FIG. 6  shows both ends of an embodiment of the component shown in  FIG. 4 , enlarged; and 
       FIG. 7  shows a section from a side part of the carrier. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is based on the idea of mounting one or several components of the read-out unit on the carrier instead of the read-out unit as a whole. The mounting of the individual components on the carrier is carried out over bearings with a translatory degree of freedom. The components of the read-out unit can therefore be moved in the direction of this translatory degree of freedom within a specific movement area, by means of which jolting, changes to length resulting from temperature fluctuations and any tilting of the carrier and twisting resulting from this can be better absorbed or avoided than with systems established by the prior art. In this way, high quality is guaranteed for the reading out of X-ray information stored in the phosphor layer. 
   In a preferred embodiment of the invention, it is proposed that at least two components of the read-out unit are mounted individually on the carrier over at least a first bearing which respectively has a translatory degree of freedom in a first direction. By means of individual, ie. separate from one another, mounting of the components, it is possible for the individual components to be able to move independently of one another in relation to the carrier. In this way it is prevented that changes in length, twisting or jolts in individual components effect one another, and in certain cases amplify one another. In this way, particularly high quality is guaranteed for the X-ray picture read-out. 
   With this embodiment, at least two of the following components of the read-out unit are mounted individually and independently of one another in a manner in accordance with the invention: 
   a stimulation radiation source used to produce stimulation radiation; 
   a first optical device for focussing the stimulation radiation onto the phosphor layer; 
   a detector used to collect the emission radiation stimulated by the stimulation radiation in the 
   phosphor layer; 
   a second optical device for focussing the emission radiation coming from the phosphor layer 
   onto the detector; 
   a filter device between the phosphor layer and the detector which is essentially penetrable for 
   emission radiation and essentially impenetrable for stimulation radiation. 
   In another preferred embodiment, it is proposed that the component of the read-out unit has an elongated form in a lengthwise direction which essentially runs parallel to the first direction. In this way, a particularly high improvement in picture quality is achieved because twisting along the lengthwise direction of the component, which is particularly pronounced in the case of thermal expansion lengthwise, can be avoided or at least reduced. 
   In another embodiment of the invention, the component of the read-out unit has a first end and is mounted over the first bearing onto the carrier in the area of its first end. Preferably, a third bearing with a translatory degree of freedom in the first direction and another translatory degree freedom in a second direction is located in the area of the first bearing, whereby the second direction preferably runs at right angles to the first direction. By means of the additional third bearing, tipping of the component along its lengthwise direction in the area of the first end is prevented, without limiting any further rotatory degree of freedom. 
   In a further development of the invention, it is proposed that the component of the read-out unit has a second end, and is mounted over a second bearing, which has no translatory degree of freedom, onto the carrier in the area of its second end. In this way it is possible for the component to be mounted so as to be translatorily movable only on a—first—end, whereas at the other—second—end, no translatory movement is possible. This means that thermal expansion of the component is made possible, and at the same time susceptibility to mechanical jolting is reduced. 
   It is also advantageous to locate a fourth bearing with a translatory degree of freedom in the first direction and a further translatory degree of freedom in a second direction in the area of the second bearing. By means of the fourth bearing, tipping of the component around its lengthwise direction in the area of the second end is prevented, without limiting any further rotatory degree of freedom. 
   Preferably, the respective bearings are in the form of point bearings. The individual bearings here respectively include in particular a ball, by means of which, in connection with the correspondingly formed carrier or the correspondingly formed component, the different degrees of freedom for the corresponding components can be provided. By the use of balls as point bearings, the advantage is achieved at the same time, that rotatory degrees of freedom at right angles to the lengthwise direction of the respective component are generally maintained and only by means of the third bearing and/or fourth bearing described above around a rotatory degree of freedom, namely the tipping around the lengthwise direction of the component, can be reduced. 
   In another preferred embodiment of the invention, it is proposed that the carrier includes two side sections onto which at least one component of the read-out unit is mounted. The side sections have corresponding supports for this, for example in the form of projections or indentations. Both side sections are connected to one another by means of one or several connecting elements. Preferably, three connecting elements are provided for this in order to guarantee the most stable connection possible of both side sections, with at the same time a small number of connecting elements. The connecting elements are preferably made from a synthetic or from a synthetic reinforced by fibres, in particular glass or carbon fibres. In this way, a carrier with high stability and at the same time a low weight can be produced. 
   Preferably, the connecting elements have a lower thermal expansion coefficient than the components of the read-out unit. In this way, in the case of temperature deviations, the carrier remains relatively rigid in comparison with the individual components of the read-out unit, ie. thermal changes to the length of the carrier are negligible in comparison to those of the individual components. 
   Preferably, the connecting elements are elongated in form and have a cross-sectional profile which stabilizes the elongated form. The cross-sectional profile here is preferably in the form of a v, polygonal or circular. This means that there is a reduction in the amount of material used, and so also of weight, and so the carrier can be extremely rigid. 
   Another preferred embodiment of the invention proposes that at least one component of the read-out unit is made up from two or more part components with different thermal expansion coefficients, and the part components are arranged and connected together in such a way that any bending forces arising between both respective part components of this component as a result of changes in temperature cancel one another out, whereby bending of the component can be avoided. The component of the read-out unit is constructed in such a way that any “bimetallic effects” in the area of the contact surface of two part components of different materials can be prevented. 
   With a variation of this embodiment, the part components of the component can be mechanically coupled. This is achieved, for example, by using an elastic connection, eg. an elastic layer of adhesive, between the part components, by means of which movement of the part components in relation to one another—at least within specified limits—is possible. By means of this moveability of the part components in relation to one another, the occurrence of tensions and in certain cases bending forces in the component as a result of different thermal expansion coefficients is avoided in a simple manner. 
   The system in accordance with the invention preferably has a holding device onto which the carrier is mounted, and which can move the carrier over the phosphor layer. Because the individual components of the read-out unit can be inserted into the carrier on the production side, and can be adjusted, the carrier together with the components can be inserted into the holding device with relatively little assembly and adjustment expenditure. Re-adjustment of the components when the carrier is inserted, or after insertion into the holding device can therefore generally be dispensed with. In this way, it is possible to change the complete read-out unit for repairs and servicing in a simple manner. 
   Preferably, the carrier is mounted onto the holding device over at least a fifth bearing which has a translatory degree of freedom in the first direction, so that movement of the carrier in the first direction is made possible. In this way it is guaranteed that the carrier can also move in relation to the holding device in the first direction, and in particular, can expand. In this way, tensions as a result of jolting or thermal expansion of the carrier can be avoided. 
     FIG. 1  shows a side view of the system in accordance with the invention for reading out X-ray information stored in a phosphor layer  1 . The system has a read-out unit which includes the following components: 
   a stimulation radiation source  11  used to produce stimulation radiation  12 ; 
   a first optical device  13  used to focus the stimulation radiation  12  onto the phosphor layer  1 ; 
   a detector  17  used to collect the emission radiation  14 , and which is stimulated by the stimulation 
   radiation  12  in the phosphor layer  1 ; 
   a second optical device  15  used to focus the emission radiation  14  onto the detector  17 ; and 
   a filter device  16  which is essentially penetrable for emission radiation  14  and essentially impenetrable for stimulation radiation  12 . 
   Preferably, the read-out unit is in the form of a so-called line sensor whereby the stimulation radiation source  11  is in the form of a line light source which, for example, includes a number of laser diodes arranged in a line at right angles to the plane of the figure. In this case, the detector  17  has a number of radiation-sensitive surfaces which are also arranged in a line at right angles to the plane of the figure, for example in the form of a so-called CCD Array. 
   The first optical device  13  is one or more cylinder lenses running at right angles to the plane of the figure, and which focus the stimulation radiation  12  onto the phosphor layer  1  on the plane of the figure. The same applies for the second optical device  15 , whereby this has in addition a lens array which also runs at right angles to the plane of the figure, and which brings about focussing of the emission radiation  14  coming from the phosphor layer  1  onto the individual light-sensitive elements of the detector  17  at right angles to the plane of the figure. 
   The specified components of the read-out unit are set on a bearer  20 , which is itself coupled to a holding device (not illustrated), and can be guided by this in conveyance direction T over the phosphor layer  1 . In so doing, by means of the conveyed read-out device, successive different areas of the phosphor layer  1  can be read out, whereby an X-ray picture stored in the phosphor layer  1  can be read out. 
   The carrier  20  includes two side parts  21  of which only one can be identified in the side view chosen here. For stable mechanical connection of the side parts  21 , three connecting elements  22  are provided, and these are preferably pipes made from glass or carbon fibre reinforced synthetic. 
     FIG. 2  shows a front view of a first embodiment of the system shown in  FIG. 1 , in viewing direction A. In order to better clarify the principle which forms the basis of the discovery, just one highly schematised component  10  of the read-out device from  FIG. 1  is shown here. The following embodiments relating to this component  10  also apply correspondingly for one or several of the components  11 ,  13 ,  15 ,  16  and  17  of the read-out device shown in  FIG. 1 . 
   In this view, both side parts  21  of the carrier  20  and the connection of the same by means of the connecting elements  22  can be easily identified. In the embodiment shown as an example, the side parts  21  have projections  23  and  24 , onto which the component of the read-out unit is mounted by means of a first bearing  25  and a second bearing  26 . 
   In accordance with the invention, the first bearing  25  is formed such that the same has a translatory degree of freedom in a first direction R 1 , by means of which movement of the component  10  in relation to the carrier  20  in the first direction R 1  is made possible. The other end of the component  10  is mounted over a second bearing  26  on the projection  24  of the side part  21 , whereby the second bearing  26  has no translatory degree of freedom in the first direction R 1 . By means of this mounting of the component  10  over the first bearing  25  and the second bearing  26 , it is possible for the component  10  to deviate in the first direction R 1  with simple and reliable locking in the second bearing  26  at the same time as the occurrence of jolting or changes in length as a result of temperature fluctuations. In this way, undesired tensions in the component  10  of the read-out unit can be prevented, or at least reduced. 
     FIG. 3  shows a front view of a second embodiment of the system in accordance with the invention, whereby two components  10  and  10 ′ are mounted on the carrier  20  individually, ie. independently of one another. Each of the components  10  and  10 ′ here is respectively mounted over a first bearing  25  or  27  and a second bearing  26  or  28  on the side parts  21  of the carrier  20 . The first two bearings  25  and  27  are formed in such a way, in accordance with the invention, that they have a translatory degree of freedom in the first direction R 1 , and thus allow movement of the respective components  10  and  10 ′ in relation to the carrier  20  in the first direction R 1 . Because the two components  10  and  10 ′ are respectively mounted individually and independently of one another on the carrier  20 , the movements of the same in the first direction R 1  happen independently of one another. The components  10  and  10 ′ are therefore separate from one another, such that any twisting as a result of different thermal expansion coefficients can be avoided. 
   In the example illustrated, the two first bearings  25  and  27  are located respectively on the same (in  FIG. 3 : on the right) end of the respective components  10  and  10 ′. With certain applications it can be an advantage if the first bearing  25  of the one component  10  and the first bearing  27  of the other component  10 ′ is located on the opposite ends (in  FIG. 3 : on the right or on the left end) of the respective components  10  and  10 ′. 
     FIG. 4  shows a view of the component  10  shown in  FIGS. 2 and 3 , in viewing direction B. As can be seen, the component  10  is of elongated form which extends parallel to a lengthwise direction L. The first bearing  25  is located in the area of a first end  18  of the component  10 , whereas the second bearing  26  is located in the area of a second end  19  of the component  10 . As can also be seen from the illustration, the lengthwise direction L, along which the elongated form of the component  10  extends, and the first direction R 1 , in which the component  10  can move, run parallel to one another. This is particularly advantageous so as to avoid twisting arising from changes in length as a result of temperature fluctuations. The first and second bearing  25  and  26  are only schematically shown in the illustration chosen here. Its structure will be described in greater detail below, in connection with  FIG. 5 . 
     FIG. 5  shows both ends  18  and  19  respectively as an enlarged section of the component  10  shown in  FIG. 4 . The first bearing  25  located in the area of the first end  18  of the component  10  includes a groove  31  made in the component  10  and a ball  32  which can move in the groove  31  in the first direction R 1 , for example by rolling and/or sliding. In the area of the second end  19  of the component, a circular cutout  33  is provided, into which a ball  34  can be partially sunk. By means of a corresponding cutout in the support, in particular the projection  24  on the side part  21  (see  FIG. 2 ) it is possible for the second bearing  26  to have no translatory degree of freedom. Moreover, by means of the second bearing  26  shown here, rotational degrees of freedom of the component  10  are maintained around a rotation axis running parallel to the first direction R 1  and around an axis running at right angles to the rotation axis on the plane of the figure. 
     FIG. 6  shows both ends  18  and  19  of an embodiment of the component  10  shown in  FIG. 4 , enlarged. In the area of the first end  18  of the component  10 , in addition to the first bearing  25 , a third bearing  29  is provided which has a translatory degree of freedom both in the first direction R 1  as well as a translatory degree of freedom in a second direction R 2 . The third bearing  29  can be created easily by means of a ball on which the first end  18  of the component  10  lies and which is partially sunk into a circular indentation in the support, in particular a projection  23  of the side part  21  of the carrier  20  (see  FIG. 2 ). By means of the third bearing  29  in the area of the first bearing  25 , tipping of the first end  18  of the component  10  around an axis of rotation running parallel to the lengthwise direction L of the component  10  is prevented. In this way, tensions in the component  10  at the same time as high tipping stability can be prevented or reduced. 
   Also in the area of the second end  19  of the component  10 , a fourth bearing  30  with two translatory degrees of freedom in the first and second direction R 1  and R 2  can be provided in addition to the second bearing  26 . By means of this, the tipping stability in relation to a rotation axis running parallel to the lengthwise direction L is guaranteed with particularly high reliability. 
     FIG. 7  shows a section from the right-hand side part  21  of the carrier with one embodiment for the first bearing  25  in accordance with the invention. With this embodiment as an example, the component  10  is mounted over a ball  32  on the projection  23  of the side part  21 . Here, the ball  32  lies in an indentation  35  made in the projection. At the same time, the ball  32  lies in the groove made in the component  10  which acts as a guide. The component  10  is pre-tensioned by means of a spring  37  against the ball  32  in order to avoid an undesired jumping out of the ball and/or the component  10  from the bearing. The spring  37  for this purpose is preferably set on another projection  36  of the side part  21 . 
   The second, third and fourth bearings  26 ,  29  and  30  are created in a corresponding manner, whereby with the second bearing  26 , the guide groove  31  is replaced by a round indentation, similar to the indentation  35 , and with the third and fourth bearing  29  and  33 , the optical component  10  generally has no indentation or guide groove.