Patent Publication Number: US-2011047700-A1

Title: Longitudinal Drive for Patient Support Systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Gelman application No. 10 2009 038 785.4 filed Aug. 25, 2009, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a patient table arrangement for a medical examination device. 
     BACKGROUND OF THE INVENTION 
     During the examination of a patient in an imaging system such as a Computed Tomograph, Magnetic Resonance Tomograph or PET system, as a result of the restricted volume able to be recorded (Field Of View (FOV)) of the imaging system, an object under examination or a patient, depending on the region of the body to be investigated, has to be positioned differently in the imaging system. 
     As a rule in such cases a patient lying on an examination plate or an object under examination is moved a different distance into the imaging system. The necessary travel is then at its maximum when the patient has to be positioned in the FOV over the entire length of their body (whole body scanning). This means that the patient table carrying the patient or the object under investigation has to be moved into the imaging system far enough to enable an image of the head to be recorded, after which further regions of the body are recorded successively thereafter, down to the feet. 
     With the usual dimensions of FOV and length of an imaging system this type of examination (whole body imaging) results in a greater necessary movement path of the support plate from the start position ( FIG. 1 ). 
     Frequently in such cases the necessary movement path is greater than the length of the patient table itself, which is essentially predetermined by the size the patient. 
     In these cases the transmission of the drive force necessary to move the patient cannot be applied directly to the support plate. A mechanism is to be used which transmits force between a drive motor and the patient table. During the examination this mechanism should have no influence or only a very slight influence on the quality of the examination result. 
     Particular technical difficulties emerge in the case of magnetic resonance tomography from the fact that the drive motor must either be magnetically compatible or must be accommodated sufficiently far away from the examination area. The support plate and the transmission mechanism should be embodied compatible with magnetic fields in such cases (i.e. completely non-magnetic where possible and generally non-conductive) and also be embodied not to appear in the image. In the event of imaging with ionizing radiation all parts of the plate and of the transmission system which enter the path of the beam should where possible only have a minimal effect on this radiation (e.g. x-ray or Gamma radiation). 
     In accordance with DE102004052265-A1 this problem was previously resolved by a transmission system coupling an MR-compatible motor to a patient support plate sufficiently far away from the imaging area of a magnetic resonance tomograph. 
     The disadvantage of this solution is that a comparatively high looseness (or play) between a table position (or a drive wheel on the patient support plate) and the motor shaft makes the drive control difficult and is expensive to compensate for. Where the position on the drive shaft is determined a positioning of the patient is also only possible with restricted accuracy. Because of the high demands on mechanical accuracy of the transmission and the necessary magnetic compatibility this solution is very expensive. 
     WO 03/037182 offers a solution in the form of a conveyor belt for a patient support table. 
     W09846903A describes a general principle of a conveyor belt without reference to medical examination systems. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to make an optimized movement of a patient support table possible. The relevant object is achieved by the subject matter of the independent claim. Advantageous embodiments emerge from the dependent claims. 
     The surface of the patient support table, on which surface an object under examination or patient is able to be positioned, can extend in accordance with the invention in parallel (and not at right angles) to a direction in which the belts or chains are able to be moved. 
     An inventive patient table arrangement or medical examination device patient table arrangement is especially able to be used in a medical examination device in the form of an MRT or a Computed Tomography device or a Positron Emission Tomography device. 
     A pull or push belt is also known from FR1136948A from the year 1955 which relates not to medical examination devices, but for lifting samples, with the surface of the support table, on which surface an object under examination is able to be positioned, extending at right angles to the direction in which the belts or chains are able to be moved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further possible features and advantages of embodiments of the invention emerge from the dependent claims and from the subsequent design of an exemplary embodiment which refers to the drawing. The figures show: 
         FIG. 1  a schematic diagram of the introduction of a patient or object under examination into the imaging area of an imaging system with a patient support table with a support plate, 
         FIG. 2  an overhead view of a patient support table and a movement device in the form of a pull-push belt system, 
         FIG. 3  a detailed diagram of the movement device in the form of a pull-push belt system with drive wheels and returns and 
         FIG. 4  meshing of the movement device in the form of a pull-push belt system with drive wheels and returns. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic diagram of a patient table arrangement  22  with a patient support table  104  of a Magnetic Resonance Tomography device  101  or other examination device which is arranged movably on the carrier arrangement  27  in and against the direction of the arrow z. 
     The carrier arrangement in this case contains a guide system for the support plate  104  as well as a movement device which is not shown in any greater detail here. 
     The carrier arrangement with the support plate can be moved in the vertical direction by a further drive system (which is not the subject matter of this application) when the table plate has been completely moved out of the magnets of the magnetic resonance tomography device  101 . 
       FIG. 2  shows a carrier arrangement  27  with an integrated movement device  200  comprising two belts  31 ,  32  each in the form of a chain, the teeth of which are meshed with each other in the left-hand area in  FIG. 2  (to the left of the dashed line L) in the center of the support plate in the manner of a zip, while the teeth of the two belts  31 ,  32  in the right-hand area in  FIG. 2  (to the right of the dashed line L) or on the outer side of the support plate are not meshed with each other in the manner of a zip (i.e. are separated from each other or are out of engagement). 
       FIG. 3  shows a movement device  200  with the zip area in which the teeth (depending on the direction of movement of the belt in or against the direction z) of the two belts  31 ,  32  engage or disengage respectively. 
     The two belts or chains  31 ,  32  are movable in parallel along an essentially straight path (to the left of the line L) in parallel to one another. 
       FIG. 4  shows that the belts  31 ,  32  (or chain elements in the case of belts in the form of the chain) each feature belt drive engagement devices  51  on a side facing the drive wheels  3  (here in the form of toothed wheels) of the drive device  28 ,  29 ,  30 , which engage in the drive engagement devices  52  (here in the form of a plurality of teeth) of a drive wheel  3  of the drive. In addition return wheels  4  for redirecting the belts  5  (at the point which they are diverted by 180°) and conveyor wheels  1  for conveying or stabilization are provided. 
     The pull and push belt system of the movement device  200  consists of two flexible parts (the belts, especially chains) and can be combined by meshing in a zip-like manner into a tension and compression-proof rod-type arrangement which can transfer the drive force from a transmission engaging on an outer toothing to a patient support plate. 
     The maximum possible movement path is produced from the total length of the pull-push belt system. 
     In such cases it is also advantageous if, when the patient support plate is moved out of the gantry (the inside of the whole-body coil), the two parts of the belts are flexible and for example can be accommodated rolled-up in a schematically indicated store  53  in a very compact manner. 
     The pull and push belt system consists here of (essentially) completely non-magnetic or non-metallic plastic components. This means that it is very good for use in an MRT magnetic field and also in the field of view (FOV) of magnetic resonance tomographs and, because of its small interaction with ionizing radiation, also gives great advantages in the construction of imaging systems which operate with ionizing radiation. 
     In view of the forces to be transmitted, the proposed solution can also be manufactured easily and at low-cost. The option of easy construction and enabling the components of the chain to be easily stored makes this drive especially suitable for use in mobile patient support systems for which particular requirements are imposed on the low weight to be maneuvered. 
     The positioning can be undertaken with very little play or looseness since the two components of the chain engage without play. 
     The pull and push belt system is made of plastics here which make possible a lubrication-free and maintenance-free function over its entire lifetime. 
     A specific arrangement of drive wheels and guides or return rollers avoids irregularities which can arise in the meshing of the individual belts during the forward movement of the table plate or which can also arise during the separation of the individual belts during the backwards movement of the support table plate  104 . 
     If the entire drive unit is matched geometrically precisely to the belt guides high transport speeds are also possible. 
     The drive unit can contain an additional arrangement which allows the table plate or the pull and push belt system to be mechanically separated from the drive or the motor. This makes manual movement of the table plate possible more easily in the event of an error, in that the remaining braking moment of the motor is uncoupled. This function can be provided if there is a power failure and the patient has to be manually removed from the imaging system. 
     Stops which restrict the maximum movement of the patient table plate can be realized by simple push-on parts which prevent further meshing of the belt system. By moving or latching these parts onto other parts of the zip a flexible option is provided for setting the possible movement length of the table plate. 
     The very simple and low-cost push-pull belt system allows almost any given movement lengths and is completely compatible with magnetic fields and also has very good compatibility with other imaging methods such as Computed Tomography and Positron Emission Tomography (especially a good attenuation and scatter behavior for x-ray and Gamma radiation). 
     An especial advantage in the integration into a drive system can be produced by the fact that
         the toothed system is very rigid and represents an almost ideal push rod and   that the separate individual belts or bands are very flexible and therefore the necessary storage spaces can be designed very variably.       

     The reference signs in the claims only serve as examples and are not intended in any way to be a restriction on the area of protection.