Patent Publication Number: US-2023141736-A1

Title: Sterile cover for a medical imaging device and sterile medical imaging system

Description:
The present invention relates to a sterile cover for a medical imaging device and a sterile imaging system with such cover, in particular, a microscope. 
     The use of medical imaging devices in a sterile environment requires a sterile handling of such medical imaging device. Accordingly, medical imaging devices are usually covered by a foils and a sterile cover, wherein the sterile cover is adapted to at least partially enclose the imaging portion of the medical imaging device. Presently, such sterile cover is pushed over the imaging portion of a medical imaging device and is affixed thereto by frictional locking due to pressing forces. The fixing portion of the medical imaging device is provided by parallel surfaces to allow a secure frictional locking. However, parallel surfaces may not always be desired, e.g. in view of a medical microscope with inclined objectives, wherein the housing should also provide inclined surfaces to reduce the outer potentially interfering contour. In such event, surfaces deviating from a parallel arrangement may not qualify to provide a secure frictional locking. 
     Accordingly, it is an object of the present invention to provide a sterile cover that enhances the freedom of design of a medical imaging device while still allowing a secure fastening of a sterile cover. 
     The object is solved by a sterile cover for a medical imaging device according to claim  1  and a sterile medical imaging system according to claim  10 . Further aspects of the present invention are subject of the dependent claims. 
     According to one aspect, a sterile cover for a medical imaging device, comprises a frame member configured to cover an imaging front side of the medical imaging device, wherein a side intended to face the imaging front side of the medical device is a facing side of the frame member, and at least one transparent cover portion within the frame member arranged to allow at least imaging by the medical imaging device when the frame member is attached to the medical imaging device, wherein the frame member comprises at least two attachment portions configured to provide a positive-fit connection with corresponding attachment portions of the medical imaging device. 
     The sterile cover may therefore be affixed to the medical imaging device by a positive-locking or form-fit connection instead of only providing a frictional locking. However, such frictional locking may still be provided to support the positive-fit connection. The terms positive-fit, positive-locking or form-fit may be used synonymously. The respective attachment portions of the sterile cover may not only allow the use of inclined fixing portions by the medical imaging device but may also provide an enhanced freedom of design of the outer surfaces as long as the medical imaging device provides at least respective counter connection portions for engagement with the attachment portions in terms of a positive-fit connection. Furthermore, the proposed positive-fit connection may be less sensitive to manufacturing tolerances than a frictional locking. 
     Due to the at least two attachment portions the frame member may be less likely to be loosely affixed to the medical imaging device or prone to tilt. 
     As another advantage, the sterile cover may be affixed to and detached from the medical imaging device without the use of any tools due to the positive-fit connection. 
     Advantageously, the at least two attachment portions are provided on two opposing positions on the facing side of the frame member. 
     The likelihood of the frame member or the sterile cover, respectively, to tilt is thereby further decreased. Furthermore, by providing the at least two attachment portions on the facing side of the frame member further reduces potential interfering contours during the sterile handling of the medical imaging device with the sterile cover affixed thereto. 
     Two opposing attachment portions may also support a parallel attachment of the sterile cover on the medical imaging device. A parallel attachment may reduce the likelihood of the sterile cover being bent or otherwise distorted and therefor the risk of the breakage of the transparent cover portion. 
     In some embodiments, the at least two attachment portions are configured as resilient snap-fit members, preferably protruding from a periphery of the frame member in a direction extending from the facing side of the frame member. 
     Resilient snap-fit members may be easily implemented and may only require corresponding recesses and/or projections provided by the medical imaging device for a positive-fit connection. In particular, if such snap-fit members protrude from a periphery of the frame member in a direction extending from the facing side of the frame member, the medical device may not have to provide corresponding positive-fit connection members or portions on the imaging front side but on the peripheral surface with respect to the imaging front side. Accordingly, the imaging front side of the medical device may be unaffected by the positive-fit connection and the medical imaging device may also be retrofitted more easily. 
     Alternatively or in addition, the attachment portions may be configured as bayonet connectors, tongue and groove members or the like. 
     Advantageously, the snap-fit members are configured to provide a gap between respective snaps of the snap-fit members and the imaging front side of the medical imaging device in parallel to the facing side of the frame member, preferably less than 4 mm, when the medical imaging device extends outwardly with a positive convergence angle from the imaging front side. 
     In other words, the distance between two opposing snaps is greater than the imaging front side of the medical device when the sterile cover is oriented to be attached to the medical imaging device. Accordingly, the snap-fit members are not elastically deformed at the beginning of the attachment procedure but in the course of moving the sterile cover further in an attachment direction, i.e. moving the respective snaps beyond the imaging front side. 
     Due to the gap, the required elastic deformation may be reduced and thus, the choice of materials and designs may be enhanced. 
     However, as the size of the gap and the convergence angle affect the moving distance of the sterile cover to provide sufficient elastic deformation to achieve a snap-fit locking, it may be desirable to limit such moving distance by limiting the gap. Advantageously, the gap is limited to less than 4 mm, in particular, of a convergence angle of about 84° to 87°. 
     In some embodiments, the frame member further comprises at least one guiding member protruding from the facing side of the frame member intended to be received by a recess on the imaging front side of the medical imaging device. 
     The guiding member may support the attachment process by its guiding function in terms of at least indicating a proper orientation. In particular, the guiding member provides at least a length protruding from the facing side of the frame member that allows the guiding member to be received by a corresponding recess of the medical imaging device before or when the attachment portions are in engagement with corresponding attachment portions of the medical imaging device. 
     Preferably, a ratio of a protruding length of the at least one guiding member and a protruding length of the snap-fit members protruding from the facing side of the frame member to the respective ends of snaps opposite to the facing side is less than 1, preferably between 0.41 and 0.74. 
     With a protruding length of the guiding member or guiding members being less than the protruding length of the snap-fit members, the guiding member may be likely to interfere with an imaging component or any other component or contour of the medical imaging. Specifically, a ratio of 0.41 to 0.74 has been identified to reduce the protruding length of the guiding member while still allowing sufficient guidance. 
     Furthermore, a ratio of a cross section perpendicular to the protruding length of the at least one guiding member and a corresponding cross-section of the recess on the imaging front side of the medical imaging device may be less than 1, preferably between 0.15 and 0.9. 
     Due to the cross-section of the guiding member being less than the one of the corresponding recess on the imaging front side, the guiding member may be easily introduced into the recess. Additionally, the configuration may be less sensitive to manufacturing tolerances and the like. To enhance such effects, a ratio of 0.9 or less may be advantageous. However, a ration less than 0.15 may result in an insufficient guiding of the guiding member within the recess and the likelihood of tilting may increase. 
     In some embodiments, at least one of the at least two attachment portions of the frame member and/or the at least one guiding member are/is configured to open or close an electric circuit of the medical imaging device, preferably to function as a limit switch or electrical contact. 
     The opening or closing of such an electric circuit may be required to operate the medical imaging device or particular functions thereof. The opening or closing of such electric circuit may provide, alternatively or in addition, an optic and/or acoustic indicator indicating a proper attachment of the sterile cover to the medical imaging device. For example, a light is turned on or off when the guiding member has closed or opened a respective electric circuit. 
     With the guiding member functioning as limit switch, the closing and/or opening of an electric circuit is linked to the final attachment position of the sterile cover. Accordingly, the functionality of a limit switch may support safety aspects. Alternatively or in addition, with the guiding member functioning as a electrical contact the closing of a contact or circuit is less prone to be a result of anything else but the electrical contact. For example, opening of a circuit may also occur due to a breakage of wires or the like. Instead, closing an electric circuit is less likely to happen unintentionally. 
     Advantageously, the transparent cover portion has a thickness in an imaging direction of 0.4 to 0.6 mm. Preferably, it has a refraction index of about 1.49. 
     Due to the combination of the thickness in the imaging direction when attached to a medical imaging device and a refraction index of substantially 1.49, the focus of the medical imaging device or the imaging components, respectively, may not be shifted significantly when the medical imaging device orbits a point of interest. With other words, the focus remains substantially constant at the point of interest during orbiting of the medical imaging device. Even though a control may compensate a focus shift by adapting the distance between the medical imaging device and the point of interest in dependence of the rotational angle, such control may become extremely complex. 
     A refraction index of substantially 1.49 may be achieved by using PMMA, i.e. polymethylmethacrylate, as material for the transparent cover portion. Increasing deviations from the defined refraction index in combination with the respective thickness of the transparent cover, impairs the control of the focus. 
     In other aspect, the present invention relates to a sterile medical imaging system, comprising: a medical imaging device and the sterile cover as described above, wherein an outer portion of the medical imaging device extends outwardly with a positive convergence angle from the imaging front side of the medical imaging device, and wherein the outer portion of the medical imaging device extending outwardly from the imaging front side of the medical imaging device comprises at least two attachment portions, preferably recessed in said outer portion, corresponding to the attachment portions of the sterile cover. 
     Accordingly, the attachment portions of the medical imaging device are configured to engage with corresponding attachment portions of the sterile cover to form a form-fit connection. Depending on the design of the attachment portions of the medical imaging device and/or sterile cover, the form-fit connection may be further supported by force-fitting elements. For example, a snap of a snap-fit member as attachment portion of a sterile cover may not only engage with a recess of a medical imaging device in terms of a form-fit connection. If the snap-member is still deformed elastically when arranged in a form-fit connection, the snaps may also apply a compressive force on the recess or the medical imaging device, respectively. Thus, the attachment may be secured more efficiently. 
     Furthermore, when the attachment portions of the medical imaging device are recessed in the outer portion of the medical imaging device, the number of potentially outwardly protruding contours and thus, interfering contours of the medical imaging device may be reduced. 
     Preferably, the positive convergence angle is equal to or less than 15°. 
     The positive convergence angle may correspond to a convergence angle of the optical components of the medical imaging device. Consequently, a compact medical imaging device may be provided. Furthermore, a limited convergence angle may also ease the design of the attachment portions of the sterile cover to engage with an attachment portion of the medical imaging device on an outer portion. 
     In some embodiments, the surface of transparent cover portion facing at least one imaging component forms an angle of about 84° to 87° with the optical axis of the at least one imaging component, wherein the distance between the surface of the transparent cover and the surface of the imaging component facing the transparent cover is preferably equal to or less than 25 mm. 
     The angle of 84° to 87° between the surface of the sterile cover facing the medical imaging device and the optical component of the medical imaging device also supports a sufficiently stabile focus, in particular, in further view of a thickness the transparent cover portion of the sterile cover and a refraction index of the transparent cover portion of substantially 1.49. 
     Furthermore, if the distance between the surface of the transparent cover and the surface of the imaging component facing the transparent cover is more than 25 mm, the amount of light scattered from the field of interest due to its illumination may impair the imaging by the imaging components of the medical imaging device. In other words, the amount of scattered light entering any imaging component may be sufficiently limited by restricting the distance between the surface of the transparent cover and the surface of the imaging component. 
     Preferably, the at least two attachment portions of the sterile cover and the at least two attachment portions of the medical imaging device, respectively, and/or the guiding member of the sterile cover are configured to provide only one attachment orientation. 
     The attachment portions may, for example, be positioned such that the sterile cover is only attachable in one orientation of the sterile cover with respect to the medical imaging device. This may be advantageous, if the transparent cover portion may only allow an unobstructed view through the imaging components in one orientation of the sterile cover. Un unambiguous orientation of the sterile cover to be attached may also be provided, alternatively or in addition, by at least one guiding member and/or attachment portion with a protruding length that, for example, fits only in one corresponding recess of the medical imaging device to allow the attachment portions of the sterile cover to be moved into engagement with the attachment portions of the medical imaging device. In other words, any measure to reduce the likelihood of a misalignment is directed to allowing an attachment only in a defined orientation of the sterile cover with respect to the medical imaging device and/or at least restricts the functionality of the medical imaging device and/or indicates a misalignment in the event of an undesired positional relationship. 
     Advantageously, the medical imaging device comprises an electric circuit ( 13 ) closable by at least one of the at least two attachment portions of the sterile cover ( 30 ) and/or the at least one guiding member of the sterile cover. 
     As already described in the context of the sterile cover, such electric circuit may be used to indicate a predetermined attachment of the sterile cover to the medical imaging device. Further, the electric circuit may, alternatively or in addition to the above measures, only be opened or closed if the sterile cover is attached to the medical imaging device in a proper orientation. 
     In some embodiments, the medical imaging device of the sterile medical imaging system is a microscope. 
     Further advantages, aspects and details of the disclosure are subject to the claims, the following description of preferred embodiments applying the principles of the disclosure and drawings. In the figures, identical reference signs denote identical features and functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic cross-section of a sterile cover and medical imaging device according to an exemplary embodiment; 
         FIG.  2    is a schematic cross-section of the sterile cover and medical imaging system according to  FIG.  1    when the sterile cover is attached to the medical imaging device; 
         FIG.  3    is an enlarged view of the sterile cover and the region of the medical imaging device facing the sterile cover according to  FIGS.  1  and  2   ; and 
         FIG.  4    is an exemplary view of a design of a guiding member and recess. 
     
    
    
       FIG.  1    is a schematic cross-section of a medical imaging device  10  and a sterile cover  30  of a sterile medical imaging system  1 . The medical imaging device  10  comprises an imaging front side  10   a  facing the sterile cover  30  in an attachment orientation, in which the sterile cover  30  can be attached to or detached from the medical imaging device  10  by a bidirectional movement as indicated by the double arrow. An outer portion  10   b  of the medical imaging device  10  extends outwardly from the imaging front side  10   a  of the medical imaging device  10 . The convergence angle α ( FIG.  3   ) of the outer portion  10   b  is similar to the convergence angle of the imaging components  20   a ,  20   b  of an imaging unit  20 . Here, each imaging component  20   a ,  20   b  is configured as an ocular, which provide an angle in-between thereof to be aligned on a common field of interest. Due to the similar convergence angle, the contour of the medical imaging device  10  may be designed compact. In the shown embodiment, the outer portion  10   b  also comprises two attachment portions  11  formed by notches to receive corresponding attachment portions of the sterile cover  30 , as addressed later. Additionally, the imaging front side  10   a  provides two recesses  12  to allow the sterile cover  30  to be guided by moving corresponding guiding members  43  within the recesses  12 . It should be noted that the number of attachment portions  11  and/or recesses  12  is not limited to the number as shown in the exemplary embodiment of  FIG.  1   . However, at least two of respective attachment portions  11  and/or recesses  12  provide at least some stability in terms of reducing the likelihood of the sterile cover to tilt without an excessive number of connection components. However, an increased number of attachment portions  11  and/or recesses  12  may provide more options to attach and/or guide different types of sterile covers  30  to a medical imaging device  10 . 
     The sterile cover  30  comprises a frame member  40  and a transparent cover portion  50 . The transparent cover portion  50  is affixed to the frame  40  and configured to allow the imaging unit  20  of the medical imaging device  10  to image a field of interest through the transparent cover portion  50  while being disposed in front of the medical imaging device  10  by the attachment of the frame member  40  to the medical imaging device  10 . The frame member  40  provides a facing side  41  which is intended to face the imaging front side  10   a  of the medical imaging device  10  in an attachment orientation. The transparent cover portion  50  may be disposed in the frame member  40  with its surface opposite to the facing side  41  being flush with the frame surface also opposite to the facing side  41  to be disinfected or sterilized without interfering contours. Alternatively, such surface of the transparent cover portion  50  may be recessed within the frame member  40  to enhance the protection of the transparent cover portion  50 . 
     The frame member  40  also comprises two attachment portions  42  intended to engage with the attachment portions  11  of the medical imaging device  10  to attach the sterile cover  30  to the medical imaging device  10 . According to the illustrated embodiment, the attachment portions  42  are configured as snap-fit members protruding from the facing side  41  of the frame member  40  at opposite ends of the frame member  40 . Here, the snap-fit members protrude perpendicular to the facing side  41 . However, the attachment portions  42 , irrespective of their specific design, may also protrude at an angle deviating from 90°, for example, according to design constraints. The attachment portions  42  configured as snap-members provide a snap at each respective end opposite to the facing side  41 . 
     Further, the frame member  40  comprises to guiding members  43 , which also protrude from the facing side  41 . As per the guiding function, the guiding members  43  protrude substantially perpendicular to the facing side  41 . However, slight deviations may be possible according to specific design options. 
       FIG.  2    shows the sterile cover  30  attached to the medical imaging device  1  in the same cross-section as per  FIG.  1   . The sterile cover  30  is attached by a relative movement to reduce the distance between the facing side  41  and the imaging front side  10   a . Accordingly, the attachment portions  42  as resilient snap-fit members with snaps  42   a  are elastically deformed over at least some extension of the outer portion  10   b  before arriving at the corresponding attachment portions  11 . When the snaps  42   a  arrive at attachment portions  11  formed as notches in this exemplary embodiment, the snaps  42   a  are forced into the notches due the elastic restoring forces of the resilient attachment portions  42 . 
     The imaging components  20   a ,  20   b  of the imaging unit  20  or their optical axis, respectively, are each inclined by 5° with respect to a vertical axis in  FIG.  2   . In other words, the imaging components  20   a ,  20   b  provide a convergence angle of 10° between each other. Accordingly, the optical axis of each imaging component  20   a ,  20   b  forms an angle of 85° with the transparent cover portion  50 . Such angle is preferably between 84° and 87°. To reduce a focus shift in such configuration to an acceptable minimum, the transparent cover portion has a thickness in direction of the optical axis of the respective imaging component  20   a ,  20   b  of 0.5 mm+/−0.1 mm, i.e. between 0.4 mm and 0.6 mm. Further, the refraction index is about 1.49 with PMMA selected as material for the transparent cover portion  50 . To reduce the amount of scattered light entering the imaging components  20   a ,  20   b , the transparent cover portion  50  is distanced less than 25 mm from each imaging component  20   a ,  20   b . The size of the transparent cover portion  30  in this embodiment is limited to the size required for imaging. The amount of scattered light entering the imaging components may therefore be optimized by the combination of the distance and sized of the transparent cover portion  50 . 
       FIG.  3    is an enlarged view of the sterile cover  30  and the region of the medical imaging device  10  facing the sterile cover  30  according to  FIGS.  1  and  2   . The guiding members  43  provide a protruding length L 1 . However, the guiding members  43  may also provide different hides. For example, if one guiding member  43  provides a greater length L 1 +ΔL and the medical imaging device  10  comprises a corresponding recess, the sterile cover  30  may only be able to be attached, if each guiding member  43  enters its corresponding recess  12 . Assuming that the corresponding recesses  12  have a depth of L 1  and L 1 +ΔL, respectively, the length of the protruding length L 2  for engagement should be at least L 1  minus the difference in length ΔL, i.e. L 2  min=L 1 −ΔL. Thus, the sterile cover  30  may only be attached in one attachment orientation. In other words, the attachment portions  42  cannot engage with the attachment portions  11  when the sterile cover is, for example, turned around a vertical axis in  FIG.  3    by 180°. 
     Irrespective of different lengths of the guiding members  43  and depths of the recesses  12 , the protruding length L 2  for engagement of the attachment portions  42  in the embodiment of  FIG.  1    is greater than the protruding length of the guiding members  43 . Accordingly, a ratio between l 1  and L 2  is less than 1, preferably between 0.41 and 0.74. Furthermore, the ratio of the cross-section A 1  of the guiding member  43  perpendicular to its protruding length L 1  to be received by the corresponding recess  12  to the cross-section A 2  of said recess  11  perpendicular to its depth is also less than 1, preferable in general between 0.15 and 0.9. In the embodiment according to  FIG.  3    the medical imaging device  10  comprises an electric circuit  13  that is closed when the sterile cover  30  is attached to the medical imaging device  10  due to engagement of the attachment portions  42 ,  11 . In such embodiment, the ratio of A 1  to A 2  should be rather in a range of 0.9 than in a range of 0.15 to ensure closing of the electric circuit  13 . On the other hand, a lower ratio may be less sensitive to manufacturing tolerance that may result in frictional forces or otherwise impede the insertion of the guiding members  43  in the recesses  12 . To allow a low ration A 1  to A 2  in combination with the electric circuit  13 , the electric circuit may form a contact area at the bottom of the recesses  12 . The contacts can be closed by the end surfaces of the guiding members  43 . Thus, such configuration is less sensitive to lateral tolerances but to tolerance in corresponding lengths. To reduce tolerance in length, the end surfaces of the guiding members and/or the bottom of the recesses  11  may comprise resilient surface portions to compensate potential tolerances. The combination of the guiding members  43  and recesses  12  in view of closing or opening an electric circuit may also be configured as e mechanical switch, e.g. a button or actuator disposed in a corresponding recess  12  that is movable in the insertion direction of the guiding member  43  to close or open an electric circuit. Even though the embodiment of  FIG.  3    illustrates an example of an electric circuit  13  to be closed by the two guiding members  43 , the electric circuit  13  may also be configured to be closed by at least one of the guiding members  43 . The same applies vice versa in the event of an electric circuit to be opened. 
     Further, the attachment portions  42  are configured to provide a gap a between respective snaps  42   a  of the snap-fit members as attachment portions  42  and the imaging front side  10   a  of the medical imaging device  10  in parallel to the facing side  41  of the frame member  40 , here less than 4 mm, when the medical imaging device  10  extends outwardly with a positive convergence angle α from the imaging front side  10   a . The convergence angle α in the exemplary embodiment is 5°. Due to the gap a, the resilient attachment members  42  are not elastically deformed when initially moved over the imaging front side  10   a  but during the course of the movement to approach the corresponding attachment portions  11  of the medical imaging device  10 . Thus, the elastic deformation may be reduced to a minimum to ensure an elastic deformation required for the snaps  42   a  to be moved in a locking position into the notches as attachment portions  11  due to the elastic restoring forces. However, the gap a should still be restricted to reduces the protruding length L 2  for engagement under consideration of the convergence angle α, here 5°. 
       FIG.  4    is an exemplary view of a design of a guiding member  43  and a corresponding recess  12 . The end surface of the guiding member  43  facing the bottom surface of the recess  12  is tapered and forms a concave surface with an inclination angle β with respect to a plane perpendicular with the longitudinal axis z. Preferably, the inclination angle β is between 20° and 45°, which may also provide a centering functionality. Alternatively to the concave surface the end surface of the guiding member may be conical. However, a concave shape with respect to a radius near the longitudinal axis z may provide manufacturing advantages. The bottom surface of the recess  12  provides a corresponding surface shape in term of a positive-negative configuration. Due to such design, said combination is particularly advantageous, if the guiding member  43  is intended to actuate the bottom surface of the recess  12  as an actuator to close or open, for example, the electric circuit  13 . Specifically, the actuator is also actuated by the guiding member  43  even if such actuation takes place under bending or skewed actuation. 
     It is to be noted that the given examples are specific embodiments and not intended to restrict the scope of protection given in the claims. In particular, single features of one embodiment may be combined with another embodiment as long as such combination is not reasonably excluded. As an example, the electric circuit to be opened or closed may be provided, alternatively or in addition, by the sterile cover. 
     LIST OF REFERENCE SIGNS 
     
         
           1  sterile medical imaging system 
           10  medical imaging device 
           10   a  imaging front side 
           10   b  outer portion 
           11  attachment portion (medical imaging device  10 ) 
           12  recess 
           13  electric circuit 
           20  imaging unit 
           20   a  imaging component 
           20   b  imaging component 
           30  sterile cover 
           40  frame member 
           41  facing side 
           42  attachment portion (sterile cover  30 ) 
           42   a  snap 
           43  guiding member 
           50  transparent cover portion 
         a gap 
         A 1  cross-section (guiding member  43 ) 
         A 2  cross-section (recess  12 ) 
         L 1  length (guiding member  43 ) 
         L 2  length for engagement (attachment portion  42 ) 
         z longitudinal axis 
         α convergence angle 
         β inclination angle