Abstract:
The invention relates to a medical imaging means including a movement mechanism ( 10 ). The movement mechanism ( 10 ) comprises a first mounting part ( 21 ) and a second mounting part ( 22 ) and at least three link arm members. The link arm assemblies of the mechanism include actuator means and a link arm member or a set of link arm members. The movement mechanism is used for moving a medical imaging device or a part thereof.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a medical imaging means including a movement mechanism having a first mounting part and a second mounting part and at least three link arm assemblies, said link arm assemblies including actuator means and a link arm member or a set of link arm members, whereby said movement mechanism is used for moving a medical imaging device or a part thereof. 
     BACKGROUND OF THE INVENTION 
     A great number of medical imaging methods require the movement of the imaging device or parts thereof. Such a movement can be orbital, rotational or linear. In conventional systems, the implementation of the movements requires extremely complicated arrangements. 
     The use of parallel-arm mechanisms is known from robotic systems for implementing a 3-dimensional movement. Such an arrangement has two essentially planar elements connected to each other by link arms or pairs of link arms of a controllable length. In the following text, such an arrangement is called a parallel-arm mechanism. One of the planar elements is fastened to a support structure, while the other planar element carries mounted thereon the means whose movement is desired. By adjusting the length of the link arms by active actuator means, a complete 3-dimensional freedom of movement is attained over spatial area needed for a specific task. Such a mechanism is commonly used in, e.g., machining equipment, aircraft simulators and placement of electronic components. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved medical imaging means and particularly an improved movement mechanism for use with the same. 
     It is a particular object of the present invention to provide an improved movement mechanism for use in conjunction with a panoramic radiography apparatus. 
     It is a still further particular object of the present invention to provide an improved movement mechanism for use in conjunction with a mammography apparatus. 
     To achieve the above-described goals and others to be mentioned later in the text, the invention is principally characterized in that 
     a first mounting part is adapted mountable on a support structure such as a wall, ceiling or support beam, 
     medical imaging device or a part thereof, 
     link arm members are pivotally connected at pivot points to said first mounting part and said second mounting part, 
     the length or position of said link arm members is adapted controllable by an actuator means, and 
     the position, inclination and/or rotation of said second mounting part is adapted controllable by virtue of adjusting the length of the link arm members and/or the height of their pivot point. 
     In the invention, the above-mentioned parallel-arm mechanism has been adapted to a novel application, namely, for implementing the trajectory of dynamically moving members in medical imaging apparatuses. No movement mechanism of a medical imaging apparatus is known in the art to be constructed using this type of parallel arm mechanism. 
     Medical imaging apparatuses pose extremely tight requirements on the accuracy of an arrangement implementing a trajectory. The use of a parallel-arm mechanism in such demanding applications as machining equipment has proved its capability of accomplishing an extremely precise and smooth trajectory. 
     The unlimited degree of freedom achievable by a parallel-arm mechanism in 3-dimensional dynamic movements over a desired area facilitates the implementation of all known imaging modes including fluoroscopy, 3D tomography, tomosynthesis imaging and slit fluoroscopy. 
     The use of a parallel-arm mechanism for implementing the trajectories required in a medical imaging apparatus is particularly advantageous owing to the simple construction of such a movement mechanism. Hence, the structure of the mechanism is more cost-efficient in production than conventional constructions and it is easily connectable to other parts of an imaging apparatus. The accuracy of the trajectory thus accomplished is excellent which is a significant benefit in medical imaging. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention is described in greater detail with reference to a preferred embodiment thereof having a nonlimiting character to the scope and spirit of the invention, said embodiment being illustrated in the appended drawings in which 
     FIG. 1 shows a general view of a parallel-arm mechanism; 
     FIG. 2 shows a parallel-arm mechanism connected to the C-arcuate body part used in a panoramic radiography apparatus; 
     FIG. 3A shows the parallel-arm mechanism from below in its basic position; 
     FIG. 3B shows the parallel-arm mechanism from below with its second mounting parts rotated; 
     FIG. 3C shows the parallel-arm mechanism from below with its second mounting part rotated and moved; 
     FIG. 3D shows the parallel-arm mechanism from below with its second mounting part moved into its first limit position; 
     FIG. 3E shows the parallel-arm mechanism from below with its second mounting part moved into its second limit position; 
     FIG. 4A shows the parallel-arm mechanism in a side view illustrating the situation of FIG. 3C; 
     FIG. 4B shows the parallel-arm mechanism in a side view illustrating the situation of FIG. 3E; 
     FIG. 5 shows the parallel-arm mechanism in a situation having one of its mounting parts inclined; 
     FIG. 6 shows a side mounting of the parallel-arm mechanism; 
     FIG. 7 shows a side mounting of the parallel-arm mechanism; now connected to a C-arcuate body part suited for use in a mammography application; and 
     FIG. 8 shows an alternative mechanism for implementing a parallel-arm mechanism. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now referring to FIG. 1, therein is shown a parallel-arm mechanism  10  in an upright position. There are mounted six link arm members between its first mounting part  21  and its second mounting part  22 . While in the illustrated embodiment, the first mounting part  21  and the second mounting part  22  have a triangular shape of essentially planar structure, also mounting parts of any alternative shape are possible in practice. 
     In the embodiment shown herein, each corner of each triangular mounting part  21 ,  22  has two connection points for the link arm members. To each triangular corner of the first mounting part  21 , there are connected two link arm members having their other ends connected to separate connection points on the second mounting part  22 . Either end of the link arm members  11 , 12 , 13 , 14 , 15 , 16  is provided with a ball joint N fixed on the mounting parts  21 , 22 . To each link arm member  11 , 12 , 13 , 14 , 15 , 16  is adapted an actuator M capable of controlling the length of its dedicated link arm member. By controlling the lengths of the link arm members individually, it is possible to implement a linear, rotational or tilting movement or a combination of these. The lengths of the link arm members are steered according to a predetermined control program. 
     In FIG. 2 is shown a parallel-arm mechanism  10  having its one mounting part carrying a body part  41  shaped as a C-arm. In this embodiment, the C-arm  41  is used in panoramic radiography for the imaging of the jaw bone and the teeth. For this application, the height position of the C-arm  41  and its position in the horizontal plane are controlled. The actual rotating movement required in panoramic radiography is accomplished with the help of an active actuator  18 . The actuator M and the active actuator means  18  connected to the link arm members of the parallel-arm mechanism  10  are controlled by a microprocessor-based control system or, using any other type of predetermined control program. 
     In FIG. 3A is shown the parallel-arm mechanism as seen from below in its basic position. In this position, all the link arm members are controlled equally long. The first mounting part  21  and the second mounting part  22  are then parallel and their center points fall on the same axis. 
     In FIG. 3B is shown the parallel-arm mechanism as seen from below with its second mounting part  22  rotated with respect to the basic position (cf. FIG.  3 A). The rotational movement is implemented by controlling the lengths of the link arm members. 
     In FIG. 3C is shown the parallel-arm mechanism as seen from below with its second mounting part  22  rotated and moved away from the center axis of the first mounting part  21 . 
     In FIG. 3D is shown the parallel-arm mechanism as seen from below with its second mounting part  22  moved into its first limit position. The link arm members  13  and  16  are controlled into their longest position. From this position, the center point of the second mounting part  22  cannot be moved farther away from the center point of the first mounting part  21 , but however the second mounting part  22  can still be rotated or inclined from said position by controlling the lengths of the link arm members 
     In FIG. 3E is shown the parallel-arm mechanism as seen from below with its second mounting part  22  moved into its second limit position. Now the link arm members  11  and  16  are controlled into their longest positions. 
     In FIG. 4A is shown the situation of FIG. 3C in a side view. In this position, the first mounting part  21  and the second mounting part  22  are situated parallel to each other. 
     In FIG. 4B is shown the situation of FIG. 3E in a side view. 
     In FIG. 5 is shown the parallel-arm mechanism  10  in a position having the second mounting part  22  controlled into an inclined position. 
     In FIG. 6 is shown a side mounting of the parallel-arm mechanism  10 . Herein, the first mounting part  21  is now oriented upright thus permitting its fastening on, e.g., a wall, support beam or a part of a medical imaging apparatus. The movable part of the imaging apparatus is mounted on the second mounting part  22 . 
     In FIG. 7 is shown a side mounting of the parallel-arm mechanism, now connected to a C-arcuate body part  42  which in this embodiment is suited for use in a mammography application. This kind of movement mechanism according to the invention offers a greater number of degrees of freedom than conventional constructions of mammography equipment. To the C-arcuate body part  42  of a mammography apparatus is connected an active actuator means  19  in order to provide a rotating movement. The actuators M and the active actuator means  19  that are connected to the fink arm members of the parallel arm mechanism  10  are controlled by a microprocessor-based control system or using any other type of predetermined control program. 
     In FIG. 8 is shown an alternative mechanism for implementing a parallel-arm mechanism. Herein, the first mounting part comprises an upper support plate  51  with actuator motors M and a support ring  52  connected thereto, and threaded control link arms S connecting said support ring  52  to said upper support plate  51 . Actuator driven nuts N are adapted to run on the threaded control link arms S. Between the actuator nuts N and the second mounting part  22 , there are disposed stiff link arm members  61 , 62 , 63 , 64 , 65 , 66 , each of which having their first end pivotally connected to the actuator nut N running on the threaded control link arm S and their other end similarly pivotally connected to said second mounting part  22 . Each actuator motor M is adapted to rotate the threaded control link arm S connected to the motor output. With the rotation of the threaded control link arm S, the position of the nut N running on the arm.can be changed thus imparting a linear motion on the link arm member  61 , 62 , 63 , 64 , 65  or  66  which is respectively connected to the nut. Thus, the controlled movement of the connection points of the link arm members on the first mounting part implements the controlled steering of the position, rotation and inclination of the second mounting part  22 . The actuators M are controlled by a microprocessor-based control system or using any other type of predetermined control program. 
     In FIGS. 1-8 are shown the positions of the parallel-arm mechanism members in different stationary positions. Typically, a parallel-arm mechanism is used to accomplish a continuous dynamic movement, and the purpose of the above-described examples is to elucidate the instantaneous positions of the parallel-arm mechanism during its dynamic movement. 
     According to the needs of any specific application, the above-described movement mechanism may be modified in a plurality of different fashions within the scope and spirit of the invention. For instance, the first mounting part  21  and the second mounting part  22  may be designed into the shape of any feasible and practicable structure. The first mounting part  21  of the parallel-arm mechanism may alternatively be fastened to the ceiling of the radiography room or to a separate support beam or other part of the imaging apparatus. 
     The scope of the invention is defined in the appended claims.