Abstract:
An apparatus for thermal treatment of tissue comprises a compact manipulator ( 37 ) for positioning and orienting an energy radiator ( 50 ) for heat treatment of biological tissues. The energy radiator ( 50 ) is adapted to emit energy in the direction of a focal axis into a focal volume. The manipulator ( 37 ) can adjust the position and orientation of a suspension body ( 20 ) in a plane. The plane wherein the suspension body can be maneuvered is parallel to a support face of the apparatus. The energy radiator ( 50 ) is suspended from the suspension body ( 20 ). The energy radiator ( 50 ) can be manipulated with five independent degrees of freedom relative to said support face.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an apparatus for thermal treatment of tissue, provided with a support face for supporting at least a portion of a patient&#39;s body and comprising an energy radiator mounted to a holder, for directing energy along a focusing axis into a focal volume, and a manipulator comprising a manipulator transmission unit including a suspension body, a transmission driver unit mounted to the manipulator transmission unit, the transmission driver unit comprising at least one transmission driver and the holder suspended from the suspension body, wherein the manipulator transmission unit is driveable by the transmission driver unit and the holder is driveable by the manipulator transmission unit. 
       BACKGROUND OF THE INVENTION 
       [0002]    An apparatus for thermal treatment of tissue is known from the international application WO 2005/107870. The apparatus described in application WO 2005/107870 is claimed to be suitable for treating tumors in breast tissue by means of High Intensity Focused Ultrasound (HIFU). In HIFU systems the ultrasound energy generated by an energy radiator is focused into a small focal volume at the specific target locations of for example cancerous tissue. During treatment, the beam of focused energy penetrates through tissue and causes localized temperature rises in a well-defined region being the focal volume. Thus, ultrasound beams are focused on a tissue, and due to the energy deposition at the focus, temperature within the tissue rises to a level, completely destroying it. The temperature rise produces preferably well-defined regions of protein denaturisation, irreversible cell damage and necrosis. A single exposure of focused ultrasound energy is called a sonication. Sonication is a process of dispersing, disrupting or deactivating biological materials by the use of sound waves. Multiple sonications are necessary to ablate the targeted tissue. Tight focusing is needed to limit the ablation only to the targeted location of a patient&#39;s lesion, myoma, uterine fibroid or the like. This technology can achieve precise ablation of diseased tissue, if the procedure is guided and controlled using Magnetic Resonance Imaging (MRI). Applying power to a patient needs planning, targeting of the energy and monitoring of the energy delivery. No energy must be scattered or dissipated unnecessarily in risky regions of e.g. nerves or vital organs. In general, the energy is emitted in an aiming direction along a focusing axis into a focal volume located at a focal distance from the energy radiator. The apparatus described in WO 2005/107870 relates to a device for positioning an energy-generating means of an assembly for heat treatment of biological tissues. Positioning of the energy-generating means of WO 2005/107870 is enabled in a plane between the bottom section of an MRI scanning apparatus and a support holding the patient. The energy-generating means of WO 2005/107870 are adapted to emit energy along a focusing axis, wherein the focusing axis is oriented substantially parallel to the coronal plane and the focal volume is positioned outside the torso while avoiding the regions inside the torso underneath the breast tissue. The coronal plane separates the human body into a ventral portion and a dorsal portion. The coronal plane is perpendicular to the median plane that separates the body into a left and right side. The device of WO 2005/107870 avoids emitting energy parallel to the median plane into risky regions accommodating vital organs. For that purpose the positioning device of WO 2005/107870 comprises an energy-generating means suspended from an annular frame. The device of WO 2005/107870 enables two perpendicular translations of the energy-generating means parallel to the coronal plane of the patient, in WO 2005/107870 indicated as T1 and T2. Perpendicular rails are provided to enable the perpendicular translations T1 and T2 of a suspension frame. The positioning device of WO 2005/107870 enables two rotations of the energy-generating means, in WO 2005/107870 indicated as R1 and R2. Thus, the maneuverability of the energy-generating means of WO 2005/107870 comprises two translations T1 and T2 and two rotations R1 and R2 to position and orient the energy-generating means relative to the support holding the patient. 
         [0003]    However, if treatment is needed of tissue, located inside the torso underneath the breast cover or if treatment aims at prostate ablation or in case of treatment of the uterus, the component of the aiming direction of the energy transversal to the coronal plane is relatively large compared to the component of the aiming direction comprised by the coronal plane. To minimize and preferably eliminate the risks of emitting energy into unintended regions of e.g. the inner torso, accommodating vital organs or nerves or the like, the energy radiator should be positioned and oriented with high precision and high reproducibility relative to the tissue to be treated. Accurate positioning of the energy radiator or transducer is important to localize the focal volume only at the targeted tissue. Accurate orientation of the energy radiator is essential to align the focusing axis of the energy emission with a permissible path to the targeted tissue to get round possibly risky regions, vital organs, nerves and the like. Use can be made of MRI equipment to give feedback to the operator on the location of the temperature rise relative to the region of the disorder to be treated. The positioning of the focal volume and the orientation of the focusing axis should be realized by a compact device to enable treatment of tissue in combination with diagnostic equipment as MRI. This kind of equipment provides only limited space to mount and operate the positioning device. As is commonly known, the space that is available to a patient inside the bore or scanning area of MRI equipment is very limited and this may cause distress especially to patients suffering from claustrophobia. The positioning device of application WO 2005/107870 is not apt for precise positioning and alignment of the energy penetrating into regions of the body inside the torso, because the positioning device of application WO 2005/107870 is arranged to focus the energy in a plane mainly parallel to the coronal plane outside the torso and through the beast tissue covering the torso and not for positioning the focal volume and the energy generating means along a direction substantially perpendicular or transverse to the coronal plane into the torso. A further problem of the device of application WO 2005/107870 is that the device is inherently space consuming because of stacking of components as will be explained hereafter. An annular frame is positioned between a set of rails to enable translation T2. The device of application WO 2005/107870 comprises two elongated bodies to enable translation T1. The bodies need to be elongated because cranks should remain outside the bore of the MRI to be accessible for manual operation. Also if electric equipment is used to drive said cranks the electric equipment must remain outside the bore of the MRI to prevent interference and disturbance of the magnetic field of the equipment with the magnetic field generated and interpreted by the MRI equipment and used to give feedback for guidance and control of the position and orientation of the energy-generating means. Thus, in the device of application WO 2005/107870 four components are needed to enable two translations T1 and T2. If the positioning range of the annular frame is maximized, the range of possible translations T1 and T2 should be maximized. This is commonly realized by stacked straight-guides. In case of maximization of T1 and T2 in the device of application WO 2005/107870, it is not possible to position the length axes of said rails in the same plane as the plane defined by the length axes of said elongated bodies, because the rails cannot intersect with the elongated bodies. For this reason, the plane containing the length axes of the rails should have a distance to the plane containing the length axes of the elongated bodies. The distance needed to stack the rails and bodies in different planes is conflicting with the requirement of a flat and compact device, to fit into the narrow bore of an MRI apparatus without unacceptable limitation of space that remains available for patients. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to provide an apparatus for thermal treatment of tissue of the kind set forth in the opening paragraph, which can accurately position and orient the energy radiator in a space saving way with five independent degrees of freedom for substantially positioning the focal volume of the energy along a focusing axis. 
         [0005]    With the apparatus for thermal treatment of tissue of the invention this object is realized in that the manipulator transmission unit has a first transmission subunit for translating and rotating the suspension body in a plane substantially parallel to the support face and has a second transmission subunit for moving the energy radiator along the focusing axis and for rotating the energy radiator around two distinct axes perpendicular to the focusing axis. 
         [0006]    To analyze and characterize the performance of a positioning device use will be made of the degrees of freedom of a rigid body. The degrees of freedom of a rigid body are the set of independent translations and rotations that specify completely the position and orientation of the rigid body relative to a coordinate system. The translations of the rigid body represent the ability of the rigid body to move in each of the three dimensions. The rotations of the rigid body represent the ability of the rigid body to change angle around the three perpendicular axes characterizing the three dimensions. Thus, a rigid body can have a maximum of six independent degrees of freedom. The energy generating means of the device of application WO 2005/107870 has two degrees of freedom R1 and R2 relative to the annular frame from which said means is suspended and the annular suspension frame has two degrees of freedom T1 and T2 relative to its support. The manipulator transmission of the invention has a first subunit for translating and rotating the suspension body in a plane substantially parallel to the support face instead of the rails and elongated bodies of the device of application WO 2005/107870. The device of application WO 2005/107870 uses four components, being two rails and two elongated bodies. The components, needed in the first subunit to realize the translation and the rotation of the suspension body, may be arranged, such that inherently little mounting space is needed to realize a compact apparatus according to the invention. As a further advantage, it can be mentioned that with the apparatus according to the invention no stacking of components is needed to position the suspension body. The energy radiator is suspended from the suspension body. The second transmission subunit can move the energy radiator along the focusing axis and can rotate the energy radiator around two distinct axes perpendicular tot the focusing axis. Thus, the energy radiator has three independent degrees of freedom relative to the suspension body. The suspension body has two independent degrees of freedom relative to the support face. The energy radiator of the invention can thus be positioned and oriented relative to the support face with five independent degrees of freedom. Three translations are possible to position the focal volume and two rotations are possible to orient the focal axis relative to the support face. However, to provide maximum maneuverability to the radiator a maximum of six degrees of freedom could be realized. Realization of six independent degrees of freedom goes at the expense of a considerable amount of hardware. The energy is usually emitted in a volume enclosed by a surface of substantially conical shape. The focusing axis is an axis of rotation symmetry with respect to said conical surface. Because of said rotation symmetry around the focusing axis the rotation of the energy distribution around the focusing axis is considered less important than the rotation around two distinct axes perpendicular to the focusing axis. For this reason the hardware needed to realize a rotation of the radiator around the focal axis is omitted and the radiator can be maneuvered with five independent degrees of freedom comprising the ability to move in a direction transversal to the support face. The possibility of translation perpendicular to the support face enables treatment of tissue inside the human torso underneath the beast tissue. 
         [0007]    Because the invention inherently leads to compact embodiments, more design freedom is created to optimize the geometry of the construction with respect to stiffness of the construction. Stiffness of the device enables accurate and reproducible maneuvering of the radiator. Deformation in general leads to a compliant construction that is difficult to control via feedback from the MRI. The radiator will be in the proximity of the patient&#39;s disorder, i.e. inside the bore of the MRI, while the motor will be positioned outside the detecting volume of the scanning equipment to prevent interference of the magnetic field produced by e.g. a driving motor with magnetic resonance signals to be detected by the MRI equipment. Several transmission parts are needed to bridge the distance between the motor and the radiator. A geometrically stiff construction enables the use of materials that do not necessarily have a high Young&#39;s modulus or modulus of elasticity. Furthermore, these parts should be made of materials having magnetic properties that are suitable for use in equipment for magnetic resonance imaging. A wide class of synthetic resins have magnetic properties suitable for use in magnetic resonance imaging. These synthetic resins can be reinforced with fibres to improve their mechanical strength. However, said resins do not necessarily have a high Young&#39;s modulus. For this reason it is very advantageous, that the geometrical stiffness of the construction enables the use of non-magnetic materials as synthetic resins possibly reinforced with fibres. The geometrical stiffness enables the use of these relatively compliant materials in the apparatus of the invention. Very suitable for application is a material called Werkstoff “S”®. Besides having suitable magnetic properties it has good resistance against wear and against chemicals and does retain its shape in the presence of water because it does not combine with water. If Werkstoff “S”® is used, the mechanism to position the radiator is made water-resistant and the energy radiator can be submerged into water to transmit its ultrasound waves. The sliding properties are favorable, which is desirable for good mechanical hysteresis. Suitable magnetic properties do however not necessarily exclude a high modulus of elasticity or Young&#39;s modulus, as in the case of ceramic materials. In the components loaded with bending moments ceramic materials can be used, because they retain shape, are magnetically compatible with magnetic resonance imaging and have a high modulus of elasticity. Among the ceramic materials the material category of oxides comprises materials as Aluminium oxide (Al2O3) and zinc oxide (ZnO). Said materials are suitable for use in preferred embodiments of the apparatus. Also the material category of carbides is suitable for use. Silicon carbide (SiC) can be mentioned as example of a material that is widely commercially available. Also more design freedom is created to optimize friction of the construction. High friction in combination with low stiffness causes mechanical hysteresis. Mechanical hysteresis manifests by a lag between displacement or rotation of the holder and a change in angle of rotation of a driver. This lag between action of the driver and response of the holder hinders accurate control of the positioning system via feedback provided by the MRI system. The overall ratio of stiffness of the device to friction in the device must preferably be high to prevent suffering from hysteresis. Because the invention inherently leads to compact embodiments with a limited number of stiff components, the friction in the construction can be optimized more easily. On the one hand the number of contacts is limited because of the limited number of components and on the other hand the components can be designed stiff as explained above. Stiff components allow for less deformation of the components, leading to well-defined contact situations between cooperating components. Well-defined contact between components leads to a better control of friction between components. 
         [0008]    An embodiment of the apparatus according to the invention is defined in that the suspension body comprises distant portions and the first transmission subunit comprises moveably guided abutments and abutment guides, each of the distant portions being rotatably connected to at least one of the moveably guided abutments and each moveably guided abutment being guidably supported by at least one of the abutment guides. If the suspension is rotatably connected to a moveably guided body, pretension and friction can be minimized in the connection between the distant parts of the suspension body and the moveably guided abutments and between the moveably guided abutments and the abutment guides. This is advantageous for positioning accuracy and reproducibility as explained before. Connecting distant portions instead of close portions of the suspension body to separate moveably guided abutments is beneficial for the accuracy attainable in the rotation of the suspension body in a plane substantially parallel to the support face. 
         [0009]    An embodiment of the apparatus according to the invention is defined in that the first transmission subunit comprises at least one transmission body for cooperation with one of the moveably guided abutments and being coupled to a separate transmission driver of the transmission driver unit. In the case of a rotatable transmission body, the transmission body can be arranged to convert a rotation into a guided translation of the moveably guided abutment. The moveably guided abutment can be positioned in a range of positions along its abutment guide. By driving the moveably guided abutment by a rotatable transmission body the total length of the system between the separate transmission driver and the abutment guide can be confined to a fixed length. Also a slideable transmission body can be used as e.g. a hydraulic cylinder. The hydraulic cylinder can be operated with water and the water can be pressurized by a hydraulic pump as embodiment of a transmission driver. The rotatable transmission body can be replaced by a slideable component, arranged such that the distance between the motor and the moveably guided abutment can be changed, as for example by a rack from a rack and pinion combination. The transmission body can also be a gear-drive, a belt-drive or a chain-drive. A further advantage of the transmission body is that the transmission driver unit may be kept outside the scanning volume to prevent possible interference of electromagnetic fields of the driver and the MRI device, if applied in an MRI device, or to be accessible for manual operation. A further advantage of a rotatable transmission body is, that it is easy to mount a measuring device to the transmission body to obtain feedback on the number of revolutions of the driver and the position of the guided body. 
         [0010]    An embodiment of the apparatus according to the invention is defined in that the distant portions each have a first axis of rotation with respect to the moveably guided abutment to which the respective distant portion is connected and wherein the transmission body cooperating with the respective moveably guided abutment comprises a first threaded portion, said portion having a first length axis, said first length axis intersecting with said first axis of rotation. The first threaded portion may have a ridge of for example a helical or spiral shape cooperating with the moveably guided abutment. One rotation of the transmission body is transmitted via the first threaded portion into a translation of the moveably guided abutment over a defined length referred to as the pitch. Application of a small pitch is favorable for accurate adjustment of the moveably guided abutment along its abutment guide and for accurate positioning and rotation of the suspension body. Because of the intersection of said axes no side forces or bending moments are introduced on the first threaded portion and the transmission body comprising said first threaded portion. Side forces and bending moments lead to relatively large deformations compared to the deformations associated with pure push and pull loads. As explained above, large deformations are detrimental for accuracy and reproducibility of positioning of the suspension body. 
         [0011]    An embodiment of the apparatus according to the invention is defined in that at least part of a moveably guided abutment is elastically deformed to establish pretension between the moveably guided abutment and the first threaded portion comprised by the transmission body cooperating with the respective moveably guided abutment. By controlled pretension, the mechanism can be kept free from backlash. A possible play resulting from loose connections between gears or other mechanical elements may cause a sudden or violent backward whipping motion. Such motion is harmful for positioning the radiator with a positioning accuracy in the order of magnitude of 0.1 mm. 
         [0012]    An embodiment of the apparatus according to the invention is defined in that the holder comprises three levers, moveably suspended from the suspension body. The energy radiator preferably should not be deformed. The energy radiator may contain a number of components that can suffer from mechanical strain. It is desired, that the holder positions the energy radiator in a statically determinate way, such that the static equilibrium equations are sufficient for determining the internal forces in the holder and the reaction forces on the energy radiator. A statically determinate structure as e.g. the radiator can be defined as a structure where, if it is possible to find internal actions in equilibrium with external loads, those internal actions are unique. In general six equations are needed to establish the static equilibrium of a structure in general and of the radiator in particular. Said six equations define the magnitude of six independent external forces exerted on the radiator. The three levers comprised by the holder exert these three external forces. Each lever may e.g. exert two perpendicular forces on the radiator. By applying three levers it is possible to hold the radiator with minimal deformation of the radiator. Each of the three levers may be moveably suspended from the suspension body such that it can pivot around a pivoting point on a pivoting axis, the pivoting point and the pivoting axis being fixed relative to the suspension body. Besides its pivoting point a lever has two more characterizing points, viz. the two lever ends, the lever ends being different from the pivoting point. In the lever ends the lever is connected to other components. One end of the lever may be rotatably connected to the radiator, while the other end can be rotatably connected to a mechanism comprised by the second transmission subunit. The end of the lever, connected to the radiator will be referred to as the radiator end. The end of the lever, connected to the mechanism comprised by the second transmission subunit will be referred to as the mechanism end. The lever can be arranged such that the line connecting the radiator end and the pivoting point is perpendicular to the line connecting the pivoting point and the mechanism end. The pivoting axis may be oriented such that the pivoting axis is perpendicular to the plane through the pivoting point and the two end portions of the lever. The lever may be suspended from the suspension body such that the line connecting the pivoting point and the mechanism end is perpendicular to the support face in a reference state of the lever. By using such a pivoting lever, a movement of the mechanism end is substantially parallel to the support face. Because the lever is rigid, the movement of the mechanism end is transmitted into a movement of the radiator end transversal to the support face. For this reason a lever is advantageous to transmit a movement in a first direction, e.g. parallel to the support face and transversal to the direction of the pivoting axis, into a movement transversal to the first direction. In an advantageous construction the holder comprises three such levers. Each lever having one radiator end, the holder comprises three radiator ends, referred to as a first, a second and a third radiator end. The three levers can be arranged such that the radiator ends define a plane referred to as the radiator plane. The radiator emits its energy along a focusing axis. The focusing axis defines a plane perpendicular to the focusing axis and running through the focal volume, referred to as the focal plane. The radiator can be mounted to the holder such that the focal plane remains parallel to the radiator plane. The focusing axis is now perpendicular to the radiator plane. The first and second radiator ends define a first line in the radiator plane. The third radiator end can be positioned such that the third radiator end is not on the first line. In the remainder of this paragraph it is assumed that translations and rotations are small. If the third radiator end is translated parallel to the focusing axis while at the same time not translating the first and second radiator ends, the radiator plane and the radiator are rotated around the first line, the first line being perpendicular to the focusing axis. This first line is thus a first axis of rotation of the radiator. If the first and second radiator ends are translated over an equal distance parallel to the focusing axis but oppositely directed while at the same time the third radiator end is not translated, the radiator plane and the radiator are rotated around a second axis of rotation. The second axis of rotation runs through the third radiator end and through a fourth point on the first line, said fourth point being the mid point between the first and second radiator end. The second axis of rotation is distinct from the first axis of rotation and perpendicular to the focusing axis. If the first and second radiator ends are translated parallel to the focusing direction but not over an equal distance the fourth point is positioned somewhere on the first line but not necessarily between the first and the second radiator end. If the first, the second and the third radiator end are translated over the same distance and in the same direction, the orientation of the radiator plane remains unaltered and the radiator is moved along the focusing axis. It can be concluded that three levers are advantageous because two independent rotations and a translation of the energy radiator can be realized while minimizing the mechanical strain of the energy radiator. 
         [0013]    An embodiment of the apparatus according to the invention is defined in that the second transmission subunit comprises three mechanisms, each mechanism cooperating with one of the three levers and each lever moveably connected to one of the three mechanisms. The advantage of coupling a separate mechanism to each lever is that no clutches are needed to have more than one lever being operated by just one transmission. 
         [0014]    An embodiment of the apparatus according to the invention is defined in that the transmission driver unit comprises three further transmission drivers, each mechanism being coupled to one of the three further transmission drivers and each of the three further transmission drivers being coupled to one of the three mechanisms. The advantage of coupling a separate transmission driver to each mechanism is that no clutches are needed to have more than one mechanism being driven by only one driver. 
         [0015]    The invention also relates to a MRI device provided with the apparatus according to the invention for thermal treatment of tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    These and other aspects of the apparatus according to the invention will be exemplarily elucidated and described with reference to the drawings, in which: 
           [0017]      FIG. 1  is a perspective view, schematically depicting an embodiment of the MRI device according to the invention. 
           [0018]      FIG. 2  is a schematic representation of an embodiment of the apparatus according to the invention. 
           [0019]      FIGS. 3 to 14  are schematic representations of portions of the embodiment depicted in  FIG. 2 . 
           [0020]      FIG. 15  is a cross-section according to XV-XV in  FIG. 5 . 
           [0021]      FIG. 16  is a schematic representation of a portion of the embodiment depicted in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    In  FIG. 1  an embodiment of a device for Magnetic Resonance Imaging (MRI)  3  according the invention is schematically depicted. The bore  7  of the MRI device  3  is visible and indicated. The MRI device  3  comprises a table  9  and an embodiment of the apparatus according to the invention  1000 . The apparatus  1000  comprises a support face  1  for supporting at least a portion of a patient&#39;s body and a transmission driver unit  5 . One or more step motors, wheels for manual operation, drivable racks cooperating with rods, hydraulic pumps and the like can be mentioned as possible embodiments of the transmission drivers comprised by the transmission driver unit  5 . The apparatus  1000  can be shifted from a table  9  into the narrow space of bore  7  of the device for magnetic resonance imaging (MRI)  3 . The space available for a patient positioned on the support face  1  is limited to the space within the bore  7  above the support face  1 . The space available for an energy radiator and a device for positioning the energy radiator is limited to the space within the bore  7  underneath the support face  1 . To relieve the patient possibly suffering from claustrophobia as much as possible the space occupied by the positioning device of the invention should be kept as small as possible. The transmission driver unit  5  should be accessible outside the bore and electrical devices possibly comprised by the transmission driver unit  5  should remain outside the bore  7  to prevent possible interference of fields generated by the transmission drivers of transmission driver unit  5  with the magnetic field used by the device for magnetic resonance imaging  3 . 
         [0023]      FIG. 2  shows the apparatus according to the invention in a plane of cross-section perpendicular to the support face  1 . The plane of cross-section is parallel to the median plane  12  and perpendicular to the support face  1 . The support face  1  and the coronal plane  13  of the patient&#39;s body  11  are assumed to be parallel, but different positions of the patient&#39;s body  11  relative to the support face are possible. The position of the patient&#39;s body  11  as exemplarily depicted in  FIG. 2  is not limiting the scope of application of the invention. An energy radiator  50  is mounted on a holder  22 . The holder  22  is suspended from a suspension body  20 . The holder  22  comprises a lever  300 . The lever  300  comprises a mechanism end  320 . In its mechanism end  320  the lever  300  is rotatably connected to a mechanism  24 . The energy radiator  50  directs energy along a focusing axis  52  into a focal volume  54 . The direction of the focusing axis  52  can be decomposed in a direction parallel to the coronal plane  13  and a direction perpendicular to the coronal plane  13 . The energy is radiated in a direction that is transverse to the coronal plane  13 . The orientation of the energy radiator  50  determines the orientation of the focusing axis  52  and the position of the energy radiator  50  determines the position of the focal volume  54 . The suspension body  20  can be shifted according to a translation of the suspension body  400  and rotated according to a rotation of the suspension body  411  around an axis of rotation of the suspension body  410 , the axis of rotation  410  being transverse to the support plane  1  and the coronal plane  13 . The translation  400  and rotation  411  are in a plane substantially parallel to the support face  1  and the coronal plane  13  and oriented perpendicular to the plane of the drawing. The energy radiator  50 , the holder  22 , the lever  300  and the mechanism  24  are coupled to the suspension body  20  and are translated according to the translation  400 . The energy radiator  50 , the holder  22  and the lever  300  also follow the rotation  411  of the suspension body  22 . The mechanism  24  enables an additional adjustment of the energy radiator  50  and the holder  22 . The additional adjustment is superposed on the translation  400  and rotation  411  of the energy radiator  50  according to the translation  400  and rotation  411  of the suspension body  20 . The mechanism  24  is connected to transmission driver unit  5 . During treatment of the patient the transmission driver unit  5  remains fixed relative to the support face. For this reason, the end of mechanism  24  connected to a part of the transmission driver unit  5  remains fixed relative to the support face  1  also. The other end of the mechanism  24  translates according to the translation  400  if the lever  300  does not rotate around a pivoting point  305 , where the lever  300  is rotatably connected to the suspension body  20 . For this reason the mechanism  24  is further arranged to change its length between the lever  300  and the transmission driver unit  5 . The energy radiator  50  is positioned at a rotation radius  412  from the axis of rotation  410 . As a result of the rotation RS  411  around the axis of rotation  410 , the energy radiator  50  describes a circle segment around the axis of rotation  410 . The resulting position of the radiator  50  relative to its position before rotation  411  around the axis of rotation  410  can be described by a translation  413  and a translation  414 . The translation  413  is perpendicular to the plane of drawing and perpendicular to the median plane  12  of the patient&#39;s body  11 . The translation  414  is in the plane of the drawing parallel to the direction of translation  400 . The holder  22 , the lever  300  and the mechanism  24  are included in a second transmission subunit  39 . The second transmission subunit  39  is arranged for moving the energy generator  50  along the focusing axis  52  and for rotating the energy radiator  50  around two distinct axes perpendicular to the focusing axis  52 . The holder  22  of the embodiment of  FIG. 2  comprises one lever  300 . If the mechanism  24  lengthens while the suspension body  20  and the transmission driver unit  50  remains fixed relative to the support face  1 , the mechanism end  320  of lever  300  moves away from unit  5  in a direction substantially parallel to  400 . Lever  300  is rotatably suspended from the suspension body  20  in the pivoting point  305 . As a result lever  300  rotates around a center of rotation  305  while its mechanism end  320  moves away from driver unit  5 . Due to the rotation of lever  300  around center of rotation  305 , the holder  22  moves in the direction of the support face  1 , i.e. transversal to the coronal plane  13 . If the focal volume  54  should describe a translation perpendicular to the support face  1  while orientation of the focusing axis  52  remains unaltered, the displacement of holder  22  has no component parallel to support face  1 . For this reason the lever  300  comprises a compliant part  307  to allow for the change in distance between center of rotation  305  and the holder  22 . Further means for positioning and orienting the energy radiator  50  are not indicated in  FIG. 2  but will be elucidated later. Said further means may be incorporated into the lever  300 , but they can also be provided by a different arrangement of the holder  22 . 
         [0024]      FIG. 3  shows the apparatus according to the invention in a plane parallel to the coronal plane of a patient&#39;s body  11 . A manipulator  37  comprises a manipulator transmission unit  38   a  including the suspension body  20 , the transmission driver unit  5 , mounted to the manipulator transmission unit  38   a  and the holder  22  not visible in  FIG. 3 . The plane of the cross-section of  FIG. 3  is parallel to the support face  1 . The transmission driver unit  5  comprises five transmission drivers  5   a,    5   b,    5   c,    5   d  and  5   e.  Transmission driver  5   a  and  5   b  are mounted to a first transmission subunit  38 . Transmission driver  5   c,    5   d  and  5   e  are mounted to a second transmission subunit  39 . The manipulator transmission unit  38   a  comprises both the first transmission subunit  38  and the second transmission subunit  39 . The mechanism  24  is partly indicated and an embodiment of mechanism  24  will be explained later. The suspension body  20  is partly visible. The energy radiator  50  suspended from the suspension body  20  is not visible in  FIG. 3 . The suspension body  20  comprises distant portions  28  and  29 . The distant portions  28  and  29  are rotatably connected to moveably guided abutments  32  and  33 . Distant portion  28  rotates around an axis of rotation  34   b  relative to moveably guided abutment  32 . Distant portion  29  rotates around an axis of rotation  35   b  relative to moveably guided abutment  33 . Transmission bodies  34  and  35  are connected to transmission driver  5   a  and  5   b  respectively and cooperate with the moveably guided abutments  32  and  33  respectively. In the embodiment of  FIG. 3  the transmission bodies  34  and  35  comprise threaded portions  34   a  and  35   a  respectively. The threaded portions  34   a  and  35   a  each have a length axis respectively  34   c  and  35   c.  The first transmission subunit  38  comprises the moveably guided abutments  32  and  33 , the abutment guides  30  and  31  and the transmission bodies  34  and  35 . Abutment guides  30  and  31  guide the moveably guided abutments  32  and  33  and are loaded by the weight of the suspension body and components suspended from the suspension body  20 . The abutment guides  30  and  31  are fixed relative to the support face  1 . The abutment guides  30  and  31  of the embodiment of  FIG. 3  are elongated bodies. These elongated bodies should preferably be stiff to minimize their deformation. Stiff abutment guides  30  and  31  can be construed by adapting the shape and the dimensions of the cross-section of the abutment guides  30  and  31  to obtain geometrically stiff bodies. This however is not always possible, because it leads to rather voluminous components. Use can be made of materials having magnetic properties that are compatible for use with magnetic equipment and have a high Young&#39;s modulus or modulus of elasticity. Among the ceramic materials the material category of oxides comprises materials as Aluminium oxide (Al2O3) and zinc oxide (ZnO) suitable for use in the abutment guides  30  and  31 . Also materials from the category of carbides can be used. Silicon carbide (SiC) is an example of a suitable material that is commercially available. The position of the axes of rotation  34   b  and  35   b  of suspension body  20  relative to abutments  32  and  33  respectively is important for forces and torques exerted between the abutment  32  and  33  and the transmission bodies  34  and  35  respectively. For geometrical stiffness it is advantageous if rotation axes  34   b  and  35   b  intersect with length axes  34   c  and  35   c  respectively. 
         [0025]    An embodiment of the manipulator  37  according to the invention is schematically depicted in  FIG. 4  in a plane parallel to the support face  1 . The holder  22  comprises three levers  300 ,  301  and  302 . The levers  300 ,  301  and  302  are rotatably suspended from the suspension body  20  and are rotatably connected to three separate mechanisms  24   d,    24   e  and  24   c  in mechanism ends  320 ,  319  and  321  respectively. The mechanism  24   c,    24   d  and  24   e  comprise connecting rods  241  to  246 , moveably guided bodies  40 ,  41  and  42  and transmission elements  43 ,  44  and  45  and mechanism guides  46 ,  47  and  48 , not indicated in  FIG. 4 . The transmission elements  43 ,  44  and  45  comprise threaded portions  43   a,    44   a  and  45   a.  The levers  241  to  246  are rotatably connected to the moveably guided bodies in transmission ends. Axes of rotation  70 ,  71  and  72  characterize the connection between said levers and moveably guided bodies. The moveably guided bodies  40 ,  41  and  42  cooperate with the threaded portions  43   a,    44   a  and  45   a  of rotatable transmission elements  43 ,  44  and  45 . The transmission elements  43 ,  44  and  45  are each connected to a transmission driver  5   c,    5   d  and  5   e  respectively. The interaction between the mechanisms  24   c,    24   d  and  24   e  and the lever  302 ,  300  and  301  respectively is according to the interaction of lever  300  of  FIG. 2  with mechanism  24  of  FIG. 2  and as explained above. The holder  22  and the energy radiator  50  are positioned and oriented relative to the suspension body  20  as a result of the displacement of the mechanism ends  321 ,  320  and  319 . To maintain the position and orientation of the holder  22  and the energy radiator  50  relative to the suspension body  20 , the mechanism ends  321 ,  320  and  319  of said levers should maintain their position relative to the suspension body  20 . The mechanism ends  321 ,  320  and  319  being fixed relative to the connecting rods  241  to  246  or at least to first end portions  241  a to  246   a  (indicated in  FIG. 6 ) of the connecting rods  241  to  246 , said connecting rods should maintain their position relative to the suspension body  20 . If the suspension body  20  is translated and rotated in the plane of the drawing as a result of a rotation of transmission driver  5   a  and  5   b,  the mechanism ends  321 ,  320  and  319  and the first end portions  241   a  to  246   a  ( FIG. 6 ) are translated according to the translation and rotation of the suspension body  20 . To keep the position and orientation of the holder  22  and the energy radiator  50  unaltered with respect to the suspension body  20 , the moveably guided bodies  40 ,  41  and  42  and second end portions  241   b  to  246   b  ( FIG. 6 ) of the connecting rods  241  to  246  positioned around the axes of rotation  70 ,  71  and  72  should be translated according to the translation and rotation of the suspension body  20 . For this reason, the transmission drivers  5   c,    5   d  and  5   e  should compensate for a translation and a rotation of the suspension body  20  in the plane of the drawing by driving the transmission elements  43 ,  44  and  45  if the position and orientation of the holder  22  and the energy radiator  50  relative to the suspension body  20  are to remain unaltered. The rotations of the transmission drivers  5   a  and  5   b,  driving the first transmission subunit  38  are thus coupled to adjustment of the second transmission subunit  39  by transmission driver  5   c,    5   d  and  5   d  if the position and orientation of the radiator  50  relative to the suspension body  20  is not changed during the translation and the rotation of the suspension body  20 . 
         [0026]    In  FIG. 5  the adjustment of the suspension body  20  of an embodiment of the apparatus according to the invention is schematically depicted. Transmission driver  5   a  drives the rotatable threaded transmission body  34 . The transmission body  34  cooperates with moveably guided abutment  32  and as a result of the rotation of the transmission driver  5   a  the moveably guided abutment  32  and the distant portion  28  of suspension body  20  are translated along abutment guide  30  over a distance  101 . Similarly, transmission driver  5   b  causes a translation of distant portion  29  of the suspension body  20  over a distance  102 . In general, the distance  101  will not be equal to distance  102  and the suspension body will rotate around the axis of rotation  410 . As a result of this rotation  411  around axis of rotation  410  the energy radiator  50  will be positioned by a translation  413  transversal to abutment guide  32  and in the plane of the drawing. Also shown in  FIG. 5  are the transmission elements  43 ,  44  and  45 . The transmission elements of the exemplary embodiment as depicted in  FIG. 5  comprise threaded portions  43   a,    44   a  and  45   a  ( FIG. 4 ). The threaded portions each have a length axis  80 ,  81  and  82 . The connecting rods  241  to  246  are rotatably connected to the moveably guided bodies  40 ,  41  and  42 , having axes of rotation  70 ,  71  and  72 . It is advantageous for geometrical stiffness if the length axes  80 ,  81  and  82  intersect with the axes of rotation  70 ,  71  and  72 . In that situation the mechanisms  24   c,    24   d  and  24   e  are designed as push and pull mechanisms. Shear forces and bending moments, causing significant deformation of the transmission elements  43 ,  44  and  45  and causing a bad contact situation by tilting the moveably guided bodies can be minimized. A further advantage of the embodiment of  FIG. 5  is that the transmission element  40  is symmetrically loaded by connecting rods  241  and  242 . Due to the symmetric arrangement of the connecting rods around the transmission element  40 , bending moments in the transmission element  40  and deformation of the transmission element  40  will be minimized. The symmetrical arrangement of rods  241  and  242  around axis  80  prevents tilting of the moveably guided body  40  around a tilting axis perpendicular to the plane through axes  70  and  80 . The same applies to the topology of transmission elements  41  and  42  relative to the connecting rods attached to the transmission elements  41  and  42 . Again hysteresis is minimized for good positioning accuracy. 
         [0027]    In an embodiment according to the invention as schematically depicted in  FIG. 6  the mutual influencing between the positioning of connecting rods  241  to  246  on the one side and the position of the moveably guided abutments  32  and  33  on the other side is illustrated for another position and rotation of the suspension body  20 . Again it is assumed that the position and orientation of the energy generator  50  relative to the suspension body  20  is the same as in  FIG. 4  and  FIG. 5 , implying that the position of the connecting rods  241  to  246  (and in particular first end portions  241  a to  246  a of said rods  241  to  246 ) relative to the suspension body  20  is the same as in  FIG. 4  and  FIG. 5 . The suspension body  20  is positioned close to the transmission driver unit  5 . The second end portions  241   b  to  246   b  of connecting rods  241  and  242  are almost at their ultimate position to compensate for the position of the suspension body  20  along the abutment guides  30  and  31 . The suspension body  20  is rotated relative to the length axis  34   c  of transmission body  34 . To compensate for this rotation the rotation axes  70 ,  71  and  72  of connecting rods  241  to  246  are not aligned. The suspension body  20  is rotatably connected to the moveably guided abutments  32  and  33 . The distance between the moveably guided abutments  32  and  33  changes according to the rotation of the suspension body  20 . A slot  23  is provided to the suspension body  20  to allow for this varying distance and to enable a stress-free rotation of the suspension body  20 . 
         [0028]    An embodiment of the lever  301  or  302  comprised by the holder  22  as indicated in  FIG. 4  is schematically shown in  FIG. 7  in elevated view. The lever  301  (or  302 ) is rotatably suspended from an axle  60  with length axis  601 . The axle  60  is fixed relative to the axes of rotation  34   b  and  35   b  (see also  FIG. 3 ), being the axes of rotation of the suspension body  20  with respect to the moveably guided abutments  32  and  33  (not indicated in  FIG. 7 ). The lever  301  is rotatably suspended from the suspension body such that it can pivot around a pivoting point  602  on a pivoting axis  601  being the length axis of axle  60 . The lever  301  has two more characterizing points or lever ends  603  and  604 , the lever ends being different from the pivoting point  602 . In the lever ends the lever  301  is connected to other components. One end  603  of the lever  301  is rotatably connected to the radiator  50  (not indicated in  FIG. 7 ), while the other end  604  is rotatably connected to the connecting rods  245  and  246  of mechanism  24   e  (not indicated in  FIG. 7 ). The end of the lever, connected to the radiator  50  will be referred to as the radiator end  603 . The end of the lever  301 , connected to the mechanism  24   e  comprised by the second transmission subunit  39  will be referred to as the mechanism end  604 . Line  605  connects the radiator end  603  and the pivoting point  602 . Line  606  connects the mechanism end  604  and the pivoting point  602 . The lever  301  is arranged such that line  605  is perpendicular to line  606 . The pivoting axis  601  is oriented such that it is perpendicular to lines  605  and  606 . In the remainder of this paragraph it is assumed that line  606  is substantially perpendicular or transversal to the support face  1  (not indicated in  FIG. 7 ). Than, the support face  1  is substantially parallel to the plane defined by pivoting axis  601  and line  605 . In the remainder of this paragraph it is assumed that translations and rotations are small. The connecting rods  245  and  246  can impose a translation  607  on mechanism end  604 . Translation  607  is parallel to line  605  and substantially parallel to the support face  1 . Because the lever  301  is rigid, translation  607  is transmitted into a translation  608  of the radiator end  603 . Translation  608  is parallel to line  606  and substantially perpendicular or transversal to the support face  1 . It can thus be concluded that lever  301  transmits a translation  607  of mechanism end  604  into a translation  608  of radiator end  603 , translation  607  having a component, which component is perpendicular to translation  608 . 
         [0029]    In an embodiment of the holder  22  according to the invention as schematically depicted in  FIG. 8  the holder  22  comprises three levers  300 ,  301  and  302 . The levers  300 ,  301  and  302  comprise radiator ends  613 ,  603  and  610  respectively and mechanism ends  614 ,  604  and  611  respectively. The levers  300 ,  301  and  302  have the axis of rotation  601  parallel to the support face  1  as a common axis of rotation. The levers  300 ,  301  and  302  can pivot around pivoting points  612 ,  602  and  609  respectively. The arrangement and the operation of the lever  300 ,  301  or  302  is similar as explained according to  FIG. 7 . Lever  300  however has a length change device or compliant portion  307  as explained in relation to  FIG. 2 . Center of rotation  305 , indicated in  FIG. 2 , corresponds with pivoting point  612  and pivoting axis  601  as indicated in  FIG. 6 . Compliant portion  307  is compliant along the line connecting radiator end  613  and pivoting point  612 . In  FIG. 6  also the energy radiator  50  and the focusing axis  52  are indicated. The energy radiator  50  can e.g. be mounted to the levers  300 ,  301  and  302  by ball-joints. The focusing axis intersects a face of the energy radiator  50  in a radiator face point  615 . The radiator ends  603 ,  610  and  613  together form a triangle  616 . The energy radiator is mounted to the levers  300 ,  301  and  302  in the radiator ends  603 ,  610  and  613 . The energy radiator  50  is a rigid body. For this reason the triangle  616  remains its shape irrespective of the orientation of the levers  300 ,  301  and  302 . The focusing axis  52  is perpendicular to the triangle  616 . In  FIG. 8  the holder  22  and the energy generator  50  are represented in a reference state with respect to the support face  1 . In the reference state the triangle  616  is parallel to the support face  1  and the focusing axis  52  is transversal to the support plane  1 . Radiator ends  610 ,  613  and  603  can be translated in a direction parallel to the direction of the focusing axis  52  by rotation of the levers  302 ,  300  and  301  respectively. 
         [0030]    In  FIG. 9  a detail of the embodiment as described in  FIG. 8  is shown. It is assumed that radiator ends  603  and  610  are not translated and that the levers  301  and  302  to which these ends are connected ( FIG. 8 ) are not rotated, i.e. the levers  301  and  302  stay in their reference state. A rotation of lever  300  around axis of rotation  601  ( FIG. 8 ) will result in a small translation or displacement  618  of radiator end  613 . Actually, radiator end  613  describes a small circle segment around an axis of rotation  617 . The direction of this displacement  618  is parallel to the focusing axis  52  of the energy generator  50 . As a result the triangle  616  and the radiator  50  will rotate around a first axis of radiator rotation  617 . The radiator ends  603  and  610  remain in the reference position relative to the pivoting axis  601  ( FIG. 8 ). A rotation of the energy radiator  50  around axis of rotation  617  will result in enlargement of the distance between pivoting point  612  (fixed relative to the suspension body  20 ) and radiator end  613  ( FIG. 8 ). For this reason the lever  300  comprises the compliant portion  307  ( FIG. 8 ). 
         [0031]    In  FIG. 10  a detail of the embodiment as described in  FIG. 8  is shown. It is assumed that radiator end  613  is not translated and that the lever  300  to which this end is connected ( FIG. 8 ) is not rotated, but that lever  300  is still in its reference state. Opposite rotations of equal magnitude of identical levers  301  and  302  around axis of rotation  601  ( FIG. 8 ) will result to opposite displacements  619  and  620  of equal magnitude of radiator ends  603  and  610  respectively. The direction of said displacements  619  and  620  is parallel to the direction of the focusing axis  52  of the energy generator  50 . As a result the triangle  616  and the radiator  50  will rotate around a second axis of radiator rotation  621 . The levers  300 ,  301  and  302  can pivot around pivoting points  612 ,  602  and  609  respectively ( FIG. 8 ). The pivoting points  612 ,  602  and  609  are on the pivoting axis  601  ( FIG. 8 ). The second axis of rotation  621  runs through pivoting point  612  because lever  300  is not rotated from its reference state and the plane of triangle  616  comprises the second axis  621 . Radiator points  610  and  603  keep their distance  622  because they are attached to the rigid energy radiator  50 . After rotation of the energy radiator  50  around the second axis of rotation  621  the projection of distance  622  on pivoting axis  601  along a direction perpendicular to the pivoting axis  601  is shorter than the distance between the pivoting points  602  and  609  ( FIG. 8 ) in the reference state. This effect causes a deformation of the levers  301  and  302  ( FIG. 8 ). Radiator ends  610  and  603  of levers  301  and  302  bend towards each other as a result of a rotation around the second axis of rotation  621 . This deformation may cause damage to the energy generator  50  because bending forces and moments are introduced as a result of the deformation of levers  301  and  302 . To absorb this deformation, the levers should be compliant in the direction of the deformation, being the direction perpendicular to the second axis of rotation and parallel to the support face  1  in the reference state of the holder  22 . 
         [0032]    In  FIG. 11  a detail of the embodiment as described in  FIG. 8  is shown. If the levers  300 ,  301  and  302  are rotated such that the resulting translation  618 ,  619  and  620  of radiator ends  613 ,  603  and  610  are equal and in the same direction, the energy radiator  50  is translated along its focusing axis  52 . Relative to the suspension body  20  and pivoting axis  601  ( FIG. 8 ), the energy radiator  50  describes a circle segment while remaining its orientation relative to the suspension body  20 . 
         [0033]    In  FIG. 12  an embodiment of lever  301  is schematically depicted. The lever  301  is compliant in the direction of pivoting axis  601  and stiff in the direction of axes  34   b  and  35   b  through the distant portions  28  and  29  of the suspension body  20  ( FIG. 3 ). The lever  301  is also stiff in a direction perpendicular to axes  601  and  34   b.  The stiffness distribution is determined e.g. by height  623  and thickness  622  of the lever  301 . The lever  301  as schematically depicted in  FIG. 12  has a portion  308 . The portion  308  is compliant in the direction parallel to axis  601 . To achieve compliance of lever  301  along the direction of pivoting axis  601 , the pivoting point  602  could be implemented as a slideable hinge along axis  601 . 
         [0034]    In an embodiment of the holder  22  according to the invention as schematically depicted in  FIG. 13  the holder  22  comprises three levers  300 ,  301  and  302 . Due to rotations  624 ,  625  and  626  of levers  300 ,  301  and  302  the energy radiator  50  and the focusing axis  52  are positioned and oriented relative to the coronal plane  13 . 
         [0035]    In  FIG. 14   a  a detail of the embodiment according to the invention as described in  FIG. 8  is shown in its reference state relative to the support face  1  and relative to a line of reference X=0  627  perpendicular to the support face  1 . In  FIG. 14   b  the same detail as in  FIG. 14   a  is depicted but in a state different from the reference state. The energy radiator  50  and the focusing axis  52  as shown in  FIG. 14   a  have the same orientation relative to the support face  1  and the suspension body  20  as shown in  FIG. 14   b.  The only difference between the energy radiator  50  of  FIG. 14   a  and  FIG. 14   b  is, that the position of the energy radiator  50  relative to the suspension body  20  and the support face  1  is shifted over a vertical translation  628  of the energy radiator  50 . In the direction parallel to the support face  1  and in the plane of the drawing, indicated as the X-direction, the energy radiator  50  is not translated and the distance of the focal volume  54  to the line of reference  627  as depicted in  FIG. 14  a is the same in  FIG. 14   b.  To realize the vertical translation  628  of the energy radiator  50 , the lever  301  rotates around pivoting  602 . Pivoting point  602  is fixed relative to the suspension body  20  and the vertical distance between the suspension body and the support face  629  is constant because the abutment guides remain fixed and parallel to the support face (see description of  FIG. 3 ). Lever  301  is rigid, so the distance between pivoting point  602  and radiator end  604  remains unaltered during rotation of the lever  301 . For this reason the suspension body  20  must be repositioned parallel to the X direction over a correction distance  630 . The connecting rods  245  and  246  are shifted and reoriented as a result. The connecting rods are rotatably connected to the mechanism end  603  of the lever  301  and are rotatably connected to the moveably guided body  45  in axis of rotation  72 . Axis of rotation  72  intersects with the length axis  82  of the threaded portion  45   a  ( FIG. 4 ) of the transmission element  45  ( FIG. 4 ). The position and orientation of the length axis  82  is fixed with respect to the support face  1 . As a consequence the connecting rods  245  and  246  describe a combined translation and rotation during rotation of the lever  301 . The motion of the connecting rods  245  and  246  arises from the restrictions that one end of the connecting rods  245  and  246  is rotatably connected to the mechanism end  603  of lever  301  and rotates around pivoting point  604  while the other end is rotatably connected to the moveably guided body  42  in a point on axis  72  and translates along the direction of axis  82 . The translation  631  of the axis of rod rotation  72  relative to the moveably guided body  42  is indicated in  FIG. 14 . The transmission driver  5   e  realizes translation  631 , while the transmission drivers  5   a  and  5   b  realize the translation of the suspension body  630 . It is thus illustrated that a translation of the energy radiator  50  towards the support face  1  and a matching repositioning of the focal volume  54  can be realized by a coupled and coordinated action of several transmission drivers  5   a,    5   b  and  5   c.  Mechanism guide  48  as schematically depicted in  FIG. 15  prevents the rotation of the moveably guided body  42  around the length axis  82 . 
         [0036]    In  FIG. 15  an embodiment of part of the second transmission is schematically shown. The cross-section depicted in  FIG. 15  is according to view XV-XV as indicated in  FIG. 5 . The connecting rods  245  and  246  are rotatably connected to moveably guided body  42 . Axis of rotation  72  intersects with the length axis  82  of a threaded portion  45   a  of rotatable transmission element  45 . Friction between the threaded portion  45   a  of transmission element  45  and the cooperating internal portion of the moveably guided body  45  exerts a friction moment  49  on moveably guided body  45  around the length axis  82  of its threaded portion  45   a.  A mechanism guide  48  prevents a rotation of the moveably guided body  42  according to the friction moment  49 . Mechanism guide  48  is parallel to the support face  1 . In the embodiment of  FIG. 15  only one mechanism guide  48  is guiding the body  42 . More guides can be applied to obtain even higher stiffness of the second transmission unit. The connecting rods  245  and  246  are symmetrically arranged around the moveably guided body  42  and the length axis  82  to prevent bending of the transmission element  45  and tilting of the moveably guided body  45  around tilting axis  73 . The tilting axis  73  is perpendicular to the support face  1  and to the axis of rotation  72 . Similarly, mechanism guides  47  and  48  (not indicated) may be provided to prevent a rotation of the moveably guided bodies  40  and  41  respectively. In  FIG. 16  an embodiment of moveably guided body  40  of the second transmission subunit is schematically shown. The moveably guided body  40  is depicted disassembled from the rotatable threaded transmission element  43 . In assembled state the moveably guided body  40  can be moved by rotation of element  43 . The moveably guided body  40  comprises a compliant portion  40   b  and two rigid portions  40   d  and  40   e.  The rigid portions  40   d  and  40   e  are provided with an internal thread  40   ad  and  40   ae  respectively. Internal threads  40   ad  and  40   ae  correspond to the threaded portion  43   a  of rotatable transmission element  43 . The threads  40   ad,    40   ae  and  43   a  are provided with a corresponding pitch  100 . The compliant portion  40   b  of moveably guided body  40  has a length  40   c  in a state, wherein the moveably guided body is not mounted to the transmission element  43 . The length  40   c  of compliant portion  40   b  differs by a distance  100   a  from zero or more whole pitches  100 . For this reason, the compliant portion  40   b  will be deformed over a distance of at least  100   a  when it is mounted to the transmission element  43  in a compressed state. The compliant portion  40   b  can also be expanded over a distance of at least pitch  100  minus distance  100   a.  More pretension can be introduced by compression or expansion of compliant portion  40   b  over more than one pitch  100 . Pretension can be introduced elsewhere in the apparatus according to the embodiment as depicted in  FIG. 16 . 
         [0037]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single mechanism or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.