fig1 schematically shows a nuclear magnetic resonance tomography apparatus of the type sold by siemens ag under the name &# 34 ; magnetom open ®&# 34 ;. the nuclear magnetic resonance tomography apparatus 10 has a c - shaped magnet , so that the examination space remains easily accessible during the examination and the patient being examined has full freedom of motion toward at least one side . this nuclear magnetic resonance tomography apparatus is therefore very well - suited for dynamic examinations . one arm of the patient can be freely moved toward the outside examination of the shoulder joint . the examining physician or technician can perform movements of the patient during the image acquisition without being exposed to a radiation load . the patient can also be instructed to perform unassisted specific arm movements . exposures of the shoulder joint in different positions have far greater diagnostic utility than purely static examinations in only one position . the positioning aid set forth below makes it possible to implement , or to have the patient implement , abduction and rotation of the shoulder joint in a reproducible way during an image acquisition procedure . the schematic structure of the positioning aid is shown in fig2 . a table support 1 on which a patient 13 lies is placed on the patient table 12 according to fig1 . a guide plate 2 is attached laterally to the table support 1 . an arm rest 5 is guided on this guide plate 2 , this arm rest 5 being described in greater detail with reference to the other figures . as schematically indicated by a scale in fig2 this arm rest 5 is movable by about 180 ° in the plane of the table support 1 . fig3 shows a front view of the table support 1 with the guide plate 2 attached thereto . fig4 shows a plan view of the guide plate 2 . it can be seen that the guide plate 2 has a semicircular shape , with the center of the circle being disposed at a pivot point 4 on which the shoulder joint is positioned during imaging . the guide plate 2 has an approximately semicircular recess 8 forming a guide path , with the midpoint of this semicircle coinciding with the pivot point 4 . recesses 2a in the form of notches are distributed at defined angular positions along the semicircular arc at the outer face of the semicircular guide plate 2 . a guide carriage 9 , as shown enlarged in fig9 and 10 , is put in place on the guide plate 2 . this guide carriage 9 engages into the recess 8 of the guide plate 2 with a pin 9a . alternatively , the guide carriage 9 can have an arcuate projection 9b ( shown with broken lines in fig9 ) that slides in the recess 8 . the guide carriage 9 has a further projection 9c that engages around the end face of the guide plate 2 and which has an interior shape matched to the arcuate shape of the guide plate 2 . a resilient catch element 9d that , dependent on the position of the guide carriage 9 , engages into one of the notches 2a of the guide plate 2 is provided in this projection 9c . fig1 shows the projection 9c with the catch element 9d again in a front view . a carrier 3 that is shown in a front view in fig5 and in section in fig6 is secured on the guide carriage 9 . this carrier 3 is generally in the shape of a half shell , with the end disposed away from the pivot point 4 being angled . a resilient catch element 3a that engages in notches of the arm rest ( described below ) is provided in the carrier 3 . a pin 3b is also introduced into the carrier 3 ; the purpose thereof is described below . an arm rest 5 shown in plan view in fig7 and from the end in fig8 is introduced into the carrier 3 . the arm rest has a part 5b adjacent the guide plate 2 and a part 5c angled with respect thereto . the planar part 5b is intended for accepting the upper arm of a patient ; the angled part is intended for accepting the patient &# 39 ; s lower arm . both the part 5b and the part 5c of the arm rest 5 are in the form of half shells . catch notches 5a are provided at the outside circumference of the part 5b , the resilient catch element 3a of the carrier 3 engaging into these catch notches 5a in the assembled condition . at its outer circumference , the arm rest 5 also has a channel 5d into which the pin 3b of the carrier 3 engages . this prevents a dislocation of the arm rest 5 in longitudinal direction of the carrier 3 . an upper arm of the patient under examination can be fixed in the arm rest 5 with the assistance of a belt 6 . the belt 6 is adjustable and can , for example , be a velcro ® fastener 6a . motion of the arm in the plane of the guide plate 2 is thus possible with the described positioning aid in the assembled condition . locked positions are provided in various positions at which the resilient catch element 9d of the guide carriage 9 engages into the recesses 2a of the guide plate 2 . defined positions of the arm can thus be set in a simple way . at the same time , however , the arm can be moved around its longitudinal axis , with the arm rest 5 then turning in the carrier 3 . various locked positions are thereby also possible , these being defined by the catch notches 5a of the arm rest 5 in conjunction with the resilient catch element 3a of the carrier 3 . no disturbing revolute joints are required in the pivot point of the shoulder joint since the abduction is guided by the recess 8 in the guide plate 2 . the shoulder blade itself is expediently fixed during the examination , so that only the desired rotational movements are possible but , for example , no dislocation occurs . the fixing is unproblematically possible because of the lack of a revolute joint ; it can , for example , be implemented with a vacuum pillow . a reproducible abduction and rotation in the shoulder joint are thus possible with the illustrated arrangement . movement - dependent modifications in the shoulder joint can thus be evaluated extremely well , particularly for the impingement syndrome and the instability of the shoulder joint . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art .
a guide plate , on which a carrier runs in a guide element around a pivot point , is laterally secured to the examination table . an arm rest is arranged at the carrier , this arm rest being rotatable in the carrier around an axis that lies on a line extending between the pivot point and the arm rest .