a frame 100 in accordance with the principles of the present invention is illustrated in the side elevation view of fig1 . the frame 100 includes a base 102 and a linear guide 104 . the linear guide 104 may include a linear race , ball bushing bearings , or a shaft rail assembly , for example . the linear guide 104 provides for translational support of one or more annular gantries . such guides are available , for example , from thomson industries , inc ., port washington , n . y ., u . s . a . the frame 100 includes a plurality of gantries : an annular ct scanner gantry 106 and an annular pet scanner gantry 108 in this illustrative embodiment . the linear guide 104 operates as a movable support , allowing the pet scanner gantry 108 and associated movable stand 110 to be separated from the ct scanner gantry 106 , by rolling upon ball bushing bearings for example , with very little effort . the linear guide may include a linear race , ball bushing bearings , or a shaft rail assembly , for example . one or more clamps 112 , which may be frictional clamps , may be employed to hold the pet scanner gantry 108 and associated movable stand 110 in place after positioning . a frictional clamp such as may be employed may include a clamp piece with a radius machined into it to mate with a portion of the linear guide when activated . in this illustrative embodiment , the ct scanner gantry is associated with a fixed stand 114 and the pet and ct scanners are aligned along a common axis 116 . a patient may be placed on a table and inserted along the common axis 116 scanned by both scanners 106 , 108 . the movable stand 110 and pet scanner gantry 108 may be positioned , as shown , in close proximity to the ct scanner gantry 106 for normal operation , or may be separated from the ct scanner gantry in order to provide access to tomography components housed in or supported by either of the gantries 106 , 108 . in the side elevation view of fig2 the movable stand 110 and pet scanner gantry 108 have been moved in the direction indicated by the arrow 116 to separate the ct scanner gantry 106 and pet scanner gantry 108 . by separating the gantries 106 , 108 in this fashion , access to the contents of either gantry is increased . service personnel may use such access to carry out regular maintenance or to service equipment supported by the one or both of the gantries . additionally , the additional space between the gantries 106 , 108 provides sufficient room for a gantry , the ct gantry 106 in this illustrative embodiment , to be tilted . such tilting provides even greater access to the components supported by the tilted gantry , gantry 106 in this illustrative embodiment . a gantry that includes means for pivotally mounting its outer support ring is discussed , for example , in u . s . pat . no . 6 , 337 , 894 b1 , issued jan . 18 , 2001 to tybinkowski et al ., which is hereby incorporated by reference in its entirety . in this illustrative embodiment , the base 102 includes a retractable extension 118 , which can be pulled out to extend the track of the frame and allow the movable stand to be moved further from the fixed stand . the linear guide 104 may also be retractable , corresponding to the retractable base 118 . the top plan view of fig3 illustrates the components of a two - gantry frame in accordance with the principles of the present invention . in this illustrative embodiment , the pet scanner gantry 108 , mounted on movable stand 110 , has been separated from the ct scanner gantry 106 that is mounted on the fixed stand 114 . in this view , the ct scanner gantry 106 is tilted to provide better access to components housed within the gantry 106 . the base 102 is fully extended , as is the linear guide 104 . the end elevation view of fig4 illustrates the ct scanner gantry 106 tilted on the fixed stand 114 , which supports it . the fixed stand is supported , in turn , by the base 102 . although various exemplary embodiments of the invention have been disclosed , it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention . it will be evident to those reasonably skilled in the art that other components performing the same functions may be suitably substituted . the foregoing description of specific embodiments of the invention has been presented for the purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise forms disclosed , and many modifications and variations are possible in light of the above teachings . the embodiments were chosen and described to best explain the principles of the invention and its practical application , and to thereby enable others skilled in the art to best utilize the invention . it is intended that scope of the invention be limited only by the claims appended hereto .