Gantry and Slip Ring

The gantry servers as the backbone of a CT System. With increasingly demanding scan speeds, requirement on the gantry performance have increased significantly (the centrifugal force increases with the square of the rotation speed). The CT Component mounted on the gantry weigh several hundred pounds. With such a large load , the gantry still must maintain angular accuracy as well as position accuracy. Angular accuracy requires the gantry to be free of significant vibration in all directions (both in-plane and cross –plane)/ Lets us consider, for example , clinical applications in which submilimeter slice thickness is required. Since the width of the x ray beam is less than a millimeter, the position of the x ray beam should not vary more than a small fraction of bean, width during gantry rotation to ensure true sub millimeter imaging.  The gantry needs to be stable within a fraction of millimeter for all projection angles.

Another key component of the CT System is the slip ring. Although the slip ring was introduced to CT in nearly 1980s to facilitate continues  gantry and sthe stat rotation , it became the de facto standard only after x ray tube flow between continuously rotating gantry and stationary CT component through electrical, optical or RF connection on the slip rings, The amount of data that must be transmitted is large. For a typical multi slice scanner there are roughly 1000 channels per detector row. Each rotation contains nearly 1000 projections or views. To avoid large storage side of the scanner, the data transfer rate must be sync with the data generation rate. For illustration the data transfer rate, R. for a 0,5 sec per revolution eight slice scanner is :

R=number of samples per rotation/time per revolution= 1.6 x 10 ⁷ sample/sec

If each sample is digitized in a floating point format (32 Bits), the bandwidth of the slip ring must be at least 500 Mbaud. The bandwidth required of slip rings will certainly increase with the introduction of new CT Scanners.