Telescopic cylinder and x-ray imaging system

A telescopic cylinder, comprising:

• a plurality of sleeves, wherein the plurality of sleeves are arranged in a nested configuration and central axes of the plurality of sleeves are parallel to each other, and each inner sleeve of the plurality of sleeves is configured to be slidably connected to an outer sleeve adjacent thereto such that each of the inner sleeves can move to an extended position and a collapsed position relative to the corresponding outer sleeve;
• and
• guide assemblies, wherein each of the guide assemblies comprises rollers and a rail that are configured as a set, the rollers are provided on left and right sidewalls and rear walls of at least some of the inner sleeves and the rails are correspondingly provided on left and right sidewalls and rear walls of at least some of the outer sleeves, the rollers and the rail in the same guide assembly are provided on an outer wall surface of the inner sleeve and an inner wall surface of the corresponding outer sleeve, respectively, such that the rollers can roll on guide surfaces defined by the rail during sliding of the inner sleeve relative to the corresponding outer sleeve, thereby guiding movement of the inner sleeve relative to the outer sleeve.