An imaging system, comprising a first portion comprising a base having a length dimension； a second portion that rotates with respect to the first portion and translates relative to the first portion along the length dimension of the base； and a locking mechanism that prevents the first portion from translating relative to the second portion when the second portion is rotated to a first angular position relative to the first portion and the first portion is at a first translation position along the length dimension. The locking mechanism is configured to permit the second portion to translate relative to the base when the second portion is not rotated to the first angular position.
