Abstract: An apparatus for holding a sample tube includes a plurality of rollers circumscribing a clearance space along a central axis, and an actuator configured for moving the rollers between a non-gripping position and a gripping position. At the non-gripping position, the rollers are oriented relative to the central axis such that a diameter of the clearance space is at a maximum; and at the gripping position, the rollers are at a twisted angle relative to the central axis, and the diameter is reduced such that the rollers contact the sample tube.

Abstract: A multiple tuned birdcage coil structure has a plurality of birdcage coils arranged coaxially one inside another around a central axis. Each of the birdcage coils has two conductor rings separated along the central axis and a plurality of mutually separated and parallel linearly elongated conductor legs and generates B1 field which rotates around the central axis by a specified twist angle between the two rings. The twist angles of different ones of these birdcage coils are different by an integral multiple of 360 degrees such that the assembled birdcage coils are mutually inductively transparent. Such a multiple tuned birdcage coil structure may be formed by assembling individually prepared single tuned birdcage coils each having a specified twist angle with a cylindrically shaped insulating bodies in between.