A magnetic-resonance-compatible limb-positioning device to facilitate magic angle experiments in vivo.

Owing to their highly ordered structure, tendons and cartilage appear with low signal intensity when imaged using magnetic resonance imaging (MRI) scanners. A significant increase in signal can be observed when these structures are oriented at 55 degrees (termed the magic angle) with respect to the static field B0. There is a clear clinical importance in exploiting this effect as part of the diagnosis of injury. Experimental studies of this phenomenon have been made harder by the practical difficulties associated with tissue positioning and orientation in the confined environment of closed-bore scanners. An MRI-compatible mechatronic system has been developed, which is capable of positioning a number of limbs to a desired orientation inside the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor consisting of a heavily geared-down air turbine, presenting high torques and good accuracy. The system is shown to be magnetic resonance compatible and the results of preliminary trials using the device to image the Achilles tendon of human volunteers at different orientations are presented. An increase of four fold to thirteen fold in signal intensity can be observed at the magic angle.