A MR Compatible Mechatronic System to Facilitate Magic Angle Experiments in Vivo

When imaging tendons and cartilage in a MRI scanner, an increase in signal intensity is observed when they are oriented at 55 degrees with respect to Bo (the "magic angle"). There is a clear clinical importance for considering this effect as part of the diagnosis of orthopaedic and other injury. Experimental studies of this phenomenon have been made harder by practical difficulties of tissue positioning and orientation in the confined environment of cylindrical scanners. An MRI compatible mechatronic system has been developed to position a variety of limbs inside the field of view of the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor comprised of a heavily geared down air turbine, and is controlled in a closed loop using standard optical encoders. MR compatibility is demonstrated as well as the results of preliminary trials used to image the Achilles tendon of human volunteers at different orientations. A 4 to 13 fold increase in signal at the tendon is observed at the magic angle.