MRI compatible mechatronic devices to aid medical diagnosis and intervention

• Main Author: Elhawary, Haytham
• Published: Imperial College London 2008
• Subjects: 615.84
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487989

The excellent soft tissue contrast of Magnetic Resonance Imaging (MRI) makes it an invaluable tool for guiding and monitoring interventional procedures. This has encouraged the development of MR compatible manipulators capable of combining the high precision and repeatability of robotic systems with the image capabilities of MRI. A system capable of performing transrectal prostate biopsy inside a high field 1.5T MRI scanner was developed to improve the pathological diagnosis of prostate cancer. The 5 DOF device is actuated using piezoceramic motors and can position an endorectal probe inside of the rectum in order to align a biopsy needle to a target position in the prostate. A specially developed MR pulse sequence was capable of tracking two passive fiducials in the head of the endorectal probe, and could thus update the image scan planes to always include the biopsy needle. Phantom tests demonstrate the needle target accuracy was always within the \pm3mm limit specified in the requirements. A preliminary clinical trial has been performed with the manipulator showing a very successful outcome. A second system developed was able to position limbs at a desired orientation within the confined space of a closed bore scanner in order to exploit the magic angle effect to aid diagnosis of tendinous and other muskoloskeletal injury. The 3 DOF device can position tendons in the hand, knee and ankle, proving to be very versatile. The system kinematics were derived such that the device can locate the target tissue as close as possible to the isocentre, while avoiding collision between the patient anatomy and the scanner bore. Preliminary clinical trials with healthy volunteers were performed, where the signal at the Achilles tendon was measured as a function of orientation, showing clear magic angle effects in accordance with the theory.