Design and Experimental Assessment of an Elastically Averaged Binary Manipulator Using Pneumatic Air Muscles for Magnetic Resonance Imaging Guided Prostate Interventions

Early diagnostic and treatment of prostate cancer could be achieved using magnetic resonance imaging (MRI) to improve tumor perceptibility. Nonetheless, performing intra-MRI interventions present significant challenges due to intense magnetic fields and limited patient access. This paper presents an MRI-compatible manipulator using elastically averaged binary pneumatic air muscles (PAMs) to orient a needle into a targeted region of the prostate under the command of a physician. The proposed manipulator is based on an all-polymer compliant mechanism designed to make a completely MRI-compatible positioning system. A model based on the PAMs deformation energy is used to design the manipulator so that its discrete workspace, stiffness, and size meet clinically relevant design requirements. The model is also used to study the motion of the device during a state shift. A laboratory prototype of the device shows that the covered workspace, stiffness, and size of the manipulator can meet clinical requirements. Repeatability and accuracy are also acceptable with values of 0.5 mm and 1.7 mm, respectively. Finally, the manipulator’s behavior during state shift describes a hook-shaped motion that is both analytically predicted and experimentally observed.