Design and implementation of a pneumatically-actuated robot for breast biopsy under continuous MRI

Magnetic Resonance Imaging (MRI) is superior to other imaging modalities such as Ultrasound and Computed Tomography and is used for both diagnostic and therapeutic procedures. However, current breast biopsy procedures based on MR images obtained apriori, use a blind targeting approach, which can be long and painful. Current approaches, due to possible patient motion, can lead to tool tip positioning errors thereby affecting diagnostic accuracy and causing significant patient discomfort, if repeated procedures are required. Hence, it is desired to develop a MRI-compatible robot for breast biopsy procedures without removing the patient from the MRI bore. This approach could potentially avoid multiple biopsy needle insertions and minimize sampling errors. Due to the working principle of MRI, material, actuation, and sensing techniques are limited as the MR images must not be affected significantly during the procedure. In addition, the limited space of the MRI bore requires the robot to be compact. This paper presents a four degrees of freedom robot with a compact parallel mechanism of which three degrees of freedom are pneumatically actuated while the needle driver mechanism is actuated by a piezo motor. Fiber-optic force sensor is also designed, developed, and mounted on the top mobile platform of the parallel mechanism to sense the needle and tissue interaction forces. Position control of the pneumatic cylinders is implemented using PI control with a modified integration term to achieve a slow and smooth motion.