An MRI compatible manipulator for prostate cancer detection and treatment

Abstract

Prostate cancer is the most frequently diagnosed cancer in men and the second most common cause of cancer related death in men. Prostate specific antigen (PSA) blood tests and digital rectal exams (DRE) are preliminary tests that can suggest the presence of prostate cancer. Following these tests, a needle biopsy is required to determine if a suspected tumor is benign or malignant. Currently, an ultrasound image is used to help guide a needle to the prostate and to the suspected region. However, ultrasound images are not of good enough quality to accurately hit a tumor. Too often, false negative results are returned because the tumor is missed. This can be prevented by using more accurate images, which can be obtained using Magnetic Resonance Imaging (MRI). This presents a technical challenge because it requires robotic assistance since there is very limited access to a patient inside the bore. Additionally, the high magnetic fields prohibit the use of conventional actuators in the procedure. Dielectric Elastomer Actuators (DEAs) are MRI compatible due to their entirely polymer construction. Studies show that DEAs must be actuated in a bistable manner to be reliable. In this thesis, bistable DEAs were used in the design of an MRI compatible robotic needle manipulator.

(cont.) The concepts of elastic averaging and parallel mechanisms were applied to achieve high precision and adequate stiffness. The manipulator parameters were chosen to fit the specifications established with collaborators at Harvard Medical School's Brigham and Women's Hospital. A design to orient the needle has been developed, analyzed and built. This research shows that the design is feasible for development into a clinical device if manufacturing processes allow for fabrication of multi-layer actuators. Calculations and experiments show repeatability, precision and MRI compatibility.