Development and evaluation of an MRI-compatible control system for pneumatically powered wasp-inspired needles

Abstract

The second most common diagnosed cancer is prostate cancer and the number of cases is only expected to rise in the future. Current surgical treatments remove the whole prostate and surrounding tissue and come with severe risks and side effects. Therefore, a non-surgical treatment, which can remove only the cancerous tissue with lower risks is considered a better option. One such treatment is the ablative treatment for which research on novel methods of reaching the cancer have been developed. An example method is using a wasp-inspired steerable needle which requires minimal force to propel through the tissue. So far, such devices have been designed to work in pair with MRI imaging for better positioning of the needles. However, none of the developed devices were able to be flexible in their positioning and be fully MRI-compatible. To address the identified need, this paper focused on developing a control system for the needles with which the operator would dictate the speed of needle movement and be fully MRI-compatible as well as adjustable to any distance from the patient as required. The developed prototype is a manually controlled air distributor which would be connected to a pneumatic stepper motor, rotating a cam and translating force onto the needles. It was entirely made from MRI-compatible materials and the main manufacturing method was 3D printing. In the experiments multiple conditions were tested, including different numbers of outputs, operation speeds and input pressures. From the results, it was concluded that the prototype was promising, however it failed to reach the desired actuation pattern and pressure threshold of 0.1 MPa. The limitations of the design have been identified via pressure analysis and additional testing. The main limitation was the pressure build-up present on the bottom surfaces of the bearing and hollow shaft which caused the frame and the bearing to lift up. Consequently, that causes an internal air leak around the bearing which enables the air to circumvent the frame and the belt and exit the prototype via the outputs. Solutions to the issues were generated such as a clamp that would fix the bearing in place and making the wall thickness of the hollow shaft thinner to limit upward force generation from air pressure. With these solutions, the prototype would reach its full operating potential.