MRI-Compatible Pneumatic Actuation Unit for a Self-Propelling Needle

Abstract

Focal laser ablation is a new, promising method to treat tumors. The current focal laser ablation approach is to insert an optical fiber into the patient using rigid needles. A side effect of this approach is that during the needle insertion, tissue damage occurs. The larger the diameter of the needle, the more tissue damage. If the diameter of a rigid needle is reduced, the risk increases that buckling occurs during insertion. Buckling can result in tissue damage due to unwanted movements of the needle tip. By using wasp-inspired, self-propelling needles, the size of the needles can be reduced, thereby reducing tissue damage, while preventing needle buckling. The needle can advance through tissue with no net insertion force by moving parallel needle segments in a specific order. In this work, we present the design and evaluation of an MRI-compatible, pneumatic actuation unit for such a self-propelling needle. A prototype was created that was, except for the screws that were used, fully 3D printed with MRI-compatible materials. Guidelines were formed on how to approach such a 3D-printing process. The screws were also made of an MRI-compatible material. The prototype has the option to change the distance that the needle segments travel each cycle, called the stroke. By using a control unit for the air supply of the prototype, the needle segments were moved automatically. The needle consists of six needle segments with a diameter of 0.25 mm. We tested the performance of the prototype in 10 wt\% gelatin tissue phantoms in terms of the slip ratio of the needle with respect to gelatin tissue phantoms. The results showed that the prototype was functional for small strokes (i.e., 2 mm and 4 mm), as the needle was able to advance through 10 wt\% gelatin tissue phantoms using the self-propelling mechanism with a mean slip ratio of 0.912-0.955. The prototype is the next step in developing self-propelling needles suitable for focal laser ablation to treat tumors.