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Patient-Specific Design of Concentric Tube Robots
Robot-assisted minimally invasive surgical (RMIS) systems offer enhanced dexterity, vision, and control compared to traditional open surgery. Numerous procedures are performed using RMIS systems due to the potential to decrease a patient's pain, recovery time, and scarring. Current commercial systems are built to accommodate a wide range of procedures and patients, resulting in a highly general system that is not necessarily optimal for any specific case. These systems can also be limited by their large size, high cost, and inability to move in highly curved paths. While a large part of the population can benefit from the advantages of RMIS systems, the anatomical differences of specialized patient groups, including pediatric patients, exceed the range of what these generalized systems can accommodate. To address the unmet needs of specialized patient groups, a patient- and procedure-specific (i.e., personalized) surgical robot design paradigm is proposed. This paradigm leverages the surgeon's expertise to design and fabricate robots based on preoperative medical images.
The type of robot used for this personalized design process is a dexterous continuum robot known as a concentric tube robot (CTR). CTRs consist of a set of hollow, pre-curved elastic tubes that fit concentrically inside each other. As the tubes are rotated and inserted relative to each other, the interaction between overlapping tubes enables the entire robot to change shape. CTRs are highly customizable and lend themselves well to personalized design.
We ground this work in clinical applications related to nonlinear renal access in pediatric patients to access diseased sites such as kidney stones and tumors. Although access to the kidney via needle puncture of the skin is straightforward in adults, the procedure is more difficult in pediatric patients. Because of the small body surface area of children, accessing diseased sites with a straight needle and catheter risks damaging nearby tissue, in particular puncturing the pleural cavity. The design of a tool that can safely navigate through the compact anatomy of a pediatric patient to access hard-to-reach sites could improve outcomes in this specialized patient group.
To design a personalized CTR, a virtual reality-based surgeon design interface is presented. This interface leverages the surgeon's expertise of anatomy and surgical procedures. The interface immerses the surgeon in a virtual environment where he or she can view a 3-D model of the specific patient, enabling iterative design of patient-specific tools and simulation of the tool being used in a procedure. Once a specific CTR has been designed, the next step in the personalized design process is fabrication. 3-D printing, or additive manufacturing, enables personalization, and a thorough investigation of 3-D printing methods and materials is presented. Experiments demonstrate the feasibility of using certain 3-D printing materials to create concentric tubes that behave as predicted. A biodegradable polyester was selected and further testing was performed to validate its ability to withstand forces required to drive through tissue.
A novel, compact, lightweight, modular actuation and control system for driving these patient-specific concentric tube robots is presented. In addition to evaluating the precision and accuracy of the actuation modules, an integrated set of three modules was used to demonstrate the ability to drive a three-tube concentric tube robot to reach a tip position that was on average less than 2 mm from a desired target. Finally, the overall patient-specific paradigm was demonstrated, which combines the creation of a 3-D model from preoperative images, design and fabrication of patient-specific tools, and deployment into a phantom patient model.
