Reconfigurable Fiducial-Integrated Modular Needle Driver for MRI-Guided Percutaneous Interventions

Needle-based interventions are pervasive treatments in Minimally Invasive Surgery (MIS), which can be used in a number of diagnostic and therapeutic procedures, including biopsy, radioactive seed implantation, delivery of therapeutic agents, and thermal therapy. Intra-operative medical imaging promises high precision and improved workflow for interventional procedures, by offering intuitive anatomic structure of the tissue in situ. Magnetic Resonance Image (MRI) can provide high quality, real time, high soft tissue contrast imaging without ionizing radiation, and therefore is an ideal guidance tool for image-guided therapy (IGT). To date, a variety of robotic devices for image-guided interventional procedures have been developed such as these described in [1–4]. However, most of these devices are driven manually or by the actuators that are not compatible with MRI, and thus not suitable for MRI-guided therapy.In this study, we designed and evaluated a compact, reconfigurable MRI-compatible needle driver, using modular design approach, to support various needle-based interventions (e.g. straight needle insertion, asymmetric tip-based needle steering, and concentric-tube needle deployment). Integrated with an imaging coordinate registration fiducial frame concentric with the needle, the needle driver could be visualized and localized in the image space directly, and therefore enable the real-time MRI-guided percutaneous interventions with high precision and reliability.A modular design approach is utilized in the design of the needle driver to enable universal and multipurpose needle intervention. This driver is designed to couple with an existing base platform described in [5], or a variety of other existing and yet to be developed platforms such as [6]. The needle driver consists of multiple actuation units, which are essentially identical and have independent, decoupled motion, as show in Fig. 1. Each individual actuation unit drives a single needle, cannula, or tube, and offers 2 degrees of freedom (DOF) motion - 1 DOF linear translation and 1 DOF axial rotation, as show in Fig. 2. The actuation units ride on a common lead screw and linear guide which is firmly fixed on the base, and the nut is rotated by a timing belt drive mechanism, enabling linear translation (DOF #1). The needle clamping mechanism is attached to a pulley which is driven by similar timing belt drive mechanism, implementing axial rotation of the tube (DOF #2). The needle is gripped by a universal collet supporting varying sizes of standard needles from 25 Gauge (0.51 mm) to 16 Gauge (1.65 mm). An insert may be used to ensure sterility of all needle-contacting components. An eccentric belt tensioner is utilized to adjust the center distance between the motor and the tube clamping mechanism, by twisting the motor housing to varying angles with respect to the tube clamping mechanism, and thus guarantee the effective and smooth power transmission [5]. Nonconductive materials were utilized to build the majority of the components of the needle driver, non-ferrous aluminum is chosen for linear guide and lead screw, which require high stiffness, to maintain MRI compatibility. Piezoelectric motors (PiezoMotor actuators, Uppsala, Sweden) are selected as the actuators, for its high accuracy, dynamic performance and robustness as well as MRI compatibility utilizing the custom-developed MRI-compatible piezoelectric drive system described in [7]. Optical encoders with shielded, filtered differential signaling (US Digital, Vancouver, Washington) are utilized as the position feedback sensors.The most import feature of the design is modularity, which makes it possible to readily add more concentric needles, tubes, or cannulas, and thus enables more complex controlled motion profiles for procedures such as biopsy, brachytherapy, interstitial ablation, and concentric-tube needle deployment. The needle driver can also potentially be lengthened or shortened based on the requirement of specific applications, by modifying the length of lead screw and linear guide.To register the robot to the patient coordinate system in the MR image space, a compact cylindrical helix imaging coordinate registration fiducial frame is designed and integrated in this needle driver such that its axis is concentric with the needle base. The mathematical model of this new fiducial frame design is developed and evaluated in [8]. With compact size (37 mm OD, 30 mm long), the tubular shaped fiducial frame is particularly suitable for attaching to the distal end of the needle, to offer direct visualization and localization from in situ MR imaging. In this design, the fiducial frame is attached concentrically with the axis of the first actuation unit such that it translates and rotates with the needle synchronously.To validate the feasibility and evaluate the accuracy of this design, individual joint space accuracy tests and phantom experiments were performed. In the process of test, individual joints were set to 10 target positions driven by the robot controller, and a digital dial gauge was used to measure the actual position. An 18G Nitinol tube was placed in the needle driver and inserted into a gelatin phantom to validate the motion performance and driving power of the needle driver.The prototype needle driver is shown in Fig. 3 with two actuation units (total of 4-DOF). The dimensions of individual actuation units are 73×116×96 mm, and the overall dimensions of the needle driver set are 300×116×96 mm. In this configuration with two actuation units, the needle driver set is able to offer a 130 mm linear translation and 360 degrees axial rotation for each needle or tube attached. The RMS accuracy for the individual joints was determined to be 0.18 mm (SD = 0.17 mm), which is clinically sufficient for most needle-based interventional therapy. During the phantom experiments, the needle proved to be capable of deploying the tube to arbitrary target points within its workspace freely, with no stall. MRI compatibility has been previously demonstrated for equivalent system architecture in [5,7].A modular design approach is employed in this compact needle driver to control delivery of various tubular shaped surgical tools, including straight needle insertion, asymmetric tip needle steering or compensation, and concentric-tube deployment. Integrated with a concentric compact fiducial frame, the robot can be visualized and localized in the MRI image space directly and in a real-time fashion, and thus potentially improve the workflow and enhance the accuracy of the surgery. The accuracy evaluation test demonstrates a 0.18 mm RMS error for individual joints, indicating a clinically satisfactory result.In the future work, the accuracy of the full multi-DOF needle driver set will be evaluated in tissue using real-time MR image-guidance. The needle driver may be useful for various needle-based interventional surgeries, including prostate biopsy, brachytherapy as well as stereotactic neurosurgery.

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