Using Navi-robot and a CT scanner to guide biopsy needles

Purpose of this study was to control the suitability of Navi-Robot, a robotic system developed by our research group, to guide percutaneous needle placement under computed tomography (CT) in order to achieve lower radiation exposure and a shorter procedure. The system consists of a high precision six-degrees-of-freedom self-balanced arm, able to move both in passive and active modes, which allows the physician an accurate needle-insertion. The target and the needle entry points are selected by the surgeon on a desktop computer, that acquires DICOM images from the CT scan, and that, using software developed for this purpose, detects also the position of at least three radio opaque markers placed on the patient or on the stretcher. Once these data are obtained, a new system of reference is established based on the markers position, obtaining the coordinates of target and entry point in the new frame of reference. Going then to touch the tip of the spheres with the tip of the robot end effector in passive mode, and recording their position, the robot learns where the two points of interest are located in its frame of reference. A first test was performed on a Plexiglas board; the accuracy achieved was measured as the distance between the needle tip and the target. The results of the in vitro experiment showed that the system is able to reach the target with an accuracy of 1.2 mm.