Purpose: To design a simple, cost-effective system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy (PCNL). Materials and Methods:The design consists of a low-cost, light-weight, portable mechanical gantry with a needle guiding device. Using C-arm fluoroscopy, two images of the contrast-filled renal collecting system are obtained: at 0-degrees (perpendicular to the kidney) and 20-degrees. These images are relayed to a laptop computer containing the software and graphic user interface for selecting the targeted calyx. The software provides numerical settings for the 3 axes of the gantry, which are used to position the needle guiding device. The needle is advanced through the guide to the depth calculated by the software, thus puncturing the targeted calyx. Testing of the system was performed on 2 target types: 1) radiolucent plastic tubes the approximate size of a renal calyx (5 or 10 mm in diameter, 30 mm in length); and 2) foam-occluded, contrast-filled porcine kidneys. Results: Tests using target type 1 with 10 mm diameter (n = 14) and 5 mm diameter (n = 7) tubes resulted in a 100% targeting success rate, with a mean procedure duration of 10 minutes. Tests using target type 2 (n = 2) were both successful, with accurate puncturing of the selected renal calyx, and a mean procedure duration of 15 minutes. Conclusions: The mechanical gantry system described in this paper is low-cost, portable, light-weight, and simple to set up and operate. C-arm fluoroscopy is limited to two images, thus reducing radiation exposure significantly. Testing of the system showed an extremely high degree of accuracy in gaining precise access to a targeted renal calyx.

At present, manual needle-positioning techniques known as "triangulation" and "keyhole surgery" are implemented during percutaneous nephrolithotomy (PCNL) to gain initial kidney access. These techniques do not ensure correct needle placement inside the kidney, resulting in multiple needle punctures, unnecessary hemorrhage, excessive radiation exposure to all involved and increased surgery time. A cost-effective fluoroscopy-guided needle-positioning system is proposed for aiding urologists in gaining accurate and repeatable kidney calyx access. Guidance is realized by modeling a C-arm fluoroscopic system as an adapted pinhole camera model and utilizing stereovision principles on an image pair. Targeting is realized with the aid of a graphical user interface operated by the surgeon. An average target registration error of 2.5 mm (SD = 0.8 mm) was achieved in a simulated environment. Similar results were achieved in the operating room environment with successful needle access in two in-vitro porcine kidneys.

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