Development of a computer assisted gantry system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy
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.