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

Abstract

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.

Kidney Access Device

“…With technological advances, there have been endeavors to invent a device that would make this procedure safe while decreasing the learning curve associated with it. Even though many innovative devices have been reported, 12 – 17 each has its drawbacks, and most have not been evaluated in an animal trial. The main concern when performing PCNL is the location of the stone and an accurate initial renal puncture to target it.…”

“…A method that uses computer software along with a gantry also exists. 13 In this method, images of the renal calyceal system are taken and then sent to a laptop computer containing the software. 13 With these images, the surgeon can mark the area to puncture by clicking the computer mouse on a specific image.…”

“… 13 In this method, images of the renal calyceal system are taken and then sent to a laptop computer containing the software. 13 With these images, the surgeon can mark the area to puncture by clicking the computer mouse on a specific image. Once the surgeon clicks on the image, the software determines the needle trajectory and provides the settings for 3 axes on the gantry.…”

“…After this is done, the needle can be placed on the needle holder, and by using the calculations the software provided, the targeted calyx can be punctured. 13 This software-based method involves a lot of equipment and requires knowledge on how to use the software, and these limitations make it difficult to use on a routine basis.…”

“…Given these needs, there have been a few recent studies reported in the literature that have attempted special techniques or used devices to help in renal puncture. 12 – 16 The biggest drawback of the described devices is the lack of in vivo testing. It is well understood that in vivo, muscle and fascial deformation as well as kidney movement may diminish calyceal puncture success.…”