  Background and Purpose: Percutaneous renal access in the context of
percutaneous nephrolithotomy (PCNL) is a difficult technique, requiring rapid
and precise access to a particular calix. We present a computerized system
designed to improve percutaneous renal access by projecting the ultrasound
puncture tract onto fluoroscopic images. Materials and Methods: The system
consists of a computer and a localizer allowing spatial localization of the
position of the various instruments. Without any human intervention, the
ultrasound nephrostomy tract is superimposed in real time onto fluoroscopic
images acquired in various views. Results: We tested our approach by laboratory
experiments on a phantom. Also, after approval by our institution's Ethics
Committee, we validated this technique in the operating room during PCNL in one
patient. Conclusion: Our system is reliable, and the absence of
image-processing procedures makes it robust. We have initiated a prospective
study to validate this technique both for PCNL specialists and as a learning
tool.
