To date, the examination of the effect of PERC on renal function has been restricted to gross measures of function as defined by serum creatinine, and radionuclide studies performed at a sub-acute interval following PNL, often without differential measurements or controls. Importantly, the investigators' recent studies in a porcine model demonstrate that PERC may cause significant alterations in renal function. There is a need to define in a rigorous fashion the effect PERC has on renal blood flow and renal function. If a deleterious effect is identified, future efforts can be focused on minimizing this insult.