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Roberts RW, Fugita OE, Kavoussi LR, et al. Measurement of needle-tip bioimpedance to facilitate percutaneous access of the urinary and biliary systems: first assessment of an experimental system. Invest Radiol 37;2:91–94.Percutaneous access to the renal collecting system or biliary system is most frequently performed under image guidance. However, current techniques lack a feedback mechanism to help confirm successful access. A percutaneous needle system has been developed consisting of a modified 18-gauge percutaneous access needle that measures tissue impedance at its needle tip. Initial results in utilizing this novel system to determine successful access into dilated kidney and gall bladder specimens are reported.Impedance measurements were recorded as the needle was precisely advanced through ex vivo kidney and liver/gall bladder specimens. In an anesthetized porcine model, impedance values were recorded with laparoscopic visualization as the needle was advanced percutaneously through abdominal wall, liver, and into gall bladder.A characteristic, reproducible drop in impedance was noted with successful entry into ex vivo distended kidney and gall bladder specimens. This feature was also noted during in vivo percutaneous cholecystostomy.A measurable, characteristic drop in tissue impedance signifies successful entry into the urinary and biliary systems. This impedance needle system may facilitate current percutaneous access techniques.