title: A robotic system for percutaneous renal access.
abstract: OBJECTIVE
  Percutaneous renal access can be challenging, particularly when the collecting system is not distended. Precise entry into a selected calyx facilitates subsequent percutaneous manipulations, but this skill requires extensive experience. In an attempt to improve accuracy while decreasing technical challenges, we developed a robotic system that automates the task of fluoroscopic image-guided percutaneous needle placement.
  
  
  METHODS
  The prototype system consisted of a three degree-of-freedom robot with a needle injector end-effector. Imaging was provided by a biplanar fluoroscope. After correction of image distortion and fluoroscope calibration, robot to image-space registration was completed. To validate the system's ability to insert a needle into a calyx, ex vivo porcine kidneys suspended in agarose gel and distended with iodinated contrast solution were used as a model. In situ renal access tests with three 20 kg. pigs were performed. Access was confirmed by passing a flexible wire or aspirating iodinated contrast from the collecting system.
  
  
  RESULTS
  The diameter of target calyces ranged from 3 to 7 mm. The in vitro accuracy of final needle tip positioning was 0.43 mm. In the ex vivo model, successful "one stick" access occurred on 10 of 12 attempts (83%). In situ access on the first attempt was successful for 6 of 12 target calyces (50%). Needle or tissue deflection accounted for each failure.
  
  
  CONCLUSIONS
  The feasibility of a robotic system to assist in the percutaneous access of small and delicate renal calyces has been demonstrated. Additional work in reducing procedural steps and correcting for tissue deflection during needle passage is necessary to improve accuracy and to allow for clinical application.
authors.affiliation: James Buchanan Brady Urological Institute and the Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21224, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Cadeddu
authors.forename: A
authors.initials: A
authors.lastname: Bzostek
authors.forename: S
authors.initials: S
authors.lastname: Schreiner
authors.forename: A C
authors.initials: AC
authors.lastname: Barnes
authors.forename: W W
authors.initials: WW
authors.lastname: Roberts
authors.forename: J H
authors.initials: JH
authors.lastname: Anderson
authors.forename: R H
authors.initials: RH
authors.lastname: Taylor
authors.forename: L R
authors.initials: LR
authors.lastname: Kavoussi
mesh_terms: D000818:Animals; D004867:Equipment Design; D007670:Kidney Calices; D009403:Nephrostomy, Percutaneous / Q000295:instrumentation*; D012371:Robotics; D013552:Swine