PERCUTANEOUS RENAL PUNCTURE: REQUIREMENTS AND PRELIMINARY RESULTS A. LEROY 1 , P. MOZER 1,2 , Y. PAYAN 1 , F. RICHARD 2 , E. CHARTIER-KASTLER 2 , J. TROCCAZ 1 1 Laboratoire TIMC - Faculté de Médecine - Domaine de la Merci 38706 La Tronche cedex 2 Service d’urologie et de transplantation rénale. CHU Pitié-Salpêtrière. AP-HP 75013 Paris Author for correspondence : A. Leroy, Antoine.Leroy@imag.fr INTRODUCTION Percutaneous access to kidney is a challenging technique that meets with the difficulty to reach rapidly and accurately an intra-renal target. Today, puncture guidance is performed under fluoroscopic or echographic imaging, each of which presents drawbacks: fluoroscopy provides limited 2D information on localization, whereas echography mostly gives fuzzy images of the target and the puncture trajectory [6]. This paper introduces the principles of computer assisted percutaneous renal puncture (PRP), that would provide the surgeon with an accurate pre-operative 3D planning on CT images and, after a rigid registration with space-localized echographic data, would help him to perform the puncture through an intuitive 2D/3D interface. The whole development stage relied on both CT and US images of a healthy subject. We carried out millimetric registrations on real data, then guidance experiments on a kidney phantom showed encouraging results of 4.7mm between planned and reached targets. PRE-OPERATIVE PLANNING 1. CT Images Acquisition Modern CT scanners can provide high-quality images. We acquired two exams of a healthy volunteer, the voxel size being submillimetric (0.6x0.6x0.6). Such an exam is systematically performed on the patient before intervention, thus does not induce more irradiation than necessary. The first CT-exam was performed early after the injection of a contrast product, to highlight the renal cortex, whereas the second exam, 5min later, gives accurate information on the Pyelo- Calicial Cavities (PCC) (often the target to reach). See fig. 1.