One of the goal of the Nephron-Sparing Surgery preoperative planning is to delineate as exactly as possible the renal carcinoma and to specify its relations to the renal arterial, venous and collecting system anatomy. The classical preoperative imaging system is the Spiral CT Urography, which gives successive 3D acquisitions of complementary information about the kidney anatomy. The fusion of this information can be achieved by intra-patient registration techniques. However, because the kidney is difficult to demarcate from the liver or the spleen, a partial information registration technique should be used. In our paper we propose a methodology based on spherical harmonics, which can be used for partial information registration and also for the 3D kidney form modeling.