Renal Ultrasound, Lasix Renogram and Retrograde Pyelogram Patient is a 14-month-old infant born with prenatally detected hydronephrosis. Postnatal evaluation demonstrated mild left hydronephrosis. Serial US demonstrated progressive left hydronephrosis (b). Lasix Renogram demonstrated a significant increase in the T1/2 drainage of the left renal pelvis (102 min) (c). A left retrograde pyelogram demonstrates obstruction of the left UPJ (d). (a) US demonstrating normal right kidney