Contrast Enhanced Ultrasound for Renal Obstruction

Inclusion Criteria: * Unilateral renal obstruction confirmed by Nuclear Medicine MAG3 Dynamic Renal Scan (diuretic t (time) ½ \>20 minutes) * Obstructed kidney with differential function \>15% confirmed by Nuclear Medicine Mercaptoacetyltriglycine (MAG3) Dynamic Renal Scan within less or equal (\<=) 6 months from enrollment * Patient has elected to move forward with pyeloplasty or proximal ureteroureterostomy to correct the obstruction Exclusion Criteria: * Solitary kidney * Any abnormalities of contralateral collecting system (for example (e.g.) hydronephrosis, renal calculi, duplicated collecting system) * Known vesicoureteral reflux * Ureteral stent in place in the obstructive kidney * Patients without a Nuclear Medicine MAG3 Dynamic Renal Scan * Previous history of hypersensitivity to Ultrasound Contrast Agents or Definity (perflutren lipid microspheres)) * Previous sensitivity to polyethylene glycol * Pregnant or breastfeeding females * Body mass index (BMI) \>=40 without prior ultrasound confirming ability to adequately visualize the kidneys (Elevated BMI is known to decrease ability to image the kidneys) * Global renal function with a Glomerular Filtration Rate (GFR) \<30 (chronic kidney disease Stage 4 \& 5 excluded) * Unstable cardiopulmonary conditions (acute myocardial infarction, acute coronary artery syndromes, worsening or unstable congestive heart failure, serious ventricular arrhythmias, presence of a cardiac shunt)