Ultrasonography: A technique that uses high frequency sound waves to find position, structure and function of anatomical structures. The sound waves bounce off tissues and produce echo. The echo is then converted to picture and viewed on a video screen. This is a noninvasive technique that can distinguish between a solid tumor and a cyst containing fluid. Ultrasound: High frequency sound waves are used that bounce off tissues and produce echo. The echoes are then converted to pictures and viewed on a video screen. This is a noninvasive technique that can distinguish between solid tumor and cyst containing fluid. Urinary incontinence: Constant or frequent involuntary passage of urine. Urokinase: An enzyme of the hydrolase class that catalyzes the conversion of inactive plasminogen to active plasmin by preferential cleavage of a peptide bond (arginine-valine bond). Also known as plasminogen activator. Urothelial cancer: Cancer of the epithelium of the urinary bladder. Urticaria: A vascular reaction, usually transient, involving the upper dermis, representing localized edema caused by dilatation of the capillaries, and marked by the development of wheels. Uveal melanoma: Melanoma in the vascular middle coat (uvea) of the eye, comprising the iris, ciliary body, and choroid.