A venous ultrasound uses sound waves to create images of the veins in the body. It is often used to detect blood clots, especially in the veins of the legs — called deep vein thrombosis. There have been no reports of harm from ultrasound. Sometimes, you may be asked not to eat or drink anything other than water for six to eight hours beforehand. Otherwise, little or no special preparation is needed for the procedure. Leave your jewelry at home and wear loose, comfortable clothing. You may be asked to wear a gown.