Hemodialysis represents a life line of patients with end stage renal disease, who are commonly maintained on hemodialysis through catheters. Prolonged exposure to these catheters eventually damages the walls of veins, which results in stenosis at the local site. This condition is called central venous stenosis (CVS) and affects number of patients on hemodialysis in the United States and can compromise the dialysis efficacy. The current diagnostic modality for CVS is venography, which has several limitations. This study proposes to examine intravenous ultrasound (IVUS) as a potentially superior modality, which will provide additional information.