Thrombolysis is a catheter-directed procedure that treats blood clots within the arteries or veins and improves blood flow by dissolving abnormal blood clots. X-Ray imaging is used for guidance. A blood clot, also known as a thrombus, can block off blood supply to certain parts of the body, which may cause serious damage. Using the x-ray and a catheter, the doctor is able to direct a special medication or medical device to dissolve the blockage, remove it, or prevent the artery or vein from becoming permanently blocked. Due to the medications used, this procedure may require a longer, overnight stay in the hospital. An overnight stay will also allow doctors to determine the initial cause of the blood clot.