Before performing endovenous thermal ablation, the skin and surrounding tissues are numbed. The proceduralist makes a small cut in the skin into which he or she inserts a very thin tube called a catheter. The catheter is guided into the vein to be treated using ultrasound imaging. The proceduralist applies radiofrequency or laser energy to the enlarged vein through the catheter's tip. As the catheter is pulled out, the heat causes the vein to collapse and eventually heal shut. The blood will then reroute through other veins.