The C-TRACT Referral Tool app is designed to help researchers on this study submit referrals securely and conveniently. C-TRACT is a large, well-designed study of new treatments for vein damage caused by blood clots. The goal of the study is to understand whether new image-guided procedures (endovascular therapy or EVT) reduce the severity of Post-Thrombotic Syndrome (PTS) and improve quality of life. The long-term safety and costs of the EVT procedure(s) will also be considered. Findings from the study may change how doctors care for patients with PTS. If volunteers who underwent EVT procedures as part of the study have improved symptoms and quality life, clinicians may consider offering EVT procedures more frequently as part of their treatment plan. If EVT proves ineffective or unsafe, the findings from this study may reduce or eliminate the use of unnecessary and expensive procedures.