Graft Enhancement, Immunologic: The induction of prolonged survival and growth of allografts of either tumors or normal tissues which would ordinarily be rejected. It may be induced passively by introducing graft-specific antibodies from previously immunized donors, which bind to the graft's surface antigens, masking them from recognition by T-cells; or actively by prior immunization of the recipient with graft antigens which evoke specific antibodies and form antigen-antibody complexes which bind to the antigen receptor sites of the T-cells and block their cytotoxic activity.Graft Survival: The survival of a graft in a host, the factors responsible for the survival and the changes occurring within the graft during growth in the host.Graft Occlusion, Vascular: Obstruction of flow in biological or prosthetic vascular grafts.Blood Vessel Prosthesis: Device constructed of either synthetic or biological material that is used for the repair of injured or diseased blood vessels.Polytetrafluoroethylene: Homopolymer of tetrafluoroethylene. Nonflammable, tough, inert plastic tubing or sheeting; used to line vessels, insulate, protect or lubricate apparatus; also as filter, coating for surgical implants or as prosthetic material. Synonyms: Fluoroflex; Fluoroplast; Ftoroplast; Halon; Polyfene; PTFE; Tetron.Vascular Patency: The degree to which BLOOD VESSELS are not blocked or obstructed.Polyethylene Terephthalates: Polyester polymers formed from terephthalic acid or its esters and ethylene glycol. They can be formed into tapes, films or pulled into fibers that are pressed into meshes or woven into fabrics.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Saphenous Vein: The vein which drains the foot and leg.Image Enhancement: Improvement of the quality of a picture by various techniques, including computer processing, digital filtering, echocardiographic techniques, light and ultrastructural MICROSCOPY, fluorescence spectrometry and microscopy, scintigraphy, and in vitro image processing at the molecular level.Kidney Transplantation: The transference of a kidney from one human or animal to another.Blood Vessel Prosthesis Implantation: Surgical insertion of BLOOD VESSEL PROSTHESES to repair injured or diseased blood vessels.Veins: The vessels carrying blood away from the capillary beds.Primary Graft Dysfunction: A form of ischemia-reperfusion injury occurring in the early period following transplantation. Significant pathophysiological changes in MITOCHONDRIA are the main cause of the dysfunction. It is most often seen in the transplanted lung, liver, or kidney and can lead to GRAFT REJECTION.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Liver Transplantation: The transference of a part of or an entire liver from one human or animal to another.