a Postthrombotic thickening of a venous valve (VK) with adhesion to the wall prevents closure, which is indicated by reux during Valsalva’s maneuver or the valve function test (compression and release). Postthrombotic sclerosis and valve incompetence of the popliteal and calf veins cause immediate backward ow upon compression of the calf (KOMP) with subsequent release (DEKOMP) as a sign of complete valve failure. Once the blood column expulsed from the calf has owed back, a decrease in the reux signal induced by release of compression is noted. The example illustrates valve incompetence of the anterior tibial vein (V.TIB.ANT) before it enters the popliteal vein (V.POP). b The popliteal vein also shows postthrombotic valve adhesion and wall sclerosis (W), reected sonographically as hyperechoic wall thickening (wall near transducer). The Doppler waveform from the popliteal vein (V.POP) depicts the prompt and pronounced reux (toward transducer) upon release of compression (DEKOMP) as a sign of complete valve failure. c Primary chronic venous insuciency with preservation of some residual valve function due to dilatation is indicated by delayed reux upon Valsalva’s maneuver or release of compression. This is illustrated in the example by delayed reux (toward transducer) with a lower but constant ow in the popliteal vein. d A similar pattern of backward ow is seen in this case of varicosis of the great saphenous vein with early, mild valvular incompetence. There is delayed but constant reux through the leaking valve after Valsalva’s maneuver. e Marked varicose dilatation produces severe valve incompetence without residual function, as in the postthrombotic syndrome, resulting in immediate and pronounced reux with high-velocity ow toward the periphery during Valsalva’s maneuver. f The reux resulting from postthrombotic valve incompetence is additionally inuenced by ow obstruction due to residual thrombus. In the example, the popliteal vein is still partially thrombosed (TH) with only slow spontaneous ow. Compression (KOMP) of the calf induces constant ow from the periphery to the heart, while the backward ow occurring upon release of compression (DEKOMP) is less pronounced and less per­sistent than would be expected in extensive, recanalized thrombosis. The reduced backward ow is due to ow obstruction by residual thrombus. g When the ultrasound examination is performed with a high- resolution transducer and low PRF or in the power mode (for detection of slow ow), even slight reux through a small leak in a valve leaet during prolonged Valsalva’s maneuver can be detected. The power mode image on the left shows only little ow (red) directly behind the leaking valve leaet in the proximal supercial femoral vein. In such situations, the sample volume must be placed close to the valve to depict the slight reux during Valsalva’s maneuver (ow toward periphery, away from transducer). As only little blood leaks back into the vein, no ow signals are detectable elsewhere in the vein. Such slight leakage as in this case should not be overinterpreted as valve incompetence but merely illustrates the high sensitivity of high-resolution ultrasound to low ow. However, repeat Dop­pler sampling along the course of the vein with provocative maneuvers is necessary to denitely rule out clinically relevant reux. Anterior to the vein, the supercial femoral artery (A.F.S, red) is depicted; and posterior to it, the deep femoral vein (V.P.F, without ow signals during Valsalva’s maneuver)