'Triphasic waveform' on colour Doppler is of
Ans. b (Hepatic vein) (Ref. Sutton radiology 7th ed., 764)VesselUltrasound/Doppler CharacteristicsPortal veinApproximately 25% of the flow into the liver is supplied by the hepatic artery, the remainder by the portal vein. The portal vein walls are seen as well-defined parallel reflective thin lines. Normal portal venous flow is hepatopetal and is usually monophasic with some fluctuation due to respiration and cardiac activity. Thus, when color flow is being used to assess the portal vein, flow into the liver will conventionally appear red. Portal vein pulsatility may beseen in thin healthy subjects, in patients with congestive heart failure and in a very few patients with liver disease. The pulse repetition rate (PRF) may need to be ito detect flow in patients with portal hypertension.Hepatic arteryThe hepatic artery can be identified in most patients at the porta hepatis lying between the portal vein and common bile duct. In a small percentage of patients this anatomy may be altered and the hepatic artery may lie anterior to the bile duct. Color flow imaging allows rapid differentiation of bile duct from hepatic artery. In older patients with an ectatic hepatic artery or in patients with a dilated hepatic artery, which can occur in alcoholic hepatitis and cirrhosis, this may prevent misinterpretation of a dilated common duct. The hepatic arterial wave form characteristically has a high diastolic phase due to the low resistence of the hepatic bacular bed.Hepatic veinsThere are usually three hepatic veins-the right, the middle and the left -which drain into the TVC. These may be differentiated from portal vein radicals not only by their anatomical positions and patterns of drainage but also by the lack of reflectivity of the hepatic vein walls. They are best interrogated either by scanning transversely in the epigastrium or by scanning transversely using an intercostal approach. The hepatic veins characteristically have a triphasic wave form which reflects right atrial and inferior vena caval pressures. This result in flow in the hepatic veins being predominately coded blue, i.e., away from the probe on the colour Doppler, but with some phases being coded red. Loss of the triphasic wave form of the hepatic vein is seen in patients whose livers have lost compliance, for example, in cirrhosis, acute hepatitis and liver transplant rejection. Educational point:In peripheral arteries the normal waveform is triphasic due to the relatively high distal resistance in the resting lower limb, which reflects the pulse pressure wave.
Hepatic artery
Hepatic vein
Portal vein
All of the above
G.I.T.