The portal vein is a large blood vessel that delivers blood from the gastrointestinal tract, spleen, and pancreas to the liver. Unlike most veins, which carry blood back to the heart, the portal vein carries blood to another organ (the liver) for processing before it returns to the heart through the hepatic veins. On ultrasound, the portal vein is identified in the hepatic hilum (porta hepatis) and can be followed as it branches into the right and left portal veins within the liver. It is characterized by bright, echogenic walls that distinguish it from the hepatic veins, which have thinner walls. Doppler ultrasound evaluates the portal vein for flow direction, velocity, and patency. Portal vein thrombosis, an important finding, appears as echogenic material within the vein with absent or decreased flow on Doppler.