The normal reference value of liver plain scan is about 40~80HU, and the uniform CT value of liver parenchyma density of 40~55 means that it indicates that the density of liver parenchyma is in the range of 40~55HU, so it belongs to the normal situation. CT can clearly observe the pancreas, spleen, liver, gallbladder and other parenchymal organs, and can clearly reflect the density changes caused by lesions. Normal liver contains high glycogen, so the density of liver parenchyma is slightly higher than that of the surrounding pancreas, spleen and kidney. Intravenous contrast-enhanced CT shows a uniform increase in the density of the liver parenchyma. Liver hyperdense lesions can be seen in hematomas, calcifications, and hemochromatosis. Liver hypodense lesions can be seen in cysts, fatty liver, infectious diseases, benign and malignant tumors.