Currently, imaging methods include ultrasound, CT, MRI and PET-CT. Ultrasound is commonly used in clinical practice because it is economical, convenient and non-radioactive, but the disadvantage is that it depends on the operator’s level. In addition, ultrasonography is also widely used and has high value in the diagnosis of liver cancer as well as differential diagnosis. For PET-CT, its imaging agent F18-FDG is not shaped for hepatocellular carcinoma, especially highly differentiated hepatocellular carcinoma, so the application of PET-CT is somewhat limited, but like C11-labeled FDG still has some specificity, because there is like the influence of accompanying organs, especially bile, so it needs to be used only where there is a cyclotron. Imaging contrast studies For how to choose ultrasound, CT, MRI, and PET-CT. (1) Comparative study of the diagnostic efficacy of MDCT and MRI for intrahepatic lesions less than 3 cm. Using ROC curve analysis, the area under the ROC curve for diagnostic efficacy was 0.91 for MDCT and 0.92 for MRI, with no statistically significant difference, but the sensitivity of MRI was better than CT scan, P=0.04, so MRI is recommended for lesions less than 3 cm. (2) Initial diagnosis of liver occupancy The results showed that the accuracy of MRI was better than that of ultrasonography, P=0.02. (3) Comparison of the diagnostic efficacy of CT and ultrasonography in primary cases of hepatic occupancy showed no statistically significant difference between the two. Imaging preferences were as follows: MR was recommended as the first choice for efficacy evaluation after interventional treatment of hepatocellular carcinoma. CT scan CT scan is divided into two types: plain scan and enhanced scan. For hepatocellular carcinoma, the value of plain scan is low, and generally cannot make qualitative diagnosis, so enhancement scan is necessary. Enhancement scan has ionic and non-ionic contrast agents, and non-ionic type is generally used. CT enhancement scan is more complicated because of the dual blood supply to the liver, which is divided into arterial phase, venous phase (portal phase, parenchymal phase), equilibrium phase and delayed scan. The arterial phase is the period when the contrast agent reaches its highest concentration in the vascular arteries and has the best effect, the venous phase is similar, and the equilibrium phase is the period when the contrast agent reaches equilibrium between the vessels and the parenchyma, with the following approximate time differences: early arterial (15-25s), late arterial (25-35s), early portal (40-50s), portal (55-85s) (60-70s is best), and equilibrium phase (90-120s), and delayed scan (after 2min). Conventional MR scan techniques of the liver Conventional MR scan techniques of the liver include T1WI (double echo), T2WI and T2WI fat suppression, DWI, and multi-phase dynamic enhancement scan techniques. Among them, multi-phase dynamic enhancement scan technique is better than CT, which is a true same-body dynamic scan with more sweeps, while CT is a static bed scan with long sweep time and long delay period. In addition, the multi-phase dynamic imaging technique of liver-specific contrast agent (Pulmonary contrast) uses a deliberate contrast agent and is able to obtain dynamic imaging and hepatobiliary phase imaging with a single injection, which is mainly used in the diagnosis and differential diagnosis of FNH, hepatic adenoma, detection of liver metastases, early liver cancer detection, and determination of liver function.