Liver tumors are one of the most familiar categories of tumor occurring nowadays. These can be either malignant or benign. The major reason for this is due to alcohol based cirrhosis and hepatitis. There is also another category of liver cancer termed metastatic liver cancer which begins in some other organs and then spreads to liver. The early detection of liver tumors are essential as it can avoid loss of life.Tumor status should be analyzed during different stages of treatment. The segmentation and detection of tumors manually are really time consuming. Also different types of tumors have different appearance and these appearances change when contrast is being injected. Here comes the role of various computer -aided diagnosis methods for the accurate detection of liver tumors. This paper describes various techniques which were used for the detection of liver tumors from Computed Tomography Angiography (CTA) images which can assist the radiologists