Although CT is one of major diagnostic imaging methods, the role of CT in the detection and diagnosis of early carcinomas depends on the organ and character of the tumors. Because difference in attenuation between lung parenchyma and carcinomas is large, contrast enhanced CT is not effective to diagnose early lung carcinoma. However, difference in attenuation between parenchyma and tumor is small and change of the contour of the organ is not seen in many cases of small carcinomas in the liver, pancreas and kidneys, therefore helical (spiral) CT with contrast enhancement has markedly improved the diagnostic capability of small carcinomas in these organs. In the biliary tract, bladder, uterus and prostate small carcinomas can not be detected even on enhanced helical CT.