Scintigraphy, ultrasound and CT scanning of the liver

Isotope examination of the liver depends on the functional activity of the liver phagocytes, while ultrasound and CT scanning display the anatomical structure. Cold areas on an isotope scan may be due to impaired function or space-occupying lesions. The method is nonspecific and does not differentiate between cysts, abscesses and metastases. Both ultrasound and CT scanning can differentiate space-occupying lesions with a high degree of accuracy so that both techniques can be used to improve the accuracy and specificity of the radioisotope examination. CT scanning of the liver is limited by relatively slow data acquisition and the small differences in X-ray absorption within soft tissues unless contrast agents are used. In comparison, ultrasonic data are rapidly collected and displayed and liver consistency is imaged without contrast media or ionizing radiation. Diffuse abnormalities of the liver, such as cirrhosis, cannot be detected by CT scanning but are apparent on ultrasound examination. In addition, equipment purchase and maintenance costs for ultrasound are a fraction of those for CT scanning. Experience to date at Yale indicates that ultrasound and CT scanning are complementary and supplementary to isotope examination of the liver but that ultrasound in most patients produces better resolution and enhanced tissue differentiation at considerably less cost.