Studies on CT image of the liver, especially on the attenuation coefficients (CT units)

The diagnosis of the liver mass lesions by computed tomography (CT) is well documented. Most of the papers, however, concern only the morphological appearance of the lesions and, I think, papers which describe the attenuation coefficient (CT unit) are still few. This paper reports the CT units of various liver mass lesions in both before and after contrast enhancement and also diagnostic key points in combination extends the consideration in the relation with the morphological appearance of the liver masses, especially tumors. The CT units were measured in 227 cases, in which the final diagnosis was obtained clinically. The CT images were studied on following four points: 1) sharpness of the contour 2) uniformity in the lesion 3) presence of necrosis 4) comparison of density of the lesion with those of liver and spleen Results: The contour of metastatic liver cancer was clearer than the primary. In both of primaly and metastatic liver cancer, most of large masses were apt to be heterogeneous although homogeneous in small ones. The primary liver cancers are, often, of isodensity with the liver parenchyma or of isodensity in the outer zone and of low density in the center. The metastatic cancers are usually of low density. In plain CT, the CT unit of normal parenchymas was 57.8 +- 4.5 HU, primary liver cancer; 43.3 +- 6.5 HU, metastatic liver cancer; 41.3 +- 8.1 HU, necrosis; 24.6 +- 7.3 HU, liver cyst; 5.8 +- 3.7 HU, liver abscess; 31.0 +- 2.9 HU, and fatty liver; 24.9 +- 12.1. The increase of CT unit after contrast enhancement was highest in normal liver parenchyma, and then primary liver cancer, metastatic liver cancer, necrosis, and cyst in this order. In the plain CT, CT unit of normal parenchyma of the liver was higher than that of spleen. If the CT unit of the liver is lower that of than the spleen, the presence of hepatic abnormality should be suspected. (author)