[Optimal concentration of contrast medium in helical CT of the thorax]

In 99 examinations of 89 patients, we took CT images of the chest after administering one of three concentrations of contrast medium (iohexol 140 mgI/ml, 240 mgI/ml, 300 mgI/ml) to determine the optimal iodo-concentration for intravenous contrast enhancement in spiral CT. Attenuation values of the superior vena cava, ascending aorta, descending aorta, and pulmonary artery were measured to evaluate the degree of contrast enhancement. Five radiologists judged the image quality by scoring factors such as vascular opacification, delineation of the lung and chest wall, detectability of calcification, lymphadenopathy and pulmonary nodules, and the presence of artifacts. The relationships between the iodo-concentration and the scores were analyzed statistically. The higher the iodo-concentration of the contrast medium administered, the stronger the vascular structures were opacified. There was also a concurrent improvement in the detection of lymphadenopathy. However, artifacts appeared on the administration route as a result of the high-concentration contrast medium, and the image quality was degraded. Among the three groups, iohexol 240 mgI/ml exhibited the best performance, namely, good image quality, so that a high degree of contrast enhancement of the vasculature was obtained with few artifacts due to the contrast medium. However, we believe that iohexol 140 mgI/ml presents no significant problems in routine studies.