Contrast media in body computed tomography: experimental and theoretical background background, present limitations, and proposals for improved diagnostic efficacy.

The aim of contrast enhancement is to increase the difference in attenuation coefficients between pathological lesions and the surrounding normal tissues. Unlike cranial CT, in body CT the contrast-enhanced scans should be taken when the blood and normal tissue levels of contrast enhancement are at their maximum possible levels. This has not been feasible in most currently available scanners, and most reports in the literature on contrast enhancement in CT have used suboptimal enhancement. In most cases, maximal enhancement will occur immediately at the end of a rapid intravenous injection using a high dose of contrast media. Repeat scans of certain slice levels at fixed time intervals may further improve diagnostic accuracy. Computers are only beginning to be used to analyze the reconstructed CT image, and recent increases in scanning rapidity make optimum contrast enhancement much more feasible. Renal toxicity from high doses of contrast media places a rather indefinite upper limit to contrast enhancement, which can be partially overcome with intra-arterial contrast media injection at CT. Nonenhanced scans should always precede contrast enhancement in body CT. In this article the experimental and theoretical background to CT contrast enhancement is reviewed and suggestions for optimum application are made in the light of present limitations of the technique. Improvement in both detection and differentiation of pathological lesions should result from minimizing the overlap of CT attenuation measurements of normal and pathological tissue by increasing the difference between their means and decreasing the range of variability of individual attenuation measurements.