Liver-specific contrast media for MRI and CT experimental studies.

MRI and CT are modalities appropriate for liver imaging. To obtain higher sensitivity in diagnoses of focal lesions in the liver, contrast media (CM) are used. Non-specific extracellular CM are not optimal as they rapidly diffuse into both normal tissue and tumorous tissue. By two different mechanisms, the hepatobiliary route and targeting to the reticuloendothelial system, agents may accumulate in normal liver tissue, thereby giving liver-specific CM. So far no such agents have been approved for clinical use. In the present studies, animal models were used to investigate the imaging efficacy of experimental liver-specific CM and answer the following questions: i) Do these new liver-specific CM result in enhancement of normal liver? ii) If enhancement in normal liver is present, does this result in higher contrast of normal liver to tumorous tissue? iii) If higher contrast of normal liver to tumorous tissue is present, does this result in higher tumour detection-rates? Relative to non-enhanced and contrast-enhanced CT, what tumour detection-rate is obtained using non-enhanced and contrast-enhanced MRI? All the liver-specific CM studies possessed the ability to significantly alter the signal in normal liver tissue. Compared to precontrast values, the liver-specific CM studied in MRI (Mn-DPDP) and CT (IEEC-particles and iodixanol-liposomes) were able to increase significantly the contrast of normal liver tissue to tumorous tissue and the tumour detection-frequency in VX2-carcinoma liver tumour-bearing rabbits. In CT using a non-specific extracellular CM, iohexol, no improvement in contrast or tumour detection-frequency was obtained. As reflected in the values of contrast-to-noise obtained, MRI and CT have the same potential for tumour detection in the liver model used in the present studies. Liver-specific CM have the property of improving the contrast of normal liver tissue to tumorous tissue in MRI and CT, giving higher tumour detection-rates. Permitting intravenous administration and the use of long imaging-windows, liver-specific CM are easy to use.