LIVER-SPECIFIC CONTRAST-MEDIA FOR MRI AND CT - EXPERIMENTAL STUDIES

MRI and CT are modalities appropriate for liver imaging. To obtain hig her sensitivity in diagnoses of focal lesions in the liver, contrast m edia (CM) are used. Non-specific extracellular CM are not optimal as t hey rapidly diffuse into both normal liver 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-sp ecific CM and answer the following questions: i) Do these new liver-sp ecific CM result in enhancement of normal liver? ii) If enhancement in normal liver is present, does this result in higher contrast of norma l liver to tumorous tissue? iii) If higher contrast of normal liver to tumorous tissue is present, does this result in higher tumour detecti on-rates? Relative to non-enhanced and contrast-enhanced CT, what tumo ur detection-rate is obtained using non-enhanced and contrast-enhanced MRI? All the liver-specific CM studied possessed the ability to signi ficantly alter the signal in normal liver tissue. Compared to precontr ast values, the liver-specific CM studied in MRI (Mn-DPDP) and CT (IEE C-particles and iodixanol-liposomes) were able to increase significant ly the contrast of normal liver tissue to tumorous tissue and the tumo ur detection-frequency in VX2-carcinoma liver tumour-bearing rabbits. In CT using a non-specific extracellular CM, iohexol, no improvement i n contrast or tumour detection-frequency was obtained. As reflected in the values of contrast-to-noise obtained, MRI and CT have the same po tential for tumour detection in the liver tumour model used in the pre sent studies. Liver-specific CM have the property of improving the con trast of normal liver tissue to tumorous tissue in MRI and CT, giving higher tumour detection-rates. Permitting intravenous administration a nd the use of long imaging-windows, liver-specific CM are easy to use.