Quantitative study of the growth of experimental hepatic tumors in rats by using magnetic resonance imaging

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Abstract
Precise estimation of the volume and growth rate of hepatic metastases would represent an important step forward not only in clinical oncology but also for the evaluation of experimental treatments in animal models. In the present study, an original method of volumetry of hepatic metastatic tumors in vivo has been tested in rats using magnetic resonance imaging (MRI). Three different hepatic tumor models mimicking liver metastases were established in syngeneic BDIX rats by injection of DHD/KI2 rat colon cancer cells either directly under the liver capsule or via the portal system. The liver tumor volumes were estimated in vivo by using MR imaging of the liverand summing the individual tumor volumes in the sequential MR liver sections. The values of the tumor volumes measured by MRI were compared with those determined by a classical method of water displacement in vitro after killing the animals and excising the tumors. At 3 weeks after tumor implantation, liver tumors as small as I mm in diameter could be detected by MRI. The difference between the tumor volumes estimated by MRI in vivo and those measured by water displacement in vitro was 9% for single liver tumors and 16% for multiple liver tumors. Close correlation between the values of the tumor volumes measured by MRI and those determined by water displacement was observed in solitary liver tumors (r = 0.985, p < 0.01) as well as in multiple liver tumors (r = 0.985, p < 0.01), indicating the high accuracy of MRI volumetry for liver tumors. Estimation of the liver tumor volumes by MRI in the same animals at successive time intervals made it possible to construct tumor growth curves and to calculate tumor growth parameters. These data suggest that MRI volumetry represents an effective means of evaluating the efficacy of experimental treatments in small animals and may have potentially important applications in clinical patients.