1999 ARRS Executive Council Award - Contrast-enhanced CT of small hypovascular hepatic tumors: Effect of lesion enhancement on conspicuity in rabbits

OBJECTIVE. The purpose of this study was to evaluate the effect of lesion e nhancement on the conspicuity of small hypovascular hepatic tumors in an an imal model. MATERIALS AND METHODS. Seven VX2 hepatic tumors in five rabbits were imaged . Dynamic contrast-enhanced CT was performed at a single level centered ove r the lesions at 5-sec intervals for 119 sec after injection of 2 ml/kg IV contrast material at 2 ml/sec. Attenuation was measured over time within re gions of interest in the tumor and normal liver, aorta, inferior vena cava, and postal vein. Lesion conspicuity, defined as the difference between the attenuation of the uninvolved liver and neoplasm, was calculated. RESULTS. The mean diameter of the tumors on CT was 10 mm (range, 6-15 mm). The tumors appeared as low-attenuation lesions with progressive enhancement during the arterial phase and early portal phase. Peak mean lesion attenua tion was 60 +/- 27 H (enhancement, 23 H) at 64 sec. Peak mean lesion conspi cuity was 80 +/- 18 H at 39 sec, occurring 10 sec before the peak mean hepa tic attenuation of 135 +/- 15 H (enhancement, 67 H) at 49 sec. Relative les ion conspicuity paralleled relative enhancement of the liver throughout the imaging period. CONCLUSION. Although low-level tumor enhancement during the arterial phase and early portal phase reduced the conspicuity of small hypovascular tumors in this animal model, our results support the use of maximum liver enhance ment as a marker for peak lesion conspicuity.