Enhanced sonography using carbon dioxide gas for small hepatocellular carcinoma: a comparison study between pure carbon dioxide gas and carbon dioxide microbubbles.

PURPOSE: To evaluate the feasibility of enhanced sonography using arterial injection of pure carbon dioxide gas (CO(2)) for detecting small hepatocellular carcinoma (HCC) nodules. MATERIALS AND METHODS: We performed enhanced sonography on 51 HCC nodules of 35 patients with HCC. The patients underwent enhanced sonography with two methods: injection of pure CO(2) (26 nodules), or injection of CO(2) microbubbles (25 nodules) using CO(2) and soy bean oil. We observed the enhancement effect of HCC on enhanced sonography, and measured the accumulation time of CO(2) in the nodules. RESULTS: Twenty-three nodules appeared hyperechoic on enhanced sonography, and 12 of the nodules could be found on enhanced sonography only. Sixteen of the hyperechoic nodules on baseline sonography revealed no enhancement. Multiple regression analysis with regard to the method of injection of CO(2), nodule location, and nodule size revealed that method (p<0.0001) and nodule size (p=0.02) remained significant. The accumulation time of CO(2) microbubbles in the nodules was 4.4+/-0.8 minutes, whereas pure CO(2) accumulation time was 14.7+/-1.5 minutes, significantly longer than the CO(2) microbubbles regardless of nodule size and location. CONCLUSION: Enhanced sonography of arterial injection of pure CO(2) is a feasible technique for detecting small HCC nodules.