Ultrasonographic portography with low mechanical index gray-scale imaging in hepatic VX2 tumor

To evaluate the characteristics of portal blood supply of hepatic tumors by ultrasonographic portography (USP), an in vivo model was studied using SonoVue, a second-generation ultrasound contrast agent (UCA) and low mechanical index (MI), gray-scale harmonic imaging. SonoVue (0.05 mL) was administrated through catheter placed into the main trunk of portal vein at laparotomy, followed by a 0.5 mL saline flush, in 12 rabbits with hepatic VX2 tumor, implanted by VX2 tumor tissue cubes of approximately 1 mm3 from carrier rabbit. Results showed that low MI gray-scale imaging delineated clearly the dynamic enhancement of tumors and liver parenchyma. Among 22 tumors, seven tumors were diffusely increased, with the intensity of enhancement weaker than that of the surrounding liver parenchyma. The UCA was washed out earlier from tumors than from surrounding liver parenchyma. Three tumors showed the branches of portal vein. Five tumors showed peripheral contrast enhancement and a central coarse unenhanced hypoechoic area. Seven tumors displayed no actual enhancement. All lesions (100% 22 of 22]) were depicted clearly in the whole duration of enhancement, especially in the early and late phase, regardless of enhancement pattern, and portal blood flow was manifested in 15 of 22 (68%) tumors, by USP. The enhancement pattern of the tumors corresponded to the pathologic findings. The results indicated that ultrasonographic portography, combined with low MI levels and second-generation UCA, is a sensitive and safe method to study portal blood supply for liver cancer. It may contribute to improvement of the detectability and diagnostic ability and assist the choice of a therapeutic strategy for treatment of liver cancer. However, applicability of the method to human may be problematic because of high invasiveness and great difficulty in administering contrast medium.