Characterization of Various Canine Focal Liver Lesions with Sonazoid, a Novel Ultrasound Contrast Agent
Department of Veterinary Internal Medicine, Graduate School of Agricultural and Life Sciences, The University of Tokyo
Contrast-enhanced ultrasound (CEU) using microbubble-based contrast agents is a method that has begun to garner attention as a practical and useful examination in human medicine. In Japan, a new contrast agent Sonazoid was introduced in 2007. Compared to other contrast agents, Sonazoid has a greater advantage in liver CEU in that it has not only a vascular phase but also a true parenchymal phase (Kupffer phase). Kupffer phase, which is characterized by phagocytosis of the agent by the reticuloendothelial cells in the liver, enables continuous observation of enhanced images and a more accurate detection and diagnosis of liver diseases. The aim of this study was to characterize the time course enhancement by Sonazoid in the liver of healthy dogs and to evaluate the enhancement pattern of various canine focal liver lesions (FLLs) in clinical cases.
Five healthy beagles and 15 dogs with FLL detected by conventional B-mode ultrasound were recruited for this study. FLLs were diagnosed by liver biopsy and were classified as follows: benign lesions, 4; hepatocellular carcinomas (HCCs), 8; cholangiocellular carcinoma (CC), 1; hematopoietic tumors (HTs), 2. Sonazoid 0.015 ml/kg was intravenously administered to dogs, and ultrasonographic examination was performed from immediately after the injection till 15 min after the injection. The time course enhancement of hepatic parenchyma and the portal vein was examined in healthy dogs. In the clinical study, the enhancement pattern of FLL by Sonazoid injection was examined during the arterial, portal, and parenchymal (Kupffer) phases.
In the Sonazoid CEU of healthy beagles, sustained enhancement was observed in the liver parenchyma for more than 15 min, whereas in the portal vein, the enhancement dramatically decreased after the peak enhancement at 30 s. Based on the time-intensity curve, the arterial, portal, and parenchymal phases of Sonazoid CEU in dogs were defined as 0 to 20 sec, 20 sec to 1 min, 7 to 15 min, respectively. In HCCs, 5 lesions were hypervascular and 2 were hypovascular in the arterial phase, whereas in the parenchymal phase, irregular enhancement was observed in all cases. In CCs and HTs, we observed early enhancement washout during the vascular phase and clear defect in the parenchymal phase. In contrast to these malignant lesions, benign lesions showed sustained uniform enhancement in the parenchymal phase in 3 of 4 cases. Moreover, additional FLLs that had not been detected by conventional B-mode ultrasound were observed in some cases in CCs or HTs.
In conclusion, incomplete enhancement in the parenchymal phase was characteristic for malignant canine FLLs in Sonazoid CEU, whereas most of the benign lesions showed sustained uniform enhancement. This agent was thought to be useful in characterization and detection of canine FLLs, particularly during the parenchymal (Kupffer) phase. Further investigation of a large number of cases is required to clarify the usefulness of CEU with Sonazoid.