Delineation of Experimental Liver Tumors in Rabbits by a New Ultrasound Contrast Agent and Stimulated Acoustic Emission

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Abstract
A new ultrasound contrast agent (SH U 563 A), consisting of hollow biodegradable polymeric microparticles, and a new imaging technique(stimulated acoustic emission) were used for delineation of experimental liver tumors. After intravenous injection, these microparticles are phagocytosed by cells of the reticuloendothelial system (RES) and create a color-coded signal using color Doppler. Because of the different distribution of phagocytic cells in healthy liver tissue and tumors, the delineation of focal lesions was to be tested. Sixteen rabbits with VX2 liver tumors received doses of 0.15-mL SH U 563 A per kilogram of body weight intravenously. Liver investigations (UM9, HDI, L10-5, ATL, Bothell, USA) were performed in vivo before and after SH U 563 A application in B and color Doppler modes. Additionally, the liver and spleen of these rabbits were examined ex vivo in color Doppler. The sonographic diagnosis was confirmed by pathology. After application of SH U 563 A, the healthy liver tissue of all rabbits was characterized by a typical mosaic color pattern in vivo and ex vivo, using color Doppler. Entire VX2 liver tumors were detectable exclusively in color Doppler after SH U 563 A application. This was possible in 14 of 16 rabbits in vivo and in all 16 livers ex vivo. Furthermore, all ex vivo investigated spleens were color enhanced homogeneously. Sonographic diagnoses were in accordance with pathologic findings. SH U 563 A, combined with stimulated acoustic emission, provides potential for delineation of small isoechogenic liver lesions by sonography.