Gray-scale liver enhancement in VX2 tumor-bearing rabbits using BR14, a new ultrasonographic contrast agent

We evaluated the potential of BR14, a novel gas-based echo contrast agent, for gray-scale liver imaging and VX2 tumor detection/delineation in the conventional and harmonic imaging modes.

A single dose (0.2 mL/kg) of BR14 was administered to eight VX2 tumor-bearing rabbits. Imaging was performed with an ATL-HDI 3000. The B-mode gray levels were analyzed by videodensitometry in areas selected in the liver tissue, tumors, aorta, and the portal vein from frames recorded up to 1 hour after injection. The tumors were further assessed using subjective scores just before and after contrast injection, as well as 15 minutes later in both conventional gray-scale and harmonic imaging modes.

Gray-scale enhancement of the liver tissue was detectable soon after BR14 injection and remained at a high level even after clearance of the agent from the blood stream. On precontrast, of 42 observed tumors, 4 were perfectly detected (4/42). After injection of BR14, the number rose to 10/20 in the vascular phase and 12/20 in the delayed phase. In harmonic imaging, the corresponding numbers were even higher, 17/22 in the vascular phase and 18/22 in the delayed phase. The number of tumors perfectly delineated increased after BR14 from 1/42 to 3/20 in the vascular phase and 5/20 in the delayed phase. In the harmonic mode, 9 of 22 tumors were perfectly delineated in the vascular phase and 10 of 22 in the delayed phase.

BR14 is a promising new agent for the study of tissue perfusion and in particular for liver imaging. It shows not only strong, but also persistent gray scale enhancement of the parenchyma but not of the tumors. The increased conspicuousness allows considerable improvements in tumor detection and tumor delineation in conventional imaging and even more so in harmonic imaging.