Gray scale second harmonic imaging of acoustic emission signals improves detection of liver tumors in rabbits.

This study evaluates a new reticuloendothelium specific sonographic contrast agent NC100100 (Sonazoid) for detection of liver VX-2 tumors in rabbits. Gray scale imaging of five groups of three rabbits, with hepatic VX-2 tumors implanted 7, 10, 12, 14, and 18 days previously, was performed prior to injection of Sonazoid (dosages, 0.01-0.5 ml/kg). Sonazoid produces induced acoustic emission after uptake in the liver. Therefore, harmonic gray scale images were obtained immediately after injection as well as delayed (by up to 2(1/2) h). Five rabbits (one from each group) also had angiography performed, while all animals were evaluated by pathologic examination. Non-contrast enhanced sonography detected 17 of 61 tumors (29%), as well as three false-positives, while the addition of Sonazoid detected 57 tumors (93%) and one false-positive (P<0.001). Acoustic emission made 2 x 2 mm tumors (invisible in conventional B-mode sonography) clearly perceivable in harmonic gray scale. In the subgroup that received angiography, 12 of 36 tumors (33%) were detected with conventional sonography compared to 22 tumors (61%) seen with angiography (P = 0.002). After injection of Sonazoid the ultrasonographic detection rate increased to 97% (35 of 36 tumors), which was a significant improvement over angiography (P = 0.00024). Improved detection of hepatic VX-2 tumors with second harmonic gray scale imaging of Sonazoid is possible because of this agent's acoustic emission capabilities.