Detection of Hepatic VX2 Tumors in Rabbits: Comparison of Conventional US and Phase-Inversion Harmonic US During the Liver-Specific Late Phase of Contrast Enhancement

Abstract

ObjectiveTo compare phase-inversion sonography during the liver-specific phase of contrast enhancement using a microbubble contrast agent with conventional B-mode sonography for the detection of VX2 liver tumors.Materials and MethodsTwenty-three rabbits, 18 of which had VX2 liver tumor implants, received a bolus injection of 0.6 g of Levovist (200 mg/ml). During the liver-specific phase of this agent, they were evaluated using both conventional sonography and contrast-enhanced phase-inversion harmonic imaging (CE-PIHI). Following sacrifice of the animals, pathologic analysis was performed and the reference standard thus obtained. The conspicuity, size and number of the tumors before and after contrast administration, as determined by a sonographer, were compared between the two modes and with the pathologic findings.ResultsCE-PIHI demonstrated marked hepatic parenchymal enhancement in all rabbits. For VX2 tumors detected at both conventional US and CE- PIHI, conspicuity was improved by contrast-enhanced PIHI. On examination of gross specimens, 52 VX2 tumors were identified. Conventional US correctly detected 18 of the 52 (34.6%), while PIHI detected 35 (67.3%) (p < 0.05). In particular, conventional US detected only three (8.3%) of the 36 tumors less than 10 mm in diameter, but CE-PIHI detected 19 such tumors (52.8%) (p < 0.05).ConclusionCompared to conventional sonography, PIHI performed during the liver-specific phase after intravenous injection of Levovist is markedly better at detecting VX2 liver tumors.

Review of clinical characteristics and applications of contrast-enhanced ultrasonography in dogs

“…34,46,81,82 Lesions measuring up to 5 mm are clearly revealed via CEUS, and even lesions < 5 mm can be detected. 78,81,83,84 Unlike CECT and CEMRI, CEUS permits realtime analysis of tumor perfusion, which provides better temporal resolution, and does not require that subjects be anesthetized. 43,85 In addition, compared with CECT and CEMRI, CEUS is more cost-effective, can be performed faster, and does not involve ionizing radiation.…”

Role of Sonography for Implantation and Sequential Evaluation of a VX2 Rabbit Liver Tumor Model

“…This wash-out change was also confirmed in other studies, 25,26 which prompted a method to allow clear detection of tumors and surrounding satellite lesions during the late period of CE sonography. 27,28 Lee et al 29 compared the capability of detecting VX2 rabbit liver tumors during the late period of CE PIH sonography using SH U 508A (Levovist; Schering AG, Berlin, Germany) with that of conventional sonography, and the results showed that conventional sonography correctly showed 18 of 52 VX2 tumors, whereas CE PIH sonography showed 35 of 52. In particular, conventional sonography showed only 3 of 36 tumors smaller than 10 mm in diameter, but CE PIH sonography showed 19 such tumors.…”

“…In particular, conventional sonography showed only 3 of 36 tumors smaller than 10 mm in diameter, but CE PIH sonography showed 19 such tumors. 29 Dynamic CE sonography depicted the vascularity of the VX2 tumors, which is also considered effective in evaluation after thermal therapy, ie, radio frequency or high-intensity focused ultrasound ablation, for differentiation of necrotic and residual viable tissues. 14,30 Some limitations were also found for the sonographically guided implantation method.…”