In vivo high-frequency contrast-enhanced ultrasonography of choroidal melanoma in rabbits: imaging features and histopathologic correlations.

Purpose To evaluate the use of in vivo imaging of rabbit model of choroidal melanoma using high-frequency contrast-enhanced ultrasound (HF-CE-US) with two-dimensional (2D) or three-dimensional (3D) modes and to correlate the sonographic findings with histopathologic characteristics. Methods Five New Zealand white rabbits, which were immunosuppressed with daily cyclosporin A (CsA), were inoculated into their right eyes with aliquots of 1.5x10(6)/50 mu l of 92.1 human uveal melanoma cells cultured in RPMI. At week 4, the tumour-bearing eyes were imaged using high-frequency ultrasound (HF-US) with microbubble contrast agent to determine the 2D tumour size and relative blood volume and by 3D mode to determine tumour volume. Histologic tumour burden was quantified in enucleated eyes by ImageJ software, and mean vascular density (MVD) was determined by counting vascular channels in periodic acid Schiff (PAS) without haematoxylin sections. Results Using HF-CE-US, melanomas were visualised as relatively hyperechoic regions in the images. The correlation coefficients of sonographic size and volume compared with histologic area were 0.72 and 0.70, respectively. The sonographic tumour relative blood volume correlated with the histologic tumour vascularity (r(2)=0.92, p=0.04). Conclusions There is a positive correlation between in vivo sonographic tumour volume/size and histologic tumour size in our rabbit choroidal melanoma model. HF-CE-US corresponds to MVD and blood volume.