Measurement of human choroidal melanoma xenograft volume in rats using high-frequency ultrasound

The purpose of this study was to test the hypothesis that the volume of primary orthotopic human choroidal melanoma xenografts can be quantified noninvasively in the same nude rat over time using a portable, high-resolution, high-frequency ultrasound (HF-US) system.

C918 human choroidal melanoma spheroids were implanted in the superior suprachoroidal space of 26 WAG/RijHsd-rnu nude rats. Fourteen rats were anesthetized 14 days after tumor implantation, and HF-US B-scan images of the tumor-bearing eye were captured at 250-mum intervals. Tumor areas were measured on each image and numerically integrated to calculate volume. Tumor volumes were also estimated from serial histologic sections in six rats. Twelve other rats were anesthetized and weighed every 4 to 5 days after implantation for 2 weeks, and HF-US B-scan image series were acquired for subsequent measurement of tumor volume.

Tumors could be visualized as heterogeneous, relatively hyperechoic regions in the superior portion of the eye. These regions were verified as tumor by comparison with histologic sections, and histologic and HF-US volumes were highly correlated (r = 0.961; P = 0.002). For the determination of HF-US volume, the intraobserver variability was 9.7% +/- 5.1% (n = 8), and the coefficient of variation for multiple measurements was 12.1% +/- 6.8% (n = 12). Tumor volume could be repeatedly measured in the same rat every 4 to 5 days for 2 weeks without significant weight loss.

HF-US is a safe, practical method to measure tumor volume in the same nude rat over time in this orthotopic xenograft model of human choroidal melanoma.