Choice and normalization of contrast ultrasound parameters for detection of anti-angiogenic response

Contrast ultrasound can detect perfusion modifications during anti-angiogenic therapy preceding tumor size regression. However, contrast imaging would benefit from better standardization of the technique. This work compared discrimination of renal neuroblastoma (Wilm's tumor) in placebo and Sorafenib-treated mice using Sonovue microbubbles. Orthotopic renal neuroblastoma tumors were induced in 15 nude mice randomized into a control and a treated group. Conventional and contrast ultrasound were performed periodically prior to and up to 8 day after onset of therapy. At each day of contrast ultrasonography, tumor size was monitored and three replenishment parameters (relative blood volume (rBV), mean transit time (mTT) and wash in rate (WiR)) were measured. Measurements were made with and without normalization with respect to flow in adjacent renal cortex. No significant difference in tumor size between treated and nontreated groups was detected, even at study end. Normalization reduced estimate variability due to injection and improved functional contrast assessment. After normalization, the WiR parameter (nWiR) provided significant discrimination between the placebo and treated groups (p=0.05 at 6 days of treatment). The nWiR parameter was more sensitive to differences between the two groups than were nmTT and nrBV. Results demonstrate the importance of choice in perfusion parameters for follow-up of anti-angiogenic therapy and demonstrate the interest of parameter normalization.