The objective was to optimize the detection of angiogenesis and follow-up using high frequency ultrasonography with perfusion software allowing contrast uptake quantification after injection of an ultrasound contrast agent.
METHOD AND MATERIALS
Twenty B16F10 melanoma, xenografted onto nude mice, were examined 3 times a week over 23 days (D). Investigations were conducted with an Aplio sonograph (Toshiba®) equipped with a 9 MHz linear probe allowing the use of a perfusion software (Vascular Recognition Imaging, VRI) working on the harmonic imaging principle. Sonograph settings remained unchanged over time. The protocol was as follows : 1- in B mode : detection of tumor dimensions ; 2- In VRI mode after the injection of Sonovue (Bracco®), maximum contrast uptake, expressed in a grey scale, and the time to reach it, were quantified inside a region of interest in the largest cross-sectional area of the tumor . This time was computed by modeling the contrast uptake curve by a sigmoid equation. Tumors were resected at D23, oriented as they were in the animal and were sliced cross-sectionally in the same area studied with VRI. Histological sections were compared to VRI scans for correlation.
The tumor volume grew from 6.4 to 2234 mm³ between 7 to 23 days after xenografting of tumor cells. Concerning VRI parameters : 1- contrast uptake was constant and maximal between D9 and D17 and a rapid 65 % decline occurred between D17 and D23. This parameter was significantly correlated with the tumor volume (R2=0.85, p<0.001) ; 2- Contrast uptake started immediately after Sonovue injection (time < 2 s) and was maximal at 11.2 s at D9 and 52.5 s at D23. Vascularized zones were identified in the same locations on the sonographic and histological scans.
Sonovue associated with Vascular Recognition Imaging is a powerful tool for the characterization of vascularization during tumor development with objective and quantitative parameters. The activity of anti-tumor treatments could be evaluated early and functionally based on tumor contrast uptake.