Correlation of ultrasound contrast agent derived blood flow parameters with immunohistochemical angiogenesis markers in murine xenograft tumor models

Abstract

PurposeIn this study we used temporal analysis of ultrasound contrast agent (UCA) estimate blood flow dynamics and demonstrate their improved correlation to angiogenesis markers relative to previously reported, non-temporal fractional vascularity estimates. Materials and methodsBreast tumor (NMU) or glioma (C6) cells were implanted in either the abdomen or thigh of 144 rats. After 6, 8 or 10days, rats received a bolus UCA injection of Optison (GE Healthcare, Princeton, NJ; 0.4ml/kg) during power Doppler imaging (PDI), harmonic imaging (HI), and microflow imaging (MFI) using an Aplio ultrasound scanner with 7.5MHz linear array (Toshiba America Medical Systems, Tustin, CA). Time-intensity curves of contrast wash-in were constructed on a pixel-by-pixel basis and averaged to calculate maximum intensity, time to peak, perfusion, and time integrated intensity (TII). Tumors were then stained for four immunohistochemical markers (bFGF, CD31, COX-2, and VEGF). Correlations between temporal parameters and the angiogenesis markers were investigated for each imaging mode. Effects of tumor model and implant location on these correlations were also investigated. ResultsSignificant correlation over the entire dataset was only observed between TII and VEGF for all three imaging modes (R=−0.35, −0.54, −0.32 for PDI, HI and MFI, respectively; p<0.0001). Tumor type and location affected these correlations, with the strongest correlation of TII to VEGF found to be with implanted C6 cells (R=−0.43, −0.54, −0.52 for PDI, HI and MFI, respectively; p<0.0002). ConclusionsWhile UCA-derived temporal blood flow parameters were found to correlate strongly with VEGF expression, these correlations were also found to be influenced by both tumor type and implant location.