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

Abstract

Purpose: In 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 methods: Breast tumor (NMU) or glioma (C6) cells were implanted in either the abdomen or thigh of 144 rats. After 6, 8 or 10 days, rats received a bolus UCA injection of Optison (GE Healthcare, Princeton, NJ; 0.4 ml/kg) during power Doppler imaging (PDI), harmonic imaging (HI), and microflow imaging (MFI) using an Aplio ultrasound scanner with 7.5 MHz 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.

Results: Significant 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).

Conclusions: While 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.

Figure 1

Example images showing baseline (with tumor circled) and peak enhancement of a C6 thigh implanted tumor imaged with PDI (a–b), HI (c–d), and MFI (e–f).

Figure 2

Example parametric images generated from the harmonic case in Figure 1, showing maximum intensity (a), time to peak (b), perfusion (c), and time integrated intensity (d) (A.U. = arbitrary units).

Figure 3

Data from correlation of time integrated intensity (TII) with vascular endothelial growth factor (VEGF) expression from power Doppler (a), harmonic (b), and microflow (c) imaging.