Quantification of viable tumor microvascular characteristics by multispectral analysis

Tumor heterogeneity complicates the quantification of tumor microvascular characteristics assessed by dynamic contrast‐enhanced MRI (DCE‐MRI). To address this issue a novel approach was developed that combines DCE‐MRI with diffusion‐based multispectral (MS) analysis to quantify the microvascular characteristics of specific tumor tissue populations. Diffusion‐based MS segmentation (feature space: apparent diffusion coefficient, T2 and proton density) was performed to identify tumor tissue populations and the DCE‐MRI characteristics were determined for each tissue class. The ability of this MS DCE‐MRI technique to detect microvascular changes due to treatment with an antibody (G6‐31) to vascular endothelial growth factor‐A (VEGF) was evaluated in a tumor xenograft mouse model. Anti‐VEGF treatment resulted in a significant reduction in Ktrans for the MS viable tumor tissue class (−0.0034 ± 0.0022 min−1, P < 0.01) at 24 hr posttreatment that differ significantly from the change observed in the control group (0.0002 ± 0.0025 min−1). Viable tumor Ktrans for the anti‐VEGF group was also reduced 62% relative to the pretreatment values (P < 0.01). Necrotic tissue classes were found to add only noise to DCE‐MRI estimates. This approach provides a means to measure physiological parameters within the viable tumor and address the issue of tumor heterogeneity that complicates DCE‐MRI analysis. Magn Reson Med, 2008. © 2008 Wiley‐Liss, Inc.