Sensitivity to Tumor Microvasculature Without Contrast Agents in High Spectral and Spatial Resolution MR Images

Contrast-enhanced (CE)-MRI Is sensitive to cancers but can produce adverse reactions and suffers from insufficient specificity and morphological detail. This research investigated whether high spectral and spatial resolution (HISS) MRI detects tumor vasculature without contrast agents, based on the sensitivity of the water resonance line shape to tumor blood vessels. HISS data from AT6.1 tumors inoculated in the hind legs of rats (N = 8) were collected pre- and post-blood pool contrast agent (iron-oxide particles) injection. The waterline in small voxels was significantly more asymmetric at the tumor rim compared to the tumor center and normal muscle (P < 0.003). Composite images were synthesized, with the Intensity in each voxel determined by the Fourier component (FC) of the water resonance having the greatest relative image contrast at that position. We tested whether regions with high contrast in FC images (FCIs) contain vasculature by comparing FCIs with CE-MRI as the "gold standard" of vascular density. The FCls had 75% +/- 13% sensitivity, 74% +/- 10% specificity, and 91% +/- 4% positive predictive value (PPV) for vasculature detection at the tumor rim. These results suggest that tumor microvasculature can be detected using HISS imaging without the use of contrast agents. Magn Reson Med 61:291-298, 2009. (c) 2009 Wiley-Liss, Inc.