Magnetic resonance imaging of tumor necrosis

Abstract

Background. The prognostic and predictive value of magnetic resonance (MR) investigations in clinical oncology may be improved by implementing strategies for discriminating between viable and necrotic tissue in tumors. The purpose of this preclinical study was to investigate whether the extent of necrosis in tumors can be assessed by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and/or T₂-weighted MR imaging. Material and methods. Three amelanotic human melanoma xenograft lines differing substantially in tumor necrotic fraction, necrotic pattern, extracellular volume fraction, and blood perfusion were used as experimental models of human cancer. MRI was performed at 1.5 T and a spatial resolution of 0.23 × 0.47 × 2.0 mm³. Gadolinium diethylene-triamine penta-acetic acid (Gd-DTPA) was used as contrast agent. Plots of Gd-DTPA concentration versus time were generated for each voxel, and three parameters were calculated for each curve: the extracellular volume fraction (ν_e), the final slope (a), and the Gd-DTPA concentration at one minute after the contrast administration (C_1min). Parametric images of ν_e, a, C_1min, and the signal intensity in T₂-weighted images (SI_T2W) were compared with the histology of the imaged tissue. Results. The ν_e, a, and C_1min frequency distributions were significantly different for necrotic and viable tissue in all three tumor lines. By using adequate values of ν_e, a, and C_1min to discriminate between necrotic and viable tissue, significant correlations were found between the fraction of necrotic tissue assessed by MRI and the fraction of necrotic tissue assessed by image analysis of histological preparations. On the other hand, the SI_T2W frequency distributions did not differ significantly between necrotic and viable tissue in two of the three tumor lines. Conclusion. Necrotic regions in tumor tissue can be identified in parametric images derived from DCE-MRI series, whereas T₂-weighted images are unsuitable for detection of tumor necrosis.