Measurement of cell density and necrotic fraction in human melanoma xenografts by diffusion weighted magnetic resonance imaging.

The aim of this study was to investigate whether apparent diffusion coefficients (ADCs) could be used as measures of cell density and necrotic fraction of tumors. Tumors of four human melanoma xenograft lines were subjected to diffusion-weighted magnetic resonance imaging (DWI). ADCs were calculated from the images and related to cell density and necrotic fraction, as determined from histological sections. A significant correlation was found between the ADC of the viable tissue and cell density, regardless of whether tumors of different lines or different regions within individual tumors were considered. Necrosis was found in two of the lines. A single region of massive necrosis that could be differentiated from the viable tissue in ADC maps was found in one line, whereas a number of smaller necrotic regions that could not be identified in ADC maps were found in the other line. Tumor ADC was significantly correlated with the necrotic fraction of the former, but not of the latter line. Our results suggest that ADCs can be used as measures of cell density and necrotic fraction of some but not of all tumors, depending on whether the individual necrotic regions are large enough to be differentiated from the viable tissue with the obtained spatial resolution of the DW images. Magn Reson Med 43:828-836, 2000. Copyright 2000 Wiley-Liss, Inc.