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 coeffic ients (ADCs) could be used as measures of cell density and necrotic fractio n of tumors. Tumors of four human melanoma xenograft fines were subjected t o diffusion-weighted magnetic resonance imaging (DWI). ADCs were calculated from the images and related to cell density and necrotic fraction, as dete rmined from histological sections. A significant correlation was found betw een the ADC of the viable tissue and cell density, regardless of whether tu mors of different lines or different regions within individual tumors were considered. Necrosis was found in two of the lines. A single region of mass ive necrosis that could be differentiated from the viable tissue in ADC map s 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 measu res of cell density and necrotic fraction of some but not of all tumors, de pending on whether the individual necrotic regions are large enough to be d ifferentiated from the viable tissue with the obtained spatial resolution o f the DW images. Magn Reson Med 43:828-836, 2000. (C) 2000 Wiley-Liss, Inc.