OSTEOGENIC-SARCOMA - NONINVASIVE IN-VIVO ASSESSMENT OF TUMOR NECROSISWITH DIFFUSION-WEIGHTED MR-IMAGING

PURPOSE: To evaluate diffusion-weighted magnetic resonance (MR) imagin g for detecting tumor necrosis in an animal model of osteogenic sarcom a. MATERIALS AND METHODS: Twelve rats with osteogenic sarcoma underwen t T1-weighted unenhanced and gadolinium-enhanced spin-echo and diffusi on-weighted spin-echo MR imaging. Histologic correlation was performed . Signal intensities, T2 relaxation times, normalized apparent diffusi on coefficients, and relative signal intensity increases were calculat ed. RESULTS: On diffusion-weighted images, necrotic tumor showed low s ignal intensity (mean normalized apparent diffusion coefficient, 0.46 +/- 0.20 [1 standard deviation]), indicating rapid diffusion of water molecules as a result of loss of membrane integrity, while viable tumo r showed high signal intensity (mean normalized apparent diffusion coe fficient, 0.16 +/- 0.05; P < .0001). Differences in the T2 relaxation times and relative signal intensity increases between viable and necro tic tumor were not statistically significant. CONCLUSION: Normalized a pparent diffusion coefficients are more accurate in differentiating be tween viable and necrotic tumor than are T2 relaxation times or relati ve signal intensity increases on contrast-enhanced images. Signal inte nsity overlap between viable and necrotic tumor on gadolinium-enhanced images may be caused by the small molecular size of the agent, which permeates the interstitial space freely, thereby also enhancing necros is. Diffusion-weighted MR imaging depicts differences in diffusion and , ultimately, in membrane integrity between viable and necrotic tumor and may be used to monitor tumor viability during treatment.