Chemoembolization of liver tumor in a rabbit model: Assessment of tumor cell death with diffusion-weighted MR imaging and histologic analysis

PURPOSE: To assess the efficacy of chemoembolization of liver tumors by determining the fraction of viable tumor cells remaining after treatment with use of diffusion magnetic resonance (MR) imaging and histologic analysis. MATERIALS AND METHODS: VX2 tumor was grown in the livers of 12 rabbits. Animals were divided into a chemoembolization group and an untreated group. Conventional, perfusion, and diffusion MR imaging was performed on all rabbits. Histopathologic analysis of explanted livers was performed to document tumor cell death and measure Bcl-2 levels (inhibitor of apoptosis). RESULTS: Diffusion-weighted MR imaging delineated zones of tumor cell death as regions of lower signal intensity in both groups. Apparent diffusion coefficients were significantly greater in the area of tumor necrosis than in the area of viable tumor. Histologic analysis demonstrated a significantly lower percentage of viable cells in the treated group (<1%) than in the control group (55%). Bcl-2 expression detected within the viable areas of the tumor was greater in the treated group than in the control group. CONCLUSIONS: Chemoembolization causes extensive tumor cell destruction. Diffusion MR imaging can detect tumor cell death and can be used to assess the efficacy of chemoembolization, Bcl-2 was expressed in the treated group, suggesting an apoptotic pathway of cell death.