Application of diffusion-weighted MR Imaging to the diagnosis of bone metastasis. A fundamental study using rabbit bone tumor model

The purpose of this study was to evaluate diffusion-weighted magnetic resonance imaging (DW-MRI) for the diagnosis of bone metastasis, using rabbit bone tumor models. Skeletal tumor lesions and inflammation were induced by the injection of VX-2 tumor cells in suspension and in croton oil, respectively, into the distal femur of Japanese white rabbits. Ten to fourteen days after the injection, MRI was performed under intravenous anesthesia. Single-shot echo planar DW images were obtained. After MRI, the diseased femurs were extirpated, histologically analyzed, and compared with DW images. The apparent diffusion coefficient (ADC) values for the different tissue regions were compared, and the relationships with histological measurements were examined. In the necrotic regions of intraskeletal tumors, ADC values were higher than those in regions with abundant viable tumor cells (p<0.0001). In extraskeletal tumors, necrotic cells were numerous, and ADC values were similar to those in the intraskeletal necrotic tumors. Intraskeletal inflammatory lesions and normal bone marrow showed the highest and lowest ADC values, respectively (p<0.0001). ADC values were negatively correlated with cell area density and the nuclear/cytoplasmic ratio. ADC values in various skeletal lesions correlated with histological features, suggesting the potential usefulness of ADC mapping in differentiating osteomyelitis from bone metastasis. (author)