The magnetic resonance imaging (MRI) characteristics of primary malignant bone tumors are evaluated in determination of the surgical margin. Fifteen patients were examined with Toshiba MR imager (0.22-T resistive magnet). Eight patients had osteosarcoma, three had chondrosarcoma, three had giant cell tumor of bone, and one had angiosarcoma of bone. All patients had CT scans available for comparison. The extra-and intra-osseous extension of the lesion were separately studied. MRI was

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... superior to CT in all cases with osteolytic lesion. MRI was, especially, superior to CT for demonstrating the extent of tumor in marrow. Moreover, MRI was extremely useful for the assessment in the lesion of thoracic wall. CT was only superior to MRI for depicting the extraosseous extent in screlotic type of osteosarcoma. Above all, MRI was the imaging method of choice in determination of the surgical margin for malignant bone tumors.