Background and Aim of the Work: Early detection of skeletal metastasis is critical for accurate staging and optimal treatment. Among the various imaging modalities currently available for imaging skeletal metastasis, hybrid techniques which fuse morphological and functional data are the most sensitive and specific, and positron emission tomography (PET)/computed tomography imaging will almost become increasingly important in this regard. We tried to assess the efficacy of fluorine-18 fluoro-deoxy-glucose Positron Emission Tomography/Computed Tomography (PET/CT) ((18) F-FDG-PET/CT) scan in detecting bone metastases among various primary malignancies. In order to detect accuracy of fused PET/CT in the initial detection & characterization of osseous metastases compared to isolated PET and CT with contrast.
Patients and methods:   The study included thirty patients (with a mean age = 27) with various primary malignancies (pathologically proven) to whom PET/CT was done. In this study population, a detailed retrograde lesion based analysis was performed for a total of 80 detected bone lesions on PET, CT and fused PET/CT images. Sensitivity, specificity, PPV and NPV of each modality were calculated. Stastical analysis of the lesions were performed to study the relationship between the lesion's SUV and its corresponding morphologic pattern on CT and to set a reliable SUVmax cut-off value that can predict the presence of malignant lesion.
Results: The calculated fused PET/CT sensitivities and specificities in various malignancies ranged from 95.2% to 99.6% and 75% to 100%, respectively. The combined PET/CT has significantly improved the low CT sensitivity (especially in lymphoma) as well as both separate CT and PET specificities (using SUVmax of 3 as a cut off value for malignant osseous lesions).
Conclusion: Detection of early bone marrow infiltration not apparent on CT, resolution of metabolic activity before definite signs of complete healing on CT, detection of missed sclerotic metastases on PET due to their relatively low metabolic activity, detection of intra and extra osseous recurrence and differentiation of benign from malignant bone lesions.