To establish a "gold standard" necessary to assess the performance of the SPECT bone scans, the investigators will compare number of malignant lesions detected in patients who are proven to have metastatic skeletal bone lesions on PET F-18 whole-body scans, with whole-body Tc-99m SPECT lesions. The investigators also propose to compare the detection of SPECT scans with standard planar bone scans. This will allow for two major comparisons (a) the accuracy of SPECT bone studies compared to planar bone studies, and (b) the accuracy of SPECT bone scans compared to F-18 PET studies. Most prior studies purporting to show the superiority of F-18 bone scans to Tc-99 bone scans were done only against either planar scans or a combination of planar scans and partial SPECT studies over the spine. We anticipate that F-18 bone scans, due to the higher counting statistics of PET agents, will show more lesions than SPECT, but the exact increase in sensitivity has never been compared to whole-body SPECT scans.