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FIGURE 2. Image coregistration of 18F-FDG PET and MRI. (A) A 45-y-old woman with radiation necrosis. MRI showed a new contrast-enhancing lesion 4 mo after stereotactic radiosurgery for metastatic breast cancer. 18F-FDG PET showed mild uptake not higher than background level of adjacent brain tissue. Radiation necrosis was diagnosed, and MRI lesion regressed during follow-up. (B) A 54-y-old man with recurrent glioblastoma. MRI showed a new contrast-enhancing lesion. 18F-FDG PET showed moderate uptake lower than that of normal gray matter but higher than expected background level of adjacent brain tissue and corresponding to abnormal contrast-enhancing region on MRI. Surgery demonstrated recurrent glioblastoma with Ki-67 of 40%.
