Significant head motion can cause either hypermetabolic or hypometabolic cerebral activity on 18F-FDG PET/CT.

We report 2 separate cases with significant head motion causing apparent hypometabolic and hypermetabolic cerebral activity on FDG PET/CT. Case 1 is a 57-year-old man with facial numbness status post chemotherapy for mantle cell lymphoma. Restaging attenuation-corrected PET showed increased left frontal region activity, whereas nonattenuation-corrected PET demonstrated evidence of patient motion with normal physiologic left frontal cortical activity.