FDG-PET metabolism — MRCPsych Paper A MCQ

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EasyNeuroimaging, neuroendocrinology and psychoneuroimmunologyFDG-PET metabolismMRCPsych Paper A

A 72-year-old woman with atypical cognitive decline undergoes FDG-PET, which shows temporoparietal hypometabolism. What does FDG-PET principally measure?

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Correct answer: D — Regional cerebral glucose metabolism

FDG-PET principally estimates regional cerebral glucose metabolism. The radiolabelled glucose analogue 18F-fluorodeoxyglucose is taken up by metabolically active tissue, so reduced regional uptake appears as hypometabolism and acts as an indirect marker of reduced neuronal and synaptic activity. Temporoparietal hypometabolism is a recognised neurodegenerative pattern, particularly in Alzheimer disease, although the question asks about the measured physiological process rather than the diagnosis. Amyloid plaque burden requires an amyloid-specific PET tracer. Dopamine receptor occupancy requires an appropriate receptor ligand, while white-matter tract directionality is assessed using diffusion MRI. Cerebrospinal fluid flow can be evaluated using specialised phase-contrast MRI or radionuclide techniques, but it is not the principal signal measured by FDG-PET.

Reference: Bischof GN, Ewers M, Franzmeier N, et al. PET Agents in Dementia: An Overview. Seminars in Nuclear Medicine. 2021;51(3):196–217. https://pubmed.ncbi.nlm.nih.gov/33500121/