# Fludeoxyglucose F-18 (brain metabolism)

Source: https://nuclide.cc/drugs/f-18-fdg-brain/  
Nuclide record `f-18-fdg-brain` (Agent). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

The standard PET tracer for measuring how the brain is using energy; a pattern of low activity in particular brain regions can help doctors work out which type of dementia a patient has.

## Summary

Fludeoxyglucose F-18 (FDG) is the general-purpose PET metabolic tracer used across oncology, cardiology and neurology; it is not brain-specific as a product, but brain FDG PET is a distinct, well-established clinical application. Reduced glucose metabolism follows a regional pattern that differs by disease: temporoparietal and posterior cingulate hypometabolism is typical of Alzheimer's disease, while frontal and/or anterior temporal hypometabolism points to frontotemporal dementia, and this pattern difference is the main clinical use of FDG-PET in cognitive impairment.

In the United States, Medicare's national coverage determination for FDG-PET in dementia (NCD 220.6.13) covers a scan specifically to help differentiate Alzheimer's disease from frontotemporal dementia, in patients with a recent dementia diagnosis and at least 6 months of documented cognitive decline whose presentation leaves this distinction clinically uncertain after a comprehensive specialist evaluation; a prior brain SPECT or FDG-PET scan for the same question generally precludes a repeat scan within a year. All other dementia uses of FDG-PET (for example distinguishing other neurodegenerative diseases, or use outside a CMS-approved clinical trial in mild cognitive impairment) remain nationally non-covered under this determination, a materially narrower coverage pathway than the one now in force for amyloid PET.

FDG-PET brain imaging does not require thyroid blockade or specialised handling beyond standard F-18 PET radiopharmacy practice, and dosing follows general oncologic/neurologic FDG protocols (typically around 185-370 MBq IV, imaging beginning about 30-45 minutes later, with the patient resting quietly in a darkened, low-stimulation room during uptake to standardise regional brain activity). Because FDG uptake reflects neuronal activity rather than a specific pathological protein, it complements rather than replaces amyloid and tau PET: FDG shows the functional consequence of neurodegeneration, while amyloid and tau tracers show the underlying molecular pathology.

## Fields

- Kind: Agent
- Status: approved
- Last checked: 2026-09-22
- Also known as: FDG-PET brain; 18F-FDG
- Tags: FDG PET; diagnostic; neurology; metabolic imaging
- Modality: PET tracer
- Mechanism: A glucose analogue labelled with fluorine-18 that is taken up by cells in proportion to glucose metabolism and trapped after phosphorylation; in the brain, regional FDG uptake reflects synaptic activity, so characteristic patterns of reduced metabolism can distinguish different neurodegenerative diseases.
- Approvals: US 2004: FDG-PET nationally covered by Medicare specifically to differentiate Alzheimer's disease from frontotemporal dementia in patients with an uncertain diagnosis after comprehensive specialist evaluation (NCD 220.6.13)
- Dosing: Intravenous injection; Typical adult brain FDG-PET protocol: ~185-370 MBq IV, patient rested in a quiet, dimly lit room during the ~30-45 minute uptake phase, then PET imaging

## Sources

- CMS NCD 220.6.13: FDG PET for Dementia and Neurodegenerative Diseases: https://www.cms.gov/regulations-and-guidance/guidance/transmittals/downloads/r24ncd.pdf
- CMS coding article: PET scan coverage reference table including FDG dementia indication (A53134): https://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=53134

## Connected records

- indications: [Alzheimer's disease](https://nuclide.cc/indications/alzheimers-disease/)
- drugs: [Fludeoxyglucose F-18 (FDG)](https://nuclide.cc/drugs/fludeoxyglucose-f18/), [Technetium-99m exametazime (brain perfusion)](https://nuclide.cc/drugs/tc-99m-hmpao-brain/)
- technologies: [FDG PET](https://nuclide.cc/technologies/fdg-pet/)
- isotopes: [Fluorine-18](https://nuclide.cc/isotopes/f-18/)

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