Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) is a molecular imaging technique that measures cerebral glucose metabolism, providing critical information about neuronal function and health in neurodegenerative diseases. FDG-PET is essential for differential diagnosis of dementias, Parkinsonism, and atypical parkinsonian syndromes.
- Radiotracer administration: [18F]FDG (fluorodeoxyglucose) is injected intravenously
- Glucose uptake: FDG is taken up by cells via glucose transporters (GLUT)
- Phosphorylation: Hexokinase phosphorylates FDG, trapping it in cells
- Positron emission: 18F decays, releasing positrons
- Detection: PET scanner detects annihilation photon pairs
- Reconstruction: Images showing regional glucose metabolism are created
- Neuronal activity indicator: Glucose is the primary energy source for neurons
- Synaptic function: Metabolism reflects synaptic activity
- Early detection: Metabolic changes precede structural atrophy
- Disease-specific patterns: Different disorders show distinct hypometabolism patterns
- Posterior cingulate hypometabolism: Early and prominent finding
- Precuneus hypometabolism: Central to AD pathophysiology
- Temporoparietal hypometabolism: Especially posterior temporal
- Frontal metabolism: Variable, often preserved early
- Early detection: Can identify AD years before symptoms
- Differential diagnosis: Distinguishes AD from other dementias
- Prognostication: Hypometabolism predicts progression
- Treatment monitoring: Metabolic changes with therapy
FTD subtypes show distinct patterns:
| FTD Variant |
Hypometabolism Pattern |
| Behavioral variant |
Frontal and anterior temporal |
| Semantic dementia |
Anterior temporal, especially left |
| Nonfluent/agrammatic PPA |
Left perisylvian region |
| Logopenic PPA |
Left posterior temporal/parietal |
- Occipital hypometabolism: Posterior cingulate often spared
- Primary visual cortex: Reduced metabolism
- Pattern distinguishes from AD: Less posterior cingulate involvement
- Useful for DLB vs. AD differentiation
¶ Parkinson's Disease and Atypical Parkinsonism
- Presynaptic dopaminergic imaging: More commonly used than FDG
- Metabolic patterns: Less characteristic than in atypical parkinsonism
- Cognitive impairment: Posterior cortical hypometabolism
- Brainstem/cerebellar hypometabolism: Characteristic
- Striatal hypometabolism: Putamen more than caudate
- Cerebellar atrophy pattern: In MSA-C variant
- Midbrain hypometabolism: Most characteristic finding
- Frontal cortex: Reduced metabolism
- Superior cerebellar peduncle: Decreased activity
- Differential from PD: Midbrain vs. striatal patterns
- Asymmetric cortical hypometabolism: Contralateral to more affected side
- Frontal and parietal: Most affected
- Basal ganglia: Often involved
- Corpus callosum: Reduced metabolism
| Disease |
Posterior Cingulate |
Occipital |
Frontal |
Temporal |
Striatum |
Brainstem |
| AD |
↓↓ |
↓ |
↓ |
↓↓ |
↔ |
↔ |
| DLB |
↔ |
↓↓ |
↔ |
↔ |
↓ |
↔ |
| bvFTD |
↓ |
↔ |
↓↓ |
↓ |
↔ |
↔ |
| SD |
↔ |
↔ |
↔ |
↓↓ |
↔ |
↔ |
| PSP |
↔ |
↔ |
↓ |
↔ |
↓ |
↓↓ |
| MSA |
↔ |
↔ |
↓ |
↔ |
↓↓ |
↓↓ |
| CBS |
↓ |
↓ |
↓↓ |
↓ |
↓ |
↔ |
| PD |
↔ |
↔ |
↔ |
↔ |
↓ |
↔ |
Legend: ↓↓ = severely reduced, ↓ = reduced, ↔ = preserved
- Fasting: 4-6 hours before injection
- Radiotracer dose: 185-370 MBq (5-10 mCi)
- Uptake period: 30-45 minutes
- Scan duration: 15-30 minutes
- Reconstruction: OSEM or filtered backprojection
- Standardized Uptake Value (SUV): Normalized to body weight
- SUVr (SUV ratio): Relative to reference region
- Statistical parametric mapping (SPM): Voxel-wise comparisons
- PCA (principal component analysis): Pattern recognition
- Cerebellum: Often used for normalization
- Pons: Common reference for cortical ratios
- Whole brain: For global metabolism
- Specific regions: Disease-dependent choice
- Clinical assessment: Initial neurological evaluation
- FDG-PET ordered: For uncertain diagnosis
- Pattern interpretation: Disease-specific hypometabolism
- Integration with other findings: Imaging, CSF, genetics
- Metabolic information: Functional vs. structural
- Early detection: Before atrophy on MRI
- Pattern specificity: Different diseases show different patterns
- Quantitative: Objective measures
- Radiation exposure: Though lower than CT
- Cost: Higher than SPECT
- Accessibility: Fewer PET scanners than MRI
- Non-specificity: Some pattern overlap between diseases
- AD progression: Metabolic decline tracks clinical decline
- Preclinical AD: Hypometabolism in normal-appearing brain
- Treatment trials: Endpoint measure for disease-modifying therapies
- Genetic forms: Metabolic patterns in familial AD, FTD
- Enrollment criteria: Ensuring correct diagnosis
- Outcome measures: Change in metabolism
- Mechanistic insights: Drug effects on brain metabolism
- Biomarker validation: Against other markers
- PET/MRI: Combined functional and structural
- PET/CT: Anatomical localization
- Simultaneous acquisition: Better registration
- Machine learning: Pattern classification
- Deep learning: Automated diagnosis
- Radiomics: Feature extraction
- Predictive modeling: Individual prognosis
- Amyloid PET: Pittsburgh compound B (PiB)
- Tau PET: FLTAU, AV-1451
- Dopamine tracers: More specific targeting
- Synaptic density: SV2A ligands