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General Principles for FDG PET Dementia Imaging

The use of PET radiotracers allows molecular imaging of brain processes. In clinical practice, there are two such tracers in use for dementia: F-18 FDG and F-18 Amyloid binders. 

In general, FDG PET is highly sensitive in distinguishing Alzheimer's dementia (AD) from other neurodegenerative disorders which look clinically similar. 


This is a pattern associated with Alzheimer's dementia: decreased metabolism in the temporoparietal cortex and posterior cingulate gyrus with sparing of the primary sensorimotor cortex, occipital cortex and subcortical structures.  The decrease may be asymmetric, and in more advanced cases tend to be symmetric in these area and also decreased in the frontal cortex 
Picture
On the other hand, "Amyloid PET" is promoted as more specific for AD, although the FDA dictates the interpretation be on amyloid plaque burden in the cortex.  
Picture
Below are normal FDG patterns on PET imaging, including of normal aging changes (primarily brain atrophy, which decreases FDG activity in parts of the brain that is more robust in younger healthy people). 
Picture

On FDG PET/CT, in general and in early stages:
  • Alzheimer dementia is associated with decreased temporoparietal and posterior cingulate activity with sparing of the pre-/postcentral gyrus and occipital cortex
  • Diffuse Lewy body disease and Parkinson dementia are associated with decreased temporoparietal and occipital activity
  • Frontotemporal dementia is associated with decreased frontal and temporal activity
  • Multiple system atrophy (MSA) is associated with decreased putamen, brainstem, and cerebellum activity
  • Progressive supranuclear palsy (PSA) is associated with frontal, basal ganglia, and mid brain activity
  • Cortical basal degeneration is associated with decreased parietal, central, striatal and thalamic activity
  • Huntingon's disease is associated with decreased basal ganglia activity relative to cerebral cortex.

Sources:

Brown RKJ et al. Brain PET in Suspected Dementia: Patterns of Altered FDG Metabolism. RadioGraphics 2014; 34:684–701.

Herholz K. PET studies in dementia. Annals of Nuclear Medicine Vol. 17, No. 2, 79–89, 2003.

Ishii K. PET Approaches for Diagnosis of Dementia. AJNR Am J Neuroradio...

Teune LK et al. Typical cerebral metabolic patterns in neurodegenerative brain diseases. Mov Disord. 2010 Oct 30;25(14):2395-404.

Silverman D. Brain 18F-FDG PET in the Diagnosis of Neurodegenerative Dementias: Comparison with Perfusion SPECT and with Clinical Evaluations Lacking Nuclear Imaging. J Nucl Med April 1, 2004 vol. 45 no. 4 594-607.

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