Australian study confirms superiority of PET over SPECT for Alzheimers diagnosis

Neurodegenerative disorders

By Michael Woodhead

13 May 2020

The first direct comparison of brain imaging techniques for diagnosing Alzheimer’s disease in real world patients has found that positron emission tomography (PET) is superior to single photon emission computerised tomography (SPECT).

Clinicians at the Austin Hospital, Melbourne found that cerebral blood flow 18F-FDG PET had markedly superior accuracy compared to SPECT in the assessment of people with dementia or mild cognitive impairment referred for diagnostic work-up by memory disorders specialists.

In a head-to-head comparison in 126 patients who underwent both imaging procedures they found that FDG PET was superior on almost all assessed performance measures including accuracy, sensitivity and reviewer confidence for diagnosing Alzheimer’s disease as verified by β-amyloid PET.

On the primary outcome of accuracy, FDG PET showed an overall AUROC of 0.71 compared to 0.61 for SPECT when images were reviewed by five nuclear medicine clinicians.

The investigators, led by Professor Christopher Rowe said this difference in accuracy was both clinically and statistically significant and was observed across all five reviewers irrespective of clinical experience.

FDG PET showed markedly superior sensitivity in identifying patients with Alzheimer’s disease (76% vs. 43%), whilst specificity was 74% vs 83%.

The greater accuracy using FDG PET was seen equally in the 56% with mild cognitive impairment (68.6% vs 50.0% SPECT), and the 44% of patients with dementia (81.4% vs 65.1%).

The nuclear medicine clinicians also had greater confidence in selecting a primary diagnosis with FDG PET than SPECT, with an average confidence level of 75.5% vs 64.6% respectively (p< 0.001). Likewise the reviewers reported high confidence in differentiating Alzheimers disease from other diagnoses in 83.1% of FDG PET studies compared to 67.2% for SPECT

The study authors said that amongst patients with a positive β-amyloid scan, reviewers identified greater regional reductions in metabolism on FDG PET than perfusion on SPECT. These metabolic changes were observed in areas typically associated with Alzheimer’s Disease, including the posterior cingulate, posterior parietal, lateral temporal and frontal lobes.

“Our results therefore provide the most robust head-to-head confirmation of 18F-FDG PET’s superiority amongst a clinically referred cohort of patients,” they said.

“18F-FDG PET showed significantly higher accuracy and sensitivity with greater reader confidence and therefore should be performed in clinical practice in preference to CBF-SPECT,” they concluded in Internal Medicine Journal.

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