Head-to-head comparison of cerebral blood flow single-photon emission computed tomography and 18 F-fluoro-2-deoxyglucose positron emission tomography in the diagnosis of Alzheimer disease

Abstract

Background: Clinical diagnosis of Alzheimer disease (AD) is only 70% accurate. Reduced cerebral blood flow (CBF) and metabolism in parieto-temporal and posterior cingulate cortex may assist diagnosis. While widely accepted that ¹⁸ F-fluoro-2-deoxyglucose positron emission tomography (¹⁸ F-FDG PET) has superior accuracy to CBF-SPECT for AD, there are very limited head-to-head data from clinically relevant populations and these studies relied on clinical diagnosis as the reference standard.

Aims: To compare directly the accuracy of CBF-SPECT and ¹⁸ F-FDG PET in patients referred for diagnostic studies in detecting β-amyloid PET confirmed AD.

Methods: A total of 126 patients, 56% with mild cognitive impairment and 44% with dementia, completed both CBF-SPECT and ¹⁸ F-FDG PET as part of their diagnostic assessment, and subsequently underwent β-amyloid PET for research purposes. Transaxial slices and Neurostat 3D-SSP analyses of ¹⁸ F-FDG PET and CBF-SPECT scans were independently reviewed by five nuclear medicine clinicians blinded to all other data. Operators selected the most likely diagnosis and their diagnostic confidence. Accuracy analysis used final diagnosis incorporating β-amyloid PET as the reference standard.

Results: Clinicians reported high diagnostic confidence in 83% of ¹⁸ F-FDG PET compared to 67% for CBF-SPECT (P = 0.001). All reviewers showed individually higher accuracy using ¹⁸ F-FDG PET. Based on majority read, the combined area under the receiver operating characteristic curve in diagnosing AD was 0.71 for ¹⁸ F-FDG PET and 0.61 for CBF-SPECT (P = 0.02). The sensitivity of ¹⁸ F-FDG PET and CBF-SPECT was 76% versus 43% (P < 0.001), while specificity was 74% versus 83% (P = 0.45).

Conclusions: ¹⁸ F-FDG PET is superior to CBF-SPECT in detecting AD among patients referred for the assessment of cognitive impairment.

Keywords: 18F-fluoro-2-deoxyglucose; Alzheimer disease; positron emission tomography; single-photon emission computed tomography imaging.

Figure 1

Neurostat 3D‐SSP analysis of an ¹⁸F‐fluoro‐2‐deoxyglucose positron emission tomography study. Areas of regional hypometabolism >2 standard deviations below the normal database are represented in green. In this example, Neurostat 3D‐SSP demonstrates metabolic changes typical of Alzheimer disease, including regional hypometabolism in the posterior cingulate, posterior parietal lobes (including precunei), lateral temporal and bilateral frontal lobes.

Figure 2

Transaxial slices from a cerebral blood flow‐single‐photon emission computed tomography (CBF‐SPECT) (A) and ¹⁸F‐fluoro‐2‐deoxyglucose positron emission tomography ( ¹⁸F‐FDG PET) study (B) acquired from the same patient, demonstrating the superior resolution and image characteristics of ¹⁸F‐FDG PET. In this example, the significant parietal abnormalities (left > right) are much better appreciated on ¹⁸F‐FDG PET than CBF‐SPECT.

Figure 3

Individual reviewer accuracy in diagnosing Alzheimer disease using cerebral blood flow‐single‐photon emission computed tomography (CBF‐SPECT) and ¹⁸F‐fluoro‐2‐deoxyglucose positron emission tomography ( ¹⁸F‐FDG PET); all five reviewers showed significantly higher area under the receiver operating characteristic curve with ¹⁸F‐FDG PET. Left to right: (), Reviewer 1 (P = 0.04); (), Reviewer 2 (P = 0.005); (), Reviewer 3 (P = 0.001); (), Reviewer 4 (P = 0.001); (), Reviewer 5 (P = 0.001).

Figure 4

Reviewer confidence in selecting a primary diagnosis with cerebral blood flow‐single‐photon emission computed tomography (CBF‐SPECT) () compared to ¹⁸F‐fluoro‐2‐deoxyglucose positron emission tomography (18F‐FDG PET) ().