Direct comparison of fluorodeoxyglucose positron emission tomography and arterial spin labeling magnetic resonance imaging in Alzheimer's disease

Abstract

Background: The utility of fluorodeoxyglucose positron emission tomography (FDG-PET) imaging in Alzheimer's disease (AD) diagnosis has been well established. Recently, measurement of cerebral blood flow using arterial spin labeling magnetic resonance imaging (ASL-MRI) has shown diagnostic potential in AD, although it has never been directly compared with FDG-PET.

Methods: We used a novel imaging protocol to obtain FDG-PET and ASL-MRI images concurrently in 17 AD patients and 19 age-matched control subjects. Paired FDG-PET and ASL-MRI images from 19 control subjects and 15 AD patients were included for qualitative analysis, and paired images from 18 control subjects and 13 AD patients were suitable for quantitative analyses.

Results: The combined imaging protocol was well tolerated. Both modalities revealed similar regional abnormalities in AD, as well as comparable sensitivity and specificity for the detection of AD after visual review by two expert readers. Interobserver agreement was better for FDG-PET (κ: 0.75, standard error: 0.12) than ASL-MRI (κ: 0.51, standard error: 0.15); intermodality agreement was moderate to strong (κ: 0.45-0.61); and readers were more confident of FDG-PET reads. Simple quantitative analysis of global cerebral fluorodeoxyglucose uptake (FDG-PET) or whole-brain cerebral blood flow (ASL-MRI) showed excellent diagnostic accuracy for both modalities, with area under receiver operating characteristic curves of 0.90 for FDG-PET (95% confidence interval: 0.79-0.99) and 0.91 for ASL-MRI (95% confidence interval: 0.80-1.00).

Conclusions: Our results demonstrate that FDG-PET and ASL-MRI identify similar regional abnormalities and have comparable diagnostic accuracy in a small population of AD patients, and support the further study of ASL-MRI in dementia diagnosis.

Figure 1

Comparison of ASL and FDG images. Representative images from control (A&B) and AD patients (C&D) comparing structural MRI images (T1 and FLAIR), ASL-MRI, and FDG-PET. All four patients were diagnosed correctly by both readers using both modalities. White arrows highlight areas of concordant hypometabolism on FDG-PET and hypoperfusion on ASL-MRI.

Figure 2

Qualitative assessment of brain regional image intensity. Each image was scored from 1-4 (1 = severe hypointensity, 4 = normal). The pooled average of right and left for both readers is shown. Grey bars are control, black bars are AD. *p<0.01 vs. regional control by one-way ANOVA. FL: frontal lobe, TL: temporal lobe, PL: parietal lobe, OL: occipital lobe, BG: basal ganglia, CBL: cerebellum.

Figure 3

Quantitative measures of global cerebral perfusion and metabolism. The ASL CBF (A) and FDG SUV ratio (B) data for AD patients (black triangles) and controls (grey circles) are compared. In both cases, AD was significantly different than control (*p<0.001 by unpaired 2-tailed t-test). ROC curves were constructed for ASL CBF (C) and FDG SUV ratio (D) data. The cutoff points for sensitivity/sensitivity calculation are marked with an “x”. The area under the curve (AUC) values were 0.91 for ASL (standard error 0.053, p<0.001) and 0.90 for FDG (standard error 0.055, p<0.001).

Figure 4

Parieto-occipital hypoperfusion artifact on ASL-MRI. ASL-MRI images (left) from patient 9 (control) show areas of hypoperfusion in the parietal-occipital junction (arrows) that were not present on FDG-PET images (right). These were present in 4 control patients and are a potential source of diagnostic error.