Voxel-level comparison of arterial spin-labeled perfusion MRI and FDG-PET in Alzheimer disease

Abstract

Objective: We compared the ability of arterial spin labeling (ASL), an MRI method that measures cerebral blood flow (CBF), to that of FDG-PET in distinguishing patients with Alzheimer disease (AD) from healthy, age-matched controls.

Methods: Fifteen patients with AD (mean age 72 ± 6 years, Mini-Mental State Examination score [MMSE] 20 ± 6) and 19 age-matched controls (mean age 68 ± 6 years, MMSE 29 ± 1) underwent structural MRI. Participants were injected with 5 mCi of FDG during pseudocontinuous ASL scan, which was followed by PET scanning. Statistical parametric mapping and regions of interest (ROI) analysis were used to compare the ability of the 2 modalities in distinguishing patients from controls. Similarity between the 2 modalities was further assessed with linear correlation maps of CBF and metabolism to neuropsychological test scores.

Results: Good agreement between hypoperfusion and hypometabolism patterns was observed, with overlap primarily in bilateral angular gyri and posterior cingulate. ROI results showed similar scales of functional deficit between patients and controls in both modalities. Both ASL and FDG-PET were able to distinguish neural networks associated with different neuropsychological tests with good overlap between modalities.

Conclusions: Our voxel-wise results indicated that ASL-MRI provides largely overlapping information with FDG-PET. ROI analysis demonstrated that both modalities detected similar degrees of functional deficits in affected areas. Given its ease of acquisition and noninvasiveness, ASL-MRI may be an appealing alternative for AD studies.

Figure 1. Results of voxel-wise statistics between patients and controls

Areas of (A) atrophy, (B) hypoperfusion, and (C) hypometabolism rendered onto 3-dimensional brains, with color intensity representing depth from brain surface. Red represents Alzheimer disease–related decreases. Representative slices with color bar representing range of t values are shown in (D–F). (G) Results of conjunction analysis showing areas of overlap between hypoperfusion and hypometabolism. All images were statistically thresholded at p < 0.05, false discovery rate correction for multiple comparison, cluster >50. No increases in gray matter volume, cerebral blood flow (CBF), or CMRGlc were detected.

Figure 2. Bar plots of (A) relative cerebral blood flow (rCBF) and (B) CMRGlc (rCMRGlc) extracted from regions of interest (ROIs)

Both rCBF and rCMRGlc show similar degrees of functional deficit between control and patients in affected areas, which were statistically significant at p < 0.005 (*). Cohen d value was 2.05 for rCBF and 1.92 for rCMRGlc extracted from the composite ROI.

Figure 3. Cerebral blood flow (CBF) and CMRGlu correlation maps with neurosychological test scores

(A) Correlation between CBF (left) and CMRGlu (right) with Boston Naming Test scores. (B) Correlation between CBF (left) and CMRGlu (right) with Digit Symbol Substitution scores. Red and green represent positive and negative correlations respectively. Color intensity represents depth from brain surfaces. Statistical images were thresholded at p < 0.005, uncorrected for multiple comparisons, cluster size >50.