Purpose To investigate the reliability and accuracy of two pseudo-continuous arterial spin labeling (pCASL) sequences, using 2D gradient-echo echo planar imaging (EPI) and 3D gradient and spin echo (GRASE) as the readout respectively. Materials and Methods Each sequence was performed twice four weeks apart on 6 normal control subjects, 6 elderly subjects with mild cognitive impairment (MCI), and one participant with Alzheimer’s’ disease (AD). Eight of these subjects also underwent H215O positron emission tomography (PET) scans on the same day or proximal to their second MRI scan. The longitudinal repeatability of EPI and GRASE pCASL were evaluated with the intra-class correlation coefficient (ICC) and within-subject coefficient of variation (wsCV). Results The ICCs of global perfusion measurements were 0.697 and 0.413 for GRASE and EPI based pCASL respectively. GRASE pCASL also demonstrated a higher longitudinal repeatability for regional perfusion measurements across 24 regions-of-interests (ICC=0.707, wsCV=10.9%) compared to EPI pCASL (ICC=0.362, wsCV=15.3%). When compared to PET, EPI pCASL showed a higher degree of spatial correlation with PET than GRASE pCASL, although the difference was not statistically significant. Conclusion 3D GRASE pCASL offers better repeatability than 2D EPI pCASL, thereby may provide a reliable imaging marker for the evaluation of disease progression and treatment effects in MCI and early AD subjects.

Background Early-onset Alzheimer’s disease (EOAD) has been overshadowed by the more common late-onset AD (LOAD). Yet, the literature indicates EOAD may have less hippocampal-memory presentations and more focal neocortical localization early in the disease. Objective To evaluate these proposed differences between these two forms of AD and to explore what they inform about differences in AD-pathophysiology. Methods 21 EOAD and 24 LOAD patients matched for disease progression and severity were compared on neurocognitive measures and resting state fluorodeoxy-glucose positron emission tomography (FDG-PET). Results EOAD patients had worse executive functions with greater hypometabolism in the parietal regions; whereas LOAD patients had worse confrontation naming and verbal recognition memory with greater hypometabolism in inferior frontotemporal regions. Conclusions In addition to highlighting significant differences between EOAD and LOAD, these results reveal dissociation between executive deficits in AD and frontal hypometabolism, suggesting early disturbances of the parietal-frontal network in EOAD.

Background Posterior cortical atrophy (PCA) may represent a discrete syndrome of Alzheimer’s disease (AD) rather than amnestic AD with visual deficits. Methods We separated 30 patients with PCA based on ventral and dorsal visual symptoms using cluster analysis and analyzed the demographic, cognitive, and functional imaging features. Results This analysis revealed subgroups of 26 dorsal and 4 ventral patients. The ventral subgroup had greater confrontational naming impairment, and the dorsal subgroup had greater hypofunction in the parietal regions. The PCA cohort had memory retrieval rather than encoding deficits, and clinical follow-up showed relative isolation of dorsal and ventral visual manifestations. Conclusion These results support 2, mostly nonoverlapping syndromes in patients with PCA, with the commonest affecting the dorsal visual pathway; moreover, the memory retrieval difficulty in the patients with PCA was dissimilar to the amnestic pattern in typical AD. These results suggest that, in most cases, PCA syndromes are discrete clinical variant of AD.