The Evaluation of Tau Deposition with [¹⁸F]PI-2620 by Using a Semiquantitative Method in Cognitively Normal Subjects and Patients with Mild Cognitive Impairment and Alzheimer’s Disease

Abstract

Background. Some studies have reported the effectiveness of [18F]PI-2620 as an effective tau-binding radiotracer; however, few reports have applied semiquantitative analysis to the tracer. Therefore, this study’s aim was to perform a semiquantitative analysis of [18F]PI-2620 in individuals with normal cognition and patients with mild cognitive impairment (MCI) and Alzheimer’s disease (AD). Methods. Twenty-six cognitively normal (CN) subjects, 7 patients with AD, and 36 patients with MCI were enrolled. A dynamic positron emission tomography (PET) scan was performed 30–75 min postinjection. PET and T1-weighted magnetic resonance imaging scans were coregistered. The standardized uptake value ratio (SUVr) was used for semiquantitative analysis. The P-Mod software was applied to create volumes of interest. The ANOVA and post hoc Tukey HSD were used for statistical analysis. Results. In the AD group, the occipital lobe had a significantly higher mean SUVr ( 1.46 ± 0.57 ) than in the CN and MCI groups. Compared with the CN group, the AD group showed significantly higher mean SUVr in the fusiform gyrus ( 1.06 ± 0.09 vs. 1.49 ± 0.86 ), inferior temporal ( 1.07 ± 0.07 vs. 1.46 ± 0.08 ), parietal lobe, lingual gyrus, and precuneus regions. Similarly, the AD group demonstrated a higher mean SUVr than the MCI group in the precuneus, lingual, inferior temporal, fusiform, supramarginal, orbitofrontal, and superior temporal regions. The remaining observed regions, including the striatum, basal ganglia, thalamus, and white matter, showed a low SUVr across all groups with no statistically significant differences. Conclusion. A significantly higher mean SUVr of [18F]PI-2620 was observed in the AD group; a significant area of the brain in the AD group demonstrated tau protein deposit in concordance with Braak Stages III–V, providing useful information to differentiate AD from CN and MCI. Moreover, the low SUVr in the deep striatum and thalamus could be useful for excluding primary tauopathies.

Discriminative binding of tau PET tracers PI2620, MK6240 and RO948 in Alzheimer’s disease, corticobasal degeneration and progressive supranuclear palsy brains

“…Our 3 H-PI2620 regional distribution studies in the five regions of interest (frontal, temporal and parietal cortices, hippocampus and cerebellum) demonstrated that AD and control cases can be differentiated by 3 H-PI2620, especially in the FC and TC regions (p < 0.001) and the hippocampal region (p = 0.02). This observation is in accordance with in vivo PET studies in AD and control patients [50,51]. Interestingly, when we divided the AD cases according to disease onset (EOAD before and LOAD after 65 years of age), binding of 3 H-PI2620 was significantly higher in EOAD brains than in LOAD brains in the cortical regions (FC: p < 0.01, PC and TC: p < 0.01) but not in the hippocampus.…”

Imaging pathological tau in atypical parkinsonisms: A review

“…Although [18F]PI-2620 is shown to be an effective tracer in imaging 3R/4R tau in AD and distinguishing these patients from mild cognitive impairment (MCI) patients and controls [84] , more work is needed to lend similar support to its utility in APs. Thus far, studies using this tracer demonstrate improvements in off-target binding to the basal ganglia, white matter, and cortex [81] , [85] , but new areas of non-specific binding have been identified.…”