This issue presents Hsu and associates' "The Imaging Features and Clinical Associations of a Novel Tau PET Tracer—18F-APN1607 in Alzheimer Disease". They propose in vivo tau PET imaging with the novel agent 18F-APN1607 to demonstrate the spatial distribution of tau deposition in Alzheimer disease (AD) and as a potential aid in the differential diagnosis of tauopathies.
They applied 18F-APN1607 in 12 normal controls (NCs) and 10 patients with mild to moderate probable AD. Detailed clinical information, cognitive measurements, and disease severity were documented. Regional SUV ratios (SUVRs) from 18F-AV-45 (florbetapir), 18F-APN1607 PET and regional gray matter (GM) atrophic ratios were calculated.
Quantitative analyses showed significantly elevated SUVRs in the frontal, temporal, parietal, occipital lobes, anterior and posterior cingulate gyri, precuneus, and parahippocampal region (all P's < 0.01) with medium to large effect sizes (0.44–0.75). The SUVRs from 18F-APN1607 PET imaging showed significant correlations with the Alzheimer's Disease Assessment Scale (ADAS-cog) scores (all P's < 0.01) and strong correlation coefficients (R2 ranged from 0.54 to 0.68), even adjusted for age and sex effects.
Parahippocampal region 18F-APN1607 SUVRs showed rapid saturation as the ADAS-cog scores increased, and the SUVRs of the posterior cingulate gyrus and the temporal, frontal, parietal, and occipital regions slowly increased. Combined SUVRs from amyloid, tau PET, and regional GM atrophic ratio showed regional specific patterns as the ADAS-cog scores increased.
The authors concluded that 18F-APN1607 tau tracer correlated well with cognitive changes and demonstrated the spatial pattern of amyloid, tau deposition, and GM atrophy in the progression of AD.
In addition, unlike other tau agents, 18FAPN1607 PET imaging has a clear background and no off-target binding in the basal ganglia or the thalamus.