18F-THK5351 PET image processing

The PET image of each participant was precisely co-registered to respective T1-weighted MRI data using the SPM8 (Statistical Parametric Mapping) tool (Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London) in MATLAB R2014b software for Windows (The MathWorks, Natick, MA, USA). A global region of interest (ROI) concerning the regions of the cerebral cortex was created on the basis of images of the frontal, temporal, parietal, and occipital lobes and the posterior cingulate gyri, as described previously.¹⁸ The aforementioned regions of the cortex were segmented from individual T1-weighted MR images using SPM8 and an automated anatomical labeling template.¹⁹ In the present study, global standardized uptake value ratio (SUVR) was calculated using weighted-mean volumes of ROIs and normalized to the mean intensity of the cerebellar gray matter using a mask image.²⁰

The present study employed iterative outlier methods with global SUVR values to evaluate ¹⁸F-THK5351 PET positivity. A total of 34 cognitively normal participants above the age of 59 years (range: 59–79 years) was assessed to determine the cut-off value of ¹⁸F-THK5351 PET global SUVR, which was computed as 1.37. Accordingly, in this study, if the estimated SUVR value of ¹⁸F-THK5351 PET exceeded 1.37 the patient was considered to be ¹⁸F-THK5351 positive.