Centiloid scale analysis for ¹⁸F-THK5351 PET imaging in Alzheimer's disease

A standardized method for quantification is required for analyzing PET data, but such standards have not been established for tau PET imaging. The Centiloid scale has recently been proposed as a standard method for quantifying amyloid deposition on PET imaging. Therefore, the present study aimed to apply the Centiloid scale to ¹⁸F-THK5351 PET imaging in Alzheimer's disease (AD).

We acquired ¹⁸F-THK5351 PET, ¹¹C-PiB PET, and MR images from 47 cognitively normal (CN) individuals and 28 patients with AD with mild to moderate dementia. PET images were spatially normalized to Montreal Neurological Institute space. The PET signals were then normalized using the signal in the reference volume of interest (VOI). Target VOI for specific ¹⁸F-THK5351 retention in AD was extracted by voxel-wise comparison of PET images between the 47 CN individuals and 16 AD patients with moderate dementia. Scale anchor points were defined by the CN individuals as 0-anchor points and by that of the average of the typical AD patients as 100-anchor points.

Specific retention of ¹⁸F-THK5351 was predominant in the angular gyrus, inferior temporal cortex, and parieto-occipital regions in patients with AD. Standardized uptake value ratio (SUVR) of 1.227 and 1.797 were defined as 0- and 100-anchor points, respectively. ¹⁸F-THK5351 PET data could be expressed using the Centiloid scale, with the SUVR of the ¹⁸F-THK5351 PET images converted to Centiloid using our VOI, the standard Centiloid reference VOI, and the following equation: Centiloid = 169.0 × SUVR-204.6.

Centiloid methods can be applied to tau PET imaging using ¹⁸F-THK5351.