Application of the Centiloid transformation to ¹⁸F-florbetaben

Objectives: A common quantitative output value for Aß imaging across tracers and methods will improve clinical and research use. A method has recently been developed for this purpose that produces a unit of measurement called the Centiloid (CL) (Klunk et al, Alzheimers Dement, 2015). This approach was implemented on Aß imaging studies performed with ¹⁸F-florbetaben (FBB) and ¹¹C-PiB (PiB).

Methods: Thirty-five participants underwent PET imaging between 50-70 min after injection of PiB and between 90-110 after injection of FBB: 10 healthy young controls (32±9 yo), 5 healthy elderly controls (71±8 yo, MMSE 29±1), 9 mild cognitive impairment (72±5 yo, MMSE 28±2), 2 frontotemporal dementia (73±8 yo, MMSE 23±1), and 8 Alzheimer’s disease (69±6 yo, MMSE 23±3) patients. Young controls were used to establish the “relative variance” (^FBBCL_Std/^PiBCL_Std) of FBB. Spatially normalized images were analyzed using the standard Centiloid regions (cortex and whole cerebellum reference region) downloaded from the Global Alzheimer's Association Investigators Network website (GAAIN; http://www.gaain.org). The non-standard reference regions, cerebellar cortex, pons, and whole cerebellum + pons were also investigated.

Results: FBB SUVR_WCb had a smaller dynamic range in neocortex compared to PiB SUVR_WCb. Both tracers were highly correlated (R²>0.93), irrespective of the reference region used for the scaling. The average Aß burden for the young controls was -0.32±6.81 CL for FBB and -1.08±3.48 CL for PiB, yielding a FBB “relative variance” of 1.96. The resulting conversion equation for FBB SUVR (Centiloid method) to Centiloid units was CL = 153.4 x FBB SUVR_WCb - 154.9.

Conclusion: ¹⁸F-florbetaben results can now be expressed in the common language of Centiloids by centers across the world using data that will be available through the GAAIN website. This is an important step towards better use of the clinical and research potential of Aß imaging. Research Support: Funding for this Investigator Sponsored study was provided in part by Piramal Imaging