Centiloid scaling for quantification of brain amyloid with [18F]flutemetamol using multiple processing methods

Introduction: A standardised method for quantifying beta-amyloid PET tracers would allow comparison across different tracers and different sites. The development of the Centiloid scale has aimed to achieve this, applying a common scale to better aid the diagnosis and prognosis of Alzheimer's disease (AD) and to monitor anti-amyloid therapeutic interventions. Here, we apply the Centiloid method to [F-18]flutemetamol and [C-11]PiB (PiB, Pittsburgh compound B) PET images and derive the scaling factor to express their binding in Centiloids. Methods: Paired PiB and [F-18]flutemetamol scans for 74 subjects, including 24 young healthy controls (37 +/- 5 years), were analysed using the standard Centiloid method. The same subjects were also analysed using PMOD- and FSL-based pipelines as well as SPM8. Test-retest analysis of 10AD subjects was also performed with each pipeline. Results: The standard uptake value ratios (SUVR), determined using the standard SPM8 Centiloid process, showed a strong correlation between [F-18]flutemetamol (Flute) and PiB binding (SUVR-Flute=0.77 x SUVR-PiB+0.22, R-2=0.96). Application of the standard Centiloid process allowed the calculation of a direct conversion equation for SUVR-Flute to Centiloid units (CL) (CL=(121.42*SUVR-Flute) - 121.16). Analysis of the data via the two alternate Centiloid pipelines allowed us to derive standardised, SPM8-equivalent equations for both PMOD (CL= (115.24*SUVR-Flute) - 107.86) and FSL (CL= (120.32*SUVR-Flute) - 112.75) respectively. Test-retest analysis of 10AD subjects showed an approximate 2% difference for each pipeline. Conclusions: [F-18]flutemetamol data can now be expressed in Centiloid units, enhancing its utility in clinical and research applications for beta-amyloid imaging. The standard Centiloid method also demonstrates that [F-18]flutemetamol has favourable performance compared with PiB and other beta-amyloid tracers. Test-retest difference averaged 2%, with no difference between image processing pipelines. Centiloid scaling is robust and can be implemented on a number of platforms.