Standardized Expression of 18F-NAV4694 and 11C-PiB β-Amyloid PET Results with the Centiloid Scale

A common quantitative output value for PET measures of β-amyloid (Aβ) binding across tracers and methods would allow better comparison of data across sites and application of universal diagnostic and prognostic values. A method has recently been developed that generates a unit of measurement called the centiloid. We applied this method to 2-[2-18F-fluoro-6-(methylamino)-3-pyridinyl]-1-benzofuran-5-ol (18F-NAV4694) and 11C-Pittsburgh compound B (11C-PiB) Aβ images to derive the scaling factor required to express tracer binding in centiloids. Methods: Fifty-five participants, including 10 young controls (33 ± 7 y old), underwent both 11C-PiB and 18F-NAV4694 imaging no more than 3 mo apart, with the images acquired 50–70 min after tracer injection. The images were spatially normalized and analyzed using the standard centiloid method and regions (cortex and whole-cerebellum reference) downloaded from the Global Alzheimer Association Interactive Network website. Results: SUV ratios (SUVRs) showed a strong correlation in tracer binding (18F-NAV4694 SUVR = 1.09 × 11C-PiB SUVR – 0.08, R2 = 0.99). The equation to convert 18F-NAV4694 to centiloids [100 × (18F-NAV4694 SUVR – 1.028)/1.174] was similar to a published equation for 11C-PiB [100 × (11C-PiB SUVR – 1.009)/1.067]. In the young controls, the variance ratio (18F-NAV4694 centiloid SD divided by 11C-PiB centiloid SD) was 0.85. Conclusion: The results for both 11C-PiB and 18F-NAV4694 can now be expressed in centiloids, an important step that should allow better clinical and research use of Aβ imaging. The standard centiloid method also showed that 18F-NAV4694 has slightly higher Aβ binding and lower variance than 11C-PiB, important properties for detecting early Aβ deposition and change over time.