Abstract
PurposeThe Centiloid (CL) method enables quantitative values from Aβ-amyloid (Aβ) imaging to be expressed in a universal unit providing pathological, diagnostic and prognostic thresholds in clinical practice and research and allowing integration of multiple tracers and methods. The method was developed for 11C-PiB scans with zero CL set as the average in young normal subjects and 100 CL the average in subjects with mild Alzheimer’s disease (AD). The method allows derivation of equations to convert the uptake value of any tracer into the same standard CL units but first requires head-to-head comparison with 11C-PiB results. We derived the equation to express 18F-florbetaben (FBB) binding in CL units.MethodsPaired PiB and FBB PET scans were obtained in 35 subjects. including ten young normal subjects aged under 45 years (33 ± 8 years). FBB images were acquired from 90 to 110 min after injection. Spatially normalized images were analysed using the standard CL method (SPM8 coregistration of PET data to MRI data and the MNI-152 atlas) and standard CL regions (cortex and whole cerebellum downloaded from http://www.gaain.org).ResultsFBB binding was strongly correlated with PiB binding (R2 = 0.96, SUVRFBB = 0.61 × SUVRPiB + 0.39). The equation to derive CL values from FBB SUVR was CL units = 153.4 × SUVRFBB − 154.9. The CL value in the young normal subjects was −1.08 ± 6.81 for FBB scans compared to −0.32 ± 3.48 for PiB scans, giving a variance ratio of 1.96 (SDFBB CL/SDPiB CL).Conclusions18F-FBB binding is strongly correlated with PiB binding and FBB results can now be expressed in CL units.
Highlights
There is an urgent need to standardize the results of quantitative measurements of Aβ-amyloid (Aβ) tracer binding measured with positron emission tomography (PET) in a way that permits integration of results from different tracers and different analysis methods and in a way that is readily accessible to scanning sites worldwide
In this report we describe the acquisition of the data and the derived linear equation required to convert FBB standardized uptake value ratios (SUVR) to CL units
Validation of local implementation of the standard CL method on the PiB scans obtained from the CL Global Alzheimer’s Association Interactive Network (GAAIN) website gave a linear fit of CLAustin = CLGAAIN – 0.07, with R2 = 0.9999
Summary
There is an urgent need to standardize the results of quantitative measurements of Aβ-amyloid (Aβ) tracer binding measured with positron emission tomography (PET) in a way that permits integration of results from different tracers and different analysis methods and in a way that is readily accessible to scanning sites worldwide. Eur J Nucl Med Mol Imaging (2017) 44:2053–2059 and each Aβ radiopharmaceutical or rely on subjective visual reading. This lack of consistency in image analysis methods and highly variable expression of the results impedes the pooling of data across sites and comparison of studies [17]. Lack of standardization prevents the application of universal cut-off values for diagnostic and prognostic purposes [18] It limits comparison of the relative effectiveness of therapies that claim to reduce Aβ burden [17], and limits comparison of the relative merits of Aβ tracers including in-vivo affinity for human Aβ and measurement variance. These limitations are important when considering the need for earlier detection of plaque and the measurement of changes over time and the effects of treatment
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