Abstract
BackgroundCentiloid (CL) scaling has become a standardized quantitative measure in amyloid PET because it facilitates the direct comparison of results across institutions, even when different analytical methods or tracers are used. Standard volumes of interest must be used to calculate the CL scale after the anatomic standardization of amyloid PET images using coregistered MRI; if the MRI is unavailable, the CL scale cannot be accurately calculated. This study sought to determine the substitutability of low-dose CT, which is used to correct PET attenuation in PET/CT equipment, by evaluating the measurement accuracy when low-dose CT is used as an alternative to MRI in the calculation of the CL scale. Amyloid PET images obtained using 18F-flutemetamol from 24 patients with possible or probable Alzheimer’s disease were processed to calculate the CL scale using 3D T1-weighted MRI and low-dose CT of PET/CT. CLMRI and CLCT were, respectively, defined as the use of MRI and CT for anatomic standardization and compared. Regional differences in the CT-based and MRI-based standardized anatomic images were also investigated. Trial registration: Japan Registry of Clinical Trials, jRCTs031180321 (registered 18 March 2019, https://jrct.niph.go.jp/latest-detail/jRCTs031180321).ResultsA Bland–Altman plot showed that CLCT was slightly but significantly underestimated (mean ± standard deviation, − 1.7 ± 2.4; p < 0.002) compared with CLMRI. The 95% limits of agreement ranged from − 2.8 to − 0.7. Pearson correlation analysis showed a highly significant correlation of r = 0.998 between CLCT and CLMRI (p < 0.001). The linear regression equation was CLMRI = 1.027 × CLCT + 0.762. In a Bland–Altman plot, Spearman correlation analysis did not identify a significant association between the difference in CLMRI versus CLCT and CL load (ρ = − 0.389, p = 0.060). This slight underestimation of CLCT may derive from slightly higher uptake when the cerebellum is used as a reference area in CT-based anatomically standardized PET images versus MRI-based images.ConclusionsLow-dose CT of PET/CT can substitute for MRI in the anatomic standardization used to calculate the CL scale from amyloid PET, although a slight underestimation occurs.
Highlights
Centiloid (CL) scaling has become a standardized quantitative measure in amyloid PET because it facilitates the direct comparison of results across institutions, even when different analytical methods or tracers are used
Because highly accurate anatomic standardization to standard Montreal Neurological Institute (MNI) space is required to use standard volumes of interest (VOIs) supplied from GAAIN to calculate the CL scale converted from standardized uptake value ratio (SUVR), anatomic standardization of amyloid PET images should be performed using coregistered MRI obtained around the same period
The purpose of the present study was to establish the substitutability of low-dose CT of PET/CT proposed by Pressoto et al by verifying the measurement accuracy at the global and regional levels when low-dose CT is used as an alternative to MRI in the calculation of the SUVR and CL scales in amyloid PET
Summary
Centiloid (CL) scaling has become a standardized quantitative measure in amyloid PET because it facilitates the direct comparison of results across institutions, even when different analytical methods or tracers are used. SUVR values vary according to the target and reference regions used, and according to the particular amyloid tracer used This variability can be resolved through a Centiloid (CL) scaling process that standardizes the quantitative amyloid imaging measures by standardizing the outcome of each analytical method or PET ligand to a scale from 0 to 100 [5]. Because highly accurate anatomic standardization to standard Montreal Neurological Institute (MNI) space is required to use standard volumes of interest (VOIs) supplied from GAAIN to calculate the CL scale converted from SUVR, anatomic standardization of amyloid PET images should be performed using coregistered MRI obtained around the same period. The purpose of the present study was to establish the substitutability of low-dose CT of PET/CT proposed by Pressoto et al by verifying the measurement accuracy at the global and regional levels when low-dose CT is used as an alternative to MRI in the calculation of the SUVR and CL scales in amyloid PET
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