Centiloid scale measure of amyloid PET by CT‐guided anatomic standardization

Abstract

AbstractBackgroundCentiloid (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 CT, which is used to correct PET attenuation in PET/CT equipment, by evaluating the measurement accuracy when CT is used as an alternative to MRI in the calculation of the CL scale.MethodAmyloid PET images obtained using 11C‐PiB from 19 patients with possible or probable Alzheimer’s disease were processed to calculate the CL scale using 3D T1‐weighted MRI (Optima MR450w, 1.5T, GE healthcare) and CT of PET/CT (uMI780, United Imaging Healthcare). CLMRI and CLCT were respectively defined as the use of MRI and CT for anatomic standardization and compared. We followed the method advocated by the Global Alzheimer’s Association Interactive Network for the calculation of the CL scale. The whole cerebellum was chosen as a reference area for the CL calculation.ResultA Bland–Altman plot showed that CLCT did not significantly differ from CLMRI (mean ± standard deviation, −0.1 ± 1.5; p = 0.734). The 95% limits of agreement ranged from −0.8 to 0.6. Pearson correlation analysis showed a highly significant correlation of r = 0.999 between CLCT and CLMRI (p < 0.001). The linear regression equation was CLCT = 0.992 × CLMRI + 0.144. 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 = −0.045, p = 0.853).ConclusionCL scales based on CT show a highly significant positive correlation with those based on MRI, regardless of the degree of amyloid accumulation in possible and probable AD patients. A key advantage of the use of CT is the simultaneous acquisition of PET and CT. This method would be applicable to subjects who are unable to undergo MRI.