Amyloid PET quantification using low-dose CT-guided anatomic standardization

Abstract

Background 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. 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). Results A 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. Conclusions Low-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.

Deep Learning-Driven Estimation of Centiloid Scales from Amyloid PET Images with 11C-PiB and 18F-Labeled Tracers in Alzheimer’s Disease

“…The prediction accuracy was significantly higher in the YC than the AD group (p < 0.05). The reported cut-off for the Centiloid scale for normal cognition and AD is 10-35 [6,[30][31][32][33]. The present findings showed that the respective Centiloid ranges for YC and AD were −18.26-28.7 and −22.2-160.7.…”

“…It involves co-registration of the PET and MRI images of the same subject, anatomical standardization, VOI analysis using specific VOIs, and the conversion process from SUVR to the Centiloid scale. To overcome this, a simple method of calculating the Centiloid scale using low-dose CT instead of MRI has been reported [5][6][7]. However, manual image analysis and acquisition of anatomical images are still required, and no studies have been reported that automatically calculate the Centiloid scale using only PET images.…”

Development of software for measuring brain amyloid accumulation using 18F‐florbetapir PET and calculating global Centiloid scale and regional Z‐score values

“…Although MRI is used to anatomically standardize PET for the calculation of the CL scale, another study purpose was to determine whether low-dose CT for attenuation correction used in PET/CT equipment can be a substitute for MRI. We have already confirmed the substitutability of low-dose CT in the calculation of the CL scale with 18 F-flutemetamol PET (Matsuda et al, 2021) and, in this study, we examine its application to 18 F-florbetapir.…”

“…Previous studies have examined the use of low‐dose CT of PET/CT equipment as a substitute for MRI in the calculation of the CL scale (Kim et al., 2022 ; Matsuda et al., 2021 ; Presotto et al., 2018 ). Our study using 18 F‐flutemetamol revealed that low‐dose CT provided a CL scale comparable to that of MRI.…”

Comparison of consistency in centiloid scale among different analytical methods in amyloid PET: the CapAIBL, VIZCalc, and Amyquant methods

“…In recent years, substantial progress has been made in calculating CL values and/or SUVR from amyloid PET images. Some of these methods use computed tomography (CT) instead of magnetic resonance imaging (MRI) for anatomical reference because they are more readily available [ 6 , 7 ]. Additionally, some methods do not require MRI or CT anatomical assistance, allowing automated analysis of amyloid PET images while optimizing accurate spatial normalization [ 8 ].…”