In Alzheimer’s Disease dual-tracer positron emission tomography (PET) studies with 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) and 11C-labelled Pittsburgh Compound B (PIB) are used to assess metabolism and cerebral amyloid-β deposition, respectively. Relative cerebral metabolism and blood flow (rCBF) are closely coupled, both providing an index for neuronal function. Pharmacokinetic modelling of PIB can be used to provide information on amyloid-β deposition, but also an estimation of rCBF. The present study explores the use of PIBderived rCBF, approximated by the ratio of tracer influx in target regions relative to reference region (R1), as a surrogate for FDG scans.
Materials and Methods:
Thirty subjects underwent both FDG and PIB scans. Based on visual inspection, they were classified as PIB positive (+) or negative (-). Each group was composed of fifteen subjects. Then, discriminative performance (PIB+ versus PIB-) of R1 parametric maps, derived from SRTM2, were compared with normalized standardized uptake value FDG uptake (SUVR).
The resemblance between the R1 and SUVR images was noticeable, with similar AD patterns. Strong positive correlations were found between R1 and FDG analysis (0.86 for the PIB+ group, and 0.84 for the PIB-), suggesting that R1 provides information that is closely related to that seen on FDG scans. Yet, overall higher SUVR values were found. While SUVR had a mean of 0.96 ± 0.15 for the PIB+ patients and 1.01 ± 0.15 for the PIB-, R1 presented 0.88 ± 0.13 and 0.90 ± 0.11 respectively. Moreover, distinct differences in R1 and FDG SUVR occur in specific regions such as midbrain and precuneus, which in turn depend on the subject classification, suggesting that R1 is not entirely an alternative biomarker for FDG SUVR. Voxel-based analysis between groups showed that the main discrepancy between tracers was the size of the clusters, despite that their main core could be seen in both R1 and SUVR, implying that R1 might not be as sensitive as SUVR (a difference in volume of 7.51% of the total number of voxels).
Pharmacokinetic analysis of dynamic PIB PET studies provides high-quality rCBF images comparable with those obtained by FDG SUVR. The high correlation between R1 and normalized FDG uptake suggests that the first might be used as an alternative to FDG PET for diagnostic purposes. However, despite the good correlation between SUVR and R1, the lower sensitivity of the latter may result in difficulties to assess small differences between subjects. Moreover, some distinct differences between R1 and FDG SUVR were seen in the midbrain and the precuneus, depending on amyloid status, suggesting that R1 cannot be considered as an alternative biomarker for FDG SUVR, in particular in studies focussed on studying pathophysiology or drug effects.
|Conference||XII International Symposium of Functional Neuroreceptor Mapping of the Living Brain|
|Periode||09/07/2018 → 12/07/2018|