Comparative examination of the cerebellum and pons as reference regions for quantitative evaluation in PET imaging for Alzheimer's disease using¹¹C-Pittsburgh Compound-B

Objectives: Amyloid imaging with positron-emission tomography (PET) is an important tool for the early diagnosis of Alzheimer's disease (AD). Standardized uptake value ratio (SUVR) is used as a quantitative evaluation measure, and is obtained by dividing SUV of the region of interest (ROI) by that of the reference region. ¹¹C-Pittsburgh Compound-B (¹¹C-PiB) accumulates specifically in the cerebral cortex of AD patients, but it does not accumulate significantly in the cerebellum and pons. Therefore, for obtaining SUVR, ROI is set to the cortical region, using the cerebellum or pons as the reference region. At present, the cerebellum is generally used as the reference region for quantitative evaluation. However, it has been reported that in some AD cases Aβ accumulated in the cerebellum; and therefore it may not be a suitable reference. The purpose of this study was to compare the suitability as the reference region between the cerebellum and pons for quantitative evaluation in brain PET imaging of AD using ¹¹C-PiB.

Methods: Eight patients with dementia (four AD and four MCI patients) and 19 healthy controls (HCs) were selected for this study and evaluated retrospectively. Volumes of interest (VOIs) were manually placed in the cerebellum and pons, while six spherical VOIs (diameter 5 mm each) were placed in the frontal and temporal cortex to obtain mean SUV (SUVmean) and maximum SUV (SUVmax). These values were obtained for the cerebellum and pons and were compared them between the patients and HCs. SUVR was calculated using the cerebellum or pons as a reference region, and the frontal or temporal cortex as an ROI, and compared them between the patients and HCs.

Results: Both SUVmean and SUVmax of the cerebellum and pons were similar, and SUVR was different between the patients and HCs when either the cerebellum or pons was selected as a reference region. Therefore, this study suggests that both the cerebellum and pons can be used as a suitable reference region. Furthermore, using SUVmean of the cerebellum as a reference region, the difference in the values between the patients and HCs was found to be the largest when compared to any of the other measures.

Conclusions: With respect to SUVR, both the cerebellum and pons can be used as a suitable reference region. This study also suggests that a more accurate quantitative evaluation can be performed when SUVmean of the cerebellum is used as a reference region.