Comparing parametric methods for longitudinal measurement of β‐amyloid pathology with PET in elderly individuals
Authors: Heeman Fiona , Hendriks Janine , Tristão‐Pereira Catarina , Collij Lyduine E. , Young Peter , van Berckel Bart N.M. , Visser Pieter Jelle , Hanseeuw Bernard J , Vandenberghe Rik , Garibotto Valentina , Frisoni Giovanni B , Altomare Daniele , Shekari Mahnaz , Buckley Christopher , Farrar Gill , Schmidt Mark E , Gismondi Rossella , Stephens Andrew W. , Ritchie Craig W , Wimberley Catriona , Martinez‐Lage Pablo , Manber Richard , Wolz Robin , Gispert Juan Domingo , Schöll Michael , Alves Isadora Lopes , Barkhof Frederik , García David Vállez , Lammertsma Adriaan A. , Yaqub Maqsood 
Published: December 2023

Background

Amyloid‐ß (Aß) PET is commonly used for studying the earliest phases of Alzheimer’s disease (AD) in cognitively unimpaired (CU) individuals. In this group, the expected changes in Aß pathology are small, which emphasizes the importance of selecting a method with the highest possible precision for measuring these changes. This study compared several methods for quantifying Aß pathology longitudinally in mostly CU individuals from the AMYPAD‐PNHS cohort.

Method

Participants were scanned with either [18F]flutemetamol (baseline N = 360, follow‐up N = 243) or [18F]florbetaben (N = 66 baseline, N = 49 follow‐up), according to a dual‐time window protocol(Table 1). A subset of participants had = 2 timepoints available (N = 206, N = 43, respectively). SUVRs were calculated, and parametric modelling was performed using RPM, SRTM2, RLogan, MRTM0, MRTM and MRTM2 using PPET software to generate parametric BPND or DVR images for a global cortical region, all with cerebellar cortex as reference tissue. Annual percentage change (APC) was calculated and compared between methods using an ANOVA. To check for changes in Aß pathology over time, a linear mixed effects model was used. Bland‐Altman analyses were used to explore agreement between SUVR, and the outcome parameter from the parametric methods. All analyses were run per tracer, separately for visual Aß‐positive and Aß‐negative individuals, with a p‐value threshold of p<0.05.

Result

For both tracers, there were no differences in APC between methods. However, method‐dependent differences in interquartile range of the APC were observed(Figure 1,2). For [18F]flutemetamol, only the Aß‐negative group showed a significant change in Aß pathology for SUVR and SRTM2 (both ‐0.004/year). For [18F]florbetaben, only the Aß‐positive group showed a significant change in Aß pathology for all methods except MRTM2 (range: +0.020‐0.032/year). No significant bias was observed between APC in SUVR and the other methods for either tracer or Aß‐group.

Conclusion

There were no significant differences in APC between methods, despite method‐dependent variability. In the [18F]flutemetamol‐cohort, two methods showed a minimal decrease in Aß pathology in the Aß‐negative‐group, possibly related to measurement variability, which requires further investigation. In the [18F]florbetaben‐cohort, which included more participants with a very mild cognitive impairment, a significant increase in Aß pathology was observed in the Aß‐positive‐group, except for MRTM2.