# Elapsed time changes of the brain radiopharmaceutical accumulation of the amyloid PET examination using 18F-flutemetamol

## TL;DR

This study shows that the amount of a brain imaging tracer decreases over time after injection, affecting key measurements used in amyloid PET scans.

## Contribution

The study demonstrates that radiopharmaceutical washout over time affects quantitative amyloid PET indices, which is novel in clinical imaging timing research.

## Key findings

- Pixel values in PET images decreased with elapsed time after radiopharmaceutical administration.
- SUVr and Centiloid Scale values changed due to radiopharmaceutical washout.
- Quantitative indices are affected by the timing of PET image acquisition.

## Abstract

The purpose of this study was to examine how the radiopharmaceutical accumulation in the brain changes with the elapsed time between the administration of 18F-flutemetamol and the start of imaging, and to determine its effect on quantitative indices.

The study population consisted of 25 subjects who agreed to participate in the study. After visual evaluation by the radiologist, 14 subjects tested negative for Aβ accumulation, and 11 subjects tested positive as well. The study population was treated with 18F-flutemeamol, and list mode acquisition was performed for 50 min starting at 60 min after the time of administration. From the acquired list data, five PET images were extracted at 10-min intervals from the start to the end of acquisition, a PET image corresponding to 20 min of acquisition from 60 min after administration, and a PET image corresponding to 20 min of acquisition from 90 min after administration, respectively. Pixel values were measured for the PET images created and quantitative indices (pixel value, SUVr, Centiloid scale) were calculated and compared.

In most of the PET images, pixel values showed a decreasing trend with elapsed time after radiopharmaceutical administration. Accordingly, calculated SUVr and Centiloid Scale also changed.

Elapsed time after radiopharmaceutical administration resulted in a washout of the radiopharmaceutical accumulation in the brain. From this, it was suggested that the quantitative indices change.