# Test-retest properties of [11C]PXT012253 as a positron emission tomography (PET) radiotracer in healthy human brain: PET imaging of mGlu4

## TL;DR

This study evaluates the reliability of [11C]PXT012253 as a PET radiotracer for measuring mGlu4 in the human brain, showing high test-retest consistency and suitable quantification methods.

## Contribution

The study provides new evidence on the test-retest reliability and optimal quantification methods for [11C]PXT012253 in human brain imaging.

## Key findings

- VT in subcortical regions was higher than in cortical regions.
- Test-retest variability of VT was under 7% in key brain regions with ICC > 0.93.
- VT estimates using 63 min of imaging were within 10% of 93 min estimates.

## Abstract

The metabotropic glutamate receptor 4 (mGlu4) has been proposed as a target for Parkinson’s disease to measure levodopa-induced dyskinesia. [11C]PXT012253 is a PET radioligand for mGlu4 (3.4 nM), previously characterized in non-human primates. We aimed to determine the optimal method for quantification, duration for acquisition, and test-retest reliability of the binding parameters for [11C]PXT012253 in healthy volunteers.

Six subjects (4 females) completed. [11C]PXT012253 displayed high uptake and rapid wash-out. Unchanged [11C]PXT012253 at 20 min was 10–20%. VT in subcortical regions was higher than in cortical regions. 2TC provided better fits than 1TC. VT by Logan GA and MA1 analysis correlated with that of 2TC-CM. MA1 showed better identifiability and standard error than Logan. The test-retest metrics in pons, putamen and thalamus showed absolute variability of VT<7% and ICC > 0.93 using the 2TC, Logan and MA1 graphical analyses. Time stability analysis showed that VT values estimated using 63 min of imaging were within 10% of the values obtained with 93 min with all three models.

[11C]PXT012253 showed a high brain uptake, with rapid washout and metabolism. VT was reliably estimated using 2TC, Logan GA and MA1. The test-retest metrics showed high repeatability, indicating [11C]PXT012253 to be a suitable PET radioligand for mGlu4.

The online version contains supplementary material available at 10.1186/s13550-025-01266-y.