The Dementias Platform UK PET/MR harmonisation and test-retest study: assessment of PET repeatability and reproducibility across the national network.

PURPOSE: Positron emission tomography combined with magnetic resonance imaging (PET/MR) has not yet achieved the level of adoption of PET/CT. This study aimed to harmonise PET imaging protocols across a national PET/MR network and to quantitatively assess whether PET/MR can achieve reliability comparable to PET/CT. While previous PET test-retest studies have demonstrated good repeatability, they have typically been limited to small cohorts or restricted site configurations.

METHODS

We conducted a multi-site harmonisation and rigorous test-retest study across the network of eight PET/MR scanners. Thirty-seven healthy older participants (65-90 years) underwent harmonised one-hour amyloid PET/MR scans using either [[Formula: see text]F]flutemetamol or [[Formula: see text]F]florbetaben on two occasions. Retest scans were performed under conditions of same-site repeatability or multi-site reproducibility. Harmonised acquisition and reconstruction protocols were applied, and amyloid burden was quantified on the Centiloid (CL) scale.

RESULTS

CL values across 74 scans showed excellent test-retest agreement (ICC = 0.968), improving to 0.987 after exclusion of one attenuation correction related outlier. Mean test-retest variability was 2.58%. No statistically significant differences were observed across repeatability versus reproducibility conditions, scanner types, or tracers. CL measurements were highly consistent with three independent blinded visual reads.

CONCLUSION

This study demonstrates that harmonised PET/MR achieves high reliability comparable to PET/CT. Although the accuracy of attenuation maps requires checks, this study supports the use of PET/MR for quantitative amyloid imaging in research and therapeutic trials, and provides a valuable open resource of image and raw PET/MR data for further methodological development.