A harmonisation framework for multi-centre preclinical PET imaging across a national research infrastructure.

Quantitative preclinical positron emission tomography (PET) 
imaging plays an important role in translational research, yet variability 
across scanners, sites, and analysis workflows remains a major barrier 
to robust multi-centre studies. In this work, we developed and evaluated 
a harmonisation framework across a national network of preclinical PET 
facilities. 

Approach. Six identical NEMA NU~4-2008 image quality phantoms were 
manufactured and distributed to six sites, where they were imaged using 
local acquisition and reconstruction protocols across multiple scanner 
platforms.

Main Results. Substantial variability in contrast recovery, uniformity, 
and spill-over ratios was observed under site-specific conditions. 
Centralised automated re-analysis produced only minor reductions 
in variability, indicating that inter-user effects were relatively small, 
compared to site-specific protocol variations. In contrast, optimisation 
of reconstruction parameters led to a marked reduction in inter-scanner 
variability (an average of 60\% reduction across larger rods), particularly 
for voxel-wise maximum contrast recovery coefficients (CRC_max^vox), 
which are more sensitive to noise and reconstruction settings than the 
standard axial averaging NEMA CRC metric. Following harmonisation, 
the variability of CRC_max^vox approached and was lower that of 
conventional axial-averaged NEMA analysis (CRC_max^avg), with 
reductions ranging 7--33\% across the 1--5 mm rods, demonstrating 
improved quantitative consistency even at the voxel level.

Significance. These findings show that scanner and site-specific 
protocol variations are the dominant factors for harmonisation in preclinical 
PET. By systematically evaluating acquisition, image reconstruction 
and analysis related sources of variability across a national network of 
heterogeneous preclinical PET systems, this work provides a practical 
framework for harmonisation. The proposed framework is conceptually 
aligned with clinical harmonisation initiatives such as EARL and provides a 
practical basis for the future development of harmonised performance 
ranges across preclinical scanners. This enables more reliable multi-centre 
studies and supports the use of quantitative, voxel-wise imaging biomarkers 
in translational research.