Harmonisation of PET imaging features with different amyloid ligands using machine learning-based classifier

In this study, we used machine learning to develop a new method derived from a ligand-independent amyloid (A$\beta$) positron emission tomography (PET) classifier to harmonise different A$\beta$ ligands. We obtained 107 paired ${}^{18}$F-florbetaben (FBB) and ${}^{18}$F-flutemetamol (FMM) PET images at the Samsung Medical Centre. To apply the method to FMM ligand, we transferred the previously developed FBB PET classifier to test similar features from the FMM PET images for application to FMM, which in turn developed a ligand-independent A$\beta$ PET classifier. We explored the concordance rates of our classifier in detecting cortical and striatal A$\beta$ positivity. We investigated the correlation of machine learning-based cortical tracer uptake (ML-CTU) values quantified by the classifier between FBB and FMM. This classifier achieved high classification accuracy (area under the curve = 0.958) even with different A$\beta$ PET ligands. In addition, the concordance rate of FBB and FMM using the classifier (87.5%) was good to excellent, which seemed to be higher than that in visual assessment (82.7%) and lower than that in standardised uptake value ratio cut-off categorisation (93.3%). FBB and FMM ML-CTU values were highly correlated with each other (R = 0.903). Our findings suggested that our novel classifier may harmonise FBB and FMM ligands in the clinical setting which in turn facilitate the biomarker-guided diagnosis and trials of anti-A$\beta$ treatment in the research field.