“…Machine learning-based biomarkers have been introduced with some success but the results are not necessarily understandable in terms of disease mechanisms ( Katako et al, 2018 , Peña-Nogales et al, 2019 ). Increasing interest has also arisen in multivariate approaches to map changes in metabolic connectivity in disease states ( Carli et al, 2021 , Hahn et al, 2018 , Sala et al, 2017 , Yakushev et al, 2017 ). In Parkinson’s disease (PD) ( Obeso et al, 2017 , Politis, 2014 ), principal component analysis (PCA) ( Jollife and Cadima, 2016 ) has been applied to positron emission tomography (PET) metabolic group image data both regionally ( Alexander and Moeller, 1994 , Eidelberg et al, 1994 , Moeller and Strother, 1991 ) and in voxel-based analysis ( Eidelberg, 2009 , Spetsieris and Eidelberg, 2011 ) to identify orthogonal overlapping PC partition layers of the data that reflect specific spatial covariance patterns associated with the disease.…”