Figure 3: Unsupervised learning techniques (e.g., hierarchical clustering, tree classification) can be used for clustering analysis. This hierarchical clustering was constructed based on Euclidean distance (between T1 relaxation and T2relaxation) and its´ quantitative linkages (e.g., inter/intra cluster similarity) shown in a heat map. (A, A´, B, B´, C, C´, C´´, D) were the variants of the same oil content taken from different manufacturers. Tree classification method is shown for comparison (Supp. Fig. 2).