FIGURE 2.

Internal cluster validation and primary ¹²⁹Xe magnetic resonance imaging (MRI) signatures for final clusters. a) Internal cluster validation using Davies–Bouldin index (minimised; 1.1644, 0.9236, 0.9132, 0.9167), Dunn's index (maximised; 0.0356, 0.0535, 0.0832, 0.0786) and silhouette width (maximised; 0.4521, 0.5122, 0.5223, 0.4984) for two to five clusters. Four was the optimal number of clusters across all three indices (bold data values and dashed box). b) Radar plot showing the primary ¹²⁹Xe MRI signatures associated with each cluster. Scales show minimum and maximum for each MRI metric on one of the four radial axes and points represent mean cluster values. VDP: ventilation defect percent; Mem/Gas: membrane-to-gas ratio (membrane uptake); RBC/Mem: red blood cell-to-membrane ratio; RBC/Gas: red blood cell-to-gas ratio (red blood cell transfer).