Fig. 1

Description of the projected cartilage area and the projected cartilage area ratio (PCAR). a Schematic diagram of cross-sectional view of cartilage and the projected cartilage area (cartilage thickness > 1.0 mm). The cross-sectional view is indicated by the brown line in the projected cartilage area. The PCAR is defined as the ratio of the green area to the area enclosed by the blue line (ROI). b Practical example of the projected cartilage area (cartilage thickness > 0.0 mm) in the medial tibial cartilage and the PCAR at middle central medial tibia (mcMT) subregion. The ROI of the medial tibial cartilage was defined based on bone morphology and is circled by the blue line. The ROI was divided into nine subregions and the mcMT subregion was surrounded by red square. In this case, mcMT PCAR0.0 was 1.00. c Practical example of the projected cartilage area (cartilage thickness > 1.0 mm) in the medial tibial cartilage and the PCAR at mcMT subregion. In this case, mcMT PCAR1.0 was 0.92. d Cartilage thickness mapping in the medial tibial cartilage. The color bar shows the cartilage thickness