Fig. 3: Quantitative evaluation of the spatial correspondence between tractography-derived bundles and layer-by-layer white matter dissection.

Panel (A) displays the evolution of the signed distance between the arcuate fasciculus (AF) from the SCIL atlas and dissection models of spc-01 across multiple epochs. The photogrammetric model of each epoch displays distance values mapped onto its surface using a green–yellow–red color gradient (green = closer, red = farther from the bundle). Below each model, a histogram illustrates the distribution of signed distances between the bundle and the corresponding epoch. The progression illustrates how the tractography bundle increasingly overlaps with the dissection planes, with distances approaching zero, thus indicating greater anatomical overlap. By epoch 07, the closest match is observed, highlighting the best spatial correspondence between tractography and dissection evidence. Panel (B) illustrates the spatial correspondence between the tractography bundle and the manual annotation of that same connection on epoch 07. The distance between the tractography bundle and the dissection epoch is filtered with a distance threshold of 1 mm to identify areas of close spatial proximity. The corresponding WM fibers in the dissection are manually annotated based on visual inspection of the same model. To evaluate spatial correspondence between the two, the signed distance between the annotated fibers and the thresholded tractography overlap is computed and projected onto the annotation as a scalar field. This field is visualized using a green–yellow–red color scale, where green indicates the closest proximity. A quantitative measure is then derived by calculating the proportion of annotated points falling within a 1 mm distance of the tractography overlap. In this example, 98.3% of the annotated AF fibers fall within this range, supporting a strong spatial match between tractography and dissection evidence at this stage. spc specimen.