Fig. 4

Misclassification example with 200 % hotspot and 10 % background Spatial distribution of misclassified voxels displayed as a sum of voxels in the anterior-posterior direction. The middle column shows the true objects in greyscale, where the greyscale level illustrated the number of superimposed object voxels, for 20 ml (upper), 35 ml(middle) and 50 ml (lower). All images have relative hotspot activity concentration of 200 % and relative background activity concentration of 10 %. The left column shows the sum of segmentation errors from Chan–Vese, with missed object voxels in red and misclassified background voxels in blue, and the right column shows the corresponding results from Otsu. These colour brightnesses describe the number of superimposed erroneous voxels. The misclassifications are displayed on a solid gray background of the true object, for orientation purposes