Lymph Node Candidate Region Detection
After obtaining the blob structure-enhanced image, initial candidate regions of lymph nodes are extracted by simply thresholding the enhanced images. However, some lymph nodes are observed as contacting other regions like fat, muscle, and other organs on CT images. Intensity contrasts between lymph nodes and other structures are not high. False-positive identifications can occur in high-contrast regions such as border areas of organs or air-containing regions. Eq. (3.1) is easily and strongly affected by the magnitude of A3 . Furthermore, |A3| becomes high in areas containing linear/tubular structures such as blood vessels. If |A3| becomes high at a certain voxel, such a voxel has a higher possibility of false positivity. Considering this situation, lymph node candidate region image C can be obtained as
where Tbse and TA3 are the threshold values for the blobness and the contrast, respectively .
We obtain lymph node candidate region images for different scales (different о).