Intensity targeted radial structure tensor analysis and its application for automated mediastinal lymph node detection from CT volumes

This paper presents a new blob-like enhancement filter based on Intensity Targeted Radial Structure Tensor (ITRST) analysis to improve mediastinal lymph node detection from chest CT volumes. Blob-like structure enhancement filter based on Radial Structure Tensor (RST) analysis can be utilized for initial detection of lymph node candidate regions. However, some of lymph nodes cannot be detected because RST analysis is influenced by neighboring regions whose intensity is very high or low, such as contrast-enhanced blood vessels and air. To overcome the problem, we propose ITRST analysis that integrate the prior knowledge on detection target intensity into RST analysis. Our lymph node detection method consists of two steps. First, candidate regions are obtained by ITRST analysis. Second, false positives (FPs) are removed by the Support Vector Machine (SVM) classifier. We applied the proposed method to 47 cases. Among 19 lymph nodes whose short axis is no less than 10 mm, 100.0 % of them were detected with 247.7 FPs/case by ITRST analysis, while only 80.0 % were detected with 123.0 FPs/case by RST analysis. After the false positive (FP) reduction by SVM, ITRST analysis outperformed RST analysis in lymph node detection performance.