Pre-Classification of Chest Radiographs for Improved Active Shape Model Segmentation of Ribs

Janakiramanan Ramachandran, Marios S. Pattichis, Peter Soliz

Abstract: The parenchymal and skeletal structure as recorded on chest radiographs can vary significantly from person to person. The active shape model (ASM) rib-parenchyma model is defined using the 14 chest radiographs from the International Labor Organization (ILO) set of standard chest X-rays. Groundtruth was established by manually segmenting the ribs for the standard X-rays. A "leave one out" procedure was used to perform the tests on the ILO set. The measure of success was defined by the sensitivity of the segmentation in correctly classifying a pixel as parenchyma, ie, not rib. In one experiment, the chest radiographs were first pre-classified according to the number of parenchymal regions visible in each lung, and consecutive ASM model training and testing was performed over each class. In a second, similar experiment, the X-rays were first pre-classified by the height of the lungs, e.g., "tall" and "short" X-rays. It was found that the sensitivity improved an average of 0.20 over the baseline test (no pre-classification), when pre-classifying the lung by the number of parenchymal regions (8 or 9). Sensitivity improved an average of 0.19 over the baseline, when pre-classifying the lung by height (tall or short).