Research studies have shown that advances in computed tomography (CT) technology allow better detection of pulmonary nodules by generating higher-resolution images. However, the new technology also generates many more individual transversal reconstructions, which as a result may affect the efficiency and accuracy of the radiologists interpreting these images.
The goal of our research study is to build a content-based image retrieval (CBIR) system for pulmonary CT nodules. Currently, texture is used to quantify the image content, but any other image feature could be incorporated into the proposed system. Unfortunately, there is no texture model or similarity measure known to work best for encoding nodule texture properties or retrieving most similar nodules. Therefore, we investigated and evaluated several texture models and similarity measures with respect to nodule size, number of retrieved nodules, and radiologist agreement on the nodules' texture characteristic.
The results were generated on 90 thoracic CT scans collected by the Lung Image Database Consortium (LIDC). Every case was annotated by up to four radiologists marking the contour of nodules and assigning nine characteristics (including texture) to each identified nodule. We found that Gabor texture descriptors produce the best retrieval results regardless of the nodule size, number of retrieved items or similarity metric. Furthermore, when analyzing the radiologists' agreement on the texture characteristic, we found that when just two radiologists agreed, the average precision increased from 88% to 96% for both Gabor and Markov texture features. Moreover, once three or four radiologists agreed the precision increased to nearly 100%.
Automatic liver segmentation from abdominal computed tomography (CT) images based on gray levels or shape alone is
difficult because of the overlap in gray-level ranges and the variation in position and shape of the soft tissues. To address
these issues, we propose an automatic liver segmentation method that utilizes low-level features based on texture
information; this texture information is expected to be homogenous and consistent across multiple slices for the same
organ. Our proposed approach consists of the following steps: first, we perform pixel-level texture extraction; second, we
generate liver probability images using a binary classification approach; third, we apply a split-and-merge algorithm to
detect the seed set with the highest probability area; and fourth, we apply to the seed set a region growing algorithm
iteratively to refine the liver's boundary and get the final segmentation results. Furthermore, we compare the
segmentation results from three different texture extraction methods (Co-occurrence Matrices, Gabor filters, and Markov
Random Fields (MRF)) to find the texture method that generates the best liver segmentation. From our experimental
results, we found that the co-occurrence model led to the best segmentation, while the Gabor model led to the worst liver
segmentation. Moreover, co-occurrence texture features alone produced approximately the same segmentation results as
those produced when all the texture features from the combined co-occurrence, Gabor, and MRF models were used.
Therefore, in addition to providing an automatic model for liver segmentation, we also conclude that Haralick cooccurrence
texture features are the most significant texture characteristics in distinguishing the liver tissue in CT scans.
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