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Papers by sachin chhillar
American Journal of Roentgenology, 1998
We aim at improving quantitative measures of emphysema in computed tomography (CT) images of the ... more We aim at improving quantitative measures of emphysema in computed tomography (CT) images of the lungs. Current standard measures, such as the relative area of emphysema (RA), rely on a single intensity threshold on individual pixels, thus ignoring any interrelations between pixels. Texture analysis allows for a much richer representation that also takes the local structure around pixels into account. This paper presents a texture classification-based system for emphysema quantification in CT images. Measures of emphysema severity are obtained by fusing pixel posterior probabilities output by a classifier. Local binary patterns (LBP) are used as texture features, and joint LBP and intensity histograms are used for characterizing regions of interest (ROIs). Classification is then performed using a nearest neighbor classifier with a histogram dissimilarity measure as distance. A 95.2% classification accuracy was achieved on a set of 168 manually annotated ROIs, comprising the three classes: normal tissue, centrilobular emphysema, and paraseptal emphysema. The measured emphysema severity was in good agreement with a pulmonary function test (PFT) achieving correlation coefficients of up to = 0 79 in 39 subjects. The results were compared to RA and to a Gaussian filter bank, and the texture-based measures correlated significantly better with PFT than did RA.
American Journal of Roentgenology
The purpose of this study was to quantify the heterogeneous distribution of a carbon particle rad... more The purpose of this study was to quantify the heterogeneous distribution of a carbon particle radioaerosol in the lungs of patients with pulmonary emphysema using single-photon emission computed tomography (SPECT) and fractal analysis. Ventilation SPECT was performed on 19 patients with pulmonary emphysema, seven patients with suspected pulmonary emphysema, and 14 healthy volunteers. We delineated the lungs using five cutoff levels (15%, 20%, 25%, 30%, and 35% of the maximal pixel radioactivity) and measured the total number of pixels in the areas surrounded by the contours obtained with each cutoff level. We calculated fractal dimensions from the relationship between the total number of pixels and cutoff levels transformed into logarithms. The fractal dimensions increased with the severity of pulmonary emphysema. The fractal dimensions for patients with pulmonary emphysema, patients with suspected pulmonary emphysema, and healthy volunteers were 2.03+/-0.61 (mean +/- SD), 0.77+/-0....
American Journal of Roentgenology, 1998
We aim at improving quantitative measures of emphysema in computed tomography (CT) images of the ... more We aim at improving quantitative measures of emphysema in computed tomography (CT) images of the lungs. Current standard measures, such as the relative area of emphysema (RA), rely on a single intensity threshold on individual pixels, thus ignoring any interrelations between pixels. Texture analysis allows for a much richer representation that also takes the local structure around pixels into account. This paper presents a texture classification-based system for emphysema quantification in CT images. Measures of emphysema severity are obtained by fusing pixel posterior probabilities output by a classifier. Local binary patterns (LBP) are used as texture features, and joint LBP and intensity histograms are used for characterizing regions of interest (ROIs). Classification is then performed using a nearest neighbor classifier with a histogram dissimilarity measure as distance. A 95.2% classification accuracy was achieved on a set of 168 manually annotated ROIs, comprising the three classes: normal tissue, centrilobular emphysema, and paraseptal emphysema. The measured emphysema severity was in good agreement with a pulmonary function test (PFT) achieving correlation coefficients of up to = 0 79 in 39 subjects. The results were compared to RA and to a Gaussian filter bank, and the texture-based measures correlated significantly better with PFT than did RA.
American Journal of Roentgenology
The purpose of this study was to quantify the heterogeneous distribution of a carbon particle rad... more The purpose of this study was to quantify the heterogeneous distribution of a carbon particle radioaerosol in the lungs of patients with pulmonary emphysema using single-photon emission computed tomography (SPECT) and fractal analysis. Ventilation SPECT was performed on 19 patients with pulmonary emphysema, seven patients with suspected pulmonary emphysema, and 14 healthy volunteers. We delineated the lungs using five cutoff levels (15%, 20%, 25%, 30%, and 35% of the maximal pixel radioactivity) and measured the total number of pixels in the areas surrounded by the contours obtained with each cutoff level. We calculated fractal dimensions from the relationship between the total number of pixels and cutoff levels transformed into logarithms. The fractal dimensions increased with the severity of pulmonary emphysema. The fractal dimensions for patients with pulmonary emphysema, patients with suspected pulmonary emphysema, and healthy volunteers were 2.03+/-0.61 (mean +/- SD), 0.77+/-0....