Overview of the method steps for fissure detection and lobe segmentation.
Mean right horizontal (subscript h) and right oblique (subscript o) boundaries for a typical case (center rendering) together with changes in the first mode of variation.
Rendering of fissure particles resulting from each step of the proposed method. Particles are rendered with plate-like glyphs, and lungs are rendered semitransparently for context (sagittal view). From left to right: ridge particles sampling result and initial connected components (Subsection II A ), particles data after classification (Subsection II D ), and particles before lobe labeling (Subsection II E ). (Top) left lung; (bottom) right lung.
Amount of emphysema as measured by the fraction of the lung region falling below the −950 HU threshold for the cases used in this study. Reported amounts for the expiratory cases were taken from the cases' corresponding inspiratory scans.
Sagittal, axial, and coronal views illustrating segmentation results for two INSP test set cases. Note the severe emphysema and the resulting fissure distortion in the topmost case.
Sagittal, axial, and coronal views illustrating segmentation results for two EXP test set cases.
Dice scores for the left upper lobe (LUL), left lower lobe (LLL), right upper lobe (RUL), right middle lobe (RML), and right lower lobe (RLL) reported for the expiratory (top) and inspiratory (bottom) datasets. (No Dice scores equaling 1.0 were observed).
Left lung failure case (left: sagittal CT slice, middle: automatic segmentation result, right: reference standard). The severe lower lobe emphysema in combination with the relatively unusual fissure location caused the model fitting stage to fail. Therefore, subsequent classification, filtering, and segmentation stages failed as well.
Case for which the right horizontal fissure model was initialized too far from the true fissure location and became heavily distorted as it latched on to nonhorizontal fissure particles. The mean right horizontal fissure boundary was therefore used, but this still results in an unsatisfactory segmentation. Solid arrows indicate the true fissure location. Open arrows indicate a region of the right oblique that curls downward and was not properly captured with the automatic segmentation.
A difficult expiratory case (left: sagittal CT slice, middle: automatic segmentation result, right: reference standard). The right horizontal fissure is mostly incomplete, and the particles sampling were not able to adequately capture the right oblique fissure. The final automatic segmentation reflects good lobe boundary detection near well-sampled areas (arrows, left), but the reference standard segmentation indicates poorly captured regions (arrows, right).
(Top) Left and right lung particles sampling result for one of the training set cases (sagittal view). Particles are rendered with plate-like glyphs, and lungs are rendered semitransparently for context. (Bottom) corresponding ground truth particles.
ROC analysis of prefiltering parameter settings. Four θthresh values are considered (70°, 75°, 80°, and 85°) across a wide range of n thresh values.
Convergence rate of model fitting to a typical fissure for various numbers of variation modes.
Left: Scatter plot of the 2D features space. The grouping in the lower left represents true fissure particles; the grouping towards the middle represents noise particles. (Middle) histograms of projected noise particles (left-most distribution), and fissure particles (right-most distribution). The x axis is unitless. (Right) corresponding ROC curve representing the distributions of the projected data.
Fissure completeness breakdown for the left oblique (LO), right oblique (RO), and right horizontal (RH) fissures. Tallies are given for the inspiration (INSP) and expiration (EXP) cases. Descriptions of categories are provided in the text.
Mean, RMS, and max distances between manually traced fissure locations and automatically determined lobe boundaries for LO, RO, and RH fissures. Total results are reported for INSP and EXP datasets and are also given with respect to fissure completeness.
Mean, RMS, and max distances between manually and automatically determined lobe boundaries for LO, RO, and RH fissures. Total results are reported for INSP and EXP datasets and are also given with respect to fissure completeness.
Dice score statistics for the INSP and EXP cases evaluated in our study.
Elaboration on selected cases for which the segmentation algorithm performed poorly. Surface discrepancy measures are computed considering the total surface, not just in regions with clearly visible fissures.
Average execution time for each stage of the overall segmentation algorithm using a 2.4 GHz Intel Xeon CPU with 128 GBs RAM.
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