Lung lobar segmentation in CT images is a challenging tasks because of the limitations in image quality inherent to CT image acquisition, especially low-dose CT for clinical routine environment. Besides, complex anatomy and abnormal lesions in the lung parenchyma makes segmentation difficult because contrast in CT images are determined by the differential absorption of X-rays by neighboring structures, such as tissue, vessel or several pathological conditions. Thus, we attempted to develop a robust segmentation technique for normal and diseased lung parenchyma. The images were obtained with low-dose chest CT using soft reconstruction kernel (Sensation 16, Siemens, Germany). Our PC-based in-house software segmented bronchial trees and lungs with intensity adaptive region-growing technique. Then the horizontal and oblique fissures were detected by using eigenvalues-ratio of the Hessian matrix in the lung regions which were excluded from airways and vessels. To enhance and recover the faithful 3-D fissure plane, our proposed fissure enhancing scheme were applied to the images. After finishing above steps, for careful smoothening of fissure planes, 3-D rolling-ball algorithm in xyz planes were performed. Results show that success rate of our proposed scheme was achieved up to 89.5% in the diseased lung parenchyma.
We propose an automatic segmentation of Ground Glass Opacity (GGO) nodules on chest CT images by histogram
modeling and local contrast. First, optimal volume circumscribing a nodule is calculated by clicking inside of GGO
nodule. To remove noises while preserving a nodule boundary, anisotropic diffusion filtering is applied to the optimal
volume. Second, for deciding an appropriate threshold value of GGO nodule, histogram modeling is performed by
Gaussian Mixture Modeling (GMM) with three components such as lung parenchyma, nodule, and chest wall or vessels.
Third, the attached chest wall and vessels are separated from the GGO nodules by maximum curvature points linking and
morphological erosion with adaptive circular mask. Fourth, initial boundary of GGO nodule is refined using local
contrast information. Experimental results show that attached neighbor structures are well separated from GGO nodules
while missed GGO region is refined. The proposed segmentation method can be used for measurement of the growth rate
of nodule and the proportion of solid portion inside nodule.
To analyze lung regional ventilation using two-phase Xe-enhanced CT with wash-in and wash-out periods, we propose
an accurate and fast deformable registration and ventilation imaging. To restrict the registration to the lung parenchyma,
the left and right lungs are segmented. To correct position difference and local deformation of the lungs, affine and
demon-based deformable registrations are performed. The lungs of wash-out image are globally aligned to the wash-in
image by narrow-band distance propagation based affine registration and nonlinearly deformed by a demon algorithm
using a combined gradient force and active cells. To assess the lung ventilation, color-coded ventilation pattern map is
generated by deformable registration and histogram analysis of xenon attenuation. Experimental results show that our
accurate and fast deformable registration corrects not only positional difference but also local deformation. Our
ventilation imaging helps the analysis of lung regional ventilation.
While accurate diagnosis of pure nodular ground glass opacity (PNGGO) is important in order to reduce the number of
unnecessary biopsies, computer-aided diagnosis of PNGGO is less studied than other types of pulmonary nodules (e.g.,
solid-type nodule). Difficulty in segmentation of GGO nodules is one of technical bottleneck in the development of
CAD of GGO nodules. In this study, we propose an automated volumetric segmentation method for PNGGO using a
modeling of ROI histogram with a Gaussian mixture. Our proposed method segments lungs and applies noise-filtering in
the pre-processing step. And then, histogram of selected ROI is modeled as a mixture of two Gaussians representing lung
parenchyma and GGO tissues. The GGO nodule is then segmented by region-growing technique that employs the
histogram model as a probability density function of each pixel belonging to GGO nodule, followed by the elimination
of vessel-like structure around the nodules using morphological image operations. Our results using a database of 26
cases indicate that the automated segmentation method have a promising potential.
Airway wall thickness (AWT) is an important bio-marker for evaluation of pulmonary diseases such as chronic
bronchitis, bronchiectasis. While an image-based analysis of the airway tree can provide precise and valuable airway size
information, quantitative measurement of AWT in Multidetector-Row Computed Tomography (MDCT) images involves
various sources of error and uncertainty. So we have developed an accurate AWT measurement technique for small
airways with three-dimensional (3-D) approach. To evaluate performance of these techniques, we used a set of acryl
tube phantom was made to mimic small airways to have three different sizes of wall diameter (4.20, 1.79, 1.24 mm) and
wall thickness (1.84, 1.22, 0.67 mm). The phantom was imaged with MDCT using standard reconstruction kernel
(Sensation 16, Siemens, Erlangen). The pixel size was 0.488 mm × 0.488 mm × 0.75 mm in x, y, and z direction
respectively. The images were magnified in 5 times using cubic
B-spline interpolation, and line profiles were obtained
for each tube. To recover faithful line profile from the blurred images, the line profiles were deconvolved with a point
spread kernel of the MDCT which was estimated using the ideal tube profile and image line profile. The inner diameter,
outer diameter, and wall thickness of each tube were obtained with full-width-half-maximum (FWHM) method for the
line profiles before and after deconvolution processing. Results show that significant improvement was achieved over the
conventional FWHM method in the measurement of AWT.
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