Microstructural analysis of secondary pulmonary lobule imaged by synchrotron radiation micro CT using offset scan mode

The recognition of abnormalities relative to the lobular anatomy has become increasingly important in the diagnosis and differential diagnosis of lung abnormalities at clinical routines of CT examinations. The purpose of this study is to analyze microstructure of the lobular anatomy with isotropic spatial resolution in the range of several micrometers to quantitatively describe relation between the architectures and abnormalities. Recent commercial micro CT scanners play a vital role in imaging the lung micro-architectures. However, only a limited number of attempts have been conducted because of difficulties to image the secondary pulmonary lobule beyond the scan field of view and the limited contrast lung parenchyma. This paper demonstrates the ability of synchrotron radiation micro CT (SRμCT) using offset scan mode in microstructural analysis of the secondary pulmonary lobule. The inflated and fixed lung specimen was imaged with resolution of 5.87x5.87x5.87 μm3 by using offset scan mode of the SRμCT (15 keV) at the synchrotron radiation facility (SPring-8). The 3-D SRμCT image which was stacked 2624 slices (each slice:7287x7287 voxels) covered the secondary pulmonary lobule being included in the lung specimen. A proper threshold value for appropriate segmentation was interactively determined to the volume of interest representing the secondary pulmonary lobule. Following transformation of the segmented binary image to a skeletonized surface representation, each voxel was classified as a curve, surface, or junction. The interlobular septa region was extracted interactively by using the voxel classification result which offered geometrical information. Each component of lobular airway, artery, and vein were extracted by using a seeding technique, considering equal attenuation values and connectivity. The resulting volumetric image from the SRμCT using offset scan mode made 3-D microstructural analysis of the lobular anatomy possible.

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