Chronic obstructive pulmonary disease (COPD) is a type of obstructive lung disease characterized by chronically poor airflow, which is the result of breakdown of lung tissue (known as emphysema) and small airways disease. It typically worsens over time. Most treatments are limited to the management of symptoms, which makes early detection more valuable to treat the disease etiology itself. With the advancement of computed tomography (CT), it is able to provide high resolution structural and functional imaging to distinguish the lung anatomic structures, as well as characterize their changes over time. Previously, the majority of CT-based measures have focused on quantifying the extent of airway and parenchymal damage. Recent studies suggests that pulmonary vascular dysfunction is an early lesion in COPD and associated with an emphysematous phenotype. Few studies attempted to quantify pulmonary vessel morphology and compared those measures across COPD groups. However, the scope of examined vascular structures in these studies was limited, majorly due to the lack of a standardized method to quantify a broad range of vascular structures.
In this thesis, we propose to use anatomically defined airway branches as references to locate and morphologically quantify central pulmonary arteries in different lung regions. Although pulmonary vessel trees have complex topologic and geometric structures, airway tree possesses much simpler and consistent branching patterns and standardized anatomic nomenclatures are available up to sub-segmental levels. It is also well-known that airway and arterial branches have a unique pairing that is established by their spatial proximity and parallel configuration. Therefore, anatomically labeled airway tree provides a robust benchmark to locate consistent arterial segments for both intra- and inter-subjects. New methods have been developed for quantitative assessment of arterial morphology matched and standardized by associated airways at different anatomic branches. First, the skeletons of airway and vessel trees are generated to provide simple and hierarchical representations. Then, topologic and geometric properties of airways and arteries, such as distance, orientation and anatomic positon information, are explored to locate the target arterial segments. Finally, the morphologic properties, e.g. cross-sectional area, of target arterial segments are robustly computed.
The developed methods in this thesis provides a standardized framework to assess and compare the vascular measurements in intra- and inter- subjects from a broad range of vessel branches in different lung regions. The work also serves as a practical tool for large longitudinal or cross-sectional studies to explore the pulmonary vessel roles played at the early stage of COPD.
The major contribution of this thesis include: (1) developing two novel skeletonization methods that are applicable to airway and pulmonary vessel trees; (2) developing a semi-automatic method to locate and quantify central pulmonary arterial morphology associate to anatomic airway branches; (3) developing a fully automatic method to identify and reconstruct central pulmonary arterial segments associated to anatomic airway branches and quantify their morphology; (4) validating the methods using computerized phantoms, physical phantoms and human subjects; (5) applying the developed methods to two human lung disease studies.