Reconstruction of the Human Airways
Construction of a computational model of the human airways can be divided into three stages: image acquisition, segmentation and surface/volume reconstruction. Image acquisition involves medical images that can be obtained from various sources such as com
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Reconstruction of the Human Airways
3.1
Introduction
Construction of a computational model of the human airways can be divided into three stages: image acquisition, segmentation and surface/volume reconstruction. Image acquisition involves medical images that can be obtained from various sources such as computed tomography (CT) and magnetic resonance imaging (MRI), which essentially provide similar information. A 3D matrix of a series of 2D cross-sections, separated by an interval distance, contains information about tissues and structures which are distinguished from one another by differences in brightness or greyscale. These images provide medical practitioners with 3D realistic computational models that can assist clinical diagnosis and medical treatment and planning. Visualisation and reconstruction of morphological structures from the medical image series involves segmentation of the desired region of interest of organs or structures. The general problem of segmentation can be summarised as the partitioning of an image into a number of homogeneous segments, such that any two neighbouring segments yields a heterogeneous segment. Some common algorithms based on thresholding, edge detection, and region characteristics are given in this chapter. The basics of these algorithms are given to introduce the reader to this active research field. While each segmentation technique is presented individually, in practice it is common to apply multiple segmentation techniques to a given problem. Finally the chapter concludes with examples to demonstrate different methods to develop respiratory airway models.
3.2 3.2.1
Medical Image Acquistion Computed Tomography (CT)
Computed Tomography (CT) or by its older name computed axial tomography, is a medical imaging procedure that using x-rays to create a series of planar crosssectional images along an axis. It is a combination of mechanical and computer engineering which was first developed in 1972 by Sir Godfrey Hounsfield (Richmond J. Tu et al., Computational Fluid and Particle Dynamics in the Human Respiratory System, Biological and Medical Physics, Biomedical Engineering, DOI 10.1007/978-94-007-4488-2_3, © Springer Science+Business Media Dordrecht 2013
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3 Reconstruction of the Human Airways
Fig. 3.1 Three different types of computed tomography scanners and how they work
2004). During a typical CT procedure, the patient is placed on a table. The table then moves the patient in a supine position through a rotating gantry (a donut-shaped device), which houses the x-ray tube and electronic x-ray detectors. Multiple x-rays are taken in thin cross-sections in the region of interest along the person’s body forming slices (like slicing a loaf of bread). The detectors collect the x-ray information from each cross-section and send them to a computer that combines them into a single image. In helical (spiral) CT continuous rotation can occur which averts the need to stop and start (Fig. 3.1). These helical CT scanners provide quick scans which are significant for entire
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