Computed Tomography (Textbook Chapter)

by Oliver Taubmann, Martin Berger, Marco Bögel, Yan Xia, Michael Balda, and Andreas Maier

ABSTRACT

The first computed tomography (CT) clinical scan was performed in 1971. Since the introduction of these early systems, which were slow to acquire and reconstruct data, improvements in temporal and spatial resolution, including dual-source CT and other approaches to increase the number of slices acquired in parallel, now permit the capture of complete organs in a single rotation, thereby reducing noise and the generation of motion artifacts. The imaging itself is mathematically grounded in the Radon transform, the underlying algebraic principle of CT technology, which allows computation of the original function values from line-integral values and the reconstruction of the final image. Using the Fourier slice theorem, a related property, further grounds the process of filtered back-projection.

Three-dimensional CT image volumes are obtained by acquiring, reconstructing, and stacking multiple picture slices at slightly offset axial locations using a variety of analytic and algebraic algorithms. The development of third-generation CT scanners, combined with the introduction of multiple detector rows, facilitates the capture of large fields-of-view containing the entire target object in a single rotation. Moreover, the invention of helical CT technologies, in which projections from all angles in an axial plane can be interpolated, enables the use of standard reconstruction methods to visualize larger parts of the body with only a small number of detector rows.

This book chapter will cover practical aspects of CT image reconstruction, including the spatial resolution of small objects, the prevention of noise and various artefacts (eg, scan, scatter, and motion), and polychromatic aberrations, are considered, as these imperfections can compromise the quality of the scan. Finally, the special calculations required for spectral CT detection, such as dual kVp and dual-kVp/dual-source techniques, are described, as these approaches generate measures directly related to the physical properties of the object or tissue under investigation.