Chapter 4

Computed Tomography

Stefan Ulzheimer and Thomas Flohr

Computed Tomography Department, Siemens Healthcare, Forchheim, Germany

4.1 Basics

4.1.1 History

The first commercial medical X-ray Computed Tomography (CT) scanner was built in 1972 by the English engineer G.N. Hounsfield for the company EMI Ltd. as a pure head scanner with a conventional X-ray tube and a dual-row detector system moving incrementally around the patient.

It was able to acquire 12 slices, each 13 mm thick, and reconstruct the images with a matrix of 80 × 80 pixels in approximately 35 min. Figure 4.1 shows the image of the head on one of these early scanners and how it compares to the image quality of a state-of-the-art CT scanner today. Today, the whole brain can be visualized with high quality from a 10-s scan.

Figure 4.1 Development of computed tomography over time. (a) Cross-sectional image of a brain in the year 1971 and (b) the whole brain with sagital, coronal, and cross-sectional slices in the year 2007. Courtesy of Mayo Clinic, Rochester.


Until 1989 there were no principally new developments in conventional CT, although of course the performance of the CT scanners increased dramatically with the engineering progress. By then, the acquisition time for one image decreased from 300 s in 1972 to 1–2 s, slices as thin as 1 mm became possible, and the in-plane resolution increased from 3 line pairs ...

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