Computed Tomography: Physical Principles and Recent Technical Advances

This Directed Reading article describes the physical principles and instrumentation of computed tomography (CT) and outlines several recent advances in CT technology. First, the history of CT is presented with emphasis on the contributions of two pioneers who earned the Nobel Prize for the development of the first clinically useful CT scanner. Second, the essential physical principles-most notably radiation attenuation, Lambert-Beer's Law-and the calculation of CT numbers using attenuation data are described. The third major topic will focus on CT technology, including a description of the major system components, the evolution of CT data acquisition systems, image reconstruction fundamentals and common digital image postprocessing operations such as windowing and three-dimensional (3D) techniques. The next section of this article addresses the elements of spiral/helical CT principles and technology. The limitations of conventional CT are first presented and provide a motivation for the development of volume CT scanners. Data acquisition, including detector technology and slip-ring technology, is reviewed, followed by a description of image reconstruction basics for multislice CT (MSCT) scanning. In particular, MSCT detector technology, pitch and various advantages are outlined, followed by a discussion of the advantages of MSCT scanning. The final section of this reading reviews the elements of MSCT applications, such as 3D imaging, virtual reality imaging and the basics of cardiac CT imaging. The article concludes with an introduction of the use of CT in other areas, such as radiation therapy and nuclear medicine.