The three CT components with the greatest impact on image quality are the X-ray source, detection system and reconstruction algorithms. In this paper, we focus on the first two. We describe the state-of-the-art of CT detection systems, their calibrations, software corrections and common performance metrics. The components of CT detection systems, such as scintillator materials, photodiodes, data acquisition electronics and anti-scatter grids, are discussed. Their impact on CT image quality, their most important characteristics, as well as emerging future technology trends for each, are reviewed. The use of detection for multi-energy CT imaging is described. An overview of current CT X-ray sources, their evolution to support major trends in CT imaging and future trends is provided.

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Why took it nearly four decades, from the first evidence of artificial creation of bremsstrahlung, noted indirectly in literature in 1857 by Julius Pluecker, Professor of mathematics and physics in Bonn, Germany, to Professor Conrad Wilhelm Roentgen's breaking discovery and announcement of X-rays in 1895? Following introductory remarks on the difficulties adjusting the parameters required to generate X-rays and the way medical X-rays occupied clinical routine after Roentgen's revolutionary discovery, and answering the question at the beginning, this paper will discuss in depth the paths taken for improvement up to the present, and some of the culs-de-sac.the University of Pennsylvania, USA, in 1890, but were unable to elucidate them, see [50]. A single year after Roentgen sparking it, scientific, medical, and industrial development had exploded. Enabling technologies and physics in the 19th centuryThe history of medical and industrial X-rays and the evolution of the technology of its sources has fascinated now for about 125 years, see e.g. [2,[5][6][7][8][9][10]12,26,29,30,41,43,48]. Although alternative sources exist and despite of their deficiencies, see [6], vacuum electronics in the form of sealed-off X-ray tubes will remain the affordable sources of medical diagnostic X-rays also in the future, see [3,5]. This paper will track the various branches of the development of the technology, and briefly honor a few of those many scientists, developers, craftsmen, business leaders, and artisans, who have pushed innovation.Repeating Pluecker's, Hittorf's and later Lenard's experiments on cathode rays, Roentgen recognized X-rays on Friday, November 8th, 1895 in the Physical Institute of the University of Würzburg, Germany, see Fig. 1. Pluecker had begun reporting his findings in 1857, see footnote 1and [45], pg. 89. The British Professor of Physics at the University of Cambridge, UK Joseph John Thomson qualified cathode rays in 1896 as magnetically deflectable beams of "electrons". As Roentgen discovered in 1895, X-rays were something different. Hard scattering of electrons impacting on the atomic nuclei of, first, glass targets turned out essential to generate those highly energetic X-ray photons which are capable of transitioning portions of a human body