**1. Introduction**

In the beginning of computed tomography (CT) era, the beating heart could not be examined suitably by this technique due to its motion artefacts. While scan times and consecutively temporal resolution, enhanced rapidly it has become a more accurate noninvasive imaging method for cardiac morphology. The first attempts in using CT to visualize coronary arteries have been made in the early 1980s and were followed by the back then newly emerging

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electron beam computed tomography (EBCT), which already had scan times lower than 100 ms [1]. Clinical relevance of the coronary CT angiography (cCTA) increased distinctly with the introduction of multi detector CT (MDCT) in the late 1990s—initially with four parallel detectors, the launch of the 64-slice MDCT generation enabled cCTA to become established in routine clinical practice [2, 3]. Nowadays, there are systems with up to 320-slices in clinical use, providing even lower scan times and a very high spatial resolution. Another landmark development was the introduction of the dual-source CT (DSCT) technology. DSCT contains of two tubes and detectors arranged in a 90° angle, also resulting in a higher temporal resolution due to the halved rotation time. The dual-energy CT (DECT) scans allow two different tube voltages, resulting in a significant lower radiation exposure for the patient [4]. As spatial and temporal resolution achieved remarkable dimensions, recent technologic improvement emphasized particularly the reduction of radiation dose on the one hand (see Section 3.1) [5], and the expansion of cCTA on additionally functional and morphological aspects, e.g., plaque characterization, myocardial perfusion imaging, or even CT-based fractional flow reserve (CT-FFR).
