This article reports on recent research findings into the factors that influence the detectability performance of different systems of computed tomography (CT) scanners. These systems include multidetector CT (MDCT) of different slice numbers, dual-source CT (DSCT), and cone-beam CT (CBCT). The introduction of more slices for MDCT, DSCT, and the new technology of CBCT increases the need to optimize the image quality and to examine the potential reduction of radiation doses to the patient. Low-contrast detail detectability is a method that has proven to be an appropriate evaluation method for this purpose. However, it is essential to recognize factors that affect detectability performance and understand how these factors influence image quality and radiation dose. It is argued that deep understanding of the influences of these factors is the key to image quality optimization in terms of contrast-detail detectability and radiation dose reduction. The purpose of this article is, therefore, to specify these factors and to explain their influence on detectability performance and hence on CT image quality. Further low-contrast detail studies are required to optimize imaging performance of different CT systems and scanners.