This article provides the rationale for using helical (aka spiral, conventional, and mechanical) computed tomography (CT) systems from measuring coronary calcium. The current state and active research concerning measuring coronary calcium with single-and multi-slice systems is reviewed. The components of image quality, which are important to cardiac imaging with CT, are discussed. Companion articles will review electron beam CT (EBCT) for measuring coronary calcium and perhaps most importantly the scientific data relating coronary calcium to coronary heart disease and atherosclerosis.