A useful state of the art review of calcium imaging in the coronary arteries by Harvey Hecht appeared recently in JACC Imaging (Hecht, H.S. J Am Coll Cardiol Img. 2015; 8(5):579–96).
The paper is behind the Journal's paywall, but you can request a reprint from the author by emailing: email@example.com.
I enjoyed particularly the discussion on repeat calcium imaging, asymptomatic screening and radiation dose reduction strategies.
This (free) figure sums it up well.