Non-invasive CT coronary angiography: can high diagnostic image quality be achieved with less radiation exposure?

Non-invasive coronary CT angiography (CTA) has come a long way since the first presentation at the American College of Cardiology Scientific Sessions and the ensuing publication by the group from Erlangen, Germany, in 1995.1 Electron beam computed tomography (EBCT) was used for the first years.2 Despite an inferior spatial resolution, EBCT was the only CT machine able to freeze the motion of the beating heart at the time. In contrast to other CT machines, EBCT has no moving mechanical parts. The electron beam, which produces the X-rays by striking the anode, is steered by an electromagnetic deflection system. In the 1990s, these systems achieved an image acquisition time of 100 ms. Images were acquired in a step-and-shoot fashion, and accordingly the table was moved sequentially. Because of the short stagnant phase of ventricular motion in late diastole, usually a time point at 80% of the R–R interval was chosen for image acquisition. However, movement artefacts caused by atrial contraction were observed, in particular in the mid right coronary artery, and some investigators changed the image acquisition window to 40% of the R–R interval to improve right coronary artery visualization.