Further reducing the gantry rotation time (to below the currently achieved 270–350 ms) is an obvious approach to improving temporal resolution and reducing heart rate dependency. However, our ability to shorten the rotation time is limited by the dramatic increase in centrifugal forces that occurs as the rotation time is reduced. For instance, at a 400-ms rotation time, the relative centrifugal force is 18–20 g, which already requires considerable centripetal force to counteract. However, at 200 ms (equal to an image acquisition window of 100 ms with halfscan reconstruction), the relative centrifugal forces rise to 74–80 g because they are equal to the square of the velocity. New technologies such as an air-bearing CT gantry and faster data transfer systems might alleviate this problem and make it feasible to reduce the rotation time to 200 ms or even shorter. However, it is not very likely that a reduction in the rotation time alone will be pursued as a strategy for further improving temporal resolution. Instead, it is much more likely that the three concepts of (1) multisource scanning, (2) adaptive multisegment reconstruction and novel intelligent algorithms for improving temporal resolution by reconstruction methods, and (3) shortening the gantry rotation time will be developed further and combined in some fashion to improve temporal resolution.

The current slice collimation of coronary CT angiography (between 0.5 and 0.75 mm) limits its application to small structures such as coronary plaque and its internal makeup. Thus, thinner slice collimation (e.g., of 0.2–0.3 mm) or better in-plane resolution (Chap. 9c) have the potential to improve the assessment of plaques and stents and facilitate the quantification of stenoses by coronary CT angiography (Fig. 26.2). However, reducing the slice collimation by a factor of 2 requires the radiation exposure to be increased by a factor of 2 (if the same detector technology is used) to keep the image quality constant. Thus, improvements in spatial resolution are not easily achieved using the current technology, and further developments (e.g., detector material) are necessary for clinical applications if one does not wish to increase radiation exposure again.

The expected upcoming clinical developments are summarized in List 26.2.