Timing on 16-slice scanner and implications for 64-slice cardiac CT: do you start scanning immediately after breath hold?

Rationale And Objectives: Slow heart rate and small changes in heart rate are factors for improving image quality on spiral cardiac computed tomography (CT). The purpose of this study is to investigate whether it is possible to improve non-enhanced cardiac CT quality by delaying the data-acquisition window after breath hold.

Materials And Methods: Electrocardiograph files (n = 240) for 16-slice non-enhanced cardiac CT scans were analyzed. Mean heart rates and maximal changes in heart rates between adjacent cardiac cycles were compared between phase 1 (defined as cardiac cycles 1-5), phase 2 (cardiac cycles 2-6), ... , and phase 6 (cardiac cycles 6-10).

Results: Heart rates gradually increased by phases, but were limited to a range of 66.8-68.0 beats/min. Maximal changes in heart rates were 2.5 beats/min (phase 1) at the highest and 1.3 beats/min (phases 5 and 6) at the lowest (t-test; P < .01). Maximal changes in heart rates for more than five beats/min occurred in 24, eight, and eight patients on phases 1, 5, and 6, respectively (chi-square test; P < .01).

Conclusion: The delayed scan (four or five cardiac cycles after breath hold) has the potential to improve the quality of non-enhanced cardiac CT.