Step and shoot coronary CT angiography using 256-slice CT: Effect of heart rate and heart rate variability on image quality

Objective: To evaluate the effect of heart rate variability (HRV) and heart rate (HR) on intra-image "motion" and inter-image "stairstep" artefacts in step-and-shoot coronary CT angiography (CCTA) using a wide detector CT scanner. Methods: 66 patients underwent step-and-shoot CCTA using 256-slice CT. Patients were divided into two groups (Group 1: HR <65 bpm, Group 2 ≥65bpm). Motion artefacts were quantified using a 5-point-scale. Stairstep artefacts were defined by measurements of misalignment. Image noise, contrast-to-noise-ratio (CNR), signal-to-noise-ratio (SNR), and radiation dose were assessed. Results: Mean HR was 66±16.7 bpm (range: 45-125 bpm) and mean HRV was 10.7±17.5 bpm. A significant correlation between HR and stairstep artefacts (r=0.46, p<0.001) and motion artefacts (r=0.63, p<0.001) was found. Group 2 showed significantly increased step artefacts with a mean misalignment of 1.4 mm compared to 0.4 mm in Group 1 (p<0.001). There was no significant effect of HRV on stairstep artefacts (r=0.15, p=0.416) and motion artefacts (r=0.13, p=0.311). No significant differences in image noise, CNR, SNR, and radiation dose were seen. Conclusions: Unlike CCTA using narrow CT detectors, HRV has no significant effect on motion and stairstep artefacts using a wide CT detector with high z-coverage. However, a higher HR still increases stairstep and motion artefacts.