Optimal end-systolic cardiac phase prediction for low-dose ECG-synchronized cardiac CT

To predict optimal end-systolic (ES) cardiac phase for low-dose ECG-synchronized cardiac computed tomography (CT).

ECG-synchronized ES cardiac CT examinations of 2441 patients from September 2010 to December 2016 were reviewed. Of them, 891 examinations acquired with an extended period of full tube current in a cardiac cycle (i.e., 10 % of RR interval or ≥100 ms) and adequate image quality (median patient age, 7 years; age range, 0 day‒60 years) were included. Absolute and relative delays (n = 861 and n = 30, respectively) of the cardiac CT were correlated with the heart rates. Best-fit equations were developed from the trend line with the highest coefficient of determination (R²) value for the two delays, and their success rates to obtain optimal ES phase in a padding with full tube current were calculated and compared with that of the T wave location method. CT radiation dose ratio was calculated as a width ratio of paddings with full tube current.

The absolute and relative delays in the Pearson correlation test demonstrated a strong negative correlation (R = -0.9, p < 0.001) and a nearly moderate positive correlation (R = 0.5, p < 0.001) with heart rates, respectively. Two best-fit equations could be developed separately for both relative (R² = 0.3) and absolute delays (R² = 0.8). When adjusting the period of full tube current to a 114 ms for absolute delay and a 17.4 % of RR interval for relative delay, success rates of 94.9 % and 95.1 %, respectively, could be achieved and were significantly higher than that determined by the T wave location (82.7 %, p <  0.001).

The best-fit equations method has a higher success rate for predicting the optimal end-systolic phase of ECG-synchronized cardiac CT than the T wave location method.