Defining the optimal systolic phase targets using absolute delay time for reconstructions in dual-source coronary CT angiography

Abstract

To define the optimal systolic phase for dual-source computed tomography angiography using an absolute reconstruction delay time after the R-R interval based on the coronary artery motion, we analyzed images reconstructed between 200 and 420 miliseconds (ms) after the R wave at 20 ms increments in 21 patients. Based on the American Heart Association coronary segmentation guidelines, the origin of six coronary artery landmarks (RCA, AM1, PDA, LM, OM1, and D2) were selected to calculate the coronary artery motion velocity. The velocity of the given landmark was defined as the quotient of the route and the length of the time interval. The x, y and z-coordinates of the selected landmark were recorded, and were used for the calculation of the 3D route of coronary artery motion by using a specific equation. Differences in velocities were assessed by analysis of variance for repeated measures; Bonferroni post hoc tests were used for multiple pair wise comparisons. 1488 landmarks were measured (6 locations at 12 systolic time points) in 21 patients and were analyzed. The mean values of the minimum velocities were calculated separately for each heart rate group (i.e. <65; 65-80; and >80 bpm). The mean lowest coronary artery velocities in each segment occurred in the middle period of each time interval of the acquired systolic phase i.e. 280-340 ms. No differences were found in the minimal coronary artery velocities between the three HR groups, with the exception of the AM1 branch (p = 0.00495) between <65 and >80 bpm (p = 0.03), and at HRs of 65-80 versus >80 bpm (p = 0.006). During an absolute delay of 200-420 ms after the R-wave, the ideal reconstruction interval varies significantly among coronary artery segments. Decreased velocities occur between 280 to 340 ms. Therefore a narrow range of systolic intervals, rather than a single phase, should be acquired.

Keywords: Absolute delay time; Coronary CT angiography; Dual-source CT; Systolic phase targets.

Fig. 1

Raw data sets reconstructions in 20 ms increments after R peak with 1 mm thick slices. Mulitple axial reconstructions of the right heart during systole (absolute delays after the R-wave from 180 ms through 460 ms in 20 ms increments) demonstrate the optimal phase time of 340 ms at the level of an acute marginal branch (white arrow). The right atrium (RA), left atrium (LA), aortic valve (AV), and right ventricular outflow tract (RVOT) are marked

Fig. 2

Defining end systolic phase and the end of isovolumic relaxation phases following the aortic valve closure and initiation of mitral valve opening on the 3 chamber cine view. Three-chamber cine view reconstructed throughout the acquired systolic intervals demonstrate the aortic (AV) and mitral (MV) valves. Aortic valve closure can be identified (asterisk, 300 ms reconstruction) and the initiation of mitral valve opening (plus, 340 ms reconstruction), which denote the end of the systolic reduced ejection phase, and the end of the isovolumetric relaxation phases, respectively

Fig. 3

Landmark position for manual velocity mapping based on the AHA coronary segmentation guidelines

Fig. 4

Mean coronary artery velocities in each of the three time periods. The lowest coronary velocity was detected in the mid period of the reconstructed interval (280–340 ms). The mean velocities in this period are significantly lower than in the early and/or late periods

Fig. 5

Reconstruction interval for evaluation of the RCA, placed at 40 % of the R–R cycle for HR = 78 and 57 bpm. Velocity maps of two different patients’ RCAs using relative (top, % R–R x-axis), and absolute (bottom, ms x-axis) demonstrate differences in minimal systolic velocities and their variable definitions using the two methods. Note that despite highly disparate heart rates, the minimal velocity time point lies similarly close to 400 ms after the R-wave despite nearly 10 % difference between the relative portion of the R–R intervals