The Study Of CTCA Image Quality Improvement By Using Snapshot Freeze Technique Under Prospective And Retrospective ECG-gating

ObjectiveCoronary Snapshot Freeze (SSF) is a new reconstruction algorithm to reduce coronary motion artifacts. The purpose of this study was to assess the image quality of coronary computed tomography angiography (CCTA) by using SSF under prospective and retrospective ECG-gating, and to evaluate the image qualities of different levels (per-segment, per-artery and per patient level) and the difference effect of SSF in different R-R interval under retrospective ECG-gating.Material and Methods60consecutive patients were enrolled in the current study.30patients (heart rate <70bpm) underwent CCTA with prospective ECG-gating and30patients (heart rate≥70bpm) underwent CCTA with retrospective ECG-gating. Image quality and interpretability were compared between standard (STD) and snapshot freeze (SSF) reconstructions algorithms.75%R-R interval were used for the reconstruction as the central phase under prospective ECG-gating, while45%and75%R-R interval were selected as the central phases under retrospective ECG-gating. Likert5-points score, which were interpreted by two experienced radiologists, was used as the image quality criterion. The image qualities and interpretabilities were assessed on per-patient, per-artery and per-segment levels, respectively. Wilcoxon rank sum test and McNemar test were used to compare the differences of the variables.Results1. In30patients with prospective ECG-gating (56.1±1.1years old; male15), the mean heart rate was63.8±5.9(50-75) bpm, and the mean BMI was25.2±3.6. SSF reconstructions showed higher interpretability than STD reconstructions on per-artery level [97.8%(88/90) vs87.8%(79/90),P=0.004] and per-segment level [99.1%(427/431) vs96.1%(414/431), P=0.000], but there were no significant difference on per-patient level [93.3%(28/30) vs76.7%(23/30), P=0.062]. Image quality (graded1-5) were higher by using SSF than STD reconstructions on a per-patient level (3.5±0.9vs2.9±1.2, P=0.004), per-artery level (3.5±0.8vs3.1±1.0, P=0.000) and per-segment (3.7±0.8vs3.4±1.0, P=0.000). Image quality (graded:1-5) were higher by using SSF than STD reconstructions on LAD (left anterior descending artery)[3.3±0.7vs2.9±1.0, P=0.007]、LCX(left circumflex artery)[3.1±0.8vs2.5±1.1, P=0.001] and RCA(right coronary artery)[3.3±0.6vs2.1±0.9, P=0.000].2. In30patients with prospective ECG-gating (55.5±10.1years old; male10), the mean heart rate was80.5±9.9(70-107) bpm. Heart rate variability during study was6.2±7.3bpm. SSF reconstructions showed higher interpretability than STD reconstructions on a per-patient level [80.0%(24/30) vs53.3%(16/30), P=0.039], per-artery level [90.0%(81/90) vs71.1%(64/90), P=0.000], and per-segment level [98.1%(413/421) vs90.7%(382/421), P=0.000] of45%of the R-R interval images. SSF reconstructions showed higher interpretability than STD reconstructions on a per-artery level [70.0%(63/90) vs55.6%(50/90), P=0.02] and per-segment level [82.7%(348/421) vs78.4%(330/421), P=0.018], but there were no significant difference on per-patient level [50.0%(15/30) vs30.0%(9/30), P=0.07] of75%of the R-R interval images.45%of the R-R interval images by SSF reconstructions showed higher interpretability75%of the R-R interval images on a per-patient level (P=0.035), per-artery level (P=0.001) and per-segment level (P=0.000). Image quality (graded:1-5) were higher by using SSF than STD reconstructions on a per-patient level (2.8±1.0vs2.1±1.2, P=0.013)(2.1±1.2vs1.6±1.0, P=0.026), per-artery level (3.0±0.9vs2.4±1.0, P=0.000)(2.6±1.2vs2.2±1.2, P=0.000) and per-segment level(3.3±0.9vs2.9±1.0, P=0.000)(2.9±1.2vs2.7±1.1, P=0.000) of45%and75%of the R-R interval images, respectively. Image quality (graded:1-5)by using SSF of45%of the R-R interval images showed higher than which of75%of R-R interval images on a per-patient level (P=0.016), per-artery level (P=0.002) and per-segment level (P=0.000). Image quality (graded1-5) were higher by using SSF than STD reconstructions on LAD (2.7±1.0vs2.3±1.2, P=0.018)(3.1±1.2vs2.6±1.1, P=0.013), LCX (2.6±0.8vs2.2±1.1,P=0.021)((2.7±0.9vs2.4±1.2, P=0.009) and RCA (3.2±0.9vs2.7±1.1,P=0.000)(2.3±1.0vs1.7±1.1, P=0.000)of45%and75%of the R-R interval images. Image quality (graded:1-5) by using SSF of45%of the R-R interval images was higher than which of75%of R-R interval images on RCA (P=0.000), and lower than which of75%of R-R interval images on LAD (P=0.007). There was no significant difference between45%and75%of the R-R interval images on LCX (P=0.06).3. The average ED(effective dose) with prospective ECG-gating and retrospective ECG-gating group was (2.8±1.4)mSv and (8.2±4.3)mSv,respectively. ED decreased by71%by using the prospective ECG-gating.ConclusionSSF could improve the image quality and interpretability in patients undergoing CCTA with prospective ECG-gating and retrospective ECG-gating. Especially, SSF could improve the image quality on RCA by using the45%R-R interval as the central phase with retrospective ECG-gating.