| ObjectiveTo investigate the main factors affecting the imaging quality of coronary CT angiography and the improvement measures through the evaluation of the effects of different heart rates, heart rate variability, and means of reconstruction of angiographic images and through the evaluation of the degrees of improvement of override scan mode ,multi-phase imaging reconstruction and electrocardiogram editing functions for the purpose of the improvement of success rate and image quality by 64-slice CT in diagnosis of rheumatic heart disease.Materials and Methods1. We performed 64-slice CT scan on a dynamic cardiac phantom, simulating different heart rate variability at low heart rate (50 bpm), medium heart rate (70 bpm) and high heart rate (90 bpm). Override mode was set on and off respectively before the scan. Reconstruction was performed by 4 means: snapshot segment (SSEG), snapshot segment plus (SSEGP), snapshot burst-2(SSB2), and snapshot burst-4 (SSB4), and then the reconstructed data were transmitted to AW4.3 Workstation for imaging processing and analysis.2. After performance of 64-slice CT scan in 289 patients with rheumatic heart disease, imaging post-processing and evaluation were conducted at AW4.3 Workstation for the analysis of the factors influencing the quality of coronary angiography and further analysis of the main influencing factors was performed. (1) A total of 289 cases were divided into 3 groups: low heart rate (≤65 bpm, 133 cases), low heart rate (66-80 bpm, 104 cases), and high heart rate (≥81 bpm, 52 cases); (2) All the patients were divided into 4 groups according to different degrees of heart rate variability: Group A (≤7 bpm, 124 cases), Group B (8-14 bpm, 96 cases), Group C (15-21 bpm, 41 cases), and Group D (≥22 bpm, 28 cases). The quality of imaging formation in each group was evaluated. In addition, multi-phase imaging reconstruction and electrocardiogram editing processing were performed in 102 cases with poor quality of imaging formation, and the pre-processed and post-processed images were evaluated.Volume rendering (VR), multi planar reconstruction (MPR), curved planar reconstruction (CPR), and maximum intensity projection (MIP), etc. were employed for post-imaging processing.A 5-grade scoring system was conducted: 5 for clear coronary artery without constructed defect, 4 for slightly blurred coronary arteries or light ladder-like constructed defect, 3 for moderately blurred coronary arteries with darkened ladder-like constructed defect, 2 for blurred or broken or dislocated but recognizable coronary arteries, 1 for seriously blurred or broken or dislocated and illegible coronary arteries. Scoring above 3 was classified as evaluable coronary arteries but scoring lower than 2 as non-evaluable ones.ResultsI. CTA of phantom coronary arteries1. Relationship between imaging quality and heart rate The average scoring was (4.88士0.35), (4.88士0.35), (4.90士0.47), (5.00士0.00), (4.75士0.46), (4.45士0.74), (4.00士0.93), (4.25士0.38), and (3.25士1.58), from 40 bpm to 120 bpm heart rate .The imaging quality declined increasingly with the increase of heart rate, which was more remarkable in cases of high heart rate.2. Relationship between imaging quality and heart rate variability(1) Comparison of imaging quality in the low, medium, and high groups showed that the imaging quality declined increasingly with the increase of heart rate variability, which was more remarkable in the group of high heart rate.(2) Comparison of the imaging quality among the low, medium, and high groups showed that the average scoring was (3.54士0.95), (3.16士0.87), and (1.57士0.63), respectively. There was significant difference (P<0.01) between each group. The imaging quality in low heart rate group was better than that in the high heart rate group.(3) Comparison of the scoring of high fluctuation rate in low heart rate group (15%, 20%, and 30%) and the scoring of low fluctuation rate in high heart rate group (2%, 5%, and 7%) after regrouping showed that the average scoring was (2.71士0.45) and (2.04士0.87), respectively (P<0.05). Higher heart rate fluctuation was allowed in low heart rate group.3. Relationship between imaging quality and the reconstruction modesReconstruction of the raw data in low, medium, and high heart rate groups by SSEG, SSEGP, SSB2, and SSB4 showed that the best quality was achieved by SSEGP(P<0.01). In low heart rate group, SSEG was better than SSB2 and SSB4 (P<0.05) but no difference was found between SSB2 and SSB4 (P>0.05). In medium heart rate group, no difference was found between SSEG, SSB2, and SSB4 (P<0.05). In high heart rate group, however, difference was found between SSEG, SSB2, and SSB4 (P<0.01), but SSB2 was better than SSB4, and SSB4 better than SSEG.4. Effects of Override mode on imaging qualityComparison of the imaging quality with Override mode on and off when scanning showed there was significant difference between low, medium, and high heart rate groups (P<0.01). When high heart rate fluctuation occurred, override mode ON could avoid loss of raw data, but not very helpful for the improvement of imaging quality. II. CTA of coronary arteries of rheumatic heart disease1. Main factors influencing CTA images of coronary arteriesIn a total of 2551 blood vessel segments from 289 cases were included for evaluation, no constructed defect was found in 1726 segments (67.66%), but different degrees of constructed defect in 825 segments (32.34%). Among the factors resulting in constructed defect, 551 segments (66.79%) resulted from heart rate and heart rate variability, 160 (20.12%) from respiratory cause, and 108 (13.09%) from technical cause. Heart rate and heart rate variability were the main influencing factors in imaging quality.2. Effects of average heart rate on CTA imaging quality of coronary arteriesA total of 2551 blood vessel segments from 289 cases were divided into 3 groups for evaluation, 1185, 919, and 447, respectively, and the evaluable blood vessel segments were 1128 (95.19%), 825 (90.53%), and 328 (73.38%), but non-evaluable blood vessel segments were 57 (4.81%), 94 (10.23%), and 119 (26.62%). Comparison of the 3 groups showed significant difference (P<0.01). The imaging quality declined increasingly with the increase of heart rates. The imaging quality declined significantly when heart rate was over 81 bpm.3. Effects of heart rate variability on CTA imaging quality of coronary arteries A total of 2551 blood vessel segments from 289 cases were included into 4 groups for evaluation: 1099, 854, 354, and 241, respectively, and the evaluable blood vessel segments were 1045 (95.09%), 790 (92.51%), 275 (77.68%), and 168 (69.71%), but non-evaluable blood vessel segments were 54 (4.91%, 64 (7.49%), 79 (22.32%), and 73 (30.29%). Comparison of the 4 groups showed significant difference (P<0.05). The imaging quality declined with the increase of heart rate variability and declined remarkably when heart rate variability was higher than 22 bpm.4. Effects of multi-phase reconstruction and electrocardiogram editing function on CTA imaging quality of coronary arteriesA total of 892 blood vessel segments from 102 cases were included for evaluation. Before and after multi-phase reconstruction, the evaluable blood vessel segments were 605 (67.83%) and 769 (86.21%), respectively, increasing by 18.38% (P<0.01). Before and after electrocardiogram editing function, the evaluable blood vessel segments were 769 (86.21%) and 845 (94.73%), respectively, increasing by 8.52% (P<0.01).Conclusion1. Various kinds of factors may have effects on 64-slice CT coronary angiography, but the main influencing factors may include heat rates and heart rate variability. Low heart rate and light heart rate variability can result in good imaging quality, but higher heart rate variability are allowed at low heart rate.2. The reconstruction of SSEGP may be the optimal mode out of the 4 means: SSEG, SSEGP, SSB2, and SSB4.3. When high frequency of heart rate variability occurred, Override ON could avoid loss of data collection but had limited effect on the improvement of imaging quality.4. Measures such as optimized operation procedures, personally designed scanning scheme, comprehensive psychological counseling, training of respiration, reduced heart rate, efficient utilization of override mode, electrocardiogram editing function, etc., are helpful for the improvement of the success rate and imaging quality of 64-slice CT coronary angiography in patients with rheumatic heart disease. |
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