Feasibility Of Single-phase Scan With Retrospective ECG-gating In Computed Tomorgraphy Coronary Angiography

PartⅠThe study of phase window and radiation dose in computed tomography coronary angiographyObjective: To reduce radiation dose effectively on patients by studying the relationship of phase window and radiation dose with retrospective ECG- gating and the effect on image quality. Materials and Methods: The phantom(Catphan600) was scanned at simulated heart rate 55 beat per minute (bpm) in the heart mode of 64-VCT.Scanning parameters were fixed except phase window.The phase window was set at 75% (single-phase scan, SPS), 35-80% (half-phase scan, HPS) , 0-95%(full-phase scan, FPS). CTP515 was used to measure image noise (represented by SD), signal-noise ratio(SNR) and contrast-to- noise ratio(CNR). CTP528 was used to measure high-density resolution of image, represented by line pairs. 20 datas were reconstructed in 5% steps from 0 to 95% of the R-R interval, milliampere in each cardiac mass at per R-R interval was recorded and calculated average value, the distribution of milliampere in the whole cardiac cycle was displayed by polygram. The radiation dose volume computed tomography dose index (CTDIvol) and dose length product(DLP) was recorded.Results:the distribution of SD,SNR,CNR through SPS, HPS, FPS was familiar with milliamp ere, and there was no significant difference among SD,SNR,CNR of SPS at reconstruction of 70-80% R-R interval (p=0.352). The high-density resolution of three scan mode was seven line pairs/cm. Corresponding to SPS, HPS and FPS, CTDIvol was 39.91 mGy,64.04 mGy,78.32 mGy and DLP was 561.28 mGycm, 900.57 mGycm, 1101.4mGycm,respectively. Compared with FPS, the radiation dose of HPS and SPS was reduced by 37.7%和49.0%, respectively.Conclusion:single-phase scan could reduce radiation dose obviously with no impairment of image quality.PartⅡ: Factors analysis of single-phase scan in computed tomography coronary angiography and Clinical feasibilityObjective: to evaluate image quality and the optimal phase window of Coronary artery, to analyze the factors influencing coronary artery imaging with retrospective-gating VCT at single-phase. Materials and Methods: A review analysis was performed on all images datas of 108 patients who using HPS in 64-detector spiral CT for coronary angiography. Obtained the incidence of optimal phase window at 70-80%R-R interval and the relationship of heart rate , to formulate the suitable qualification of 75% SPS initially. SPS was performed on 43 patients who meet the qualification. Using a double-blind by two physicians to assess the image quality of each coronary artery, and image noise of the ascending aorta were measured .The dose length product (DLP) were recorded and effective dose were calculated .finally, statistic achievement ratio of SPS. Results: 1. In 108 cases , 78 cases (72.2%) reconstruction at 75% R-R interval; a total of 95 cases (88%) reconstruction at 70-80% R-R interval; when HR below 65 beats per min, 70 in 81 cases the optimal phase at 75% R-R interval, accounting for 87.4%, when HR more than 65 beats per min,17in 27 cases the optimal phase at 75% R-R interval, accounting for 62.9%,and there was significant difference between heart rate and optimal phase(p=0.00). The suitable qualification of 75% SPS were①. sinusoidal and predictions canning heart rate less than 65bpm②. predictions canning heart rate variability less than 5bpm;③.the duration of breath holding more than 15 seconds;④.no motion artifacts of right coronary artery at the calcium scoring scanning. The achievement ratio of 48 patients using SPS was 100%,41 were at 75% , 2 patients were 70% and 80% R-R interval, respectively, the mean score of image quality was 4.34±0.68, and there was no significant difference among image noise of the ascending aorta at the reconstruction 70%,75% and 80%(p=0.935).conclusions: With the heart rate <65bpm,and heart rate variability≤5bpm,It was feasible of SPS in CTCA with retrospective ECG-gating. PartⅢ: Comparative study between single-phase scan and half-phase scan in computed tomography coronary angiographyObjective: To evaluate radiation dose and image quality between single-phase scan and half-phase scan in CTCA with retrospective ECG- gating, to approach the feasibility of single-phase scan in CTCA and its clinical application. Materials and Methods: 80 patients consecutive underwent CTCA and were divided into two groups randomly, 40 were in group A, using half-phase scan, 40 were in group B, using single-phase scan. .Two radiologists quantitatively evaluated the image quality blindly in terms of the number of coronary arteries and smaller branches identified, the sharpness of vessel edges and the clarity of contrast agent in the vessel using scores of 1-4 with 4 excellent. The CT value and image noise of the ascending aorta , coronary artery and the fat tissue nearby were also measured, and calculate the SD,SNR and CNR of ascending aorta and coronary artery. The dose length product (DLP) was recorded. Results: 90% of the patients gained the best image at 75% reconstruction, the other 10% best reconstruction were at 70% and 80%R-R interval. respectively. The image quality score of A,B was(3.80±0.54),(3.79±0.58), by Mann-Whitney U-test, there was no significant difference(p=0.945). Image noise of ascending aorta was 27.48 HU±6.64,26.83 HU±5.24, respectively. By t-test,there was no significant difference too(p=0.627),SD,SNR and CNR of the whole coronary artery was 19.06 HU±6.67,19.95 HU±6.65 , 25.22±10.86,25.45±9.55, 18.94±5.24,18.99±4.49,respectively. there was no significant difference among SD,SNR,CNR of the whole coronary artery(p=0.423,0.981,0.941).The radiation dose of group A,B was(12.70±1.04)mSv vs (8.48±0.83)mSv, the group B patient's ED were significantly lower than A group (P <0.05), was reduced by approximately 35%. Conclusion: Single-phase scan in CTCA could reduce radiation dose by 35% with no impairment of image quality. Follow the principle ALARA (As low As reasonably achievable)...