| Objective Nowadays, multi-detector rows CT (MDCT) coronary angiography has been widely applied as an attractive noninvasive diagnostic modality for detecting coronary artery disease. However, a growing concern about the high effective radiation dose of coronary CTA has aroused more and more attention of underlying adverse consequences. A practical solution is the prospective electrocardiogram (ECG)-gating technique to preset pulsing windows at only a fraction of the R-R interval. It has been proved to be an advanced method to reduce the exposure dose. Previous studies showed that the relationship between optimal phases of image reconstruction and heart rate at CT coronary angiography were different with temporal resolution. Our purpose was to investigate the optimal exposure intervals for coronary CT angiography using 320-detector row dynamic volume CT(DVCT) and evaluate the effects on image quality, radiation dose and diagnostic accuracy.Materials and Methods From December 2008 to July 2009, 77 patients (mean heart rate 69.5±12.8, range: 46～102 beats per minute, bpm) whose coronary vessel and cardiac function needed assessment were scanned by retrospective electrocardiographic (ECG)-gating. For evaluation of the relationship between image quality and R - R interval, image reconstruction based on relative timing was performed in 10% steps of the R - R interval. In those patients for whom a motion-free phase was not identified, image reconstruction was preceded by 1 % intervals around the 10% intervals with fewest motion artifacts to determine the optimal image quality.The reviewers assessing image quality semi-quantitatively for both the diastolic and the systolic phases by using a previously described 4-point ranking scale(1): 1, excellent (no motion artifacts and clear delineation of the segment); 2, good (minor artifacts and mild blurring of the segment); 3, adequate, (moderate artifacts and moderate blurring without structure discontinuity); 4, not evaluable (doubling or discontinuity in the course of the segment preventing evaluation or vessel structures not differentiable severe motion artifacts).The relationship between heart rate and optimal reconstruction windows was analyzed. From September 2009 to August 2010, 53 patients who were scheduled clinically-indicated invasive coronary angiography (ICA) were scanned by applying the predicted triggering windows. The effects of prospective ECG-gating on image quality, radiation dose and diagnostic accuracy were evaluated.Results The proportion of systole was influenced by heart rate statistically(r=0.78,P<0.001). As heart rate increased, the optimal systolic and diastolic reconstruction interval shifted to later intervals. The image quality of systolic and diastolic was significantly influenced by heart rate(r=0.38,P<0.001;r=0.82,P<0.001). On the analysis of the regulation of image quality score in different heart rate groups, the optimal exposure phases were determined as followed: when heart rate<70bpm, the exposure windows should be preset at 65～80%; if 70 to 80bpm, 70～85%; if 80 to 90bpm, 70～90%; if heart rate >90bpm, 35～50%. Compared with retrospective ECG-gating, prospective ECG-gating could decrease radiation dose while provide diagnostic image quality. On a segment analysis, the sensitivity was 96.1%,specificity 98.3%,positive predictive value 92.5%,negative predictive value 99.1%. However, with higher heart rate, the dose increased significantly(r=0.64,P<0.001).Conclusion 1. As heart rate increased, the optimal systolic and diastolic image quality deteriorates significantly, with diastolic image quality decreases faster. When heart rate>90bpm, the optimal reconstruction intervals shift from diastole to systole; 2. The optimal exposure phases were determined as followed: when heart rate<70bpm, the exposure windows should be preset at 65～80%; if 70 to 80bpm, 70～85%; if 80 to 90bpm, 70～90%; if heart rate >90bpm, 35～50%; 3. DVCT has potential to provide high image quality in a wide range of heart rate with an optimized ECG pulsing window; 4. However, it is recommended to control heart rate below 70bpm, if possible, to decrease radiation dose.
|
PDF Full Text Request