Résumé
Objective To analyze retrospectively the impact of different heart rates on image quality and radiation dose of coronary angiography using 640-slice dynamic volume CT.Methods A total of 461 patients with suspected coronary artery disease or referred to health check underwent coronary angiography with 640-slice dynamic volume CT.Two groups were created according to their heart rates:Group A had heart rate < 65 beats per minute (n=337)and Group B had heart rate between 65 to 122 beats per minute (n=124).Image quality was assessed by analyzing the 1 5 segments of the main coronary branches using 3-grade scale (grade I-good,grade Ⅱ-acceptable,grade Ⅲ-poor).Effective radiation dose was also evaluated.Results Patients in both A group and B group performed successful CT coronary angiography with a total of 6 91 5 coronary segments.Among them,coronary segments that could be evaluated reliably accounted for 94.5% (6 535/6 91 5)while 5.5% (380/6 91 5)were too small (≤1.5 mm)to be assessed. For the image quality,Group A and Group B had grade I in 90.5% (305/337)vs 74.2% (92 /124),grade Ⅱ in 9.5% (32/337)vs 21.0% (26 / 124)and grade Ⅲ in 0 % (0 / 337 )vs 4.8% (6 / 124),respectively.Image quality was significantly different be-tween Group A and Group B (P <0.001).In addition,32 patients (9.5%)in Group A had slight cardiac motion artifacts but with-out affecting image quality,whereas 26 patients (21.0%)in Group B had higher degree of cardiac motion artifacts thus graded as grade Ⅱ.Stair-step artifacts were not found in all patients.The effective radiation dose was higher in Group B than in Group A by 32.05%(7.91±0.34 mSv vs 5.99±0.17 mSv).Conclusion Coronary angiography using 640-slice dynamic volume CT can guarantee excellent image quality when heart rate < 65 beats per minute.Although the image quality would decrease in some extent it is still diagnostic when heart rate is between 65 to 122(include 65 and 122)beats per minute.