Radiation dose and image quality from coronary angiography in 320-detector row computed tomography

Abstract

Coronary Computed Tomography Angiography (CCTA) examinations are increasing rapidly. Computed Tomography (CT) has been developed to improve image quality with the patient dose reduction. The purpose of this study is to evaluate radiation dose and image quality of CCTA in patients using 320-detector row CT. Forty-one patients referred for cardiac CT examinations at King Chulalongkorn Memorial Hospital were included in this study. All CCTA examinations were performed on the 320-detector row CT, Toshiba Aquilion ONE. Scanning protocol was investigated on dose estimates and image quality. Patients were scanned based on heart rate (HR) by HR < 65 bpm, using prospective gating 70-80% of R-R interval of cardiac cycle (1 heart beat), HR 66 – 70 bpm, using prospective gating 30 -80 % R-R(1 heart beat), HR 71 - 74 bpm, using prospective gating 30 -80 % R-R(2 heart beats) and HR > 75 bpm using retrospective with dose modulation. Scanning parameters, kVp, mA, HR, BMI, CTDIvol(mGy) and DLP(mGy.cm) were recorded to study the factors affecting the image quality and patient dose. The mA and kVp settings depend on BMI of the patient. Effective dose was calculated from DLP using specific conversion factor. The image quality was evaluated by two radiologists. Noise assessment was also studied quantitatively. The results show patient effective dose in prospective gating technique (PGT) 70-80% R-R interval as 3.6 ± 0.9 mSv, prospective gating 30-80% (1R-R) = 6.3 ± 1.9 mSv, 30-80% (2R-R) = 10.8 ± 1.8 mSv and in retrospective gating technique (RGT) with tube current modulation = 12.1 ± 7.7 mSv. Image noise was highest in PGT 70-80% (1R-R) and decreasing in orderly from RGT with tube current modulation to PGT 30-80% (1R-R) and the lowest in PGT 30-80% (2R-R). Overall qualitative image quality was mostly good to excellent scores. The heart rate, heart rate variability and disease of the patient affected in the radiation dose and image quality so the suitable acquisition protocols used are necessary. In conclusion, for cardiac CTA in 320-detector row, good to excellent image quality and patient dose reduction during CCTA are obtained especially in prospective technique when compared to earlier designed MDCTs using retrospective technique. The narrowing phase window width and single heart beat could be used for advantage of patient. Pre-examination HR controlling less than 65% R-R interval is still necessary for the highest dose reduction.