Uniform Image Quality Achieved By Individual Tube Current Modulation In Coronary CT Angiography: Preliminary Study

Part one The Analysis of Correlation between CACS Noise and CCTA Noise in Coronary CT AngiographyObjective To analyze the relationship of noise of calcium scoring(CACS)image (SD₁) and noise of coronary CT angiography(CCTA)image (SD₂), and develop one new method of predicting the CCTA image noise on the basis of individual tube current modulation.Materials and Methods Eighty two consecutive patients were analyzed retrospectively. The CCTA scanning protocol and exposure parameters were fixed. The noises of CACS and CCTA were measured on the root of aorta. The body mass index (BMI) was calculated. The linear correlation between SD₁and SD₂ was calculated and the linear equation was obtained. So did between BMI and SD₂. The subjective scoring of image quality in both groups was graded by two radiologists.Results In 82 cases, the average BMI was 24.37±3.18 kg/m2, the average SD was 20.11±4.48 Hu, the average SD₂ was 27.27±6.18 Hu. The linear correlation coefficient between SD and SD₂ was r=0.94(P < 0.0001),it's linear equation was SD₂ = 1.29624×SD₁ + 1.20457. The linear correlation coefficient between BMI and SD₂ was r=0.80(P < 0.0001),it's linear equation was SD₂= 1.56067×SD₁– 10.76960. Individual tube current modulation table were made according to linear equations based on BMI and CACS noise, in case of the target noise of CCTA being 27 Hu.Conclusion There was a high linear correlation between noise of CACS image and noise of CCTA image, using fixed CCTA scanning protocol and exposure parameters. The noise of CCTA was predictable based on CACS noise and its accuracy was more high than that of BMI. Part two Uniform Image Quality Achieved by Individual Tube Current Modulation Based on CACS Noise in CCTA: Preliminary Clinical StudyObjective To explore the feasibility of uniform image noise achieved by individual tube current modulation based on noise of CACS and BMI in CCTA, and compare the effectectiveness and accuracy between two methods.Materials and Methods This prospective study was proved by the ethics committee in our institution and Informed consent was obtained from all patients. 86 consecutive patients with heart rates below 65 bpm by given metoprolol from 0 to 200 mg were randomly divided into SD group and BMI group. In both groups, mA of CCTA was modulated with individual tube current modulation tables. The retrospective ECG-gating phase window was set at 75% R-R interval. Supposing CACS noise higher than 22.36 Hu in SD group or BMI higher than 26.24 kg/m2 in BMI group, the set tube current was larger than 750 mA and the patients would be excluded. The noise of CCTA was measured on the root of aorta in both groups. DSD was defined as the absolute value of difference between actual noise and target noise (27 Hu) in CCTA. Effective radiation dose (ED) was calculated. The subjective scoring of image quality in both groups was graded by two radiologists.Results 62 patients were included, 33 cases in SD group and 29 cases in BMI group. In BMI group, average value of BMI, SD₁, SD₂ and ED of CCTA were 23.27±2.21 kg/m2, 19.14±3.65Hu, 25.98±3.79 Hu, 9.13±2.14 mSv respectively. In SD group, average value of BMI, SD₁, SD₂ and ED of CCTA were 23.31±2.39 kg/m2, 18.10±3.10 Hu, 26.56±1.63 Hu, 8.71±2.66 mSv. There were no statistical differences in both groups. Standard deviation of SD₂ was 3.79 Hu (coefficient of variation was 14.58%, range was 13.80 Hu ) in BMI group and 1.63 Hu (coefficient of variation was 6.13%, range was 6.13 Hu) in SD group. DSD was 3.44±1.79 Hu in BMI group and 1.20±1.16Hu in SD group, the former was obviously higher than the latter (P < 0.0001). The subjective scoring in group SD was better than in BMI group (P = 0.0312). Conclusion Compared with BMI, noise of CACS is a more precise parameter of adjusting individually the tube current in CCTA. The individual tube current modulation with CACS noise may provide a consistent image quality of CCTA.