Dose reduction In coronary artery imaing with 64-row multi-slice helical CT with body mass index-dependent mA selection / 中华放射学杂志

ABSTRACT

Objective To evaluate the robustness of body mass index (BMI) adapted tube current selection method for obtaining consistent image quality in MSCT coronary artery imaging Methods Initially one hundred patients in the control group ( C group) underwent cardiac scans using GE 64-row VCT with standard scan protocol (640 mA, 120 kV, 0.35 see, body bewtie, C2 filter). Noise measurement was obtained for each patient using the average of three consecutive slices in the ascending aorta with ROI of 10 mm×10 mm to establish the relationship between BMI, desired image noise (IN) and required mA. An excel table was established to predict the required mA to achieve a desired IN for each patient with different BMI. A second group of one hundred cardiac patients (L group) was scanned with BMI-aclapted mA from the table to evaluate the practicability of this method. BMI, IN, CT dose index(CTDI),effective dose (ED) were all recorded. Results For the control group of 100 patients, the mean values and standard deviations of image quality score (IQS), BMI, IN and ED were 3.71±0.54, 25.08±2.63, 24.56±5.03 and (17.63±1.68 ) mSv (with range of 15-22 msy). Regression analysis indicated linear relationship between BMI and image noise with fixed mA. Using the relationship between tube current and image noise and noise ratio between large bowtie and cardiac bowtie, the following equation for the required tube current Xma to achieve present image noise of Ins for patient with certain BMI value when using cardiac bowtie could be then obtained Xma = Fma×( k1 x BMI + c1 )/Ina]2, where Fma = 640 mA, k1 = 1. 033, c1 = - 3.2, Ins = 27 in the study. (2) For the patients in L group, the mean values and standard deviations of IQS, BMI, and IN were 3.69±0.53, 25.07±2.91, and 26.61±3.44, respectively. The average tube current used was (469.95±113.45) mA, depending on patient's BMI values. The average effectively dose was(9.08±2.25) mSv. There was no statistically difference between the two groups in image quality( F= 0.068,P=0.794). Conclusions In 64-MSCT cardiac imaging, the use of BMI dependent tube current selection method, in conjunction with dose reduction techniques, can provide individualized scan protocol to obtain consistent image quality across patient population and to optimize dose delivery to patients.