256-slice Coronary Computed Tomography Angiography Using Low Tube Voltage Of100kV

Background: While using coronary computed tomography angiography (CCTA), theradiation dose is found to be higher than the examination done of other parts of thebody using CT scanner. The high radiation dose may cause increase in cancer riskwhich is of great importance. So, we want to do comparative study between twodifferent protocols of120kV as a standard group and100kV as a reduced group forreduction of the radiation dose while performing CCTA.Purpose: To evaluate the image quality and radiation dose of100kV with1000mAsretrospective electrocardiography (ECG)-gated CCTA protocol, compared to thestandard protocol of120kV with800mAs retrospective ECG-gated CCTA.Material and Methods: We evaluated the CCTA images of70patients with normalbody mass index (BMI between18.5kg/m2and25kg/m2). We divided70patientsinto two groups. One group as reduced dose group with thirty-five patients (18Males,17Females; Mean age56.94±11.51years) were examined by100-kV with1000mAs retrospective ECG-gated CCTA, and other standard group with thirty-fivepatients (21Males,14Females; Mean age54.03±9.81years) were examined by120-kV with800mAs retrospective ECG-gated CCTA. Then two blinded radiologistsanalyzed image quality of the coronary arteries independently. They performed asubjective image quality and objective image quality. The subjective image qualitywas assessed according to5-point scoring scale. The objective image quality wasmeasured in terms of a signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR].The radiation dose was also measured in both groups. The effective radiation dose[ED] was calculated using CT dose volume index [CTDIvol.], dose-length product[DLP] and conversion coefficient for chest (conversion factor k=0.014mSv mGy-1cm-1). Results: Although the objective image quality of the reduced protocol of100-kV with1000mAs was significantly better than the standard protocol of120-kV with800mAs (mean SNR,36.65±2.95vs.33.47±3.86, P <0.0001; mean CNR,34.27±2.92vs.30.62±3.90, P <0.0001), there was no significant variation in the subjectiveimage quality between two groups of patients with normal body mass index (meanimage score,4.54±0.37vs.4.56±0.25for radiologist1, P=0.781;4.52±0.25vs.4.56±0.25for radiologist2, P=0.486). The radiation dose was found to be reducedby28%with the100-kV/1000mAs protocol than with the standard protocol of120-kV/800mAs retrospective ECG-gated CCTA (7.87±0.59vs.10.95±1.67mSv, P <0.0001).Conclusion: The protocol of low tube voltage CCTA using100kV/1000mAsretrospective ECG-gated shows significant reduction of the radiation dose withoutdisturbing the subjective image quality of CCTA.