Association between the mean CT value on a scout view and the dependent mA selection method in coronary artery imaging on 64-row multi-slice spiral CT / 中华放射学杂志

ABSTRACT

Objective To characterize the association between the mean CT value on a scout view and the dependent mA selection method, and to evaluate the clinical value of a mA selection method based on scout view mean CT value in obtaining individualized scan protocol and consistent image quality for patient population on 64-row MSCT CT coronary angiography (CTCA).Methods One hundred patients (group A) underwent CCTA consecutively using standard protocol with a fixed mA.The mean CT value of a fixed ROI (region of interest) from the scout AP view and the CTCA image noise (standard deviation on the root of ascending aorta) were measured.The correlation between CT values and noise was studied establish a formula and a list to determine the required mA for obtaining a consistent CTCA image noise based on the measured SV CT value.Another 100 patients (group B) were scanned using the same parameters as group A except the mA and the CT value was also measured.The mA was determined by the list established previously.The CTCA image quality (IQ) as well as the image noise (IN) and the effective dose (ED) from the two groups were statistically analyzed using t-test.The CT findings for the 32 patients in the group B were also compared with the selective coronary angiography (SCA) results.The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of CCTA for detection of significant stenosis were obtained.Results The formula between the required mA and the CT value was XmA=FmA×[(K1×CTscout + C1)/INa]2.The CCTA images in B group had statistically higher IN (27.66±2.57,22.22±4.17,t=11.33, P=0.000), but no statistical difference between IQ scores for the two groups (3.29±0.66,3.37±0.67,t=0.009, P=0.990), and ED[(8.72±2.51) versus (12.53±0.90) mSv]was 30% lower for the B group (P<0.01).For the 32 patients in the B group who had SCA, the CCTA sensitivity, specificity, positive predictive value, negative predictive value, and stenosis detection accuracy were 94.92% (56/59), 92.13% (82/89) ,88.89% (56/63) ,96.47% (82/85) and 93.24% (138/148) wspectively for stenosis greater than 50%.Conclusion The mA selection method based on the SV CT value for CCTA in 64-row MSCT provides individualized protocol to obtain consistent image quality and to optimize dose delivery to patients.