Individualized tube current selection for 64-row cardiac CTA based on analysis of the scout view

To obtain consistent CCTA image quality and patient dose optimization with an individualized tube current selection method based on analysis of CT scout scans.

The study received a waiver of informed consent from the institutional review board. Initially 100 patients (Group A) underwent CCTA with a fixed mA. The scout view pixel value and CCTA image noise were measured. Their correlation was studied to establish a formula to determine the required mA for obtaining a CT exam with a specific image noise. One hundred patients (Group B) were then scanned with the formula-determined mA. CCTA image quality, image noise and effective dose from the two groups were statistically analyzed. CT findings for 32 Group B patients were compared with the conventional coronary angiography.

An average CCTA image noise of 27.6 HU was obtained (target 27 HU) using the formula with more uniform image noise in Group B (standard deviation 2.4 HU) than in Group A (4.1 HU). There was no statistical difference between image quality scores for the two groups. The effective dose for Group B (7.8 mSv) was 30% lower than for Group A (11.2 mSv) (p<0.01). CCTA sensitivity, specificity, positive predictive value, negative predictive value, and stenosis detection accuracy were 94.9%, 92.1%, 88.9%, 96.5% and 93.2%, respectively, for stenosis greater than 50%.

CCTA mA selection based upon the image characteristics of the CT scout view provides an individualized protocol that generates consistent image quality and helps to reduce overall patient dose.