Radiation dose proportions of localizer radiograph and bolus tracking in low-dose pediatric cardiothoracic computed tomography.

Abstract

Background: Optimization of localizer radiograph and bolus tracking doses is necessary, as their dose proportion may increase with a decreasing diagnostic scan dose in pediatric cardiothoracic computed tomography (CT).

Objective: To evaluate the radiation dose proportions of the localizer radiograph and bolus tracking in low-dose pediatric cardiothoracic CT.

Materials and methods: For low-dose pediatric cardiothoracic CT, a posteroanterior localizer radiograph was acquired with 80 kV, and 35 mA or 20 mA in 852 infants (age<1 year). Propensity score matching was employed in comparing the 35 mA and 20 mA groups on dose proportion, over z-axis proportion, visibility of anatomic landmarks, and image noise. The over z-axis coverage proportion was correlated with the dose proportion of the localizer radiograph in both groups. Additionally, bolus tracking was performed in 1,015 children (≤2 years). The effects of the number of monitoring scan, dose-length product of the diagnostic scan, age, and water-equivalent area of the scanned patient body on the radiation dose proportion of bolus tracking were evaluated.

Results: The dose proportion of the localizer radiograph was significantly lower in the 20 mA group (2.5%, n = 94) than in the 35 mA group (6.5%, n = 94) (P < 0.001). While image noise was higher in the 20 mA group (2.1 Hounsfield units versus 1.0 Hounsfield units of the 35 mA-group, P < 0.001), all the anatomic landmarks remained visible in all cases. The over z-axis coverage proportion demonstrated high correlations with the dose proportion for both groups (R = 0.736, P < 0.001 for the 35 mA group and R = 0.660, P < 0.001 for the 20 mA group). The bolus tracking dose-length product proportion demonstrated the strongest positive correlation with the number of monitoring scans (R = 0.93, P < 0.001), while age, diagnostic scan dose-length product, and water-equivalent area showed weak negative correlations (R-values = -0.46~-0.50, P-values < 0.001).

Conclusions: In low-dose pediatric cardiothoracic CT, the dose proportion of the localizer radiograph can be substantially reduced with a low tube current setting while maintaining image quality. Additionally, minimization of the over z-axis coverage proportion merits attention. The number of monitoring scans is the most significant factor for increasing the radiation dose proportion of bolus tracking, especially in young ages.