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

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.