[Optimal scanning collimation for segmental bronchi: experimental study with low-dose helical CT].

Objective: To evaluate the effects of low-dose helical CT with different scanning collimation on the visualization of segmental bronchi and to determine the optimal scanning collimation in CT screening for early central lung cancer.
Methods: Forty healthy volunteers were randomly assigned to undergo the low-dose helical CT at 120 kVp, 50 mA, 0.75 s and pitch 1. One group (n = 20) underwent the sequential subsection scan of chest with the collimation of 10 mm for the apical and basilar zone, and of 8 mm and 5 mm for the hilar zone. The other (n = 20) went through CT scan with 10 mm collimation of the whole lung. The visualizations of lobar, segmental bronchi were compared at different collimations. ANOVA and multiple comparison were performed.
Results: The visualization of segmental bronchi on low-dose scan at 10 mm collimation was 60%, being lower than that at 8 mm (88%) or 5 mm (91%) collimation (P < 0.01). The segmental bronchi of right upper lobe were easily identified at collimation of 10 mm (82%), 8 mm (96%) and 5 mm (98%), as well as those of left upper lobe at 10 mm (83%), 8 mm (95%) and 5 mm (97%), whereas those of lingular lobe were difficultly identified at 10 mm (30%), 8 mm (60%) and 5 mm (70%).
Conclusion: The lobar and segmental bronchi were visualized reliably by CT with 50 mA and 8 mm collimation, and therefore the sequential subsection scan of chest divided into three zones can be adapted to CT screening for early lung cancer.