[Measurement and analysis of tracheal inner diameter in Chinese adults using multi-slice spiral CT, multi-planar reconstruction and special window technique]

Objective: To measure the inner diameter of tracheal(TD) in Chinese adults by multi-slice spiral CT(MSCT), multi-planar reconstruction(MPR) with special window technique and analyze its influencing factors. Methods: A total of 824 normal adults(male 435, female 389) and 16 patients with small peripheral pulmonary nodules(SPN) receiving chest multi-slice spiral CT (MSCT) in the physical examination at the First Affiliated Hospital of Guangzhou Medical University between January, 2014 and December, 2015 were included and their records were retrospectively analyzed. The 16 patients with SPN received bronchoscopy and the images were recorded followed by measurement of tracheal diameter using software. MSCT and MPR images were obtained by the 3Dview software, and the inner diameter of the trachea at 4 horizontal positions were measured by special window technique (window width 500 Hu, window level 100 Hu): thoracic entrance (TD(1)), aortic arch (TD(2)), 2 cm higher than the carina of trachea (TD(3)) and the narrowest trachea (TD(4)). Results: The results of bronchoscopy and software measurement in 16 patients were consistent with those of MSCT and MPR combined with special window technique (P>0.05). The TD at 4 positions in adult males were larger than those of adult females (P<0.01). The TD values at each position for males and females were as follows: (18.9±1.7) and (15.6±1.3) mm (t=30.9, P<0.01) for TD(1), (18.8±1.6) and (16.1±1.2) mm (t=28.0, P<0.01) for TD(2), (19.0±1.6) and (16.3±1.3) mm (t=26.5, P<0.01) for TD(3), (18.4±1.5) and (15.5±1.1) mm (t=31.3, P<0.01) for TD(4), respectively. The age, weight and BMI were not significantly correlated with the tracheal diameter (P>0.05). The height was linearly correlated with the tracheal diameter: for males, TD(1)=0.071× height (cm) + 6.964 (r=0.249, P<0.05), TD(2)=0.064 × height (cm) + 7.898 (r=0.246, P<0.05), TD(3)=0.074 × height (cm) + 6.533 (r=0.279, P<0.05), TD(4)=0.056 × height(cm) + 8.811(r=0.226, P<0.05); while for females, TD(1)= 0.046× height (cm) + 8.331 (r=0.183, P<0.05), TD(2) = 0.058 × height (cm)+ 6.950(r=0.248, P<0.05), TD(3)=0.059 × height (cm)+ 7.052 (r=0.235, P<0.05), TD(4) =0.044× height (cm) + 8.520 (r=0.208, P<0.05). Conclusion: MSCT and MPR combined with special window technique are accurate and feasible for the measurement of adult tracheal diameter. The diameter of the trachea in males is larger than that in females, and it is positively correlated with height, but not with age, body weight and BMI. The tracheal diameter can be evaluated by linear regression equation.