Measurement of inspiratory and expiratory lung density: a quantitative CT study in children under 5 years old

Objective To measure the average value of CT lung density at the phase of end inspiration and end expiration in children under 5 years. Methods Sixty patients with normal lungs who underwent chest CT for reasons caused by trauma etc. in our institute from January 2010 to March 2012 were enrolled to the study. All of the patients were divided into end inspiration group and end expiration group through random number table. CT images of the phase of end inspiration and end expiration were taken. Three levels of CT images were chosen to measure the lung density, which were 2 cm above the arch, 1 cm below the carina and 2 cm above diaphragm. Lung density was measured at anterior, posterior, lateral, medial and central of the images at each level in each lung. The average lung density of each and entire lung were respectively calculated. The influence of phase, level, location was quantified using analysis of variance methods and LSD method. Results The average lung density at end inspiration was(-766 ±56)HU for the left, right and both lung. At end expiration, the average lung density of the left, right and both lungs was(-625 ±86), (-647 ±85) and(-636 ±86) HU respectively. The average densities at anterior, posterior, lateral, medial and central of the left lung at end inspiration were(-798±63), (-733±68), (-767±64),(-754±65), (-775±63)HU respectively. The average densities at anterior, posterior, lateral, medial and central of the right lung were(-796±70), (-736±65), (-769±64), (-754±62), (-776±59) HU respectively. At end expiration phase, the average densities at anterior, posterior, lateral, medial and central of the left lung were(-692±91),(-555±116), (-639±91), (-598±103), (-640±98) HU respectively. The average densities at anterior, posterior, lateral, medial and central of the right lung were (-712±90),(-575±121),(-657±90), (-619±95), (-670±87) HU respectively. The statistical differences of these five measurement areas were significant at both inspiration and expiration phase (F=12.55, 11.29, 23.31, 25.47, P<0.01). The posterior lung density was the highest and the anterior was the lowest. As for the other measurement areas, in descending order were medial, lateral, and central. Conclusion The lung density at end inspiration and end expiration in children under 5 years old is described to provide reference for the clinical work. Key words: Child; Tomography, X-ray computed; Controlled ventilation; Lung density