THE RELATIONS BETWEEN EXPIRATORY CHEST CT USING HELICAL CT AND PULMONARY-FUNCTION TESTS IN EMPHYSEMA

Chest computed tomography (CT) and pulmonary function tests are usuall y used for the evaluation of emphysema. We performed the present study to evaluate more accurately the relationship between the degree of mo rphological change and the functional abnormality in emphysema. We use d a helical CT apparatus to obtain the CT images both at full inspirat ion and full expiration, We classed the degree of emphysema into 5 gra des (0-4) by visual observation on CB image obtained at the two levels , upper and lower fields, on each side. We assigned each of these grad es a visual score. We also calculated the average ratio of CT numbers of each of the lung fields at full expiration to :hat at full inspirat ion far each level. We designated this the Ell ratio. We then examined the relationship between the findings acquired by each of these two m ethods and pulmonary function test results. nle visual score showed co rrelations with FEV(1)(% predicted) (-0.592, p < 0.0001), RV/TLC(%)(0. 425, p < 0.025), and DL(CO)/VA(% predicted)(-0.538, p < 0.0001). The V I ratio showed correlations with FEV(1)(% predicted) (-0.620, p < 0.00 01), RV/TLC(%)(0.661, p < 0.0001), and DL(CO)/VA(% predicted) (-0.299, p < 0.05). Compared with the E/I ratio, the visual score showed much higher correlation with DL(CO)/VA(% predicted), but the E/I ratio show ed stronger correlation with RV/TLC(%) than did the visual scare. The visual score may reflect the degree of emphysema, whereas the E/I rati o reflects the air trapping. These findings suggest that the helical C T is useful in the evaluation of emphysematous changes and that the E/ I ratio reflects the air trapping.