The relations between expiratory chest CT using helical CT and pulmonary function tests in emphysema.

Abstract

Chest computed tomography (CT) and pulmonary function tests are usually used for the evaluation of emphysema. We performed the present study to evaluate more accurately the relationship between the degree of morphological change and the functional abnormality in emphysema. We used a helical CT apparatus to obtain the CT images both at full inspiration and full expiration. We classed the degree of emphysema into 5 grades (0-4) by visual observation on CT image obtained at the two levels, upper and lower fields, on each side. We assigned each of these grades a visual score. We also calculated the average ratio of CT numbers of each of the lung fields at full expiration to that at full inspiration for each level. We designated this the E/I ratio. We then examined the relationship between the findings acquired by each of these two methods and pulmonary function test results. The visual score showed correlations with FEV1(% predicted) (-0.592, p < 0.0001), RV/TLC(%)(0.425, p < 0.025), and DL(CO)/VA(% predicted)(-0.538, p < 0.0001). The E/I ratio showed correlations with FEV1(% predicted) (-0.620, p < 0.0001), 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 showed stronger correlation with RV/TLC(%) than did the visual score. The visual score may reflect the degree of emphysema, whereas the E/I ratio reflects the air trapping. These findings suggest that the helical CT is useful in the evaluation of emphysematous changes and that the E/I ratio reflects the air trapping.

Quantitative computed tomography assessment of lung structure and function in pulmonary emphysema

“…It was concluded that expiratory CT reflects expiratory airflow limitation and the subsequent air trapping more than reduction of the alveolar wall surface. These findings were confirmed by EDA et al [59] and by LAMERS et al [60] who also found higher correlations between PFTs reflecting the airflow obstruction and CT data obtained in expiration than in inspiration, whereas the correlations between diffusing capacity and CT data were similar.…”

“…In summary, expiratory CT is thus not as adequate as inspiratory CT for measuring the extent of pulmonary emphysema. This conclusion suggests that possible errors, secondary to variations of lung volume at which the CT scans are obtained, could be avoided by using spirometric triggering [53][54][55]59]. …”

Decreased computed tomographic lung density during exacerbation of asthma

“…They speculated that abnormalities in the expiratory CT are more reflective of air trapping than of a genuine reduction in terminal airspace volume. EDA et al [33] found that the helical CT images acquired at full expiration reflect air trapping and that CT visual scores at full inspiration showed significant correlation with emphysema. The cut-off point between areas of normal lung density and LAAs used was -950 HU.…”

Report of a workshop: quantitative computed tomography scanning in longitudinal studies of emphysema

“…A number of cross sectional studies [14,31,32,51] have shown moderate, statistically significant, inverse correlations between CT measures of severity of emphysema and both FEV1 and carbon monoxide diffusing capacity. For FEV1, the coefficient of correlation (r) ranged -0.41--0.57; for diffusing capacity, r was higher, ranging -0.54--0.65.…”