Abstract
Objective: The purpose of this study was to evaluate the effect of radiation dose reduction on the quantification of air trapping on expiratory CT. Materials and methods: This study was conducted as a retrospective evaluation of inspiratory and expiratory CT studies performed in routine clinical practice before and after alteration of the scanning protocol for expiratory CT at our institute. Eighty-six patients who had a clinical diagnosis of chronic obstructive pulmonary disease (COPD) and underwent inspiratory and expiratory CT and pulmonary function testing (PFT) were included. For the quantitative analysis, CT scans were obtained at six evenly spaced levels from the lung apices to the bases. The area of segmented lung without emphysema between －500 to －950 HU was obtained from the summation of six slices. The relative area between －900 and －950 HU for the area of the segmented lung (RA900-950) was calculated on both the inspiratory and expiratory scans. Comparisons of the RA-change between the standard-dose group (200 mA) and the low-dose group (80 mA) were performed by Mann-Whitney U test. Results: There was no significant difference between the standard-dose group and the low-dose group in the mean RA-change, and RA-change in both the standard-dose and low-dose groups correlated significantly with the results of PFT. In addition, there were no prominent differences in the correlation coefficients between the two groups. Conclusions: Low-dose CT could evaluate air trapping objectively and was not inferior to standard-dose CT for this purpose.
Highlights
Air trapping is indicating the retention of excess gas in the lung of expiration, and is well known that it is correlated with pulmonary function
Because small airway disease cannot be visualized directly with current radiographic techniques, the extent of air trapping on expiratory computed tomography (CT), or paired inspiratory and expiratory CT scans can be used to evaluate small airway obstruction [4]-[11]
We found that objective quantitative CT evaluation of air trapping was possible with low-dose CT
Summary
Air trapping is indicating the retention of excess gas in the lung of expiration, and is well known that it is correlated with pulmonary function. Because small airway disease cannot be visualized directly with current radiographic techniques, the extent of air trapping on expiratory CT, or paired inspiratory and expiratory CT scans can be used to evaluate small airway obstruction [4]-[11]. Bankier et al evaluated the effect of radiation dose reduction on the visual quantification of air trapping on expiratory CT [6]. Air trapping has been evaluated with objective quantitative methods using densitometric parameters such as the changes in relative percentage areas of certain attenuation values among entire lung volume between inspiratory and expiratory CT scans, or the ratio of the mean lung attenuation value of inspiration and expiration in previous studies [4] [7]-[10].
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