***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: PURPOSE The purpose of this study was to directly and prospect ively compare the capability of dynamic O(2)-enhanced MRI and quantitatively assessed thin-section MDCT to assess smokers ' COPD in a large prospect i ve cohort . MATERIAL S AND METHODS The GOLD criteria for smokers were used to classify 187 smokers into four clinical stage groups as follows : smokers without COPD ( n=56 ) and with mild ( n=54 ) , moderate ( n=52 ) and severe or very severe COPD ( n=24 ) . All smokers underwent dynamic O(2)-enhanced MRI , MDCT and pulmonary function tests .  Mean relative enhancement ratio and mean wash-in time on MRI and CT-based functional lung volume ( CT-based FLV ) as well as the ratio of airway wall area to total airway area on MDCT were computationally calculated . Then , all indexes were significantly correlated with functional parameters . To determine the efficacy of all indexes for clinical stage classification , the indexes for the four clinical groups were statistically compared by using Tukey 's honestly significant difference multiple comparison test . RESULTS All indexes had significant correlations with functional parameters ( p<0.0001 ) . All indexes except CT-based FLV in all groups had significant differences each other ( p<0.05 ) . CONCLUSIONS Dynamic O(2)-enhanced MRI for assessment of COPD in smokers is potentially as efficacious as quantitatively assessed thin-section MDCT Computed Tomography ( CT ) has been proved to be the most accurate imaging modality to diagnose emphysema in vivo . Our study was aim ed at comparing different CT methods for pulmonary emphysema quantification in patients with severe chronic obstructive pulmonary disease ( COPD ) . Forty-six consecutive in patients affected with COPD underwent high resolution CT ( H RCT ) .  Three scans were acquired at 3 preselected anatomic levels at both full inspiration and expiration . Three different observers were asked to subjectively evaluate , under blind conditions , the extent alone and both the severity and the extent of emphysema on the 6 scans . H RCT findings were also analyzed quantitatively by measuring the mean CT number in Hounsfield Units ( HU ) and the % of lung area with CT numbers < -900 HU ( pixel index ) . Quantitative CT data were compared with reference values obtained in 7 normal nonsmokers . The CT visual score of emphysema exhibited medium-high interobserver reproducibility with correlation coefficients ranging from 0.80 to 0.96 and a good correlation with pulmonary function tests , particularly relative to the assessment of the extent of emphysema alone as expressed by one observer . CT quantification demonstrated an excellent correlation with functional indices of expiratory airflow , lung volumes and diffusion coefficients ( p < 0.001 ) . The expiratory measurements were better than the inspiratory ones while the analysis of both CT number and pixel index gave comparable results . Only the CT expiratory quantitative data allowed to differentiate the patients affected with COPD from the controls . In conclusion , the severity of emphysema as expressed by CT correctly reflects the functional impairment of patients with severe COPD . ( ABSTRACT TRUNCATED AT 250 WORDS 
    Output:
    
Conclusions CT measurements of emphysema or peripheral airways are significantly related to airflow obstruction in COPD patients .
CT provides a morphological method to investigate airway obstruction in COPD .Key Points• Computed tomography is widely performed in patients with chronic obstructive pulmonary disease ( COPD ) • CT provides quantitative morphological methods to investigate airflow obstruction in COPD • CT measurements correlate significantly with the degree of airflow obstruction in COPD • Expiratory CT measurements correlate more strongly with airflow obstruction than inspiratory CT• Low-dose CT decreases the radiation dose for diagnosis and quantitative emphysema