High resolution computed tomography in smoking induced disease

Abstract

Chronic obstructive pulmonary disease (COPD), usually caused by smoking, is common. It has high morbidity and mortality, and the prevalence is expected to increase. In Sweden about 500 000 individuals are affected, and COPD is the third most common cause of death among men. COPD is due to various combinations of small airway disease and emphysema. Early detected small airways disease is in contrast to emphysema potentially reversible. The overall aim with the thesis was to evaluate the potential of high resolution computed tomography (HRCT) to diagnose early smoking induced disease. We wanted to investigate I. if the disability of emptying the lungs at expiration, in terms of diffuse or focal retention of air, is a sensitive indicator of obstruction in bronchiolitisII. which type of parenchymal findings are to be expected in smokers, and to evaluate what happens to these findings when smoking is continued or stoppedIII. which factors influence the computerized quantification of mild emphysema, and validate a new software especially developed for this purposeIV. the relationship between the density of lung parenchyma and lung volume, and to evaluate whether it is possible to visually recognize full inspiration on HRCT images In study I-III healthy smokers and never smokers from a population study were investigated. HRCT was done twice, with a time elapse of six years. The lung was examined in full inspiration and at three levels in full expiration. In study I the general ability to exhale was investigated by a computerized method, and the focal visually. Neither the general nor the focal ability to exhale differed between smokers without emphysema and never smokers. No correlation to lung function tests sensitive to small airways disease was found. In study II emphysema and other HRCT variables related to smoking were evaluated visually. All variables except emphysema were also found in never smokers. Some variables were found in significantly more smokers, and increased at follow-up. No progress was seen in those who stopped smoking. In study III mild emphysema was analyzed by conventional and new software. The influence of slice thickness, reconstruction algorithm, motion artifacts and gravity was analyzed. The new software could separate the group with mild emphysema form those without. In study IV life long never smokers where investigated by HRCT at different levels of inspiration under spirometrical control. A great variation in lung attenuation at full inspiration was found. The relationship between lung attenuation and volume was inverse linear in the examined interval. It was not possible to visually evaluate if an image was taken in full inspiration or not. Conclusion: Images taken at expiration do not contribute to diagnosis of early smoking induced disease. Emphysema, but also parenchymal nodules and ground glass opacities, indicate smoking induce disease. The disease seems to cease when smoking is stopped. It is not possible to reliable quantify mild emphysema with conventional software. The problem may be solved with specially developed software and proper examination technique. It is not possible to visually evaluate if an image is taken in full inspiration or not. The detection of mild emphysema by HRCT may prevent the occurrence of obstructive ventilatory impairment by giving support for smoking cessation programs. Therefore, HRCT examination should be added to the basic investigation when smoking induced disease is suspected.