Tomosynthesis in pulmonary cystic fibrosis
Abstract: The aims of this thesis were to investigate whether chest tomosynthesis might be used in pulmonary cystic fibrosis, to design and validate a tomosynthesis scoring system, and to determine the effective dose from chest tomosynthesis in children. In a prospective study starting in 2008 clinical chest radiography or computed tomography (CT) were supplemented with a tomosynthesis examination of the lungs. Tomosynthesis findings were characterized in comparison with radiography and CT findings, and used to design a scoring system for tomosynthesis. Conversion factors for paediatric chest tomosynthesis were determined by Monte Carlo simulations and used to estimate the effective dose from the registered dose-area-product from the patient examinations included in the study. The typical imaging findings of pulmonary cystic fibrosis were much better depicted with tomosynthesis compared with radiography. Most pulmonary changes visualised with computed tomography could also be evaluated well with tomosynthesis. A dedicated tomosynthesis scoring system was designed and validated, and proved to be robust. Bronchiectasis and mucus plugging are the most specific pulmonary changes of cystic fibrosis, and were in a review of commonly used radiological scoring systems generally considered the most important scoring components. For chest tomosynthesis in children the conversion factor was considerably higher for young children than previously reported for adults. The conversion factor increased with increasing tube energy and filtration. The mean paediatric effective dose from posteroanterior chest tomosynthesis was 0.17 mSv, which is about 40 times less than recently reported effective doses from paediatric chest CT. Using the previously reported conversion factor for adults the paediatric effective dose was estimated to 0.11 mSv. Consequently, when using conversion factors not adapted to children for paediatric examinations, the radiation dose may be underestimated. Anteroposterior exposures should be avoided, as the effective dose is approximately three times higher than for posteroanterior exposures. In these studies tomosynthesis has been shown to be a valuable tool for monitoring pulmonary cystic fibrosis, as typical imaging findings of this lung disease are well depicted and the radiation dose is low. The dedicated scoring system may improve diagnostic precision. At our radiology department, tomosynthesis now has to a great extent replaced radiography in the follow-up of these patients. CT is only performed in selected cases. Further studies are planned to determine the roles of tomosynthesis and CT in the evaluation of cystic fibrosis lung disease.
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