Reproducibility of pulmonary structures on conventional chest films

All available chest films of 26 patients with pulmonary noduli (3 to 15 mm in diameter) were compared. Great variations in the appearance of one and the same nodule was noted. On 7 films the nodule could not be detected at all, in spite of the fact that other films taken in the same geometric projection did show it and no technical faults were apparent. Blurring caused by pulsating pulmonary blood flow and minute variations in the background surrounding the noduli are considered to be the main causes of a certain 'from exposure to exposure' variability of the conventional chest film.