Evaluation of time interval difference digital subtraction fluoroscopy in patients with cystic fibrosis.

In this study the potential of thoracic subtraction fluoroscopy has been evaluated on the basis of our experience with this functional imaging modality in patients presenting with cystic fibrosis. The method, which consists of subtracting dynamic digital fluoroscopic images of the breathing chest in the time interval difference (TID) mode, applies to the study of the lucency variations during the respiratory cycle and provides dynamic functional information about ventilation and/or perfusion and diaphragmatic kinetics, without any injection and with minimal irradiation. To assess the validity of the TID procedure, our results were compared with standard roentgenography, clinical data, and scintigraphic findings, with emphasis on the latter. The limitations and advantages of TID compared with scintigraphy are discussed. Three groups of discrepancies emerge which do not discredit TID. TID offers rather the advantage of providing anatomic pictures and unique dynamic information, which is emphasized.