Dynamic pulmonary imaging: performance properties of a digital fluoroscopy system

The physical characteristics of dynamic pulmonary imaging with digital fluoroscopy, which differ from those in DSA equipment, have been determined. The spectral distributions and mean energies were calculated and corresponding exposures with varying high voltage and copper filtration (60-100 kVp, 0-2.83 mm Cu) were measured. The utilization of 90-100 kVp with a filter consisting of 1.39 mm Cu and 3 mm Al minimized disturbing skeletal artifacts and reduced the radiation exposure by a factor of approximately 5 in comparison with imaging at 60 kVp without copper filtration. Simultaneously, the measured signal decreased by about 25%. The mean energy of this spectrum exceeded that of 140 kVp chest imaging. The dynamic pulmonary imaging method produces logarithmically transformed x-ray transmittance values linearly related (r = -0.999) to water thickness between 7-10.5 cm, which is equivalent to the normal range of the chest in pediatric patients. A good linear correlation (r = 0.933,N = 92) was obtained when the change in transmitted radiation was compared with tidal volume measured in a rabbit model using a pneumotachometer. The results indicate that the method is applicable for quantitative measurements of pulmonary ventilation. Changes in tidal ventilation can be measured with this noninvasive x-ray imaging technique.