Dynamic measures of regional lung air volume using phase contrast x-ray imaging

Abstract

Phase contrast x-ray imaging can provide detailed images of lung morphology with sufficient spatial resolution to observe the terminal airways (alveoli). We demonstrate that quantitative functional and anatomical imaging of lung ventilation can be achieved in vivo using two-dimensional phase contrast x-ray images with high contrast and spatial resolution (<100 microm) in near real time. Changes in lung air volume as small as 25 microL were calculated from the images of term and preterm rabbit pup lungs (n = 28) using a single-image phase retrieval algorithm. Comparisons with plethysmography and computed tomography showed that the technique provided an accurate and robust method of measuring total lung air volumes. Furthermore, regional ventilation was measured by partitioning the phase contrast images, which revealed differences in aeration for different ventilation strategies.

Establishing lung gas volumes at birth: interaction between positive end-expiratory pressures and tidal volumes in preterm rabbits

“…These lung gas volume measurements are accurate to within 25 μl, closely agreeing with plethysmograph measurements (23). The X-ray energy used was 24 keV and the imaging detector was placed 3 m downstream from the pups to optimize the phase contrast effects.…”

“…Phase contrast X-ray imaging techniques were used to measure lung gas volumes and the regional distribution of ventilation within and between successive breaths as previously reported (23). These lung gas volume measurements are accurate to within 25 μl, closely agreeing with plethysmograph measurements (23).…”

“…Distribution of tidal ventilation was determined from image analysis as previously described and validated (23). The position of the pup was tracked using skeletal landmarks and a fiducial marker.…”

“…This creates a pressure gradient that facilitates the movement of liquid across the distal airways into the surrounding tissue (19), from where it is cleared (13,20). Because hydrostatic pressure gradients facilitate lung aeration, we investigated the effect of PEEP and sustained inflations on lung aeration at birth in preterm rabbits (9,21,22) using synchrotron-based imaging techniques (23). These studies demonstrated that both pressure and the time over which the pressure is applied (pressure-time integral) are important for facilitating and maintaining FRC immediately after birth.…”

Effect of Sustained Inflation Length on Establishing Functional Residual Capacity at Birth in Ventilated Premature Rabbits

“…We have recently used phase contrast x-ray imaging to determine the rate and spatial pattern of lung aeration at birth in spontaneously breathing (10) and mechanically ventilated preterm rabbit pups (11). Using this technique, the entry of air into the lung and its spatial distribution can be imaged and measured breath-by-breath (12).…”