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Phase Contrast X-ray Imaging of the LungsConventional X-ray imaging relies upon differences in X-ray absorption to provide image contrast of internal anatomy. The contrast between soft tissues is often too poor to detect subtle changes in tissue structure, which are often associated with disease. This is particular true of the air-filled lung since the average tissue density is already very low. However, recent developments pioneered at synchrotron radiation facilities around the world have shown that soft tissue contrast can be enhanced with the use of partially coherent radiation. Use of coherent radiation enables subtle differences in tissue structure to be rendered visible by exploiting small differences in the refractive indices between tissues. Phase Contrast X-ray Imaging is the collective title under which the various methods of producing refraction-sensitive images are categorized. These imaging methods exploit the relatively large change in refractive index between the air/tissue boundaries to reveal the lung with incredible contrast [1-5]. Moreover, the spatial resolution afforded by X-ray imaging makes it possible to observe the smallest respiratory units (alveoli) where gas exchange occurs[6]. Physicists from the School of Physics and the Monash Centre for Synchrotron Science have teamed up with Physiologists from the Department of Physiology (at Monash) and Neonatologists from the Royal Women’s Hospital to investigate novel phase contrast X-ray imaging techniques for studying lung development, physiology and disease states using coherent synchrotron radiation. In particular, this collaborative effort seeks to understand the mechanisms by which the lungs aerate at birth, which is critical to the survival of all neonates. Insight into this complex process will enable clinicians to provide better care for infants born preterm with under-developed lungs, thereby increasing their survival rate. Phase contrast imaging experiments have enabled lung aeration to be observed in rabbit pups in vivo, using the SPring-8 synchrotron facility in Japan. One particular experiment is dynamically illustrated in the movies shown on this webpage. Two movies show sequences of phase contrast images of very preterm rabbit pups (delivered by caesarian section) being mechanically ventilated for their first breaths. In the first movie air can be seen to fill the major airways, but little air remains trapped in the minor airways, thereby preventing significant gas exchange. In the second movie an initial sustained inflation of 20s duration is given to the pup before commencing normal ventilation. This technique ensures the lungs reach a critical “functional residual capacity” such that gas exchange can occur.  Ventilation Strategy: 5cmH2O PEEP, no sustained inflation.  Ventilation Strategy: 5cmH2O PEEP, 20s sustained inflation. Dr Marcus Kitchen has developed new methods of extracting quantitative information from various phase contrast imaging modalities. This work has been critical for the study of lung development. He has successfully devised a method of calculating regional volumes of lung aeration from 2D images sequences of newborn rabbit pups [7]. This information is crucial for assessing the rates and patterns of lung aeration at birth.
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