• Stanislao Fichele, Neil Woodhouse, Andrew J Swift, Zead Said, Martyn N J Paley, Larry Kasuboski, Gary H Mills, Edwin J R van Beek, and Jim M Wild.
• Academic Unit of Radiology, The University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK.
• J Magn Reson Imaging. 2004 Aug 1; 20 (2): 331-5.

PurposeTo probe the variation of alveolar size in healthy lung tissue as a function of posture using diffusion-weighted helium-3 hyperpolarized gas imaging.Materials And MethodsMeasurements of the helium-3 apparent diffusion coefficient (ADC) were made on six healthy subjects. These were used to show the variation of alveolar size between the lowermost dependent regions of the lung compared to the uppermost regions of the lung in four postures: supine, prone, left-lateral decubitus, and right-lateral decubitus.ResultsThe distribution of acinar size in the lungs was found to be heterogeneous, and influenced by lung orientation. In nearly all postures, the ADC was significantly higher in the non-dependent uppermost regions of the lung compared to the dependent lowermost regions of the lung; the greatest variation was found in the left-lateral decubitus position. The difference in ADC between uppermost and lowermost regions was on average 0.012 cm(2)second(-1), which represents 20% of the average ADC value for the whole lung. A systematic decrease in ADC from the apex of the lung to the base was also found, which corresponds to an inherent gradient in alveolar size.ConclusionThe posture dependent variations in ADC were attributed to compression of the parenchyma under its own weight and the mass of the heart.

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