MRI of helium-3 gas in healthy lungs: posture related variations of alveolar size.
OBJECTIVE
To probe the variation of alveolar size in healthy lung tissue as a function of posture using diffusion-weighted helium-3 hyperpolarized gas imaging.


METHODS
Measurements 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.


RESULTS
The 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.


CONCLUSIONS
The posture dependent variations in ADC were attributed to compression of the parenchyma under its own weight and the mass of the heart.
Academic Unit of Radiology, The University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK.
Stanislao
S
Fichele
Neil
N
Woodhouse
Andrew J
AJ
Swift
Zead
Z
Said
Martyn N J
MN
Paley
Larry
L
Kasuboski
Gary H
GH
Mills
Edwin J R
EJ
van Beek
Jim M
JM
Wild
D000328:Adult; D006371:Helium; D006801:Humans; D001239:Inhalation; D008171:Lung Diseases / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011187:Posture; D011650:Pulmonary Alveoli / Q000033:anatomy & histology* / Q000502:physiology
D006371:Helium