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1 Lovelace Respiratory Research Institute, and 2 New Mexico Resonance, Albuquerque, New Mexico 87108; and 3 Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
We
partially obstructed the left bronchi of rats and imaged an inert
insoluble gas, SF6, in the lungs with NMR using a technique that clearly differentiates obstructed and normal
ventilation. When the inhaled fraction of O2
is high, SF6 concentrates dramatically in regions of the
lung with low ventilation-to-perfusion ratios (
A/
);
therefore, these regions are brighter in an image than where
A/
values are
normal or high. A second image, made when the inhaled fraction of
O2 is low, serves as a reference because the
SF6 fraction is nearly uniform, regardless of
A/
. The quotient of the first and second images displays the
low-
A/
regions and
is corrected for other causes of brightness variation. The technique
may provide sufficient quantification of
A/
to be a useful
research tool. The noise in the quotient image is described by the
probability density function for the quotient of two normal random
variables. When the signal-to-noise ratio of the denominator image is
>10, the signal-to-noise ratio of the quotient image is similar to
that of the parent images and decreases with pixel value.
perfusion; sulfur hexafluoride; lung; quotient; magnetic resonance imaging; probability density function; nuclear magnetic resonance
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