Imaging obstructed ventilation with NMR using inert fluorinated gases

We partially obstructed the left bronchi of rats and imaged an inert insolu ble gas, SF6, in the lungs with NMR using a technique that clearly differen tiates obstructed and normal ventilation. When the inhaled fraction of O-2 is high, SF6 concentrates dramatically in regions of the lung with low vent ilation-to-perfusion ratios (Va/Q); therefore, these regions are brighter i n an image than where VA/Q values are normal or high. A second image, made when the inhaled fraction of O-2 is low, serves as a reference because the SF6 fraction is nearly uniform, regardless of VA/Q. The quotient of the fir st and second images displays the low-VA/Q regions and is corrected for oth er causes of brightness variation. The technique may provide sufficient qua ntification of VA/Q 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 denomin ator image is >10, the signal-to-noise ratio of the quotient image is simil ar to that of the parent images and decreases with pixel value.