Initial assessment of a simple functional image of ventilation.

Several methods for quantitatively measuring regional ventilation using an inert gas such as Xe133 have been described. One such method provides a functional image of washout. A particularly simple functional image may be derived from the mean transit time for clearance. Regional ventilation may thus be represented as a single image in which the spatial distribution of washout from multiple small regions of the lung is displayed. In 100 patients for whom such a functional image of ventilation was obtained, the functional image was found to be generally more useful and easier to interpret than sequential images taken during the period of washout. Distributions of half-time (t1/2) for washout and the mean transit time (t) in the same population were similar in shape, but the t distribution peaked about 15 sec later than the t1/2 distribution. The mathematical simplicity of the functional image described here should permit its implementation on virtually any nuclear medicine computer system.