We have compared the distribution in the lungs of submicronic aerosols of either Tc-99m sulfur colloid or Tc-99m DTPA immediately after inhalation with the distribution 20 minutes later in 83 patients. Thirty-two of the 83 patients were active smokers. Of the 28 smokers who received Tc-99m DTPA aerosol, the total lung count fell by a mean of 27 plusmn; 14percnt; between the 0 and 20 minute image. Eleven of these patients also had a major change in distribution of isotope during this time. In the nonsmoking patients total lung counts from Tc-99m DTPA fell by only 16 plusmn; 8percnt; and none had a major change in distribution pattern. None of the smoking or nonsmoking patients who received Tc-99m sulfur colloid had a significant change in count rate or distribution pattern over 20 minutes. The effects on the ventilation images of these rapid changes in count rate and distribution pattern after Tc-99m DTPA aerosol can be minimized by completing the ventilation study as quickly as possible after inhaling Tc-99m DTPA or by using a nondiffusible agent such as Tc-99m sulfur colloid.
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