A rapid method for the evaluation of diagnostic radioaerosol delivery systems

The effective delivery (ED) in MBq/min of a 100 MBq/ml nebuliser solution was defined as the rate of delivery of droplets in the respirable size range (aerodynamic diameter below 3.3 micron) to the mouthpiece of the aerosol delivery system (ADS). Wasted delivery (WD) was defined as the rate of delivery of droplets above 3.3 microns. ED and WD were measured on four types of commercially available ADS. The aerosols were sampled at the mouthpiece of each system and droplet size distribution measured with a seven stage cascade impactor. The effect of ambient air humidity on the droplet size produced by the Cadema delivery system was also evaluated. The ED values ranged from 6 to 15 MBq/min and WD values from 0.01 to 15 MBq/min. Two ADS produced low ED and WD values (6.1-9.0 and 0.01-0.07 MBq/min, respectively) due to a low output, while another produced higher ED and WD values [11.3 +/- 0.2 (SD) and 15.4 +/- 0.5 (SD) MBq/min, respectively] due to a larger droplet size. The Cadema delivery system gave the optimum characteristic of high ED [13.9 +/- 0.8 (SD) MBq/min] and low WD [1.24 +/- 0.61 (SD) MBq/min] values. The mass median aerodynamic diameter (MMAD) of the Cadema ADS fell by 22% (P less than 0.01) as the ambient dilution air was dried from a high relative humidity (RH) (88%-100%) to a low RH (12%-17%). The variability of both MMAD and geometric standard deviation (sigma g) was increased with dry dilution air (P less than 0.01).