Aerosol deposition and clearance measurement: a novel technique using dynamic SPET

Planar gamma camera scintigraphy is a well-established technique for charac terising the deposition and clearance of radiolabelled aerosols. While sing le-photon emission tomography (SPET) can offer superior assessment of radio aerosol deposition and better differentiation between peripheral and centra l deposition, the long acquisition times of single-headed SPET have largely prevented its use for measuring clearance or deposition of fast-clearing r adioaerosols. This study investigated the feasibility of fast dynamic SPET imaging (1 min/frame) using a three-headed gamma camera to assess the regio nal and total deposition and clearance of different radioaerosols over a pe riod of 26 min. Six subjects inhaled nebulised technetium-99m diethylene tr iamine penta-acetic acid radiolabelled aerosols with small and large drople t sizes [mass median aerodynamic diameter (MMAD) 3.2 +/-0.2 and 6.5 +/-0.2 mum, span 1.8 and 1.7, respectively] and in normal (0.9%) or hypertonic (7% ) saline with controlled breathing on four separate occasions. The penetrat ion indices (Pls) calculated from the SPET data for normal saline were 0.50 +/-0.04 and 0.36 +/-0.02 for the small and large droplet sizes, respective ly. Consistent with the hygroscopic growth of the hypertonic aerosols, the PIs for hypertonic saline were lower, at 0.43 +/-0.02 and 0.34 +/-0.02 for the small and large droplet sizes, respectively. PIs calculated from the pl anar data showed similar trends, but failed to detect the significant diffe rence seen with SPET between small normal and small hypertonic saline radio aerosols. In conclusion, the feasibility of using fast dynamic SPET for ima ging radioaerosol deposition and associated radiolabel clearance in the lun g has been successfully demonstrated. The fast SPET was able to reveal impo rtant differences in aerosol deposition that were not detected by planar im aging.