Practical Aspects of Imaging Techniques Employed to Study Aerosol Deposition and Clearance

Since the last edition of this book in 2004, a number of changes have occurred in the areas of aerosol characterisation and methods for imaging the lung. Techniques to measure aerosol performance characteristics, required to support, confirm, and correlate with imaging outcomes of dose and distribution have been further developed with improved accuracy in outcomes. However, the need by investigators for correlating in vitro sizing measurements with in vivo imaging outcomes and clinical response still remains an elusive goal for a number of reasons. The human lung is not a cascade impactor, the resolution of 2D and 3D imaging tools is far below the actual airway dimensions of the distal airways of the lung, and variables related to lung disease, which are not incorporated into any in vitro lung deposition model, play the major role in determining regional airway deposition and clearance of inhaled medicinal products. Imaging studies are still not required by US and Canadian regulatory agencies when pharmaceutical companies seek approval for a therapeutic aerosol to treat respiratory disease, but this could change with better substantiated procedures to support the imaging outcomes. In Europe, imaging studies are, however, considered supportive information.