Abstract
Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition in complex models of lungs. It allows not only the evaluation of regional deposition characteristics but also precisely detects deposition hot spots. The method is based on a detection of a pair of annihilation photons moving in opposite directions as a result of positron – electron interaction after the positron emission decay of a suitable radioisotope. Liquid di(2-ethylhexyl) sebacate (DEHS) particles tagged with fluorine-18 as a radioactive tracer were generated by condensation monodisperse aerosol generator. Aerosol deposition was measured for three different inhalation flowrates and for two sizes of particles. Combination of PET with Computed Tomography (CT) in one device allowed precise localisation of particular segments of the model. The results proved correlation of deposition efficiency with Stokes number, which means that the main deposition mechanism is inertial impaction. As a next task the methodology for tagging the solid aerosol particles with radioactive tracer will be developed and deposition of porous and fiber aerosols will be measured.
Highlights
Inhaled aerosolized medication has a great potential to contribute to more effective, comfortable and cheaper treatment of both lung and systemic diseases
The results proved correlation of deposition efficiency with Stokes number, which means that the main deposition mechanism is inertial impaction
Particle may deposit by the effect of following deposition mechanisms: 1) interception – when particle following its natural gas streamline contacts the surface of lungs due to its physical size 2) inertial impaction – when air changes its direction, high inertia particles are unable to follow the streamlines, they continue in straight direction and deposit on the lung surface 3) sedimentation – settling of particles due to gravitational forces in smaller airways with low air velocities 4) diffusion – predominant deposition mechanism for submicrometer particles
Summary
Inhaled aerosolized medication has a great potential to contribute to more effective, comfortable and cheaper treatment of both lung and systemic diseases. General description of mechanisms controlling deposition of aerosol in human lungs was published by Lippmann [1] Swift [2] and Heyder [3]. Particle may deposit by the effect of following deposition mechanisms: 1) interception – when particle following its natural gas streamline contacts the surface of lungs due to its physical size 2) inertial impaction – when air changes its direction, high inertia particles are unable to follow the streamlines, they continue in straight direction and deposit on the lung surface 3) sedimentation – settling of particles due to gravitational forces in smaller airways with low air velocities 4) diffusion – predominant deposition mechanism for submicrometer particles. The aerosol deposition induced by inertial impaction is usually expressed in terms of Stokes number, which is defined as:
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