Revision as of 11:33, 2 October 2019

Aerosol deposition in the human upper airways

Application Challenge AC7-01 © copyright ERCOFTAC 2019

Test Data

Overview of Tests

Major portions of this section were adopted from Lizal et al. (2015). The positron emission tomography (PET) method provides the best spatial resolution (among radiological methods). In addition to local deposition in the various sections, the deposition hot spots can also be evaluated. However, in comparison to the PET methodology, which is routinely applied to clinical examination, using this method in the in vitro design requires major modiﬁcations both in the aerosol preparation and, in particular, in the experiment evalu— ation approach. The method, based on PET and fulﬁlling the above mentioned criteria, is presented in the following.

The aerosol exposure procedure

It is a common practice to coat the inner surface of the model, especially when using solid particles, to prevent bouncing of the particles hitting the surface. Since we used liquid di-ethylhexyl sebacate (DEHS) particles, we did not need to coat the inner surface of the model. Another reason for the coating is to prevent surface wetting. In our case the exposure time was short (5 to 15 mins) and only small amounts of DEHS deposited on the walls, therefore the possible ﬂooding of the surface was not an issue. Aerosol particles were generated by a TSI 3475 Condensation Monodisperse Aerosol Generator (CMAG) from TSI, Inc., which works on the controlled heterogeneous condensation principle. Vapours of a suitable material, speciﬁcally DEHS, condense by a controlled method on small sodium chloride particles serving as the condensation nuclei. The advantage of DEHS is that it is not hydrophilic and does not evaporate, resulting in a constant size of generated particles. In a standard operating mode, the generator can produce particles with aerodynamic diameters within the 0.1 to 8μm range. The density of DEHS used for the experiments was 0.914 g/cm³ at 25°C. Radioactive aerosol particles were needed for the PET measurement of deposition. Therefore, the solution in the atomizer of the generator had to be tagged by a suitable radioactive substance. Fluorine 18 was the logical Choice of the positron emitter, being easily available at the cooperating PET center and possessing a suitable half-life (109 minutes). A solution of ﬂuorine 18 in the form of ﬂuoride ions was prepared by irradiation of H₂¹⁸0 enriched water on an IBA Cyclone 18/9 cyclotron (irradiation time 25 min7 integrated irradiation current 11 μAh) at the UJV Rez7s PET Centre in Brno. The irradiated water was transferred by a capillary transport system to a shielded dispensing box, where the ﬂuorine 18 ions were captured on an ion—exchange resin (AG1—X8, BioRad) column and subsequently eluted with 300 ml of 10% sodium Chloride solution, followed by 1A ml of water for injection. The resulting solution was repeatedly diluted with water for injection until the desired initial radioactivity was achieved. The CMAG was modiﬁed for the deposition measurement by using PET so that the atomizer vessel was accommodated in a protective lead container to shield of ionizing radiation. The atomizer was ﬁlled with a sodium Chloride solution containing ¹⁸F at an initial activity of 2.5 GBq. The concentration of sodium Chloride solution was 20 mg/L. The experimental rig is shown in Figure 5.

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