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IMPORTANCE
OF PARTICLE SIZE
Conventional
radioaerosol delivery systems utilise venturi nebulizers that
deliver a broad spectrum of particle sizes at high pressure to the
patient in the range of 1 to 5 microns, with an MMAD of 3-4
microns. In order to achieve satisfactory alveolar deposition,
systems based on the venturi principle require the large particles to
be removed before the patient breathes in the aerosol. Incorporating
baffles, settling bags or subjecting the airflow within the nebulizer
to a swirling pattern may achieve this.
These
systems suffer from inefficient use of the Tc-99m DTPA, as the 'dead
volume' is typically 50% or more of the added dose. Moreover, due to
the relatively high particle size variation of these systems, a
significant proportion of the generated aerosol is unusable, as the
circuit will baffle it out.
Systems
with inadequate baffling will result in poorer image quality with
relatively high uptake in the throat, oesophagus, stomach and central airways.
SmartVent
does not suffer from these inefficiencies. The starting MMAD is 2.2
microns at the generator level, with a delivered MMAD of 1-1.5
microns. This, combined with the virtual zero dead volume, results in
a delivery efficiency that is 4 to 8 times better than conventional
radioaerosol delivery systems, with exceptional image quality.
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