A generator for the production of radiolabelled ultrafine carbonaceous particles for deposition and clearance studies in the respiratory tract

A generator for the production of radiolabelled ultrafine carbonaceous particles for inhalation and clearance studies is described. A Technegas generator in combination with 99m99mTc labelling is a device used in clinical routine to investigate the ventilation of the human lung. However, under standard operating conditions the Technegas generator does not provide ultrafine particles with a stable radiolabel. The removal of saline from the Tc-eluate by an ion exchange column yielded low leaching rates of the radiolabel from the particles of below 4% within 24 h (12% under standard conditions) and guaranteed non-hygroscopic aerosol properties. Short burning times (2 s; standard 15 s) and immediate dilution of the generated aerosol into a conductive bag yielded stable ultrafine particles in the size range between 40 and 100 nm count median diameter (standard 200 nm), with a geometric standard deviation of 1.6. We adapted the generator to a bolus inhalation system, allowing regional aerosol deposition into different lung regions and appropriate clearance studies. In addition the particles can be labelled by 111111In instead of 99m99mTc, extending the investigation time of clearance studies from 1 day to some weeks.