Technegas (technetium Tc-99m labelled carbon inhalation aerosol)

Technegas is an inhaled ventilation agent generated at the bedside: a Technegas generator flash-heats dried Tc-99m pertechnetate in a carbon crucible at roughly 2,700 C in argon, producing technetium encapsulated in carbon nanoparticle agglomerates measured at 60-160 nm, themselves built from 7-23 nm primary particles, with a radioactivity aerodynamic diameter below 500 nm. That size is the point: unlike a wet aerosol such as Tc-99m DTPA, which impacts in the central airways and gives hot spots in obstructive disease, Technegas distributes to the lung periphery and holds still long enough to image in multiple projections.

The FDA approved Technegas on 29 September 2023 under NDA 022335, held by Cyclomedica Australia, after decades of use elsewhere. The approved indication is narrow and precise: used with sodium pertechnetate Tc-99m in the Technegas Plus System, it is a radioactive diagnostic agent for adults and paediatric patients aged 6 years and older for visualisation of pulmonary ventilation and evaluation of pulmonary embolism when paired with perfusion imaging. Dosing is count-rate driven rather than fixed: 400-1,000 MBq (10.8-27 mCi) is loaded in the crucible to reach a lung count rate of 1,500-2,500 counts per second for adults, 500-1,000 for children, with inhalation completed within 10 minutes of preparation.

The US registration study, CYC-009 (NCT03054870), was a phase 3 non-inferiority comparison against xenon-133 planar ventilation imaging; its ClinicalTrials.gov record shows 226 participants actually enrolled and a terminated status. The label itself specifies imaging with a gamma camera and a low-energy collimator and does not use the words SPECT or planar, though the agent's stability in the lung is exactly what makes V/Q SPECT practical, and the EANM V/Q SPECT guideline is built around it.