Tc-99m DTPA (aerosol)

Tc-99m DTPA (diethylenetriamine-pentaacetic acid) (aerosol) is one of the technetium agents and is used in VQ imaging.

Characteristics

• photon energy: 140 KeV
• physical half life: 6 hours
• biological half life: 1 hour
• normal distribution: lungs
• pharmacokinetics:
  • aerosol deposited in bronhoalveolar spaces and diffuses into capillaries
• excretion: renal
• target organ: lungs

Uses, doses and timings

• V/Q ventilation
  • adult dose: 1.11 GBq (30 mCi), (1.665 GBq (45 mCi) if after perfusion) in 3 mL saline nebuliser
  • timing: image immediately for 5 minutes

History

DTPA is a potent chelator of metals. In the 1950s and 60s, aerosolised DTPA had been studied as a way to chelate inhaled radioactive metals, as nuclear power, and thus the presence of, and possible exposure to, radioactive metals were becoming more commonplace ¹.  The DTPA would chelate the inhaled radioactive metal, subsequently be absorbed into the blood stream, and finally be excreted in the urine with the chelated radioactive metal.

With the development of inexpensive small plastic nebulizers allowing submicron aerosols in the 1970s, DTPA was considered an appealing alternative to Xe-133 (half-life 5 days) or Kr-81m (half-life 13 seconds) for ventilation imaging. The Nuclear Regulatory Commission was petitioned to allow for the use of aerosols of Tc-99m-DTPA for inhalation studies, which it approved in 1983 ².