TC-99M LABELED MICRO-AEROSOL PERTECHNEGAS - A NEW AGENT FOR VENTILATION IMAGING IN SUSPECTED PULMONARY EMBOLI

In this preliminary study, four patients suspected of having pulmonary emboli underwent ventilation imaging after inhaling approximately 1 m Ci (37 MBq) of Tc-99m Pertechnegas (micro aerosol carbon particles lab eled with Tc-99m) in five breaths or less. Planar images in multiple p rojections were recorded for preset counts. A final posterior image wa s acquired to evaluate residual lung background activity. Immediately following ventilation imaging, perfusion imaging in the identical proj ections was performed using 4 mCi (148 MBq) of Tc-99m MAA. Two of the four patients demonstrated matched uniform ventilation and perfusion a nd two showed segmental ventilation-perfusion ''mismatched'' defects c onsistent with pulmonary emboli. In each case, residual Pertechnegas b ackground lung activity (count rate) at the end of the last ventilatio n image was less than 10% of the initial Tc-99m MAA counts (count rate ). The advantages of Pertechnegas, in comparison to aerosolized DTPA, include: less residual ventilation image activity superimposed on the MAA perfusion images, reduced demand for patient cooperation due to fe wer required breaths (five or less), and lack of deposition of activit y in the central airways. The authors conclude that Pertechnegas has p roperties that make it ideally suited for routine lung ventilation ima ging.