How do aerosols compare to xenon 133 for use in a ventilation scan?
133 Xe is a radioactive isotope of an inert noble gas. It can be inhaled into the lungs and will wash out quickly in a normal lung, although there will be persistent radiotracer activity (gas trapping) in parts of the lung affected by obstructive airways disease such as with asthma or chronic obstructive lung disease (COPD). These areas of gas trapping will typically correspond to matching perfusion defects on the perfusion scan, thereby increasing the specificity of the V/Q scan.
Radioaerosols are typically made from 99m Tc radiolabeled diethylene triamine pentaacetic acid (DTPA) particles suspended in air. Following inhalation, such aerosols are deposited on the lining of the alveolar spaces and therefore do not wash out. Although the presence of gas trapping in the lungs cannot therefore be assessed, the particles remain in the lungs and allow for images to be obtained in multiple projections that can be more easily compared to the perfusion images or via single photon emission computed tomography (SPECT) imaging.