What is the lung mechanism of localization when using Tc DTPA?

• A. Filtration
• B. Compartmental
• C. Active transport
• D. Dissolution

Answer: (B)

The lung mechanism of localization for Tc DTPA (technetium-99m diethylenetriaminepentaacetic acid) is best described by the compartmental mechanism. Tc DTPA is a radiopharmaceutical commonly used for lung scanning, particularly in the evaluation of pulmonary function and assessments of ventilation.

In this mechanism, the radiotracer is inhaled into the lungs and subsequently moves into the alveolar spaces. The uniform distribution of Tc DTPA throughout the lung parenchyma is primarily due to the passive diffusion through the alveolar-capillary membrane rather than any active process. Since the compound is large and water-soluble, it does not get absorbed into the surrounding tissues, and thus remains relatively confined to the pulmonary compartment, allowing for clear imaging.

This compartmental localization is critical in lung imaging as it provides a specific insight into regional lung function, helping clinicians evaluate conditions such as obstructive and restrictive lung diseases, pulmonary embolism, and other disorders affecting lung ventilation.