Extrapulmonary radioactivity in lung permeability measurements.

Area of Science:

• Nuclear Medicine
• Pulmonary Physiology
• Radiopharmacology

Background:

• Pulmonary epithelial permeability is assessed using the clearance rate of aerosolized technetium-99m diethylenetriamine penta-acetate ([99mTc]DTPA).
• Potential sources of non-pulmonary radioactivity, such as the chest wall and vasculature, may affect measurement accuracy.

Purpose of the Study:

• To determine if corrections for chest wall and pulmonary vascular radioactivity are required for accurate [99mTc]DTPA pulmonary clearance measurements.
• To evaluate the impact of non-pulmonary radioactivity on the assessment of lung epithelial permeability.

Main Methods:

• Studied five patients with unilateral lung ventilation to assess chest wall contribution to radioactivity.
• Measured [99mTc]DTPA aerosol clearance rates in normal hemithoraces, with and without chest wall correction.
• Quantified thoracic radioactivity after intravenous [99mTc]DTPA injection in adults and children to simulate high systemic radioactivity.

Main Results:

• Correcting for chest wall radioactivity resulted in a minor change in the average pulmonary clearance half-time (T1/2) from 56 min to 52 min.
• Thoracic radioactivity from intravenous [99mTc]DTPA was a small fraction (2.7%-11%) of that from lung deposition.
• The contribution of non-pulmonary radioactivity to overall thoracic counts is minimal.

Conclusions:

• Corrections for radioactivity in the chest wall and pulmonary vasculature are not necessary for accurate [99mTc]DTPA pulmonary clearance measurements.
• The study simplifies the methodology for assessing pulmonary epithelial permeability using [99mTc]DTPA scintigraphy.