Pulmonary scintigraphy is an examination method of nuclear medicine. It allows a functional examination of the lungs. Depending on the problem, ventilation scintigraphy, lung perfusion scintigraphy, or combined ventilation-perfusion scintigraphy is performed. The actual function of the lungs is gas exchange, which occurs in three steps: Ventilation, diffusion, and perfusion.
- Perfusion: blood flow to the lungs occurs via the vasa publica (small circuit containing venous blood from the body that is transported to the lungs for oxygenation/oxygenation) and via the vasa privata (vessels native to the lungs that supply lung tissue; inflammation or tumors are also supplied via these vessels). Perfusion scintigraphy uses radioactively labeled particles whose size of 15-40 µm is slightly larger than the diameter of the pulmonary capillaries (approx. 8 µm). For intravenous application (administration into the vein) of the particles, their number is estimated to block approximately every 1,000th capillary. Radiopharmaceuticals (radioactive drugs) of choice are 99mTc-MAA (macro-aggregated albumin particles). Perfusion scintigraphy is particularly well suited for imaging an intrapulmonary right-to-left shunt (disruption of the circulation of the lung in which deoxygenated blood from the venous limb of the circulation passes directly into the arterial limb of the circulation).
- Ventilation: ventilation describes gas exchange in the respiratory tract and can be detected by inhalation of radioactive noble gases or radioactive aerosols. Today, the latter method is used, usually with 99mTc-percentate vaporized on graphite and given for inhalation so that the airborne particles reach the alveoli where they can be quantified. Ventilation scintigraphy with 99mTc aerosol is usually followed by perfusion scintigraphy with 99mTc-MAA. This method is particularly indicated in cases of V. a. (suspected) acute thromboembolism (a thrombus (blood clot) leads to embolism, i.e., partial or complete occlusion of a blood vessel of the lung).
- Diffusion: quantification of diffusion is more difficult and is usually done by recording the reabsorption of liquid (fluid) particles from the alveoli (pulmonary alveoli) and terminal bronchioli (resorptive clearance of the lung in the terminal small branches of the bronchi). Disease patterns with increased alveolar permeability include pneumonia, allergic alveolitis, radiation pneumonitis (synonym; irradiation pneumonia; this is an interstitial pneumonia (pneumonia that affects the interstitium, i.e., the narrow connective tissue of the lungs). i.e., the narrow layer of connective tissue between the alveoli and the blood vessels), which can occur after large-volume irradiation in a radiatio (radiotherapy) as an acute or chronic side effect), etc.
In addition, the lungs have self-cleaning mechanisms such as macrophage activity or mucociliary transport of mucus and invaded particles out of the bronchi. This mucociliary clearance can also be detected by scintigraphy, although its clinical use is rather limited today. Both ventilation scintigraphy and lung perfusion scintigraphy are presented below.
