Ventilation can be assessed by radioactive gas (e.g. xenon-133 or krypton-81m) or radiolabeled small particles (e.g. Technegas). Pulmonary blood flow is usually assessed with radiolabeled macroaggregated albumin or microspheres ( Diotefal 1.993). A typical application is the ventilation-perfusion scintigraphy used for the diagnosis of pulmonary emboli. A further development of the scintigraphic techniques has led to single-photon-emission CT where the gamma counter is moved around the body during the investigation and, if the condition under examination is stable, a two- or three-dimensional distribution of the isotope activity can be reconstructed.
Positron emission tomography can be used to estimate the lung blood flow, ventilation, ventilation-perfusion ratio, permeability to proteins, density of receptors, and many other biologically relevant aspects in vivo. However, this technique is an expensive research tool that is limited to a few research centers.
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