[Clinical application of 133-Xe ventilation scintigraphy]

Xenon-133 ventilation scintigraphy provides three sets of scintigrams: wash-in, equilibrium, and washout images. Krypton-81m or 99mTc-Technegas can be used as alternatives depending on their physical characteristics and the purpose of scintigraphy. Xenon-133 scintigraphy is compatible with SPECT when a multi-detector gamma camera is used. Ventilation images are analyzed by the height/area method to calculate regional lung volume and the mean transit time of the posterior planar view. If perfusion scintigraphy is done during the same examination, a ventilation/perfusion ratio image is also obtained. Factor analysis is applicable to the washout phase and permits a more detailed depiction of uneven ventilation. Series of consecutive SPECT during washout (dynamic SPECT) visualize ventilation in cross section and provide three-dimensional images of regional lung volume and poorly ventilated areas. A major indication for 133Xe scintigraphy is acute pulmonary thromboembolism (PTE) when used in combination with perfusion scintigraphy. The scintigraphic diagnosis of PTE is not inferior to that of contrast-enhanced helical CT, although the latter was initially reported to have higher sensitivity and specificity than scintigraphy. Other important indications are differentiation between primary pulmonary hypertension and chronic pulmonary thromboembolism, and the prediction of postoperative pulmonary function. Ongoing trials are attempting to create functional images of ventilation by CT or MRI, both of which may become rivals of scintigraphy because of their higher image resolution.