Wash In Equilibrium tl If

Wash Out

Figure 6. Xenon-133 ventilation study in the posterior projection demonstrating decreased ventilation within the left lung on wash-in and equilibrium images (arrowheads). On serial wash-out images diffuse air-trapping is present within the left lung (arrow).

biological distribution of activity. When inhaled, both agents distribute homogeneously within the lung proportional to regional lung ventilation and very little central deposition of activity is seen even in patients with COPD. Pertechnegas readily penetrates the alveolar epithelial membrane and the biological half-life in the lungs is quite short measuring approximately 6-10 minutes. On the other hand, there is very little transalveolar or mucociliary clearance of Technegas and the effective half-life approaches the physical half-life of the 99mTc label. Both agents require minimal patient cooperation and only 2-3 breaths are required to obtain sufficient counts in the lungs to perform ventilation imaging. In general, ventilation imaging with both Technegas and Pertechnegas is performed prior to perfusion imaging. Similar to 99mTc-radiolabeled aerosols, views of the lungs are obtained in multiple projections corresponding to the views obtained during perfusion imaging.

Thrombus Imaging

More recently, there has been considerable interest in radiolabeled antibody fragments and peptides directed against the GPIIb/IIIa receptor on activated platelets. The platelet aggregation process, which occurs in arterial and venous thrombosis,

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