Abstract
Since first suggested in 1964, 131I-labeled macroaggregated albumin (MAA) has been used as a pulmonary perfusion scanning agent. 99mTc has the favorable physical characteristics of high photon yield, low radiation dose and easily collimated 140 keV gamma-ray emission. Many reports have appeared in the literature on the preparation and use of 99mTc-MAA for lung scintigram. However, there has been technical difficulties that preclude the use of 99mTc-MAA in routine clinical practice. Recently, a kit for 99mTc-labeled stannous macroaggregated albumin has become supplied commercially.
The purpose of this study is to evaluate animal tissue distribution, clearance and clinical utility of 99mTc-Sn-MAA.
In comparison with 99mTc-human albumin microspheres which was the first commercially available agent of this type, its preparation is easier and labeling efficiency is better.
In experiment of mice, 96.5% of the particles were deposited in the lung and few per cent, which was in the liver and the kidney, was increased at 2 hours after injection. Biological clearance from the lung occurred with a T50% of about 7 hr contrary to the simultaneous increase in hepatic activity, in rabbits.
In clinical experience, the quality of lung image was excellent and lesions were more distinctly defined with 99mTc-Sn-MAA than 131I-MAA And no severe reactions were observed in a series of 124 patients with a variety of pulmonary disorders. Liver and kidney activity never interfered with interpretation of the lung scintigram obtained immediately after injection.
99mTc-Sn-MAA should prove to be a very useful agent for pulmonary perfusion imaging.
