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Abstract
Radioembolization is used in diagnostic imaging of the lungs and for radioembolization therapy of hepatic tumours. Presently, 99mTc labelled macroaggregates or microspheres of human serum albumin (HAM) are used for this purpose. Poly lactic acid (PLA) is biodegradable, like HAM, and, unlike HAM, is not a blood product. The aim of the present study was to evaluate the uptake and biodegradation of PLA microspheres in lungs. PLA (MW=48720Da) microspheres of 1.0-100mum (mean=39.5mum) in diameter were prepared by solvent evaporation frommethylene chloride. They were labelled with 99mTcby stannous chloride reduction at pH3, with an efficiency of 98%and a stability of 96%at 24h. For biodistribution studies, 15 mice were i.v. injected with 20muCi 99mTc-PLA microspheres in 0.1ml and sacrified at 15min, 1, 3, 6 and 24h (three at each time point). All the organs were removed, weighed and counted against a standard prepared from 1/100 dilution of the injected radioactivity. Some mice were similarly injected and sacrified at 30min, 15 and 30 days. The lungs were removed and frozen, and 10mum sections were obtained, stained with haemotoxylin and eosin and examined under a light microscope. Five rabbits were i.v. injected with 1mCi of 99mTc-PLA microspheres. Scintigrams were obtained at various intervals up to 24h. In mice, the lung uptake was significant at 30min-1h post-injection. In rabbits, the lungs were the only organs visualized up to 24h. Microscopic examination of tissue sections demonstrated slow biodegradation of PLA particles. In conclusion; (1) The high lung uptake obtained in mice and rabbits indicates the suitability of PLA microspheres for lung imaging, and (2) although the slow biodegradation rate might be a disadvantage in patients with lung disorders in diagnostic studies, it may be an advantage in therapeutic applications with radionuclides which have long physical half lives.
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