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Radiochemistry of macroaggregated albumin and newer lung scanning agents

1971; Elsevier BV; Volume: 1; Issue: 2 Linguagem: Inglês

10.1016/s0001-2998(71)81013-9

1558-4623

G.V. Taplin, Norman S. MacDonald,

Radiation Dose and Imaging

The original development of human serum 131I albumin macroaggregates for lung scanning began at the UCLA Laboratory of Nuclear Medicine and Radiation Biology in January 1963 as an extension of previous work on shortening and simplifying Benacerraf's 3-day protocol for preparing colloidal size 131I albumin to a I-hr clinical laboratory procedure. Solutions of human serum albumin can be converted to molecular aggregates of any desired size range from 10 nm to 100 μ or larger by combinations and variations of albumin concentration, pH adjustment, heat treatment and simultaneous agitation. The ideal particulate material for lung scanning in man is a suspension of particles made of a normal, rapidly meta-bolizable body constituent in the size range of 20–50 μ, which is nonantigenic, reaction free, readily labeled in the clinic or hospital laboratory with short-lived 99m technetium or 113mIn nuclides, and prepared with sterile, nontoxic, pyrogen-free physiological materials. Its extraction efficiency by the pulmonary arteriolar capillary network should be 90% or higher and its disappearance rate from the lung must not exceed a few hours. From a practical viewpoint, currently available MAA preparations labeled with 131I meet most of the requirements of the ideal agent except for the 131I label, which results in more than ten times as much radiation exposure to the lungs as 99mTc. However, its 2–3-wk shelf life and commercial availability currently made it the agent of choice in most community hospital nuclear medicine facilities today. The recent growth in the number of in-house preparations of MAA and of inorganic particles labeled with 99mTc or 113mIn is likely to continue as the result of simplified procedures and materials (kits) made available from the radiopharmaceutical manufacturers. The most versatile preparation, albumin microspheres, in narrow size ranges, delivered unlabeled but in “kit” form for in-house labeling with shortlived nuclides shows promise for the future, provided that the early findings can be verified and the agents and kits meet the requirements of the federal regulatory agencies. Much the same can be said for commercially prepared suspensions of unlabeled macroaggregates along with “kits” for in-house labeling with 99mTc.