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The Quarterly Journal of Nuclear Medicine and Molecular Imaging 2005 December;49(4):308-18

Copyright © 2009 EDIZIONI MINERVA MEDICA

lingua: Inglese

Radiolabelled leukocytes for imaging inflammation: how radiochemistry affects clinical use

Ballinger J. R., Gnanasegaran G.

Department of Nuclear Medicine Guy’s and St Thomas’ NHS Foundation Trust, London, UK

Indium-111 (111In)-labelled leukocytes were introduced for imaging inflammation about 25 years ago. A few years later methods to label leukocytes with Technetium-99m (99mTc) were developed, but the two radiolabels cannot be used interchangeably. The amount of radioactivity which can be administered with 111In is low, because of its 67-h half-life and associated radiation dose. This results in low count density in images. However, 111In labelling is very stable, with binding to intracellular macromolecules and particulates, and there is minimal urinary or faecal excretion. In contrast, 99mTc has a half-life of 6 h and can be administered in higher doses, resulting in improved image quality. However, 99mTc labelling is less stable because the trapped form is soluble and there is excretion of 99mTc through both the kidneys and intestine, which limits imaging of disease in the abdomen except at early times. There is interest in extending inflammation imaging to PET. Although leukocytes can be labelled with 18F-FDG, its half-life and stability are not optimal and radiometals such as Copper-64 are being evaluated. Despite the laborious nature of leukocyte labelling, it has yet to be replaced by direct injection agents.