A consensus protocol for white blood cells labelling with technetium-99m hexamethylpropylene amine oxime. International Society of Radiolabeled Blood Elements (ISORBE)

Since its introduction in 1976 as an imaging procedure, the use of labelled leucocyte scintigraphy has continued to increase. Nowadays it is a routine procedure in most nuclear medicine departments for the investigation of different inflammatory pathologies involving leucocytic infiltration. These include bone and soft tissue infections, inflammatory bowel disease, vascular prosthesis infection and fever of unknown origin [1–4]. Despite their non-specificity, the use of non-polar, lipid-soluble chelates is still the most efficient way to label leucocytes. Indium-111 oxine was the first to be described in 1976 [5] and has been the agent of choice for many years. Other indium chelates such as 111In-tropolone [6] and 111In-mercapto-pyridine-N-oxide [7] have been demonstrated to label leucocytes as efficiently as 111In-oxine in plasma medium, but their use has not been so widespread. Although efficient in many ways, the use of 111In-oxine has become less attractive due to its cost, inconvenient supply, and the unfavourable physical characteristics of 111In. Technetium-99m has excellent characteristics for scintigraphic imaging and is cheap and available at any time. For this reason, many investigators have tried to find a 99mTc-chelate able, like 111In-chelates, to enter cells and to bind a cytoplasmatic component without loss of leucocyte viability. 99mTc-propylene amine oximes (PnAO) were originally developed as lipophilic diffusible radiopharmaceuticals for brain imaging [8]. The dl diastereoisomer complex of 99mTc-hexamethylpropylene amine oxime (HMPAO) was found to have the highest brain concentration [9]. Because of its neutral, lipophilic character, this radiopharmaceutical is able to diffuse through the cell membrane and bind intracellular components. Soon 99mTc-HMPAO proved to be useful as a leucocyte labelling agent [10, 11]. Since 1988 99mTc-HMPAO has been commercially available. Nevertheless, its use is accompanied by a large variety of labelling methodologies which, although they in general do not induce any significant damage on labelled cells, can influence the image quality and interpretation of results. The International Society of Radiolabelled Blood Elements (ISORBE), founded in 1989 in Vienna (Austria) with the primary objective of providing a forum for exchange of knowledge and experience, decided to scrutinize various methods and to suggest a uniform procedure for radiolabelling leucocytes with 99mTc- HMPAO