99Tcm hexamethylpropyleneamineoxime (HMPAO) as a platelet label: evaluation of labelling parameters and first in vivo results.

The lipophilic 99Tcm hexamethylpropyleneamineoxime (HMPAO) complex can be used for labelling platelets as well as granulocytes. For the evaluation of optimal labelling parameters, platelets were isolated according to standard isolation procedures. The labelling efficiency (%) depends on incubation temperature (22 degrees C: 40%; 37 degrees C: 50%), incubation time (3 min: 20%; 25 min: 55%) and the incubation medium (plasma: 40%; saline: 50%). The 60 min 99Tcm elution from the platelets is around 8%. The platelet recovery, used as a quality parameter, is around 25 +/- 4% and is stable for at least 240 min. The high elution rate from the platelets leads to renal excretion of the label and so to significant kidney and bladder activity. Intestinal excretion of the label can also be frequently demonstrated. Fresh thrombotic lesions can usually be detected 4 h after reinjection of the labelled platelets, and in some patients as early as 1 h after reinjection of the platelets. In conclusion, 99Tcm HMPAO seems to be a promising platelet label for imaging thrombotic lesions but not for platelet-survival studies because of the short physical half-life of 99Tcm.