A comparative study of 99Tcm-HMPAO and 99Tcm-ECD as a leukocyte labelling agent

An attempt was made to use 99Tcm-ethyl cysteinate dimer (99Tcm-ECD) (Neurolite, Du Pont Merck, N. Billerica, MA) to label leukocytes. The radiochemical purity of 99Tcm-ECD, labelling efficiency of leukocytes, cell viability of labelled leukocytes and stability of 99Tcm-ECD-labelled leukocytes were calculated. Compared with the commercial cell-labelling agent, 99Tcm-hexamethylpropyleneamine oxime (99Tcm-HMPAO): (1) the radiochemical purity of 99Tcm-ECD was higher than that of 99Tcm-HMPAO and at immediately, 1, 2, 4, 6, 8 and 24 h after 99Tcm labelling; (2) the labelling efficiency of 99Tcm-ECD-labelled leukocytes was lower than that of 99Tcm-HMPAO; (3) the viability of the labelled white blood cells (WBC) was high for both agents; and (4) the stability of 99Tcm-ECD-labelled leukocytes was worse than that of 99Tcm-HMPAO at 1, 2, 4, 6, 8 and 24 h. It is concluded that although 99Tcm-ECD is more stable than 99Tcm-HMPAO, because of the lower labelling efficiency and power stability of 99Tcm-ECD-labelled leukocytes, 99Tcm-ECD is not a good choice as a leukocyte-labelling agent to replace commercial 99Tcm-HMPAO.