Semi in vitro labelling of red blood cells with99mTc: a comparison with the in vivo labelling

A method ofsemi in vitro labelling of red blood cells (Rbc) is described.Rbc, pre-tinned in the body, were labelledin vitro with99mTc. The labelling efficiency, expressed as the percentage of the administered activity found in the blood, appeared to be higher with this preparation method compared toin vivo labelling ofRbc, respectively 91.3±3.6 and 71.3±3.5 (mean±Sem). There was no difference between both methods in elimination of the label in the urine up to one hour (4.6% of the administered activity).The data here presented, show that thesemi in vitro method provides a preparation with a high cell-bound activity of 96%. Because of a better labelling efficiency, application of thesemi in vitro method results in more circulating activity and a higher left ventricle to background ratio.