VIABILITY AND BIODISTRIBUTION OF GA-68 MPO-LABELED HUMAN PLATELETS

The viability and biodistribution of Ga-68-mercaptopyridine-N-oxide (M PO)-labelled autologous platelets was studied in 10 patients. The aver age platelet labelling yield was 36 +/- 12% and injected activity was 2.0 +/- 0.9 mCi Ga-68. The % activity in platelets per ml whole blood was 64 +/- 20% at 15 min-1.0 h postinjection and 76 +/- 14% at 2-4 h. The average recovery of platelets (% injected platelets circulating in peripheral blood) was 31 +/- 21% at 15 min-I h and 39 +/- 20% at 2-4 h. The positron emission tomographic (PET) images showed high circulat ing vascular background. Two patients had technically inadequate scans , and six were false negative due to high blood background. One patien t with a massive pulmonary embolus occurring 24 h prior to scanning ha d marked uptake of 68Ga platelets in a large clot in the superior bran ch of the right main pulmonary artery. A second patient, with Ga-68 pl atelets circulating during angioplasty of a left posterior tibial arte ry stenosis, had intense uptake in the lesion shown on the PET scan ob tained 4 h following the procedure. These results indicate good viabil ity of 68Ga-MPO-labelled autologous human platelets, but poor visualiz ation of clots by PET imaging, due to the high blood background at ear ly times.