Rapid developments in the field of medical imaging have opened new avenues for the use of positron emitting labeled microparticles. The radioisotope used in our research was 68Ga, which is easy to obtain from a generator and has good nuclear properties for PET imaging. Methods. Commercially available macroaggregated albumin (MAA) microparticles were suspended in sterile saline, centrifuged to remove the free albumin and stannous chloride, relyophilized, and stored for later labeling with 68Ga. Labeling was performed at different temperatures and times. 68Ga purification settings were also tested and optimized. Labeling yield and purity of relyophilized MAA microparticles were compared with those that were not relyophilized. Results. MAA particles kept their original size distribution after relyophilization. Labeling yield was 98% at 75°C when a 68Ga purification system was used, compared to 80% with unpurified 68Ga. Radiochemical purity was over 97% up to 4 hours after the labeling. The relyophilized MAA and labeling method eliminate the need for centrifugation purification of the final product and simplify the labeling process. Animal experiments demonstrated the high in vivo stability of the obtained PET agent with more than 95% of the activity remaining in the lungs after 4 hours.

Chitosan (CHS) is used to prepare microspheres of 31 ± 8 µm size. Surface modification with p-SCN-Bn-DOTA was performed. A maximum90Y capacity was found to be 12.1 ± 4.4 µCi/particle. The best obtained labeling yield was 87.7 ± 0.6%. More than 90%in vitrostability was found. Particlein vitrodegradation half-life in PBS was found to be greater than 21 days.In vivostudies with90Y-DOTA-CHS showed more than 95% of the injected activity (decay corrected) in the lungs 24 hours after tail vein administration.90Y-DOTA-CHSin vivolabel stability was superior to resin microspheres. The addition of p-SCN-Bn-DOTA served as a radioprotectant for bone marrow as the 5%90Y released, during the first 24 hours, was quickly eliminated via urine.

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