Lyophilized Kit for the Preparation of the PET Perfusion Agent [68Ga]-MAA

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. 1. Introduction Starting in 1964, several efforts have been made to find an agent for perfusion and embolization [1, 2]. A lyophilized kit for the preparation of 99mTc-MAA was created in 1974 for Single Photon Emission Tomography (SPECT) imaging. With the arrival of Positron Emission Tomography (PET) the formulation of an analogue drug with a positron emitter was needed. Among the available PET isotopes 68Ga is easily obtained from its parent nuclide 68Ge by chromatographic column separation with different inorganic exchangers. The long lived parent allows the construction of a generator that can last up to two years [3] compared to a 99mTc/99Mo generator which lasts only for 1-2 weeks. MAA was first successfully labeled with 68Ga in 1989 [4] but never used, probably due to unreliability of the existing 68Ge/68Ga generators and low availability of PET imaging cameras. Revived interest has been shown recently [5, 6], and the first PET lung perfusion studies in humans have been performed [7, 8]. Selective internal radiation treatment (SIRT), a technique used to treat metastatic liver cancer, could also benefit from a PET perfusion tracer. During the planning stage, a 99mTc-MAA perfusion scan is performed to assess the allocation in lung and gastrointestinal tract. It is also