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

Abstract

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 (68)Ga, 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 (68)Ga. Labeling was performed at different temperatures and times. (68)Ga 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 (68)Ga purification system was used, compared to 80% with unpurified (68)Ga. 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.

Figure 1

MAA microscope images, (a) from original unmodified MAA kit and (b) from relyophilized MAA.

Figure 2

Purification System Setup.

Figure 3

⁶⁸Ga recovery and ⁶⁸Ge elimination during the purification process.

Figure 4

⁶⁸Ga-MAA labeling yield results.

Figure 5

Normalized and radio-decay-corrected lung allocation for ⁶⁸Ga-MAA and ^99mTc-MAA at 1, 2, 3, and 4 hours (n = 2 per time point).

Figure 6

Non decay-corrected, uncollimated full body autoradiography for free ⁶⁸Ga (T _1/2 = 68 min), ⁶⁸Ga-MAA, ^99mTc-MAA, and hydrolyzed ^99mTc (T _1/2 = 6.02 h) at 1, 2, 3, and 4 hours. Labeling of ⁶⁸Ga-MAA was performed with relyophilized MAA and purified ⁶⁸Ga at 75°C for 15 minutes. The autoradiograph is superimposed on an X-ray image of the same animal in the unaltered supine position.