Manganese is necessary for life because it is a cofactor for many enzymatic reactions, but can be toxic in large doses. Manganese also has medical imaging applications; manganese can be used for magnetic resonance imaging (MRI) while the radionuclide manganese-52 (52Mn) can be used for positron emission tomography (PET). Based on the biological roles of manganese and the fact that MR and PET complement one another in terms of sensitivity and resolution, 52Mn could be a useful radiotracer for PET/MR imaging. 52Mn was produced by bombarding a natural chromium foil with ~13 MeV protons from the CS-15 cyclotron at Washington University School of Medicine (WUSM) and purified using a cation-exchange column. The foil was dissolved in concentrated hydrochloric acid to produce Cr3+ and Mn2+ ions and brought to dryness. It was then reconstituted in 1.5 M sulfuric acid and loaded onto the column. Most of the Cr3+ went into the flow through, while the 52Mn was immobilized on the column. For some experiments, 0.5 M HCl was used to wash more Cr3+ off the column. Next, 10 mM hydrazine sulfate was used to ensure proper manganese oxidation state. Finally, multiple experiments were conducted to elute 52Mn2+ in various solutions, including hydrochloric acid and ammonium oxalate. Additionally, a variety of methods were used to quantify the Cr3+ fractions eluted from the column. Phantoms consisting of 28 15 mL tubes in a rack with a gradient of both 52MnCl2 and nonradioactive Mn(II)Cl2 were imaged using the mMR scanner, a PET scanner inside of an MRI machine that takes simultaneous PET and MR images. A 30 minute PET scan was conducted, as well as many MR scans with varying inversion times (TI). MR and PET signal gradients were observed for MnCl2 and 52Mn concentrations, respectively. Two male C57-Black 6 mice were injected with 50 mL (41 uCi) of 52MnCl2­. The injection was prepared by eluting with ammonium oxalate, and then evaporating and reconstituting the product in 6 M HCl. Two PET scans, at one hour and three days post-injection, were taken before sacrificing the mice to investigate the manganese biodistribution. The PET/CT showed a large amount of activity in the kidney and salivary gland, and the biodistribution study showed that much of the injected manganese went to the pancreas and kidney. The study indicated that manganese-52 could be purified sufficiently for injection, and also provided a sensitive reading of the in vivo kinetics of manganese.

Manganese-52: cyclotron production and PET/MR imaging

249th National Meeting (2015)

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