Abstract
Manganese has long been employed as a T1-shortening agent in magnetic resonance imaging (MRI) applications, but these techniques are limited by the biotoxicity of bulk-manganese. Positron emission tomography (PET) offers superior contrast sensitivity compared with MRI, and recent preclinical PET studies employing 52gMn (t1/2: 5.6 d, β+: 29%) show promise for a variety of applications including cell tracking, neural tract tracing, immunoPET, and functional β-cell mass quantification. The half-life and confounding gamma emissions of 52gMn are prohibitive to clinical translation, but the short-lived 51Mn (t1/2: 46 min, β+: 97%) represents a viable alternative. This work develops methods to produce 51Mn on low-energy medical cyclotrons, characterizes the in vivo behavior of 51MnCl2 in mice, and performs preliminary human dosimetry predictions. 51Mn was produced by proton irradiation of electrodeposited isotopically-enriched 54Fe targets. Radiochemically isolated 51MnCl2 was intravenously administered to ICR mice which were scanned by dynamic and static PET, followed by ex vivo gamma counting. Rapid blood clearance was observed with stable uptake in the pancreas, kidneys, liver, heart, and salivary gland. Dosimetry calculations predict that 370 MBq of 51Mn in an adult human male would yield an effective dose equivalent of approximately 13.5 mSv, roughly equivalent to a clinical [18F]-FDG procedure.
Highlights
Rapid blood clearance was observed with stable uptake in the pancreas, kidneys, liver, heart, and salivary gland
Macroscopic quantities of stable manganese may be employed as a T1-shortening agent in manganese-enhanced magnetic resonance imaging (MEMRI)[10]
Electrodeposition was found to be complete in approximately 24 hours with residual Fe concentration dropping to
Summary
Rapid blood clearance was observed with stable uptake in the pancreas, kidneys, liver, heart, and salivary gland. 52gMn (t1/2: 5.591 d, β+: 29.4%, Eβave: 0.24 MeV) can be produced in sufficient quantities (~500 MBq/h with 60 μA of 16 MeV protons) and radionuclidic purity (>99.5%) on a low energy cyclotron by irradiation of natural chromium metal[12]. Because of this accessibility, 52gMn has been used extensively in preclinical research in recent years[13, 14]. The clinical use of 51Mn appears promising, for pancreatic β cell imaging, there has been little previous work done on producing 51Mn on low-energy medical cyclotrons. The aims of this work were to (A) develop and characterize 51Mn production methods by 54Fe(p,α), to (B) characterize the in vivo behavior of 51MnCl2 in healthy mice, and to (C) evaluate the dosimetric feasibility of clinical 51Mn studies
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