A combined inorganic-organic titanium-44/scandium-44g radiochemical generator

Abstract

Scandium-44g (t1/2 = 4.0 h) is an emerging radioisotope for positron emission tomography. It can be produced with a radiochemical generator using its long-lived parent, titanium-44 (t1/2 = 59.1 years). This work presents a new inorganic substrate for 44Ti/44gSc radiochemical generator design based on porous TiO2 microbeads (80 µm and 110 µm particle size, 60 Å pores). Comprehensive evaluation of conditions optimal for generator construction (44Ti loading) and use (44gSc elution) is provided in three steps. For stable 44Ti loading onto titania, heat-treatment at 180 °C for 90 min is shown to be effective while 0.3 M HCl(aq) is identified as the medium of choice for 44gSc elution. Two titania-based 3.6 MBq generators prepared under optimized conditions are characterized with respect to 44gSc recovery and 44Ti breakthrough. Each of these generators employed a different guard substrate to minimize 44Ti breakthrough, TiO2 microbeads and ZR resin. Both are shown to provide comparable 44gSc recoveries close to 50% but differ in 44Ti breakthrough, which is significantly lower with the organic ZR resin guard substrate at 0.0002%. This concept represents a new inorganic-organic approach to 44Ti/44gSc generator design. Benefits of both substrates are exploited: TiO2 has potential for durability necessary for utilizing the long half-life of the 44Ti parent while ZR resin guard segments minimize 44Ti breakthrough.