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

Abstract

Scandium-44g (t_1/2 = 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 (t_1/2 = 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.

Keywords: Radiochemical generator; Scandium-44; Titania; Titanium-44; ZR resin.