Improved quantification for Tc-94 m PET imaging

The positron emitter Tc-94 m (52.5 min half-life) has the potential to improve quantification of tracers currently labeled with Tc-99 m. The successful production of Tc-94 m and the development of an accurate multi-isotope decay correction have improved quantification for Tc-94 m PET imaging. However, the presence of gamma rays emitted in coincidence with the positrons produces an apparent increase in scatter of 40-90%. Furthermore, the contaminant positron emitter Tc-94 (293 min half-life) produced with Tc-94 m also has positron-coincident gammas, so the effect is time dependent. In this study, modification of the kernel parameters of the Bergstrom 2D scatter correction is proposed as a simple way to improve technetium PET quantification. Parameter optimization was performed using line source scatter phantom data for F-18 and technetium for a variety of positions in cylindrical and technetium for a variety of positions in cylindrical and elliptical phantoms over a 3-hour period. The accuracy of the correction was evaluated with remnant scatter fraction measurements using uniformly filled phantoms with 5 cm cold cylindrical inserts. On average, remnant scatter fractions of 10% were observed when parameters optimized for F-18 were used. The use of parameters optimized for technetium reduced the remnant scatter fractions to 1%, showing that accurate quantification with Tc-94 m can be achieved.