Improved quantification for Tc-94m PET imaging

The positron emitter Tc-94m (52.5-min half-life) has the potential to improve quantification of tracers currently labeled with Tc-99m. The successful production of Tc-94m and the development of an accurate multiisotope decay correction have improved quantification for Tc-94m positron emission tomography (PET) imaging. However, the presence of gamma rays emitted in coincidence with the positrons produces an apparent increase in scatter of 40% to 90%. Furthermore, the contaminant positron emitter Tc-94 (293-min half-life) produced with Tc-94m also has positron-coincident gammas, so the effect is time-dependent. In this study, modification of the kernel parameters of the Bergstrom two-dimensional (2-D) 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 elliptical phantoms over a 3-h 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 2-D scatter fractions of 10 +/- 3% were observed when parameters optimized for F-18 were used. The use of parameters optimized for technetium reduced the remnant scatter fractions to 1 +/- 3%, showing that accurate quantification with Tc-94m can be achieved.