Quantitative capabilities of 2 state-of-the-art SPECT/CT imaging systems

Abstract

SPECT/CT using 3D iterative reconstruction techniques allows for the absolute quantification of radioactivity in vivo. This is essential for internal dosimetry in radionuclide therapy. The SPECT images are affected by attenuation, scatter and partial volume effects. The goal of this study is to compare 2 state-of-the-art SPECT-CT systems (Siemens Symbia T16 and GE Discovery 670). The SPECT images were reconstructed using commercial iterative reconstruction algorithms. First, the systems were cross-calibrated with a radionuclide calibrator and a well counter using a large cylindrical phantom. Calibration factors (CF) were determined, converting image counts to activity concentration (kBq/ml). The influence of various acquisition and reconstruction parameters were investigated. Second, recovery values (RV) were determined for spheres with different diameters using the NEMA/IEC body phantom.The quantitative accuracy in a large cylindrical phantom was 4%. The CF of the Symbia T16 and GE Discovery 670 were 11.59 cpm/kBq and 6.11 cpm/kBq, respectively. Oscillation and cupping artefacts were observed for the GE Discovery 670. The RV of the smallest spheres in the NEMA phantom dropped below 3.5% at 4 updates. The RV increased with the number of updates, but levelled at 64 updates. Quantification seems feasible within 4% for large objects. A partial volume correction technique is necessary for the smallest objects. The influence of reconstruction artefacts remains a challenge in SPECT/CT and should be the focus of further research.