Abstract
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Objectives: We have investigated the processing of dual radionuclide studies (Tl-201 and Tc-99m) acquired on a dedicated cardiac D-SPECT system (Spectrum Dynamics, Israel) based on CZT detectors. We developed an approach for comprehensive correction of spill-over effects, due to both in-patient down-scatter (DS) and photons detected with reduced energy as a result of collimator and intra-detector effects (CD).
Methods: Data were acquired in list-mode so that multiple energy windows can be selected to estimate Tl-201 and Tc-99m photo-peaks as well as DS and CD events. Studies were performed with several line sources to quantify spectral and spatial response of the system. These characteristics were combined with the triple energy window scatter correction method to form a set of equations for the counts measured in six selected energy windows as functions of primary photons at each projection pixel. The maximum likelihood approach was used to find iteratively the estimated solution for primary photon Tc-99m and Tl-201 projections, which can then be reconstructed using standard OSEM.
Results: The approach has been evaluated using a physical phantom of the thorax whose cardiac insert contained separate Tc-99m and Tl-201 defects. The reconstructed images without correction showed reduced lesion contrast and significant artefacts particularly for Tl-201. In images reconstructed after iterative pre-correction of acquired data these artefacts were no longer evident. The contrast of a large (180° x 2 cm) 100% Tl-201 defect improved from 2.1 to 3.5 and that of a small (45° x 2 cm) 100% Tc-99m defect from 2.2 to 2.9 with similar uniformity of the normal LV wall.
Conclusions: The approach provides potential for efficient simultaneous dual radionuclide cardiac imaging.
- Society of Nuclear Medicine, Inc.