Simultaneous technetium-99m/thallium-201 SPECT imaging with model-based compensation for cross-contaminating effects

Simultaneous acquisition of dual-isotope SPECT data offers a number of adva ntages over separately acquired data; however, simultaneous acquisition can result in cross-contamination between isotopes. In this work we propose an d evaluate two frameworks for iterative model-based compensation of cross-c ontamination in dual-isotope SPECT. The methods were applied to cardiac ima ging with technetium-99m-sestamibi and thallium-201, and they were compared with a subtraction-based compensation method using a cross-talk estimate o btained from an auxiliary energy window. Monte Carlo simulations were perfo rmed to carefully study aspects of bias and noise for the methods, and a to rso phantom with cardiac insert was used to evaluate the performance of the methods for experimentally acquired data. The cross-talk compensation meth ods substantially improved lesion contrast and significantly reduced quanti tative errors for simultaneously acquired data. Thallium image normalized m ean square error (NMSE) was reduced from 0.522 without cross-talk compensat ion to as low as 0.052 with model-based cross-talk compensation. This is co mpared with a NMSE of 0.091 for the subtraction-based compensation method. The application of a preliminary model for cross-talk arising from lead flu orescence x-rays and collimator scatter gave promising results, and the fut ure development of a more accurate model for collimator interactions would probably benefit simultaneous Tc/Tl imaging. Model-based compensation metho ds provide feasible cross-talk compensation in clinically acceptable times, and they may ultimately make simultaneous dual-isotope protocols an effect ive alternative for many imaging procedures.