Simultaneous dual-isotope SPECT with a single CdZnTe detector

Summary form only given. Regional myocardial perfusion in patients with ischemic heart disease can be assessed with sequential rest/stress radionuclide imaging of ^99mTc-sestamibi and ²⁰¹Tl. However patient comfort, patient through-put, and registration of the rest and stress images could be improved if the dual-isotope SPECT images were acquired simultaneously rather than sequentially. In simultaneous acquisitions, the ²⁰¹Tl image can be contaminated by down-scatter from ^99mTc and by K fluorescence when photons from ^99mTc and ²⁰¹Tl interact in the lead collimator. These errors may be reduced by recording the dual-isotope data using a detector with improved energy resolution. We therefore have evaluated the performance of a SPECT system using a CdZnTe detector for simultaneous ^99mTc and ²⁰¹Tl imaging. A comparison between resolution phantom images reconstructed from data with different sized energy windows for ²⁰¹Tl could determine if improved detector energy resolution can reduce or eliminate the need for cross-talk correction. The SPECT projection data, taken with various ²⁰¹Tl energy windows, are convolved with a Ramachandran-Lakshminarayan kernel and backprojected to reconstruct a 256×256 pixel tomographic image. Results indicate improved ²⁰¹Tl images with a 20% window compared to a 30% window at 70 keV. The FWHM energy resolution of the CdZnTe detector is 5% at 140 keV and 8% at 70 keV. Development of a dual-isotope SPECT camera with increased energy resolution compared to current clinical systems can reduce the errors introduced in the ²⁰¹Tl image when simultaneous ²⁰¹Tl/^99mTc data are acquired.