Optimization of acquisition parameters for simultaneous 201Tl and 99mTc dual-isotope myocardial imaging

In ²⁰¹Tl/^99mTc dual-isotope simultaneous-acquisition (DISA) myocardial imaging, crosstalk due to Tc photons results in significant contamination of the Tl data. The objective of this work is to seek the acquisition parameters (i.e., energy window width and center) that have the optimal tradeoff between minimizing the crosstalk and maximizing the detection efficiency. The optimization criterion was based on maximizing an ideal observer signal-to-noise ratio (SNR) for the myocardial defect detection task using single-isotope and DISA projection images acquired from a torso phantom. For single-isotope images, the optimal energy windows (width/center: 26 keV/75 keV and 28 keV/165 keV for ²⁰¹Tl, 30 keV/142 keV for ^99mTc) are wider than typical windows. For DISA imaging, the optimal windows varied with the ^99mTc to ²⁰¹Tl activity ratio and are thus likely to depend on the uptake ratio in each patient. Using the optimal ratio 2.25-2.75 (148 MBq ²⁰¹Tl and 333-407 MBq ^99mTc) with the corresponding optimal windows (22 keV/72 keV, 24 keV/167 keV, and 24 keV/140 keV) gives ²⁰¹Tl images with substantially increased SNRs as well as ^99mTc images with SNRs same as those of 370 MBq ^99mTc-only images. However, without the addition of crosstalk compensation, the use of the optimal activity and energy windows alone is likely not sufficient to restore the DISA Tl SNR to that of Tl-only image.