Dual radionuclide myocardial perfusion SPECT may be planned with much lower radiation doses on CZT cameras

Objectives High effective doses, around 29 mSv, constitute a main limit for myocardial perfusion SPECT imaging (MPI) scheduled with a dual 99mTc/201Tl radionuclide method on conventional cameras. This study was aimed at assessing a lower dose dual radionuclide MPI method applied on a CZT camera with a stress first 99mTc-Sestamibi MPI followed only if necessary by a rest 201Tl one.

Methods Eighty-two patients, who had a low dose stress MPI with 99mTc-Setamibi on a CZT camera and for whom a rest 99mTc-Setamibi MPI was subsequently prescribed, also had as a part of the protocol, a rest-MPI with201Tl (36 to 63 MBq) at one hour from stress imaging. The 201Tl images were processed for spill-over and scatter corrections and uptake differences with stress-MPI were analyzed: 1) for the 201Tl (ΔTl) and 99mTc-Sestamibi (ΔTc) rest acquisitions and 2) in segments for which a definite diagnosis of ischemia or necrosis was achieved with the combined analysis of 99mTc-Sestamibi SPECT and gated-SPECT.

Results Mean effective dose was 13.9±1.4 mSv for the dual radionuclide procedure. ΔTl was dramatically higher in the 42 ischemic segments than in the 89 necrotic ones (14.5±10.2% vs. 6.5±8.9%, p<0.001). However, the corresponding uptake levels were much lower for ΔTc (8.4±6.4% and 2.5±7.2%, respectively, p<0.001 for all comparisons), presumably because of the higher background counts of 201Tl compared to 99mTc rest images (background-to-myocardium count ratio: 0.33±0.9 vs. 0.27±0.15, p<0.001). Finally, the best threshold to separate ischemic from necrotic segments was higher for the dual radionuclide method (ΔTl > 13%) than for the single 99mTc one (ΔTc>8%).

Conclusions A dual 99mTc/201Tl radionuclide method may be applied on last-generation CZT cameras with a 蠅 50% decrease in radiation doses, compared with conventional protocols (14 vs. 29 mSv). However, this stress-first 99mTc-Setamibi protocol requires adapting diagnostic criterion to the higher noise level of 201Tl rest images.