Simultaneous dual isotope acquisition for myocardial perfusion imaging with a cadmium-zinc-telluride camera: Preliminary study with 109 patients

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292 Objectives Cadmium-zinc-telluride (CZT) cardiac cameras have an increased counts sensitivity and an improved energy resolution. To determinate if it allows to perform simultaneous dual isotope acquisition for myocardial perfusion imaging , we studied in vivo the impact of technetium-99m in the thallium-201 energy window (70keV) with a GE DNM530c CZT camera. Methods We prospectivly included 109 patients. We injected 0.7MBq/kg of thallium-201 at stress, performed immediatly a 10-min list mode first scan (image Tl 1), then injected at rest 2MBq/kg of tetrofosmin-Tc99m and acquired immediatly a 10-min list mode second scan with reconstruction in both energy windows of technetium (image Tc) and thallium (image Tl 2). Impact of technetium 99m in the thallium 201 energy window was studied by spectrum analysis with modelisation by polynomial of degree 4 and by blinded comparison of images Tl 1 and Tl 2: quality on a five-point scale; automatic quantitative analysis; visual analysis of the 17 segments and calculation of summed stress scores. Results Diagnosis was normal in 48 and abnormal in 61 patients.Scatter counts from technetium in thallium energy window was correlated with body mass index and contributed in more than 50% of the activity in the window. Image Tl 2 was acquired less than 30 mn after Tl 1 image, avoiding redistribution. Comparitively with image Tl 1, quality of image Tl 2 was worse in 50% of cases; there was a change of two or more in the number of abnormal segments in 27% of cases with automatic quantitation and in 20% of cases with visual analysis; the stress summed score decreased of 4 or more in 25% of cases. Conclusions Despite the improved energy resolution of CZT cameras and optimized injected activities, downscatter of technetium in the thallium window leads to an underestimation of the pathological territory in 20 to 25 % of cases. It does not allow to use simultaneous dual-isotope in clinical practice without additional tools for scatter correction. Research Support This work was partly supported by GE Healthcare

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