Effects of CT-based attenuation correction of rat microSPECT images on relative myocardial perfusion and quantitative tracer uptake

Purpose: Our goal in this work was to investigate the impact of CT-based attenuation correction on measurements of rat myocardial perfusion with Tc-99m and Tl-201 single photon emission computed tomography (SPECT). Methods: Eight male Sprague-Dawley rats were injected with Tc-99m-tetrofosmin and scanned in a small animal pinhole SPECT/CT scanner. Scans were repeated weekly over a period of 5 weeks. Eight additional rats were injected with Tl-201 and also scanned following a similar protocol. The images were reconstructed with and without attenuation correction, and the relative perfusion was analyzed with the commercial cardiac analysis software. The absolute uptake of Tc-99m in the heart was also quantified with and without attenuation correction. Results: For Tc-99m imaging, relative segmental perfusion changed by up to +2.1%/-1.8% as a result of attenuation correction. Relative changes of +3.6%/-1.0% were observed for the Tl-201 images. Interscan and inter-rat reproducibilities of relative segmental perfusion were 2.7% and 3.9%, respectively, for the uncorrected Tc-99m scans, and 3.6% and 4.3%, respectively, for the Tl-201 scans, and were not significantly affected by attenuation correction for either tracer. Attenuation correction also significantly increased the measured absolute uptake of tetrofosmin and significantly altered the relationship between the rat weight and tracer uptake. Conclusions: Our results show that attenuation correction has a small but statistically significant impact on the relative perfusion measurements in some segments of the heart and does not adversely affect reproducibility. Attenuation correction had a small but statistically significant impact on measured absolute tracer uptake. (C) 2015 American Association of Physicists in Medicine.