Kangasmaa Tuija, Kuikka Jyrki, Sohlberg Antti
Department of Radiation Therapy, Vaasa Central Hospital, Hietalahdenkatu 2-4, 65100 Vaasa, Finland.
Int J Mol Imaging. 2012;2012:695632. doi: 10.1155/2012/695632. Epub 2012 Nov 19.
Simultaneous Tl-201/Tc-99m dual isotope myocardial perfusion SPECT is seriously hampered by down-scatter from Tc-99m into the Tl-201 energy window. This paper presents and optimises the ordered-subsets-expectation-maximisation-(OS-EM-) based reconstruction algorithm, which corrects the down-scatter using an efficient Monte Carlo (MC) simulator. The algorithm starts by first reconstructing the Tc-99m image with attenuation, collimator response, and MC-based scatter correction. The reconstructed Tc-99m image is then used as an input for an efficient MC-based down-scatter simulation of Tc-99m photons into the Tl-201 window. This down-scatter estimate is finally used in the Tl-201 reconstruction to correct the crosstalk between the two isotopes. The mathematical 4D NCAT phantom and physical cardiac phantoms were used to optimise the number of OS-EM iterations where the scatter estimate is updated and the number of MC simulated photons. The results showed that two scatter update iterations and 10(5) simulated photons are enough for the Tc-99m and Tl-201 reconstructions, whereas 10(6) simulated photons are needed to generate good quality down-scatter estimates. With these parameters, the entire Tl-201/Tc-99m dual isotope reconstruction can be accomplished in less than 3 minutes.
锝-99m（Tc-99m）向铊-201（Tl-201）能量窗的下散射严重阻碍了同时进行的Tl-201/Tc-99m双同位素心肌灌注单光子发射计算机断层扫描（SPECT）。本文提出并优化了基于有序子集期望最大化（OS-EM）的重建算法，该算法使用高效的蒙特卡罗（MC）模拟器校正下散射。该算法首先通过衰减、准直器响应和基于MC的散射校正来重建Tc-99m图像。然后，将重建的Tc-99m图像用作基于MC的Tc-99m光子向Tl-201窗下散射模拟的输入。该下散射估计最终用于Tl-201重建，以校正两种同位素之间的串扰。使用数学四维数字人体模拟（NCAT）体模和物理心脏体模来优化OS-EM迭代次数（在此期间更新散射估计）以及MC模拟光子的数量。结果表明，对于Tc-99m和Tl-201重建，两次散射更新迭代和10^5个模拟光子就足够了，而生成高质量的下散射估计则需要10^6个模拟光子。利用这些参数，整个Tl-201/Tc-99m双同位素重建可以在不到3分钟内完成。
