Angelis G I, Ryder W J, Gillam J E, Boisson F, Kyme A Z, Fulton R R, Meikle S R, Kench P L
Imaging Physics Laboratory, Brain and Mind Centre, Camperdown, NSW 2050, Australia. Faculty of Health Sciences, The University of Sydney, NSW 2006, Sydney, Australia.
Phys Med Biol. 2017 May 21;62(10):3923-3943. doi: 10.1088/1361-6560/aa68cd. Epub 2017 Mar 23.
Awake and/or freely moving small animal single photon emission imaging allows the continuous study of molecules exhibiting slow kinetics without the need to restrain or anaesthetise the animals. Estimating motion free projections in freely moving small animal planar imaging can be considered as a limited angle tomography problem, except that we wish to estimate the 2D planar projections rather than the 3D volume, where the angular sampling in all three axes depends on the rotational motion of the animal. In this study, we hypothesise that the motion corrected planar projections estimated by reconstructing an estimate of the 3D volume using an iterative motion compensating reconstruction algorithm and integrating it along the projection path, will closely match the true, motion-less, planar distribution regardless of the object motion. We tested this hypothesis for the case of rigid motion using Monte-Carlo simulations and experimental phantom data based on a dual opposed detector system, where object motion was modelled with 6 degrees of freedom. In addition, we investigated the quantitative accuracy of the regional activity extracted from the geometric mean of opposing motion corrected planar projections. Results showed that it is feasible to estimate qualitatively accurate motion-corrected projections for a wide range of motions around all 3 axes. Errors in the geometric mean estimates of regional activity were relatively small and within 10% of expected true values. In addition, quantitative regional errors were dependent on the observed motion, as well as on the surrounding activity of overlapping organs. We conclude that both qualitatively and quantitatively accurate motion-free projections of the tracer distribution in a rigidly moving object can be estimated from dual opposed detectors using a correction approach within an iterative reconstruction framework and we expect this approach can be extended to the case of non-rigid motion.
清醒和/或自由移动的小动物单光子发射成像允许对具有缓慢动力学的分子进行连续研究，而无需限制或麻醉动物。在自由移动的小动物平面成像中估计无运动投影可被视为一个有限角度断层扫描问题，不同的是我们希望估计二维平面投影而非三维体积，其中所有三个轴上的角度采样取决于动物的旋转运动。在本研究中，我们假设通过使用迭代运动补偿重建算法重建三维体积估计值并沿投影路径进行积分来估计的运动校正平面投影，无论物体运动如何，都将与真实的、无运动的平面分布紧密匹配。我们使用蒙特卡罗模拟和基于双对面探测器系统的实验体模数据，针对刚体运动的情况测试了这一假设，其中物体运动以6个自由度进行建模。此外，我们研究了从相反运动校正平面投影的几何平均值中提取的区域活性的定量准确性。结果表明，对于围绕所有三个轴的广泛运动范围，估计定性准确的运动校正投影是可行的。区域活性几何平均值估计中的误差相对较小，在预期真实值的10%以内。此外，定量区域误差取决于观察到的运动以及重叠器官的周围活性。我们得出结论，使用迭代重建框架内的校正方法，可从双对面探测器估计刚体运动物体中示踪剂分布的定性和定量准确的无运动投影，并且我们预计这种方法可扩展到非刚体运动的情况。
