Department of Mathematics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
Med Phys. 2011 Aug;38(8):4489-97. doi: 10.1118/1.3589129.
Dynamic tracer behavior in the human body arises as a result of continuous physiological processes. Hence, the change in tracer concentration within a region of interest (ROI) should follow a smooth curve. The authors propose a modification to an existing slow-rotation dynamic SPECT reconstruction algorithm (dSPECT) with the goal of improving the smoothness of time activity curves (TACs) and other properties of the reconstructed image.
The new method, denoted d2EM, imposes a constraint on the second derivative (concavity) of the TAC in every voxel of the reconstructed image, allowing it to change sign at most once. Further constraints are enforced to prevent other nonphysical behaviors from arising. The new method is compared with dSPECT using digital phantom simulations and experimental dynamic 99mTc -DTPA renal SPECT data, to assess any improvement in image quality.
In both phantom simulations and healthy volunteer experiments, the d2EM method provides smoother TACs than dSPECT, with more consistent shapes in regions with dynamic behavior. Magnitudes of TACs within an ROI still vary noticeably in both dSPECT and d2EM images, but also in images produced using an OSEM approach that reconstructs each time frame individually, based on much more complete projection data. TACs produced by averaging over a region are similar using either method, even for small ROIs. Results for experimental renal data show expected behavior in images produced by both methods, with d2EM providing somewhat smoother mean TACs and more consistent TAC shapes.
The d2EM method is successful in improving the smoothness of time activity curves obtained from the reconstruction, as well as improving consistency of TAC shapes within ROIs.
人体中的示踪剂行为是由于连续的生理过程而产生的。因此，感兴趣区域（ROI）内示踪剂浓度的变化应该遵循平滑曲线。作者提出了对现有的缓慢旋转动态 SPECT 重建算法（dSPECT）的修改，目的是提高时间活动曲线（TAC）的平滑度和重建图像的其他特性。
新方法，记为 d2EM，对重建图像中每个体素的 TAC 的二阶导数（凹度）施加约束，允许其在最多一次改变符号。进一步施加约束以防止出现其他非物理行为。使用数字体模模拟和实验性动态 99mTc-DTPA 肾 SPECT 数据，将新方法与 dSPECT 进行比较，以评估图像质量的任何改善。
在体模模拟和健康志愿者实验中，d2EM 方法提供的 TAC 比 dSPECT 更平滑，在具有动态行为的区域中具有更一致的形状。在 ROI 内的 TAC 幅度在 dSPECT 和 d2EM 图像中仍然明显变化，但在基于更完整投影数据的每个时间帧单独重建的 OSEM 方法产生的图像中也是如此。使用任何方法对区域进行平均后，TAC 相似，即使是对于小 ROI。实验性肾数据的结果表明，两种方法产生的图像都表现出预期的行为，d2EM 提供了稍微平滑的平均 TAC 和更一致的 TAC 形状。
d2EM 方法成功地提高了从重建中获得的时间活动曲线的平滑度，并且提高了 ROI 内 TAC 形状的一致性。
