A combination of conventional computed tomography and single photon emitted computed tomography (SPECT/CT) provides simultaneous data on the intensity and location of osteoblastic activity. Currently, since SPECT/CT scans are not spatially aligned, scans following knee arthroplasty are compared by extracting average and maximal values of osteoblastic activity intensity from large subregions of the structure of interest, which leads to a loss of resolution, and hence, information. Therefore, this paper describes the SPECT/CT registration platform (SCreg) based on the principle of image registration to spatially align SPECT/CT scans following unicondylar knee arthroplasty (UKA) and allow full resolution intra-subject and inter-subject comparisons. SPECT-CT scans of 20 patients were acquired before and 1 year after UKA. Firstly, scans were pre-processed to account for differences in voxel sizes and divided in volumes of interest. This was followed by optimization of registration parameters according to their volumetric agreement, and alignment using a combination of rigid, affine and non-rigid registration. Finally, radiotracer uptakes were normalized, and differences between pre-operative and post-operative activity were computed for each voxel. Wilcoxon signed rank sum test was performed to compare Dice similarity coefficients pre- and post-registration. Qualitative and quantitative validation of the platform assessing the correct alignment of SPECT/CT scans resulted in Dice similarity coefficient values over 80% and distances between predefined anatomical landmarks below the fixed threshold of (2;2;0) voxels. Locations of increased and decreased osteoblastic activity obtained during comparisons of osteoblastic activity before and after UKA were mainly consistent with literature. Thus, a full resolution comparison performed on the platform could assist surgeons and engineers in optimizing surgical parameters in view of bone remodeling, thereby improving UKA survivorship.

中文翻译：

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SCreg：基于注册的平台，用于比较un突膝关节置换术SPECT / CT扫描

常规计算机断层扫描和单光子发射计算机断层扫描（SPECT / CT）的组合可提供有关成骨细胞活动强度和位置的同时数据。当前，由于SPECT / CT扫描未在空间上对齐，因此通过从目标结构的较大子区域提取成骨细胞活动强度的平均值和最大值来比较膝关节置换术后的扫描，这会导致分辨率降低，从而导致信息丢失。因此，本文介绍了基于图像配准原理的SPECT / CT配准平台（SCreg），以在单lar膝关节置换术（UKA）后在空间上对齐SPECT / CT扫描，并允许全分辨率受试者内部和受试者间比较。在UKA之前和之后1年进行了20例患者的SPECT-CT扫描。首先，对扫描进行预处理，以解决体素大小的差异并划分感兴趣的体积。然后根据其体积一致性优化配准参数，并结合使用刚性，仿射和非刚性配准进行对齐。最后，将放射性示踪剂的摄取标准化，并为每个体素计算术前和术后活动之间的差异。进行Wilcoxon签名秩和检验以比较注册前后的Dice相似系数。评估SPECT / CT扫描正确对齐的平台的定性和定量验证导致Dice相似系数值超过80％，并且预定义解剖学界标之间的距离低于（2; 2; 0）体素的固定阈值。在比较UKA前后成骨细胞活性期间获得的成骨细胞活性升高和降低的位置主要与文献一致。因此，在平台上执行的全分辨率比较可以帮助外科医生和工程师根据骨骼重塑来优化手术参数，从而提高UKA的生存率。