Development and Regeneration Department, Institute for Orthopaedic Research and Training, KU Leuven, 49 Herestraat - Box 805, 3000, Leuven, Belgium.
Radiology and Cardiology Department, University Hospitals Leuven, 49 Herestraat, 3000, Leuven, Belgium.
BMC Musculoskelet Disord. 2020 Mar 12;21(1):162. doi: 10.1186/s12891-020-3185-9.
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.
常规计算机断层扫描（CT）与单光子发射计算机断层扫描（SPECT）的结合提供了成骨活性的强度和位置的同步数据。目前，由于 SPECT/CT 扫描没有空间对准，因此在膝关节置换术后，通过从感兴趣结构的大子区域提取成骨活性强度的平均值和最大值来比较 SPECT/CT 扫描，这导致分辨率降低，从而导致信息丢失。因此，本文描述了基于图像配准原理的 SPECT/CT 配准平台（SCreg），用于空间对准单髁膝关节置换术（UKA）后的 SPECT/CT 扫描，并允许在个体内和个体间进行全分辨率比较。
对 20 例患者的 UKA 术前和术后 1 年的 SPECT-CT 扫描进行采集。首先，对扫描进行预处理，以考虑体素大小的差异，并将其分为感兴趣的体积。然后，根据其体积一致性优化配准参数，并使用刚性、仿射和非刚性配准的组合进行对齐。最后，对示踪剂摄取进行归一化，并计算每个体素的术前和术后活性差异。采用 Wilcoxon 符号秩和检验比较配准前后的 Dice 相似系数。
通过对 SPECT/CT 扫描正确对准的平台进行定性和定量验证，得到的 Dice 相似系数值超过 80%，且在预定义解剖标志之间的距离小于（2；2；0）体素的固定阈值。在 UKA 前后成骨活性比较中获得的成骨活性增加和减少的位置主要与文献一致。
因此，在平台上进行的全分辨率比较可以帮助外科医生和工程师优化考虑到骨重塑的手术参数，从而提高 UKA 的存活率。
