SCreg: a registration-based platform to compare unicondylar knee arthroplasty SPECT/CT scans

Abstract

Background: 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. Methods: SPECT-CT scans of 20 patients were acquired before and 1 year after UKA. Firstly, scans were preprocessed 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. Results: 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. Conclusions: 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.

Remodeling pattern of the medial tibial metaphysis after a cementless unicondylar knee replacement; a radiological study

“…SPECT/CT scans of chronically painful knees have shown increased uptake at the proximal medial tibial metaphysis, especially in cases with aseptic loosening and with misaligned implants. [24] In time this osteoblastic activity is supposed to decrease and then end completely, hence the disappearance of pain in the medial tibia after 8-12 months after surgery. It is not clear why in some cases the pain is persistent and sometimes leads to revisions, but studies suggest it could be linked to continuous remodeling.…”

“…[20] Increased osteoblastic activity has also been shown to be a cause of pain in the subchondral bone and has also been linked with pain after unicondylar knee replacements. [21][22][23][24] Considering that unicondylar implants tend to subside after surgery, the new subchondral bone that appears after the removal of the original one, tends to remodel itself in light of Wolff's law. [25][26][27] The radiological changes documented by this research might be linked to this remodeling process.…”

Advancing frontiers in rheumatic and musculoskeletal imaging

“…Some interesting papers on Single-photon emission computed tomography (SPECT)/CT have been published in this Collection. Dandois and Colleagues developed and validated a novel registration-based platform to compare SPECT/CT examinations performed before and after uni-condylar knee arthroplasty to accurately assess and locate changes in osteoblastic activity [ 21 ]. Tabotta et al reported the improved diagnostic performance of SPECT/CT (87% sensitivity, 92% specificity) compared with that of bone scintigraphy in detecting prostate cancer bone metastases in 26 patients, thus highlighting the added value of the former to distinguish neoplastic locations from osteoarthritic changes [ 22 ].…”