de Jong Joost J A, Christen Patrik, Plett Ryan M, Chapurlat Roland, Geusens Piet P, van den Bergh Joop P W, Müller Ralph, van Rietbergen Bert
NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, Maastricht, The Netherlands.
Department of Rheumatology, Maastricht University Medical Center, Maastricht, The Netherlands.
PLoS One. 2017 Jul 25;12(7):e0179413. doi: 10.1371/journal.pone.0179413. eCollection 2017.
For accurate analysis of bone formation and resorption during fracture healing, correct registration of follow-up onto baseline image is required. A per-fragment approach could improve alignment compared to standard registration based on the whole fractured region. In this exploratory study, we tested the effect of fragment size and displacement on a per-fragment registration, and compared the results of this per-fragment registration to the results of the standard registration in two stable fractures and one unstable fracture. To test the effect of fragment size and displacement, high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of three unfractured radii were divided into subvolumes. Different displacements in x-, y, or z-direction or rotations around each axis were applied, and each subvolume was registered onto the initial volume to realign it. Next, registration of follow-up onto baseline scan was performed in two stable and one unstable fracture. After coarsely aligning the follow-up onto the baseline scan, a more accurate registration was performed of the whole fracture, i.e. the standard registration, and of each fracture fragment separately, i.e. per-fragment registration. Alignment was checked using overlay images showing baseline, follow-up and overlap between these scans, and by comparing correlation coefficients between the standard and per-fragment registration. Generally, subvolumes as small as 300 mm3 that were displaced up to 0.82 mm in x- or y-, or up to 1.64 mm in z-direction could be realigned correctly. For the fragments of all fractures, correlation coefficients were higher after per-fragment registration compared to standard registration. Most improvement was found in the unstable fracture and one fragment of the unstable fracture did not align correctly. This exploratory study showed that image registration of individual subvolumes, such as fracture fragments, is feasible in both stable and unstable fractures, and leads to better alignment of these fragments compared to an approach that is based on registration using the whole fractured region. This result is promising for additional analysis of bone formation and resorption in HR-pQCT studies on fracture healing.
为了准确分析骨折愈合过程中的骨形成和吸收情况，需要将随访图像正确配准到基线图像上。与基于整个骨折区域的标准配准相比，逐片段方法可以改善对齐效果。在这项探索性研究中，我们测试了片段大小和位移对逐片段配准的影响，并将这种逐片段配准的结果与两个稳定骨折和一个不稳定骨折的标准配准结果进行了比较。为了测试片段大小和位移的影响，对三根未骨折桡骨的高分辨率外周定量计算机断层扫描（HR-pQCT）图像进行子体积划分。在x、y或z方向上施加不同的位移或绕每个轴的旋转，然后将每个子体积配准到初始体积上以使其重新对齐。接下来，对两个稳定骨折和一个不稳定骨折进行随访图像到基线扫描的配准。在将随访图像粗略对齐到基线扫描后，分别对整个骨折（即标准配准）和每个骨折片段（即逐片段配准）进行更精确的配准。使用显示基线、随访以及这些扫描之间重叠的叠加图像，并通过比较标准配准和逐片段配准之间的相关系数来检查对齐情况。一般来说，小至300 mm³的子体积，在x或y方向上位移达0.82 mm，或在z方向上位移达1.64 mm时，都可以正确重新对齐。对于所有骨折的片段，逐片段配准后的相关系数高于标准配准。在不稳定骨折中发现的改善最为明显，且该不稳定骨折的一个片段未能正确对齐。这项探索性研究表明，对单个子体积（如骨折片段）进行图像配准在稳定骨折和不稳定骨折中都是可行的，并且与基于整个骨折区域配准的方法相比，能使这些片段更好地对齐。这一结果对于在HR-pQCT骨折愈合研究中进一步分析骨形成和吸收具有重要意义。
