Survival of pediatric patients with brain tumor has increased over the past 20 years, and increasing evidence of iatrogenic toxicities has been reported. In follow-ups, images are acquired at different time points where substantial changes of brain morphology occur, due to childhood physiological development and treatment effects. To address the image registration complexity, we propose two multi-metric approaches (Mplus, Mdot), combining mutual information (MI) and normalized gradient field filter (NGF). The registration performance of the proposed metrics was assessed on a simulated dataset (Brainweb) and compared with those obtained by MI and NGF separately, using mean magnitude and mean angular errors. The most promising metric (Mplus) was then selected and tested on a retrospective dataset comprising 45 pediatric patients who underwent focal radiotherapy for brain cancer. The quality of the realignment was scored by a radiation oncologist using a perceived misalignment metric (PM). All patients but one were assessed as PM ≤ 2 (good alignment), but the remaining one, severely affected by hydrocephalus and pneumocephalus at the first MRI acquisition, scored PM = 5 (unacceptable). These preliminary findings suggest that Mplus might improve the registration accuracy in complex applications such as pediatric oncology, when data are acquired throughout the years of follow-up, and is worth investigating. Graphical abstract Graphical abstract showing the clinical workflow of the overall registration procedure including the three rigid steps, the fourth deformable step, the reference MRI and the registered MRI as well as the contoured ROIs. The registration performance is assessed by means of the Perceived Misalignment score (PM).

中文翻译：

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用于小儿肿瘤学中纵向脑图像对齐的多指标配准策略。

在过去的20年中，患有脑肿瘤的小儿患者的存活率有所提高，并且有越来越多的医源性毒性证据被报道。在随访中，由于儿童时期的生理发育和治疗效果，会在发生大脑形态发生重大变化的不同时间点获取图像。为了解决图像配准的复杂性，我们提出了两种多度量方法（Mplus，Mdot），它们结合了互信息（MI）和归一化梯度场滤波器（NGF）。拟议指标的配准性能在模拟数据集（Brainweb）上进行了评估，并使用平均幅度和平均角度误差与MI和NGF分别获得的配准性能进行了比较。然后选择最有前途的指标（Mplus），并在回顾性数据集上进行测试，该数据集包含45位接受了脑癌局部放疗的儿科患者。放射肿瘤学家使用感知的未对准度量标准（PM）对重新对准的质量进行评分。除一名患者外，所有患者均被评估为PM≤2（良好对齐），而其余患者在首次MRI采集时受到脑积水和气脑病的严重影响，其PM = 5（不可接受）。这些初步发现表明，当在整个随访期中都获得数据并且值得研究时，Mplus可能会提高诸如儿科肿瘤学等复杂应用中的配准准确性。图形摘要显示整个注册程序的临床工作流程的图形摘要，包括三个固定步骤，第四变形步骤，参考MRI和注册MRI以及轮廓ROI。注册性能是通过感知的未对准分数（PM）进行评估的。