背景:图像引导的神经外科手术需要很高的定位和配准精度,以实现有效的治疗并避免并发症。然而,基于术前MR或CT图像的精确神经导航受到手术干预期间发生的大脑变形的挑战。
目的:为了促进脑组织的术中可视化和与术前图像的可变形配准,提出了一种3D深度学习重建框架(称为DL-Recon),以改善术中锥形束CT(CBCT)图像质量。
方法:DL-Recon框架将基于物理的模型与深度学习CT合成相结合,并利用不确定性信息来提高对看不见的特征的鲁棒性。开发了具有条件损失函数的3D生成对抗网络(GAN),该条件损失函数由aleatoric不确定性调制,用于CBCT到CT合成。综合模型的认识不确定性通过蒙特卡罗方法进行了估计。使用从认知不确定性中得出的空间变化的权重,DL-Recon图像将合成CT与伪影校正的滤波反投影(FBP)重建相结合。在高度认知不确定性的地区,DL-Recon包括来自FBP图像的更大贡献。使用20个配对的头部真实CT和模拟CBCT图像进行网络训练和验证。和实验评估了DL-Recon在包含训练数据中未出现的模拟和真实脑部病变的CBCT图像上的性能。根据结果图像的结构相似性(SSIM)与病变分割中的诊断CT和Dice相似性度量(DSC)与地面实况相比,量化了基于学习和物理学的方法之间的性能。进行了一项涉及7名在神经外科期间获得CBCT图像的受试者的初步研究,以评估DL-Recon在临床数据中的可行性。
结果:通过基于物理校正的FBP重建的CBCT图像由于图像不均匀性而对软组织对比度分辨率提出了通常的挑战,噪音,和残留的文物。GAN合成改善了图像均匀性和软组织可见性,但在模拟病变的形状和对比度方面存在错误,这在训练中看不到。在综合损失中加入aleatoric不确定性改善了认知不确定性的估计,具有可变的大脑结构和看不见的病变,表现出更高的认知不确定性。DL-Recon方法减轻了合成错误,同时保持了图像质量的改善,与FBP相比,SSIM(与诊断CT相比的图像外观)增加15-22%,病变分割中的DSC增加高达25%。在真实的脑部病变和临床CBCT图像中也观察到视觉图像质量的明显提高。
结论:DL-Recon利用不确定性估计来结合深度学习和基于物理的重建的优势,并证明了术中CBCT的准确性和质量的实质性改善。改进的软组织对比度分辨率可以促进大脑结构的可视化,并支持与术前图像的可变形配准。进一步扩展了术中CBCT在图像引导神经外科手术中的应用。本文受版权保护。保留所有权利。
BACKGROUND: Image-guided neurosurgery requires high localization and registration accuracy to enable effective treatment and avoid complications. However, accurate neuronavigation based on preoperative magnetic resonance (MR) or computed tomography (CT) images is challenged by brain deformation occurring during the surgical intervention.
OBJECTIVE: To facilitate intraoperative visualization of brain tissues and deformable registration with preoperative images, a 3D deep learning (DL) reconstruction framework (termed DL-Recon) was proposed for improved intraoperative cone-beam CT (CBCT) image quality.
METHODS: The DL-Recon framework combines physics-based models with deep learning CT synthesis and leverages uncertainty information to promote robustness to unseen features. A 3D generative adversarial network (GAN) with a conditional loss function modulated by aleatoric uncertainty was developed for CBCT-to-CT synthesis. Epistemic uncertainty of the synthesis model was estimated via Monte Carlo (MC) dropout. Using spatially varying weights derived from epistemic uncertainty, the DL-Recon image combines the synthetic CT with an artifact-corrected filtered back-projection (FBP) reconstruction. In regions of high epistemic uncertainty, DL-Recon includes greater contribution from the FBP image. Twenty paired real CT and simulated CBCT images of the head were used for network training and validation, and experiments evaluated the performance of DL-Recon on CBCT images containing simulated and real brain lesions not present in the training data. Performance among learning- and physics-based methods was quantified in terms of structural similarity (SSIM) of the resulting image to diagnostic CT and Dice similarity metric (DSC) in lesion segmentation compared to ground truth. A pilot study was conducted involving seven subjects with CBCT images acquired during neurosurgery to assess the feasibility of DL-Recon in clinical data.
RESULTS: CBCT images reconstructed via FBP with physics-based corrections exhibited the usual challenges to soft-tissue contrast resolution due to image non-uniformity, noise, and residual artifacts. GAN synthesis improved image uniformity and soft-tissue visibility but was subject to error in the shape and contrast of simulated lesions that were unseen in training. Incorporation of aleatoric uncertainty in synthesis loss improved estimation of epistemic uncertainty, with variable brain structures and unseen lesions exhibiting higher epistemic uncertainty. The DL-Recon approach mitigated synthesis errors while maintaining improvement in image quality, yielding 15%-22% increase in SSIM (image appearance compared to diagnostic CT) and up to 25% increase in DSC in lesion segmentation compared to FBP. Clear gains in visual image quality were also observed in real brain lesions and in clinical CBCT images.
CONCLUSIONS: DL-Recon leveraged uncertainty estimation to combine the strengths of DL and physics-based reconstruction and demonstrated substantial improvements in the accuracy and quality of intraoperative CBCT. The improved soft-tissue contrast resolution could facilitate visualization of brain structures and support deformable registration with preoperative images, further extending the utility of intraoperative CBCT in image-guided neurosurgery.