Diffusion magnetic resonance imaging (dMRI) is pivotal for probing the microstructure of the rapidly-developing fetal brain. However, fetal motion during scans and its interaction with magnetic field inhomogeneities result in artifacts and data scattering across spatial and angular domains. The effects of those artifacts are more pronounced in high-angular resolution fetal dMRI, where signal-to-noise ratio is very low. Those effects lead to biased estimates and compromise the consistency and reliability of dMRI analysis. This work presents HAITCH, the first and the only publicly available tool to correct and reconstruct multi-shell high-angular resolution fetal dMRI data. HAITCH offers several technical advances that include a blip-reversed dual-echo acquisition for dynamic distortion correction, advanced motion correction for model-free and robust reconstruction, optimized multi-shell design for enhanced information capture and increased tolerance to motion, and outlier detection for improved reconstruction fidelity. The framework is open-source, flexible, and can be used to process any type of fetal dMRI data including single-echo or single-shell acquisitions, but is most effective when used with multi-shell multi-echo fetal dMRI data that cannot be processed with any of the existing tools. Validation experiments on real fetal dMRI scans demonstrate significant improvements and accurate correction across diverse fetal ages and motion levels. HAITCH successfully removes artifacts and reconstructs high-fidelity fetal dMRI data suitable for advanced diffusion modeling, including fiber orientation distribution function estimation. These advancements pave the way for more reliable analysis of the fetal brain microstructure and tractography under challenging imaging conditions.

翻译：扩散磁共振成像（dMRI）对于探究快速发育中的胎儿大脑微观结构至关重要。然而，扫描过程中的胎儿运动及其与磁场不均匀性的相互作用会导致伪影，并在空间与角度域中造成数据分散。这些伪影的影响在高角度分辨率胎儿dMRI中更为显著，因为其信噪比极低。这些效应会导致估计偏差，并损害dMRI分析的一致性与可靠性。本研究提出了HAITCH，这是首个且目前唯一公开可用的、用于校正和重建多壳层高角度分辨率胎儿dMRI数据的工具。HAITCH提供了多项技术进展，包括：用于动态畸变校正的反向blip双回波采集、针对无模型且稳健重建的先进运动校正、为增强信息捕获和提高运动容忍度而优化的多壳层设计，以及用于提升重建保真度的异常值检测。该框架开源且灵活，可用于处理任何类型的胎儿dMRI数据，包括单回波或单壳层采集，但在处理现有工具均无法处理的多壳层多回波胎儿dMRI数据时效果最为显著。在真实胎儿dMRI扫描上的验证实验表明，该框架在不同胎龄和运动水平下均能实现显著改进与精准校正。HAITCH成功消除了伪影，并重建出适用于高级扩散建模（包括纤维取向分布函数估计）的高保真胎儿dMRI数据。这些进展为在具有挑战性的成像条件下更可靠地分析胎儿大脑微观结构与纤维追踪铺平了道路。