  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.
